Organism-Substrate Relationships in Lowland Streams

Harry H. Tolkamp

Organism-substrate relationships in lowland streams

Proefschrift terverkrijgin gva nd egraa dva n doctori nd e landbouwwetenschappen, opgeza gva nd erecto rmagnificus , dr.H.C .va nde rPlas , hoogleraar in de organische scheikunde, in het openbaar te verdedigen op vrijdag 6 februari 1981 des namiddags te vier uur in de aula van de Landbouwhogeschool te Wageningen.

Centre for Agricultural Publishing and Documentation

Wageningen - 1980 Abstract

Tolkamp,H.H . (1980)Organism-substrat e relationships inlowlan d streams.Agric . Res.Rep .(Versl .landbouwk .Onderz. )907 ,ISB N9 022 0075 9 6, (xi)+ 211p. ,8 0 tables,4 3figs. ,31 9refs. ,Eng .an dDutc hsummaries , 14appendices . Also:Doctora l thesis,Wageningen .

Afiel d andlaborator y studyo nth emicrodistributio n ofbotto m dwellingmacro - invertebrates toinvestigat e therol eo fth estrea m substrate inth edevelopmen t andpreservatio no fth emacroinvertebrat e communities innatural ,undisturbe d low land streams isdescribed .Fiel d datao nbotto m substrates and faunawer e collected between 1975an d 1978fro mtw oDutc hlowlan d streams.Substrate swer e characterized byth enatur ean dth eamoun to forgani cdetritu san d theminera l particle sizes:i n afiel d classificationo nth ebasi so fth evisuall y dominant particle sizes; ina grain-size classificationo n thebasi so f exactparticle-siz e analysis inth elabora tory.Substrat epreferenc e for8 4macroinvertebrat e specieswa s demonstrated using theInde xo fRepresentation . Substrate-selection experimentswer e conducted ina laborator y stream for three Trichopteraspecie s Qiiaropterna sequax, Chaetopteryx viVtosa and Serioostoma per sonation) andon eEphemeropter a species (.Ephemera danica). An experiment on the colonizationo fartificia l substrates inth efiel dwa s also conducted. Fromth efiel d data,severa l faunal groups couldb edistinguished , each group madeu po fspecie swit h similarsubstrat epreferences .Detaile d datao n themicro - distribution inrelatio n tosubstrat eparticl e sizear egive n for 26 species,whic h represent thevariou s taxonomicalunit stha t compose thefauna l groups:Trichopter a (5species) ,Ephemeropter a (1species) ,Plecopter a (1species) ,Coleopter a (3species) , Amphipoda (1species) ,Dipter a (15species ,amon gwhic h 13specie so fChironomidae) . Themicrodistributio n isdiscusse d inrelatio n tocase-buildin g behaviour, life cycle andfoo dpreferences .Fo r several speciessubstrat epreference sma yb e different for different development stageso r indifferen t seasons. Iti sconclude d thatmos t speciessho wdistinc t preferences fora specific sub strate.Th esmal l scalespatia lvariatio n insubstrat ecompositio n of the streambe d isessentia l forth eexistenc eo fman y lowland streammacroinvertebrat e species.

Freedescriptors :substrat epreference ,microdistribution , benthos,macroinvertebrates , particlesize ,detritus ,organi cmatter ,habita t preference, environmental factors, lowland stream, laboratory stream

Communication NatureConservatio nDepartmen t 211.

This thesiswil l alsob epublishe d asAgricultura l ResearchReport s907 .

üw^,0* thlS b°0k Bay be reProduced °rPublishe d inan y form,b y print photoprint, microfilm oran yothe rmean swithou t writtenpermissio n from thepublisher s Woord vooraf

Sindsi ki n197 3voo rhe teers tkenni smaakt eme td ewetenschappelijk e aspecten vand ehydrobiologi ehe bi kgeprobeer dm eee ndee lva ndi tvakgebie d eigent emake n onderd estimulerend e leidingva nDrs .J.J.P . Gardeniers.Jean ,zonde rjou wnie taf latende ideeënstroom, critischebeschouwingen ,enthousiasm ee ndidactisch e talenten wasdi tproefschrif te rnie tgekomen .Nie t alleenhe bi khe tva kva nj egeleerd ,n a mijnstudi ebe nj ezowe lee ngewaardeer dmento ral see ngoe dvrien dgebleven .Talloze - discussies liggenachte r ons,waarva nvel eto tdie pi nd enach tduurde nterwij lonz e wederhelftend eavon d alleeno fsame ndoorbrachten .Mij ndank . Mijnpromotor ,Prof.Dr .M.F .Mörze rBruyn sbe ni kdan kverschuldig dvoo rd e gelegenheiddi ehi jmi jboo do mdi tonderzoe kbi jd evakgroe pNatuurbehee rt ever richten.Mij nbelangstellin g voorhe tnatuurbehee r isvoo ree nbelangrij kdee lt e dankenaa nU winteressant e collegese nverhalen .Teven sbe ni kU zee r erkentelijk voorU wwaardevoll e adviezentijden sd ebewerkin gva nhe tmanuscript . Prof.C.W .Stortenbeke rwi li kbedanke nvoo r zijnstimulerend e commentaaro p hetmanuscript ,hetgee n zoweld estij lals.d eopze tte ngoed ekwam . Bijzondere dankbe ni kverschuldig daa ndegene ndi ehebbe nbijgedrage naa nd e totstandkomingva ndi tproefschrift : - Ir.J.Chr . Bothbego nme td evoorbereidin gva ndi tonderzoek .Vee lva njou w ideeën zijni ndez estudi everwerkt .Teven she bj ehe tmanuscrip tmeni gmaa lcritisc hdoor genomene nd ediscussie sdi ehiero pvolgde nhe bi kzee r gewaardeerd. - Ir.P.F.M .Verdonscho tverrichtt e tweedeelonderzoeke nva ndez estudie ,welk e zoveel interessante informatie opleverdenda tw edi telder s zullenpubliceren .Dank baarhe bi kgebrui kgemaak tva nj enoest ewerklus te nj eideeë no mgegeven st ever - werken. - Ir.0 .Kno ldee dhe tonderzoe knaa rd eafbraa kva ndivers ebladsoorten .Oo kdi t werk zullenw eelder spubliceren ,maa rd evel ediscussie sdi ew evoerde nhebbe n wezenlijkbijgedrage nto td ehuidig evor mva nhe tmanuscript . - Dr.H.K.M .Molle rPillo tvoo rhe tdeterminere nva nvel emuggelarven . - Dr.L.W.G .Higle rvoo rhe tdeterminere nva ndivers ekokerjuffers . - Drs.J.G.M .Cuppe nvoo rhe tcontrolere nva nmoeilijk ekevers . - Dehere nI .Wolter se nJ.A.J .Beye rvoo rd everleend ehul pbi jhe tuitzoeke ne n analyserenva nd emonsters . - Ir. H.Breme rvoo rhe tschrijve nva nd emeest e computerprogramma's,waarva ni k veelhe bgeleerd . - Drs.P .va nIerse lvoo rzij nassistenti ebi jhe tclusteren . - Ir.D .Davelaa rvoo rhe t schrijvenva nenkel e aanvullendeprogramma's . - Dehee rI .Mad eSuwetj avoo rhe tschrijve nva nd eplotterprogramma's . - Dr.L .va nde rPla svoo rhe tbeschikbaa rstelle nva nanalysefaciliteite nvoo r de korrelgrootteanalyseva nd ebodemmonster s opd evakgroe pBodemkund ee nGeologie . - Dehee rA .Engelsm avoo rzij nassistenti ebi jdez eanalyses . - Mej.W .Hofste evoo rhaa rhul pbi jd ekorrelgrootteanalyses . - Dehere nJ .va nde rGoo re nH .Paardekope r enhu nmedewerker sva nd ewerkplaat s vanhe tBiotechnio nvoo rd ebou wva nd ekunstbee ke nkweekgoot . - Drs.J .Beunde rvoo rhe tbeschikbaa rstelle nva nruimt evoo rd e laboratorium experimenteni nhe tBiotechnion . - Ir.J .Meulema ne nIr .J . denDui kvoo rhu nhul p alse rwee reen s ietsmi s ging metee nprogramma . - Dehee rM .Keul svoo r zijnstatistisch e adviezen. - Mevr.M .Gazenbeek-Dobbi evoo rd ecorrecti eva nd eengels etekst . - Mej.A.M.N.G .Salde nvoo rhe ttype nva nd e literatuurlijsten. - Mej.E .Geurtse nva nd eafdelin gTekstverwerkin gvoo rhe tsnell ee n nauwkeurige typewerkva nhe tdefinitiev emanuscript . - Dehere nI.R.C .Cressi ee nR.J.P .Aalpo lva nPudo cvoo rd ecorrecti e en redactionele vormgevingva nhe tmanuscript . - Demedewerker sva nd evakgroe pNatuurbehee rvoo rd eprettig ewerksfee r end evel e goedecontacten . - Velecollega' s inbinnen -e nbuitenlan dvoo rhe ttoezende nva noverdrukke n end e velemondeling ee nschriftelijk eadviezen .

Tenslottemaa rnie ti nd e laatsteplaats ,dan k ikElle nvoo rd etalloz e uren dieeigenlij kvoo ron ssame nwaren ,maa rdi ei kaa ndi tproefschrif tbesteedde . Curriculum vitae

HarryHendri kTolkam pwer d geboreno p3 septembe r 1952t eAalte nt emidde nva nd e toenno ggrotendeel snatuurlijk ebeken .Hi jvolgd e inAalte nhe tkleuter- ,basis -e n voortgezet onderwijs enbrach tvee lva n zijnvrij etij ddoo ri nd ebosse ne nd ebeke n ind eomgeving .N ahe tbehale nva nhe t einddiplomaHBS-B ,bego nhi ji n196 9me td e studiei nd eMilieuhygiën e (N42)aa nd eLandbouwhogeschoo l teWageningen ,waa rhi ji n 1972he tkandidaats -e ni n197 5he tdoctoraalexame n aflegde.Voo rhe t doctoraal examenwer dhe tonderzoe kvoora l gerichto phe twaterkwaliteitsbeheer : Natuurbeheer- Hydrobiologie bijProf.Dr .M.F .Mörze r Bruynso.l.v .Drs.J.J.P .Gardeniers ;Waterzui veringbi jProf.P.G .Foh ro.l.v . Ir.J.G.de nBlanken ,T.H .Delft ,Afd .Gezondheids - techniek;Microbiologi e bijProf.E.G .Mulde ro.l.v . W.L.va nVee n(f) . Nahe tdoctoraa lexame nwa shi jwerkzaa mal swetenschappelij kambtenaa rbi jd e VakgroepNatuurbehee rva nd eLandbouwhogeschoo l totdecembe r 1975,vervolgen sal s wetenschappelijk assistentbi jdezelfd eVakgroe p voorhe tverrichte nva n voorliggend onderzoek enva njun i 1979 totjanuar i 1980wedero mal swetenschappelij k ambtenaar. Sindsdien ishi jwerkzaa m alshydrobioloo gbi jhe tWaterscha p Zuiveringschap Limburg teRoermond . Contents

1 Introduction 1.1 General 1 1.2 Purposeo fth e investigation 4 1.3 Hypotheses 5 1.4 Researchapproac h "

•7 2 Description of the streams 2.1 TheSnijdersveerbee k ' 11 2.2 TheRatumsebee k 16 Methods 1g 3.1 Fieldprocedur e 16 3.1.1 Selectiono fsamplin g sites 16 3.1.2 Samplingdate s 17 3.1.3 Fieldclassificatio no f substrates 18 3.1.4 Samplingmetho d 20 3.1.5 Additional collections 20 3.2 Laboratoryprocedur e 20 3.2.1 Samplesortin g 20 3.2.2 Substrateanalysi s 23 3.2.3 Macrofauna analysis 25 3.3 Laboratory experiments 25 3.3.1 Artificialstrea mchanne lexperiments 25 3.3.1.1 Thestrea m 27 3.3.1.2 Substratesteste d 27 3.3.1.3 Experimentaldesig n 29 3.3.1.4 Speciesteste d 29 3.3.1.5 Theinfluenc eo fcurren tvelocit yo n substrate selection 30 3.3.2 Rearingchanne l 30 3.3.3 Experimentswit hTrichopter a 30 3.3.3.1 Case-building experiments 31 3.3.3.2 Grainsiz eanalysi so fnatura lTrichopter a cases 32 3.4 Fieldexperiment s 32 3.4.1 Artificialsubstrat etray s 33 3.4.2 Artificialsubstrate s introducedwithou t trays 3.4.3 Litterbag s 34 •3.5 Dataprocessin g 34 3.5.1 Data storage 34 3.5.2 Statisticalmethod s 35

Results 37 4.1 Data 37 4.1.1 Fieldclassificatio n ofsubstrat etype s 37 4.1.2 Grain-size classification inth e laboratory 40 4.1.2.1 Substrate composition 40 4.1.2.2 Substrate types 41 4.1.3 Discussion 4.1.3.1 Theus eo fth e Indexo fRepresentatio ncompare d toothe r statisticalmethod s 4.1.3.2 The importance ofth ejoin tus eo f 11an d 10°sdetritu s classifications 4.1.3.3 The influenceo fanima l abundance onth e Indexo fRepresen 46 tation 4.1.4 Groupingo fsubstrat etype sbase do nspecie scompositio n 47 49 4.1.5 Grouping ofspecie sbase do nsubstrat epreference s 56 4.1.6 Numbers ofspecie san d specimens indifferen t substrate types 4.1.7 Field experiments 58 58 4.1.7.1 Trays filledwit h artificial substrate 59 4.1.7.2 Particle sizes introducedwithou t trays 60 4.2 Organism-substrate relationships 60 4.2.1 Outlineo fpresentatio n 4.2.2 Autecological datafo rselecte d species 62 62 4.2.2.1 Lithaxobscuru s (Hagen) (Trichoptera: Goeridae) 4.2.2.2 Sericostomapersonatu m (Spence) (Trichoptera: 68 Sericostomatidae) 4.2.2.3 Micropterna sequax (MacLachlan)(Trichoptera :Limnephilidae ) 75 4.2.2.4 Chaetopteryxvillos a (Fabricius) (Trichoptera: Limnephilidae) 91 4.2.2.5 Plectrocnemiaconspers a (Curtis) (Trichoptera: 100 Polycentropodidae) 103 4.2.2.6 Ephemeradanic a (Müller) (Ephemeroptera:Ephemeridae ) 114 4.2.2.7 Nemouracinere a (Retzius) (Plecoptera:Nemouridae ) 4.2.2.8 Limniusvolclonar i (Panzer),Elmi s aenea (Müller)an d Oulimniustuberculatu s (Müller) (Coleoptera:Elminthidae ) 116 119 4.2.2.9 Gammaruspule x (L.) (Malacostraca:Amphipoda ,Gammaridae ) 128 4.2.2.10Dicranot aZettersted t sp. (Diptera:Limoniidae ) 132 4.2.2.11 LimnophilaMarquar tspp . (Diptera:Limoniidae ) 134 4.2.2.12Ptychopter aMeige nspp . (Diptera:Ptychopteridae ) 4.2.2.13Orthocladiu sva nde rWul p spp. (Diptera:Chironoraidae , Orthocladiinae) 135 4.2.2.14Micropsectr agr .praeco x (sensuTshernowskij ) (Diptera: Chironomidae,Tanytarsini ) 137 4.2.2.15Paracladopelm aHarnisc hspp . (Diptera:Chironomidae , Chironominae) '40 4.2.2.16Prodiames aolivace aMeige n (Diptera:Oiironomidae , Orthocladiinae) 142 4.2.2.17Epoicocladiu s flavens (Malloch) (Diptera:Chironomidae , Orthocladiinae) 144 4.2.2.18Chironomida eo £detritu ssubstrate s 146 Conchapelopiamelanop s (Wiedemann) (Diptera:Chironomidae , Tanypodinae) 14° CorynoneuraWinnert z spp.(Diptera :Chironomidae , Orthocladiinae) 148 Brilliamodest a (Meigen) (Diptera:Chironomidae , Orthocladiinae) ' 148 Diplocladius cultrigerKieffe r (Diptera:Chironomidae , Orthocladiinae) 149 RheocricotopusThieneman nspp . (Diptera:Chironomidae , Orthocladiinae) I49 Eukiefferiellagr .discoloripe s (sensuMolle r Pillot, 1980) (Diptera:Chironomidae ,Orthocladiinae ) 15° Polypedilumlaetu magg . (sensuMolle rPillot ,1979 ) (Diptera: Chironomidae,Chironominae ) 1S1

5 General discussion 153 5.1 Particle size 154 5.2 Currentvelocit y 156 5.3 Foodcondition s 158

6 Conclusions 165 6.1 Substratecompositio n 165 6.2 Substratepattern s 166 6.3 Effecto fregulatio n 169

Surrmary 173 Samenvatting 176 Appendices 181 Identification references 196 References 200 Outline of substate classification

Abbreviationsuse d inth e field classificationo f substrate types

= Sand FD = FineDetritu s = Gravel St = Stable CD= Coars e Detritus Sh Shifting = Leaves B __ Bare = Detritus CD+ L CD/FD = CDwit ho r without FD

Names,ph ivalue s andph i indiceso f grain-size fractions

Fraction Phi value Phi index Nameo f fraction (mm) (-log fraction)

128 _ 256 -7 8 cobbles 64 _ 128 -6 7 cobbles 32 _ 64 -5 6 largepebble s 16 _ 32 -4 5 small pebbles 8 _ 16 -3 4 coarse gravel 4 _ 8 -2 3 medium gravel 2 _ 4 -1 2 finegrave l 1 _ 2 0 1 very coarse sand 0. 500- 1 1 1 coarse sand 0. 250- 0.,50 0 2 2 medium sand 0. 125- 0. 250 3 3 finesan d 0. 050- 0. 125. 4 4 very finesan d 0 - 0. 050 5-10 0 silt andlutu m t: 0.050 mm isuse d instead of 0..062 5 mm

Q.M.Q,inde xdescribe s the grain-size composition ofa substrateb y givingth e d 3 first (Q ), second (median) and third (Qg)quartile s expressed in integer phi values (phi indices). 1 Introduction

1.1 GENERAL

Lowland streams,wit ha strongl y fluctuating discharge,wate rlevel ,curren t velocity,botto mcompositio n andvegetatio npattern ,ar ea characteristi c typeo f stream for theNetherlands .A larg enumbe ro fbenthi cmacroinvertebrat especie sar e restrictedt othi styp eo fenvironmen t andfor m thecharacteristi c animal community ofth enatura l lowland stream. Sinceth e 1930smos t lowland streamsi nth eNetherland s havebee nregulate di n connectionwit hlan dreclamatio n schemeso rprogramme s aimeda tth eimprovemem to f streamhydrolog y toincreas edrainag e andi nth emor e recentdecade s alsot olowe r thegroundwate r level invas t areas.Thi s implies thereductio no finundation ,pea k flow,erosio nan d sediment transport.T othi s endmeander s are cutoff ,bend sar e straightened, thestrea mbe d isdeepene d andwidened ,th eslop eo fth ebank si sstan dardizedt oa 1: 2o r1: 3profile ,ban kvegetatio n isremove d andpath s arecon structed forgras smowers ;weirs andbarrage sar eplace da tregula r intervalst o reducesedimen t transportan d retaina minimu mwate rleve li nsumme rfo r irrigation purposes.Bank sar eofte nreinforce d withconcrete ,nylo nmattin go rwoo d andsome times thewhol e streambe d isreinforce dwit hconcret eblocks .Severa l termsar ei n use todescrib e thesekin do fphysica l perturbations.Hereafte r the term regulation willb eused ,t osav eth eter mchannelizatio n for streams andrivers.tha thav ebee n regulatedwit hth epurpos eo ffacilitatin g transportb yboat . Regulation strongly affects thephysica l characteristicso fth estrea m system, andinvestigation si nth eAchterhoe k (Gardeniers& Tolkamp ,1976 )an d elsewherei n theNetherland s (Heijdeman& va n 'tOever ,1976 ;Peter s& Leijten , 1977;d eGraaff , 1979)demonstrat e thatth eanima lcommunit y livingi nregulate d streamsi squit e different fromtha tlivin g inunperturbed ,natura l lowland streams,a featur efre quentlyreporte d inothe rcountrie s forothe rstrea m typesa swel l (e.g.Wen e& Wickliff,1940 ;Engelhardt ,1951 ;Stuart ,1959 ;Einsele ,1960 ;Rouyer , 1975).Th e typicalfaun apresen t innatura l lowland streamsi softe npracticall y absent from streams thathav ebee nregulated .Onl yi nstream sregulate di nth eol d fashioned way,wher emaintenanc eha sbee nneglecte d sinceth emajo rregulatio nworks ,ma y the faunao fth enatura l streamb eabl et osta yo rre-establis h itselfi nplace swher e conditions arereturnin gt oth eorigina l state.I nsuc hsemi-regulate d streamsth e faunama yconsis to famixtur eo fpond - andstream-dwellin g species.I nmos tregu lated streams,however ,th especie scompositio n resembles thato fcanals,.ditche san d

1 ponds.Thi sca nb eattribute dt oth echange s thephysica lenvironmen tha sundergone . Levellingdow nth espatia l andtempora lvariatio ni ncurren tvelocit ywil l result inmor eunifor msubstrat epatterns, whil e theabsenc eo fban kvegetatio n (trees and shrubs)whic hwoul d shadeth ewater ,result s inhighe rwate rtemperature s and the developmento fmacrophyte so reve nmicrophyte swhe ncurren tvelocit y islo wenough . Lessallochthonou smateria lwil lente rth estrea msyste man dalga ean daquati c plants willreplac eleave sa sth etrophi cbasi so fth ecommunity .Th e stream system changes fromheterotrophi c toautotrophi c (Cummins et al., 1973). Consequently,majo rchange si ncommunit y structurewil lresult .Fo r each animal speciesi ti sessentia ltha tenvironmenta l factors arepresen t inth erigh t extent withinreac ho fth eanimal .Comparin gnatura lan dregulate d lowland streams,an d notingth edifference si nspecie scompositio no fth ecommunitie spresent ,th e impressionbecome sstronge r thatth eenvironmenta l demands ofspecie s characteristic forunperturbe d lowlandstream sar es ospecifi ctha tthe yca nonl yb eme t inver y distinctplace swithi nth estream .Apparentl y thesespecie sca nonl yfin d the optimalcombinatio no fphysica lparameter si na streamwit hmuc hvariation ,wit h therigh texten to rrang eo feac hfacto r important forthei r existence (e.g.sub strateparticl esize ,curren tvelocity ,food ,oxyge n supply). Manyinvestigation shav ebee ncarrie dou ti nDutc hlowlan d streamsdurin g the lasttw odecades ,mainl yconcernin g thedescriptio no fth estrea mfaun aan d the effectso fpollutio n (e.g.Mu rAtzema ,1962 ;Gardeniers ,1966; Molle r Pillot,1971 ; Higler,1972 ;Tolkamp ,1975a ;Gardenier s &Tolkamp , 1976). These investigations on thephysica lan dchemica lqualit yo fth estream sa srelate d toth emacroinvertebrate s havele dt oa reasonabl ycomplet epictur eo fth egeographica l distributiono f the benthicmacroinvertebrate s inDutc hlowlan dstream s ando fth edifference s between naturalan dregulate d streamsi nth esens eo fth ecompositio no fth eanima l community. Thedifference si nspecie scompositio nhav eeve nbee nuse d as aninstrumen t tomea sureth edegre eo fregulatio no fa lowlan d stream (Tolkamp& Gardeniers , 1977). However,curren tvelocit y isonl yon eo fth eparameter s thatma y change after regulationan dn odetaile d informationi savailabl eo nth especifi creason sfo r the differences inanima lcommunitie sbetwee nnatura l andregulate dstreams .Curren t velocityi so fcours eon eo fth ereasons ,bu tth edistributio n offreshwate r animals isals odetermine db ya whol ecomple xo fa larg enumbe ro fphysical ,chemica l and biologicalfactor s (Wesenberg-Lund,1943 ;Engelhardt ,1951 ;Albrecht ,1953 ;Macan , 1961, 1962;Cummins ,1966 ;Thorup ,1966; Cummin s &Lauff ,1969 ;Hynes ,1970a ,b ; Meadows& Campbell ,1972 ;Macan ,1974 ;Decamp se t al, 1975;Friber ge tal , 1977). Schmitz (1954)followe dThieneman n (1912)i nth econceptio n thatcurren tvelocit y and temperaturear eth eprimar yfactor sinfluencin gth edevelopmen t of running-water zoocoenoses.Whitehea d (1935)conclude d thatth enatur eo fth e streambe d iso fgrea t importancea sa facto rdeterminin g thenatur eo fth e fauna,eithe rdirectl y (pro vidingshelter ,suitabl eattachmen t sites)o rindirectl y (providingfood , influencing thenatur eo fplan tgrowth ,givin gsuitabl eoxyge nconditions) . Thestrea mbotto m isth eproduc to ftw o sources thatprovid eth ebasi ccom ponents:minera lan dorgani callochthonou smateria l suppliedb ywate ran dair ,an d mineral andorgani cautochthonou smateria lpresen t inth estrea mbed ,originatin g fromgeomorphologica lconditions .Unde rth e influenceo fth edischarg e regimean d thefor mo f thestrea mchannel ,interactin g intw omajo rcounte rprocesses ,erosio n andsedimentation ,th ebasi ccomponent s arearrange d insubstrat epattern swit h characteristic properties concerning composition (particle sizean dnatur eo fminera l andorgani cmatter) ,structur e (spatialvariations-vertica l andhorizontal ,stability , packing,porosity )an ddynamic s (temporalchange si nstructure) .Becaus eo fth e sorting activityo fth ecurrent ,th estructur eo fth e streambotto mi s inseparably interwovenwit hth evariatio no fth ecurren t (velocity,regime ,turbulence ) (Schmitz, 1961;Scherer , 1965),resultin g ina constantl yvaryin g (inspac ean d time)mosai c patterno fsubstrat e types,eac hwit hdifferen t environmental conditions.Grain-siz e compositionma yvar ya tver yshor tdistance s and influence,fo rexample ,th eoxyge n contento fth e interstitialwater ,th eamoun to f trappedorgani cdetritus ,th egrowt h ofperiphyto nan dth enumbe ro fcrevices . Cummins &Lauf f (1969)presente da diagra mshowin g thefou rmajo rcategorie s of environmentalparameter s (Fig. 1). Theyemphasize d thatcurrent ,temperatur e andcon centration ofchemica l factorsma ylimi t therang eo fhabita t tolerances (macro- distribution)an dtha tsubstrat eparticl esiz eo rfoo dsuppl yar eprobabl yth emai n microdistributionalfactors .Althoug h several additionalphysica l factors influencing distribution areofte nmentioned ,thes ear emostl ydirectl yrelate d toon eo fth e mainfactors :flo wregime ,drought ,spates ,illumination ,suspende d solids,proximit y ofsuitabl ehabitat s (Sprules,1947 ;Hynes , 1970a).Bioti c factorsa scompetitio n andprédatio n (Macan,1962) ,ovipositio nan ddrif thabit s (Macan,1961 ;Hynes , 1970a) areals orelate d toth emai nfactor s food,curren t andsubstrate . Ulfstrand (1967)stresse d thepoin ttha tth emos timportan t factorlinke d with substrate isth eprovisio no ffoo di nth efor mo fallochthonou san d autochthonous matteran dpre yanimals .Thi s agreeswit h thevie wo fCummin s (1975),wh o stated that foodwil lundoubtedl yb e theultimat edeterminan t ofmacroinvertebrat edistributio n andabundanc e innon-perturbe d runningwaters .Bu th eadde d thatwhe nfoo d conditions arefavourable ,othe rfactors ,a s sedimentparticl e size,current ,competitio n for spaceo rprédatio nwil l determine themicrodistributio nwithi na give nsectio no f a stream.MDreover ,foo d ispar to fth esubstrat efo ralga lfeeder s (grazers,scrapers ) aswel la sdetritu sfeeder s (shredders,consumers )an d thepresenc e andabundanc e of food substances isinfluence dby ,fo rexample ,th eparticl e size (accumulation of detritus (Rabeni& Minshall ,1977)) ,sedimen t transport (scouringof f attached algae),ligh tcondition s andcurren t (distributiono fdetritus ,growt ho fhydrophytes , bringing foodt ofilte rfeeders) .Th epreferenc eo fpre yorganism sfo rcertai nsub strateo rfoo d typeswil l influence thedistributio no fthei rpredator s (Ulfstand et al., 1971;Hildre w& Townsend , 1976). Forth ever yreaso ntha tth esubstrat e isth eresultan to fan dstrongl yinter - ~> FOODSUBSTANCE S <- SUBSTRATE (Detritus,prey, PARTICLE microphytes,etc.) SIZE A

w o ss 3 g MICRODISTRIBUTION a

V V V V OTHERPHYSICA L -CHEMICA L CURRENTVELOCIT Y <- PARAMETERS (e.g O ,Temp., pH, CaC03, Fe203)

TURBULENCE andCURREN T

-> :Interaction sbetwee n environmental parameterst owhic h agive n benthic species interacts __>: Influenc eo f theenvironmen t ona benthi c specieswhic h results inrecognitio no f thehabita t .>: Influenc eo fa give nbenthi c specieso n thehabita t

Fig.1 .Genera lrelationshi pbetwee nenvironmenta l parameters and themicro - distributiono fbenthi c streammacroinvertebrate s (afterCummin s &Lauff,1969 )

linkedwit ha numbe ro fphysica lfactor san di so fgrea tecologica l importancefo r macroinvertebrates,i ti sa noutstandin gparamete rfo rth estud yo fmacroinvertebrat e microdistribition.Becaus eth esubstrat ecomposition ,structur ean ddynamic sar eth e firstt ochang eunde rth einfluenc eo falteration si ncurren tvelocit yan ddischarg e regimefollowin gstrea mregulation ,the yma yprov et ob eth emajo rreason sfo rth e differencesi nspecie scompositio nbetwee nnatura land 1regulate dlowlan d streams.

1.2 PURPOSEO FTH EINVESTIGATIO N

Thepurpos eo fth einvestigatio nwa st ogai ninsigh tint oth erol eth esubstrat e playsi nth edevelopmen tan dpreservatio no fth emacroinvertebrat ecommunitie si n natural,undisturbe dlowlan dstreams .Testin gan dquantificatio no fth erelationship s betweentempora lan dspatia lenvironmenta lfactor sa smeasure db ysubstrat echarac teristicsan dth ecompositio no fanima lcommunitie swil lincreas eth eknowledg eo f theautecolog yo fsom etypica llowlan dstrea mspecie san dwil lmak e itpossibl et o indicatesom eo fth ecritica lcondition stha tdistinguis hnatura llowlan dstream s fromothe rwatercourses . As abasi sfo rpreservatio nan dmanagemen to fthes estream sthi sknowledg ei s indispensablean di twil lcontribut et oth equantificatio no fth elimitin gcondition s concerningstrea mdimensions ,profile ,meandering ,ban kvegetation ,wei rlevel , currentspeed ,maintenance ,effluen tdischarge ,recreatio nan dban kprotection .Ther e isa nurgen tnee dfo rthi skin do finformatio nsinc eth edemand smad efro mth e hydrologicalpoin to fvie war eofte ncontradictor yt oth ewis ht opreserv eth eDutc h lowland streama sa uniqu etyp eo fenvironment .

1.3 HYPOTHESES

Itha sbee nshow nb ynumerou sauthor stha tdistinc tdifference soccu ri nth e speciescompositio nfoun d indifferen tsubstrat etype s (e.g.Penna k& va nGerpen , 1947; Thorup,1966 ;Mackay ,1969 ;Macka y& Kalff ,1969 ;Ward ,1975 ;Cummins , 1975). Manyauthor suse dth esubstrat emerel yt odescrib eth evariou shabitat sthe yencoun teredan dwer eno ttryin gt oestablis hdifference si nth efauna lcompositio no fth e substratetypes ,bu tdescribe dth estrea mfaun aitsel fan dwher et ofin di t(e.g . Thienemann,1912 ;Behning ,1928 ;Beyer ,1932 ;Geijskes ,1935 ;Sprules ,1947) .Mor e recently,studie sdirectl yrelatin gspecie sdistributio nan dsubstrat ecompositio n havebecom enumerou san dman yreference swer egive nb yCummin s (1966), Thorup (1966) andHyne s (1970a, b). Althougha specie sma ysho wa distinc tpreferenc efo ra certai nsubstrat etype , otherfeature sprevailin gi nth esam eplac eo ri nth eneighbourhoo dma ycaus eth e animalst otolerat eless-preferre dsubstrates .Cummin s& Lauf f (1969)demonstrate d thisfo rth estonefl y Pevlesta plaaida, insubstrate-selectio nexperiments .Variou s authorshav eshow nfo rsevera lspecie stha tdifferen tinstar sma yprefe ro rdeman d differentsubstrat egrai nsize so rcomposition s (e.g.Scott ,1958 ;Hanna ,1961 ; Cummins,1964 ;Schwoerbel ,1967 ;Mackay ,1969 ;Elliot ,1971 ;Harman ,1972 ;Otto , 1976). Rees (1972)foun da significan trelationshi pbetwee nth ebod ylengt ho f Gammarua psevdolirnnaeus (Amphipoda)an dth esubstrat eparticl esiz ei nlaborator y experiments,an dWesenberg-Lun d (1943)alread ygav eexample so fsevera lcaddi sfl y speciestha tus edifferen thouse-buildin gmaterial sdurin gthei rdevelopment .Macka y (1977)demonstrate dtha t Pyenopsyche scabripennis (Trichoptera)pupa eburro wi n othersubstrate stha nth elarva eprefer .Thu sman ybenthic-stream-dwellin gmacro - invertebratesma ynee dsevera lsubstrat etype st ocomplet ethei rlif ecycle . Theseobservation sforme dth ebasi sfo rth efollowin ghypothesis : Thedemand so fman ybenthi clowlan dstrea mmacroinvertebrat especie so fth esubstrat e areo fsuc ha natur etha tthe yca nonl yb eme t ina non-regulate dlowlan dstrea mwit h itstypica lsubstrat ecompositio nan dpattern . Twoworkin ghypothese swer eformulate dt otes tthi shypothesis : - Manybenthi c lowland streammacroinvertebrat e species show distinct preferences fora specifi csubstrat e composition. - Forman yo fthes especie sth esmall-scal e spatialvariatio n insubstrat ecompo sitiono fth estrea mbe d isessentia l forthei rexistence .

1.4 RESEARCHAPPROAC H

Testingo fth eworkin g hypotheseswa sperforme d inthre e steps: - Determinationo fth emicrodistributiona lpattern s ofth emacroinvertebrate s in two natural,undisturbe d lowland streams (field investigation). - Determinationo fsubstrat epreference s ofa numbe ro fcharacteristi c lowland streamsspecie si nsubstrate-selectio n experiments ina laboratory stream channel (laboratory experiments). - Determinationo fth emacroinvertebrat e colonizationo fartificia l substrates in the streambe d (fieldexperiments) .

Thisapproac hwa schose nbecaus eth e interpretation ofdat a fromfiel d research onlylead st ocorrelation sbetwee nanima l distribution and certain environmental parameters.Experiment s inth e laboratory orth e field,o rboth ,ar enecessar y to providedat atha tca nb euse d totes tth econclusion s derived from the field research. 2 Description of the streams

Theinvestigatio nwa scarrie d outi ntw onatural ,unperturbed ,unpollute d low landstreams :th eSnijdersveerbee k (Snijb)an d theRatumsebee k (Rab).Bot h streams are situatedi nth eeaster npar to fth eAchterhoe ki nth eprovinc eo fGelderland , wherenatura l streams arestil lpresen t (Fig.2) .I nbot hstream s the investigation was restricted toa sectio no f150 0metres .

2.1 THE SNIJDERSVEERBEEK (FIGS.3 AN D 4)

Onlyth efirs t 1500m o fth eSnijdersveerbee k isi nanatura lstate .Th edown streampar tha sbee nregulate d and containsonl y stagnantwate ro rn owate ra tal l forth e largestpar to fth eyear .Th e streamoriginate sa tth ewester nborde ro fth e

Twente kanaal

f FRG

Ratumsebeek

Wlllinkbeek Boven Slinge

Nijmegen

Fig. 2.Stream s inth e Achterhoek.Th eshade d area indicates theare awher enatural , unpolluted streams still exist (modified after Gardeniers &Tolkamp , 1976). O 10020 0 to—lanntam 50 150 250

25.0

30.0 Bocholt

•H-H-+++ :borde r NL-FRG

35.0: altitud e inm ^•••"•"^^: dr yi nsumme r : farm land ,-••"•—*"\ :grave l within4 0c m : hedgerowo rfores t ^•/V"-—'" below thesurfac e

Fig. 3.Th eSnijdersveerbeek , showing Sections 1-8.

'tertiaryplateau 'i na smal lvalle yapproximatel y3 mbelo wth e levelo fth esur roundingarea .I trun si na westerl ydirectio nove rth eslop eo fth eplatea uan d reaches,afte rpassin gth erelativel ystee pedg eo fth eplateau ,th efla tare acalle d 'Pleistocenebasin' .Thi sbasi ni sfille dwit hcoars esand st oagrea tdepth ,whic h givesris et oth eintermitten tcharacte ro fth edownstrea mpar to fth estream . Theuppe rpar to fth estrea mi sfe db yiron-ric hgroundwater ,whic h continuously seepsint oth estrea mthroug hth ebe dan dbanks .Eve ni nth eextremel ydr ysumme ro f 1976thi sdi dno tstop .Th econtinuou sseepag ei s connectedwit hth especifi cgeo - morphologicalan dhydro-geologica lcharacteristic so fth earea :coars esediment s (wind-blownsand san dMiddl ePleistocen efluviat il esan dan dgravel )ar esituate do n ." .'*"-. "'"C".".''f \ - ''O," --Ti '~4

: • -. *" •• •«•••• •"*. .'w^ •' 'i- -• . >;' .A.rï? • •-.*•! ,

m '** . .. • - J** 'Hl- --" , • 't* & -.. *;i*»-N-"-- •. -''«•ï

E/;* ------VÄ.- ;*._•;*.- T4 r.\& .* <>. r •. • #\ •».•*.,v, *- ' . « ^."T.-r--' -' • .'" ..-o--'- ÏY **;* ;**«! £- • V? " " •• "-.-•..• •'• :-*vtv-»Ji Ji,".-*.': .*"".-• 4 •v.' ' -""~f- " ;-...-'• .•*,'a ifc .•*.:::•- .".•-« -; =/ •• .--"*»£ —v, t":i-"''-""-- '' &•" * **••. • •-" V ;^

Fig. 4.Samplin gsit ei nSectio n6 o f theSnijdersveerbeek .

heavycla y (teriary 'old'clay) ,whic hgive sris et oa groundwate rsuppl yt oth e Snijdersveerbeekfro ma fairl ylarg ecatchmen tarea .Th egroundwate rrun sove rth e claythroug hth ecoars efluviatil esand s andgravel .Wher eth estrea mbe dreache sth e groundwaterlevel ,seepag eoccur s (Kloosterhuis, 1968).Thi shappen si nth efirs t 500m o fth estrea m (Fig.3 ,Section s1-4) . Duringth ewinter ,th ewate ri nth estrea mpartl yoriginate sfro ma mor eup streampart ,t oth eeas to fth evalley .Thi spar twa sregulate di n197 5an dpea k dischargesar ediverte db ya ditc hrunnin gi nnortherl ydirection ,reducin gth epea k flowi nth eactua lstream .Th esmal lamoun to fwate rstil lpermitte dt oflo wthroug h thestrea mi sdetermine db yth edifferenc ei nsiz ean dleve lo fth eculvert sconnec tingth eupstrea man ddownstrea mwatercourses .I nsummer ,th ewate ro fth eregulate d sectiondoe sno treac hth e investigationpar to fth estream . Aftera preliminar y investigation (Tolkamp,1975b ;Both ,1976) ,eigh tsection s weredistinguishe di nth eSnij b (Fig. 3),eac hcharacterize db ydegre eo fmeandering , bankvegetation ,strea mprofil ean dsubstrat ecompositio n (Table 1).Th ewidt ho fth e streambe dvarie dbetwee n0. 4m an d1. 0m wit hsom epool su pt o2. 0m wide .Wate r depthvarie dfro m2 c mt o3 0cm ,wit ha naverag ei nsumme ro f2-1 0c man d inwinte r 15-20cm .Th ecombinatio no fa continuou san drathe rconstan tdischarg ewit ha strongslop e (5m/km )resulte di na stead ycurren tal lyea rround .Th eaverag ecurren t speedwa s 5-10 cm/si nsummer .I nwinte ri tincrease dt o20-3 0cm/s ,wit hoccasiona l Table 1.Physica l characteristics of theeigh t sections inth eSnijdersveerbee k and theupstrea m sectiono fth eRatumsebeek .

Snijdersveerbeek sections Ratumsebeek

1 2 3 4 5 6 7 8 1

Length/m 150 200 100 50 200 200 200 150 1500 Depth/cm 0-20 5-20 10-30 5-30 10-30 5-25 80-110 0-30 0-100 Width/cm 40-60 40-60 50-100 60-100 40-80 60-100 165-20040-8 0 150-300 Meanderingstron g not strong little strong little none none strong Shade trees herbs trees trees trees trees none herbs trees herbs Substrate S;L; S;G; S+G; G+S; S;L; G;S; S;FD G;S; G;S; FD;CD Veg FD;CD; Co; FD;CD Co;L; Co; Co;L; (CD) Veg Veg FD;CD Veg FD;CD

S=Sand ;G =Gravel ;Co=Cobble s andPebble s ;L=Leave s ; ( 2D=CoarseDetritu s : FD=FineDetritu s; Veg=Vegetatio n

higherspeed safte rheav yrainfall .Th e temperature regimewa s similart otha to fth e Ratumsebeek.Measurement swer e carriedou tmonthly .Minimu m temperatures inwinte r wereabou t2°C ,whil esumme rtemperature svarie dbetwee n 13C an d 16C . Thestrea mi sshade db ytrees ,brushwood ,hig hgrowin gherb so rhig h and steep banks,excep tfo roccasiona l shortstretche si nth e fourupstrea m sectionswher eth e bankvegetatio no rth ebank sha dbee ndamage db ycattl ean dman .I nthes e unshaded places,aquati cvegetatio noccurre di nsmal lmosai cpatterns ,mainl y consistingo f Vevonicabeceabunga, Mentha aqvatioa, Myosotis palustris andi nSectio n2als o Glyeeria fluitans. Especially thestee pbank swer e coveredwit h livermosses ,amon g themMarchantia polymorpha. Substratevarie dwit hcurren tvelocit y andgeologica l conditions.Th e presence ofgrave lwa sclearl y linkedwit hth eoccurrenc eo ffluviatil eRhin edeposits .How ever,onl yi nth eSection s 4,6 an d8 di dgrave l forma majo rpar to fth e substrate. Herei toccurre dove rth ewhol ewidt ho fth estrea mbed ,whil ei tsurface donl y in cidentallyi nth eSection s 2,3 an d 5.Grave l substrateswer emostl y situatedo no r mixedwit hsand .Onl y inth eSection s6 an d8 di dcla yo rloam ysan d formth e base forgrave lo rsan dsubstrates .I nal l sections exceptSectio n 7,leave s and organic detritusforme da majo rpar to fth esubstrat e- accumulate d nearth ebanks ,i npools , againstobstacle sprojectin g fromth ebe d inriffle so rtrappe d invegetation .Larg e quantitieswer eals ofoun dt ob emixe dwit h theminera lsubstrate . Section7 wa sno tinclude d inth eroutin esamplin gprogramm ebecaus e this part ofth estrea mfunctione d asa san dcollectio nbasin ,whic hwa s redimensionedi n1976 . Thewidt han ddept ho fth estrea mchanne lwer e enlarged to sucha nexten t (andth e treesalongsid ecut )tha ti nsumme rretentio nan devaporatio nwer e higher thanth e watersuppl yfro mupstream .Thi scause dth edesiccatio no fSectio n8 i nth e summers followingJun e1976 .

10 2.2 THERATUMSEBEE K (FIGS.5 AN D 6)

This streami sfe db ya larg enumbe ro fregulated ,an dmostl yman-mad e small tributaries,mainl ysituate di nGermany ,drainin g some120 0ha .I nth eNetherlands , itdrain sa nare ao fapproximatel y 2200h ai na rathe rnarro wdrainag eare awher eth e streami sfe db ya smal lnumbe ro fshor ttributaries .T opreven t inundations,pea k dischargesar ediverte d intoa sma lconcrete-line dcana lsom e6 k mdownstrea mo fth e investigated section.Th einvestigate d sectiono fth estrea m (Fig. 5), thefirs t150 0 m afterth eGerma nborder ,i sstrongl ymeanderin g ina noak-beec h forest.Th estrea m hasbee nlef t freet ofin dit sow nway ,producin gal ldegree so fmeandering ,althoug h undermined treestha twoul d obstructth eflo wo fth ewate rar eremove db yth eloca l waterboardo r(concerned )farmers . Normallyth estrea m flowsal lyea rround .However ,i nth esumme ro f197 6 the downstreampar tdrie dou tcompletel yan di nth einvestigate d sectiononl ysom epool s remainedwit ha noccasiona l tricklefro mon et oth eother .Thi sperio d lastedonl y fora fe wweeks ,an dth eplanne d samplingprogramm ewa spostpone dunti lth efollowin g January (1977).Th eslop eo fth estrea mi srathe rconstan ti nthi ssectio n (1.5

,/45.0

border NL-FRG : the stream meadows + **++**-

45.0: altitud e inra tributary ~_" ~— : farm land *A*A :pine s road : hedgerow or forest Fig. 5.Upstrea m sectiono f theRatumsebeek .Th e arrows indicateth eroutin e samplingsit e (R)an d thesit ewher e artificial substrates (AS)wer eplaced .

11 L£*- '•< •"-,.-.' - r' •'.I S

IR.- • •'«

Fig. 6.Samplin gsit ei nth eupstrea msectio no f theRatumsebeek .

m/km). Currentvelocit yvarie di nsumme rfro mver y lowi npool st o10-1 5 cm/sa t riffles.I nwinter ,pool-riffl edifference swer eles spronounce d andthe currentwa s 30-40cm/ so nth eaverage ,wit hpeak su pt o10 0cm/ safte rheav yrainfall . Thewidt ho fth estrea mbe dvarie dfro m 1.5m t o3. 0m .Dept hrange d from0-4 0c m insumme rt o30-10 0c mi nwinter .Temperatur evarie dbetwee n0 Can d5 Ci nwinter , althoughic ewa spracticall yneve rformed .I nsummer ,temperatur eros et o12-1 6C , withoccasiona lpeak so f19°C .Fo rcomparison ,thes edat ahav ebee ninclude d inTabl e 1. Inth einvestigate dsectio nthe strea mbe dcut srathe rdee pthroug hth e land scape,i nsom eplace s2 m o rmor ebelo wth esurfac e level.A strongl yvarie d rangeo f geologicaldeposit sreac hth esurfac ei nth estrea mbe d (Bosch,1967 ;Kramer , 1972). Fromth eGerma nborde rt osom e2. 5k mdownstrea mlia sdeposit semerge ,especiall yi n theoute rbends .I nthi sarea ,wher eth estrea mmeander sbetwee nth ehig hfarmlands , localmorain ecover sth elia sdeposits .I nsom eplace sthi sboulde rcla yi scompresse d toa ver yhar dlayer .Clayston ebank s areals opresent ,forme dthroug hcompressio no f clayan dsan dunde rpressur ei nth e liasperiod .Ove ra distanc eo fabou t1 km oligocènecla yreache sthe surfac ei nsom eplace sa swell . Inth einvestigate dsectio n ofth estream ,th esubstrat econsist sfo rapproximatel y40 1o fgrave l andstone s embeddedi no ro nto po fsan do rclay .Iro nconcretions ,resemblin groug hgrave l particlesfor ma nimportan tpar to fthe minera lsubstrate .

12 The streambe dconsist s ofa numbe ro fpool san driffles .Upstrea man ddown streamo fth ehar dbank s (claystone),th eslop eo fth estrea mbe di sles sstron gan d sedimentationtake splace .Her eth e streami sdeepe ran dth esubstrat econsist so f sandan dmu d (finedetritu smixe dwit h sand),togethe rwith largeamount so fleave s andcoars edetritus .O nth ehar dbank s theslop e issteepe r anderosio ntake splace . Hereth ebotto mconsist so fcoars esand ,fin ean d coarsegravel ,iro nconcretions , claystone,cla yan dpebbles .B y thealternatio no fpool san driffles ,th ewate rrun s stepwisedownstream . Leaves andorgani cdetritu s forma n importantsubstrat ei nthi sstream .Thi s material isconstantl yblow n intoth e streamfro mth ebank san dca nb e foundi n various formso fdegradatio nal lyea rround .I nautum nan dwinte rth einpu to ffres h leafmateria l isgreatest ,whil eth e amountgraduall ydecrease sthroug hsprin gan d summer.Sometime s largeaccumulation so f leaves formdam si nth estream ,leadin gt o considerable leveldifferences .I nthi swa y ariffl eca nb etemporaril y transformed intoa pool ,althoug hthi sdi dno thappe na tth e sitessample d in1977 . Ingeneral ,substrat ecompositio nfluctuate dmarkedl ydurin gth eyear .A sa n illustration,th esurfac eview so fth esamplin gsit ei nth eRatumsebee khav ebee n presented foreach seaso n inFig .7 .I nthi ssectio no fth eRatumsebeek ,whic hi s completely shaded,n oaquati cvegetatio ngrew .

13 Cobbleso r Pebbles Water's edge Bank overhanging water's edge

Fig.7 .Substrat emosai c structureo f+> , sitefo reac hseaso no f 1977 the Stream bed at theRatumsebee k sampling

14 December o -o . . o] •o o • ..»•..•••• » o°o0oo° o • o u o . o o o •o -0 o • FineGrave l+ Gravel Sand Fine Gravel Coarse Gravel Sand

ShiftingSan d FineGrave l+ Coarse Leaves CoarseGrave l Detritus + Sand

15 3 Methods

3.1 FIELDPROCEDUR E

3.1.1 Selection ofsampling sites

A representative sampling site ofapproximatel y 5 mlengt h was chosen in each section on the basis of the substrate composition and variation. Inth e Sections 4, 5 and 6i nth e Snijb and the one section in the Rab, the same site was used on all sampling dates. This gives animpressio n of the temporal substrate variation and any related changes inmacroinvertebrat e distribution. After the selection ofa samplin g site (always working inupstrea m direction) a sketch was made of the stream bed (Fig. 7)an d the stream profile. The positiono f the various substrate types and the exposition of the substrates toth e current was thus indicated. All dimensions were measured without stepping into the stream. Places inaccessible from the banks were measured after completing the sampling programme.I n each sketch the exact position of the samples was indicated and numbered. Samples were taken from all substrate types present ata chose n site. Before actually taking the samples, the site was observed fora whil e and bottom fauna visible on the substrate surface recorded.

3.1.2 Sampling dates

th jd rSVeerbeek sam lin W 'I ^f ^ ' P § -as carried out monthly from September 1975t o September 1976 and once every two or three weeks from September 1976 toApri l 1977. SniLH'' T °nth Gf0U rd0WnStrea mSeCti0nS :th ethre e "»*"» secti°- *™ n 1 VnC y' Fr°m Table 2' WhiCh giV6S ** seasonal "*»" <* sables 1 97S6eCrT U 1S Clr that the "*"* °£ S£mÇleS in SeCtion 8 ^creased after mZl'rTir, T by tHe deSlCCati0n °f the Stream b6d f™ ™V toNovembe r 1t eTM rargSment °f thG Sand-COllect^ action upstream in June 1976 and the fact that the suraner of 1976 was extremely dry ther27LT he\7Cti0nS' SeCti°n 5 Sh0W6d lGSS SUbStrate "Nation, whichi s ZilZTe Mt sTT nmbeT °f 5mpleS takGn there: n°^ ~» ^» in 1 Lu ie aTer ithe SamPlinS freqUenCy ~ ™ed' - -ntioned geT £SamPl6 S aUtUm th^se ;i^Z'z 17^Tsiz e^iiriT" n ° T ™ ber* swer etake "* **nin i97« «»6- I ii977n sprin-* g* ampleswer ealmos tal ltake nl n 1976,excep tfo rth efirs tsample s from 16 Table2 .Numbe ro fsample stake ni nth eSnijdersveerbee kan dth eRatumsebee k byseason .

Season Weeks Snijdersveerbeeksection s Ratumsebeeksection s 6 8 Total 14 5 8 Total

Winter 51-52 8 1 32 18 39 21 124 41 41 1-11 Spring 12-24 2 3 2 20 8 22 20 77 34 - - - 34 Summer 25-37 2 - 8 18 17 22 18 85 63 7 4 6 80 Autumn 38-50 5 5 16 26 14 23 7 96 40 - - - 40 Total 14 16 27 96 57 106 66 382 178 7 4 6 195

1975 inWee k 37,th e lastwee ki nsummer . Inth eRatumsebeek ,sample swer e takenever y twoo rthre eweek s fromJanuar y 1977t oJanuar y 1978.Samplin g datesar e summarizedpe rseaso ni nTabl e 2.Sample s takeni nthi sstrea m inJul y 1976,befor e thestrea mdrie dup ,wer eals oincluded . Themor edownstrea mSection s 4,5 an d8 wer eno tsample do na routin ebasi si n197 7 butth eavailabl e dataclearl y indicate thatth esubstrat e and faunao fthes esec tionsresembl e thoseo fth eupstrea m sectionstudie di n 1977.

3.1.3 Field classification of substrates

Substrateso na samplin g sitewer echaracterize d byth edominant-particl e size atth esurfac eo fth estrea mbed .Mostl y thisconcerne d combinationso fsevera l particle sizestogethe rwit h severaltype so forgani cdetritu si ndifferen tquan tities.Nin eminera l substrate componentswer edistinguished :Cobble s (Co),Pebble s (P),Coars eGrave l (CG),Fin eGrave l (FG),Grave l (G,a mixtur eo fC G and FG),Coars e Sand (CS),Fin eSan d (FS),San d (S,a mixtur eo fC San dFS )an dSilt/Lutu m (not abbreviated).Althoug hn ograin-siz emeasurement s werecarrie dou ti nth e field,th e differences betweenth ecomponent s roughly correspondwit hth e limitsgive n inTabl e 3,combinin g twofraction sa ta time ,startin gwit hver yfin esan dan dproceedin g upward from 0.05 nm. Practically every combinationo fthes ecomponent swa s foundi nth etw oinvesti gated streams.Mos t samples consistedo fa combinatio no ftw oo rmor eo fthes ecom ponents,whic htogethe r formeda substrat e type.Thi swa snote db ymentionin g the dominant component first,followe db yth e lessabundan t components,e.g . FG+CGo nF S withP .Thi smean s thatth esubstrat emainl y consistedo fFin eGrave lmixe dwit h (less)Coars eGrave lsituate d ona bas eo fFin eSan dwit ha noccasiona l Pebblei nth e substrate.Minera l substratesno tcombine dwit horgani cmateria lwer eindicate da s Bare,i.e .Bar e Sand (BS)o rBar eGrave l (BG).Unstabl eo rshiftin gsan d substrates werenote da sShiftin gSan d (Sh.S),whil e compact,stabl esan dsubstrate swer enote d asStabl eSan d (St.S). Organicdetritu swa s distinguishedi nthre etype san da nuiibe ro fcombination s

17 ofthese : - Leaves (L): accumulationso rlayer so fintac to ronl ypartl y disintegrated leaves, predominantlyo fallochthonou s origin. - CoarseDetritu s (CD):smalle rpiece so fleaves ,lea fskeletons ,sticks ,fruit s (acorns,beec hnuts) ,bark ,bu dscale s (beech),see dcapsules ,remain so f higher plants,etc . - FineDetritu s (FD):ver yfin eorgani cmaterial ,alread yver y disintegrated (e.g. macroinvertebrateexcrements) .Ofte namorphous ,brow n incolou r and finer than 0.05mm . Organicsubstrate swer eals odesignate d accordingt oth erati obetwee nth ecom biningtype swit hth edominan t typename d first.Whe nC Dan dL occurre di nequa l amountso ra tth emos ta rati oo f2: 1 ,th e substratewa sname d CD+L (Coarse Detritus andLeaves) .Whe non eo fthes etype swa smor eabundant ,th esubstrat ewa sname d after thedominan ttyp ean dth erati obetwee nth etype swa snoted .I nth e following CD+Lo r CDo rL wil lsometime sb ereferre d toa sDetritu s (D) (e.g.Fig . 12).On eha s tobea r inmin dtha tthi sdoe sno t includeth eFin eDetritu s fraction. FineDetritu swa snoted, statin gwhethe r therewa smuc ho rlittle .Th e impres sionobtaine ddurin gth eactua lsamplin gabou t thepackin g and stabilityo fth e substrate (shiftingo rstable )an dth ecompositio no fth eunderlying ,bu t from the surface invisible,substrat ewa sals oprocesse di nth e field classification, includ ingdat ao nth eratio so fth eunderlyin gsubstrat etypes .

3.1.4 Sampling method

Sincesubstrat eheterogeneit y isver ymarke d inbot h streams,wit ha stron gal ternationo fsubstrat etypes ,resultin gi nsmall-scal emosai cpatterns ,a small-scal e samplerwa snecessar yfo rth ecollectio no fsubstrat ean dfauna .Thes emus tb e col lectedtogethe r inon esampl esinc ei ti softe nimpossibl et otak ea separat e sub stratesampl ei na certai ntyp ebecaus eo fit srestricte d area. Instream swit h more uniforman dlarge r substratetype s separate substrate and faunasample sma ywor k satisfactory (e.g.Edwards ,1975 ;Petran , 1977),bu ti tofte nprove dt ob eimpossibl e inth eDutc hsmal l lowlandstreams . A shovelsample rwa sdevised ,fi tt o samplea tth e sametim ebot h substrate and macroinvertebrateso na smal lscale .Thi s sampler,calle da micro-macrofaun a shovel (Fig. 8), ismad eo fstainles ssteel .I ti s1 0c mwide ,1 0c mhig han d 15c mlong .O n theto pan da tth erea rar eopening san dthes ear e screenedwit h 0.5m mnylo ngauze . A removablehandle-ba r isattache d toth erear .O nth e sides,adjustabl ewing sar e attached,preventin g theshove lfro mdiggin gto odee p intoth estrea mbe d andmakin g itpossibl et ooperat ewit ha standar d samplingdepth .Thi sdept hwa s fixeda t3 c m inth epresen tinvestigation .Th ewing s skiove rth e substrateo nbot h sideso fth e shovel. Theshove l ispushe d intoth esubstrat ea ta nangl eo fapproximatel y3 0- 45° C andtilte dbackwards ,bringin g ithorizonta la ssoo na sth edesire ddept hi sreached .

18 r *•..- •• • • *v^.__ ^**r *^>ï.,-.-»:-.-,*'»£l

„,... ^ -™ .*."*•• . *.'£

Fig. 8.Th emicro-macrofaun ashovel .

Attha tmomen tth ewing sar erestin go nth estrea mbottom .I nth esam emovemen tth e shoveli spushe d forwardthroug hth esubstrat e overa distanc eo f1 5c man dbrough t aboveth ewate r surfaceafte rtiltin gi tfurthe rbackwards .Th esampl ei stransferre d intoa bucke to rja rb ymean so fa large ,wide-mouthe d funnel.Remainin g substrate andanimal sar erinse dou twit hwater .A mor edetaile ddescriptio no fth emicro - macrofaunashovel ,it sconstructio nan dsamplin g efficiencyi st ob epublishe d (Tolkamp,t ob epublished) . Sampleswer ealway s takeni na nupstrea mdirection .O neac hdat ea tleas t four streamsection so fth eSnijdersveerbee kwer e sampled,whic hyielde d 15-25 samples.I n theRatumsebeek ,onl yon esectio nwa ssampled .A naverag eo f6 sample swa stake no n eachoccasion .Th enumbe ro fsample salway sdepende do nth enumbe ro fvisibl esub stratetypes .Th esample swer etransporte dt oth elaborator ya squickl ya spossibl e andstore da t2-4° C(3- 4hour safte rtakin gth efirs t sample).I na fe w exceptions thesample swer econserve dwit h1 0I (V/V)formaldehyd ean dstore dt ob esorte d later. Preliminary research (Both,1976 )showe d thati ti sno tpractica lt ous eth e shovelsample ri nlea fpack so rcoars edetritu s accumulations,becaus ei twil lpus h thesesubstrate s aheado fth esampler ,o rpar to fth eunderlyin gminera lmatte rwil l be includedi nth eorgani c sample.Sinc ethi swoul dmak eth einterpretatio no fth e datato ocomplex ,th eorgani c substratesan dth eunderlyin gminera lmatte rwer esam pled separately.Th eorgani cmateria lwa ssample db yhand ,b ypushin gth eleave so r coarse detritus intoth eshove lo rbringin gi tdirectl y intoa smal lbucket ;th e underlyingminera lmatte rwa ssample dafterward swit hth eshovel .Th eamoun to f organicmateria l sampledb yhan dwa stake nfro ma nare acomparabl et otha t sampledb y 2 theshove l (150c m) , buti fth eorgani c layerwa sto othi na nadditiona l areawa s includedt oreac ha mor eo rles sconstan tvolum eo fdetritu s (approx.75 0m li na loosepacking) . 19 3.1. S Additional collections

A numbero fanimal swer ehand-picke d fromstones ,branches ,aquati c vegetation oran yothe rsubstrat eafte rtakin gth eroutin e samples.Thes eanimal swer e collected inorde rt ochec kwhethe r speciesdwellin go nsubstrate sno tsample dwit h the shovel orb yhan dmigh thav ebee nmissed .Th ebody-lengt hmeasurement so fth eanimal s col lectedthi swa ywer euse di nadditio nt oth edat afro mth eroutin e samplest ocon structlife-histor ypattern s (especially forth eTrichoptera) .

3.2 LABORATORY PROCEDURE

3.2.1 Sample sorting

As soona sth esample sarrive di nth elaboratory ,th esortin gprocedur e was started.Thi swa scomplete dwithi n2 4hours ,mostl yo nth esam eday .N osignifican t mortalitywa sobserve ddurin gtransportatio n andstorage ,excep t for occasional Baetis nymphs.Thes enymph s areeasil y injuredi nth eproces so ftransportation .Al l macroinvertebratesvisibl ewit hth enake dey ewer ehand-picke d fromth esample s and storedi n8 0 %(V/V )ethanol .Collectin gth eanimal swa sfacilitate db ydividin g the sampleint osom efraction swit hth eai do fanumbe ro fsieves .Fro meac ho fthes e fractions,th eorgani cmateria ltha tcoul db ehandle dwit ha pai ro fpincer s was removedafte rcarefu linspectio nfo rmacroinvertebrates ,whic hwer epicke doff .O f theminera lmaterial ,th epebble san dcobble swer escrutinize d individually.Th e finerfraction swer egentl ystirre d inwater ,afte rwhic hth e animals anddetritu si n suspensionwer edecante dthroug ha 0. 5m msieve .Thi sproces swa s repeatedunti ln o moreanimal sappeare d inth esieve ,followe db y searching theminera lmatte r insmal l portionsfo rremainin ganimal s (stronglyclingin g orheav yspecies ,e.g .Elminthidae , Gastropoda,cas ebuilders) . Duringthi sproces s allth ewate rwa sretained .A ssoo na smos tanimal sha d been removed,th esil tan dlutu mfractio nwa sbrough t intosuspensio n inthi swater , pouredthroug ha 0.05 0m siev ean dcollecte di n100 0m lcylinders .Th e animals that hadslippe dthroug hth e0. 5m msiev ewer epicke dof fth e0.05 0m msieve .Thi s process wasrepeate dsevera ltime st oremov eth elarges tportion so fth esil tan d clay fraction. Thisshoul db edon ebefor edr ysievin gth ecoarse rfraction s (Cummins,1962 ) since thesefin eparticle s tendt oclin gt oth ecoarse rone s indr ycondition s and are easilymissed .

3.2.2 Substrate analysis

Theparticl esize so fth eorgani cdetritu swer eno tdetermined .Th enatur e and thecompositio nof .th eorgani cmateria lwa srecorde d (sticks,fruits ,leaves ,lea f species,etc. )durin gsampl esorting ,i nadditio nt oth efiel drecordings .Afte rdry -

20 inga t10 5C fo r2 4hour sth eorgani cmateria lwa sweighe dt oth eneares t0. 1g . A boilingwater-bat hwa suse dt oevaporat emos to fth ewater ,afte rwhic hth e mineralsubstrat ecoarse rtha n0.05 0m mwa sdrie da t105°C .Afte rcoolin gt oroo m temperatureth esubstrat ewa sdivide dint oth efraction so fth eWentwort hscal e (Wentworth,1922 ;Cummins ,1962 ;Hynes ,1970a ) (Table3) .Th eWentwort hclassificatio n wasuse dbecaus ei ti spossibl et oconver tth egeometri cparticle-siz eclassification , inwhic heac hparticle-siz efractio ni stwic eth eprecedin gone ,int oa narithmeti c onewit hequa lclas s intervalsb yusin gth eph i scale,i.e .negativ ebinar y logo f theparticl esiz ei nmm .A se to fseven ,copper-wired ,square-mes hsieve s (1/20, 1/8, 1/4,1/2 ,1 ,2 an d4 mm )wa suse dt oseparat eth efine rfractions .A tth estar to f theinvestigatio na 1/1 6 (0.0625)m mmes hsiev ewa sno tavailable ,s oa 1/2 0 (0.050) mmmes hsiev ewa sused .Thi sdeviate s fromth eWentwort hclassification ,bu tsinc e thesilt-lutu mfractio nwa s alwaysver ysmal l (mostlyles stha n21 )i twa sconsidere d unnecessaryt ochang et oa 1/1 6m mmes h sieve.A mes ho f1/2 0 (0.050)m mi sth elimi t usedi nmor erecen tgrain-siz eclassification st oseparat esilt-lutu mfro mver yver y finesan d (DeBakke r& Schelling , 1966). Thesampl ewa ssieve do na Ro-Ta pTestin gSiev eShake r (TylerCompany ,Cleveland , Ohio,USA) .Thi sshake rmove sth esiev ese ti nahorizontal ,elliptica lmovement . Aftercompletin gon eellips ea hamme rstrike sth eto po fth eset ,causin ga continuou s redistributiono fth emateria lo nth esieves .Th estandar dsievin gtim ewa s 15minute s persample ,unles sth esieve s clogged,i nwhic hcas esmalle rportion swer eused . Substratescoarse rtha n4 m mwer ehand-sieve d (8m man d1 6n msieve swit ha circula r mesh),whil elarge rparticle swer emeasure d individuallywit ha rul e (thelarges t diametero fth esmalles tprojection) .Th econtent so feac hsiev eo rotherwis edeter minedfraction swer eweighe dt oth eneares t0. 1 g. Whenevera referenc ei smad et oa certai ngrain-siz efraction ,th efractio ni s

Table 3.Grain-siz e fractions and their definition following theWentwort h classification (afterCummins,196 2 and Doeglas,1968).

Fraction Phivalu e Sievemes h Phi index of Nameo f fraction (mm) (-log„fraction ) (mm) fraction(Doeglas)

128-256 -7 rule 8 cobbles 64-128 -6 rule 7 cobbles 32- 64 -5 rule 6 large pebbles 16- 32 -4 16(round) 5 small pebbles 8-1 6 -3 8(round) 4 coarse gravel 4- 8 -2 4(square) 3 medium gravel 2- 4 -1 2(square) 2 finegrave l 1- 2 0 1(square) Ï verycoars e sand 0.500- 1 1 0.500(square) 1 coarsesan d 0.250-0.500 2 0.250(square) 2 medium sand 0.125-0.250 3 0.125(square) 3 finesan d 0.050*0.125 4 0.050(square) 4 very finesan d 0-0.050+ 5-10 pipette 0 silt andlutu m

t:used instead of0.062 5 mm

21 cumulative %o fgrai nsiz efraction s 100-

90-

60H

50"

40-

30-

20-

«25 2 10

4 phi value

Fig. 9.Exampl eo fcumulativ edistributio no fgrain-siz efraction s ina sampl e expresseda sa percentag e against the-log .o fth eparticl e size inm m (phivalue ). Theinse t illustrates thecalculatio no fa quartil e indexb y linear interpolation ofth ecumulativ epercentage s atth eneares t integer phivalue ,followin g the formulaa/(a+b )= c/(c+d ) ;|c+d |= 1 .

referredt ob yth elowe rlimit ,whic hcorrespond swit hth esiev emes h that retained thefractio n (e.g.th e2- 4m mfractio ni sreferre dt oa sth e2 m mfraction) .Some timesth ecorrespondin gph iuni twil lb eused ,e.g .ph i= Ï fo rth e$- 4m mfraction . Itshoul db enote dtha tth enegativ e signo fph iunit si splace d above thefigure . Thefractio nfine rtha n0.05 0m mi nth ecylinder swa sdetermine dwit h the pipette method.Th ecylinder swer efille du pt oth e 1000-mlline ,afte rwhic hth e contents wereresuspende db yshakin gvigorously .A sampl eo f20.0 0m lwa stake nfro mth e centreo fth ecolum nwit ha vacuum-operated ,standar dpipette .Thi s samplewa s dried andweighed .Afte rconversio nt o 1000m lth eresult so fal lcylinder suse dpe r sample wereadde dt othos efo rth esilt-lutu mfractio nobtaine di nth edry-sievin gprocedure . Thefractio nweight swer econverte d topercentage so fth etota lminera lweight .

Withth eai do fth ecumulativ epercentages ,th efirs tquartil e (Q2So rQJ , theme

dian (Q50o rM d)an dth ethir dquartil e (Q75 orQ 3)wer ecalculate dwit h the follow ingformula ,derive dfro mth ecumulativ e sedimentcurv ewher e theparticl e sizesar e

expressed inph ivalue s( - log 2o fth eparticl e sizei nmm ) (Fig. 9):

K hi + i-1 %=P i-1 ,wher e Ki- K i-1

22 p =25 ,5 0o r7 5fo rQ 25,Q 50o rQ ?5 (useda sQ 1,M d,Q 3whe nrounde d off),respective ly Kj= cumulativ epercentag eo fth eparticl esiz evàer eth e2 5I ,5 0I o r7 5 %limit , respectively,i sexceede d

K^_1= cumulativ epercentag eo fth eparticl e sizebefor e the2 5I ,5 0 %o r7 5I limit,respectively ,i sexceeded .

Thesequartil evalue sca nals ob ederive d fromth ecumulativ e sediment curve (Morgans, 1956),bu t thisi sles saccurat ean dmor etim econsuming . TheQiM,Q ,inde x (Doeglas,1968 )wa scalculate dwit h thesequartil evalues .I n this indexth eph ivalu e0 i sreserve d forth e finestcla y fraction,instea do fth e value 10,an dal lph ivalue s largertha nzer oar e substitutedb yth enex thighes t in tegervalu e (Table 3). Thismean s that,accordin gt othi s system,th efractio n index (thesubstitutin gph ivalue )fo rth eparticl e sizescoarse rtha n 1-2m mi scalculate d bytakin g thenegativ ebinar y logo fth euppe rlimi to fth e fractions,bu tfo rth e fractions finertha n 1m mthi si sdon ewit hth e lowerlimit .I nfact ,a positiv e fraction indexi srounde dof ft oth enex thighes tpositiv e integervalu e anda negative fractioninde xt oth enex t lowestnegativ eintege rvalue ,e.g .Q, r= -2.1 5

becomesQ 1= - 3o r3 an dQ 5„= 2.1 5 becomesM ,= 3 .

3.2.3 Macrofauna analysis

The lowerlimi to fth esmalles tmacroinvertebrate scollecte dwa sdetermine db y twofactors :the yha dt ob evisibl et oth enake d eyean di tshoul db epossibl et o handle themwit ha pai r ofpincers .I ngeneral ,animal swit ha bod y length smaller than 1m mwer eno tcollected .Wheneve rver y smallmidg e larvaewer e observed,thei r small tubeso nth ebotto mo fth esortin gpa nbein g clearlyvisible ,i twa s recorded. Inmos t casesth elarva ethemselve swer eno tvisibl et oth enake d eye,an dthei r numberswer eno t includedi nth efina lresults . Identificationo fthes ever y small larvae showed themt obelon gt oth eTanytarsini ,mainl y Micropsectra gr. praecox. First instarso fman y faunalgroup s aremisse db ythi smetho do fsorting .Howeve rt o include these instarsa swel lwoul dmak e itnecessar yt oexamin eal lsample sunde ra stereomicroscopeo ra larg emagnifyin g glass.Thi s isver ytim econsumin g andth e largenumbe ro fsample s didno tpermi t this. Animalswer ecollecte dquantitativel y fromth esamples .Onl yi nsample swit h hundredso f(juvenile ) Gammarus orChironomida e larvae,wer e these abundant species counted,afte rremova lo fal lothe rspecie s anda representativ epar to fth e abundant species.T othi send ,th eremainin g samplewa s splitint o4-1 0equa lportions . After identificationo fal l animals ina sample ,th ecounte dnumber swer e addedt o thecollecte dnumber so fth e speciesconcerned .I fi tconcerne dmor e species (e.g. Chironomidae),th erati o foundi nth e collectednumber swa ssuppose dt ob epresen ti n thenot-collecte dpar ta swel l and itwa suse d asa measur et odivid eth e counted

23 numbers over the species. In counting tube-building Chironomidae, the ratio between empty and inhabited tubes was taken into account. Empty cases of caddis and dead molluscs were collected as well, but they are not included in the results. Sometimes half specimens of Ephemera danioa (Ephemeroptera) and Mieropterna sequax (Trichoptera) were found. They probably had been cut in two by the shovel. These half specimens were considered to be whole. The collected macroinvertebrates were killed and preserved in 80 % (V/V) ethanol which was renewed after some days and again after identification of the material. Tricladida were identified alive and were not preserved. Identification was carried out with the most recent keys and descriptions available (the keys used are listed in aseparat e literature list). Identifications carried out with keys that proved to be out of date were redone with the latest key (e.g. Sevi- eoBtom personation and Notidobia aUiaHs (Trichoptera) larvae identified with the keys of Ulmer (1909), Hickin (1976) and Lepneva (1964) were checked with the key of Wallace (1977), which showed that itconcerne d only one species: Seriaostoma personatum. As shown in Table 4, the level of identification was not the same for all taxa. This level mainly depended on the availability of keys, but itals o proved impossible to identify certain juvenile specimens, especially of the Chironomidae and the Trichoptera. When there was doubt, identifications were checked by several Dutch specialists (Simuliidae, drs. J.J.P. Gardeniers; Chironomidae, dr. H.K.M. Moller Pillot; Trichoptera, dr. L.W.G. Higler; Coleoptera, drs. J.Cuppen) . Larval and pupal iden tifications of several species of Trichoptera, Ephemeroptera and Plecoptera were checked on the adults by rearing them in the laboratory: Potvrvphylax luatuosus,

Mtcroptema sequaxt Chaetcpteryx villosa, Sericoetonu personatum, Agapetus fuscipes, LUhax obscurus (Trich.), Ephemera danica, Habrophlebia fueaa (Ephem.), Nemoura oxnereoj Amphinemura standfusai (Plee). For the majority of the species (Table 4), body length of all specimens was measured in 1» size classes. Although measurements of head capsule width is often theïst accurate way to detexmine the instar, this method was not employed because

LstlH T COnSUmin8, BeSideS' *" °bJeCtiVe ^ ** *» «^ruction <* the life pr Ie tl51"163 bUt *" determinati0n of e<-*leTerence s insubstrat e lErger Cy0imger aad lder) certainleSZy L^accuratTe enougfh to" mak* e this distinction ° ***»»• ** i-gth is under*f T^ *"*** ^ the ^reomicroscope with millimetre graph paper T:iteZ 11**"?*** the -*** *" *»*» between the antL r ed eo f r £ W meaSUred 2T^2e cer breathin^ ° **g **" iength ' f«*** antennae and n^2 ; r -s°: **" •^ ° ««**** *«*•» ce*. uirvea animals (Gwrorue) were measured in astandar d ™<=-;^™ •«. curve. This reduced the absolute body len^ ZT ' ** ""* ** body length for /w~. ! g * approximately 25%, giving a maximm body length for Oo^orus pule, of 18 m; keys state 24 mmfo r the largest males. 24 Table4 . Identification level formacroinvertebrate san d indicationo f bodylengt hmeasurements.

Macroinvertebrates Body Identification level length measurement Order Family Genus Species/group

Tricladida Xo Oligochaeta X 1 2 Hirudinea X X Amphipoda X X Isopoda - X Hydracarina X Plecoptera X X Ephemeroptera X 3 X Odonata X X Heteroptera X Trichoptera X 4 X X Coleoptera X5 (X) X Diptera 6 X X 6 Chironomidae X X X X Tipulidae X X Dixidae X X Ptychopteridae X X Simuliidae X X 1 Psychodidae X X Ceratopogonidae X X Culicidae X X Stratiomyiidae X X

Empididae x X 11 Tabanidae X X X Dolichopodidae X xl Tetanoceridae X X X Ephydridae x X Moliusca X X Bivalvia X Gastropoda X

1-Only thehighe r level was used for results;2 : Eiseniella tetraedra and larvae;6 :Pupa e sty Lama lacustris; 3:Baetidae ; 4: Juveniles;5 : Only'• —

Offiv eTrichopter a species,hea dwidth, ,hea dlength ,cas ewidt han dcas e length weremeasure di nadditio nt obod y length.A nocula rmicromete r (10:100)i nth estereo - microscopewa sused .Th emeasurement swer eperforme di nclasse so f0.02 5mm .

3-3 LABORATORY EXPERIMENTS

^ 7 1 • •! Artifical stream channel experiments

3.3.1.1 The stream

Substrate-selection experiments were performed in an artificial stream channel. ^ design followed that of Lauff &Cu-ndn s (1964) and Feldmeth (1970). The channel «as constructed of Perspex, 42 cmwide , 200 cm long and 30 cmhig h (Fig. 10). Water

25 45- IULAJ\"

sec

Flg. 10. Plan view of the artificial stream (measurements In cm). IS = inlet section; JT-*hSfE?T*knl£ WeiV h = 18 Cm ): PP = Pipe plate < dlam-= 4 cm; h = 18 cm ); fh"- 0 « Z f V = S^Strate *****

26 wascirculate d froma coolin g reservoirwit ha n immersionpum p (maximumcapacit y30 0 1/min)tha trelease d iti na smallreservoi ri nth estream .Fro mher ei tflowe dove r aknif ewei ran d througha 4-cm-thic k tubeplat e (consistingo fpipe so f4 m m inner diameter)befor eenterin gth e experimental areai na lamina rflow .A t theen do fth e channelth ewate r flowedove ra secon dknif ewei r andthroug ha filte rbac kint oth e coolingreservoir .Th ewate rwa scoole db ypassin gi tthroug ha silver-coatedcoppe r spiralfille dwit hFreon ,whic hwa scirculate db ya compressor .Al lexperiment swer e conducted ata temperatur eo f 11°C,th eminimu mtemperatur etha tcoul db e reached witha wate rdept ho f 10c man dcurren t speedo f 10cm/ s (themaximu mspee dused) . Waterdept hwa sregulate db y theheigh to fth edownstrea mweir .Curren tvelocit y couldb eregulate db yreturnin gmor eo r lesso fth epum pflo wdirectl ybac k intoth e reservoir.Ta pwate rwa suse d inal lexperiment sbecaus e itwa so fexcellen tquality . Aftereac hexperiment ,an da tleas ttwic ea week ,th ewate rwa schanged .Sub strateswer e introduced in4 0trays ,eac h 10c mx 15c mx 3cm ,in 4 parallel rows. Itwa spossibl et odivid eth echanne l intw oparalle lchannel swit hth eai do fa Per spexpartition :tw orow so ftray s ineac hchannel .Removabl escreen s (1.3m mmesh ) coulddivid e thestrea mint osection só fa minijnu mo f2 an dmaximu mo f4 0tray spe r section.Upstrea m anddownstrea mo fth eexperimenta l areaa Perspe xplat ewa s laida s abuffe rbetwee nth eexperimenta l areaan d theen dretainin gscreens .Th esurfac eo f theseplate swa s levelwit hth esurfac eo fth efille dsubstrat e traysan d roughened bya monolaye ro f 1-2m m sand grainsglue d toth eplate . Illuminationo fth estrea mfollowe dth eoutsid eligh tpattern ,durin gth eda y supplementedwit h time-switch-operated fluorescentdayligh tlamps .

3.3.1.2 Substrates tested

Substratesuse d inth eexperiment swer eobtaine db y storingal lsample s fromth e Snijdersveerbeekb ygrai nsiz eafte rsubstrat eanalysis .I nexperiment s allgrai n sizesrangin gfro m0.05 0t o3 2m mwer eused ,togethe rwit h leafpack s and coarse detritus.Substrate swer earrange d ingrade d serieswithi neac hexperimenta l section ina numbe ro f standardposition saccordin gt oth emode lpresente d inFig . 11.A test onth einfluenc eo fth esubsträte-tra yarrangement s showedtha tfo rspecie steste d therewa sn o significantdifferenc e insubstrat e selectionconnecte dwit hth earrange ment,apar t from theinfluenc eo fth ecurren tvelocity .

3.3.1.3 Experimentaldesig n

All experimentswer ereplicated ,partl y atth e sametim ei n2 o r4 paralle l series.Th efina lnumbe ro fexperiment svarie dfro mspecie st ospecies .Substrat e selectionwa sassessse dafte ra fixe dperiod ,whic hwa sdetermine d experimentally for eachspecies .Fo rmos tspecie s thesubstrat e selectionshowe dn o significantdifference s after 2,4 ,6 ,8 , 12o r 24hours ,whic hmean t thatal lobservation scoul db emad e

27 u 1 to ï v IV « III m II » 125 125 2 2 125 125 2 2

250 250 4 4 250 250 4 4

500 8 8 500 500 8 8 500

1 16 16 1 1 16 1 "

II b. 125 16 16 125 1 500 250 125

250 8 8 250 2 4 8 16

500 4 4 500 125 250 500 1

1 2 2 1 16 8 4 2

IV III II • 2 16 © © © © 4 2 8 1 8 4 © 0 © © 1 8 2 4 1 ... 8 2 125 500 1 1 500 250 125 250

16 4 16 8 4 2 2 4 8 16

IV+ II I II+ I

Flg.11 .Th emos tcommo nsubstrat etra yarrangements .Eac hgrain-siz e fractioni s indicatedb yth elowe rlimi to fth efractio ni ny mo rm m (125= 0.12 5- 0.25 0mm ; 2= 2- 4 mm). Waterrun sfro mrigh tt oleft .Arrangement sa- c :Section s Ian dI I haveopposit earrangement s regardingupstrea mo rdownstrea m placemento fth efin e andcoars esubstrates .Section s IIIan dI Var ereplicate so fSection s Ian dII , respectively.Sectio nV i salternatel y areplicat eo fSection s Ian dII ,rearrange d aftereac hexperiment .Arrangemen td :Tw oparalle l streams:4 tray spe rSection s IAan dII Ai nopposit earrangements .III Aan dIV Aar eals oopposit e arrangements andcomparabl ewit h IAan dIIA ,excep tfo rth elea fpack s (circled)place do nto p ofth eminera l substrate.V Aan dV Bar eopposit earrangements .IB+II Ban dIIIB+IV B areopposit ean dca nb ecompare dwit hSection s Ian dI Ii nArrangement s a-c.Th e grainsize sma yb edifferen t insom eexperiment sbu tthi sarrangemen tmode lwa s kept:0.12 5- 1 6m mbecome s0.25 0- 3 2m mi nth esam esequenc efro mfin et ocoars e fractions.

after2 hours .However ,animal swer elef tregularl yi nth eexperimenta l area for2 4 hourst ohav ea chec ko nth eselectio nperiod . Specieslik ecase-buildin g Trichoptera thatca nb ehandle dwit ha pai ro fpincer swer e introducedi nth eexperimenta l area byplacin gthe mo nto po feac hsubstrat e tray indensitie so f2o r4animal spe r tray,althoug hdensitie so f3 ,5 ,6 o r8specime npe rtra ywer euse da swell .Thi s

28 willb e indicated foreac h experimenti nth eresults . Afterth e set selectionperiod ,th eposition so fth eanimal swer erecorde dan d theanimal scollecte db ypickin g them offth esurfac e after lightlystirrin gth esub strate in situ. Morevulnerabl e species,lik e Ephemera danioa, wereintroduce db y placingthe mo nth e filled traysi na smal lpetr idis h andlettin gth enymph s swim awayo fthei row nvolition .Fo rthes e animalsparticle-siz e selectionwa s determined byremovin gth e trays fromth e streaman dcarefull ybringin g thecontent si na large r traywit hwate ro fth esam etemperature .Th e sameretrievin gproces swa suse dfo r speciesdifficul tt otrac e in situ, e.g. smalllarva eo f Seriaostoma personation.

3.3.1.4 Species tested

Experimentswer econducte dwit hsevera l instarso ffou rTrichopter aspecie san d oneEphemeropter aspecies .Tabl e5 summarize s thespecie s andinstars ,includin g possibledifference si ncase-buildin gmateria luse db yth ecaddi slarvae .

3.3.1.5 The influenceo fcurren tvelocit yo nsubstrat e selection

Theeffec to fcurren tvelocit yo nth esubstrat e selectionwa s tested forcurren t velocitieso f1 0cm/ san d5 cm/ sfo ral lspecie si nsection swit h8 trays ,wit hiden ticalparticl e sizesi nth e4 upstrea man ddownstrea m trays.Experiment swer e conducted withsevera lparticle-siz e combinations andselectio nperiods .Fo rspecie s that showedn osignifican tdifference si nsubstrat e selectionbetwee nupstrea m anddown -

Table 5.Species , instars and casebuildin gmateria l in substrate-selection experiments.

Species Instar Length/mm Case-building material Miaropterna sequax F > 15 mineral (F ;F-l ) F-l 10-15 organic (leaves/detritus) F-2 6-10 (F-2 ;F- l jF ) 1/2 mineral-1/ 2organi c (F-2 ;F- l ;F ) 1/2 pupal (mineral,on een d enlarged Chaetopteryx villosa >1 0 mineral organic 1/3 mineral-2/ 3organi c 1/2 mineral-1/ 2organi c 1/2 pupal (mineral,oneen d enlarged) Serioostoma personation F 11--14 mineral F-•1 8--11 mineral F-•2 7--10 mineral mineral F-•3 6--7 Ephemera danioa 15--20 15--25 20--25

29 streamtray so ren dretainin g screens,th ecurren tspee dwa smaintaine da t1 0cm/ s in allexperiments .

3.3.2 Rearing channel

A smallrearin gchanne lsimila rt oth elaborator ystrea mdescribe db yHigle r (1975)wa suse dt oacclimatiz eanimal st olaborator ycondition san dt okee p themi n stockfo rexperiment si nth eartificia l streamdescribe di nSectio n 3.3.Wate r tem peraturesfollowe dth etemperatur e fluctuationso fth eRatumsebee kwit h approximately onewee kdelay .Th estrea mwa sdrive nb yfou rsmal lpump s givinga naverag e current velocityo f1-1 0cm/s ,dependin go nwate rdept han dobstacle splace di nth estream . Nylon-meshscreen sdivide dth echanne li nsection st okee pth edifferen t species apart,an dscreen so nto pprevente demergin gadult sfro mescaping .Substrat e inal l sectionsconsiste do fa 3 c mthic kmixtur eo fsan dan dgravel ,wit h additional stones andsticks .Fres hleave san ddetritu s collected fromth eRatumsebee kwer e supplieda s foodan dadditiona lsubstrate .Illuminatio nfollowe dth eoutsid e lightpattern . Severalspecie so fTrichoptera ,Ephemeropter aan dPlecopter a (seeSubsectio n 3.2.3)wer ereare dsuccessfull yt oadults .Som especie seve nmate d although only Seviaostoma personatum producedegg si nth estrea m (thesehatche d later).

3.3.3 Experiments with Trichoptera

Case-buildingmacroinvertebrate softe nus ematerial s fromth estrea mbe dfo r theircases .Trichopter afor mth emajo rgrou po fanimal stha tus eminera l and/or organicmateria lt obuil dthei rcases .Othe r groupsar etube-buildin g Chironomidae andcase-buildin gLepidoptera .Th e(grain-size )compositio no fth ecase smigh ta t leastpartl yreflec tth esubstrat ecompositio no fthei rhabitat .Th epresenc eo r absenceo fcertai ngrai nsize so rorgani csubstrate smigh tb ea facto r determining thepresenc eo rabsenc eo fcertai ncase-buildin g speciesi na habita to rstream . Caseso ffiv especie so fTrichopter awer e analysedo nthei rgrain-siz ecomposi tion.Wit hfou rspecies ,cas ebuildin gexperiment swer ecarrie dout ,offerin g several grainsize san dorgani cmaterial sa sbuildin gmaterials ,whil eth elatte rals ofunc tioneda sfood .Additiona lexperiment swer eperforme di nwhic honl y sub-optimalma terialswer eoffered .

3.3.3.1 Case-buildingexperiment s

Experimentso nth ecase-buildin gbehaviou ro ffou rspecie so fTrichopter awer e conductedi ntemperatur ean dphoto-perio d controlledclimat ecells .Da ylengt h followedth enatura lpatter nan dtemperatur ewa shel da t14° C+ 1°C.Experiment swit h Micropterna sequax, Agapetus fuscipes and Lithax obscuruswer eperforme di npetr i dishesfille dwit hwater .Fo rbuildin gexperiment swit h Sericostoma personatum, 250

30 Table6 .Grain-siz e fractionsuse d incase-buildin g experimentswit h Trichoptera.

Grain-size fractions Colour Fractionnam e (mm)

0.050- 0.12 5 notcoloure d very finesan d 0.125- 0.25 0 red finesan d 0.250- 0.50 0 white quartzsan d medium sand 0.500- 1. 0 green coarsesan d 1.0 -2. 0 blue very coarsesan d 2.0 -4. 0 notcoloure d finegrave l mlglas sbeaker swer e two-thirdsfille dwit hwate ran daerate dwit hcompresse d air blowni nthroug hpasteu rpipettes .Thi sproduce da strea mo ffin eai rbubble san d createdconstan twate rmovement .Al lwate ruse dwa sbrough ti nfro mth eRatumsebeek . Foodwa s suppliedi nth efor mo f leavesan dcoars edetritus ,collecte di nth eRatum sebeek andrinse di nta pwater . Inorde rt ofacilitat e therecognitio no fth egrai n sizesuse db yth eanimals ,al lfraction s (ranging fromver y finesan dt ofin egravel ) werecoloure ddifferentl ywit hwaterproo fEddin g ink.Thi sprove dt ob enon-toxi ct o thecaddi s larvae (M. sequax larvaewer ekep t for1 4day so ncoloure d substratesan d showedn o reductioni nactivity )an d the inkdoe sno t alterth e surfacestructur eo f thegrains .Th egrai nsiz efraction suse d areliste d inTabl e6 . Foreac hexperiment ,som eo ral lgrai nsize swer eprovide d togetherwit ha fe w freshan dol dbeec h leaves.Larva e (eachi nit sow ndis ho rbeaker )wer e introduced withoutthei rcase so rwit honl y thefron thal fo fth ecase sremoved ,afte rhavin g beenadapte dt oth eexperimenta l conditions fora fe wdays .The ywer elef ti nth e experimental cellsunti l theyha dcomplete d thebuildin go fthei r finalcase .Thi s wasmostl y reachedwithi n7 day s aftercompletin ga nemergenc y casetha twa sbuil d within 2-3 days after introduction intoth eexperimenta l area.Afte r eachbuildin g experiment,th enumbe ro fgrain si neac hsiz efractio nuse di neac hcas ewa s counted andth erelativ eproportio no feac hsiz efractio ni nth etota lcas esurfac ewa s calculated.Th emetho duse d forthi scalculatio nwil lb edescribe d indetai lb y Tolkamp& Verdonscho t (tob epublished) .

3.3.3.2 Grainsiz eanalysi s ofnatura lTrichopter a cases

To compareth egrain-siz e selectioni nth ecase-buildin g experimentswit hth e compositiono fth enatura lcase sth elatte rwer e analysed forthei rgrain-siz ecompo sition.Afte rmeasurin g case lengthan dcas ewidth ,togethe rwit hlarva lbod ylength , headwidt han dhea d length,case so fwhic hles stha napproximatel y 51o fth esurfac e consistedo forgani cmateria lwer ecombine di nclasse so f1 0o rmor efo reac h larval instar.Whe nenoug hmateria lwa s available classeswithi neac hinsta rwer edistin guishedo nth ebasi so f larvalhea dwidth .Case swit hmor etha n5 1organi cmateria l weretreate d separately.

31 Grain-sizeanalysi swa scarrie dou tafte rdissolvin gth eorgani cmateria lan d salivarysecretio nb yboilin gth ecase si n30 1 (V/V)H 202 for2 4hours ,followe db y treatingth eremainin gmateria lwit h1 N HC Lan drinsin gwit hwater .Afte rdryin gi n astov ea t110°C ,1 3grain-siz efraction swer edetermine db yhan dsieving ,usin ga s manysieve sa savailabl e (diameter1 0cm )wit hopening sof :0 - 0.05 0- 0.10 5- 0.150- 0.21 0- 0.25 0- 0.35 0- 0.50 0- 0.85 0- 1. 0- 2. 0- 4. 0- 8. 0- 16. 0mm .Eac h fractionwa sweighe dan dit srelativ eproportio nt oth etota lminera lcas eweigt hwa s calculated.It srelativ eproportio nt oth esurfac eare ao fth ecas ewa scalculate d withth eai do fexperimentall ydetermine dfactor s (seeTolkam p& Verdonschot ,t ob e published).

3.4 FIELDEXPERIMENT S

Inorde rt ochec ki nth efiel dth eselectio nb yth emacr oinvertebrate so fth e grain-sizeo fth esubstrat esevera lmethod swer euse dfo rth eintroductio no farti ficialsubstrate si nth enatura lenvironment .

3.4.1 Artificial substrate trays

Sincen oexperienc ewit hth eus eo fartificia lsubstrat esampler swa savailabl e inth eNetherlands ,a stud ywa sstarte do nth eus eo fwir ebasket s filledwit h small pebbles (16-32mm )o rlarg epebble s (32-64mm )i nth eSnijdersveerbeek .Th eresult s ofthi sstud ywil lb epublishe delsewher e (Tolkamp& Verdonschot ,t ob epublished) . Wirebasket sar eonl yfi tfo rrelativel ycoars esubstrates ,sinc efine rmaterial s needt ob eintroduce di nclose dcontainers ,e.g .plasti co rti ncan s (Khalaf, 1975). Forth eexperiment sdescribe di nthi ssubsectio ntw osize so fshallo wplasti c trayswer eused .Thes etray smeasure d13.2 5c mlengt hx 8 c mwidt hx 3 c mdept han d 18.25c mlengt hx 12.2 5c mwidt hx 3. 5c mdepth ,givin gcontent so f31 8cm 3an d 782c m, respectively .Th esmal ltray swer efille dwit happrox .60 0g o fsubstrat e andth elarg etray swit happrox .130 0g ;al ltray swer efille dt oth ebrim .Al lex perimentswer ecarrie dou ti nApri lan dMa y197 8i na sectio no fth eRatumsebee kwit h amore-or-les sunifor mgravel-san d substrate,unifor mflo wove rth etota lwidt ho f thestrea mbe dan da wate rdept ho f5-1 0cm .Tray swer eplace di nth estrea mbe di n rowso fthree ,space d5 0c mi nwidt han dlengt hfro mneighbourin gtrays . Initially,fo reac hcollectio ndat e6 smal ltray so feac hgrai nsiz ewer euse d with1 larg etray ,excep tfo rth e8-1 6m mgrai nsize ,fo rwic h4 larg etray swer e usedfo rth efirs tse to fexperiments .Late ron ,onl y2 larg etray swer euse dfo r eachgrai nsize ,th eamoun to favailabl esubstrat ean dtim et owor ku pal lsample s beingth erestrictin gfactors .Smal ltray swer euse da swel li nth elate rexperiments , butal lwer elos tdurin gon eperiod ,bein gremove d fromth estrea mb yperson sunknown . Thetray swer edu gint oth estrea mbotto ms otha tthe ywer e levelwit h it. The substratefro mth estrea mbe dwa ssmoothe dove rth eedge so fth etray san dwha twa s

32 Table7 .Numbe ro fsubstrat e traysfo reac h grainsiz ean dperio do f colonization inth eRatumsebeek .

Periodo f Number of traysb ygrai n size(mm ) colonization 0.125 0.250 0.500 1.0 2.0 4.0 8.0 16 32

4 6 S • • • 6 S 6 S • • 3L 6 6 S . . . 6 S . . . 10 6 S • • • 6 S 6 S • • 1L 1L 1L 12 2L 2L 2L 2L 2L 2L . 14 . . 2L 2L 2L 2L 2L 2L 28 2L 2L 2L 2L 2L 2L 2L 2L 2L

S-smal l tray ;L =larg etra y ;. =n o trays

leftwa sdistribute do nth ebe d downstreamo fth eexperimenta lsection .Tray swer e retrievedafte rdifferen tperiods ,rangin gfro m4 day st o4week s (Table 7).Animal s weresorte di nth e laboratory,organi cmatte rwa spicke dout ,drie dan dweighe dan d thegrain-siz ecompositio no fth eminera l substrate inth etray swa sdetermine dt o establish theamoun tan dnatur eo flos tan d gained substrate.Onl yo ntw ooccasion s wereth etra ycontent swashe dout ,i nwhic hcas eth esampl ewa somitted .

3.4.2 Artificial substrates introduced without trays

Dug-intray s filledwit hsubstrat eca nonl yb ecolonize dfro mabove .Horizonta l migrationthroug hth e streambe do rvertica lmigratio nfro mbelo wi sprevente db yth e trays,side san dbottoms .Moreover ,th etray sthemselve sma yac ta sa nattachmen t sitefo rclingin gan d suckinganunal s (e.g.snail san d leeches)an dthe yar egraduall y colonizedb ydiatoms ,bacteri aan dfungi ,trappin gfin edetritu si nthei rturn ,pro vidingfoo dan d foothold forman ymacroinvertebrates . Inorde rt oexclud ethes epossibl ydisturbin g influences,severa lgrai nsize swer e introduced intoth e streambe dwit hn ocasin garoun dthem .Channel s3 c mdeep ,1 5c m widean d7 5c mlon gwer edu g inth estrea mbotto man dfille dwit hdrie dsubstrate ; onegrai nsiz ei neac hchannel ,eigh tchannels ,i ntw orow so ffour . Theupstrea m rowcontaine dgrai nsize so f0.250 ,8.0 ,4. 0 and0.50 rnn0 an dth e downstreamro wgrai nsize so f1.0 ,16 ,2. 0 and0.12 5mm ;th ecoarses tgrai nsize si n themiddl eo fth e stream,th e finesto nth e edges.Afte ron emonth ,3 sample swer e takenfro meac hgrai nsiz ewit hth emicro-macrofaun ashovel .Th esample swer esorte d inth elaborator y andth esubstrat eanalyse dfollowin gth enorma lprocedures .Thes e experimentswer ecarrie dou t inNovember-Decembe r 1978i nth esam esectio no fth e Ratumsebeeka swher e thesubstrat etray swer e introduced.

33 3.4.3 Litter bags

Leavesfor ma nimportan tsubstrat efo rsevera lspecie so fmacroinvertebrate san d thebreakdow nrat ean dcolonizatio no fsevera l leafspecie sar equit ewel l documented. A studywa sundertake ni nth eRatumsebee ko nth ebreakdow nrate san dcolonizatio nb y macroinvertebrateso falde r (A),oa k (Q),beec h (F)an dpopla r (P)leave s during differentincubatio nperiods .A detaile ddescriptio no fthi sstud ywil lb epublishe d byTolkam p& Kho l(t ob epublished) .

3.5 DATA PROCESSING

3.5.2 Data storage

Allfiel ddat awer eprocesse dwit hth eai do fth ecompute ro fth eAgricultura l universityo fWageningen .Samplin gdate swer etransforme dt oyea r andwee knumbers . Fieldclassificatio no fth esubstrate swa sbinar y codedb yth epresence/absenc eo f theseve nmai ngrain-siz eclasse smentione di nsubsectio n3.1. 3(th e smallestan d largestparticl e sizeswer eno tused )an dth epresence/absenc eo fth ethre e detritus classes.Th esubstrat estabilit ywa srecorde da sstabl eo rshifting .Weight so f particle-size fractionswer erounde dof ft oth eneares t gram,sinc e this hardly influencesth epercentage so feac hfractio no rth equartil evalue s calculated later. Animalswer ecode db ynumber s (Appendix 1). Length classeswer e indicatedb yth e upper limito fth eclas s( i.e .1- 2m m= 2),wit ha separat e codefo rpupa e (99) and adults(98) . Datawer estore di ntw odat afile sfo reac hstream .Th efirs tfil ewit hth edat a ofth esampl e (stream,section ,sampl enumber ,year ,week ,fractio nweights , field classification,numbe ro fspecies/taxa ,numbe ro fspecimens) .Th esecon d filewit h the-dat aconcernin gth especie san dth enumbe ro fspecimen si neac hlengt h class, togetherwit hth esampl ecode .Mistake smad ei nth eproces so ffillin gi nth epunc h listswer epartl ychecke db ycomparin gth enumbe ro fspecimen san dspecie sa scounte d byhan d (inth esampl efile )an db yth ecompute r (fromth especie s file).Afte r these andothe rchecks ,t oeconimiz eth eprograms ,th esampl e filewa sextende dwit hth e QlMd^3 ixïâex znda binar y filefo rth epresence/absenc eo feac hspecies . Withth eai do fsevera lprograms ,develope di nclos ecooperatio nwit hth eCompute r Centreo fth eAgricultura lUniversity ,variou sparameter swer e calculated,e.g .longi tudinaldistributio no fspecie si nth eSnijb ,distributio no fdifferen t development stagesi ntim ean dplace ,Inde xo fRepresentatio n (I.R.)value sfo rsevera lclassifi cations,percentag eoccurrenc ei ndifferen tsubstrat etype san dWhittaker' s Indexo f Association.

34 3.5.2 Statistical methods

Statisticalmethod suse d fortestin g significanceo fcertai n (calculated)dat a areexcellentl y describedi nsevera l textbooks.Th ebette rpar to fth emethod s used inthi s thesis canb e found inEllio t (1977b). Distributiono ftax aove rdifferen t substratetype swa sexpresse d asth e Index ofRepresentatio n (I.R.)(Hildre w& Townsend , 1976) (Table8 )an dstatistica l signifi cancewa s testedwit h thechi-square d test.Calculatio no fth e I.R. values isbase d onth enul lhypothesi s (H) tha ta specie soccur si nal lsubstrat e typesi nequa l densities.H isaccepte dwhe n thedifferenc ebetwee nobserve d andexpecte d densities isno tenoug ht oyiel dchi-square d values aboveth e 51level .H isrejecte dwhe n chi-squaredvalue sar ehighe rtha nth eS Ileve li na chi-square d distribution table (e.g.Lindgre n& McElrath ,1970 ,Tabl eII) . WhenH isrejected ,thi s isa nindicatio no funde ro rove r representationi n oneo rmor eo fth esubstrat etypes .Positiv e I.R. values indicate over representation andnegativ evalue s indicateunde rrepresentation .However ,difference si nI.R . valueswer eonl y consideredt ob esignifican twhe nth evalue sdeviate d2 o rmor e from zero.Onl yvalue soutsid ethi srang e(- 2t o+2 )wer e consideredt ob eindicativ efo r aversiono rpreference ,respectively , forcertai n substrate types.A nexampl eo fth e calculationo fth e I.R. values andchi-square si sgive ni nTabl e8 . Whittaker's (1952)Inde xo fAssociatio nwa suse dt ocalculat e thedegre eo fcom - paribilitybetwee n substratetype so nth ebasi so fspecie s composition.Thi s indexi s calculatedb ysummarizin g theminimu mpercentage so foccurrenc eo feac hspecie si na seto ftw osample so rsubstrat etypes : S W= I min (a-, b.), n=1 x x where a. andb . areth epercentage so foccurrenc eo fth ei speciesi nth esample s A andB ,an dS i sth enumbe ro fspecie s occurring inbot hsamples .

Table 8.Exampl e for thecalculatio n of the Indexo fRepresentatio n (I.R.).

Substrate type Total

I II III Number of samples 20 15 15 50 O= observe d number of species i 120 30 0 150 E= expected number of species i 60 45 45 150 I.R. value 7.75 -2.24 -6.71 X2 = 110.00

P 2 I.R. = (0- E)/ /E and x2 = £ (0- E )/ E n=l where E= thetota l number of species imultiplie d by theproportio no f thesample s ina substrate type inth e total set of samples.with p substratetypes .

35 Clusteranalyse swer ecarrie dou twit hth eClusta n 1Cprogra mwritte nb y Wishart (1975)tha ti spresen t inth e library fileso fth eCompute rCentre .I.R .value s were useda sra wdat afo rsevera l linkagemethod s todistinguis h groups ofspecie s with similarpreference so raversion sfo rcertai nsubstrat etypes .Sinc e othermethod s testeddi dno tlea dt oothe rconclusions ,th emetho duse d forpresentin g the results isWard' smetho do fhierarchica l linkageusin g theerro rsu mo fsquares .

36 4 Results

4.1 DATA

4.1.1 Field classification of substrate types

Forstatistica l treatment themultitud e ofpossibl e combinationso fth eindivi dualsubstrat e characteristics hadt ob erestricte dt oamaximu mo f1 4substrat e classes.Thi smeans thatsom e types distinguishedi nth efiel dwer e combined lateri n ordert oobtai nsubstrat e classes containing enoughsample st oallo w statistical treatment. Fourclassificatio n levelswer eused ,wit h3 (Sor t 3),5 (Sor t 4),7 (Sor t2 )an d1 4 (Sort 1)substrat e classes (Fig.12) ,respectively .Appendi x2 give sth enumbe ro f samples ineac hsubstrat e class forth eSnijdersveerbee k andAppendi x3 thos e forth e Ratumsebeek. Onth efirs t level (Sort3 )sample swit hminera l substratewer e distinguished fromsample s consistingmainl yo forgani cmatte r (coarsedetritu s and/orleaves) . Samples classifieda sorgani c always contained lesstha n 150g minera lmateria l and theaverag edr yweigh to fth eorgani cmatte rwa s2 1g pe rsample .Minera lsample sal ways contained lesstha n8 g detritu s anda naverag eo f90 0g minera lsubstrate .

Sort dlviilon criterion 3 Sand Gravel Detritus S/D/FD O/D/FD D/FD

S+D/FD G+D/FD D/FD

D/FB

Snijb CD,L

S+FD S+L S+L S+L StCD S+L BG G+L/FD G+CD/FD CD/TO L/FD CD+L/FD +CD •CD +FD +FD +FD Fig.12 .Substrat e typesbase d on thefiel d classificationo f thesubstrate s at four levels (Sorts1 ,2 ,4 ,3) .S =Sand ;G =Gravel ;CD =Coars eDetritus ;L =Leaves ; D=Coars eDetritu s and/órLeaves ;FD =Fin eDetritus ;B =Bare ;St = Stable; Sh= Shifting; += with ; -= without ; /= wit ho rwithout .S+L+C Doccurre d only inth e Snijdersveerbeek (Snijb). S+L+CD+FDoccurre d only inth eRatumsebee k (Rab).

37 Mineralsample swer edistinguishe d inSan dan dGrave lo nth ebasi s ofth e domi nantgrai nsize s (Subsection 3.1.3).However ,t oobtai na mor e objectivemean s to separatesan dan dgrave lsubstrates ,th emedia nparticl esiz edetermine d afterdr y sievingwa suse da swell .Sample swit ha negativ emedia nph ivalu e (Md< 0 ,i.e . 50$ ormor ecoarse rtha n1 mm )wer ereckone damon ggrave lan dsample swit h apositiv e medianph ivalu e (M,> 0 ,i.e . 50»»o rmor efine rtha n1 mm ) amongsand . Thisclassificatio nca neasil yb eobtaine di nth efiel da swell ,usin g a standard comparisonsystem .Thi s isa metho dt ob e recommendedfo rfutur estudies ,bu t itwa s notuse di nthi sstud ybecaus eth eautho r learnedo fi tto olate .Figur e 13give sth e quartilepercentag eo fth esample s classifiedwit hthi smetho d asGrave lo rsand .

Very littleoverla poccur sbetwee nth efirs t (C^)an dth ethir d (Q3)quartil evalue s ofGrave lan dSand .Th etw opeak s ineac hquartil e illustrateth e correctness ofth e choicefo ra media nparticl esiz eo f1 m m (Md= 0 )a sth eboundary .Compariso no f thisdivisio nwit hth efiel dcod eshowe dtha tth epresenc eo fa relativel y small proportiono fcoars eparticle s iseasil yover-estimate dbecaus eth e coarsemateria l ismor eabundan ta tth esurfac eo fth esubstrat etha ndeepe ri nth ebottom .Thes e sampleswer eofte ncode da sFG+S ,whic hshoul dhav ebee nS+FG .However ,suc h differences arever ydifficul tt oquantif yi na classificatio nsystem ,emphasizin g thenee d for a parametert odistinguis hthes esubstrates . Onth esecon dclassificatio nleve l (Sort 4), thetw ominera l classeswer efur therdivide do nth ebasi so fth epresenc e ofCoars eDetritu sand/o rLeave s into Sand orGrave lwit ho rwithou tCoars eDetritu s and/orLeaves .Togethe rwit h thepurel y organicsubstrat eclas so fth efirs tleve lthi sgive s fivesubstrat e classes forthi s classificationlevel . Onth ethir dleve l (Sort 2), theminera lclasse swer e furtherdivide d into classeswit han dwithou tFin eDetritus ,givin gseve nclasse s intotal ,sinc e Gravel substratescombine dwit hCoars eDetritu swithou tFin eDetritu sdi dno toccur . Onth efourt hleve l (Sort 1), allclasse swit hdetritu swer e divided into classeswit ho rwithou tLeaves ,Coars eDetritu s ora combinatio no fboth .Thi s isth e firstleve lwher eth eorgani cclas si sdivided .O nan yo fth efirs tthre e levels a moredetaile dclassificatio no fth edetritu s sampleswa sno tpossibl e since some classeswoul dhav econtaine dto ofe wsamples . Forth eminera lsubstrate ssom etheoreticall ypossibl eclasse sha dt ob e combined toobtai nclasse s largeenoug ht ojustif ystatistica ltreatment .I norde rt o include allspecie sexcep tincidenta lone si ti snecessar yt ocombin ea t leastsi xsample s in eachsubstrat eclas s (Tolkamp,t ob epublished) .However ,on esubstrat e class inth e Snijdersveerbeek (S+L+CD)containe donl y3 samples .Thi s classwa smaintaine d anyway becausei twoul dhav eobscure dpreference s ofsom especie sfo rS+ Lo rS+CD ,althoug h oneshoul dbea ri nmin dtha tpossibl eover-representatio n inthi s three-sample class mustb econsidere dcritically .I nth eRatumsebeek ,severa lclasse s contained less thansi xsamples ,whic hmean stha tcompariso no fth eresult so fth etw o streams shouldb emad eo na les sdetaile dlevel .

38 frequency(% )

frequency(% )

0- 7654 32112 3 phi index frequency (%) 80

Fig.13 .Frequenc y distribution of thefirs t (Q^)quartil e ,secon d (median)

Becauseo fth eus eo fth emedia nparticl esiz e (phivalue )t odistinguis h Gravel andSand ,th efiel d classifications FineSand ,Coars eSand ,Fin eGrave lan d Coarse Gravel,Larg ean dSmal lPebble swer eno tuse di nth eclassificatio npresente dabove . This informationwil lb euse dagai nwhe nreferrin gt oth epreference so fth e individ ualspecie san dwhe ncomparin gwit h literaturedat ao nth emicrodistributio no fthes e species. 39 Siltan dlutu msubstrate s onlyoccurre dsporadicall y andwer eno t includedi n thisresearch .Mu dsubstrate s occurredregularly ,bu t thesewer enormall y accounted fori nth eclasse sS+CD+F Do rS+FD .Mostl yi tconcerne da thic ksuspensio no ffin e sand,coloure dbrow nb yth eFin eDetritus .Onl yoccasionall ywer e thesesubstrate s blackan danaerobe ,bu tthe nn oanimal swer epresen t andth esample swer eno t included inth eprogramme . Substrates onlyoccurrin g incidentally (e.g.branches ,tre etrunks ,bricks , kettles,plasti cbags ,bee rtins ,aquati cvegetation )wer eno t includedi nth eclassifi cationbecaus e theycoul dno tb esample dwit ha comparabl emethod . Referencet oth e presenceo fcertai nspecie so nthes esubstrat ewil lb emad ewhe ndiscussin g the microdistribution ofth especie s involved.

4.1.2 Grain-size classification in the laboratory

4.1.2.1 Substrate composition

The substrate compositiono feac hsampl ewa s expressed as the QIMJQ, index accordingt oDoegla s (1968) (Subsection 3.2.2).Th e exact 2S%, 50$an d 751quartile s arepresente d inFig . 14a sth e QIMJQT grapho r substrate-characteristic of the streamfo rth eSnijdersveerbeek ,an di nFig .1 5fo rth eRatumsebeek .Th e graphs shouldb erea dfro mbotto mt oto pa sM jvalue s arei na 4 5degre e angle between

abcissaan dordinate ,whil eQ 1 andQ 3 areplotte dbelo wan dabov e theM ,value ,

respectively,o fth esample .Thi smean sQ 1 andQ ,shoul db e read from the ordinate (yaxis) ,whil eM ^ca nb erea dfro mbot h axes. Iti s quiteobviou stha tbot hgraph s aresimila r andtha tth e only difference betweenth etw ostream sconsist so ffewe rdat ai nth eRatumsebeek , especiallyo nth e coarse (lefthand )side .I tca nb e concluded fromthi s observation thatth etw o streams canfunctio na seac hother s twinconcernin g themineral-substrat e composition. Tochec kth ereliabilit yo fth eQ^Q j grapha sbein g representative forth e substrate compositiono fth estream ,a separat e seto f6 4sample swa s takeni nth eSnijders veerbeek (coveringal lsection swit h6 (Sectio n 7),8 (Section s1 ,2 an d 3),1 0 (Section5 )o r1 2(Section s4 an d 6)samples) .Th eresultin g QiMjQ-grap h (not presented)fitte dexactl yove rth egrap ho fFig . 14.I tagai n illustrated the abundance offine ,more-or-les sunifor msubstrate s (Md> 1 )an dth escarcenes so fcoars esub strates,whic hwer efoun dincidentall y inth eRatumsebee k andmore-or-les s restricted toStation s6 an d8 i nth eSnijdersveerbee k (the latterwa sdr ya tth e timeo fth e check).Fo rbot hgraph si ti sclea rtha tth e largestnumbe ro fsample swa s takeni n homogeneous,fin esubstrates ,whil eth eothe rsample s arecompose do fa heterogeneou s mixtureo fcoars ean dfin eparticles .Homogeneou s coarse substrateswer ever y scarce. Toseparat eGrave lfro mSan dsample s andSan dfro mSil tsample sDoegla s (1968) drewhorizonta l linesthroug hph i= Ï an dph i= 4 ,respectively .Thi si sth e accepted distinctionbetwee nSan dan dGrave l (Cummins,1962) ,wher e substrateswit ha media n M. (phi value) a

M Fig.14 .Q 1 .Q~ graph for theminera l substrate of theSnijdersveerbeek .Th e graph should berea d frombotto m to topbecaus e Q and Q areplotte d below and above the M value,respectively , which isplotte d ina 4 5degre e anglebetwee n abcisan d ordinate. particlesiz elarge rtha n2- 4m mar eclassifie da sGravel .However ,th e Q^Cv graphs illustratetha tespeciall yth eSan dsubstrate scove ra wid e rangeo fgrai n sizes.Th e compositiono fth eSan dsubstrat evarie s fromver ywel lsorte d (e.g. 222) topoorl ysorte d (e.g.Î23 )t over ypoorl ysorte d (e.g.312) .Thu sth ewell-sorte d sandysubstrate sca nb edenominate d aspur eSand ,whil eth epoorl ysorte done sar ea combinationo fGrave lan dSand ,wit hSan ddominating .

4.1.2.2 Substratetype s

Todistinguis hsubstrat etype so nth ebasi so fth egrain-siz eanalysi san dth e amounto forgani cdetritu si ti snecessar yt ohav ea reproducibl emeasure .T ofin d sucha measur esevera lratio' sbetwee nminera lan dorgani cmatte rwer etested .T o thisen dsample swit h lesstha n1 ,2 ,4 , 6,8o r10 1Coars eDetritu sand/o rLeave s wereconsidere dminera lsamples .Comparin gth eclassification swit heac hother ,thes e

41 M. (phivalue ) a

Fig. 15.QjM.Q .grap h forth eminera l substrateo f theRatumsebeek .Th e graph should berea d frombotto m toto pbecaus eQ.an dQ areplotte dbelo wan d aboveth eM value, respectively,whic h isplotte d ina 4 5degre eangl ebetwee n abcis andordinate .

ratio'sshowe dtha t2 ,4 ,6 an d8 1adde d little informationt oth e1 4an d10 1 division andtha tthi sconcerne d onlya limite dnumbe ro fsamples .Th elatte rtw opercentage s weremaintained ,expectin gtha tcompariso no fth etw oclassification s wouldyiel d informationabou tanimal spreferrin ga combinatio no fminera lan dbetwee n1 an d10 4 organicmaterial .Fo ranimal spreferrin gbetwee n1 an d10 4organi cmaterial ,th epre ferencefo rorgani cclasse sa tth e1 1leve lmus tshif tt oth e'mineral 'classe sa t the10 4level . Afterthi sseparatio no fth eorgani csamples ,th eminera lsample swer eclassi fiedi nsevera lclassification so nth ebasi so fth eph iinde xo fth efirs t quartile

(Q1 :Sort 5),th emedia n (Md :Sor t6 )an dth ethir dquartil e (Q :Sor t7 )usin gth e rounded-offquartil evalue s (Doeglas,1968) .Togethe rwit hth ethre edetritu s classes

(CD/FD;L/FD;CD+L/FD) thisgive s1 3classe sfo rQ 1 (7t o3) ,M d (7t o3 )an dQ 3( 6 to4 )i nth eSnijdersveerbeek .Appendi x4 give sth enumbe ro fsample si neac h class. Inth eRatumsebee k lesssample si ncoars e substrateswer e takenan d1 3classe s forQ ,

42 (7t o3) , 11 forM ^( 5t o3 )an donl yeigh t forQ ,( Tt o4 )coul db eseen ,includin g thethre edetritu s classes.Appendi x5 present sth enumbe ro fsample spe rclass . Severalclasse s inSor t5 t o7 containe donl ya fe wsamples .Thes eclasse swer e notcombine d furthersinc epreference so fspecie swit ha relativel y lowabundanc ebu t a specific substrate selectioncoul db emaske do na less-detaile d levelb yth ecom binationwit hother ,no tpreferre d classes.However ,apparen tover-representatio ni n thesesmal lclasse s shouldb econsidere d criticallybefor edrawin g conclusions regardingpreferences . Finally,a classificatio nwa smad eo nth ebasi so fa combinatio no fth ethre e quartilest oinclud esubstrat e complexity.Arrange d fromcoars et ofin eminera lsub strates 77differen tQiMjQ ,indice swer e combinedi nsevera lminera lclasse si nSor t 8,als ousin gth e U and 101organi cmatte rdivisio ni nth esam ethre eorgani cclasse s (Appendices4 an d5) . InFig .1 6thes esubstrat e classes areindicate di nth eQ^Q j graph,whil eth e

M. (phivalue ) a Fig. 16.Substrat eclasse s inSor t8 projecte d onth e«AQ , grapho fth e Snijdersveerbeek,xx x indicates theQ,M,,Q inde xo f eacKsubstrat eclas s "TcrQ 3 (cf. Appendices 4 and5) .

43 ^1Md^3i^ 1053 £orthes e classesar egive ni nAppendice s4 an d5 .However ,whe nmor e

thanon eQ ^ Mjo rQ 3 indexoccurre di nasubstrat eclas si nSor t 8,th eindice swer e replacedb ya nx .On eshoul dbea ri nmin dtha tthi sx doe sno tmea ntha tal lvalue s

canb efille din .Onl yth eph iindice soccurrin gi nth eQ-,M dQ3grap han dcorrespondin g withth eothe rtw oquartile sar evalid . Classes1 an d2 i nSor t8 ar eth ecoarses tsubstrates ,characterize db yth e

median (Mjsmalle rtha n3 )an dfirs tquartil e (Qrnegativ ean dpositiv e forclas s1 and2 ,respectively) .I nxx xcod ethi si spresente da sxx xan dx5 x+ x4x. I nclas s2 ,

infac txx xshoul db eused ,bu tth eon esampl etha tha da nM d indexsmalle rtha n5 wasa sampl econsistin go fa cobbl eplu sa littl ebi to fsan da spar to fa detritu s substrate. Classes3 t o6ar echaracterize db yth emedia nparticl esiz eo f3 ,2 ,Ïan d1 ,

combinedwit hal lpossibl enegativ eQ 1 andpositiv eQ 3 indices (x3x,x2x ,xTx ,x1x , respectively).Classe s7 an d8 ar echaracterize db yamedia nparticl esiz ebetwee n1

and3 .Clas s7 ha sa negativ eQ 1 (xxx)whil eclas s8 ha sa Q 1 between0 an d 1 (1xx).

Inclas s9 ,Q 1 andM jph ivalue sar ebetwee n1 an d2 (22x) .Clas s1 0contain s the23 x substrates.Clas s1 1contain sth e33 xsubstrates .

•meright-han dpar to fth egrap hwit hM d values largertha n3 i sforme db yth e smallamount so fminera lmatte rpresen ti norgani csubstrate san di stherefor epar t ofth eclasse s1 2- 14 .Compariso no fth edetritu sclasse si nth efiel dclassificatio n withth edetritu sclasse si nth egrain-siz eclassificatio nusin gth e 101organi c detritusleve lshowe dtha tthi sconcerne dth esam esample si nth eRatumsebeek .Thi s confirmsth ecorrectnes so fth echoic eo fth e 101level .I nth eSnijdersveerbeek , onlysmal ldifference swer epresent ,especiall yconcernin gth eCoars eDetritu ssamples . Furtherreferenc et oth eU and10 1detritu sclassificatio nwil lb emad eb y adding1 and 101,respectively ,t oth eclassificatio nnumber ,e.g .Sor t6 , 101o r oorti 8y 1% ,

4,1. 3 Discussion

4.1.3.1 Theus eo fth eInde xo fRepresentatio ncompare dt oothe rstatistica lmethod s ofthe" 0!?0* T, meth0dU8e dt 0detemin eSUbStm e Preference> i- a» -liability 1Z nul" ^r:rati0n (I'R°Mt00a 1t 0^ dif£— betweenth e d^lvT " SUbStratCS'SeVera l^ 0àS m Studied« * -d inci- vIÏÏTotZT"^ °£ the °utcane' ^ & Lau£f C1969) «* *» p«**iuiy r suit fTSainP KOta0g0rOV-Smimof »-$> *st (DeJonge , 1963) for evaluating oTf rSj ^experiments in a laborator stream. This test can also be used v^L n^: " 1S ra*er time <*"*" - •"»* it gives the probability values indicating the significance of differences between substrate types it does T^TlZrel^TffeTenCeS * S^Strate -f— *** -'be re lated or assessed m another way. Canins & Lauff (1969) do this graphically, but

44 usingthei rmetho dn oinformatio nwa sobtaine dtha tcontradicte dth eprobabilit y valuesobtaine dwit hth ecalculatio no fth echi-square dvalue ,whic hmake sth eus eo f theK- Stes trathe rsuperfluous .Applicatio no fth eanalysi so fvarianc e(Elliot , 1977,p.108 )t oth efrequencie so fa specie swithi nth esubstrat eclasse si naSor t didno tgiv ean ysupplementar yinformatio neither . Allthes emethod sfo rth ecalculatio no flevel so fsignificanc ean dprobabilit y valuesindicat eth esam etendency :fo rmos tspecie sdifference sbetwee nsubstrat e classesexis ta ta highl ysignifican tlevel ,al lindicatin ga distributio no fth e negativebinomia lcontagiou stype .

4.1.3.2 Theimportanc eo fth ejoin tus eo f1 1an d10 %detritu sclassification s

Comparingth enumbe ro fsample si nth e1 1an d10 %detritu s classifications (Sort 5-8)i nAppendice s4 an d5 show stha ti nth eSnij b6 8sample schang efro mth e3 detritussubstrate st oth eminera lsubstrates .Thi shappen st o3 3sample si nth e Ratumsebeek.Appendi x6 illustrate swhic hkin do fminera lmateria li scombine dwit h 1-10%organi cdetritu san di ti sapparen ttha ti nbot hstream sthi smainl yconcern s substrateswit hQ 1 =2 ,M ,= 3 o r2 an dQ ,= 3 .Onl ya ver ysmal lnumbe ro fsample s incoarse rsubstrate scontai n1-10 %organi cdetritu s (CD).Thu sa sa genera lconclusio n itca nb estate dtha ta preferenc eshif tfro mdetritu st ominera lsubstrate so rvic e versaconcerned : - thatthe yhav ea preferenc efo rminera lsubstrate scombine dwit h1-10 %organi c detritus,especiall ysubstrate swhic har ewel lsorte dwit hQ 1= 2 o rmore . - thatthe yhav ea preferenc efo rminera lsubstrate swit hles stha n1 %organi cde tritus;o rfo rorgani csubstrate swit hmor etha n 10%organi cdetritus ,whic hconcern s onlytw ospecie si nth eRatumsebeek , Amphinemura standfussi and Proaladius, both showingpreferenc efo rC Dan dQ ,= 4 i nth e1 %classification ,bu tfo rL an dC Di n the10 %classification . Only Gammarus pulex, Maropseotra gr. praecoxan dApsectrotanypus trifasaipennis showa shif tfro mC Dt osubstrate swit ha negativ eQ 1 (whichconcern s1 6sample si n total),togethe rwit ha shif tt oth esubstrate swit hQ 1 >2 .Al lothe rspecie stha t showdifference sbetwee nth e1 %an d10 %detritu sclassification sshif tt osubstrate s withQ 1= 2 o r3 ,M d= 2 o r3 an dQ 3= 3 .Thi s concernsth efollowin gtax ai nth e Snijdersveerbeek:Oligochaeta ,Hydracarina , Palpomyia, Stiatoahironomus, PolypedUvm breviantennatum, Macropelopia nebulosa and Tonytarsus. Inth eRatumsebee ki tconcerns : Hydracarina, Amphinemura standfussi, Nemoura cinerea, Proaladius, Prodiamesa olivacea, Epoicoaladius flavens and Paratendipes. Onlytax awit hmor etha n10 0specimen si non e ofth estream si nth etota lspecie slis tar ementioned .

45 4.1.3.3 Theinfluenc eof?anima labundanc eo nth e Indexo fRepresentatio n

Workingwit hth eInde xo fRepresentatio nth equestio naros ewhethe rdifference s inabundanc eo fa specie sbetwee nseason so rinstar swoul dinfluenc e theoveral lsub stratepreference smeasure dwit hth eindex . Ephemera danica wasselecte d as test organismsinc ethi smayfl yi smuc hmor eabundan ti nit searlie rinstar s (likemos t invertebrates)an dals obecaus ehig hdensitie so frathe rsmal lindividual swer e only foundi nlat esumme ran dearl yautumn . FromAppendi x7 i tca nb esee ntha ti nth eRatumsebee khig hdensitie s of Ephemera danica aremor eo rles srestricte dt oanimal si nthei rfirs tyea r (<1 0mm ) whichwer eespeciall yfoun di nOctober .Three-hundre dan dte no fth etota lo f48 2 individualswer efoun di n1 1samples ,whil eth eremainin g 172animal soccurre di n6 2 samples.Two-hundre dan dthirt ythre eo fthes e31 0specimen swer epresen t in 8sample s inS+D+FD ,4 6i n2 sample si nS+F Dan d3 1 in 1sampl ei nBS ,illustratin gth e clear preferenceo fthes esmal lnymph sfo rS+D+F Dan dS+FD .Th esampl ei nB S (no.142 ) presenteda nextr adifficult ysinc eth esubstrate ,consistin go fShiftin gSan dwit h FineDetritus ,wa sclassifie da sSh. Si nSor t 2,althoug hth epresenc e ofF Dwa s probablymor eimportan tfo r E. danica. Thesampl ecoul dals ohav ebee n classifieda s S+FD. Inth eSnijdersveerbeek ,neve rmor etha n2 0individual s of E.danica occurred in a sample,ye t18 3animal soccurre di n1 3samples ,al lbu ton etake ni nSectio n6 .One - hundredan dfift yo fthes e 183wer epresen ti n 7sample s (Appendix 8). Calculationo f theI.R .value sfo r E.danica inSor t2 fo rbot hstreams ,excludin gsample s containing 10o rmor especimens ,showe dtha tth ehighes tpreferenc efo rS+D+F Di smaintaine di n bothstream s (seeTable s9 an d 10). Inth eRatumsebeek ,however ,th esmal lover - representationi nS+F Di sreplace db yon efo rS+ Dan dBG .I nth eSnijdersveerbeek , thepreferenc efo rbot hG+ Dan dS+ Ddecrease s andi sreplace db y onefo rBG .Thi s showstha tth eshif tonl yconcern sth esecondar ypreference s inbot hstreams .Th e highdensit ysample sincluded ,th esecondar ypreferenc e islinke dwit h the occurrence ofhig hnumber so fsmalle rspecimen s ina fe wsample san dlo wnumber s oflarge rspeci mensi nman ysamples .Withou tthes ehig hdensit ysamples ,th esecondar ypreferenc e is linkedwit h lownumber so fsmal lan dlarg especimen si na larg enumbe ro fsamples . Highdensitie so f (especially)smal l Ephemera danica nymphsd o influence the distributionalpatter na smeasure db yth e Indexo fRepresentation .However ,n o change inth efavourit esubstrat ewa ssee nan dth eonl yconclusio n leftfro mthi s excercise istha tsmal lnymph sten dt ooccu ri nhighe rdensitie s thanlarge rspecimens ,mainl y inth emos tpreferre dsubstrat e (S+D+FD)i nbot hstream san dt oa smalle rexten ti n othersubstrat etypes .

46 Table9 .Number so f samples and specimenso f Ephemera danica inth e Snijdersveerbeek andth eI.R .value sbefor e (left)an d after (right)exclusio no fsample scontainin g moretha n 10specimen s (highdensit y samples)i nSor t2 .

Substrate type

BS S+FD S+D S+D+FD BG G+D D

Numbero f 87 86 29 28 33 30 53 49 80 79 37 34 63 63 samples Body length/mm 0 1 1 1 1 1 1 0-5 3 2 7 6 8 1 27 18 10 10 30 7 2 2 5-10 12 9 8 3 12 1 31 13 35 29 21 8 6 6 10-15 21 16 14 8 27 4 48 41 32 31 20 5 15-20 8 7 1 1 5 1 12 3 8 5 1 1 20-27 2 1 2 1 4 2 4 4 4 4 Total 46 35 30 18 54 8 133 78 90 80 75 26 8 8 I.R. value - 5.4 -3.1- •0.5- 0 1.3 2.7 - •2.8 9.3 7.7 -0.1 3.5 5.0 0.6 -7.5 -5.4

Italicvalue s indicate significant over-representation

Table10 .Number so f samples and specimens of Ephemera danica inth eRatumsebee k and the I.R. valuesbefor e (left)an d after (right)exclusio no f samples containing moretha n 10specimen s (highdensit y samples)i nSor t2 .

Substrate type D BS S+FD S+D S+D+FD BG G+D 10 47 47 Numbero f 49 47 13 12 9 9 36 28 31 31 10 samples Bodylength/m m 1 1 4 4 0-5 50 5 8 4 1 1 126 8 1 1 5-10 14 13 20 3 20 20 103 16 20 20 3 3 6 6 10-15 fi 6 9 1 5 5 16 10 5 5 6 6 15-20 8 8 5 4 11 11 14 10 11 11 2 2 1 1 20-27 2 2 1 - 5 5 39 21 5 5 1 1 sub-imago 1 1 12 12 13 13 Total 80 34 43 12 16 16 298 65 42 42 1.6 -2.7 0.5 -9.8 -5.2 I.R. value - 4.1 -2.2 1.6 -0.2 -1.5 2.1 21.3 6.5 -4.3

Italicvalue s indicate significant over-representation •

4-1.4 Grouping of substrate types based on speoies composition

Substrateswer e comparedo nth ebasi so fth efauna lcompositio no fal lsample s ineac hsubstrat e type (class)i nSor t 8,10 1usin gWhittaker' sInde xo fAssociatio n (seeSubsectio n 3.5.2).A dendrogra mwa s drawnusin gth eUnpaire dPair-Grou pmetho d usingarithmeti caverage s (UPGMA) (Sneath& Sokol , 1973),presente d forth etw o

47 similarity(% ) 30- f

SO-I

70•

80-

90•

100- 10 11 13 Class 6 8 12 14

Substrate xxx x3x x2x xlx xlx xlx xxx lxx CD CD+L 22x 23x 33x L type x5x

"*" -+ "H*" -*—H Gravel Coarse Sand Coarse Fine sand Leaves Detritus

Fig. 17. Dendrogram representing the grouping of substrate types by group averaging in Sort 8,10% in the Snijdersveerbeek, based on Whittaker's Index of Association.

similarity (Ï) 20

30 -1

70 •

100 Class 14 13 12 10 11 Substrate CD+L LL CD xxx x3x x2x xlx xlx xxx lxx 22x 23x 33x x4x type ... x5x.

NLeave s+ Coars: e+ :Coars e FineGrave l /Coars e Sand -+-Fine Sand -tzCoarsHe Detritus Gravel Gravel

Fig.18 .Dendrogra mrepresentin g thegroupin go f substrate typesb ygrou p averagingi nSor t8,10 %i nth eRatumsebeek ,base d onWhittaker' s Indexo f Association.

48 streamsi nFigure s 17an d 18,respectively .Bot hfigure s showtha tsubstrate s linked bysimila rfauna lcomposition s areals osimila ri ngrain-siz ecomposition . Inth eSnijdersveerbeek ,coars esubstrate s (Classes 1-5) areleas talike ,indi cating largedifference si nfauna lcomposition .Lea fsubstrat e (Class 13)i smor e similart oFin eSan dsubstrate s (Classes9-11 )tha nCoars eDetritu s substrates (Classes 12an d 14). CoarseDetritu s substrates haveth ehighes taffinit yt oCoars eSan d substrates (Classes 6-8).However ,i nth eRatumsebee ka simila rgroupin goccurre d withsligh tdifferences ,whic har eprobabl ydu et oth e lownumbe ro fsample s insom e substratetype s (Classes1 ,2 ,3 ,11 ,12 ,14 ) (cf.Appendi x5 ) Althoughth e informationtha tca nb eextracte d fromthi skin do fgroupin gi so f restricted significance,i tdoe sprovid ea wa yo fdistinguishin gmai ngroup so fsub strateso nth ebasi so fanima lcompositio nrathe rtha nphysica lparameters .Fo ra similarity,o f approx. 701a scriterion ,a narbitraril y chosenfigure ,i nFig .1 7fo r theSnijdersveerbee k onlynin eo fth e 14origina l substratetype sremain ,fiv eo f whichar eGrave lsubstrates .Apparentl yther e aredifference sbetwee nCoars eSan d

(Q1 < 1) an dFin eSan d (Q1 >2 )an dbetwee nLeave s andCoars eDetritus ,bu tno ts o muchwithi nFin eSan d andCoars eSan dsubstrates . Inth eRatumsebee k (Fig.18 )a mor erefine ddistinctio nwithi nFin eSan dclasse s isnecessary ,sinc e 22x,23 xan d33 xemerg ea sseparat eclusters ,whil ethes ear e combinedi non e clusteri nth eSnijdersveerbeek .Als odistinctio nbetwee nCoars ean d FineGrave l isneeded ,a swel la sth eseparatio no fLeave s fromothe rDetritu s substrates.

4.1.5 Grouping of speaies based on substrate preferences

Severalmethod so fgroupin g (clustering)wer eapplie d inorde rt ofin dtax awit h similarsubstrat epreferences .Base do nth eseve nsubstrat eclasse si nth efiel d classificationo fSor t 2,seve nfauna lgroup scoul db edistinguishe db ymanuall y rearranging the sequenceo fth especie so nth ebasi so fth eI.R .values .Thes e groups arecharacterize db yth emai npreference(s )o fth etax ainvolve dfo rGrave l (I),San d (HI), Detritus (VII),Grave lSan d (II),Gravel/Detritu s (VI),Sand/Detritu s (V) and Gravel/Sand/Detritu s (IV).I nusin gSor t 2,emphasi s ispu to nth esan dsubstrate s (4classes) .Sinc esan d isth emos tabundan tsubstrat e inbot hstreams ,thi sdoe s representth eactua l situationquit ewell . Appendix9 give s the I.R. values forth etax afoun dwit hmor etha n2 0specimen s ori nmor etha n1 0sample s inon eo fth etw ostreams .This.concerne d8 4taxa ,o f which8 0 occurredi nth eSnij ban d7 4i nth eRab . I.R.value s indicatingover-represen tationhav ebee nprinte di nitalic s andthes ewer eoutline dpe rgrou po fspecie s withinwhic hpreference so fth eindividua l speciesar esimilar .Th enumbe ro fsample s andth enumbe ro fspecimen si neac ho fth estream sar eals ogive ni nAppendi x9 . For thetax ashowin gn osignifican tover-representatio no nth ebasi so fth e chi-squared test,no tth e I.R. valuesbu tth eactua lnumber shav ebee npresented .Thes etax aar e

49 indicatedwit ha narro wafte rth enumbe ro fspecimens . Withineac hfauna lgroup ,th etax ahav ebee narrange dtaxonomicall ya si n Appendix1 .Eac htaxo nwa splace d ina grou po nth ebasi so fth eSnijdersveerbee k data,excep tfo rth etax ano toccurrin gi nthi sstrea mo rpresen ti nlowe rnumber s thani nth eRatumsebee k (e.g. LwmepMlus lunatus). Thisgroupin gemphasize sth e importanceo fCoars eDetritu san dFin eDetritu sfo rth emicrodistributio no fsevera l speciesi n'mineral 'substrates . Gammarus pulex isclassifie dt oth eS/ D groupbecaus e ofit sover-representatio ni nBan d S+Dsubstrate s inth eSnijdersveerbeek .I nthe Ratumsebeekth eover-representatio noccur sonl yi nDetritu ssubstrates ,indicatin g theimportanc eo fdetritu sfo r Gammarus. Mosttaxa/specie swit ha preferenc efo r 'mineral'substrate sbesid edetritu s substrateshav epreference s forSan do rGrave lcombine dwit hdetritu s (S+D,S+D+FD , G+D/FD),agai nindicatin gth eimportanc eo fdetritus .O nth eothe rhan dothe rtax a seemt oavoi ddetritu ssubstrate san doccu rmainl yi nBar eSan do rBar eGravel ,lik e Lithax obsaurusan d Pisidium. Thefiel dclassificatio ngive sa reasonabl yreliabl epictur eo fthe influenceo f thenatur ean damoun t (roughly)o fth eorgani cmateria li nasubstrat e type (especial lyo nth emos tdetaile dlevel ,Sor t1 wit h 14classes) .Sor t1 i sonl ypresente di n Section4. 2 forsom eselecte dspecies .However ,t ogai ninsigh ti nth epossibl e masterfactor(s )determinin gth esubstrat epreferences ,mor eobjectiv e criteriaare needed.Bia sdu et oerror smad ei nth efiel d (onlyth esurfac eo fth esubstrat ei s visible)mus tb eminimal .Thi swa salread yreduce db ytakin gth emedia nvalu e zeroa s thedivisio nbetwee nSan dan dGravel ,bu tstil lth etota lparticle-siz evariatio no f thesubstrate si shardl y includedi nth e fieldclassification . Withth eai do fWard' s (1963)metho do fhierarchica l linkage,usin g theerro r sumo fsquares ,incorporate di nth eClusta n 1Cprogra m (Wishart,1975) ,tax aoccurrin g withmor etha n2 0specimen swer egroupe do nth ebasi so fth eI.R .value si nthe grain-sizeclassificatio no fSort s6 an d8 (10$ )an dth efiel dclassificatio no fSor t 2.Compariso no fth eresult so fthes egrouping sshowe dtha tth egenera ltren di sthe samefo ral lclassification sbu ttha tdifference sd ooccur .Sneat h& Soko l (1973, p. 204)alread ydiscusse dth efac ttha tWard' smetho dma ydivid edens ecluster si na n unacceptablemanner .I nth emateria lo fthi sinvestigatio nth edivisio no fthe clusters wasno tunacceptable ,bu ti tdi dhappe ntha tsom epoint si na certai ncluste rwer e nearerth ecentroi do fanothe rcluste rtha nt oth ecentroi do fthei row ncluster . Thisespeciall yconcerne dth etax awit hver y lowo rver yhig hnumber so fspecimen s givingrathe rdeviatian tI.R . values.However ,othe rlinkag emethod sdi dno t show moreacceptabl egrouping san dWard' smetho dwa sretained ,bu tonl ya samean so f groupingtax awit hsimila rpreference st ocreat ea startin gpoin tfo rth epresentation . Sort8 ,10 $wa sselecte dt orepresen tal lSort s5-8, becaus ei tinclude sthe totalparticle-siz evariatio no fth esubstrate .I ti samor eintegrate dmetho dtha n Sort5-7 .Th e 10$limi tfo rth eorgani cmatte rwa s chosenbecaus ei tgive sa wel lde fineddistinctio nbetwee n organic andminera lsubstrates ,enablin g comparisonswit h

50 Sort 1-4.I twa snecessar yt odistinguis ha tleas t 14cluster st ogai ninsigh tint o thefactor scausin gth egrouping . Initially,al ltax aoccurrin gwit hmor etha n2 0specimen swer euse dfo rth e grouping.Thi sconcerne d 72tax ai nth eSnijdersveerbee kan d5 1 inth eRatumsebeek . Theresult sar epresente di ndendrogram s (Appendices 10an d 11). Inthes edendrogram s lettercode sfo rGrave l (G),San d (S)an dDetritu s (D)hav ebee ninserte dafterward s onth ebasi so fanalysi so fth emai nover-representatio no fth especie swithi neac h cluster. Aftercarefu lanalysi so fth ebasi cdat ause dfo rth eclusterin g (theI.R . values ofeac hspecies )i tbecam eclea rtha tmos tspecie swer egroupe dtogethe ro n thebasi so fcorrespondin gpositiv eI.R . values (over-representationo rpreference ) buttha tsom eo fth especie soccurrin gi nver y lownumber swer eclassifie do nth e basiso fsimila rnegativ eo rclose-to-zer oI.R . values,thu sinfluencin gth eultimat e averageI.R . values.I norde rt oreduc eth einfluenc eo fthes eles sabundan ttaxa , thebasi sfo rth efollowin gchapter swa s laidb yusin gonl yth etax aoccurrin gwit h 100o rmor especimen s intotal .Thi sreduce dth elis tt o4 8taxa ,4 3o fwhic hoccurre d inth eSnij bi nthi sabundanc ean d 26i nth eRab .A s illustratedwit hth eaverag e I.R. valuesfo reac hcluste r (Tables 11an d 12),thre emai ngroup sca nb edistinguished , consistingo fcluster scompose do fspecie swit hpreferenc e forGrave lsubstrate s (Classes 1-6 inSor t8 , 101),San dsubstrate s (Classes7-11 )an dOrgani csubstrate s (Classes 12-14). Comparisono fth etw odendrogram s (Figs.1 9an d20 )illustratin gth egroupin go f thespecie so nth ebasi so fthes eaverag eI.R . values inth etw ostream sshow stha t speciesbelongin gt oon eo fth etw omai ndetritu scluster s inth eSnijdersveerbee k (Fig.19 ,Cluste r6+7+ 4an d3+8+12+14 )ar eals ogroupe di non eo fth efou rmai nde trituscluster si nth eRatumsebee k (Fig.20 ,Cluste r 14,3+6+11+9 ,4+1 3an d 2). Thespecie si nth eSan dan dGrave lcluster si nth eRatumsebee k (Fig.20 ,Cluster s 1+12+5+10an dCluster s 7+8,respectively )als ooccu ri nthes ecluster si nth eSnijders veerbeek (Fig.19 ,Cluste r 11+1+9+5resp .2+13+10) .Onl ytw ospecie ssho wa differenc e betweenth estream si nthei rmai ngrouping : Baetis verrais (Taxano .50 )an d Miaropter- na seqiuxx (taxano . 128).Bot hspecie sar egroupe dwit hth eSan dspecie s inth e Snij dersveerbeek (Fig.19 )an dwit hth eDetritu sspecie s inth eRatumsebee k (Fig. 20). Consideringth eI.R . valuesfo rthes especie s inth esubstrat etype s inSor t8 ,10 $ (Appendices1 2an d 13), itca nb esee ntha t Baetis occurredi nGrave lan dSan di nth e Snijb (Appendix 12)bu ti nDetritu san dGrave l inth eRa b (Appendix 13), suggesting thatGrave lmigh tb eth emor eimportan tsubstrat efo r Baetis vernus. M.sequax isgroupe dwit hth especie spreferrin gSan dsubstrate s inth eSnijb , althoughi ti sover-represente d inGrave lan dDetritu s substrates (Appendix 12). In theRa bi tshowe dpreferenc ei nDetritu ssubstrate s (Appendix 13),indicatin gDetritu s asth efavourit esubstrat etype . InAppendice s 12an d13 ,th eI.R .value sfo ral lmor eabundan ttax aar epresente d andth eI.R . valuesindicatin gover-representatio nhav ebee noutline di nth esam ewa y

51 Table11 .Th eaverag epositiv e I.R.value s foreac hcluste r inSor t 8,10%fo r theSnijdersveerbeek .

ClUS ter Substrate class no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Gravel Sand Detritus

xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x

2 7.8 5.4 3.8 6.2 5.7 1 6 10 51.9 2.2 1.8 13 11.6 14.5 10 5 16.1 5 19. 0 1.4 4.7 10.0| 9 26.11 1 0.3 0.5 3.4 2.5 2.6 11 7.2 19.4 14.8 2.7 14 29.5 30.1 25.8 88.6 4.5 3 12.91 55.3 32.0 35.5 7 0.4 0.0 0.5 26.1 1.9 4 5.9 27.4 3.3 12 19.8 63.4 8 54.3 18.4 18.9 6 12.4 7.7 1.4

See Fig.] L9fo rtax a ineac hcluster . Boxesind i cate groupso f taxa with similar substrate preferences

thecluster si nth eTable s1 1an d1 2wer eoutlined .Th etax aar earrange di nth esam e sequencea sth ecluster si nTable s1 1an d12 .Fo rsom especie s (Hdbrophlebia fusoa, taxano . 48; Agapetus fusoipes, taxano . 103;Lirmiua volohnart, taxano . 186; Epoicooladius fiavena, taxano .283 ; Pavatendipee, taxano . 302)compariso nbetwee n thetw ostream si sno tpossible ,becaus ethes especie soccurre di nto osmal lnumber s inth eSnijb .Th esam eapplie sfo r2 2othe rtax ano tabundan tenoug ho rabsen ti nth e Rab. Gravelsubstrate s (Classes1- 6i nSor t8 ,10 %i nAppendice s1 2an d13 ) are preferredby ,fo rexample ,th ecaddi sflie s Lithax obsourus and Agapetus fusoipes, theriffl ebeetle s Elmis aenea and Lùrmius volckmari andth emidg elarva e Ovfhoaladius sp.an d Chaetooladius sp.Th elatte rspecie si sals oover-represente di nDetritu s substrates (Class 14).San d (Classes7-1 1 inSor t8 ,10 1i nAppendice s1 2an d13 )a s thepreferre dsubstrat ei sonl yinhabite db ya fe wspecies ,e.g .th emidge s Prodiamesa oUvacea, Polypedilum breviantermatum. Proeladius sp.an d Stietoehironomus sp.,th e Diptera Ptyehoptera and Palpomyia, watermite s (Hydracarina), Oligochaetaan dth e mollusc Pisidium. Manyo fth especie sclustere dt oth eSan dgrou psho wover-representatio ni nSan d substrates.However ,thei rpreferenc ema yi nfac tb efo ra Grave lo rDetritu ssub strate,e.g .th ecaddi sflie s Seriaostoma personatwi and Microptema sequax, which seemt oprefe rGrave lan dDetritu ssubstrate si nth eSnijb . (Appendix 12).I nth eRa b

52 4000 dissimilarity (squared euclidian distances)

3000

1000-

500

400-

300

200

100

Clust er 11 1 10 12 14 no. Taxa 271 11 217 50 18 280 100 127 40 32 190 277 no. 311 38 241 245 105 155 220 42 279 47 248 290 185 254 293 269 109 249 318 272 128 256 275 198 308 310 205 341

Fig.19 .Dendrogra m representing thegroupin go f the4 3mos t abundant taxa (100 specimens ormore )i nth eSnijdersveerbee k inSor t 8,10%,base d on thesimilarit y of I.R.values .Cluste r numbers correspondwit h those inTabl e 11.Tax a numbers refer to thenumber s inAppendice s 1an d 12.Th e letters S (Sand), G (Gravel)an d D (Detritus)indicat e themai npreference s of the taxa in thecluster sbelow .The y were added afteranalysi s of thebasi c data inAppendi x12 .

M.sequax prefersDetritu ssubstrate s (Appendix13) . Fromth eI.R .value so feac hindividua lspecie si tbecome sclea rtha ti nbot h streamsCluste r1 contain sman yspecie stha tar eover-represente di nbot hSan dan d Gravelsubstrates ,bu ttha tthe yar eclustere di nth eSan dgrou po nth ebasi so fth e averageI.R .value s (Tables1 1an d12) .Workin gwit haverage ssmal ldifference s soon disappear,an dbecaus epositiv ea swel la snegativ eI.R .value soccu ri nGrave lsub strates,th eaverag eapproache s zero.Befor edrawin gan yconlusion so nth ebasi so f theaverag evalues ,on eshoul dreconside rth eorigina ldata .Specie spreferrin gbot h Sandan dGrave lsubstrate sar ee.g .th emayfl y Ephemera danica andth eDipter a Limnophila sp.an dDicranota sp.Compariso no fth edat afro mth eSnij b (Appendix12 ) withtha tfro mth eRa b(Appendi x 13)show stha tspecie spreferrin g Sandan dGrave l

53 Table12 .Th eaverag epositiv eI.R .value sfo reac h cluster inSor t 8,10%fo r the Ratumsebeek.

Cluster Substrate class no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Gravel Sand Detritus

xxx xBx x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x

7 9.9 1.3 0.4 10.810. 2 8 6.0 1.5 4.0 5.6 10.3 2.3 0.9 1.8 10 0.8 0.2 3.8 0.4 6.1| 5 1.3 12.2 6.6 10.9 1 0.4 3.5 12.1 2.3 12 17.3 5.3 6.0 6 0.6 4.1 0.2 9.6 4 17.3 53.7 3 1.2 0.6 17.4 11.3 9 0.8 17.6 14.6 1.2 14 1.6 0.9 2.3 65.0 26.9 2 3.2 160.549. 2 22.6 11 0.7 26.1 13 53.2 13.4

SeeFig .2 0 fortax a ineac hcluster . Boxesind i categroup so f taxawit h similar substrate preferences

substratesi nth eSnij bar eals oclustere dtogethe ri nth eRa b(Cluste r1 i nbot h streams).I nth eRab ,th epreferenc efo rGrave li smuc hles spronounced ,however . Thesephenomen awil lb ediscusse di ndetai lwhe ndealin gwit hth eindividua lspecie s (Section4.2) . Detritussubstrate s(Classe s12-1 4i nSor t8 ,10 1i nAppendice s1 2an d13 )ar e preferredb yth elarges tgrou po fspecies ,e.g .th efres hwate rshrim pGammams pulex, twostonefl yspecies , Nemoura cinerea and Amphinemura standfussi, thecaddi s fly Chaetopteryx villosa, thene tspinnin gcaddi s Fleatvocmemia conspersa, thebeetl e larva Helodes sp.an dman yChironomidae ,e.g . BHIUa modesta, Eukiefferiella gr. discoloripes and Diplocladius cultriger. Separategroup sar eforme db ysom eindividua l species,suc ha s Micropsectra gr. praecox. ThisTanytarsin ii sstrongl yover-represente d inFin eSan dan dDetritu ssubstrate si nth eSnijb ,whil ei tprefer sDetritu ssub stratesi nth eRab .

Nemoura cinerea obviouslyprefer sDetritu ssubstrate si nbot hstreams ,a smen tionedbefore ,bu ti nth eRab ,Grave li sals ofavoured ,a phenomeno nsee ni nth e Snijbfo rAmphinemura standfussi. Baetis vernus, Macropelopia nebulosa and Tanytarsus sp.ar eover-represente di nGrave lan dSan dsubstrate si nth eSnij b(Appendi x12) . BaeUs prefersGrave li nth eSnijb .I nth eRa bi tprefer sDetritu ssubstrates ,bu ti t isals oover-represente do nGrave l(Appendi x13) . Macropelopia nebulosa and Tanytarsus sp.ar efairl yevenl ydistribute dove rth esubstrat etype si nSor t8 ,101 ,

54 5000 dissimilarity (squared euclidian distances)

4000H

3000-J

1000

500

400

300-

200-

100 _E _C 1 I 2 Cluster 12 5 10 7 14 6 4 13 no. Taxa 11 271 47 217 103 105 287 40 50 269 128 42 277 32 no. 38 308 186 48 275 190 249 311 272 283 341 302

Fig.20 .Dendrogra m representing the groupingo f the2 6mos t abundant taxa (100 specimens ormore )i nth eRatumsebee k inSor t 8,10%,base d on thesimilarit y of I.R.values .Cluste r numbers correspondwit h those inTabl e 12.Tax anumber s refer to thenumber s inAppendice s 1an d 13.Th eletter s S (Sand), G (Gravel)an dD (Detritus)indicat e themai npreference s of the taxa iath ecluster sbelow .The y were added after analysis of thebasi c data inAppendi x13 .

although theforme rprefer sCoars eGrave l (Class 7)an dth elatte rFin eSan d (Class 10). Thesean dothe rdifference si nspecie spreference sbetwee nth etw ostream swil l bediscusse di ndetai l inSectio n4.2. ,wher e2 6o fth e4 8tax apresente d inAppendice s 12an d 13,ar edeal twith .Compariso no fth emai ngroup so fspecie shavin g similar substratepreference si nth egrain-siz e classificationi nth elaborator yi nSor t8 , 101 (Appendices 12an d13 )wit h thesegroup si nth efiel dclassificatio n inSor t2 (Appendix9 )lead st oth econclusio n thatmai npreference s canb eadequatel y described

55 onth ebasi so fth efiel dclassification .However ,detaile d datao nth emicrodistribu tionca nonl yb eobtaine dwit hth eai do fa thoroug hgrain-siz e classification,in cludingth eamoun to fcombine dorgani cdetritus .

4.1.6 Numbers of species and specimens in different substrate types

Somegenera lconclusion sca nb edraw nwhe nconsiderin g numberso fspecie si n eachtaxonomica luni t (Table 13), togetherwit h theiraverag e abundance (Table14) . Frombot htable sChironomida eemerg ea sth emos t abundantgrou pi nnumbe ro fspecie s aswel la si nnumbe ro fspecimens ,bu tdistinc tdifference si nabundanc ei nth e varioussubstrat e typesar epresent .Detritu ssubstrate sar einhabite db yth elarges t numberso fanimals ,predominantl ycompose do fTanytarsin i (M.gr . praecox'), Gammarus pulex (includedi nOthers) ,Orthocladiina e (severalspecies )an dColeopter a (Helodes larvae)'.The nfollo wS+D+FD ,S+ Dan dS+F Di nthi s sequence,wher e Tanytarsini (Af.gr . praecox),. G. pulex, Chironominian dOrthocladiina epredominate .G+D/F D comes nextwit hTanytarsini ,Orthocladiina ean d G.pulex. Finallyth ebar eminera l substrates BSan dB Gsho wth esmalles tpopulatio ndensities .I nBS ,Tanytarsin ian d G.pulex are stillrathe rdominant ,bu ti nB Gth enumber so fspecimen sar efairl y equally distributed overth evariou staxonomi egroups .Chironomin i occuri nequall yhig hnumber s inSan d substrates combinedwit hDetritus ,whil eOrthocladiina ear emor e abundanti nGrave l substrateswit hDetritu san dPur eDetritu s substrates.Tanypodina ean dTanytarsin i areleas tpresen ti nB San dBG .Dipter aar erathe revenl ydistribute dwhil e Coleoptera areabundan ti nGrave lan dDetritu s substrates.Considerin gth enumbe ro fspecie s foundi neac hsubstrat e type,th edifference sbetwee nmos tgroup sar eminimal .Onl y Coleopteraan dTrichopter aoccu rwit hmor especie si nGravel ,Detritu san dBar e Sand substrates.However ,sinc eth enumbe ro fsample si sdifferen tfo rth evariou s substrate classes,absolut ecompariso ni sno tpossible ,althoug hmajo r changesar eno tlikely .

Table 13.Numbe r of speciesfo rth emal a taxonomical groups inth e substrates distinguished inSor t 2i nth e Snijdersveerbeek.

BS S+FD S+D S+D+FD BG G+D/FD D/FD Chironomini 13 14 18 21 19 18 17 Orthocladiinae 10 9 13 13 14 12 15 Tanypodinae 4 4 5 6 5 5 6 Tanytarsini 4 5 5 6 8 7 6 OtherDipter a 13 8 10 13 16 13 14 Coleoptera 15 7 5 6 18 18 16 Ephemeroptera 2 2 2 2 2 2 2 Plecoptera 2 1 2 1 2 2 2 Trichoptera 17 5 8 10 14 16 18 Mollusca 1 2 3 1 3 3 2 Oligochaeta 2 1 2 3 2 2 2 Others 7 7 4 6 7 6 6 Total 86 60 72 82 102 97 100 Number of samples 87 29 33 53 80 37 63

56 Although thesedifference si nanima lnumber si nth e7 substrat e typesi nSor t2 are illustrated forth eSnijdersveerbee ki nTabl e 14,compariso no fth etota lnumbe r ofanimal spe rsubstrat eclas sthroug hI.R .value s leadst oth esam econclusion san d thesam esequenc eo fabundance s inbot hstream s (cf.Table s7 7an d 78).O fcours eth e heighto fth e I.R. valuecanno tb etake na sa precis emeasure ,bu t thegenera ltren d issignificant .Th enumbe ro fanimal si slowe rwhe nth eI.R . valuei slowe r (more negative). Ina stud yo fa smal l woodland stream inCanada ,Macka y (1969)distinguishe d Sand,Gravel ,Stones ,Leave s andLeaf-Detritu sa ssubstrat etype san dsh efoun dtha t thediversit y andth enumbe ro fanimal s increased fromsand ,throug hgrave lan d stonest oleave san ddetritus .Sh eals odemonstrate d thatalthoug h leafan d detritus substrateswer eriches ti nspecie san dnumber s theyar epredominantl y inhabitedb y Dipteraan dtha tgrave lan dston ysubstrate shous emor ePlecoptera ,Ephemeroptera , Trichopteraan dColeoptera .I ngeneral ,difference s innumber so fspecie san dnumber s ofanimal sfollo wth esam etrend ,showin ga nincreas efro msan dthroug hgrave lt o detritus (Pennak& va nGerpen ,1947 ;Ward , 1975;Walton ,Reic e& Andrews ,1977) . However,thi s isno talway si nth esam esequence ,especiall yi nstream swher eston y substratesar escarc eo rcoars esubstrate salway sconsis to famixtur eo fstones , gravel,san dan ddetritus ,formin gver y complexsubstrates .I nthes estream son ema y findanothe rsequenc eo rdifference si nth esequenc ebetwee nth enumbe ro fanimal s andthei rbiomas s (Mackay& Kalff , 1969). Inlowlan dstreams ,substrate s areals over ycomplex ,consistin g predominantly ofsan dan ddetritus ,occasionall ymixe dwit hgrave land/o rpebbles .Althoug hn o estimationso fanima lbiomas swer emade ,th enumber so fanimal s increasefro mBar e Sandan dBar eGrave lthroug hSan dwit hDetritu st oLeave san dDetritu ssubstrates . Thereason sfo rth eoccurrenc eo fexceptionall y lownumber so fanimal so ngrave l substrates,compare dt oman yforeig nstreams ,i sprobabl ytha tth ebar egrave lsub strates aremostl ysituate di nth emos tunstabl e zoneso fth estrea mbed ,whil eth e

Table 14.Averag enumbe ro f specimens in1 0sample s inth e substrates distinguished in Sort 2 inth eSnijdersveerbeek .

BS S+FD S+D S+D+FD BG G+D/FD D/FD Chironomini 65 140 136 126 41 56 125 Orthocladiinae 15 28 125 138 63 302 466 Tanypodinae 2 48 28 63 6 49 32 Tanytarsini 114 831 428 1315 39 542 1144 OtherDipter a 37 57 48 52 38 31 72 Coleoptera 7 5 20 11 28 61 154 Ephemeroptera 10 15 33 26 26 24 1 Plecoptera 2 - 2 - 17 4 61 Trichoptera 37 16 46 21 57 56 74 Mollusca 11 14 4 6 4 3 3 Oligochaeta 10 17 24 18 32 25 5 Others 144 252 792 276 55 152 693 Total 455 1424 1686 2052 407 1304 2820

57 areaconsistin go fthi skin do fsubstrat ei srelativel ysmal lan dsan dan dsil t transport (scouring)high . Cordone& Kelle y (1961)reviewe dsom eo fth eolde rpaper so nth edifference si n productionan dstandin gcro po fsan dcompare dt omud ,detritus ,gravel ,rubbl ean d vegetation.San dappeare dt ob elowes ti nproductio nan dstandin gcrop ,whil erubbl e togetherwit horganicall yenriche dmu dshowe dth ehighes tproduction .Thes e findings areconfirme db ya larg enumbe ro fmor erecen tpaper s (Maitland,1964 ;Mackay ,1969 ; Pennak,1971 ;Nuttall ,1972 ;Ward ,1975 ;Russev ,1977 ;Petran ,1977 ;Resh , 1977). Chutter (1969a)discusse dth eeffec to fsan dan dsil ttranspor to nmacroinvertebrate s andconclude dtha tthe ycaus econsiderabl echange si nth efauna .Increase si nth e amounto fsil tan dsan dincreas eth einstabilit yo fth erive rbed ,whic h adversely affectsth efaun a (Mackay& Kalff , 1969).

4.1.7 Field experiments

4.1.7.1 Traysfille dwit hartificia lsubstrat e

Forstatistica lanalysi so fth enumbe ro fanimal san dth especie s caughti neac h substrate trayan dcompariso no fth ecolonizatio no fth egrai nsizes ,onl yth edat a ofth e1 4an d2 8day scolonizatio nperio dca nb eused .I ntabl e 15,th eI.R .value s forth emor eabundan ttax aafte r1 4day sar egiven .Tabe l1 6give s thesedat aafte r 28days .Thi sconcerne d7 an d1 0species ,respectively ,wit h5 o fthe mabundan t after bothperiods ; G.pulex, M.gr .praecox, C.melanops, E.ootoaulata and H.fusoa. Only E.oatooulata showa distinc tdifferenc ebetwee nth etw operiods ,whic hi sno tver y surprisingsinc ethes e leecheswer emostl yfoun do nth einsid eo fth etray s itself andno to nth esubstrate .Th eleeche swer eals oabundantl ypresen to nth eoutsid eo f thetrays ,bu tthes ewer ediscarded . Habrophlebia fusoa showedpreferenc efo rth e coarserparticl esize safte rbot hperiods . Gammarus pulex alsodisplaye da clea rpref erence forcoars egrai nsizes ,whil e Conohapelopia melanops preferred4 an d2m m grainsize safte rbot hperiods . M.gr . praecox wassignificantl y abundanti n8 an d4

Table15 .Numbe ro fspecimen s (N)an d I.R. values forth emos t abundant species insubstrat e traysafte r 14day so fcolonizatio n inth eRatumsebeek .

N Part iclesiz e (lower limit)/mm 32 16 8 4 2 Gammarus pulex 2034 3.6 9.7 -1.2 0.1 -12.2 Habrophlebia fusoa 183 2.9 2.2 1.1 -0.4 -5.7 Baetis vernus 89 -3.0 -2.3 -3.7 7.2 1.9 Amphinemura standfussi 130 -2.9 -0.2 0.2 6.1 -3.1 Erpobdella octoaulata 15 -1.2 -1.7 0.6 1.7 Conohapelopia melanops 97 -4.2 -4.0 -4.0 6.3 5.8 Miaropseotra gr. praecox 15 0.6 0.6 0.0 0.0 0.0

Italicvalue sindicat esignifican t over-representation

58 Table 16.Numbe ro f specimens (N)an dI.R .value s forth emos tabundan t species insubstrat e trays after 28day so f colonization inth eRatumsebeek .

N Particle size (lower limit)/mm

32 16 8 4 2 1 0.5 0.25 0.125 Gammarus pulex 5230 6.0 23.6 48.9 33.3 -16.3 -24.0 -24.0 -23.7 -23.8 Miaropseatra gr. praecox 136 -3.6 -0.0 3.8 8.7 1.5 -0.0 -3.4 -3.6 -3.4 Prodiamesa olivaoea 108 -3.5 -2.6 1.7 13.6 0.0 -2.3 -2.3 -2.9 -1.7 Maoropelopia nebulosa 53 -2.4 -2.4 -2.4 7.5 3.8 0.8 -0.4 -1.6 -1.2 Chaetopteryx villosa 42 6.2 0.6 -2.2 0.2 -1.2 -1.2 -2.2 0.2 -0.3 Erpobdella ootooulata 27 3.5 0.6 0.6 0.0 -1.2 0.0 0.0 -1.7 -1.7 Dicranota sp. 26 -1.7 -1.1 -1.7 -1.7 -1.7 1.2 5.4 3.0 -1.7 Conohapelopia melanops 23 -1.6 -1.6 -0.4 2.2 5.9 -0.4 -1.0 -1.6 -1.6 Polypedilum brevianten. 23 -1.6 -1.6 0.3 0.9 2.2 0.3 -1.6 -1.6 2.8 Habrophlebia fusoa 18 1.4 -0.7 3.5 2.8 -1.4 -1.4 -1.4 -1.4 -1.4

Italicvalue s indicates i Lgnifican t over-representation

mmsubstrate s after2 8days ,althoug hshowe dn opreferenc eafte r 14days . Comparing thesedat awit hth edistributio nshow ni nAppendi x1 3fo rth enatura l substrateso fth estrea ma sdetermine dwit hth eshove lsamples ,agreemen ti ssee nfo r somespecie san ddisagreemen tfo rothers .I twil lb edemonstrate di nSubsectio n4.2. 2 thatthi sphenomeno nca na tleas tpartl yb eexplaine db yth eabsenc eo forgani c matter,especiall yth eabsenc eo fdetritu si nth efou rfine rsubstrates ,whic h collect lessdriftin gdetritu s thanth ecoarse rparticl e sizes.Thes efou rsubstrate sar e probablybes t comparablet ounstabl e sandsubstrates ,whic har eno tric henoug hi n finean dcoars edetritu st osuppor t largepopulation so fanimal swit ha preferenc e forthes egrai nsize sunde rnatura lconditions ,whe nmor eorgani cmateria li spresen t incombinatio nwit h theseparticl e sizes.Moreover ,th etray swer eal lexpose dt oth e samecurren tvelocity ,whic hma yals o causeartificia lresults .

4.4.2 Partiale sizes introduced without trays

Onlyon eexperimen to fthi snatur ewa sperformed .Unfortunatel ya spat eoccurre d duringth eexperimenta lperiod ,washin gth efine rsubstrate s awayan dcoverin gth e coarserone swit hmuc h finematerial .Althoug hth esubstrate swer esample dafte rth e setperiod ,analysi so fth egrai nsize so fth esample sshowe d thata considerabl e changei nparticle-siz e compositionha dtake nplace .Th epopulation so fth esubstrate s showedmuc hmor e resemblance totha to fth eminera l substratesi nth estrea mtha nan y ofth esubstrat e trays,bu tth eexperimen twa sconsidere dunsuccessfu lbecaus eth e basiccondition sha dchange dto omuch .However ,th eimpressio npersiste d thatexperi mentso fthi skin d shouldb egive npriorit y overthos ewit hexperimenta ltrays .

59 4.2 ORGANISM-SUBSTRATE RELATIONSHIPS

4.2.1 Outline of présentation

Severalspecie sapparentl ydispla ya simila rdistributiona lpattern ,differin g fromtha to fothe rspecie so rgroup so fspecies . (Subsections4.1. 4an d4.1.5) .T o testth ehypothese sstate di nSectio n1. 3i ti sno tnecessar yt odea li ndetai lwit h allth especie s listedi nAppendice s9 ,1 2an d13 .Therefor ea selectio no fspecies , representativefo rth evariou sdistributiona lpattern swil lb ediscusse di ndetai lt o illustrateth edifferen tsubstrat epreferences .Emphasi swil lb epu to nth etax a foundi nnumber s largeenoug ht ojustif ystatistica l treatment,especiall y thosewit h more than10 0specimen spresen ti nth etota lserie so fsample si non eo fth estream s (Subsection 4.1.5).Thi sconcerne d4 8tax aan dfro mthes etax arepresentative sfo r eachdistributiona lpatter nwer echose no nth ebasi so fcriteri aaime da tfindin g specieswithi neac htaxonomi euni t (familyo rsub-family )tha tdemonstrat e thedifferen t mechanisms (eitherdirect ,suc ha sburrowing ,clinging ,hiding ,building ,o rindirect , sucha soxyge ncontent ,curren tvelocity , light intensityo rfoo dconditions )result ingi nsubstrat eselection . Notal lspecies/tax awer e treatedwit hth esam edegre eo fdetai lbecaus eo flac k ofsufficien tbackgroun ddat ao rbecaus e theywer e only identifiedt oa lo wtaxonomi e level.Excep tfo ra fe wspecie s- thos emor enumerou si nth eRatumsebee ko rrestricte d totha tstrea m- th edat afro mth eSnijdersveerbee kwil lb euse da sa startin g point.Thi sconcern smor esample san dyield smor e statisticallyvali dresults .Th e datafro mth eRatumsebee kwil l functiona sa chec ko nth evalidit yo fthos e results ina strea mo flarge rdimensions .Attempt swil lb emad et oexplai npossibl e differ encesi nsubstrat epreference so f(group sof )specie sbetwee nth etw ostreams .

Inth efollowin gchapters ,whic hdea lwit hth e2 6selecte dtaxa ,th eanalysi so f theresult so fth efiel dstud y (microdistribution)wil lb eemphasized .Whe n available thesubsectio no nmicrodistributio nwil lb eprecede db ydat ao nth elif ecycl ean d followedb ydat ao ncase-buildin gan dsubstrate-selectio n experiments.Thu sth efol lowingsubsection sca nb eexpected : lifecycle ,microdistribution ,case-buildin gan d substrate-selectionexperiments .Fo rsom especie sa nintroductio no nidentificatio n orpopulatio ndensit ywil lb egive nfirst .

Life cycle Animalgrowt hi nth etw ostream sstudie di spresente di na histogram , summarizingbod y lengthi n1-m mclasse sa spercentag epe rfou rwee kperiod s(e.g . Fig.21) .I nthes ehistogram sth edat ao fbot hstream sar epresente d together.U pt o 1977,thi sconcern sSnijdersveerbee k dataonly ,an dafte rWee k 15i n197 7Ratumsebee k dataonly .I nth efirs t1 5week so f197 7dat afro mbot hstream swer epooled ,bu tno t before comparisono fth ebody-lengt h distribution overth elengt hclasse si nth etw o streamsha dshow ntha tther ewer en osignifican tdifference si nbody-lengt h composition

60 ofth etw opopulations .Th edat ao nanima lgrowt hwil lb ecompare dwit hdat afro m theliteratur e onth e lifecycl eo fth especie sconcerned ,o rrelate dspecies .

Microdistribution I.R.value s forth esubstrat e typeso fth efou r levelso ffiel d classification (Sort1 - 4 )wil lb epresente d ina dendrogram-lik e table (e.g.Tabl e 26)comparabl e toFig . 12,wher e thename so fth esubstrat etype sar egiven .A tth e topo fthes etable s thesubstrat e types inSor t3 ar eindicated ,San d (S), Gravel (G) and Detritus (D),whil e atth ebotto mo feac htabl eth etype s inSor t 1ar eabbrevi ated (seeOutlin e ofsubstrat e classification,pag eafte rcontents) :Stabl e (St) Sand,Shiftin g (Sh)Sand ,San d+ Fin eDetritu s (FD),San d+ Leave s (L),San d+ Coars e Detritus (CD),Bar e (B)Gravel ,o rothe rcombination susin gth esam eabbreviations . Thesetable sca nb ecompare d toAppendi x 2o r3 ,wher eth enumber so fsample s ineac h substrate typear egiven . I.R. values^fo rth esubstrat e types inth egrain-siz e classification inth e laboratoryar epresente d forbot h levelso forgani cdetritu s (11an d 10»»;se eSubsectio n 4.1.2.2)i nSor t5- 8 (e.g.Table s 37an d 38).Whe nn odifference s insubstrat e preferencebetwee nthes etw o levelswer eobserved ,onl yth e10 1leve li spresente d (e.gTable s 19an d 20). Forsevera l taxa,a tabl ei sinclude dgivin gth eI.R . values fordifferen t animal length classes inSor t8 ,10 1 (e.g.Tabl e 21A),an dth e I.R. valuespe rseaso n (e.g.Tabl e 21B).Wee knumber scorrespondin gwit hth eseason sca n befoun di nTabl e 2. A discussion ofthes eresult swil l followi nth eligh to fdat afro mth e literature onlif ecycle ,foo dhabit san dhabita tpreferences .

Case building For thecase-buildin gTrichoptera ,dat ao nth egrain-siz e composition ofth enatura l case (e.g.Fig .22 )wil lb epresented .Whe napplicable ,dat ao ncase - building experimentswil lb ediscusse d onlybriefly ,becaus e thesewil lb epublishe d inful ldetai lo na laterdat e (Tolkamp &Verdonschot ,t ob epublished) .Th egrain - sizecompositio n (orminera lan dorgani ccomposition )o fthes ecase swil lb e compared with thegrain-siz e andorgani c compositiono fth epreferre d substrate types.

Substrate-selection experiments Forth especie ssubjecte d to substrate-selection experiments inth e laboratory stream (seeSubsectio n 3.3.1.4),th eresult so fthes e experimentswil lb egive ni nhistogram s (e.g.Fig .25 )an dcompare dwit hth eresult s obtained inth efield . Inthes e figures thegrain-siz e fractions areindicate db yth e lower limito fth efractions .Grai nsize ssmalle r than1 m mar eexpresse d inmicro metre sizes,large rgrain sar eexpresse d inmillimetr esize s (e.g.12 5stand sfo rth e 0.125- 0.25 0m m fraction; 2stand s forth e2 - 4m m fraction). Forsom especies ,th eselectio no fgrain-siz e fractions infiel dexperiment s willb ediscussed ,comparin g theresult swit hthos eo fth efiel dstud yan ddat afro m theliteratur ewhe navailable .

61 4.2 .S Auteeological data for selected species

4.2.2.1 Lithaxobscuru s(Hagen )(Trichoptera :Goeridae )

Life cyole Thelif ecycl eo f Lithax obscurus inbot hth eSnijdersveerbee kan dth e Ratumsebeeki ssummarize di nFig .21 .Dat afro m197 7ar emainl yfro mth eRa ban d earlierdat aar emainl yfro mth eSnijb .I nbot hstream spupa ear epresen tfro mth e beginningo fDecembe rt oAugust/September ,wit ha pea ki nApril/May ,whic hagree s withth eMay/Jun efligh tperio da sreporte db yBeye r (1932)an dTobia s (1967).However , theextende dpresenc eo fpupa et oth een do fsumme rpoint st oa longe rfligh tperiod , lilies (1952)foun dtha t Lithax niger emergedfro mearl yApri ltil lth een do fMay , andals ofro mearl yJul yt omid-August .Sinc eadult swer eno tcollecte dsystematically , butonl yincidentall yi nbot hstreams ,thes eemergenc edat aca nonl yb ecompare do n thebasi so fth epupae . TheF- 2(2. 2- 4. 5m mbod y length),F- 1 (3.4- 6. 7mm )an dF (4. 8- 9. 5mm ) instarlarva eoccu ral lyea rround ,wit ha pea ki nAugus tfo rth eF- 2an dF- 1instar s andi nNovember/Decembe rfo rth eF (final)instar . Lithax overwintersmainl yi nth e finalinsta ro ra sa pupa, bu tpartl yals oi nearlie r instars.However ,thes ear eon lyth emos tpronounce dpoint si nth elif ecycle ,which i sstrongl ydisperse dove rth e wholeyea rbecaus eo fth elon gfligh tperio dan ddisperse deg ghatching .Anothe r reasonmigh tb etha tlarva etha thatc hearl yi nth eyea rgro wfaste rtha nlarva etha t hatchlat ei nautumn ,becaus eo fmor efavourabl efoo dcondition s (periphyton,fin e detritus).

Microdistribution Thismembe ro fth eGoerida efamil yoccurre di nbot hstream smainl y incoars esubstrate s (BG,St. San dG+CD ,Table s 17an d18) , althoughover-represen tationi sals osee no nC Di nth eRab .Thi sover-representatio ni sprobabl ycause db y foodscarcity ,sinc e Lithax wasonl yfoun di nC Di nsummer ,whe nth eamoun to f detritusi nth emiddl eo fth estrea m (wheremos to fth ecoars esubstrate soccur )i s low.Thi si sals otru eo fperiphyto nproduction ,becaus eo fth eheav yshadin go fth e streambe db yth eban kvegetation . Lithax isa caddis ,wit hfeedin ghabit squit e similart ovariou sLimnephilida especie san dth eGlossosomatida e (Greniere tal . 1969),feedin go ndetritu san ddiatoms .A sCastr o (1975)an dDougla s (1958)showe d for Agapetus fuscipes, theconsumptio no feac hfoo dtyp evarie swit hit srelativ e abundance. Theover-representatio ni nSt. Si nSor t1 i spresen ti nbot hstreams ,bu ti nth e Rabi ti sno tsee ni nan yo fth eless-detaile dclassifications .Her eth epreferenc e forSt. Si sobscure di nSort s4 an d2 b ySh. San dS+FD ,tw onot-preferre dsubstrat e types.Thi sillustrate sth eimportanc eo fa detaile dclassification .I tals oemphasize s thefac ttha ti tma yb ever yimportan tt odistinguis hbar esubstrate sfro msubstrate s mixedwit hdetritus ,an dtha tth enatur ean damoun to fdetritu si sver yimportant . Fromth egrain-siz eclassification si nbot hstream s (Tables1 9an d20 )i ti s

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lil Tl"Wi lS LENGTH CLASS C IUI) »«.» . Mi.cycl ehistogra mo f Litho, obseurus ^*^ "S*""1" <%> °' larva!bod y length,pupa e (90)an dadult s (98)pe rfour-wee k period. 63 Table 17.I.B .value s for Lithax obsaurus (N= 451 )i nth efiel d classificationo f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -3.7 8.2 -4.7 1 , 1 1 1 1 1 1 -4.7 4 2.3 -8.3 8.9 1.6 l 1 1 1 1 1 1 1 1 2 5.6 -5.0 -4.8 -6.8 8.9 1.6 -4.7 1 I i I ,.J r i r 1 1 1 1 1 1 1 1 1 -5.0 -1.4 -6.6 -1.9 I -0.2 1.9 -2. 7 -3.3 -1.9 1 8.1 -1.3 FD -1.5 -4.5 CD+LCD+F D L+FD B L CD CD L CD+L St Sh Italicvalue s indicatesignifican L CD t over-representation

Table18 .I.B .value sfo r Lithax obsourus (N= 218 )i nth efiel dclassificatio no f thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -6.1 9.0 0.8 1 1 1 1 l 1 4 -2.2 -6.8 3. 5 0.8 I 1 1 1 l 1 1 2 -0.5 -3.8 -3.2 -6.0 8.4 3. ,5 0.8 1 1 1 1 1 1 1 1 1 1 1 1 1 2.9 -4.3 -3.8 -1.1 -3.0 -1.3 -5.5 -21.! 8.4 -1.1 4\l è.7 -l!o -0.7

St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L +FD

Italicvalue sindicat esignifican t over-representation

Table19 .I.R .value s for Lithax obsaurus (N= 451 )i nth egrain-siz e classification of thesubstrate s inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phi index detritus

CD CD+L Sort5,10 % 9.0 1.7 3.0 7.4 2.5 0.6 8.0 -0.3-8. 6-4. 4 - -3.6-3. 5-2. 4 Sort 6,10% 9.0 -1.1-0. 3 7.1 1.9 6.2 1.3 6.6 -1.3-7. 9 - -3.6 -3.5-2. 4 Sort7,10 % 9.0 -0.8-0. 8 0.8 5.7 -1.2 7.5 4.4 -3.2-2. 3-3. 6 -3.5-2. 4 QlMdQ3 lndex xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x Sort 8,10% 5.0 4.9 2.0 6.2 1.3 7.3 2.5 -0.3-5. 4-6. 7-4. 4-3. 6-3. 5-2. 4

Italicvalue s indicatesignifican t over-representation

64 Table20 .I.R .value s for Lithax obsaurus (N= 218 )i nth egrain-siz e classification of the substrates inth eRatumsebeek .

Substrateclas s

10 11 12 13 14

phi index detritus

6 CD CD+L

Sort 5,10% -1.1 1.9 3.4 -0.6 11.0 -2.6-1. 5-3. 4-7. 0-1. 9 - 5.7 -1.0-0. 7 Sort 6,10% -1.1 3.1 2.1 6.2 5.9 2.6 -6.5 -4.6 - 5.7 -1.0-0. 7 Sort 7,10% ------4.6 -1.5 5.6 -6.6-1. 1 5.7 -1.0-0. 7 QlMdQ3 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x Sort8,10 % 4.6 0.3 2.1 6.2 5.9 2.6 -2.1-3. 4-5. 9-2. 8-1. 9 5.7 -1.0-0. 7

Italicvalue s indicate significant over-representation

Table21 .I.R . valuesfo r Lithax obsewnts perlengt hclas s (A)an dseaso n (B)i nth e Snijdersveerbeek inSor t8,10% .

Length Substrate class andQ„M.Q index 1 d0J class and 1__ 23 4_ 5_ 6 7 8 9 10 11 12 13 14 Season xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x A 0 3 -0.3 3.5 -0.4-0. 4-0. 4-0. 4 1.3 -0.6-0. 5-0. 6-0. 4-0. 5-0. 5-0. 3 1- 3 18 -0.7-0. 4 0.8 7.2 -1.0-0. 1 0.1 -1.4-1. 2 0.6 -0.9-1. 1-1. 3-0. 8 4 - 5 94 0.2 -0.7 0.9 3.6 0.1 7.7 2.1 0.1 -2.8-3. 0-2. 0-1. 3-2. 6-1. 2 6 1028 3 2.8 2.3 2.0 3.8 1.7 5.6 2.6 0.4 -4.2-5. 8-3. 4-2. 6 -1.6-1. 8 99 98 53 8.5 9.3 -0.2 0.3 0.5 -1.8-1. 9 -1.0-1. 6-2. 5-1. 5-1. 9-2. 2-0. 6 Total 451 5.0 4.9 2.0 6.2 1.3 7.3 2.5 -0.3-5. 4-6. 7-4. 4-3. 5-3. 5-2. 4 B Spring 113 7.8 7.9 0.3 -0.1 3.6 0.5 -0.0-2. 8-2. 3-2. 7-1. 2-2. 8-2. 8-1. 2 Summer 143 -1.4-1. 4-0. 2 4.7 -0.7 6.7 2.9 -1.6-1. 8-5. 0-2. 9-1. 3 Autumn 106 7.5 -2.1 1.5 4.0 0.1 0.5 0.1 4.2 -3.0-3. 4-1. 8-2. 3-0. 9-1. 5 Winter 89 -1.1 4.0 1.5 0.7 -0.3 4.1 1.3 -0.0-2. 9-2. 7-2. 2-0. 0 0.9 -0.9

Italicvalue s indicate significant over-representation

cleartha t Lithax preferssubstrate swit hà larg eproportio no fth efractio ncoarse r than1- 2m m(Coars eSand ,Q 1 <ï ].A presentatio no fth edistributiona lpatter npe r lengthclas si nth eSnijdersveerbee k (Table21A )i nSor t8 ,10 1show stha tth esmal lestspecimen s (1-3mm )ar emainl yfoun do nx2x ,whic hmainl yconcern ssample swit h Qj= 5 o r4 (cf .Fig . 16).Analysi so fth epreferenc eo fthes esmal llarva ei nSor t

S,10 1 (notpresented )showe dtha tthe yprefe rQ 1= 4. Pupaear epresen to nth etw ocoarses tsubstrat etype s (coarsertha nx4x ,especial lyQ 1= 7 ,6 an d 5;M ,= 7 an d4 ,base do nlengt hclas spreferenc ei nSor t5 ,10 4an d Sort6 , 104no tpresented) .

65 Theothe rlengt hclasse sar efoun do nth etota lrang e ofsubstrat e typeswit h Q.« Ï an dM .< 1.Thi smean stha t Lithax obsauvus occursmainl y oncoars e tover y coarsesubstrat e insprin gan dautum n (pupaean dearl yinstars ,respectively ) andca n befoun do nal lothe rsubstrate sfo rth eres to fth eyear ,a sconfirme db yTabl e 21B. Inth eRatumsebee ka simila rpreferenc e ofth esmal l larvae (1-3mm )fo rx2 x wasobserved ,bu tthe yshare dthi swit hxx x .Th elarge rlarva eoccurre d inal lsub stratescoarse rtha nx1x .Pupa ewer eonl yfoun dincidentall y inshove lsample s from theRab ,bu twer ever ynumerou so nstones ,clayston ebank s andbranches ,especiall y thoseprotrudin gabov eth ewate rsurfac enea r thebanks .Thi scoul db e observed clearlyafte ra stron gfal lo fth ewate rlevel ,bringin gman y attachedpupa e above thewate rsurface ,althoug hthi sdi dno thinde rth eemergence ,whic h followedwithi n a fewdays . Theabov edat aagre ewit hth econclusion so fBeye r (1932)an dGeijske s (1935) thatth eGoerida ebelon g toth etypica lston efauna .The y arecharacteristi c for unpolluted,natura lstream swit ha moderat et ofas tcurrent ,althoug hth esevera l generaselec tdifferen tcurren tspeed sfo rthei roptima lhabita t (Scott,1958 ;Nielsen , 1942).Thi si sreflecte di nth esiz eo fth eballas tstone so nth eside so fth ecase , whichincreas efro m Lithax through Silo to Goera (.Wesenberg-Lund,1943 ;Webste r & Webster,1943 ;Grenie re tal. , 1969).

Case building Lithax obsauvus buildsa cas eo fminera lmaterial .Th ecas e isa t least6- 7m mlon gan dabou t3 m mwid e inth efina linsta r (Greniere tal ,1969) ,al thoughUlme r (1909)an dLepnev a (1964)reporte da lengt ho f9-1 0 mm,whic h agrees withou rmeasurements .Th ecas e isslightl ycurve dan dth erea ropenin g isclose db y amembran ewit ha nexcentri ccircula ropening .Thi smembran e isalway scovere dwit h somesmal lsan dgrains ,whic hi sa taxonomi echaracteristi c forth egenu s Lithax withinth eGoeridae . Thecas e 'grows'spasmodically ,whereb y thelarv aenlarge s thecase ,probabl y justbefor ea moult .Thi si sclearl yvisibl e fromth elighte rcolou ro fth enewly - addedfront ,whic hi sstil lfre efro mattache ddiatom s inth ebeginning .Th e case consistso fsan dgrain san di swel lcamouflage d (Lepneva, 1964). Thedifferen tinstar ssho wa differen tpreference ,whic hshift s fromsmal lt o largergrain swit hincreas ei nlarva lsiz e (Fig.22) .Th eF- 3 instaruse smainl y 0.105 -0.50 0m mgrain san dthi spreferenc e isreplace db yon efo r0.25 0- 2m m in thefina linstar .I nth efina linsta rcase sth e 1- 2 m mgrain s aremainl yuse d for ballaststone so nth elatera lside so fth ecas ean da sca pstone s forth epupa lcase . Comparing thegrain-siz epreference so f L. obsauvus forcas ebuildin gwit hth e grainsize spresen ti nth esubstrate s init spreferre dsubstrat e typei nth estream s showstha tthe ywil lb eabl et ofin dth esize sneede d inal lsubstrat etype s showing over-representation,eve ni nth ecoarses ttype ssinc ethi si salway ssituate d onto p offine rmaterial .Lac ko fsuitabl egrain sfo rcas ebuildin gwil lno toccu r inth e preferredsubstrates ,bu ti tma yb eon eo fth ereason s forth eunder-representatio n

66 H-F-3-H I«— F-2 .j »f Pupae

8 50

10-

I I II 1 'I ' 0.3 0.5 0.6 0.7 0.8 0.9 1.0 head width classes (mm)

Fig. 22.Distributio n(% ) ofgrain-siz efraction si nnatura lcase so f Lithax obsourus. 1= 0.10 5- 0.21 0mm ;2 = 0.21 0- 0.25 0mm ;3 = 0.25 0- 0.35 0mm ; 4= 0.35 0- 0.50 0mm ;5 = 0.50 0- 0.85 0mm ;6 = 0.85 0- 1. 0mm ;7 = 1. 0- 2. 0mm .

of L.obseiœus inth efine rsubstrates .However ,i nsubstrate swit hM ,> 1stil l enougho fth esuitabl egrain swil lb eavailable ,an dye tL.obscuru soccur sher eonl y sporadically.Thi ssuggest stha tothe rfactor stha nhouse-buildin gmateria lpla ya moreimportan trol ei ndeterminin git sdistribution ,e.g .curren tvelocit yo r availabilityo ffood .Yet ,considerin gth epreferenc eo f Lithax forth ecoars e substrates (andinseparabl ylinke dwit h this,th ehighe rcurren tspeeds) ,it sus eo f relativelylarg egrain sfo rcas econstructio nan dit schois eo fpupatio nsites ,th e conclusioni sjustifie d thata los so fcoars esubstrate san da decreas ei ncurren t velocitywil lcaus eth edisappearanc eo f L.obsourus. Especiallyth eabsenc eo f suitablesubstrate si notherwis esimila rstream s (natural,shaded ,moderat et ofas t flow)i sprobabl yth ecaus eo fth erestrictio no f L. obsourus (andGoerida ei ngeneral ) tostony ,gravell ystreams .

67 4.2.2.2 Sericostomapersonatu m(Spence ) (Trichoptera:Sericostoraatidae) .

Identification Accordingt oBotosanean u (1967), S.pedemontanum is asynony m for S.personatum. Inth eNetherlands ,Sericostomatida e arerepresente db ytw ogenera , Sericostoma and Notidobia (Geijskes& Fischer , 1971),o fwhic honl y S.personatum was foundi nthi sinvestigation ,an dthe nonl yi nth eSnijdersveerbeek .Onl y recently, Wallace (1977)clarifie dth edifference sbetwee n S.personatum and TH.ailiaris, making theidentificatio no fth etw ospecie squit esimple .Fro mWallace' swor ki tals o becameclea rtha tLepnev a (1964)presente dth epronotu mo f S.personatum astha to f N.ailiaris. Adultswer e identifiedwit hMacan' ske y (1973)afte rrearin g them from larvaei nth erearin gchannel .

Life cycle Thelif ecycl eo f S.personatum mayvar ygeographically . Iversen (1973) concludedwit hDittma r (1955)tha ti nNorther nEurop e s.personatum hasa thre eyea r lifecycle .Th eunivoltin ecycl egive nb yNielse n (1942)an dth e1.5-yea rcycl eo f lilies (1952)fi tint othi s3 yea rcycle .Ellio t (1969)foun da cycl eo f1-1. 5 years inGrea tBritain .Iverse n (1973)explaine dth eslowe rgrowt h inDenmar kan dSauerlan d asa neffec to fth elowe rtemperatur efluctuation s andmaxim aan d less-favourable foodsupply .I nth eSnij bbot ha 1. 5yea ran d3-yea rlif ecycl e arepossibl ewhe n considering thedat ai nFig .23 ,givin gbod ylengt ho fth elarva ei ntime .Measure mentso fhea dwidt hindicate dhoweve rtha ta three-yea r lifecycl ei smos tprobabl e (Tolkamp& Verdonschot ,t ob epublished) .

S.personatum has7 larva linstars ,whic har ever ydifficul tt oseparat eo nth e basiso fhea dcapsul ewidt ho rlengt h (Iversen,1973) ,Nielse n (1942)an dEllio t (1969)foun da discontinuou spattern ,o ra tleas tdistinc tpeak s foreac h instar.I n theSnijdersveerbeek ,las tinsta rlarva emeasure da tmos t 18-19mm ,whic hi sslightl y longertha nth e1 5m mUlme r (1909)an dth e16. 2m mNielse n (1942)reported .Tolkam p &Verdonscho t (tob epublished )hav eestablishe d thatoverwinterin g takesplac ei n theeg gstag ean dth efirs tan dsecon dinsta ri nth efirs tyea ri nth eSnijdersveer beek.I nth esecon dyear ,th ethir dan dfourt hinstar soverwinte ran dth ethir dyea r thesixt han dsevent hinsta ran dth e (pre-)pupaeoverwinter .Pupa ear emos tabundan t fromApri lt oJune ,whil eadult semerg efro mJun et oAugus t (cf. Svensson,1972 ; Iversen,1973) .

Microdistribution in the Snijdersveerbeek Sericostoma personatumwa spredominantl y foundi nassociatio nwit hcoars edetritus ,excep tfo rth eBar eGrave l substrate (Table 22).Thi si si nagreemen twit hth efoo dpreferences ,sinc e S.personatum isa detritivore (shredder),feedin gmainl yo nleave s (Decamps,1968) ,althoug hit sgu t doesno tcontai ncellulas e (Bjarnov,1972) ,whic hsuggest stha tth ebacteri a and fungiattache dt oleave san ddetritu sar eth emai nfoo ditem s (Thorup& Iversen , 1974).Togethe rwit hdetritus ,diatoms ,alga ean dfung iar eals oingeste d (Moon,

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las LENGTH CLASS t. m Fig.23 .Lif ecycl ehistogram so fSeriaostorra. personation showingth edistributio n (%)o flarva lbod ylength ,pupa e(99 )an dadult s(98 )pe rfour-wee kperiod .

69 Table22 .I.R .value sfo r Seviaostoma pevsovatum (N= 346 )i nth efiel d classification ofth esubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -0.3 2.5 -2.9 _J I I— I 4 -1.3 1.0 0.4 -2.9 r _l -1 I I —i 2.8 I 2 0.8 -1.2 3.0 -1.0 0.4 -2.9 J _j r 2.8 r I I -I 1 1 -0.4 -0.7 -1.2 -0.8 2.5 4.4 0.3 -2.8 2.8 -1.1 1.1 2.4 -4.1 -2.8

St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L

Italicvalue s indicatesignifican t over-representation

1934;piack , 1936),an dsometime s insectsar eeate na swel l (Dittmar,1955 ;Lepneva , 1964).Thi si swh yHicki n (1967)classifie d Seviaostoma asomnivorous ,althoug h the percentageo finsect si sonl yabou t 11 (Thorup& Iversen , 1974).Sinc e diatomsan d algaear emor eabundan to ngrave li nth eSnijdersveerbeek ,th eover-representatio ni n BGmigh tb erelate dt othi styp eo ffood ,althoug hthi sca nonl yb ea tentativ e conclusion.I nTabl e2 2th epreferenc e forS+CD+ L (I.R.= 4.4 ) shouldb e considered withcar esinc ethi sonl yconcern sthre esamples . Inth egrain-siz e classification (Table 23)w ese etha t Seviaostoma prefersth e gravellysubstrates ,togethe rwit hth edetritu ssubstrates .Th e over-representation inth efine rsubstrate s isprobabl ymainl ydetgrmine db yth epresenc eo fcoars ede tritus,sinc eonl yth eI.R . valuesfo rxx xan d23 xincreas efro mth eH toth e 101 sorting. Thever yhig hpreferenc e forcoars esubstrate si sals oclea rfro mth e field-

Table23 .I.R . values for Seviaostoma pevsonatum (N= 346 )i nth e grain-size classificationo f thesubstrate s inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phiinde x detritus

CD CD+L

Sort5,10 % -1.0-2. 2 4.5 2.9 -0.5-0. 8 1.8 -2.9-0. 5-2. 0 - 2.8 -4.2-3. 1 Sort6,10 % -1.0-1. 0-2. 5-0. 5 2.8 3.9 1.8 0.9 -2.0 1.1 - 2.8 -4.2-3. 1 Sort7,10 % -1.0-2. 1-1. 9-l. o-1. 9-2. 3-3. 7 6.9 0.6 -1.8 2.8 -4.2-3. 1 Q MQ index ln a o xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x

Sort 8,10% -3.2-0. 7 3.3 3.9 1.8 1.6 2.5 -2.9-1. 9 1.0 -2.0 2,8 -4.2 -3.1

Italicvalue s indicatesignifican t over-representation

70 Table24 .I.R .value sfo r Serioostoma personation perlengt hclas s(A )an dseaso n(B ) inth eSnijdersveerbee ki nSor t8,10% .

Length N Substrate classan dQ..M.Q inde x 1 d3 0 class and 1 2 3 4 5_ 6 7 8 9 10 11 12 13 14 Season XXX x5x x3x x2x xïx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 1- 5 46 -1.2 -0.9 0.1 -0.0 0.1 1.3 1.1 -0.8 -1.4 0.3 1.5 3.3 -2.1 -1.3 6-7 70 -1.4 0.1 -1.1 -0.3 0.9 1.4 3.3 -0.4 -1.1 1.0 -1.1 0.6 -1.7 -1.5 8-9 43 -1.1 -1.9 0.8 -0.5 -0.4 1.5 1.3 -0.7 0.3 3.5 -1.3 -0.5 -1.5 -1.2 10- 1 2 40 -1.1 -0.7 2.2 3.9 0.4 0.4 0.5 -1.5 -0.7 0.1 -1.3 -0.4 -0.9 -1.2 13- 2 0 131 -1.9 0.9 4.8 4.6 0.8 0.0 -0.1 -2.8 -0.8 -1.4 -1.5 2.4 -2.9 -1.6 99- 9 8 16 -0.7 -0.3 -1.0 -0.1 4.1 -1.0 0.3 0.3 -1.1 0.1 -0.8 0.9 -0.4 -0.7 Total 346 -3.2 -0.7 3.3 3.9 1.8 1.6 2.5 -2.9 -1.9 1.0 -2.0 2.8 -4.2 -3.1 B Spring 78 -1.0 0.3 3.4 0.4 0.9 1.5 2.4 -0.4 -0.9 -1.4 -1.0 -0.0 -2.9 -2.0 Summer 82 -1.7 -3.1 2.4 0.4 0.6 -0.3 0.1 -1.2 -0.4 0.4 -2.2 8.0 - - Autumn 92 -1.7 -2.0 -1.7 7.9 -1.2 1.5 0.9 -2.3 -1.5 2.8 -0.5 1.2 -2.9 -0.7 Winter 94 -1.7 3.1 2.3 -0.9 3.2 1.2 0.6 -1.7 -0.7 -0.9 -0.1 -0.6 -1.5 -2.3

Italicva l ues indicates i gnifleant over-représentâtio n

classificationi nTabl e2 2whe nconsidere do na les sdetaile d level.Consideratio no f thepreferenc eo fsevera l lengthclasse si nSor t8 ,10 1 (Table 24A)show stha tth e smallest (0-5mm ) larvaeprefe rCoars eDetritus ,whil e5- 7m mlarva ear emainl y found inxx x (oftencombine dwit hCD )an dth e7- 9m mlarva eespeciall yi n23 x( +CD )sub strates.Larva e larger than9 m mdistinctl yprefe rgrave l (x3x,x2x) .Pupa ear epre dominantly foundi nxTx . However,al llengt hclasse ssho wpositiv eI.R .value si na tleas t5 substrat e classes,whic hsuggest s thata wid erang eo fminera l substratesca nb einhabite db y S.personatvm andtha tth epresenc eo fdetritu splay sa nimportan trole .Compariso n betweenseason s shows (Table 24B)tha tth eanimal sar eabsen tfro mth edetritu ssub stratesi nwinte ran dspring ,whe nthe yar emos tabundan ti ngravel .Th epreferenc e fordetritu san dsan dsubstrate s (Class 12an d10 ,respectively )i smos tpronounce d insumme ran dautumn ,althoug hi nautum ngrave li spreferred .Th epreferenc efo r substrateswit ha considerabl eproportio n consistingo fdetritu si sals oreporte db y Higler (1975),wh ostate d thatthe yca nb efoun dburrowe di nsan dsubstrate so r undero rbehin dstone swher eth esan di softe nmixe dwit h leaves.The yprefe r these placesbecaus ethe yar enight-activ ean dhid edurin gth eday ,a phenomeno nofte n observedi nlaborator yexperiments ,wher e theyburro w immediatelydurin gth eday ,bu t moveove rth esurfac ea tnight ,althoug h theyma yb eobserve dmovin gove rth estrea m bedi nshade dplace sdurin gth eda ya swell .Jone s (1949)an dGeijske s (1935)bot h reportedtha t S. personation isofte nfoun di nth esam ehabita ta s Ephemera danica, namelyi ncoars egrave lan dstone snea rth ebanks ,wher eth ecurren ti sslower ,bu t iti sals ofoun di nsand yarea s (Jones,1951) .Th elarva ear edistinctl yrheophili can d canb efoun di nsprings ,stream san driver s (Higler,1975) ,a distributio nwhic h agreeswit hth eauthors 'observation si nth eNetherlands ,an dit spresenc ei nth e

71 Snijdersveerbeek.Th eabsenc ei nth eRatumsebee kremain sunexplained ,however . According toNielse n (1942) S.personation isneve rfoun d inhig hdensities , but thisi scertainl yno ttru efo rth eSnijdersveerbeek ,wher eo nsevera l occasions (when collecting larvaefo rexperiments )mor etha n4 0specimen swer efoun do n10-1 5c mo f sandmixe dwit hgrave lt oadept ho fapprox .5 cm ;a clay/loa mban kprevente d further penetrationbelow .

Case building According toWallac e (1977),las tinsta r larvaeo fS.personation dwell ina cas ewhic hi s 13m mlong ,bu tHicki n (1967)an dLepnev a (1964)mentio na cas e lengtho f15-1 6mm .Th ecas ei smad efro mlong ,narro wgrain s of,fo rexample , 0.65 mmb y0.1 3m m (Nielsen,1942) ,whic har earrange d ina characteristi cmosai c pattern ina singl e layerstuc ktogethe rwit h thick,yellow-brow n salivary secretion. The surfacei scompletel y smooth.Th ecas ei sslightl ycurved , especiallyi nsmalle r instars^I ttaper stoward sth erear ,excep ti nth elas tinstar ,fo rwhic hth ecas ei s practicallyparallel-side d becausei ti sn olonge rnecessar yt oenlarg e thecase ,

h-r-S h— F-4 »4- ^ |> F-2 H«-F-l —t* »{ Pupae TT

1 I' i ' l' i T-r T-T-TT TT 0.3 0.5 T 1.3 1.5 1.7 1.9 2.1 head width classes (mm)

Fig. 24. Distribution (%) of grain-size fractions in natural cases of Serioostoma personation. 1 = 0.050 - 0.105 mm; 2 = 0.105 - 0.150 mm; 3 = 0.150 - 0.210 mm; 4 = 0.210 - 0.250 mm; 5 = 0.250 - 0.350 mm; 6 = 0.350 - 0.500 mm; 7 = 0.500 - 0.850 mm; 8 = 0.850 - 1.0 mm; 9 = 1.0 - 2.0 mm.

72 restricting thebuildin g activityt omaintenance .Th erea ren d isclose dwit ha roun d membrane thati sperpendicula rt oth ecas ean dwithi nwhic ha nopenin gforme dlik ea spool ispresent . Analyseso fth egrai nsize suse di nth ecase sshowe da nincreas ei ngrai nsiz e with increasing larvalsiz e (Fig.24) .Firs tinsta rlarvae ,reare dfro megg s deposited andhatche di nth erearin gchanne l inth elaborator y fromadult stha temerge dthere , builda cas eo fgrain ssmalle r than0.15 0m mwithi na day .Goin g fromth einsta rF- 4 toF- 2a decreas e from 211t o0% wa s seenfo rth efractio nsmalle r than0.10 5mm , while the0.105-0.15 0m mfractio nremaine da tabou t50 1an dth efractio no f0.150 - 0.210m mincrease dfro m24° st o42% .Fro mth eF- 2t oth eF instar sth efractio n0.105 - 0.150 decreasedt ozero ,whil e thefractio n0.210-0.35 0m mincrease d significantly. Thepupa lcas ediffer s from thelast-insta rcas ei ntha ti tcontain s slightlymor eo f thever ycoars e fractions (upt o2mm) , especiallyuse d forclosin gth ecase .Befor e pupation thecas ei sextende dwit h largergrain s andattache dt ograve lo reve n stonesi nth estrea mbe d (belowth esubstrat e surface),afte rwhic hth efron ti s closedwit ha sieve-lik emembran ewit ha centra l clefto fwhic h theedge sar eben t outwards.Th e cleftsi nth efron tan drea rmembran e aresituate dperpendicula rt o eachother . Whennake d final instarlarva eo f S.personation wereoffere dal lgrai nsize s mentioned inTabl e6 fo rcas ebuilding ,th emediu msan dfractio n (0.250mm )wa s preferred (Experiment 1,Tabl e 25).Whe nthi s fractionwa s leftout ,th elarva euse d thefine ran dcoarse rsan d fractions (Experiment 2,Tabl e 25).Whe nfin esan dwa s also leftout ,the ymainl yuse d coarsesan d (Experiment 3,Tabl e 25),bu ti fthi swa s alsoabsen t (Experiment 4,Tabl e 25)th elarva ebuil ta nemergenc y caseonl yan dwer e unable tous e coarsergrain so rlea fmateria l forcas ebuilding . Comparing thegrain-siz e compositiono fth ecase swit htha to fth e substrates preferredb y S.personation inth eSnijdersveerbeek ,n o directrelationshi p canb e seen.Al l fractionsneede dfo rcas ebuildin gwil lb epresen t inth esubstrate .However , iti sstrikin g thatsubstrate swit hQ 3= 2 (0.25 0- 0.50 0mm ) (Table 23,Sor t7 ) are preferred,whic hmean s thatcoars e substrates (Sort8 )mus t includea tleas t25 1o f thefraction s finer than0.50 0m man dcoarse r than0.12 5 mm.

Table25 .Grain-siz e composition (percent)o fcase sbuil tb yfina l instar larvaeo f Sericostoma personation inlaborator yexperiments .

Proportion(% ) ofgrain-siz e fraction (lowerlevel , mm)i ncase s

0.050 0.125 0.250 0.500 Experiment 1 0 4.7 86.3 9.0 Experiment 2 0 57.5 Ab 42.5 Experiment 3 19.1 Ab Ab 80.9 Experiment4 t 0 Ab Ab Ab

Ab= Grain-siz e fraction absent T:InExperimen t4 n ocas ewa sbuil t

73 Substrate-selection experiments Ina firs tserie so fexperiments ,th esubstrat e selectiona tlo wan dhig hcurren tspeed swa steste dfo rF an dF- 1 instars (theinsta r wasonl yroughl ydetermined) .A tbot hcurren tspeed s these larvae (F,F-1 )selecte d thecoarses tparticl esiz e (16mm) ;particl e sizeso f1 t o8 m mfollowed .Ther ewa s nosignifican tpreferenc efo ran yo fthes efou rparticl e sizesa tth elo wspeed ,bu t athig hcurren tspeed s1 m man d2 m mparticle s attractedmor e larvae than4 m man d8 mmparticle s (Fig.2 5a an db) , althoughth edifference sar eno tsignificant .Th e sameexperimen tconducte dwit hF- 2and"F- 3instar s showed againtha t currentdoe sno t influenceth esubstrat eselectio nsignificantl y (Fig.2 4c an dd) . Calculationo fth esignificanc eo fth esubstrat eselectio nwit hth echi-square d testshowe d thatonl yi nth eexperimen twit hth eF- 2an dF- 3larva ea tslo w current speeds (Fig.25c )wa sth esubstrat e selectionno tsignifican tan donl ya tendenc yfo r coarserparticl esize swa sdetected .A smal lexperimen twit hF- 1an dF- 2larva eo n1 , 2,4 ,an d8 m mparticle s showedtha t S.personation significantly selectedth ecoarses t grains (8mm) ,whil eth edifference sbetwee nth eremainin gparticl e sizeswer eno t significant (Fig.2 5e ) Inconclusion ,i tca nb estate dtha tther ewer en osignifican t differencesi n substrateselectio nbetwee ndifferen t instarso f S.personatwi inlaborator y experiments, unfortunatelyn oexperiment swer ecarrie dou twit horgani c substrates.Th eselectio n frequency (%)

40- a

20-

I—' •—' o -J 125 500 1 2 4 8 16 125 5001 2 4 81 6 125 5001 2 4 81 6 S

fre luency (%) 40- d

20.

125 5001 81 6 12 4 8

Fig. 25.Substrat e selection inlaborator y experimentsb y Seriaostoma personation. Grain-size fractionsar e indicatedb y thelowe r limit inu m (under 1mm )an dm m '(over 1mm) .S = en dretainin gscreen .

Figure Instar Body Numbero f Numbero f Current no. length experiments larvaepe r velocity /mm experiment (cm/s) F ; F-1 8-14 16 5 F ; F-1 8-14 32 10 F-2; F-3 6-10 16 5 F-2; F-3 6-10 16 10 F-1; F-2 7-11 32 10

74 phivalue s Î 5 4 Î 3

Î 2

0-1

6 + 7

M (phivalue ) aJ Fig. 26.Compariso no fsubstrat epreference si nth efiel d(unshaded )wit h particle-sizeselectio ni nlaborator yexperiment s(shaded )fo r Serzaostoma personation. ofth ecoars e substratesi si nful lagreemen twit hsubstrat epreference si nth e field,a sobserve di nth eSnijdersveerbeek ,wher ex3 xan dx2 xsubstrate s arepreferred , forwhic h 501o rmor eo fparticle s arecoarse rtha n 1mm .Fo rmos to fthes esubstrate s moretha n 251i scoarse rtha n 16mm .Th e similarityo fth efiel dan d laboratory studiesi sfurthe r illustrated inFig .26 ,wher ebot hth esubstrate spreferre d inth e field (basedo nSor t5 t o8 , 104)an dth eparticle-siz e selectioni nth e laboratory experimentshav ebee nprojecte d onth eQ-^Q jgrap h (Fig.14) .

4.2.2.3 Micropterna sequax (MacLachlan) (Trichoptera:Limnephilidae )

Life cycle M.sec^ hasa clearl yunivoltin e lifecycl ei nth eSnijdersveerbee k and theRatumsebee k (Fig.27) .Larva ewer e collectednumerousl yi nshove lsamples , and alsoi nadditiona l collections.Pupa ewer e foundonl y incidentally (11specmen s in total)i nth eshove l samples andno ta tal lcollecte db yhand ,sinc epupa ear e burrowed inth esubstrate ,whil e larvaemostl yoccur.o nto po fo ri nth euppe rlayer .

75 7B; I- 3^

77: «9-EZ

77: tS-IBJ w^mfTTTV-n lÏÏTVrm

ITTTTTTTl! 111

77; J7-

77: 33-36

77: zs-za IMIIMllll'l

77: 21-21 fTTrllUnTn

77: 13-16 nTlflUUrrm

(ïïïwrnu N - H 77: 5- a V) lllllllüllil

3 ««nniTLinT? - a 76! •*•« o a.

76: 37-« urn imifllrim

76: 33-36^ ^-rfTTl>TTT>^j!l||i .fT»)l|i||ii.,

74: 29-3Z

76: ZS-ZS nuniti nrritlsKnTniTT« 76: Zl-2« 11 76: 17-28} «•YlïïIïlIIlTTlWTTTt m 76: (3-16 m mnnn 76: *>-12^

76: Ç

76: I- < iTTiHiinitllllli1! rnn

7E: *9-GZ: (TTTTTTTTTTTl I'll] TÏÏ1 7S: *s-

75: *i-n: fTTTTTTTl1 1! 1

7S: 37-«

n-r m intf!TTninnTi

LENGTH CLASS ( nil) Fig. 27.Lif ecycl ehistogram so fMicropterna sequax showingth edistributio n(% ) oflarva lbod y length,pupa e (99)an dadult s (98)pe rfour-wee k period.

76 Pupaewer efoun dfro mMarc h- September ,whic hmigh tindicat ea lon gfligh tperiod . Thiswa s alsoconclude db yCrichto n (1971)fo r Stenophylax (= Mioropterna) sequax (fromScotland )an dh esuggeste dtha tther ei sa nimagina idiapause .However ,accordin g toSvensso n (1972)matin gtake splac ewithi na fe whour st oa fe wday safte remergence . Hefoun dn oimagina idiapause ,whic hi stypica lfo r Limnephilus spp,an dtha tth e developmento fth egenitali atake splac ei nth elas tlarva lan dpupa linstar . Inth eRa ban dSnijb ,th efirs tjuvenil e (secondinstar )larva ewer efoun di n July.The ygro wi nautum nan doverwinte ri nth efourt h (F-1)an dfift h (F)instar , whichagree swit hth econclusio no fDittma r (1955).Accordin gt oth eliterature , the lastinsta rlarva ebecom e 18-19in nlong .I nth eSnij ban dRa bthe yreac ho naverag e 20-25mm ,wit hexceptionall y somesmalle rspecimen s (fifthinsta rlarva eo nth ebasi s ofhea dwidt hha da bod ylengt hrangin gbetwee n12. 5an d25. ran,2 se eTolkam p& Verdonschot,t ob epublished) .

Microdistribution Inth eRab , M.sequax occurredpredominantl y indetritu ssubstrate s andn oover-representatio nwa s foundo nminera lsubstrate s (Appendices9 an d13) .O f the28 6larvae ,25 2occurre di ndetritus ,8 i ngrave lan d2 6i nsan dwit ha negativ e 0^.Th e larvaeo nminera lsubstrat ewer emostl y lastinstars .Thre epupa ewer efoun d incoars esubstrate sonl y (Classes3 ,5 ,6 i nSor t8 ,101 ,Tabl e26 )i nth eshove l samples. Thepreferenc e forCoars eDetritu ssubstrate san dLea fsubstrate si nth eRa bwa s clearlylinke dwit hth e season.Preferenc efo rCoars eDetritu swa sonl yfoun di nsum merwhe nlea fpack sar escarce ,whil eth epreferenc efo rlea fpack si sespeciall y foundi nth eautum nwhe n leavesar eabundan t (cf.Scott ,195 8fo r Stenophylax spp.). Inspring ,onl y6 animal swer efound ;i nwinte r23 .Thes e lownumber sar eprobabl y causedb yth efac ttha tth elarva ean dpupa eburro wi nplace swher en oshove lsample s weretaken ,a fac twhic hwil lb eillustrate dfurthe ro ni nthi ssubsection . Inth eSnijb , M. sequax showsa differen tdistributiona lpattern .Althoug hth e totalnumbe ro fspecimen si slowe rtha ni nth eRab ,the yar edistinctl ydistribute d

Table26 .I.R .value s for Micvopterna sequax (N= 194 )i nth efiel d classification ofth esubstrate s inth e Snijdersveerbeek.

Italicvalue s indicate significant over-representation

77 Table27 .I.H .value sfo r Mioropterna sequax (N= 194 )I nth egrain-siz e classificationo fth esubstrate si nth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phiinde x detritus

CD CD+L

Sort5,10 % -0.7 1.9 1.0-0. 7 0.9 2.2 -0.9-3. 6-0. 4-2. 2 - 1.6 2.0 -0.2 Sort6,10 % -0.7-0. 7 1.9-0. 6-1. 2 0.4 3.3 0.2-2. 6-1. 0 - 1.6 2.0 -0.2 Sort7,10 % -0.7 1.5 2.1 -0.7 0.7-1. 8-2. 5 2.2 -1.9-0. 7 1.6 2.0 -0.2 Q.MO index L CD+L 1d 3 xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD x4x Sort8,10 % -1.1 0.7-0. 9 0.4 3.3 0.7-0. 2-3. 6-0. 7 0.0-2. 2 1.6 2.0 -0.2 Italicvalue sindicat esignifican tover-representatio n

overdifferen tsubstrat etypes .Mor e larvaeoccurre di nSan d (82)an dGrave l (69) andno ti nDetritu s (43).I nSor t3 thi s leadst oapreferenc efo rDetritu san d Gravelbu tthi spictur ei s totallydifferen twhe nconsiderin ga mor edetaile dclassi fication (Table 27).Her e M.eequax prefersS+CD+ L andS+L ,followe db yBG ,G+L ,C D andL substrates .I nth egrain-siz eclassificatio n (Table27 )thi si sreflecte di n thepreferenc efo rxï x (i.e.2Î2 ,derive d fromSort s5 t o7) , besidesL an dCD .I n table2 6i tca nb esee ntha tth eclassificatio n onth eO^M ^ index (Sort8 )seem st o obscureth einfluenc eo fth eseparat equartiles .I nSort s 5,6 an d7 ther ei sa clea r tendencytoward sth esubstrate swit hcoars e fractions (Q1= 6 , 5;M ,= 5 ;Q =5 , 4).Thi si sles sclea ri nSor t8 (xSx ,x4x) .Stil lth epresentatio ni nSor t8 wil lb e themos treliabl eon ebecaus e inth efirs tsi xclasse s inSor t7 th enumbe ro fsample s isver ylow .Th e lowQ 1 andM d values arecombine dwit ha hig hQ valuei nth e Classes 2 andS i nSor t8 . Considering thedistributio nbetwee nseason s (Table 28B),minera l substratesar e favoured inwinter ,sprin g andsumme ran dorgani cdetritu s substratesi nautumn .Th e summerdat aonl yconcer nsample s fromth elas twee ki nsumme r (Week 37). M. sequax was notfoun di nth epreviou s 12weeks .Th eautum npreferenc e forLeave si slinke dwit h larvaefro m 1-10.m m andtha tfo rCoars eDetritu swit h 16-20m mlarvae ,whil eth e 10-15m mlarva ear epresen ti n22 xan d23 x (combinedwit hdetritus ) (Table 28A).Th e largestlarva eoccu rpredominantl y inxï xan dx1x ,whil eo fth enin epupae ,eigh t occurredexclusivel y insubstrate scoarse rtha nxx x (withon especime ni n CD+L), whxchmean stha ta tleas t25 1o fth egrai nsize s arecoarse rtha n1 mm . Preferenceo f thepupa efo ra certai ngrai nsiz ecombinatio ncoul dno tb edemonstrate d signifi cantlybecaus eo fth elo wnumbe ro fspecimens .I ti sexpected ,however ,tha tsub stratespreferre db ylas tinsta r larvaewil la tleas tpartl y reflect thepreferenc e ofth epupae .Thi swil lb eteste di nexperiments .

78 Table28 .I.R .value s for Mioroptevna sequax perlengt hclas s (A)an d season (B) inth eSnijdersveerbee k inSor t 8,10%.

Length N Substrate: clas san d Q1MdQ3 index class and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Season XXX x5x x3x x2x xïx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 1- 5 6 -0.4 -0.7 -0.6 -0.6 -0.6 -0.6 0.5 -0.8 -0.7 -0.8 -0.5 -0.6 6.0 -0.5 6-9 16 -0.7 1.4 -1.0 -1.0 -1.0 -1.0 0.3 -1.3 -0.3 0.1 -0.8 -0.1 4.6 -0.7 10- 1 5 42 0.7 1.3 -1.6 0.2 -1.0 -1.6 -1.6 -1.1 2.5 2.7 -1.3 0.7 1.1 -1.2 16- 2 0 51 -0.4 -1.6 -0.7 0.4 1.1 -1.2 0.8 -1.8 -1.1 -0.4 -0.1 5.7 -1.2 1.7 21- 3 0 70 -1.4 0.9 0.8 0.2 5.3 3.8 -0.1 -1.6 -1.5 -1.1 -1.7 -2.2 -0.2 -0.9 99 9 -0.5 0.3 0.6 1.8 2.0 0.6 0.1 -1.0 -0.9 -1.0 -0.6 -0.8 -0.9 1.3 Total 194 -1.1 0.7 -0.9 0.4 3.3 0.7 -0.2 -3.6 -0.7 0.0 -2.2 1.6 2.0 -0.2 BSprin g 36 -0.7 -0.4 2.2 1.1 6.3 0.1 1.3 -1.4 -1.5 -1.5 -0.7 -2.1 -0.9 -1.4 Summer 21 -0.9 2.9 -0.6 -0.9 -1.0 -0.7 -1.4 -1.2 -1.0 2.2 -1.1 2.2 - - Autumn 84 -0.4 -0.3 -1.6 0.8 -0.6 -1.3 -1.3 -2.8 1.4 0.2 -1.6 3.4 2.7 -0.6 Winter 53 -0.5 0.8 -0.3 0.6 1.9 3.6 0.2 -1.6 -2.3 -0.6 -0.6 -1.2 -0.3 1.2

Italicvalue s indicate significant over-representation

Mackay (1977)demonstrate dfo rPyanopsyohe soabvipennis thatpupa eburro wi n particular substrates andma yb eeasil ymissed .Afte r investigationo fth esubstrat e preferencesi nth elaborator ysh ewa scapabl eo ffindin gpupa ei nAugust aCree k (Michigan,U.S.A. )wher ethe ywer e 'absent'previously .Th esam ephenomeno noccur s with M. sequax. Experimentsi nth erearin gchanne l showed that larvaeread yt opupat e selectedcoars esubstrate st oburro w intoan da subsequen t carefulchec ki nth efiel d showedtha tpupa ewer eofte nconcentrate di ncertai nplace swit hrelativel ycoars e substrates,ofte noutsid eth esamplin gsite schosen .Thi sexplain sth elo wnumbe ro f pupaei nth eregula rsample si nbot hstreams .

Case building Thecas eo fth elas tinsta rlarva eo f M.sequax consistso fa smoot h insidecocoo nsurrounde db ya noutsid ecas emad eo fsan dgrain sembedde di nth e salivarymateria lo fth ecocoon .Th ecas ei sslightl y conical,weakl ycurve dan d almostcircula ri ndiameter ,18-1 9m mlon gan d4. 5m mwid e (Ulmer,1909 ;Lepneva , 1964;Hickin ,1967) ,althoug hi nth eAchterhoe k largerspecimen s- u pt o3 ran0 lon g- arefound . M. sequax changesit sbuildin gmateria li nth esam esequenc eNielse n (1942) describedfo rStenaphylax nigricornis. Juvenile larvaeal lbuil dminera lcases ,bu t later instars,us e leavesan dminera lmatte ri nvariou s combinations (Tolkamp& Verdonschot,t ob epublished) .I nth elaboratory ,las tinsta r larvaemainl yuse dth e 0.5-1.0m mparticle sfo rcas ebuilding ,togethe rwit h leavesan d1- ran2 sand .I nth e absenceo fth epreferre dparticles ,th epreferenc eshifte dt o1- 2mm ,leave san d 0.25-0.5mm ,o rt oleave sonl y (Fig.28A) .I nth efiel dth efourt h (F-1)insta rlar vaebuil d completelyminera lan dcompletel y organiccases ,whil e fifth (F)instar s

79 %o fcase s

5~s~l| InstarInstar:F- 3 ® 3±2 5-1 Instar:F- 2 0

15- Instar: F-l 10- p-. n r 25-

20 • Instar: F

10 -i ni

n _ 1 1 I 1 0 10 20 30 40 50 60 70 80 90 100 %minera l material 100 90 80 70 60 50 40 30 20 10 0 % leaf material

% incorporated incase s 100- ® 90

70-

30-1

10 0 i_l 123456 123456 123A56 123AA6 12AAA1= 6 Substrate offerred

Fig.28 .a :Distributio n(% ) oforgani c andminera lmatte ri nnatura l caseso f Micropterna eequax forth esecon d (F-3)t oth elas t (F)instar , b:Cas ebuildin go f Mieropterna aequax underexperimenta l conditionsi nth e presenceo fvariou s grainsizes .1 = leaves ;2 = 0.12 5- 0.25 0mm ;3 = 0.25 0- 0.500mm ;4 = 0.50 0- 1. 0mm ;5 = 1. 0- 2. 0mm ;6 = 2. 0- 4. 0mm ;A = absent .

80 display thesetw oan dal lpossibl e combinationso fleave san dsan d (Fig. 28B).However , pupal cases arealway scompletel ymineral . Analysiso fth egrai nsize suse db yth edifferen t instarsshowe d thatth ethir d instaruse dfo r40 1th egrai nsiz efractio n 1-2mm ,an dfo r 201th efractio n 0.5- 0.8 5mm .Th e remaining 401wa s dividedove ral lfine rfractions .Th efourt han d fifthinsta ruse dsomewha t coarsergrain s (0.5- 0.8 5mm ,4 0- 501 ; 1-2mm , 30%). Theseratio so fth eparticl e sizeswer epresen ti nth epurel yminera lcase s (Fig. 29A), aswel la sth epartl y organiccase s (Fig.29B) . Thepupa lcas ei sbuil to fth esam emateria la sth ecas eo fth elas tinstar ,bu t iti smuc h largertha nthi sbecaus e thecas ei sextende do nbot hside swit h coarse sandan dgravel .Jus tbefor epupatio nth e larvaeattac h 1-4m mgrain st oth efron to f thecase ,completel yclosin gi tbu tfo rsmal lopening sbetwee nth egrains .O nth e inside,a siev emembran e ismad eo fsalivar ysecretion .Th e larvaturn s ino routsid e thecase ,bite sof f therea rpar tan deventuall yextend s thissid ewit hminera l materialwhe na larg eportio nha d tob eremoved ,e.g .becaus ei tconsiste do fdetritu s orwa s damagedi nsom eway .Hereafter ,th elarv adig sperpendicularl y intoth estrea m bed,ofte nwit h theenlarge drea rstil lprotrudin g fromth esurface .I nthi spositio n thene wfron ti sals o closedwit hcoars esan dan dfin egravel ,sometime seve nattache d tocoars egrave lo rpebbles .Th e insideo fth e fronti sals ocovere dwit ha membrane . Observations ofpupa ei nthi spositio nwer emad e inth elaborator yi nth erearin g channel,durin gexperiment si nth eartificia lstream ,a swel la si nth efield . Nielsen (1942)alread yoffere da nexplanatio nfo rthi skin do falternatin g case- buildingbehaviour .Whe nlarva enormall ybuil dminera l cases,th ethic klayer so f leavesi nautum nmigh tpreven t the larvaefro mreachin g thesan dbottom .Whe nthe y normallybuil d leafcases ,i ti spossibl e thatyounge ran dolde r larvaeus ecoars e sandbecaus elea fmateria lma ythe nb e scarce.O nth eothe rhan da lea fcas eoffer sa muchbette rcamouflag ewhe n leafsubstrate s dominatei nth estream ,an dlikewis efo r aminera l casewhe norgani c substrates arescarce .Th enecessit yt obuil da minera l casei nth elas tinstar ,preparin g forth epupa l case,probabl y liesi nth efac ttha t prédationo norgani ccase s couldb ehigh ,especiall y inperiod swit h lowamount so f organicmaterial .Besides ,organi ccase sar edecompose db ybacteri aan dfung i (Mackay,1972 ;Macka y& Kalff , 1973). Burrowingi nth esubstrat ei sclearl yals oa protectiv emechanis magains tpréd ationan dpossibl ydrift .I nth erearin g channel itwa s observedtha tcase sdu gint o thesubstrat e completelyo rwit h onlyth erea rprotrudin gwer elef talone ,bu tcase s removedfro mth esubstrat e andpu to nth esurfac ewer eopene db ylarva eo fth esam e speciesan dth epupa e consumed (Gallepp (1974)observe dth esam ephenomeno nfo r Braohyaentrus ooaidentalis).

Substrate-selection experiments Single grain-size fractions Mackay(1977 )performe d experimentswit h P.sedbripennis witha 1 6m mpebbl ei nth emiddl eo fth esubstrat e traysan destablishe d that thelarva eshowe dn o specialrespons et oth epebble :n o

81 teF-2-&( Pupae 0

S 80-

o 50-

30-

1 I' I' I' ' • I' I' I 'I' I' ' ' I' ' ' I ' ' ' I ' ' I " I ' I' I ' I f^T 0.8 1.0 1.2 1.4 1.6 1.8 2.0 te F-i »( h- ®

headwidt hclasse s(mm ) animalsburrowe ddirectl ybelo wth epebble .I nexperiment swher e M.sequax could choosebetwee n8 particl e sizes,rangin g from0.050- 8mm ,th einfluenc eo fa 1 6m m pebbleplace di nth emiddl eo fth etray swa steste di na simila rway .This'pebbl edi d notinfluenc eth eparticle-siz e selectiono rth epreferenc efo r2 ,4 an d8 m m (compareFigs .30 aan d31b) , although finersubstrate swit ha pebbl eattracte d relatively moreanimal stha nwithou ta pebble .A simila rexperimen twa scarrie dou twit ha beec h leafplace dunde rth epebbl ea swell .Agai nn odifference swer e observed (Fig.30 b comparedwit h30 aan d311) .I nal lfollowin gexperiment sth epebbl ewa stherefor e omitted. Iti sinterestin gt onot e thatal lobservation s doneb yda ylea dt oth esam e result,bu ta tnigh tn osubstrat epreferenc eca nb esee na tal l (Fig.30c )becaus e thecaddi si snigh tactive .A tnigh tth elarva eleav ethei rburrowin g sitesan dg oi n searcho ffood ,hous ebuildin gmaterial ,etc .Cummin s (1964)conclude dfo r Pyanopsyohe lepida thatthe yd ono tburro wi nth edark ,whic hsuggest s thatth eburro w responses arelinke dt ophotoperio di na functiona lway .H eals oconclude d thatth elarva ed o notburro wwhe nthe ybuild . Giventh echoic ebetwee n0.12 5- 1 6m mparticl e sizes, M.sequax preferred coarse substrates (coarsertha n2 mm )wit hpeak si n1 6m man d4m m(Fig .30d) .Replacin g particleso f0.12 5m mb ythos eo f3 2mm ,th epreferenc efo rparticle s over2 m mre mained,bu tth edifference sbetwee nth ecoarse rparticle sar eno tsignifican tan y more (Fig.30e) .Whe nparticle so f0.12 5m mar ereplace db yleave s (atra y filled withbeec h leaves), M. sequax againpreferre d 16an d4m mabov e8 an d2m mo rLeave s (Fig. 30f).Whe n16-m mparticle sar ereplace db yleaves ,th epreferenc e shifted from 16m mt oleave san d8-m mparticle s (Fig.30g) . Ina serie so fexperiment swher eth epreferre dparticl e size(s)wa s(were ) omitted,individuall yo ri na combination ,th epreferenc e always changedt oth e coarsestparticl e sizepresent .However ,2 ,4 an d1 6m mar epreferre dmor e strongly than8 mm .Th ecombination s offeredwere :0.05 0m mo r0.12 5mm ,0.25 0mm ,0.50 0m m and1 m mcombine dwit hon ecoarse rparticl e size (Fig.31a-g) ,tw ocoarse rparticl e sizes (Fig.31h-j) ,thre ecoarse rparticl esize s (Fig.31k-n )an d4o r5 coarse r particlesize s (Fig.30 dan de) . Theconclusio n fromal lthes eexperiment si stha t M.sequax canburro wmor e readilyi n2 ,4 an d1 6m msubstrate stha ni n8 o r1 mm .I nth epresenc eo f1 m m substratesan dth eabsenc eo fcoarse rgrains ,th emajorit yo fth eanimal sd ono t burrowan ymor ebu tkee pwalkin g around,climbin gth escreens ,o rove rth eturne d overtrays ,probabl yi nsearc hfo rmor esuitabl e sites.Th eaversio nfo r8m mparticle s

Fig. 29.Distributio n(% ) ofgrain-siz efraction si nnatura lcase so f Mieropterna sequax. a:minera lcase s b:case spartl yconsistin go forgani cmatter .J .= 0.10 5- 0.210mm ;2 = 0.21 0- 0.25 0mm ;3 = 0.25 0- 0.35 0mm ;4 = 0.35 0- 0.50 0mm ; 5= 0.50 0- 0.85 0mm ;6 = 0.85 0- 1. 0mm ;7 = 1. 0- 2. 0mm ;8 = 2. 0- 4. 0mm ; 9= 4. 0- 8. 0mm .

83 frequency(% )

20- D 0 50 250 12 4 8 S 50 250 12 4 8 S 50 250 12 4 8 S frequency(% )

40- 20 • 777), .J 125 5001 2 4e 81 6 S 250 12 4 8 1632 S

frequency(% )

40- f

0- • i 1 L 5001 2 4 81 6 S L 250 12 4 8 S

Fig. 30.Substrat eselectio ni nlaborator y experimentsb y Micropterna sequax. Grain-size fractionsar eindicate db y thelowe r limito f thefractio n in urn (under 1mm )an dm m (over1 mm) .L = leave s ;S = en dretainin gscreen . FigureCas e InstarBod y Numbero f Numbero f Note no. type length experiments larvaepe r /mm experiment a mixed F >1 5 20 16 + 16m m pebble b mixed F > 15 10 16 + 16m m pebble c mixed F > 15 10 16 idemb ,a tnigh t d mixed F >1 5 29 16 upstream(shaded).downstream e mixed F > 15 10 16 (unshaded) f mixed F > 15 10 16 + leafpac k (shaded) g mixed F > 15 15 16 + leafpac k (shaded)

wasals oapparen ti nexperiment swher eothe rcoars eparticle swer epresen t (Fig- 31i , 1an dn) . Allexperiment s indicatetha t M. sequax doesno tprefe rgrai nsize ssmalle r than 1mm ,althoug hthe yma yb efoun dher eincidentally .I nman y instances theyar ethe n buildingo rrepairin gthei rcases .

Mixtures of grain sizes Theparticl esize s2 ,4 ,8 an d1 6mm ,whic happeare dt ob e preferredabov e0.05 0m m- 1 m mi nal lpreviou sexperiments ,wer eoffere d together withmixture s (equalamount so fbot hparticl esize so nvolum ebasis )wit h0. 5an d1 mm,respectively .I na firs tseries ,th elarva ecoul dchoos efro m4 substrates ,

84 onlyth efou rparticle s sizeso rth efou rmixture s (Fig.32 a- c); ina secon d series thechoic ewa s from 8substrates ,namel yth efou rparticl e sizesan dth efou rmix tureswit h 0.5m m and 1mm ,respectivel y (Fig.32d , e). For thefirs tseries ,i ti sclea rtha tth eattractio no fth epreferre dparticl e sizes asa substrat e changeswhe n theseparticl e sizes aremixe dwit h finergrains . Thepreferenc e for2 m mdecrease d drasticallywhe nmixe dwit h 0.5 mmo r 1mm .Th e preference for 16mm ,4 m man d 8m m (decreasing inthi ssequence ) (Fig.32a )change d toth esequenc e4 mm , 16m man d 8m mi nth emixtur ewit h 0.5m m (Fig.32b) ,althoug h thechang e isno tsignificant .I nth emixtur ewhit h 1m mparticle s (Fig.32c )th e preference changed to 8mm ,4 m m and 16mm ,whic h isa complet ereversio no fth ese quence.A possibl eexplanatio n istha tth eaccessibilit y ofth e 8-mm substratein creaseswhe nth einterstice s arefille dwit hgrains .Normall y theinterstice s of8 m m areto osmal lfo r M.sequax toente ran dth e 8-mm grains tooheav y topus hasid e withoutmuc heffort .Fo r 16-mmparticle s iti sno tnecessar y andfo r4-m m particles iti sobviousl yn oproble m topus hasid eth egrains .I nth emixtur ewit h 16-mm particles,th eremova lo f1-m mgrain si sprobabl yno tenoug h tomak e the interstices accessible,whil eth e 16-mmgrain sar eto oheav y tohandle .Wh yth emixtur eo f8 m m with 1m m ispreferre dmigh tb econnecte dwit h theinstabilit y ofth emixture :th e coarsegrain sma yrol lasid eeasie rwhe nth efin egrain s areremoved .Particl esize s smallertha n 1m mar eno tpreferre d (Fig. 30),possibl ybecaus e theyoffe rto omuc h resistance anddeman dto ogrea ta neffor tfo rpenetration . Fromth eexperiment s discusses above,i ti sclea rtha t 1m mca nstil lb euse db y parto fth epopulation ,whic hmean s thatth eresistanc e ofthi sparticle s size isno t insurmountable (Fig.31b) ,whil e in0. 5m man dsmalle rparticles, th eanimal shardl y burrowa tall ,sho wn opreferenc e andkee pmovin g around (Fig.31c) . Inth esecon dseries ,i nwhic h thelarva eha dth echoic ebetwee nth efou rbar e grainsize san dth efou rmixture swit h0.5-m man d 1-mm particles (Fig.32 dan de) , M.sequax clearlypreferre d grainsize sno tmixe dwit h0. 5m mo r 1m mparticles ,wit h a significantpreferenc e for 16m mparticles .N odifference sbetwee nth emixture s were observed.

Case type and substrate selection A series ofexperiment swit h M.sequax indifferen t casetype swa s conducted: animalswit ha n 'almost'pupa lcase ,alread yclose do non e sidewit hcoars egrain s (seesubsectio no ncas ebuilding),th eso-calle dhal fpupae ; animalswit ha minera l case;an danimal swit h apartl ymineral ,partl yorgani ccas e (mixedcases)(se e table 5). Halfpupa epreferre d thethre ecoarses tgrai nsize s (Fig.32f )withou tan y preference fora specifi cgrai nsize .Thi s agreeswit h thedistributio ni nth efiel d ofth elarges tlarva ean dpupae ,whic hpreferre d substrateswit ha tleas t 25% coarser than2 mm .Al lothe rcas etype sshowe dth esam epreferenc e aspreviou s experiments (Fig.32g ,h) , although larvaewit ha minera lcas epreferre d 8m mafte rth efirs t choiceo f 16mm . Inth epreviou sexperiment s larvaewit hmixe dcase swer e always

85 used,an di ti slogica ltha tth esam epreference s for1 6an d4 m mwer e found.Th e differencebetwee nlarva ewit hminera lan dmixe dcase sca npossibl yb eexplaine db y thestronge rpenetratin g abilityo flarva ewit hminera lcases .Partl y organic cases aremor eeasil ydamaged .O nth eothe rhand ,th eanimal s inminera l casesma yb e closert opupation ,becaus eanimal swit hpartl yorgani ccase sstil lhav et oreplac e theorgani cmateria lb yminera lparticles . A serieso fexperiment swit hlarva ewit hminera lan dmixe d caseso nsubstrate s consistingo famonolaye ro f2 ,4 ,8o r1 6m mgrain so nabas eo f0. 5m man d1 m m

frequency (%)

60 -i

40-

20-

0-1 c • 50 250 1 2 A A S+B i 50 250 A A A A S+B 60 freq.(%) ST

40- d 20- w 0 125 500 2 A A A S+B 125 500 1 A A A 16 S+B 125 500 1 A A 8 A S+B

60-1 freq.(%)

40- g

20- i—i i— • 125 500 1 A 4 A A S+B 50 250 • 1 2 A 8 S+B 125 500 1 2 A 8 16 S+B

60H freq.(%)

40- j

20-1

0 D 125 500 1 2 A A 16 S+B 125 500 1 2 4 A 16 S+B 125 500 1 2 4 8 A S+B

freq.(%)

40- m

20-

0- • 125 500 1 2 4 A A S+B 125 500 1 A 4- 8 16 S+B

86 (Fig.32 ian dj) , respectively,showe dtha tth epreferenc efo r1 6m man d4 m mremain s forbot hcas etypes ,bu tth erelativ epreference sar ereversed .O fcourse ,th ediffer encei ngrai nsiz eo fth ebas ema yb eo finfluence ,bu tpossibl yals oth elarge r penetratingabilit yo flarva ei nminera lcase sma ycaus eth epreferenc efo r4mm . Larvaei n1 6m mwer emostl ypresen to nth ebase ,no to ronl yhal fburrowe dbeneat h the1 6m mgrains ,whil ethos ei n4 m mha dcompletel ydisappeare dfro mview .

Differences between instars Aserie so fexperiment swit hlarva eo fdifferen tag eo n substrateso f0.12 5- 1 6m mshowe dtha tth epreferenc efo r1 6m mi ssimila ri nal l instarsstudie d(.Fig .32k :F-2 ;Fig .321 :F-1 ;Fig .30 d: F) .F- 1an dF- 2insta r larvaewer ever yactiv ean dles sincline dt ohid eb yburrowin g intoth esubstrat e thanth eF insta rlarvae .Thi si sillustrate db yth elarg enumbe ro flarva eo nth e endretainin gscreens . Anexperimen to nth einfluenc eo fcurren tspee do nth esubstrat eselectio no f thelarva eshowe dtha tth epreferenc eo flas tinsta rlarva ei sno tinfluence db yth e current (Fig. 30d).Younge rlarva e (F2),however ,positivel yselecte dth edownstrea m substratesa thig hcurren tspee.d s(1 0cm/s )(Fig . 32m).

Leafpaaks as substrate plaaed on a mineral base Offering M.sequaxa lea fpac k(beech ) ina smal l 12m mmes hbasket ,place do nto po fth e0.12 5m msubstrate ,togethe rwit h theminera lsubstrate s0.12 5- 1 6mm ,F- 2insta rlarva epreferre dth elea fpack s (Fig.33a ,b) ,whil eth eanimal sar ever yactiv ea ssee nb yth elarg enumbe ro f screenanimals .Offerin gthes elarva ea mixtur eo f0. 5- 4 m m(al lgrai nsize si n equalproportio no fa quarter )an dth esingl egrai nsize s0.5 ,1 an d2 mm ,the y showedpreferenc efo rth emixture ,althoug hagai na larg enumbe ro fanimal swa sfoun d

Fig. 31.Substrat e selection inlaborator y experimentsb y Mieropterna sequax. Grain-size fractions are indicatedb y thelowe r limito f thefractio n in um (under 1mm )an dm m (over 1mm) .S = en dretainin g screen;B = botto mo freverse d tray (shaded);A = absent . FigureCas e InstarBod y Numbero f Numbero f Note no. type length experimentslarva epe r /mm experiment a mixed F > 15 5 16 4 and8 m m absent b mixed F > 15 5 16 2,4 and8 m m absent c mixed F > 15 5 16 1,2,4an d8 m mabsen t d mixed F > 15 1 16 4,8an d 16m mabsen t e mixed F > 15 1 16 2,4an d8 m m absent f mixed F > 15 1 16 2,4 and1 6m m absent g mixed F > 15 1 16 2,8 and 16m m absent h mixed F > 15 5 16 4 mmabsen t i mixed F > 15 4 16 4m m absent j mixed F > 15 5 16 4 and8 m m absent k mixed F > 15 14 16 8 mmabsen t 1 mixed F > 15 35 16 16m m absent m mixed F > 15 5 16 8 and 16m mabsen t n mixed F > 15 4 16 2 mm absent

87 onth escreen s (Fig.33c) .F- 1insta rlarva ewit hmixe dcase s (1/3- 1/ 2organic )o n 0.250- 2 mm ,wit ha lea fpac ko n0.25 0mm ,distinctl ypreferre dth elea fpac kan d 2mm ,wit ha relativel ylo wnumbe ro fscree nanimal s (Fig. 33d). Givinga lea fpac ko nal lminera lsubstrate s (0.5- 4 mm) ,th epac ko n4m mi s preferred (Fig.33e) ,whil ei nsection swithou ta lea fpac kan dth esam eminera l substrates (Fig.33f) ,2an d4 m mar eselecte dwit ha muc hhighe rnumbe ro fscree n animals.F- 1insta rlarva eo n1- 8mm ,eac hprovide dwit ha lea fpack ,preferre dth e leafpac ko n1m man dther ewer en osignifican tdifference sbetwee nth eothe rlea f packso rth eminera lsubstrat e (Fig.33g) .Give nth echoic ebetwee n1- 8mm , the fractionso f2 ,4 ,an d8 m mar eequall ychose nwit h largenumber s ofanimal so nth e screens (Fig. 33h). Ina nexperimen twher e0.12 5- 1 6m mparticle swer emixe dwit h coarsedetritu s "(smallpiece so fbeec hleaves ) M. sequax showedn osignifican tdifference si ngrain - sizeselectio n (compareFigs .33 ian d30d) ,indicatin g thatth eselectio no f1 6an d4

frequency (%) 60-

40-

20- Pzz 0-" CZ3 2 4 8 16 S 2 4 8 16 S 2 4 8 16 S 2 4 8 16 S + +505 + + + + + frequency (%) e 40- 20": pjy IZ 2 4 8 16 S 2 4 8 16 S 2 4 8 16 S 2 4 8 16 S frequency (%) i 40-

20-

O- D • 2 4 8 16 S 2 4 8 16 S on 500 on 1 frequency (%)

40- m 20-

O 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S 12 4 8 S

88 mmsubstrat eis- area lpreferenc e forthes eparticl esize swhe nfoo dcondition sar e favourable,bu tFigs . 33a,d ,an de indicat etha twhe nfoo dcondition s (leafpacks ) aremor e favourableo nothe rsubstrat e types,foo di sth emai nselectio ncriterion . Concludingi tca nb e statedtha t M.sequax prefers leafpack sabov eminera lsub strates.However ,whe nlea fpack sar eabsen tthe yclearl yprefe rcoars eparticl e sizes (coarsertha n2 mm) , inparticula r1 6- 3 2m man d4- 8mm .Th efractio n 8-16m m isles spreferred ;thi smigh tb erelate dt oth epenetrabilit yo fth esubstrate . No significant differenceswer e observedi nsubstrat eselectio nbetwee nth ethre elas t larvalinstars . Comparisonwit hth edistributio ni nth efiel d (Table27 )show stha tsubstrate s witha larg eproportio naroun d 8-16m m(Q 1 orM ,= 4 ) ar eavoided ,bu twhe nmos to f thesubstrat ei scoarse r than8-1 6m m(Q ,= 4 ) th esubstrat ema yactuall yb eprefer red.Th esimilarit yi nsubstrat epreference s foundi nth efiel dan dth e laboratoryi s furtherillustrate di nFig . 34,upo nwhic hbot h theparticl e sizesselecte di nexperi mentsi nth elaborator yan dth esubstrate spreferre di nth efiel d (basedo nbot h

Snijban dRa bdat ai nSort s5 t o8 ,10°« )hav ebee nprojecte do nth eQ-|M dQ3graph . Thus theresult so fth e laboratoryexperiment s confirmth esubstrat epreference sob servedi nth efield ,especiall y concerning theshif to fpreference s fromdetritu s substratesi nautum n- whe ndetritu si sabundan t- t ocoars eminera lsubstrate si n winteran dsprin g- whe ndetritu ssubstrate sbecom e lessabundan tan di tform sa mor e integratedpar to fth eminera l substrates.Th epreferenc eo fF- 1insta r larvae (10-15

Fig.32 .Substrat e selection Inlaborator y experimentsb yAfecropterr w aequax. Grain-size fractions are indicated by thelowe r limit of the fraction in um (under 1mm )an d mm (over 1mm) .S = end retaining screen. Figure Case InstarBod y Number of Number of Note no. type 1(3ngt h experiments larvae per /mm experiment a mixed F > 15 16 16 b mixed F > 15 10 8 mixtureswit h0. 5 mm mixed F > 15 2 16 mixtureswit h 0.5 mm c mixed F > 15 10 8 mixtureswit h 1.0m m mixed F > 15 2 16 mixtureswit h 1.0m m d mixed F > 15 5 32 bare (unshaded)an dmixe dwit h 0.5m m (shaded) e mixed F > 15 5 32 bare (unshaded)an dmixe dwit h 1.0m m (shaded) f i pupal F > 15 2 12 ipupa l F > 15 12 8 g mixed F > 15 6 12 mixed F > 15 8 8 h mineral F > 15 8 8 mineral F > 15 6 12 i mixed F > 15 7 16 amonolaye r on0. 5 mm i mineral F > 15 7 16 amonolaye ro n 1.0m m k mixed F-2 6--10 6 32 1 mixed F-1 10--15 6 32 m mixed F-2 6--10 6 32 upstream(shaded).downstream (unshaded)

89 frequency(% ) 60-

40H 20- 1 1 rL_n o- 125 5001 2 4 81 6 125 5001 2 4 81 6 S 5001 2mi x + L frequency(% ) d 40-

20-

O- D D L250 1 2 5001 2 4 5001 2 4 + L + + + + frequency(% )

40- g

20-

O-1 D 12 4 8 125 5001 2 4 8 16 S + + ++ + ++ + CD

Fig.33 .Substrat eselectio n inlaborator y experimentsb y Miaropterna seqvax. Grain-size fractionsar eindicate d by thelowe rlimi to f the fraction in um (under 1mm )an dm m (over1 mm) . L= leaves;S = endretainin g screen;C D = coarsedetritus . FigureCas e InstarBod y Numbero f Numbero f Note no. type length experiments larvaepe r /mm experiment a mixed F-2 6-10 5 32 leafpac k (shaded)o n0.12 5 mm b mixed F-2 6-10 5 32 leafpac k (shaded)o n0.12 5 mm c mixed F-2 6-10 5 16 mixtureo f0.5+1+2+ 4m m d mixed F-l 10-15 5 16 leafpac k (shaded)o n0.25 0m m e mixed F-l 10-15 5 16 leafpac k (shaded)o nal l f mixed F-l 10-15 5 16 g mixed F-l 10-15 4 8 leafpac k (shaded)o n all h mixed F-l 10-15 4 8 i mixed F >1 5 3 16 allmixe dwit h CD

mm)fo rsan dsubstrate s (Table28 )coul dno tb e confirmedi nexperiment s (Fig.33d - kj,bu ti ti sproblabl yexplaine db y thepresenc eo fcoars edetritu si nth esan d substrate,althoug hi ti sles stha n 101.

90 phivalue s Î S Q 3 4 Î "d 3

Î 2

O ï

6 V +

M.(ph ivalue ) a Fig.34 .Compariso no fsubstrat epreference si nth efiel d(unshaded)wit h particle-sizeselectio ni nlaborator yexperiment s (shaded) for Micropterna sequax.

4.2.2.4 Chaetopteiyxvillos a (Fabricius) (Trichoptera:Limnephilidae )

Life cycle Chaetopteryx villosa hasa univoltin e lifecycl e (Fig.35) ,wit ha relativelylat efligh tperio di nautumn .I nth erearin gchannel ,emergenc estarte d mid-Octoberan dcontinue dtil learl yDecember ,which agree swit hth epea ki nNovembe r reportedb ySvensso n (1972),althoug hh estate da tota lfligh tperio dfro mmid - Septemberunti lJanuary .Décamp s (1968)ofte nfoun dadult si nth esnow .Hicki n (1967) gavea shorte rperiod :onl yth esecon dhal fo fOctober ,bu tGledhil l (1960)reporte d thefirs tadult si nth emiddl eo fAugus twit ha pea ki nemergenc ei nth emiddl eo f October. Adultsalway sfl yi nupstrea mdirectio na tnigh t (Elliot,1971 )an ddeposi t theiregg sabov eth ewater .Th eegg sdevelo pver yfast ,partl ybefor ewinte rwhil e parto fth eegg soverwinters .I nMay ,firs tinsta rlarva eca nb estil lfound .Earl y hatchedlarva eoverwinte ri nth efirs to rsecon dinsta r (Dittmar,1955 )an dstar t

91 77: *9-SZ.

77: «S-«8

uro 77: J3-36

77: 29-32 mruIÎUnn 77; £S-2S:

77. ZI-ZI

77: 17-20

77: 13-16 *JinNi!I!I!lTTn™-._ 77; "»-iz! —im -^ 3 : Q 76; "9-SZ: o ; I-H gj 76: «S-*)8 Q.

7&: *1-*H

—». w-JTÏÏli HTHimmi 76; J7-48

—.. rniwTv-JÎÏÏIrnW-., 76; J3-36 :

76: 29-3Z

76; 17- 2Û — N - W

76: 13- 6! INIHMfNIIIül -m tiuii

76; 9- 1Z

74: S- 8

/4; I- 1

7S: «9-Sz:

7S: «5-18

7S: «1-1V

75; 37-10 mnMm

snci°iiioi-°i^ai°iadaaaaaaaasi INH LENGTH CLASS(MM ) Fig. 35.Lif ecycl ehistogram so f Chaetopteryx villosa showingth edistributio (%n ) oflarva lbod ylength ,pupa e(99 )an dadult s(98 )pe rfour-wee kperiod .

92 growingagai ni nApri l (Elliot,1971) , althoughi nth eSnijdersveerbee kthi sseem st o beearlie r (Fig.35) . Elliot (1971)distinguishe d 5larva linstar so nth ebasi so f thehea dcapsul ewidth .Thi si sconfirme db ymeasurement sb yTolkam p& Verdonscho t (tob epublished) .Larva ebecom ea tmos t 16m mlon gan d3 m mwide . Insumme r thelarva eunderg oa restin gperio d (Denis,1978 )i nth elas tinstar , inwhic hthe ypas sfro msprin gt oautumn .Thi sobservatio ndoe sno tfull yagre ewit h thelarva lsize sfoun d inth epresen tresearch ,a sgrowt hwa sstil lobserve di n summer (Fig. 35).

Case building Accordingt oEllio t (1971) Ch.villosa larvaebuil da cas eo fveg etablemateria li nth efirs tinstar ,ofte nwit hvariou spart sprojectin gi nal l directions (aso-calle dshodd y case). Startingfro mth efourt h (F-1)instar ,minera l matteri suse dalso .I nth efift h (F)insta rminera lmatte ri softe nth eonl ybuildin g materialwit hperhap ssom esmal lpiece so flea fmateria la tth erea rend . Fromth edat ao fth eSnijdersveerbee k thistendenc yi sals oapparen tan dwil lb e describedi ndetai lb yTolkam p& Verdonscho t (tob epublished) .However ,th echoic e ofbuildin gmateria ldepend sstrongl yo nth einhabite denvironment ,whic hindicate s thatmimesi sma ypla ya nimportan trole ,a salread yreporte dfo r M.sequax. Ch.villosa useslea fan dminera lmateria li nal linstars ,althoug hth efirs tthre einstar sus e relativelymor e organicmateria lan dth elas ttw oinstar smor eminera lmatter .O fth e mineralmateria lther ewa sa significan tpreferenc efo rth e 1-2m man d0. 5 -0.8 5m m fractions inth elas tinstars ,wit ha decreas eo fth estil lfine rfraction swit hin creasinginsta r (Fig. 36). Similarchange sfro mvegetabl et ominera lmatte rhav ebee nobserve dfo rman y memberso fth eLimnephilida efamil yan dhav ebee ndescribe db yCunmin s (1964)an d Mackay (1977)fo r Pyonopsyohe spp.Fro mresearc ho n Potamophylax latipennis byZint l (1976)an do n Lepidostoma hivtum byHansel l (1972;1974 )i ti sclea rfo ra tleas t thesetw ospecie s thata chang ei nbuildin gmateria lan dstyl ei sno tbase do n environmentalfactor sbu to na comple xo fendogenou sfactors .Ellio t (1971)conclude d theopposit efo r Ch.villosa. Hecorrelate dth echang efro morgani ct ominera lbuildin g materialafte rth ethir dinsta rwit ha migratio no fth elarv afro mvegetabl et o mineralsubstrates .Th e latterphenomeno ni sals oobserve di nth epresen tstudy , althoughi twa sno tdirectl ylinke dwit hth einstars ,becaus eal linstar suse dleave s aswel la sminera lparticles . Pupalcase sresembl e lastinsta rcases ,bu tthe yar eclose dwit hsieve-lik e membranescovere dwit hcoars eminera lparticles .The yresembl eth epupa lcase sfro m M.sequax, butar esmalle ran dofte nstil lcontai nsom eorgani cmaterial .A similar closingsyste mi sused :th elarv aclose s thefron twit h1- 2an d2- 4m mgrains ,open s therear ,sometime sremove sth eorgani cmateria lan dextend sth ecas ewit hminera l matteri fnecessary ,burrow sperpendicularl y intoth esubstrat ean dclose sth ene w frontwit hmateria la thand .Th egrai nsize suse dfo rclosin gbot hend svar yfro m 0.5 -8 mm .

93 ltest Pupae -Hie

S 70'

g 50

', 40-

'I' ' 'I' I •p-r MM I' | ' I ' |' ' ' I ' ' 0.7 0.9 1.3 1.5 1.7

head width classes (mm) Fig.36 .Distributio n(% ) ofgrain-siz efraction si nnatura lcase so f Chaetopteryx villosa .1= 0.10 5- 0.21 0mm ;2 = 0.21 0- 0.25 0mm ;3 = 0.25 0- 0.35 0mm ; 4= 0.35 0- 0.50 0mm ;5 = 0.50 0- 0.85 0mm ;6 = 0.85 0- 1. 0mm ;7 = 1. 0- 2. 0mm ; 8= 2. 0- 4. 0mm ;9 = 4. 0- 8. 0mm .

Elliot (1971)state dtha tth eadult sar equit ecapabl eo fflyin gint oth ewin d (atnight ,i nupstrea mdirectio nt ocompensat efo rdriftin gyoun g larvae).However , duringth eda yth eaduls tar eba dflyer s (personalobservation) .Observation sb y Tolkamp& Verdonscho ttha tman ymor ejuvenil e larvaear efoun di nth eupstrea msec tionso fth eSnij ban dmor eolde rlarva ei nth edownstrea msection sconfir mElliot' s observationo nth epresenc eo fa colonizatio ncycl e (Miller,1954) .

Mierodistribution Inal lsubstrat eclassifications , Ch.villosa obviouslyprefer sth e organicsubstrate s (Table2 9an d30) , althougha sligh tpreferenc efo rcoars eminera l substrates (Gravelan dDetritus )ca nb eobserve da swell . FromTabl e3 1A ,givin gth eI.R .value sfo ral llengt hclasses ,i ti sclea rtha t thepreferenc efo rorgani csubstrate si sprimaril ycause db yjuvenil e larvae (maximum length7 mm) . Largerlarva e (12-20mm )prefe rminera lsubstrate swit h( L< 7 an d

preferablyM d £T (coarse rtha n1 mm). Animalso fth elengt hClas s8 - 1 1m mwer emos tabundan ti nCoars eDetritus ,bu t

94 Table29 .I.R .value s for Chaetopteryx villosa (N= 386)i nth efiel dclassificatio n of thesubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 -8.7 1.7 13.2 _l J I 4 -7.2 -4.9 0.2 2.7 13.2 —J I 2 -6.0 -4.1 -0.4 -6.0 0.2 2.7 13.2 I _] I 1 -4.2 -4.3 -4.1 -2.1 0.8 -0.0 -5.4 -2.4 0'.2 -1.0 3.7 33.0 -4.2 -3.3

St Sh FD CD CD+LCD+F D L+FD CD CD CD+L

Italicvalue s indicatesignifican t over-representation

Table30 .I.R . values for Chaetopteryx villosa (N= 386)i nth egrain-siz e classificationo f the substrates inth e Snijdersveerbeek.

Substrate class 8 9 10 11 12 13 14

detritus phi index CD CD+L

Sort5,10 % 5.0 -0.6 2.6 -0.1-2. 8-2. 2-0. 5-5. 8-6. 6-3. 8 - 27.7 -3.6-3. 6 Sort6,10 % 5.0 -1.0-3. 0 3.1 2.7 -0.9-0. 7-1. 6 -6.1-6. 6 - 27.7 -3.6-3. 6 Sort7,10 % 5.0 -1.8-2. 0-1. 0-2. 0 0.8 5.7 -3.8-7. 0-2. 7 27.7 -3.6-3. 6 ^lMd^3 index xxx x5x xäx x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x S°rt8,10 % 0.9 2.1 2.0 -0.9-0. 7-1. 1-1. 5-5. 8-4. 0-5. 3-3. 8 27.7 -3.6-3. 6

Italicvalue s indicate significant over-representation

theyhav e alreadypartl ymove dt oth ecoars eminera lsubstrate swher eth e largest larvaear e found.Pupa ewer e exclusively found inminera lsubstrat ewit ha preferenc e

forM d between2 an d8 m m(ph i= 3 an d 2)o rx3x ,x2 xsubstrat e (Q1 andM d £Ï ) • In leafpack shardl y any Ch. villosa larvaewer e found. Similarpreference swer eprobabl ypresen ti nth eRatumsebeek ,bu tthi scoul dno t beteste dfo rth evariou s instarsb ylac ko fsufficien tmateria l (only6 0specimens) . Considering thedistributio nbetwee nseasons ,Tabl e 31Bshow stha ti nwinte ran d springth ehighes tpreference s arefoun di nCoars eDetritus ,i nadditio nt owhic hi n winteronl ynegativ e I.R. valuesar e foundi nminera lsubstrates .I nsprin gther ei s alsoover-representatio ni nxx xan dx4x/x5 x (Mjresp .7 an d 4). Insumme rth eprefer encei ssolel y forminera lsubstrate ,whe norgani csubstrate syiel donl ynegativ e I.R. values.I nautum nther ei sa share dpreferenc e forminera lan dorgani csubstrate s whichconcern spupae ,prepupa ean dburrowin g larvaean dfeedin g larvae.Compariso no f

95 Table31 .I.R .value sfo r Chaetopteryx villosa perlengt hclas s(A )an dseaso n(B ) inth eSnijdersveerbee ki nSor t8,10% .

classan d Q index Length N Subs träte «lMd class and 1 2 3_ 4_ 5_ 6 7 8 9 10 11 12 13 14 Season xxx x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 0 4 -0.3 -0.6 1.5 -0.5 1.6 -0.5 -0.6 -0.6 -0.6 -0.7 -0.4 -0.5 2.7 -0.4 1- 3 36 -1.0 -1.7 -0.8 -1.5 -1.5 -0.8 -1.9 -1.9 -1.7 -1.1 -1.2 18.2 -1.3 -1.1 4 - 7 119 -1.9 -0.3 -2.4 -2.4 -1.9 -1.9 -2.3 -3.5 -2.5 -2.7 -2.2 28.8 -2.1 -2.0 8 - 11 107 1.7 2.0 2.8 -0.0 -0.2 -2.1 -1.2 -3.3 -1.9 -2.7 -1.6 11.4 -1.2 -1.9 12- 15 76 3.3 3.4 1.9 0.5 0.7 3.5 1.5 -2.8 -1.7 -2.7 -1.8 -0.1 -2.3 -1.6 16- 20 29 0.2 0.4 1.6 0.8 2.5 0.2 0.6 -0.6 -0.9 -1.9 -1.1 1.4 -1.6 -1.0 99- 98 15 -0.7 0.7 3.2 3.1 -1.0 -1.0 1.2 -0.4 -0.2 -1.3 -0.8 -1.0 -1.2 -0.7 Total 386 0.9 2.0 2.0 -0.9 -0.7 -1.1 -1.5 -5.8 -4.0 -5.3 -3.8 27.7 -3.6 -3.6 B Spring 201 2.1 3.5 -2.4 -1.1 1.1 -3.2 -2.8 -4.6 -3.1 -2.0 -1.6 16.0 -2.8 -3.2 Summer 85 2.9 -1.3 7.2 -0.6 -0.5 2.1 0.4 -1.6 1.0 -3.8 -2.2 -0.7 - - Autumn 27 -0.9 -1.1 4.5 1.3 -1.3 -0.8 1.2 -1.2 -1.1 -1.8 -0.9 3.8 -0.6 -0.8 Winter 73 -1.5 -2.0 -1.8 -1.1 -2.2 -0.6 -1.5 -2.9 -2.7 -1.6 -1.5 26.5 -1.8 -2.0

Italic values Indicatesignifican t over-•representation

theseseasona ldifference swit hth edifference sbetwee nth evariou s instarsshow sa remarkable conformityi nth edistributiona l changesunde rth einfluenc eo flarva l size (age). Ch.villosa seemst ob ever ywel l adaptedt oth eseasona l changesi nth e abundanceo fsubstrat e typesan dfoo dresource s (coarse detritus). Chaeptopteryx isa detritivor ean dth elarva eus eth eenzyme spectinas ean d xylanaset obrea kdow nvegetabl ematte r (Bjarnov,1972) .Dittma r (1955)foun dtha t the larvaeoccu ri ncombinatio nwit hmacrophytes ,wher e theyfee do ndetritus , filamentousalga ean ddiatoms ,althoug hthe yals opredat eo nchironomid san dcaddi s larvae.I nth erearin gchannel ,Ch.villos awa softe nobserve d feedingo ncases , larvaeo rpupa e (mostlythos ewit hstil lsom eorgani cmateria li nthei rcases )o fit s ownspecies . Inwinter ,whe ndetritu si sabundan ti nth estreams ,th elarva ear esmal lan d theybuil dorgani ccase san dinhabi tdetritu s substrateso nwhic hthe yfeed .Durin g springan dint osummer ,whe ndetritu ssubstrate sbecom emor e scarceth elarva egro w andmov et ominera l substrates,althoug h thesewil l stillcontai nenoug h organic material,o rwil lb esituate di nth eneighbourhoo do fdetritu ssubstrates ,t oprovid e food,whic hi sconsume da tnigh t (personalobservation) .I nsumme ran dearl yautum n detritussubstrate sar ever yscarc ean dthi smigh tfor mpar to fth eexplanatio nfo ra possiblerestin gperio di nthi stim eo fyear .Apar tfro mth eobservatio nb yPetra n (1977),Kamle r& Riede l (1960)als ofoun d Ch.villosa tob eth eonl y thrichopteran occurringi ndesiccatin g sectionso fa stream . lilies (1952)state dfo rCh.villos a thati ti sa ninhabitan to flowe rcourse san dtha ti tma ypenetrat e intomiddl e courses.Th edistributio no f Ch.villosa inth eNetherland si sno tcompletel yknown , buti tprobabl yoccur smainl yi nth esmalle r (uppercours e type)streams .Sinc e

96 Ch.villosa isa neurythermou san dmoderatel yrheophilou slimnephili di toccur si n quietplaces ,i npool so fsmal lstream so rstagnatin g largerstream swher etemperatur e fluctuationsma yb ehig h (Dittmar,1955 ;Kamle r& Riedel ,1960 ;Hynes ,1970a) .Beye r (1932)foun dtha tman yLimnephilida ear eeurythermou s (e.g. M.sequax, S.rotundipennis, S.interpunatatus) andh e thoughttha t Ch.villosa mightb ecol dstenothermous .Th e observationsmad eb yth eothe rabov ementione dauthor san db yth edat afro mth e presentresearc hd ono tconfir mthis . Inhi sstud yo nth eemergenc epattern so fvariou sinsect si nth eBreitenbach , lilies (1978)foun da contradictio ni nth eemergenc eo fth emayfla y Baetis vermis and Ch.villosa, whichh eattribute dt oquantitativ ean dqualitativ echange si nsubstrat e mosaicpattern si nth einvestigate dstrea msectio n (thegree nhouse) .Afte ranalysin g severalfactor s (temperature,food ,wate rlevel )h esuppose dtha tth etempora l variabilityi nsubstrat epattern s (betweenyears )wa sth eonl ypossibl efacto r responsible forth ereciproca labundanc eo f ÔtiTvillosa and B.vermis, assumingtha t theyhav eopposit ehabita t (substrate)preferences .Th edat ao fth epresen tresearc h supportlilies 'assumption . Ch.villosa clearlyneed smor etha non esubstrat etyp et o completeit slif ecycl ei na stream ,whil e Baetis vermis largelyprefer sth e (sheltered placesof )ver ycoars eminera lsubstrate stogethe rwit hth esan d+ detritu ssubstrate s (Appendix 12).Th e latteri si naccordanc ewit hth efoo dpreference so f B. vermis (algaean ddetritus) . Ch.villosa, however,need sorgani csubstrate si nwinte ran d spring,whe nth e larvaear egrowin gfast ,an dcoars eminera lsubstrate si nsumme ran d autumnfo rrestin gan dpupation .I ti sver ylikel ytha ttempora lsubstrat evariatio n Playeda rol ei nth egreenhous ewher e theemergenc eo fthes especie swa srecorde db y lilies (1978).Whe nsan dan ddetritu ssubstrates ,perhap stogethe rwit hsom elarg e stones,ar epresen ti nspring ,thi shabita twil lb efavourabl efo r B.vermis, which emergesi nMay/June . Ch.villosa willavoi dburrowin gi nthes esubstrate st opas sth e summer.O nth eothe rhand ,whe ncoarse ,gravell ysubstrate sdominate ,thes ewil l offersuitabl eburrowin gsite sfo r Ch.villosa tospen dth esumme ran dt opupat ei n August/September.Thes econdition sar eunfavourabl efo r Baetis vermis.

Substrate-selection experiments Allexperiment swit h Ch.villosa wereconducte dwit h lastinsta rlarva ewit hvariou scas etype s (Fig.37) .Al lexperiment slaste d8 o r2 4 hours.Thi sgav en odifference s insubstrat eselection .Afte r1 4hour sth edistribu tiono fth elarva ei nth edar kwa srecorde da swell .Th elatter ,result swil lno tb e presented.I ngenera l themai npreference ssee nb yda yremaine da tnight ,althoug h thedistributio nwa s lesspronounce dan dmor egrai nsize swer einhabite da tnight . Themos tremarkabl e featurea tnigh twa stha tth elarva ewer emos tabundan to nth e endretainin gscreen so ra tth eedge so fth eexperimenta larea ,wher ethe ywer e obviouslyi nsearc hfo rmor esuitabl esubstrate so rfood . Theresult so fth eexperi mentswit hCh.villos aar esummarize di nFig . 37. Inal lexperiment swher ea leafpac kwa spresen to non eo rmor eo f *«»fl substrates,leave swer eth epreferre dsubstrat etyp efo ral lcas etype s (Fig.3/a , , 97 frequency (%)

40-

20- m s 1 mi Z2 _ 0 A] D mV 12 4 8 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S + + + + ij t frequency (%) 40- d

20-

0- • rJ HA 125 5001 2 4 8 16 S 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S + L frequency (%)

40- g M

20-

0 D D I ÖD 125 500 1 2 4 8 16 S 2 4 8 16 S 125 5001 2 4 8 16 S + L frequency (%) 40-1 j

20-

0 D • 125 500 1 2 4 8 16 S 2 4 8 16 S 12 4 8 frequency(% ) 40J m

20- 1 o- • • 12 4 8 500 1 2 4 500 1 2 4 S + + + + + + + + frequency (%) L

40- P 20- fin 0- 1 L 1 2 4 8 16 500 1 2 4 8 16 S D on 2 on 500

98 e,£ ,i ,m ,o) , exceptfo rlarva ewit hhalf-pupa l cases,whic hpreferre dminera l substratesi.e .4 an d8 m m(Fig .37c) .Togethe rwit ha preferenc efo rleaves ,th e (partly)minera l casetype sselecte dparticl esize s coarsertha n2 mm ,wit ha distinc t preferencefo rthes eminera lparticle swhe nlea fpack swer eabsen t (Fig.37 gan dj) . Larvaewit hhalf-pupa lcase sals oselecte dth esam eparticl esize si nth eabsenc eo f a leaf-pack (Fig.37d )althoug hslight ,bu tno tsignificant ,difference sdi doccur . Larvaei norgani ccases ,however ,onl yshowe da sligh tover-representatio ni n1 6mm , butwer eabundan to nth escreen so rwalkin g around (Fig.37a) . Inth eexperimen twher eth elarva e couldchoos ebetwee nal lgrai nsize s from 0.125- 1 6mm ,th epreferenc ewa sclearl yfo rth ecoarses tparticl esizes ,wher e1 6 mman d2 m mwer eselecte dmostl yb yth elarva ei nminera l cases (Fig.37e ,f , g). Larvaewit hhalf-organic ,half-mineral ,case sshowe da distinc tpreferenc efo r1 6m m only,wit ha nequa ldistributio nove rth eothe r threecoars eparticl e sizes(Fig . 37i, j). Inexperiment swit honl ya choic ebetwee nthes e4 coars eparticl esizes ,th e samepreference so fth ehalf-mineral ,half-organi c cased larvaeoccurre d (Fig.37k) , while larvaewit hminera lcase schos e1 6m mexclusivel y (Fig.37h) .Larva ewit h cases consistingo fon ethir dorgani can dtw othird sminera lmateria lals oselecte dth etw o coarsestparticl esize si nth epresenc e (Fig.37m ,o )a swel la sabsenc e (Fig. 371, n)o flea fpacks ,althoug hi nth epresenc eo flea fpack sth epreferenc ewa shighe r forleaves ,bu tespeciall yfo rth elea fpack so nth epreferre dminera lparticl esiz e (shadedare ai nFig .37 man do) . Larvaei norgani ccase ssho wa simila rselectio no fth elea fpack sbu tno t

Fig. 37.Substrat eselectio n inlaborator y experimentsb y last (F)insta r larvae of Chaetopteryx villosa.Grain-size fractionsar e indicatedb y thelowe rlimi to f the fraction in pm (under 1mm )an dm m (over 1mm) .L = leaves ;S = end retaining screen. (1/2- 1/2 :1/ 2 organic,1/ 2 mineral) Figure Case-type Numbero f Number of Note no. experiments larvae per (leafpack s : shaded) /mm experiment (mineral :unshaded ) a organic 2 16 leaf pack on 0.125 mm b organic 5 16 leaf pack on all substrates c i pupal 1 16 leaf pack on 0.125 mm d èpupa l 3 16 e mineral 4 16 leaf pack on 0.125 mm f mineral 1 32 leaf pack on 0.125 mm g mineral 3 32 h mineral 1 16 i 1/2 - 1/2 2 24 leaf pack on 0.125 mm j 1/2 - 1/2 6 24 k 1/2 - 1/2 2 32 1 1/3 - 2/3 5 16 m 1/3 - 2/3 5 32 leaf pack on allsubstrate s n 1/3 - 2/3 5 16 o 1/3 - 2/3 5 16 leaf pack on all substrates P 1/3 - 2/3 5 24 monolayer on 2m m q 1/3 - 2/3 5 24 monolayer on 0.5 mm

99 linkedt oth eminera lsubstrate ,whil eth eselectio no fth etw ocoarses tgrai nsize s isles spronounce d (Fig.37b) .Whe nthes elarva ehav e thechoic ebetwee na monolaye r ofsevera lgrai nsize so nabas eo f2mm ,togethe rwit ha lea fpac ko n2mm ,ther ei s nodistinc tpreferenc efo ran ysubstrat e (Fig.37p) .Whe nplace do n0. 5mm ,4 m man d 16m mar eselected ,whic hindicate stha tno tonl yth esurfac eo fa substrat ei s importantfo rselectio no fburrowin gsites ,bu tals oth ecompositio no fth eunderlyin g material. Fromal lthes eexperiment si ti sclea rtha tfo r Ch.villosa leafpack sfor mth e mostpreferre dsubstrate ,afte rwhic hcoars eparticl esize slarge rtha n2 m mar e favoured,especiall y1 6mm .Th eselectio no flea fpack sca nb esee nfo ral llarva l case,types ,bu tth epreferenc efo rminera lsubstrat ei shighe rfo rlarva ewit hpartl y orcompletel yminera lcase stha nfo rlarva ewit hpurel yorgani ccases .Larva ever y closet opupatio nsignificantl yprefe rcoars eminera lsubstrates ,whic hagree swit h thefiel dstud y (Table31a :16-2 0m mlarvae) .A nadditiona lobservatio ni stha t larvaefoun do nth efou rfines tsubstrate swer eofte nbuildin go rrepairin g their caseso rstartin gt obuil dthei rhalf-pupa lcase .Som eo fth ehalf-pupa eeve nclose d theircas edurin ga nexperiment ,whic hmad e itnecessar yt oreplac ethem .

Field experiments with artificial substrates Inth eRatumsebee kvariou sgrai nsize s wereoffere dfo rcolonization .Thes eartificia lsubstrate swer e collectedafte r1 4 and2 8days .I nthes e (spring)experiment s Ch.villosa occurredwit h9 larva ei nth e replicateso f5 substrat etype safte r1 4 days;6 o fthes e larvaeoccurre di n3 2m m (Table 32).Afte r2 8days ,wit h9 substrat etypes ,4 2larva ewer e found, 18o f whichoccurre di n3 2m m(Tabl e 32). Thisclearl yindicate s that Ch.villosa preferred thecoarses tgrai nsiz eabov eth efine rsubstrate s (seeTabl e 16).Moreover ,8 m mwa s avoidedafte rbot hperiod san da simila rexplanatio na stha tgive nfo r M. sequax might beapplicable ,namel yth eimpenetrabilit yo fthi sgrai nsize .

4.2.2.5 Plectrocnemiaconspers a(Curtis )(Trichoptera : Polycentropodidae)

Miovodiatvibution Pleotroonenria aonspevsai sth eonl ynet-spinnin gTrichopter aspecie s foundi nreasonabl enumber si nth eSnijb .I nth eRa bonl ya fe windividual swer e

Table32 .Numbe ro f Chaetopteryx villosa larvaeI nartificia lsubstrat e inth eRatumsebee ki nApril/Ma y197 8afte r1 4an d2 8day so fcolonization .

Dayso f Numbero flarva eb ygrai nsiz e(mm ) Total colonization 32 16 8 4 2 1 0.5 0.25 0.125 14 62. .1--- - 9 28 18 6 . 5 2 2 . 5 4 42 -= fractio nno tofferre d

100 found.Othe rnet-spinnin gTrichoptera ,suc ha s Hydropeyohe angustipennis, Lype veduota and Tinodes waeneri wereonl yfoun dincidentally . T.wa&neri wasonl yfoun di nth eRa b andneve ri nshove lsample sbu talway so nlarge rstones . Inth eSnij bth edistributio no f Pleotroonemia aoneperaa isrestricte dt oth e detritussubstrates ,especiall yC Do rL .Th ecombinatio no fC Dan dL isno tpreferre d althougha sligh tover-representatio noccurre d (Table 33).I nth egrain-siz eclassifi cation (Table34 )th esam edistributio ni sseen .Th esligh tpreferenc efo rS+C Di n Table3 3return si nTabl e3 4a samino rover-representatio ni nth efines tminera l substrate (33x),whic hresemble smu do rfin esan dwit hfin edetritus .Coars esubstrate s areonl yinhabite db yfe w P.oonepersa larvae,probabl ybecaus eth ecurren ti sto o fastan dbecaus esan dan dpebble sar eno tlyin gloosel ypacked ,whic hwoul doffe r dwellingsites ,bu tar eembedde di nsand .Relativel yhig hnumber swer efoun di nxx x and1x xsubstrate swit h1 7an d1 0individuals ,respectively ,i n3 9sample si neac h type. Pleatroanemia oonspersa mainlyoccur si nrelativel ycol dupstrea mregion s (Décamps,1968 ;Edington ,1968 ;Edingto n& Hildrew ,1973) ,wher ethe ydwel li nslowl y runningwate rwit hcurren tspeed sno texceedin g2 0cm/s ,an dpreferabl y lowertha n1 0 cm/s(Nielsen ,1942 ;Edington ,1968) .The yd ooccu ri nsite swit hfaste rcurrent s (rapids,riffles )bu tthe nalway si nsheltere dplace sunde rstones .The yar emos t abundanti npool swit hdetritu san dstone sovergrow nwit hmos so ralga e (Beyer,1932 ; Nielsen,1942 ;Wesenberg-Lund ,1943 ;Jones ,1951) .Edingto n& Hildre w (1973)demon stratedth elongitudina lzonatio no fPolycentropodidae ,wher e P.aonsperea isreplace d by Polyoentropus flavomaoulatus (cf.Nielsen , 1942)i nth edownstrea msections .Thi s isattribute dt oth einfluenc eo ftemperature ,bu ti si nfac tbase do ncircumstantia l evidencean di sno tye tproved .However ,Philipso n& Moorhous e (1976)showe dtha t thetemperatur etoleranc eo fsevera lspecie so fPolycentropodida ei sver y important inlongitudina lzonatio nan dtha tthi si sdirectl ylinke dwit hthei rventilatio n behaviourfo rth eoxyge nintak e (Philipson,1978) . Pleatroonemia aonspevsa preferssubstrat etype swher epre ydensit yi shig h

Table33 .I.B .value sfo r Pleotroanemia oonspersa (N= 233 )i nth efiel d classificationo fth esubstrate si nth eSnijdersveerbeek .

Sort Sand Gravel Detritusi

3 -4.4 -6.4 16.7 1 i I 1 I 1 1 4 -6.0 0.2 -6.3 -2.2 16.7 I 1 i 1 1 1 1 1 1 2 -6.2 -1.4 3.1 -2.2 -6.3 -2.2 16.7 , 1 1 1 1 r i 1 1 1 1 1 ' 1 1 1 ' 1 1 -1.4 -I 0.9 3.7 1.6 -1.9 -1.1 -6.3 -1.5 -1.7 12.4 12.8 1.7

1 -4.6 -4.1 FD L CD CD+LCD+F D L+FD B L CD CD L CD+L St Sh Italicvalue s indicate significant over-representation

101' Table34 .I.R .value s for Pleotvoonemia oonspersa (N= 233 )i nth egrain-siz e Classificationo fth e substrates inth e Snijdersveerbeek.

Substrateclas s

1 2 3 4 5 6 7 8 9 JLO 11 12 13 14

phiinde x detritus

7 6 5 CD CD+L

Sort5,10 % -0.8-2. 2-5. 0 -4.2-1. 4-2. 2 0.2 -2.8-4. 9 1.4 - 13.3 12.5 1.1 Sort6,10 % -0.8-0. 8-2. 2 -3.9-2. 7-2. 9-2. 1-3. 2-4. 2-2. 4 - 13.3 12.5 1.1 Sort7,10 % -0.8-1. 2 -1.6-0. 8-1. 6 -1.9-4. 4-4. 6-5. 3 1.5 13.3 12. S 1.1

QlMdQ3 lndeX xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD CD+L x4x Sort8,10 % -2.3-4. 0-2. 5-2. 9-2. 1-2. 9-1. 4-2. 8-3. 4-3. 5 1.4 13.3 12.5 1.1

Italicvalue s indicatesignifican t over-representation

(Hildrew& Townsend , 1977), regardlesso fth ekin do fprey ,becaus e theyar eno t selectivefeeders . P.oonspersa isa 'si tan dwait 'predato r (Hildrew& Townsend , 1976)tha tcatche sit sfoo db ya characteristic ,bu tirregular ,ne tconsistin go fa smalldwellin gtub e (e.g.unde ra stone )tha texpand sa tbot hend st ofor ma funnel - shapedcatchin garea .Mostl yth elarges t funneli sdirecte dupstrea m (Nielsen, 1942; Edington,1968 ;Tachet ,1971) .Thi sne ti sver y large,whic hi scharacteristi cfo r speciesinhabitin g slow-runningwate r (Wallace,Webste r& Woodall ,1977) . Iti s colouredbrow nb yattache ddetritu sparticles ,whic hwa sregularl yobserve di nth e rearingchanne lwher e P.aonepersa started spinningnet sa ssoo na si twa sintroduced . Insmal lstream sth enet sma ycove rlarg e surfaces givingth eimpressio ntha tth e streami sovergrow nwit hfung io rsom ekin do fthrea d formingbacteri a (cf.Wesenberg - Lund. 1911). P.oonspersa consumesal lanimal s driftingo rswimmin gagains tth ene t andtrappe di ni t(Dittmar ,1955 ;Edington , 1968),bu tespeciall ymicro-crustace aan d insectlarva ear eeate n (Nielsen,1942) ;Townsen d& Hildre w (1978)foun d thatal l instarsea tstoneflie san dchironomids ,bu tth esmalle rlarva econsum emor emicro - crustaceaan dth elarge rlarva emor epre y fromterrestria lorigin .Detritu s formeda n importantpar to fth egu tcontent so flarvae ,bu ti ti sno tknow nwhethe r this reflects active feedingo ndetritu so ri sth eremain so fth egu tcontent so fpre y animals (Winterbourn, 1978),althoug hi ti sknow nfo rsom especie so fPolycentropodida e that theyfee do ndetritu sa swell ,especiall y species inhabiting slow-runningwate r (Malas& Wallace ,1977) .

Capturenet sonl yfunctio nstatisfactor yi nslow-runnin gwaters ,sinc e theyar e damagedb yhig hcurrent s (Edington,1968) .Thi smake si timprobabl e that Pleotrocnemia isdependan to ndrif tfo rit sfoo dsupply .Mor elikely ,animal sswimmin gagains tth e netfor mth emai npre yorganism s (Hildrew& Townsend , 1976).Whe na positiv ecorrela tiono f P.oonpsersa witha certai nsubstrat etyp ei sseen ,thi swil lb ea functiona l

102 responseo fP . conspevsa topre ydensity ,whic hmean stha tsubstrat epreference s of thepre ywil ldétermin eth edistributio no f P.aonspersa (Hildrew& Townsend , 1977). Inth eSnijb ,detritu s substrateswer e themos tdensel ypopulate d substrates (especially chironomids),whic hexplain swh y P.conspersa prefersthes esubstrates .Moreover ,t o beabl et obuil da net , P.aonspersa needssubstrate s thatprojec tfro mth estrea m bed,suc ha sstones ,leafpack san dstick s (CD). Thesewil lb eth esite swher eon e shouldfin d P.aonspersa larvae,an dth edat apresente dabov efull yconfir mthi sfo r the Snijdersveerbeek.

4.2.2.6 Ephemeradanic a (Miller) (Ephemeroptera:Ephemeridae )

Population density E. danica wasfoun d in10 7o fth e 382sample s inth eSnijdersveer beekwit h43 6specimens .Th enymph s onlyoccurre d inth eSection s 4,5 ,6 an d8 (325 samples):i n60 $o fth esample si nSectio n6 ; in45 $o fth esample s inSectio n5 ;i n 14$o fth esample s inSectio n8 ;an di n10 $o fth esample s inSectio n4 . Inth eRatumsebeek ,50 4specimen swer e found in8 0sample s (outo fa tota lo f 195). Comparisono fth edensity-pe rsurfac euni treveal stha tthi si smuc hhighe r in theRa btha ni nth eSnijb :6.2 2 and4.0 7 specimens,respectively ,pe rsampl eo f15 0 2 cm ,givin g41 4an d27 1pe rsquar emetre .Compare dwit hth edensitie sgive nb y Percival& Whitehea d (1926)o f1850-207 5pe rsquar emete rthi s israthe rlow ,bu tth e figuresar ei nth esam eorde ro fmagnitud e asreporte d forth erelate d Ephemeridae nymph Hexagenia limbata: 266 (Lyman,1955 )an d 758pe rsquar emetr e (Neave,1932) . Theyar ehowever ,muc hhighe rtha nth efigur eNeedha m (1917/18)presente dfo r E.similans, 32pe rsquar emetr eo rHun t (1953)gav efo r Hexagenia limbata, 127-365 persquar emetre ,wit ha naverag eo f 153pe rsquar emetre .Zinmerma ne t al. (1975) showedtha tth edensitie so f B.limbata aregreatl ydependan to nth eag eo fth enymph s andar ealway shighes tfo ryounge rnymph san dlowes tfo rfina linstars ,graduall y decreasingwit hth eincreasin go fag e (size).The yquot eHudso n &Swanso n (1972),wh o statethat'migratio ni smos tintensiv ei npopulation so fmor etha n10 0specimen s persquar emetre .Thes edat ao nage-correlate d density areconfirme d for E.danica in thispresen tresearch ,which show s thesam epatter n (Table9 an d 10,Subsectio n 4.1.3.3.)

Life cycle Inth etw ostream sunde r investigation,th elif ecycl eo f E. danica appearedt ob ebivoltin e (Fig. 38),which i si nagreemen twit hdat aknow nfro mothe r areas (Landa,1968 ;Sowa ,1975b ;Svensson ,1976 ,1977) ,althoug hsom eauthor s found thati tma yb eunivoltin e (Thibault,1971 )o rtrivoltin e (Svensson,1977) ,dependan t onsuc henvironmenta lfactor sa stemperatur ean dphot operiod .Plesko t (1958,1960 ) statedtha ti ti scommonl y acceptedtha t E.danica isunivoltin e andillustrate dthi s withth efac ttha tsh ehardl yfoun dnymph s inJuly .Considerin g thestrea m (the Schwechat,i nAustria )sh einvestigated ,i ti smor elikel ytha tthes edat aar e unreliablebecaus eo fth ecrud esamplin gmetho duse dan dth ejoinin go fsample s from

103 78; i.

—,.i.,iminifiiit-TTT-f

77; -9-SZ ^

77; *S-t8 fHlïïÏÏÏTTTW-rmrtTi-^-,

77; «I-44

77; J7-« j ^^THi»rfïïT[TTlhiw*. 77; J3-36 Jfc

77; CT-3ZJ

" IHTt-rrm^,,

77: 13-14

N- as

N- 15 W 77- I

N - 7-4

N- 88 74: «S-48

N- 87 74; «1-n

N - 42 7*: J7-40

»•ii.'iiiiifnnTT'V^ N- «9 74; J3-34;

M- 3B 7«: 29-32 !

N- 29 7«; 25-28}

N- 10 74: 21-21

74: I7-2Q m

74: IJ-14J

74: ^12

ftf.IllTTTTr~v-UTninn 74: 5- a

74: I- 1 N- e

75: «9-S2 N. 19

mfült IWfTTn t^i TS: «S-48^ N- 14

75: 11-n N- a inn um 75: J7--HJ1 N- 4

t < «n nTi' iii*i3daaaaaciaassiaaasiasi 18

LENGTH' CLASS ( Mf-') Fig.38 .Lif e cyclehistogram so f Ephemera daniaa showingth edistributio n(% )o f nymphal body lengthan dadult s (98)pe rfour-wee k period.

104 upstreaman ddownstrea marea so fquit edifferen ttemperatur eregimes . Inth eSnij ban dth eRa btw ocohort s arefoun do nman yoccasions .Th emateria l wasno t investigated inenoug hdetai l (e.g.o nwingpa ddevelopmen tan ddistinctio n betweenmale s andfemale s forolde rnymphs )t oexclud ewit hcertainl y thepresenc eo f univoltine specimensbu tthei rpresenc eseem shardl y likely.Som eo fth ever ylarg e nymphsfoun d inautum nmigh t spendthre eyear s inth e streamhavin gmisse dth e previousemergenc eperiod ,althoug h iti sals opossibl etha tthe yhav egrow nfaste r duringth e lastsumme rtha nmos tother so fth esam eag ebecaus eo fextremel yfavour ablefoo dconditions .I nth eAchterhoek , E. danioa emergesfro mth een do fMa yunti l theen do fJun e (Weeks21-26) ,afte rwhic hth efirs tyoun gnymph s arefoun di nAugust . Theyar eb y thenalread y startingo nthei rsecon do rthir dmoult .I nth eautum nther e isa perio do f fastgrowth ,whil e inth ewinte rgrowt h isretarde d (cf.Thibault , 1971;Sowa ,1975 ;Svensson ,1977) .Th epresenc eo fver ysmal lnymph sfro mAugus tint o Mayindicate stha ta tleas tsom eo fth eegg so rbatche so fegg shav eretarde dhatching . Thelo wnumbe ro fsmal lt oaverag e sizednymph s inth eRa b inth esprin go f197 7 andth e largerspecimen s inth eautum nan dwinte r 1977-1978migh tb eth eresul to f thedesiccatio no fpart so f thestrea mi nth esumme ro f 1976.Earl yhatche dnymph s mayno thav esurvived ,leavin gonl yth eoffsprin go fth e 'resting'eggs ,whic hi s probablymuc hsmalle ri nnumbe rtha ntha to fearl yhatche deggs ,considerin gth e ratiobetwee nth enumbe ro fsmal lnymph s inWee k37-4 0an dthos eappearin gafte rWee k 45.

MicrodietribuUon The fieldclassificatio no fth esubstrate sshow sclearl ytha ti n bothstream s thehighes tpreferenc e isfo rS+CD+F Di nSor t 1(Table s3 5an d36) . Secondly,G+CD/E D andS+C D ispreferre d inth eSnijb .I nth eRa bonl ya sligh t preferencefo rG+ L andS+F Dwa s established.Detritu s substrateswer ealway savoide d (onlyon especime nwa scaugh ti na lea fpac kan dthi sconcerne da nymp hread yt o emergefro mth e streaman dprobabl y onit swa yt oth ewate r surface).Analysin g Tables3 5an d 36a tles sdetaile dclassificatio nlevel sreveal stha t Ephemera danioa prefersSan d farabov eGrave l inth eRab ,bu t inth eSnij bGrave li schose nquit e often,althoug halway s lesstha nSand ,excep ti nSor t3 . Inbot hstreams ,minera l substratesmixe dand/o rcovere dwit hCoars ean dFin e Detritusar ealway spreferred .Thi sagree swit hth epreliminar yconclusion sdraw nb y Tolkamp& Bot h (1978),althoug hsom edifference s canb eseen .However ,th eresult so f thelaborator yanalysi s showed thatsom esample s includedi nth eS+F Dsubstrat ei n thepreliminar y classificationi nfac tbelonge dt oth eS+CD+F Dsubstrate ,becaus e largeamount so fC Dwer ehidde nbelo wth esurfac ean dthi sknowledg eha dno tbee n includedi nth efiel dclassificatio na ttha tmoment .Anothe rreaso nfo rdifference s inth epreference s foundthe nan d laterma yhav eresulte d fromth efac ttha tth e PeriodJanuary-Apri l 1977wa sno tinclude di nth epreliminar ydata ,whic hmean stha t especiallyth esmalles tan d largestspecimen swer eunder-represente di nth earrange ant ofth epreliminar yresults .Thi s canhav econsiderabl e influenceo nth etota l

105 Table35 .I.H .value s for Ephemera daniaa (N= 436 )i nth efiel dclassificatio no f the substrates inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 2.1 2.7 -7.5 l 1 l i 1" ' 1 4 -4.9 9.0 -0.1 s'.o -7.5 i i I 1 1 1 1 1 2 -5.4 -0.5 2. 7 9.3 -0.1 -7.5 I i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -3.7 -4.0 -3.0 4.8 0.9 10.3 0.4 1 -4,. 3 -5.3 -3.3 J, -1.3 6.6 St Sh FD L CD CD+L CD+FD L+FD -0.1 CI L CD+L B L CD Italicvalue s indicate significant over-representation

Table 36.I.R .value sfo r Ephemera daniaa (N= 504)i nth e field classification of thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 9.7 -5.1 -9.8 i i 1 l 1 1 4 -2.9 18.3 -4.3 -2.7 -9.8 i i i 1 i 1 1 1 1 2 -4.1 1.6 -1.5 22.3 -4.3 -2.7 -9.8 1, , P i 1 ,l 1 1 1 1 1 1 " 1 1 II 1 1 1 1 -2.2 -3.9 1.6 • -1.6 -1.0 -1.0 24.2 -0.4 -4.3 1.5 -3.4 -3.3 -9.1 -2.0 St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L +FD

Italicvalue s indicat e significant over-representation

results,becaus enymph so fdifferen t sizessho wdifferen t substrate preferences (Tolkamp& Both ,1978) . Tables3 7an d3 8giv eth e I.R. values forth egrain-siz eclassifications .I n bothstreams ,th ehig hpreferenc e forC Dsubstrate s (Class 14o r12 )a tth e 11detritu s levelmove st oth efin eminera l substratesa tth e 101level ,whic hindicate s that thisconcern sSan dsubstrate swit h 1-10%organi c detritus.Th e distributional pattern seeni nth efiel dclassificatio ni srepeate di nSort s 5-8:i nth eSnij b therei spre ferencefo rQ 1 =2 ,M d= 3 an dQ 3= 3 ,see ni nSor t8 a s22 xan d 23x;bu tals ofo r moregravell ysubstrat ewit hQ 1= 5 , M d= 3 ,2 ,o rÏ an dQ 3= 2 (Sort s 5-7),see ni n Sort8 a sx3x ,x2 xan dxîx .I nth eRatumsebeek , Ephemera daniaa prefers thewel l sortedmaterial swit hQ v Md andQ 3= 3 ,althoug hQ 1= 3 an d4 ,M d= 2 an dQ 3= 3 o r 4i sals ofavoured ,whic hi sconfirme di nSor t8 b y23x ,33 xan dxxx .Fro mthi s grain-size classificationth edifferenc ebetwee nth etw ostream si nth epreferenc eo f E. daniaa forGrave li sagai nclear .I nth eRab , E.daniaa occursonl yi nSan dsub strates (Md- 1 o rmore )wit h lesstha n 50% gravel (Q1= 4 , 3),whil ei nth eSnij b

106 Table37 .I.R .value s for Ephemera daniaa (N= 436 )i nth egrain-siz e classificationo f the substrates inth e Snijdersveerbeek.

Substrate class

1 2 3 4 5 6 7 8 9 10 11 12 13 14

phi index detritus

7 6 5 4 3 2 Ï 1 2 3 4 CD L CD+L

Sort5,1 % -1.1 -1.6 5.3 -0.5 0.6 -3.3 -4.4 -5.5 -1.9 -0.7 10.2 -5.3 -3.0 Sort5,10 % -1.1 -2.1 6.5 0.5 0.8 -3.5 -2.9 -5.5 8.0 0.9 -3.2 -5.3 -3.3 Sort 6,1% -1.1 -1.6 -1.8 3.5 1.1 2.0 -3.1 -5.0 0.1 10.2 -5.3 -3.0 -3.3 Sort6,10 % -1.1 -1.1 -2.1 -1.9 5.8 2.3 2.1 -2.2 -1.3 7.2 -3.2 -5.3 -3.0 Sort7,1 % -1.1 -1.5 -2.1 -1.1 -1.7 -1.5 -4.6 2.8 -2.4 -0.7 10.2 -5.3 -5.3 -3.3 Sort7,10 % -1.1 -3.4 -2.1 -1.1 -1.7 -1.5 -4.6 4.2 5.1 0.9 -3.2 CD+L XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L QlMdQ3 index x4x -3.0 Sort8,1 % -2.2 -1.9 4.1 1.1 2.0 -2.6 -0.4 -5.5 -0.2 -2.6 -0.7 10.2 -5.3 -5.3 -3.3 Sort8,10 % -2.4 -2.4 6.4 2.3 2.4 -2.8 0.5 -5.5 6.0 5.4 0.9 -3.2

Italicvalue s indicatesignifican t over-•representation

Table 38.I.R . values for Ephemera danioa (N= 504)i nth egrain-siz e classification of the substrates inth eRatumsebeek .

Subsitrat e class 10 11 12 13 14 1 2 3 4 5 6 7 8 9 detritus phi index 2 3 4 CD L CD+L 7 6 5 4 3 2 Ï 1 12.4 -8.8 -1.7 7.1 -3.0 0.4 -2.8 -4.4 -1.6 Sort5,1 % -1.0 -1.0 -3.5 2.4 -3.3 -9.1 -2.0 Sort5,10 % 9.0 -2.5 0.4 -2.7 2.7 10.'9 -1.0 -1.0 -3.5 2.1 12.4 -8.8 -1.7 -3.2 -3.0 -2.0 2.0 2.0 -0.4 Sort 6,1% -1.6 -1.4 -3.3 -9.1 -2.0 -3.2 -2.0 1.3 5.7 10.4 Sort 6,10% -1.6 -1.4 -3.2 -8.8 -1.7 -1.6 -0.8 -8.3 9.8 -0.4 12.4 Sort7,1 % -3.3 -9.1 -2.0 Sort7,10 % -1.6 -0.8 -8.9 16.2 8.6 23x 33x CD L CD+L x3x x2x .xlx xlx XXX lxx 22x QlMdQ3 index xxx x5x X4x -2.8 -4.8 0.5 -1.6 12.4 -8.8 -1.7 Sort 8,1% -1.6 -1.4 -3.2 -3.0 -2.0 2.0 10.1 -2.7 -1.0 6.6 10.9 -3.3 -9.1 -2.0 Sort8,10 % -1.6 -1.4 -3.2 -3.3 -2.0 1.3 12.2

Italicvalue s indicates i gnificant over--representation

Gravelsubstrate s (M.= ï o rless )wit hles stha n50 1San d CQ3= 2 )ar eals opreferred . Calculationo £?h eI.R .value sfo rsevera l lengthclasse so f E.danica nyn-phsi n Sort5 fo rth eRatumsebee k leadst oth econclusio ntha tth eover-representatio n in

substrateswit h( L= 4 (Tabl e 38)i scause db ynymph so f5-2 0u man di nQ 1= 3 b y nymphs of0-1 0J .Th e latter (lengthclas s 1-10)ar eals oresponsibl e forth epref -

107 erencei nQ ,= 3 ,whil eth elarges tspecimen s (20-27irai )prefe r especially Q1 =2 . Consideringth emedia ngrai nsiz e (Sort6 )hardl yan ydifferenc ebetwee n length classesca nb esee ni nth eRatumsebeek ,althoug h10-2 0m mnymph shav ea stronge r preferencefo rM ,= Ï o r1 tha n2 o r3 .

Inth eQ 3 classification (Sort7 )onl yth esmal lnymph s (0-10mm) , especially thesmalles tone s (0-5 mm),prefe rbot hQ 3= 3 an dQ 3= 4 ;th elarg e specimens favour onlyQ ,= 3 .Thes edifference sbetwee nyounge ran dolde rnymph s returni na condense d ^3

Table39 .I.R .value sfo r Ephemera danica perlengt h class (A)an d season (B)i n theSnijdersveerbee k inSor t8,10% .

Length N Subs: trät e class and ig index QlMc class and 1 2 3_ 4_ 5_ 6 7 8 9 10 11 12 13 14 Season xxx x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 0 3 -0.3 1.5 -0.4 1.8 -0.4 -0.4 -0.6 -0.6 -0.5 -0.6 2.5 -0.5 -0.5 -0.3 1-5 87 -1.0 -2.0 3.7 -1.6 6.9 -2.3 0.0 -1.6 1.5 1.2 0.2 -1.2 -2.1 -1.7 6-10 179 -1.4 -2.6 2.6 1.0 -0.5 -2.1 0.9 -3.8 3.8 4.8 2.0 -1.2 -3.1 -2.1 11- 1 5 116 -1.3 -0.6 4.0 4.9 -0.8 -1.9 0.1 -3.2 3.1 3.1 -0.8 -2.5 -3.3 -2.0 16- 2 0 35 -1.0 -0.5 1.9 -0.2 -1.5 2.7 -0.3 -1.4 3.7 1.4 -1,2 -1.5 -1.8 -1.1 21- 2 7 16 -0.7 0.6 3.0 -1.0 1.0 -1.0 0.3 -1.3 1.5 -0.6 0.4 -1.0 -1.2 0.6 Total 436 -2.4 -2.4 6.4 2.3 2.1 -2.8 0.5 -5.5 6.0 5.4 0.9 -3.2 -5.4 -3.3 B Spring 78 -1.0 -1.8 2.8 -0.5 -1.8 -1.0 -2.4 -1.4 8.0 5.8 -0.0 0.6 -2.9 -2.0 Summer 88 -1.2 -2.9 4.0 -2.6 8.3 -2.5 1.0 -1.3 -1.5 0.8 0.8 -1.4 - - Autumn 110 -1.9 -2.1 -0.8 11.8 -1.9 -1.5 -0.1 -3.6 3.7 3.8 -1.9 -2.7 -3.3 -1.5 Winter 160 -1.0 1.4 5.0 -2.2 0.8 -0.8 4.8 -4.0 1.9 2.5 1.7 -3.0 -3.4 -2.3

Italicvalue s indicate significant over•representation

Table40 .I.R . values for Ephemera danioa perlengt h class (A)an d season (B)i n theRatumsebee k inSor t8,10% .

Length N Substrate i class and Q ig index class A and 1 _ 2 3_ 4_ 5 6 7 8 9 10 11 12 13 14 Season xxx x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x

A 1 - 5 198 -1.0 -2.0 -2.0 -4.0 -3.5 -3.0 11.0 -1.5 2.7 4.1 7.1 -1.8 -5.9 -1.5 6 - 10 170 -0.9 -0.3 -1.9 -0.4 -1.8 2.3 8.4 -2.0 -2.6 -2.2 12.8 -2.1 -5.2 -0.3 11 - 15 44 -0.5 1.2 -1.0 -0.5 1.6 6.1 1.8 -0.4 -2.0 -0.5 -1.1 -1.1 -2.9 -1.0 16 - 20 41 -0.5 0.2 -1.0 0.1 3.0 2.0 -0.1 0.3 -1.1 2.6 -1.0 -1.0 -2.5 -1.0 21 - 27 50 -0.5 -1.0 -1.0 -1.2 -0.3 -1.8 -0.2 -1.8 -0.9 15.2 -1.1 -1.1 -2.8 -1.0 99 1 -0.1 -0.1 -0.1 -0.3 -0.3 -0.3 -0.4 -0.3 -0.4 -0.3 -0.2 -0.2 1.8 -0.1 Total 504 -1.6 -1.4 -3.2 -3.3 -2.0 1.3 12.2 -2.7 -1.0 6.6 10.9 -3.3 -9.1 -2.0 B Spring 65 - - -1.4 -0.9 -0.7 -3.1 -1.0 -2.4 0.9 9.3 _ _ -2.8 _ Summer 99 -1.1 - -2.0 -0.7 -1.4 1.4 5.5 -1.4 -3.7 11.2 2.7 -2.2 -3.3 -1.6 Autumn 263 - - - 0.2 -2.0 1.2 13.5 -0.2 2.8 _ 8.7 _. -10. 5 -1.0 Winter 77 - -0.5 - -1.7 1.3 1.2 1.2 1.2 -1.5 -1.6 6.4 - -2.4 -1.4

Italic values indicate significant over•representation

108 formi nSor t 8 (Table 40A).Th epreferenc e forxx xan d33 xi scause db y0-1 0ran nymphs;fo r23 xb y 0-5m man d 15-27m m animals andth esligh tover-representatio ni n x1xb yanimal so f 5-20ran length .I tshoul db enote dtha t10-1 ran5 nymph sprefe rx1 x

substrates (Q1 = 5,1 ,Ï ;M d = 1; Q3 =3) . Analysiso fth eSnijdersveerbee k datafo rth enympha lsiz eclasse so f Ephemera inSor t 8 (Table39A )confirm s thepreliminar y conclusionspreviousl ydraw nfo rpar t of,thedat a (Tolkamp& Both , 1978).Large rnymph sprefe rgravell y substrates:20-2 7 mmnymph sar emostl y foundi nx3 xan d 15-20m mnymph s inx1x ,althoug hals oi nsan d (22x)wit hdetritus .Smalle rnymph soccu ri ngrave la swel la si nsan d :0- 5m m nymphsespeciall y inxT xan dx3 xsubstrate san d 5-15m mnymph si nbot h22x ,23x , 33xsubstrate swit hdetritu s andi nx3 xan dx2 xsubstrates .Fro mal lothe rclassi fications (Sort5-7 ) thesam epictur eemerged . Comparisono fth eI.R .value sfo rth esevera lnympha lsiz eclasse si nSor t2 (notpresented )wit hth edirectl ycomparabl epreliminar y resultsdoe ssho wsom edif ferences,fo rreason smentione dearlier . Betweenseason s thedistributiona lpatter nfollow sth epreference so fth emor e abundantlengt hclasse spresen t (Tables39 Ban d 40B). Inth eSnijb , E.danica prefers sandwit hdetritu s substrates (22x,23x )i nspring ,whe nal lnympha lsiz eclasse s arequit enumerous .Thi spreferenc eshift s tomor egravell ysubstrate s insumme r (xTx,x3x )whe nespeciall y thesmal lnymph sar eabundant .I nautum nthi sdistributiona l patternremains ,althoug ha sth enymph sgro wa shif tbac k tosan dca nb eobserved . Inwinte rth epreference s aremor eo rles sequall ydistribute dove rgrave lan dsand . Inth eRab ,a similarchang eo fpreferenc e fromsan dt omor ecoars esubstrate s aftersprin gi spresent ;althoug hsubstrate s ascoars ea sth eone spreferre d inth e Snijbshowe dn o over-representation,the ywer ever yscarc ei nth eRa banyway . Theseshift s inpreferenc ecoincid ewit h thedecreas ean dincreas eo fth ewate r flowi nth estreams ,whic h ishig hi nwinte ran dsprin gan dlo wi nsumme ran dautumn . Inth eRatumsebee kthi s ismuc hmor epronounce dbecaus eo fth emuc h largerdrainag e area.Som eo fth edifference s insubstrat epreferenc emigh tb e linkedt odifference s inth ecurrent-spee dpatter no fth etw ostream san dthei reffect so nth esubstrat e compositionan d spatialdistribution .I nth eSnijb ,Grave li soriginall ypresen t in thestrea mbotto mbecaus eo f thefluviatil egrave ldeposit san di toccur sove rth e totalwidt ho fth ebed ,bar eo rcovere dwit ha laye ro fsan do rdetritus .I nth eRab , Graveli spresen ti nfa rsmalle rquantitie san di tofte nconsist so firon-condensates , formedi nth estream ,an daccumulation so fth eheavie rmateria lremainin gafte r erosiono fbank san dbed .Th eRa bstrea mbe d ismuc hwide ran dth emaximu mcurren t speedsar emuc hhigher .I nth eRab ,th egrave li smor eo rles srestricte dt oth e riffleso rth emiddl eo fth ebed ,place swher eth ecurren ti shighest .San dan d Detritus substratesar emor eabundan t inth epool san dalon gth ebanks . Since E.danioa nymphsprefe rminera lsubstrate scombine dwit hdetritu s (especial lyfin edetritus) ,whic hoccu ronl y inplace swit ha lo wcurren tvelocity ,th eab senceo f E.danica fromcoarse ,gravell y substrates inth eRa bcoul db ea reactio nt o

109 theabsenc eo fdetritus ,whic h isswep tawa yb yth ecurrent .Moreover ,als oth e fine sandingeste d forit sbacteria l growth (Zimmerman &Wissing ,1978 )i sabsen there . Summarizingth e datapresente d above itca nb e statedtha t Ephemera danica pre ferssubstrate swit ha tleas t25% ,an dpreferabl y 75$fine r than0. 5mm ,o r25 1 coarser than4 m mbu t finertha n3 2mm ,althoug h forth e latter isno tcertai nbecaus e ofth e limitednumbe ro fsample s inthi s substrate type.Th e importance ofth epre senceo ffin edetritu s incombinatio nwit hminera l substratesi sbes t illustrated in themos tdetaile d field classification,an dth eknowledg e thatth e finesan dsub strates inSor t 8contai n largeamount so ffin edetritu s confirms thisver ywell . Thisrelationshi pwit hfin edetritu swil lcertainl y be linkedwit h E. danioa's feeding habits,sinc ei ti sa detritivor eo rcollecto r (Cummins, 1973),livin g fromth e microbial floraan dth eorgani cmateria l infin edetritus .The yma y also ingest large amountso finorgani csedimen t forth emicrobia l growtho ni t (Zimmerman& Wissing , 1978).Ephemerida ear ecalle d 'mud-eaters' (Bengtsson,1924 ;Hunt ,1953) , although it hast ob eoxyge nric hmu d (Wautier& Pattee ,1955 ;Erikseii ,1963a ,b ; 1964;1966 ; 1968),whic hemphasize s the facttha tdetritu s feeders isprobabl y abette r description. Although Ephemera isa eurythermou s genus (Percival &Whitehead , 1926;Kamler , 1966), E.danioa occurs instream swit h lesshig htemperatur e fluctuationstha n E.vulgata (Beyer,1932 ;Fo xe t al.,1934 ;Pleskot , 1953).Thi s isprobabl ywh y E.danioa isfoun d instreams ,whil e E.vulgata occurspredominantl y inth emu d substrates ofpond s andlarge r streams (Foxe t al, 1934;Molle r Pillot, 1971). Percival &White head (1926)foun donl y few E.danioa inmu d andthe yoccurre dpredominantl y insand y streamsi nth esubstrate swit hth ecoarses t fractionbetwee n 0.05 and 1.0m m (65$ coarse sand, 2%fin esan dan d1 $ silt).Th eabundanc e of E.danioa decreasedwit h an increasing amounto fsil tan dcla y (finertha n0.0 5 mm),whil enymph sneve r migrated toneighbourin g substrateswit h ahighe rsil tcontent . E.danioa lives inth ebotto m insmal ltunnels ,whic har eburrowe dwit h their strong front legs andmandible s and keptope nwit hth eai do fa naxia lwate r currentove rth ebac ko fth enymph s thati s theresul to fthei rdorsall yplace d gills (Eastham,1932 ;Uhlmann ,1975 ,p .66) . Apparentlya smallamoun to fcla yi snecessar y to stickcoarse r grainstogethe r in ordert oobtai na stabl etunne l structure.Eastha m (1939)suggeste d thatth e preference of E. danioa forcertai nsubstrate smigh tb edetermine d by thenee d fortunnel s of somepermanency ,eas yt omak e andeas y toleav ean dpermittin g anaxia lwate r current withoutth etunne lwall scollapsing .A highsilt/cla y contentmigh tb e detrimental becauseth eparticle s canobstruc tgil lmovemen t andclo gthem ,preventin g proper respiration. Most authorsreportin g onsubstrat epreference s of Ephemera danioa give asth e characteristichabita tth esan dsubstrat e inth ecurren t (Geijskes,1935 ;Pleskot , 1953; Collins, 1971), thequiete rplace snea rth ebank swit hmu do rcla y fractions (Percival& Whitehead , 1926;Beyer ,1932 ;Dittmar , 1955),th e shelteredplace s in stony-gravellybottoms ,wher e finegrave l (Percival &Whitehead , 1930),sand ,mu d and detritus (Sowa,1975a )accumulate ,o rcoars esubstrate s nearth ebanks ,wher e the

110 current isslac k (Jones,1949) .Thes edat aagre ewit hthos e foundi nth eRatumsebee k andth eSnijdersveerbeek , althoughth eresult so fthes einvestigation s emphasizeth e importanceo fth epresenc e oforgani cdetritu san dfin esand .

Substrate-seleetion experiments A serieso fexperiment swa sconducte dt oestablis h theeffec to fcurren tvelocit yo nth esubstrat e selectiono f Ephemera dxnioa. Sub stratesrangin g from0.05 0m mt o8 m mwer eoffere da thig h (10cm/s )an dlo w( 5cm/s ) currentvelocities ,an dsubstrat eselectio nwa sdetermine dafte r2 4hours .Th enymph s wereintroduce d intoth estagnan tstrea mo neac hgrai nsiz ei ndensitie so f1 ,2 o r4 pertray .Afte r introductionthe ywer eexpose dt oth ecurrent .Compariso no freplicate s showedn osignifican t differencesbetwee nreplicate so rth edensitie sused . Therei sa distinc teffec to fth ecurren to nth esubstrat e selection (compare Fig.39 aan d39c) . Witha stron g currentsignificantl ymor enymph swer e foundo nth e downstream screensan dburrowe d inth edownstrea m substrates,mor eo rles sindependant - lyo fgrai nsiz e (Fig.39b) . Witha slo wcurren t thiseffec t isno tnotice d(Fig . 39d).Thi s leadst oth econclusio ntha tfo ra lo wcurren tvelocit y thesubstrat e selectiono f Ephemera isvoluntary ,bu tfo ra hig hcurren tvelocit yenforced .Fig . 39cshow s that E.danioa prefers 2-4m mgrains ,an dthi spreferenc edecrease st obot h coarseran dfine rparticl e sizes,wit hth eexceptio no f0.0S 0- 0.12 5nm . Inth e lattera sligh toverrepresentatio nca nb eseen . Inexperiment swher eth e0.05 0m mparticl e sizewa ssubstitute db yon eo f1 6m m thesam epreferenc e for2- 4m mwa ssee n(Fig .39 ean d39g) .However ,als o 1,0.12 5 and1 6m mshowe dover-representation .N osignifican tdifference swer epresen tbetwee n thetw oexperiments .Whe nmixe dwit hfin ean dcoars edetritus ,practicall yth esam e substrateselectio nwa sfoun d (Fig.39f) ,indicatin g thatth epresenc eo ffoo dsub stancesdi dno tinfluenc eth esubstrat e selectioni nthes eexperiments . Experimentswit h2 ,4 ,8 an d1 6m mgrain smixe dwit h0.5.o r1 in n(Fig .39 han d 39i)showe dtha t E.danioa hasn osignifican tpreferenc efo ran yo fthes emixtures . Particle sizes8 n man d1 6m mmixe dwit h 1m mar echose nmor eofte nbu tth ediffer encesar eonl ysmall .Compariso no fFig .39 kwit hFig .39c ,39 ean d39g ,demonstrate s thatmixin g thefou rcoars eparticl esize swit h0. 5m mo r1 m msan dlevel sdow nth e differences insubstrat eselection ,althoug h8 m mseem st obecom emor eaccessible . Ina serie so fexperiment swher eonl ytw oo fth epreferre d substrateswer e offered, E.danioa favoured 16m mabov e2 m mo r0.12 5m m (Fig.39 jan d39k) ,bu tn o differencewa sobserve dbetwee n0.05 0an d0.12 5ran (Fig .391) .Also ,a nexperimen t wasstarte dwher egrain so f0.12 5- 1 6m mwer emixe dwit happroximatel y one-third 0.050n m substrate.Th eexperimen t showedtha tmixin gwit hthi sver y finesan d strongly levelleddow nth edifference sbetwee nth edifferen tgrai nsizes ,althoug hove r40 1o f thenymph sdi dno tburro wbu tsa to nth escreens ,whil e 101die ddurin gth eexperiment , probablybecaus eo flac ko ffoo dan dbecaus e theyha dbee nsubjecte dt oexperiment s formor etha n4 8hours .Thi sha dbee navoide d inpreviou sexperiment san dcar ewa s takentha ti nfollowin g experimentswel lfed ,fres hnymph swer eused .

111 Experimentswit htw osiz eclasse so f E.danioa (15-20m man d 20-25mm )wer e con ducted,givin gthe mchoic ebetwee n 1,2 , 4an d8 m mparticle s coveredwit ha thi n layero f0. 5m msan dan dbar e 1,2 ,4 an d8 m msubstrate .Larg enymph spreferre d2 ran andran8 an dn o influenceo fth e0. 5m mcoverin gwa snotice d (Fig.39m) .Smalle r nymphsdisplaye d thesam egrain-siz e selection (Fig.39n )bu tthe y differed fromth e largernymph si nthei rstron gpreferenc e forbar eparticl e sizes comparedwit hth e coveredone s (Fig.39 oan d39p) . Comparedwit hth eresult so fth efiel d investigation thepreferenc eo flarg e Ephemera nymphs forgravell y substratesi sthu sconfirme db yth eselectio no f2- 4m m particles inth elaborator y experiments.Th e(les sdistinct )selectio no fsmalle r particles sizesals oagree swit hth eoccurrenc ei nfine rsubstrate s (22x,23x )i nth e

frequency (%) 60- a b 40-

• nL DS DBUB 50 250 12 4 8 DS DB UB frequency (%)

40-

20- j^J_L=D 125 500 1 2 4 8 16 • 125 500 12 4 8 16 125 500 1 2 4 8 16 S + + + + ++ + + CD frequency (%) 75

60- h

40-

20-

0- r 2 4 8 16 2 4 8 16 2 16 125 16 D 50 125 S + + + + + + + + 1 500 frequency (%) 75 60-

40 vzz. 1 20 I 1 I 0-1 • 1 12 4 8 12 4 8 + - + + + + + + + + 500 500 500 500

112 \\X, phi values t S 4 T M d 3

Î 2^ vr5 i w»v 0 •

Ï •

5 H

6 9 + 7 4

II. (phi value) a Fig.40 .Compariso no f substratepreference s inth efiel d (unshaded)wit h particle-size selection inlaborator y experiments (shaded)fo r Ephemera danioa.

Fig.39 .Substrat e selection inlaborator y experimentsb y Ephemera danioa. Grain- sizefraction s are indicated by thelower ,limi to f thefractio ni n pm (under1 mm ) andm m (over1 mm ). S = endretainin g screen;D S= downstrea m screen ;D B= down streamburrowed ; UB= upstrea mburrowe d (fig.d) ;C D= coars edetritus . Figure Body Numbero f Numbero f Current Note no. length experiments nymphspe r velocity /mm experiment (cm/s) a+b 20-25 3 16 10 20-25 2 32 10 c+d 20-25 6 8 5 20-25 4 16 5 20-25 2 40 5 f 20-25 2 40 5 mixedwit hcoars edetritu s S 20-25 5 24 5 h 20-25 3 24 5 mixedwit h 1.0m m i 20-25 3 24 5 mixedwit h0. 5m m j 20-25 3 16 5 k 20-25 3 16 5 1 20-25 3 16 5 bare(unshaded),coveredwit h 0.5 m+o 20-25 2 24 5 mm (shaded) n+p 15-20 2 24 5

113 field.Th edifference s seenbetwee nlarg ean dsmal lnymph si nth eexperiment s with mixtures ofparticle s sizesagre ewit hth edifference s inpreferenc e seenbetwee n thesenymph si nth eRatumsebeek ,wher eth e largenymph s occurpredominantl yi nfine r substrate (23x),whil esmalle rnymph spreferre d coarsersubstrates . Conclusionsdraw nfro mth efiel dresearc h arethu sconfirme db yth e laboratory experiments,a sillustrate d inFig .40 ,i nwhic hparticle-siz e selectioni nth e experiments isprojecte do nth eQ1M.Q 3grap htogethe rwit h thesubstrat e preferences seeni nSort s5-8 ,10°s .Th enymph s select 2-4mm , 16-32m man d0.125-0.25 0m mpar ticlesi nth elaboratory .Thes eparticl e sizescorrespon dwit hth eQ ,an dM ^particl e sizeso fth esubstrate s selected inth efield .

4.2.2.7 Nemouracinere a (Retzius) (Plecoptera:Nemouridae )

Microdistribution Inth eSnijdersveerbee k thepopulatio no f Nemoura cinerea was rathersmal lan donl y 155specimen swer epresen ti n2 6samples .I nth e Ratumsebeek, 2896specimen swer ecaugh ti n8 7samples .I nbot hstreams ,th ehighes tnumber swer e presenti nlea fpacks .Thi si sclea ri nbot hth efiel dclassificatio n (Table 41) and thegrain-siz eclassification ,althoug honl ySor t 8,10 %i spresente d (Table42) . Over-representation alsooccur so nver y coarse substratesi nth eRatumsebeek . Thispreferenc ei sonl ysee ni nth ewinte rseaso n (Table 42B),whic hi sb yth ewa y theonl yperio dwhe nthi ssubstrat e classi s present,an di tconcern s all length classes (i.e.1- 3an d3-6 ) (Table 42A), althoughrelativel ymor e small (0-3mm ) specimenswer efoun do nminera l substrate (Classes2 an d4- 7i nSor t 8)tha n larger (3-6nm )ones .Thi si si ncompariso nwit hth etota lnumbe ro feac h lengthclass .Th e onlystatistica l cluefo rthi s statement liesi nth esmal ldifferenc ebetwee nth e I.R.value sfo rth e 1-3m mlengt hclas s inx5x ,xi xan dLea fsubstrates ,th eadditio naloccurence so fpositiv e I.R. values inx2 xan dxï x substrates andth e lessnegativ e valuesi nth eothe rminera lclasse scompare dt olengt hclas s 3-6mm .

Table41 .I.R . values for Nemoura cinerea (N= 2896 ) inth efiel d classification of thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -28.1 -1.9 44.2 1 I I 4 20.2 -19.6 4.5 -11.8 44.2 _J I I 1 I I 2 -15.6 -13.8 -5.7 -19.1 L -11.8 44.2 r -i I I ' 1 1 1 1 i r-1-, , 1 1 1 -6.2-16. 9-13. 8 -3.9 -4.7 -4.6 -19.2 -1.7 -3.9 -11.1 4.5 -8.5 53.7 -4.7 St Sh FD CD CD+LCD+F D L+FD L CD CD L CD+L +FD B

Italicvalue s indicatesignifican t over-representation

114 Table42 .I.R .value s for Nemoura cinerea perlengt hclas s (A)an dseaso n (B)i n theRatumsebee k inSor t8,10% .

Length N Substrate class andQ,M.Q _ index 1 a3 class and 1 2 3_ 4 5_ 6 7 8 9 10 11 12 13 14 Season XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 1- 3 680-1. 9 13.4 -3.7 0.9 2.6 -0.8-3. 6-5.1-10.5-2. 3 -3.2-3. 9 15.4 -1.3 4-6 1768-3. 0 15.4 -6.0-3. 5-2. 1-5. 0-7. 3-8.0-17.2-9. 0 -5.7-6. 7 42.4 -4.7 7-9 438-1. 5-3. 0-3. 0-5. 4-4. 9-5. 2-6. 7-2. 7-8. 6-4. 5-3. 4-3. 4 32.9 -1.0 10-12 8-0. 2-0. 4-0. 4-0. 9-0. 8-0. 9-1. 0-0. 7-1. 2-0. 7-0. 5-0. 5 5.2 -0.4 99 2-0. 1-0. 2-0. 2-0. 4-0. 4-0. 4-0. 5-0. 4-0. 6-0. 4-0. 2-0. 2 2.6 -0.2 Total 2896-3. 9 17.3 -7.7-4. 5-2. 4-6.3-10.1-9.8-22.0-9. 9 -7.3-8. 5 53.7 -4.7 B Spring 1125 - - -5.8-5.7-5.8-6.9-11.5-8.6-11.3-13.4 - - 59.8 Summer 30-0. 6 - -1.1-1. 6 -1.5-0. 7-2. 0-1. 4-2. 8-1. 1-0. 9-0. 7 6.3 12.9 Autumn 169 - - - 2.8 -2.2-3. 7-3. 1-2. 1-5. 0 - -2.1 - 7.5 0.4 Winter 1572 - 3.5 - -7.8-1.1-3.5-3.6-7.0-10.4-8.6-7.4 - 41.2-5.1

Italicvalue s indicatesignifican t over-representation

Foral llengt hclasses ,preferenc ei salway shighes tfo rleaves .I nsprin gan d autumnth edistributio n ismainl y restrictedt othes e leafpacks ,whil ei nsumme rth e preferencei shighe rfo rL+CD ,althoug h theI.R . values shouldb econsidere dscep ticallysinc eonl ytw osample swer etake ni nthi s substrate classi nsummer ,onl yon e ofwhic hcontaine d N.cinerea (12specimens) ,agains t fouro fth ete nsample si n winter inLeave s (16specimens) .Th edat afo rth eSnijdersveerbee k haveno tbee npre sentedbecaus eo fth ever y strongresemblanc et oth eRatumsebee kdata ,wit h the exceptiontha tover-representatio ni nlea fpack soccurre d inbot hseason s (winteran d spring)i nth eSnijdersveerbee k only.Similarit yi nresult swa s alsosee nfo rth e lengthclasse si nth eSnijdersveerbeek , although slightover-representatio nwa s found inC Dan dCD+ Li nsprin gfo r large (6-10mm )specimen swhic h isprobabl y the result ofth edisappearanc eo flea fpack si nspring . Nemoura cinerea nymphs areherbivorou s andfee dmainl yo nvegetabl ematte ra s detritusan ddea dleaves ,althoug hthe yals oinges tmos stissu ean dalgae ,dependan t onth eabundanc eo fth evariou s foodtype spresen t (Hynes,1941) .Thu si ti sno t surprisingt ofin da stron grelationshi po fthes estonefl ynymph st odetritu ssub strates,a fac treporte db ysevera lauthor s (Geijskes,1935 ;Dittmar , 1955). N.cinerea iswidel y distributedi nEurop e (ubiquist)an doccur s invarious , strongly-differing biotopes,suc ha strickle s fromsprings ,lowlan d streamsan d rivers.I ti sals o frequently foundi nlittora l zoneso fpond s and lakes (Brinck, 1949; Hynes,1941) .However ,i nth eNetherland si ti sonl yfoun di n(slowly )runnin g wateran d ismos tabundan ti nsmal lwoodlan d streams,whic hofte ndesiccat ei nsummer . The lifecycl eo f N. cinerea iswel ladapte dt olif ei nlea fpack san d summer-dry streams (Bontenbale tal. , 1979).I nth estud yarea ,th elif ecycl eo f N.cinerea is clearlyunivoltine ,wit hgrowt h inautumn ,winte r andspring ,whe n leafpack sar e abundant.Adult s flyfro mearl yApri l andcontinu et od os owel l intoJune ,an dfirs t

115 instarnymph sar epresen tfro mAugus tt oFebruary ,althoug hmos tnymph shatc hlat ei n autumn(October/November) . Thismean stha twhe nfoo dcondition sar eunfavourabl e inth estream , N.cinerea isi nth eadul to reg gstage .Unfavourabl enutrititiona l conditionstha texten dth elif ecycl efro munivoltin et oalmos tbivoltine ,a sreport edb yLillehamme r (1975),.wer eno tobserve di nth estream sunde rstudy .

4.2.2.8 Lùimiusvolckmar i (Panzer),Etoi saene a (Müller),an dOulimniu stuberculatu s (Müller) (Coleoptera:Elminthidae )

Microdiatribution Limnius volohnavi occurredi nth eSnijdersveerbee kwit h2 7speci mens (larvaean dadults )i n1 1samples ;42 3specimen s (larvaean dadults )wer efoun d in9 2sample si nth eRatumsebeek .Th edistributiona lpatter nwa s exactlyth esam ei n bothstreams ,wit ha significan tpreferenc efo rGrave lsubstrate san dStabl eSan d (Table 43).Thi spreferenc ei sclea ri nal lsubstrat eclassification san dth ehighes t preferencesar efoun do nsubstrate swit hM ,= Ï (1- 2mm) , althoughal lsubstrate s with( L <2 (2- 4mm )sho wover-representatio n (Table44) . Kiwis aènea wasfoun di n4 0sample si nth eSnijdersveerbee k (133specimens ) and in2 9samples.i nth eRatumsebee k (53specimens) . E.aenea showeda simila rpreferenc e as L.voldhnari, butwa srestricte dt oGrave lsubstrate sonl y (Table 45).Again ,th e distributionwa ssimila ri nbot hstreams .Th ehighe rpreferenc e forcoarse rsubstrate s than L.volahnari showedi sespeciall yclea ri nSor t5-8 ,10% ,wher eonl yth ecoarses t substratessho wsignifican tover-representation . Elmis aenea avoidsclasse s4 ,6 an d 7 inSor t8 ,10 1an dth epreferenc efo rClas s5 (xïx )i sshow nb ylarva eonly .Adult s occuri nhighes tnumber si nxx xan dx3x ,whil elarva esho wth ehighes tpreferenc efo r xxxan da lowe rpreferenc efo rClasse s2 an d5 (Tabl e46) . Inth eRatumsebee k Oulimnius tuberoulatus showsth esam epreference sa s L.volahnari withth ehighes tpreferenc efo rClas s5 i nSor t8 ,10»o .Onl y2 5larva e and2 3adult swer efound.i n2 8sample si nth eRatumsebeek .Larva eshowe dn osignifican t

Table43 .I.R .value s for Limnius volchnari (N= 423 )i nth efiel dclassificatio n ofth esubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -4.2 IS.7 -8.3 l_ I I 4 0.1 -6.6 11.8 11.0 -8.3 _J ~I I 2 2.2 -4.0 -1.5 -6.7 11.8 11.0 -J.3 I—"—I I —I I I ' 1 l —I 1 5.2 -2.8 -4.0 -1.5 -l.l- -5.7 H—, -2.2 -3.0 11.8 -0.8 11.9 -2.1 -7.7 -2.6 St Sh FD CD CD+LCD+F D L+FD CD CD L CD+L +FD

Italicvalue s indicatesignifican t over-representation

116 Table44 .I.R .value s for Limnius volohnarï (N = 42 3) inth egrain-siz e Classificationo f the substrates inth eRatumsebeek ,includin g thedistinctio n between larvaean d adults inSor t 8,10%.

Substrateclas s

10 11 12 13 14

phi index detritus

6 CD CD+L

Sort5,10 % 0.6 3.7 7.9 5.8 11.6 1.4 -1.6-3. 9-7. 7-2. 7 - -2.1-7. 7-2. 6 Sort 6,10% 4.6 4.2 5.9 5.0 14.6 2.0 -2.9 -6.2 - -2.1-7. 7-2. 6 Sort 7,10% ------7.4 6.7 7.3 -3.5-0. 3-2. 1-7. 7-2. 6

QlMdQ3 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD CD+L x4x Sort8,10 % 7.4 2.8 5.9 5.0 14.6 2.0 3.9 -3.9-6. 0-4. 9-2. 7-2. 1-7. 7-2. 6 Larvae(N=410) 7.5 2.6 6.1 4.4 14.5 2.1 4.1 -3.8-5. 8-4. 9-2. 6 -2.3-7. 6-2. 6 Adults(N= 13) 0.3 1.4 -0.5 3.5 2.1 -0.2-0. 5-0. 9-1. 5-0. 9-0. 6 1.2 -1.0-0. 5

Italicvalue s indicate significant over-representation

Table45 .I.R . values for Elmis aenea (N= 133)i nth efiel d classificationo f the substrates inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 -7.3 11.6 -2.8 _J i 4 -4.9 -5.5 13.3 1.2 -J, I— I I I 2 -4.1 -2.9 -3.4 -4.3 13.3 1.2 J, _J I T l |I r 1 -2.4 -3.4 -2.9 -1.7 -2'.8 -l'.O -3.8 -2.0 13.3 1.6 0i4 -0.5 -2.3 -2.0 St Sh FD L CD CD+LCD+F D L+FD B CD CD h CD+L

Italicvalue s indicatesignifican t over-representation

preferencealthoug hcoarse rsubstrate syielde dmor epositiv e I.R. values thanth e finersubstrates .Adult swer esignificantl y over-representedi nClasse s2 an d5 o f Sort8 ,101 .I nth eSnijdersveerbee k only2 adult so f O.tuberaulatus and2 3larva e were caughti n1 1samples .Thes e larvaeonl yoccurre di nsubstrate s coarsertha n class7 i nSor t8 ,10 1whic hi ssimila rt oth eresult sfo r L.volakmari inth eRatumse beek (seeAppendi x9) . Theseresult sconfir mtha tth ecommo nnam e forthi sgrou po fbeetles ,'riffl e beetles'i swel lchosen .Thi snam eindee dindicate sthei rpreferre dhabitat .Thes e verysmal lbeetle sca nwithstan dver ystron gcurrent s (Dittmar,1955 ;Dorie r& Vaillant,1955) .The yattac hthemselve st oth esubstrat ewit hthei rsprawling ,large - clawed legs.Th e larvaear ever ywel lstreamline d andsom especie s (e.g. Elmis aenea)

117 Table 46. I.R. values for Elmis aenea (N = 133) in the grain-size classification of the substrates in the Snijdersveerbeek, including the distinction between larvae and adults in Sort 8,10%.

Subs träteclas s

1 2 3 4 5 6 7 8 9 10 11 12 13 14

phi index detritus

7 6 5 4 3 2 Ï 1 2 3 4 CD L CD+L

Sort5,10 % 41.8 2.1 4.4 5.9 -1.7 -2.2 -2.9 -3.4 -5.1 -2.4 -1.4 -1.2 -2.1 Sort 6,10% 41.8 -0.6-2. 0 8.4 2.3 -0.9 7.1 -0.7 -5.8 -4.6 -1.4 -1.2 -2.1 Sort7,10 % 41.8 -1.3 -1.2 -0.6 -1.2 2.0 6.6 -1.1 -3.0 -1.8 -1.4 -1.2 -2.1 x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L QlMdQ3 index XXX x4x Sort8^10 % 13.4 6.0 2.6 -0.9 7.1 -0.8 -3.4 -3.4 -3.3 -4.0 -2.4 -1.4 -1.2 -2.1 Larvae(N=107) 12.5 6.7 0.1 -1.5 8.1 -1.0 -3.0 -3.0 -3.0 -3.6 -2.1 -1.2 -1.2 -2.0 Adults(N=26 ) 4.9 -0.1 5.8 1.0 -0.5 1.2 -1.6 -1.6 -1.5 -1.8 -1.0 -0.6 -0.3 -0.9

Italicvalue s indicatesignifican t over-•representation

cansea lof fth eventra lsid eo fthei rbod ywit hnumerou shair yspines ,producin ga tightgri po nth esurfac e (Hynes,1970a) . Elminthidae aremos tcommo no nsmal lstone s andgrave l inmoderatel y swift waters (Percival& Whitehead ,1929 ;Jones , 1949),sometime scovere dwit hdens e algal growth (Berge tal , 1948;Jones , 1951).Comparin g thedistributio no fE.aenea and L.volakmari asshow ni nTable s4 3an d 45,i ti sclea rtha tth epresenc eo fdetritu s ismor eimportan tfo r L. volohnaxn. thani ti sfo r E.aenea. L.volohnari hasequa l preferences forBar eGrave lan dGrave l+ Coars eDetritus ,whil e E.aenea stronglypre fersBar eGrave l (andPebbles) .Thi spreferenc eo fL.voloVmari forcoars e substrates withdetritu sdoe sno tsho wi nan yo fth egrain-siz e classifications (Table44) , whichmean stha tth eamoun to ftrappe ddetritu swa ssmalle rtha n1 1o fth esampl e weight.Thi semphasize sth eimportanc eo fusin ga fiel dclassificatio ntogethe rwit h agrain-siz eclassification .Th e importanceo fdetritu sfo r L.volokmavi wouldhav e beenobscure di nth egrain-siz eclassification ,an dth edifferenc ebetwee n E.aenea and L.volcfonari, withpreference s forver ycoars egrave lan dmediu mgravel ,respectively , wouldhav ebee nunnotice di nth efiel dclassification . Ofcours eon eshoul dbea ri nmin d thati nth egrain-siz eclassificatio ns o calledminera lsample s (Classes1-11 ) stillma y containu pt oH or10 1detritus ,

althoughthi smainl yconcern ssample swit hQ 1 >2 (cf.Subsectio n 4.1.3.2).Raben i& Minshall (1977)showe dtha t1-3. 5m msubstrate scollecte dmor edetritu stha n coarser orfine rsubstrate s andtha tth epresenc eo fdetritu sma yb eth eprimar y reason responsiblefo rinsec tcolonization .Th erelationshi pwit hminera lsubstrate sremains , however,sinc eth enatur eo fth emineral ,substrat edetermine s theamoun to fdetritu s trappedi nth einterstices .

118 Egglishaw (1964,1969 )conclude dtha tth edistributio no f Esolua pardllelopipedus, anothermembe ro fth eElminthida ei sstrongl ycorrelate dwit hth epresenc eo fdetritus , althoughthi swa smor e importantfo rth eadult stha nfo rth elarvae .Edward s (1975) showedtha t Esolus parallelopipedus hasa simila rdistributio na s Limnius volokmari. Larvaeo f E.parallelopipedus showedn ocorrelatio nwit hcurren tvelocit yan donl ya weakcorrelatio nt osubstrat ecomposition ,suggestin gtha tsubstrat e ismor e important thancurren tvelocity .Adult so f E.parallelopipedus werepositivel y correlatedwit h currentvelocitie so f30-5 0cm/ san da media nparticl esiz eo f20-4 0mm . Thedat ao fth epresen t studyar eno tsufficient ,however ,t ojustif yth estatis ticaltreatmen to flarva ean dadult sseparately .Th eI.R .value sfo rlarva ean d adultsi nTabl e4 4an d4 6shoul donl yb econsidere da sindicative ,sinc eth edifference s areno tsignificant . Iti sno tpossibl et ogiv ean ydetaile dresult so fth eseasona ldistributio no f Elmis aenea sincemos tanimal s (82o fth etota lo f 107)wer e caughti nsprin gan d showeda substrat epreferenc e similart oth edistributio npresente d inTabl e 50.I t isnoteworth y thati nsumne ra sligh tover-representatio n issee ni nC Da swel l (5 specimenso fth e 21).A similarobservatio nwa smad efo r Lithax obsourus insumme r (seeSubsectio n4.2.2.1 )an dthi smigh tb erelate dt oth eavailabilit yo ffoo d (algae anddetritus ) (Jones,1951 ;Hynes , 1961). Limnius volokmari occurred inhighes tnumber s insummer ,autum nan dwinter ,bu t inal lseason sClas s 5 (Table44 )wa spreferre d (xTx).Onl y insprin gwa sa hig h I.R. value (7.7)foun di nx3x ,bu tthi sconcerne donl yon esample ,wit h 13specimen sou t ofth etota lo f44 .Adult san dal llarva linstar sexcep tth efirs tma yb epresen t throughoutth eyea r (Holland, 1972).Th epopulatio nfoun dwil lmostl yb ea mixtur e ofyounge ran dolde rlarva ean dadults .

4.2.2.9 Gammaruspule x (L.) (Malacostraca:Amphipoda ,Gammaridae )

Life oyolé Inth eSnijdersveerbee k andth eRatumsebee kal lsize so f G.pulex are present inal lseason s (Fig.41) .Reproductio ntake splac emainl y insprin g (Weeks 17-20:May )an dsumme r (Weeks21-28 :June ,July) ,bu tals oi nautum nunti lOctober / November (Weeks 33-36). Inwinte ran dearl y spring (Weeks41-16 )ther e isa restin g period,afte rwhic hjuvenile s appearagai ni nabundance .Adult sdi eprobabl yi nJune - July,whic hwoul dexplai nth edecreas ei nlarg especimen s (above9-1 0mm )i nthi s period (Fig.41) . Theannua ltemperatur efluctuation so fth estrea mar ecomparabl ewit hthos e foundb yHyne s (1955) (varyingfro m5-15° Cmostly) ,an di tseem sprobabl e thatth e lifecycl eo fG.pule x isals oi naccordanc ewit htha tdescribe db yHyne s (1955).Rou x (1970)describe da continuou s reproductiono f G.pulex infou rstream swit hver ysmal l annualfluctuation si ntemperatur e (between1 0an d 15°C)an dals otha ta restin g periodi nreproductio noccur si nautum ni nstream swit ha stron gseasona l fluctuation ofth ewate rtemperatur e (lesstha n5° Ci nwinter ,mor etha n 15°Ci nsumner) .Th e

119 78: I- 3.

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77: J3-36 -jmHIflnTW-. N - 2159

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77: ZS-28 N - 631

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77: «-ia: N - 789

77: s- B: 55 N - 863 LU 77: 3 7*: «9-ss: Q l-H a: 7«: -s-«: It! 7«: «I-M:

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•niTii-iiiiadaaaaaaa LENGTH CLASS ( m> Fig. 41. Life cycle histograms of Gantmrus pulex showing the distribution (%) of animal body length per four-week period.

120 lattercycl e iscomparabl ewit hth eobservation so fHyne s (1955),wh ofoun dtha t breedingslowe ddow ni nSeptembe ran dstarte dagai ni nDecember .H efoun dtha tspecie s bom insprin greac hmaturit yi nJul yan dAugust ,bree dthroug hSeptember ,res tunti l December/January andbree dagai nthroughou tspring .The ythe ndie ,whic hcause sa decreasei nnumber si nJune/July .Specimen sbo m lateri nsumme roverwinte ra s juvenilesan dreac hmaturit y inMarch ,afte rwhic hthe ybree dunti lJun ean dthe n probablydie .Hyne sstate dfo roverwinterin g specimensa perio do fabou t7 month st o mature (T=5-10°C )an dfo rsumme rgrower sa perio do f3- 4month s (T= 10-15°C). Roux (1970)suggeste dtha tth ereproductiv erhyth mfoun db ysevera lauthor si s duet oa synergeti c influenceo fwate r temperaturean dda y lengths.Nilsso n (1974) showedtha ttemperatur e isth edeterminin g factorfo rgrowt ho f G.pulex andRou x (1975)demonstrate dtha ttemperatur eaffect sth etim ebetwee nth emoults .Iverse n& Jessen (1977)foun di nRol dKild etha tbreedin g isinsignifican to rabsen ti nwinte r andtha tth ene wgeneratio nappear s inMarch-April ,bu ti smos tabundan t insummer . Growtho fjuvenile si sslightl yreduce di nwinter .The yobserve dtha tpar to fa gene rationsurvive sunti lth ethir dsummer ,whic hgive sa maximu mag eo ftw oyears .The y contributeth edifference swit hth eresult so fHyne s (1955)t oth elowe rsumme r temperatures inRol dKilde .I nth etw oDutc hlowlan dstream sn oindicatio no fa reducedbreedin go rgrowt hwa sobserved ,whic hconfirm sth econclusion so fRou x (1970)an dHyne s (1955).

Microdistvibution Gammarus pulex isth emos tdominan tspecie si nbot hstream sre gardingth enumbe ro fsample si nwhic hi toccurred :i n28 2o fth e38 2sample si nth e Snijban di n15 4o fth e 195sample si nth eRab . Inth eRa bi twa sals oth emos t dominantspecie si nnumber s (9958specimens )wherea sthi swa s M. gr. praecox inth e Snijb (20138specimens) ,followe db y G.pulex (11125specimens) . G.pulex occurred in practicallyal lsample si nth eupstrea msection si nth eSnij ban di tbecam eles s frequenti nth emor edownstrea msections .Thi s isprobabl yconnecte dwit h itstendenc y tomov eupstrea m (Meijering,1972 )an dwit hth eincreasin gsubstrat eheterogeneity . Basedo nth efiel dclassification'o fth esubstrate s (Sort 1-4),G.pulex showsa significantpreferenc efo rdetritu ssubstrate s (Table4 7an d 48),especiall yfo r CoarseDetritus .Thi si sconfirme db y thegrain-siz eclassification s (Table49) . Therei sals oa clea rover-representatio ni nSan dsample smixe dwit hCoars eDetritu s and/orLeave si nth eSnijb ,whil eGrave lwit hLeave s isals opreferre d inth eRab . Comparingthi swit hth egrain-siz eclassification s itca nb esee ntha tther ei sonl y a slightpreferenc efo rQ 1 =Ï wit h 1%organi cmatte ran dQ .= Ï an d2 an dM ,= 6 with 10%organi cmatter .I nth eRa bonl ya littl eover-representatio nfo rQ ,= T i s seen (I.R.= 3.2),bu tthi sconcern s 1sampl es oi ti sno treliable .Th epreferenc e inth eSnij bfo rrathe rfin esubstrate swit ha coars eto pfractio ni sals oclea rfro m Sort8 , 10%wher exx xcontain smos tanimal safte rdetritu ssubstrates .Fro mth e slightshiftin go fth epreference sfro mdetritu ssubstrate st ominera l substrates with1-10 1organi cmatte ri nSort s5-8 ,1 1t o10 1 (Table 49), iti sapparen ttha t

121 Table47 .I.R .value s for Gammarus pulex (N= 11125)i nth e field classification of thesubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 0.1 -41.9 56.9 I L —I I 4 -25.9 30.2 -16.5 -39.I 5 56.9 2 27.2 -4.6 52.6 -3.0 -39.5 -16.5 I _l , I I 1 1 I 56.9 1-15. ,—1 -24.H 7 6.1 5.2 -39.5 -5.9 -15.( -4.6 9.2 53.5 14.5 ! 1 . St Sh FD CD CD+LCD+F DL+F D B L CD 35.2 32.4 34.2 Italicvalue sindicat esignifican t over-representation CD L CD+L

Table48 .I.R . values for Gammarus pulex (N= 9918 )i nth efiel dclassificatio n of the substrates inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -50.7 -28.5 103.2 1 1 | i 1 l 4 -43.2 -27.5 -28.0 -8.4 103.2 1 1 | 1 1 i 1 1 1 2 -39.4 -17.8 -15.6 -23.0 -28.0 -8.4 103.2 1 1 1 1 II 1 1 1 1 i i 1 -25.5-30. 9 -17.8 -7.1-14 . 1 -10.4-18. 3 -10.6 -28.0 8.7 -11.8 160.5 49.5 22.6 St Sh FD L CD CD+L CD+FD L+FD B L CD CD L CD+L +FD

Ital:i evalue s indicate significant over-representation

Table49 .I.R .value s for Gammarus pulex (N= 11125)i nth e grain-size classification ofth esubstrate s inth e Snijdersveerbeek.

Substrateclas s

8 9 10 11 12 13 14

phi index detritus

6 CD CD+L

Sort 5,1% -5.4-5. 9-34. 7-30. 3 -7.8 -3.0 6.6 -8.6-19. 9 -4.3 - 39.4 28.6 37.3 Sort5,10 % -5.4-3. 4-34. 2-23. 6 -8.7 6.5 18.1 -10.5-14 5 -7.5 - 55.3 32.0 35.5 Sort 6.1% -5.4 - -10.6-22. 6-25. 0-20. 2-13. 9 -5.7-13. 1-19. 7 - 39.4 28.6 37.3 Sort 6,10% -5.4 3.7 -10.2-22. 4-23. 9-20. 8-14. 4 -4.3 0.3-16. 2 - 55.3 32.0 35.5 Sort7,1 % -5.4 -6.6 -3.8 -4.8 -7.1-11. 2-28. 5-26. 4-21. 6-2. 3 39.4 28.6 37.3 Sort7,10 % -5.4 -3.5 -3.8 -4.8 -7.1-11. 2-28.5-27. 4 -9.7-1. 6 55.3 32.0 35.5 QlMdQ3 lndex xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x Sort 8,1% -13.4-22. 8-23. 8-20. 2-13 5 -2.6-8. 9 -8.6-9. 9 -18.8-4. 3 39.4 28.6 37.3 Sort8,10 % -11.6-22. 3-22. 7-20. 8-14. 4 -12 12.9 -105-8. 6-12. 2-7. 5 55.3 32.0 35.5

Italicvalue s indicatesignifican t over-representation

122 mineral substratescombine dwit hdetritu sar eals oselecte da sa habitat .A preferenc e forGrave lwit hLeave si nth eRa b(Tabl e48 )i ssee ni nSor t8 ,10 4i nth epreferenc e forxx xsubstrate . Divisiono fth edistributio nove rsubstrate sint olengt hclasse si nSor t5 show s thatth esligh tpreferenc efo rQ 1 =T (14detritu slevel )an dÏ an d2 (10 1detritu s level)i nthe Snij bi scause db ysmal l specimens (1-6mm )tha tprefe rsubstrate swit h atleas t25 4o fth egrain s coarsertha n1 m m(se eTabl e 50A,Sor t8 ,Classe s6 an d 7).Th epreferenc efo rM ,= Ï i scause db yanimal sfro m6 t o1 8urn ,an despeciall y theone s from 15-18mm .Tabl e50 Aillustrate s furtherfo rth eSnij btha tth esmalles t specimens (1-3mm )ar emos tabundan ti nC Do rCD+L ,whil e largerspecimen s (16-18um ) aremor eabundan ti nCD+ Lo rL .Thi s shifti npreferenc ebetwee nth ethre etype so f detritusoccur sgraduall yfro mC Dthroug hL t oCD+ Lfro msmal lt olarg eanimals .I n theRa bexactl yth esam eshif tfro mC Dt oCD+ Lwa sobserved .The preferenc efo rQ 3= Ï appearedt ob ecause db ysmal l (1-3mm )animals ,an dfo rG+ Li nth efiel dclassi ficationb y3- ran6 animals . Insumme rth epreferenc efo rdetritu ssubstrate ssee ni nal lothe rseason s shiftst o'mineral 'substrate si nSor t8 ,10 %(Tabl e 50B).Thi sshif ti sno tpresen t inSor t8 ,1 4whe nC Dshow sth ehighes tI.R .values ,indicatin gtha tpurel ydetritu s substratesar emor escarc ei nsummer ,forcin gth eanimal st ob econten twit hth e combinationo fminera lsubstrat ewit hsmal lamount so fdetritus . Specieso fth egenu s Gamnavus canb ecalle daspec tdeterminin gi nman ylowlan d streams,mountai nstream san dals oslo wflowin griver s (ofgoo dwate rqualit yan d withenoug hinpu to forgani cmaterial) .Ofte non eca nspea ko f Gammavus streams (Meijering,1971) .Als oth echoic eo fth e Gammarus groupfo rth esecon dbes twater -

Table 50.I.E .value s for Gammarus pulex per length class (A)an d season (B)i nth e Snijdersveerbeek inSor t 8,10%.

Length N Substrate class and Q.,MQ 3 index class and 1__ 2_ 3 45 6 7 8 9 10 11 12 13 14

Season xxx X5X xgx x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x A ° 2-0. 2-0. 4 -0.4-0. 4-0. 4 2.5 -0.5-0. 5-0. 4 1.6 -0.3-0. 4-0. 4-0. 3 1-3 2763-5. 2-9.7-11.5-8. 3 -5.0 2.3 10.8 -3.1-3. 4 1.3 0.0 32.6 -3.1-0. 8 4-6 4136 -7.3-13.5-13.2-11.4-9.4 3.0 13.3 -4.7-5. 1-8. 7-4. 3 41.2 10.9 7.9 7-9 2241-6. 7-9. 6 -9.8-11.3-7.2 -3.1 2.8 -7.3-3. 3-8. 1-4. 6 17.2 28.0 26.5 10- 12133 4-3. 1-9. 3-8. 6-9. 0 -5.0-3. 9 -2.5-5. 1-4. 2-8. 2-4. 4 13.1 24.4 34.5 13- 1 5 576 -2.4 -6.7-6. 0-5. 8-4. 7-5. 4 -3.5-3. 5-3. 2-4. 1-4. 9 7.5 22.2 25.4 16- 18 73-0. 1-2. 5 -2.1-2. 2-2. 1 -2.1-2. 4-2. 7-2. 0-2. 3-1. 8 0.0 9.8 17.5 Total 11125-11.6-22.3-22.7-20.8-14.4-1.2 12.9 -10.5-8. 6-12. 2-7. 5 55.3 32.0 35.5 B Spring 1656 -4.6-10.9-7.7 -9.5 0.2 -5.3-0. 3 -5.4-10.0-7.5 -2.7 21.7 15.0 15.1 Summer 1750 -6.3-5. 0 -9.3-4. 0-8. 7 2.6 12.7 1.9 10.0 5.9 -3.2-3. 1 Autumn 3917-7.5-7.8-9.5-13.9-12.7 5.9 7.5-8.4 2. 3-14. 5-4. 8 44.8 -2.5 21. 2 Winter 3802-5.7-16.1-15.9-12.0-6. 9 -0.4 4.0 -7.9-18.6-7.0 -4.0 28.2 35.4 24.3

Italicvalue s indicate significant over-representation ^

123 qualityclas s inth esyste mo fMolle rPillo tfo rth eassessmen to fth ewate rqualit y oflowlan dstream s (MollerPillot ,1971 )i sconnecte dwit hthis .Meijerin g (1971) suggestedt ocal l G.pulex the 'commonfreshwate r shrimp'an d G.fossarm the 'stream freshwatershrimp' ,base do nthei rdifferin gpreference sfo rslowe ro rfaste rcurren t velocitiesan do nth emor e limiteddistributio n of G.fossœnm. Gammâridsar eprobabl y themos tconmonl yknow ninhabitant so fdetritu s substrates,wher e theyma yoccu rver y abundantly. G.pulex isa detritivor ewhic hfeed smainl yo nth emicroflor ao nleave s (Haeckel, Meijering& Rusetzki ,1973 ;Barlöche r& Kendrick ,1975 ;Moore ,1975 ;Kostalo x& Seymour,1976 ;Monk ,1976 ;Willoughb y& Sutcliffle ,1976 ;Nilsson ,1977 ;Nilsso n& Otto,1977 ;Lautenschlager ,Kaushi k& Robinson ,1978) . Itals ofeed so na varie d assortmento fdetritus ,includin g livingan ddea dplant san danimals .I nfac tthe y arethu somnivorou s (Percival& Whitehead , 1929;Badcock ,1949 ;Hyne s 1970a,p .427 ; Roux,1975) . Inth eSnijdersveerbeek , G.pulex wasfoun dabundantl y indetritu sbu t alsoo nfo rexampl ea drowne drabbit .I nth elaborator y G.pulex fedreadil y onan y deadanima ltha thappene dt ob ei nth erearin gchanne l (e.g. Ephemera daniaa nymphs andpupa eo f M.sequax), oftenfeedin gtogethe rwit h M.sequax larvaeo nth elatter' s prey. Theabundanc eo f G.pulex indetritu ssubstrate s asdemonstrate d above,i sdeter minedb yit spreferenc e forleave s (andassociate dmicroflora )a sfood ,a swel la sb y itspreferenc efo rsheltere dsite swit hrelativel yslo wflo w (e.g.Badcock ,1949 ; Albrecht,1953 ;Hynes ,1954 ,1970a ,p . 146;Meijering ,1972 ;Franke , 1977). Fooda swel la sprotectio nca nbot hb efoun di ndetritus/lea fpack sbu t alsob y the (secondary)selectio no fcoars eminera lsubstrate swher e current isreduce d inth e crevicesan dinterstices ,especiall ywhe nals osom edetritu s istrapped .Ree s (1972) foundfo r G.pseudolimnaeus apreferenc efo r16-3 2m m substrate andh eals odemonstrate d a significantrelationshi pbetwee nth ebod y lengtho f G.pseudolimmeus andth eparticl e sizeo fth esubstrate .I nles spreferre dsubstrates ,th eoxyge nconsumptio nincreased , whichh eexplaine da sbein gth eresul to fth eabsenc eo fth e 'properparticl esiz e stimulus' (cf.Eriksen ,1963a) .Meijerin g (1972)state dtha t G.pulex isrestricte dt o thezone stha tar ealmos tcurren tfree ,behin dan dunde rstone swhe nth ecurren t velocityo fth emai nwate rbod y ishigh . Differences insubstrat epreferenc ebetwee ndifferently-size d specimenswer e observedb yman yauthors ,wh omainl y lookedfo rdifférence si ngrai nsize so fminera l substrates,an dno tfo rdifference sbetwee norgani csubstrates .Petra n (1977)foun d thesmalles tspecimen so f 'G.fossarum moreabundan ti nfin esubstrate s (M,= 0.6 mm) andlarge rspecimen smor eabundan ti ncoars emateria l (M,= 24. 5an d2 6ran) i nth e fieldsamples ,wit hsimila rdifference s inartificia lsubstrate splace d inth estream . Probablyth eavailabilit yo fspac ei sth emai nreaso nfo rthes edifferences .Whe n intersticesbetwee nstone sar eto osmal lt ooffe rshelte rfo rlarge ranimals ,onl y smallone swil lb epresen t (Whitehead, 1935). Thedifferen tpreference so flarge ran dsmalle r G.pulex inth eSnij ban dRa bca n

124 onlyb eexplaine dwit hspac e asth eselectio nmechanism . Itcoul dver ywel lb eth e explanationfo rth eover-representatio no fonl ysmalle rspecimen s inminera lsubstrate s (Table50A )bu t itdoe sno t coverth edifference sbetwee nth ethre eorgani csubstrate s types.Her eth eabilit yt ofee do nth e substratemigh tb e importanta swel la sth e carryingcapacit yo fth esubstrat etype s involved (Nilsson& Sjöstrom ,1977) .Juve nilegammarid softe nfee do nth efaece so fth eolde rone s (Hynes,1954) ,an dthe yma y feedo n finedetritu sa swell . Fromfiel dobservation s iti sclea rtha tcoars e detritussubstrate scontai nmuc hmor efin edetritu stha nlea fpacks ,whic hmigh t explainth epreferenc eo fsmal l G.pulex forCD .Large ranimal sdwel lmor eo nLeave s orth ecombinatio no fC Dan dL ,bu t theobserve ddifferenc ebetwee nth emediu man d largersize danimal s remainspuzzling . Differences infoo dpreference sbetwee nanimal so fdifferen tsiz ecoul db ea n explanation.Especiall ywhe nfoo dpreference so fmediu man d largersize danimal s overlap,competitio nfo rfoo dan dspac ewil ldetermin eth ebalanc ea ssoo na sth e carryingcapacit yo fth esubstrat ei sapproache d fora populatio no fa certai nsiz e classcompositio n (Nilsson& Sjöstrom , 1977). Morelikely ,however ,th edifferenc e inpreferenc ebetwee nmedium-size dan d larger-sizedanimal s is inherentt oth eorgani csubstrate .Lea fpack sdisappea ri n thecours eo fwinter ,sprin gan dsumme ran dar egraduall yincorporate di nth ecoars e detritussubstrate sa ssmalle rfragments .Medium-size dspecimen sar eespeciall y abundanti nwinter ,whe n leafpack sar e stilldominant .A stim egoe son ,th eanimal s growan dmov ewit hth e (remainso fthe )leave st oth eC Dsubstrate .

Field experiments Inth eRatumsebee kth ecolonizatio nrat efo r G.pulex ofth e8 m m and4 m mgrai nsiz eappeare d tob eth esam ea sNilsso n& Sjöstro m (1977)foun di n HöjeÄ (Fig.42) ,althoug hther eth ecolonizatio nstarte dsooner ,probabl ybecaus eo f astronge rdrif trat ecompare d toth eRatumsebeek .Fo ral lothe rgrai nsize sth e numbero fobservation s isto o smallt ojustif yan yconclusions . Tables5 1 and 52giv eth enumbe ro f G.pulex for6 siz eclasse safte r 14an d2 8 dayscolonization ,respectively . Iti sapparen t thatsmalle rspecimen scoloniz emuc h fastertha nlarge rones ,a phenomeno nwhic hagree swit hanothe robservatio nb yNilsso n & Sjöstrom (1977),wh o explainedthi sa sbein grelate dt oth epresenc eo feac hsiz e classi nth edrift ,whic hi shighes t forth esmalles tsizes .Summarize dove ral lsiz e classes,th epreferenc eo f G.pulex after 28day scolonizatio ndecrease si nth e sequence8 ,4 ,1 6an d3 2m m (SeeSubsectio n4.1.7 ,Tabl e 16).Lookin ga tsiz eclasse s (Table53 )animal s smallertha n6 nr ndetermin e thepreferenc efo r8 an d4 mn ,an dth e largerindividuals ,whic har epresen t insmalle rnumbers ,th epreferenc efo r1 6an d 32mm .Thi s illustrates thatavailabilit yo finterstitia lspac ema y influenceth e sizegrou po f Oamanu, thatwil l inhabitth esubstrat e (cf.Whitehead , 1935). Comparisono fthes eexperimenta ldat awit hthos eo fth efiel dinvestigatio n withoutincludin gth edetritu ssubstrate s leadst osom einterestin gconclusions . Table 54give s theI.R .value s forSor t6 , 101i nth eRab ,an dcomparin gthes ewit h

125 Table 51.Numbe ro f Gammarus pulex intw oartificia l substrate trays inth e Ratumsebeekafte r 14day so fcolonization .

Lengthc l Particle size (lowerlimit)/m m Total /mm 32 16 8 4 2 1- 3 338 330 137 222 135 1162 3- 6 25 47 54 176 25 327 6 - 9 26 55 84 11 176 9 - 12 53 125 86 - 264 12- 15 31 43 21 - 95 15- 18 6 3 1 - 10

Table 52.Numbe ro f Gammarus pulex intw oartificia l substrate trays inth e Ratumsebeek after 28day so fcolonization .

Length class Particle size (lower limit)/mm Total /mm 32 16 0.5 0.25 0.125 1-3 234 329 529 595 97 2 2 4 1793 3-6 267 535 1157 790 91 2 8 4 2844 6-9 44 51 32 9 - - - - 136 9-12 106 153 39 - 1 - - - 299 12- 1 5 66 75 2 - - - - - 144 15- 1 8 8 5 - - - _ - - 13

Table 53.I.R .value s for Gammarus pulex intw oartificia l substrate trays in theRatumsebee k after2 8day so fcolonization .

Lengthclas s Particles i ze (lowerlimit)/m m /mm 32 16 8 4 2 1 0.5 0.25 0.125 1-3 2.5 9.2 23.4 28.0 -7.3 -14.0 -14.0 -14.0 -13.8 3-6 -2.8 12.3 47.3 26.1 -12.7 -17.8 -17.7 -17.3 -17.6 6-9 7.4 9.2 4.4 -1.6 -3.9 -3.9 -3.9 -3.9 -3.9 9-12 12.6 20.8 1.0 -5.8 -5.8 -5.8 -5.8 -5.8 -5.8 12- 1 5 12.5 14.8 -3.5 -4.0 -4.0 -3.8 -4.0 -4.0 -4.0 15- 1 8 5.5 3.0 -1.2 -1.2 -1.2 -1.2 -1.2 -1.2 -1.2

Italicvalue s indicate significant over-representation

theI.R . valuesfo rth esam esiz eclasse si nth eexperiment s inTabl e5 3reveal s that theresult sonl ypartl yagree .Smal l individualsmainl ycoloniz eth ecoars e artificial substratean dar eals opresen ti nth eshove l samplestake ni ncoars esubstrate . However,large rspécimen sonl ycoloniz eth ecoarses t artificial substrates,bu tar e nearlyabsen ti nth ecoars eshove lsample san dabundan ti nth efin esan dsubstrates , whichar eofte nmixe dwit h1-10 1organi cdetritus . Comparedwit hSor t6 , 11,whic hmean stha tthe nonl yminera lsample swit h less than1 1organi cdetritu sar e included,th epreferenc eo fth esmalle r individuals hardlychanges ,indicatin gtha tthi si sa tru eselectio no fth eminera lparticles .

126 no. of'animal s 2200- t

1800

1600 -\

1200 -\

800 -\

400

colonization time (days)

Fig.42 .Colonizatio nrat eo f Gammzrus pulex inartificia l substrates inth efield . A)accordin g toNilsso n& Sjöströ m (1977) y = 75.4 x + 113.1 ; r = 0.997 ; N = 5 ; P < 0.005 B)i n8 m msubstrat e inth eRatumsebee k y =77. 6x -654. 6 ;r = 0.95 6 ;N = 5 ;P < 0.01 C)i n4 m m substrate inth eRatumsebee k y = 59.8x -402. 9 ;r = 0.95 4 ;N = 6 ;P <0.00 5

Table54 .I.R .value s for Garrmxrus Vulex inth eminera lclasse so f Sort 6,10% inth eRatumsebeek . —

Total Medianparticl e size (Md)/mm 0.5 0.25 0.125 16 8 4 2 1 14 19 67 21 Numbero f samples 148 1 18

Length class/mm N -5.2 -3.9 11.2 -0.7 0.5 7.7 1-3 1176 -2.8 3.9 -2.1 -3.6 3.8 0.7 2.9 3.4 3-6 919 -2.5 -0.2 -2.0 2.0 -2.4 1.8 -0.2 2.e 6-9 212 -1.2 -2.4 -2.3 6.6 -1.9 1.3 -3.5 0.8 9-12 131 -0.9 -1.4 8 24 3 1 3 12- 15 t 39 4 15- 18t 6 2

ese Italicvalue s indicate significantover-repr ^"°° _representation t:actua l numbero f specimensbecaus en osignifican tove rreprese n

127 However,fo rth elarge rspecimen sth epreferenc e shifted from0.12 5u m to2 m man d 0.5mm ,becaus e allsample swit h1-10 %organi cdetritu swer eno winclude di nth e detritussample s (comparewit hAppendi x 6,o nshiftin go fsample s inclasses) .How ever,th erelativ edifferenc ewit hsmall-size d individualsremains .Obviously , larger-sized G.pulex dono tselec tth esubstrat e forit sgrai nsiz ebu t forth e amounto favailabl efoo d (detritus,leaves) .

4.2.2.10 DicranotaZettersted tsp . (Diptera:Limoniidae )

Identification Dicranota larvaear eeasil yrecognisabl eLimoniida e larvaewit h5 pairso fventra lpseudopods .The ywer eonl y identified togenu sbecaus en oke ywa s availablefo rth e identificationo fth e larvaean dn oadult swer e foundo rreared . AlthoughHenni g (1968,vol.11 )mentione donl yon epossibl e species forEurop e [p.bimaculata), Mendl(1978 )give sanothe rspecie s forth elowlan dare a (D.guerini). Whichspecie si sfoun d inth eAchterhoe k streams isuncertain ;perhap sthe ybot h occurthere .

Life cycle Hennig (1968,p .420 )state stha tLimoniida eprobabl yhav e4 larval instarslik eth eTipulidae ,t owhic hthe yar eclosel yrelated .Accordin g toLev y (1919) Dicranota bimaculata pupates inFebruary ,althoug hh ewa sunabl et orea rth e pupaet oadults .Pomeis l (1953)als ostate dtha t Dicranota larvaear ever yhar dt o keepaliv e inth elaboratory .Mend l (1973)foun dtw ofligh tperiod s inth eBreiten bach (April/Ma yan dSeptember/October ) andh econclude d thatther ear e 2generation s ayear .Fro mth edat ai nFig .4 3i ti sclea rtha ti nth eRatumse - andSnijdersveerbeek , Dicranota hasindee dtw ogeneration s ina year .Althoug hn o adultswer ecaugh tth e firstfligh tperio dwil lb earoun dwee k 13-16 (April)an dth esecon d inwee k 33-36 (August/September) ,whic hcorrespond swit hth eobservation s ofMend l (1973).

Microdistribution Dicranota occurredwit h20 9specimen s in10 8sample s inth eSnijders veerbeek,an dwit h 74specimen s in4 3sample s inth eRatumsebeek .I nth efiel dclassi fication (Sort1 )i nth eSnijdersveerbee k theI.R .value s indicate significantover - representationi nS+C Dan dSh. S (Table 55),whil en osignifican tpositiv e I.R. values occurred inan yothe rsan dsubstrat eexcep tthos ewit h finedetritus .Positiv e I.R. valuesals ooccurre d inB Gan dG+CD .I nth eRatumsebee k significantpositiv e I.R. valueswer eonl yfoun di nB G andG+C D (Appendix9) . Dicranota presentsa nic eexampl eo fth edifference s thatca nb e foundwhe n usingdifferen t levelso ffiel dclassification s (Table 55). InSor t 3wit honl y3 substrateclasse sn osignifican tover-representatio ni spresen t (allI.R . valuesbe low2.0) . InSor t4 ,wit h 5classes ,over-representatio ni spresen t inSan dwithou t CoarseDetritus ,whic hshift st oS+L/C Di nSor t2 (with7 classes) ,whil e theSan d classeswithou tC Donl ygiv emoderate ,not-significan t I.R. values.I nSor t 1,th e mostdetaile dclassification ,wit h1 4classes ,th eabov ementione dpreference swer e

128 rrn trm IIIIlHlb»tflTTl

77: 46-48 I] i m ••• ifrriTiiit—jniMTiit'Ti

77; 41-

77: 37-

77: 29-32

77: Z1-Z4

77, 13-1* m nnWïnUm

N .

™ dl

f* 76- CL

76: «I-M

76: 37-40 mti nm lïïii

76: 33-36

76: Z9-3Z

76: 25-Z8

76: Z1-Z4

76: 17-20

76: 13-16 iNlililliiilNil nni

76: *»-1Z Hïïl

76: Ç- B

76: 1- 4 iraülL,

76: «9-5Z

7S: 45-48

imnTTl irrn HUI »m

iTTTfTTTflIÏÏÏIn ™

LENGTHCLAS S(MM ) Fig.43 .Lif e cyclehistogram so f Diaranota sp.shovin gth edistributio n(% ) of larval body lengthpe rfour-wee k period.

129 Table55 .I.R .value s for Dioranota spp. (N= 209)i nth eflei d classificationo f thesubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 1.1 0.5 -2.6 1 i 1 1 . 1 1 4 2.3 -1.0 ole -0.1 -2.6 l 1 1 1 ' 1 1 2 1.7 1.8 2.8 -0.1 -3.5 J., J.. 1 1 1 1 1 1 1 I 1 1 '1 1 1 1 1 0.4 2.2 1.8 i 0.3 2.9 1.1 -2.7 -2.5 ole -0.9 -2.7 -0.4 -1.3 0.7 St Sh FD L CD CD+LCD+F D L+FD B CD L CD+L L CD Italicvalue s indicate significant over-representation

found,whic hagre ewit hth eresul to fSor t 2,bu t indeedgiv emor edetaile d informa tion.Stabl eSan d isno tpreferred ,whil eo fth eS+ Dsamples ,C Di s themos t important andth ecombinatio nwit hCoars e andFin eDetritu si sles spreferred . Consideringth egrain-siz e classification for Diovanota inth e Snijdersveerbeek (Table56 )i ti sobviou sfro mth edifference sbetwee nth e 11an d 10$ classification thatsubstrate swit hles stha n1 4coars eorgani cmatte rar epreferre d above substrates with1-10* 0CD ,althoug hthi sonl yconcern s the finersan dsubstrate s (Q-,> 2 )an dno t thecoars esubstrate swhic hmostl yhav e lesstha nH detritus anyway.Onl y thesub

strateswit hQ 1= Ï sho wa nincreas ei nI.R . valuesgoin g from 11t o10* »CD ,bu t this onlyaffect sth epictur efro mSor t8 i nClas s7 (xxx) ,whil e Class5 (xïx )i sun

altered.A tth esam etim ehowever ,th e I.R. valuesi nth efin esubstrate s (Q1> 2 )

Table 56.I.R . values for Dioranota spp.( N 209) inth egrain-siz eclassificatio n of thesubstrate s inth eSnijdersveerbeek .

Substrateclas s

1 2 3 4 5 6 7 8 9 10 11 12 13 14

phi index detritus

7 6 5 4 3 2 Ï 1 2 3 4 CD L CD+L

Sort5,1 % -0.7 -0.4-0. 4 1.0 2.1 -0.4 0.9 -2.1 2.7 3.2 _ -0.7 -2.7 0.1 Sort5,10 % -0.7 -0.8-0. 7 0.7 2.2 -0.6 3.8 -2.5 1.2 1.4 - -0.6 -2.8 -0.4 Sort 6,1% -0.7 0.9 -2.0 0.4 -0.0 3.5 0.9 -1.6 5.0 - -0.7 -2.7 0.1 Sort 6,10% -0.7 -0.7 0.4 -2.1 0.2 0.1 3.5 0.7 -0.7 2.2 - -0.6 -2.8 -0.4 Sort7,1 % - -0.7-1. 1 1.9 0.6 -0.1 -0.2 -3.7 1.8 2.7 -0.1 -0.7 -2.7 0.1 Sort7,10 % - -0.7-1. 7 1.9 0.6 -0.1 -0.2 -3.7 1.7 2.1 0.0 -0.6 -2.8 -0.4 QlMdQ3 index XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x Sort8,1 % -0.2 -1.7 0.7 -0.0 3.5 0.9 -0.2 -2.1 0.2 3.8 3.2 -0.7 -2.7 0.1 Sort8,10 % -0.4 -2.0 0.5 0.1 3.5 0.7 1.7 -2.5 -0.5 1.9 1.4 -0.6 -2.8 -0.4

Italicvalue s indicate significant over--representation

130 decrease,resultin g invalue s smaller than2. 0i nSor t8 , 10%,indicatin g that Dioranota prefers substrateswit hles s than 11CD .Fro mth edrasti cshif to fover - representation inSor t5 betwee n 1an d 101an dth erelativel yunaltere d I.R.value s inSor t6 an d 7,th econclusio nmus tb edaw ntha tth eQ 1 isespeciall y importanti n connectionwit hth eamoun to fCoars eDetritu spresent .Furthermor ei tca nb e concluded that Dioranota dwellspreferabl yi nFin eSan dsubstrate s (Q1> 2 )wit honl ysmal l amountso fC Dan d inFin eGrave l substrates (Q1= Ï ; M d= Ï) . Inth e 10%classifi cationth epreferenc efo rFin eSan di sles spronounce d andhighe r forFin eGravel / CoarseSand .I nth eRatumsebeek , Dioranota alwayspreferre d thecoarse r substrates (Classes 1,3 ,4 ,5i nSor t 8,10°s :xxx ,x3x ,x2x ,xïx )wit hth ehighes tover-repre sentation inxïx ,correspondin gt oth edistributio ni nth eSnijdersveerbeek . Fromth eresult so fth efiel dexperiment spresente d inSectio n4.1. 7 (Table16 ) iti sclea rtha t Dioranota occurredmainl yi nth e0. 5-1 m mgrai nsiz e fraction (phi index =1), butals oi nth efraction s1- 2an d0.2 5- 0.5 ran,0 whic hcorrespond swit h themedia ngrai nsiz eo fth exT xsubstrates . Analysiso fth edistributio no fdifferently-size d animalsi nthre e length classes showedn osignifican tdifferences ,althoug hsmal l larvaeoccurre dpreferabl y inxïx , 33xan dxx xsubstrates ,whil elarge rone spreferre d 23xan dC Dsubstrate s (Table57) , whichmigh tb econnecte dwit hthei rjourne yt odam psite s (nearth ebanks )abov eth e watersurfac efo rpupatio n (Miall, 1893).Medium-size danimal s showedn o significant preferencea tall ,althoug hthe ymostl y occurredi nth esam esubstrate sa sth eothe r sizes. Since Dioranota iscarnivorous ,predatin gmainl yo nChironomida e and Oligochaeta (Levy,1919 ;Wesenberg-Lund ,1943 ;Hynes ,1961 )on emigh texpec ta relatio nbetwee n thedistributio no fpre yorganism s and Dioranota. Whenthes eresult s arecompare dwit h thedistributio no fOligochaet a (i.e.Tubificidae ) thepreferenc ei nSor t 8,10 1fo r23 x and33 xcorrespond swit htha to fth eOligochaet a forthes esubstrates .Als oman yChiro nomidae larvaesho wpreference s forth esam e substratesa s Dioranota (seeAppendi x12) . Amor edetaile d studyo fthi s relationship includinggu tconten t analysiswil lb eneces saryfo restablishin g relationships betweenth edistributio no fDioranota andit s

Table57 .I.R . values for Dioranota spp.pe rlengt hclas s (A)an d season (B)I n theSnijdersveerbee k InSor t8,10% .

Length N Substrateclas san dQ,M.Q _ index 1 d3 and 1__ 2 3 4 56 7 8 9 10 11 12 13 14 Season xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x A 1- 5 65 0.8 -1.9 1.4 -1.1 4.6 -2.0 2.5 -1.4 -1.9 0.5 2.8 -1.6 -2.0 -0.1 6 - 10 84 -0.3-0. 8 0.8 1.1 3.1 1.3 0.1 -1.6 -0.7 0.0 0.3 -1.6 -1.0 0.1 11- 20 60 -1.3-0. 9 -1.4 0.0 -1.9 1.8 0.4 -1.3 1.9 3.0 -1.6 2.4 -1.9 -0.7 Total 209 -0.4-2. 0 0.5 0.1 3.5 0.7 1.7 -2.5 -0.5 1.9 1.4 -0.6 -2.8 -0.4

Italic val ues indicate significantover-representatio n

131 foodanimal ssinc epossibl epre ywa sabundan ti nal lsubstrat etypes . Theabov epresente ddat ao nth emicrodistributio npartl yagre ewit h earlier data,althoug hthes ecove ra wid erang eo fsubstrates .Geijske s (1935)state dtha t Limoniidaean dTipulida ebelon gt oth emu d faunaa swel la st oth edetritu sfauna , buttha t Dicmnota occursi nsand ybottoms .Thi s agreeswit hth eobservatio no f Petran (1977)wh ofoun dtha t Dieranota prefersfin esubstrates .Edward s (1975)caugh t Dieranota specimensi nsite swit ha nabundanc eo ffin esubstrate s enrichedwit h organicmatte ran dfoun dles s specimenswit h increasingcurren t speedan dcoarse r medianparticl esize ,whic hagree swit hEgglishaw' s (1969)conclusion .However ,Jone s (1951)reporte dtha t Dioranota and Limnophila occuramon g stonesan dcoars egrave li n slackwate rnea rth ebanks .Althoug hthes edistributiona ldat aar eno t contradictory, itillustrate stha t Dioranota occursi nawid erang eo fsubstrates ,varyin g fromfin e sandan dmu dt ocoars egrave lan dstones ,preferabl ycombine dwit h finedetritus . Thispictur eals oemerge sfo rth eSnijdersveerbeek ,wher esan d substrates combined withfin eo rcoars edetritu sar epreferred ,althoug h Dioranota isabsen ti nsample s withlarg eamount so fcoars edetritus . Miall (1893)foun dtha tpupa eneve rliv eunde rwater ,bu ttha tthe ymigrat et o dampplace sabov eth ewate rsurface ,e.g .bank so rsan dridge si nth estrea mbed . Thisagree swit hth epresenc eo f Dioranota inespeciall y thesample stha twer e taken frominne rbend san dsan dbank si nth eSnijdersveerbeek .Mend l (1978)note d that D.guerini dwellsi nstream san dsmal lrivers ,bu ttha t D.bimaoulata isfoun dwithi n thedirec treac ho fth ewate r surfacei nth edam pbank so fthes ewate rtypes .Thi s emphasizesth enecessit yt oidentif yth egenu st ospecie sleve lan dth e above-cited differences inpreferre dhabita tmigh tb erelate dt odifferen tspecies .

4.2.2.11 LimnophilaMarquar tspp . (Diptera:Limoniidae )

Miorodistribution Althoughfou rdifferen t Lvm.oph-i.la specieswer e distinguished (Appendix1 :tax ano' s197 ,198 ,19 9an d208 )th eidentificatio n remaineduncertai n andi tma yhav econcerne dmor especies .Fro mth edistributio no fLimnophila inth e Snijdersveerbeek (Tables6 2an d63 )i tca nb esee ntha t Limnophila prefersbot h Gravelan dSan dsubstrates .Tabl e5 8show stha tespeciall ybar esubstrate s (without CDo rL )ar einhabited ,whic hi sals oapparen t fromth edecreas eo fth epositiv eI.R . valuescomparin gth e1 1an d10 %classificatio n inTabe l 59,excep t forClas s7 i n Sort8 .Sinc ei tconcern ssevera lspecies ,i ti s possibletha tth epreferenc efo r CoarseGrave lan dFin eSan drefer st odifferen t species.Thi s cannotb eteste dsinc e 342o fth e38 5specimen swer eclassifie da son etaxon ,th egenu s Limnophila, which mayconcer nsevera lspecies ,whil eth eremainin g4 3larva ebelonge dt oth eothe r threetax a( 9t oLimnophila sp.a ,1t oLimnophil asp .b an d3 3t o Limnophila gr. fusoipennis). Inth eRatumsebee konl y6 2specimen swer e foundan dthes eoccurre dmainl yi n BareSan dsubstrate s (Appendix 9). Inth egrain-siz e classificationa preferenc efo r

132 Table 58.I.R .value s for Lirrmophita spp. (N= 385)i nth efiel dClassificatio no f theSubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 2.6 1.1 -6.2 - l I 1 i 1 1 4 -0.4 è.2 -6.2 3.8 I I 1 1 1 1 2 z\z 2. ,7 -2.7 L J, -6.2 1 1 I 1 1 1„ 1 1 1 1 1 1 1 1 1 1 1.5r 3.2 2.2 4.2 0.2 1.7 -3.4 0.9 2.2 -1.0 -0.8 -2.6 -4.7 -3. 3 1 J

St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L

Italic values indicatesignifican t over-representation

Table 59.I.R . values for Linmophila spp.pe rlengt hclas s (A)an d season (B)i n theSnijdersveerbee k inSor t8,10 %an d forth etota l inSor t8,1 %(C) .

Length N Substrate classan d IQjM.Q - index class and 1 2_ 3 4. 5_ 6 7 8 9 10 11 12 13 14 Season XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x

A 0 1 •f 1-4 116 -0.7 2.0 -0.5 -0.6 3.4 -1.9 -1.1 -1.7 3.1 0.1 6.0 -2.5 -2.6 -2.0 5-8 155 -2.1 1.7 -0.6 -0.4 2.5 0.6 1.6 -0.7 -1.3 1.1 2.6 -1.1 -2.7 -1.9 9-12 77 -1.5 1.0 -0.8 -0.0 0.6 2.0 2.6 -0.7 1.1 -1.0 0.4 -0.5 -2.3 -1.6 13- 2 0 36 -1.0 -0.0 -1.5 0.4 -0.1 1.9 1.2 -0.4 3.6 -0.6 0.4 -1.6 -1.8 -1.1 Total 385 -2.7 2.6 -1.5 -0.4 3.7 0.8 1.9 -1.8 2.5 0.2 5.2 -2.8 -4.8 -3.3 B Spring 67 -0.9 4.9 -1.0 2.7 -0.7 0.3 -0.5 1.2 0.3 2.3 -0.9 -1.7 -2.6 -1.9 Summer 52 -1.4 -1.3 -0.1 -0.9 0.4 1.9 2.3 -1.9 -1.6 0.3 1.1 0.7 - - Autumn 97 -0.6 -2.0 1.7 0.4 -0.8 -0.7 1.2 -1.5 0.6 3.1 2.3 -1.1 -2.1 -1.4 Winter 169 -2.3 2.8 -2.3 -1.5 6.1 0.2 2.8 -1.6 2.9 -1.3 5.0 -2.4 -4.0 -2.8 C Total 385 -2.5 3.3 -1.7 -0.9 3.8 1.0 0.9 -1.6 4.3 2.1 6.5 -3.7 -2.7 -2.2

Italic values indicate significant over-•representation + :onl yon e specimenno t measured.N o I. R. values calculated

xlx,xx x and 1xxwa spresent ,whil en oover-representatio nwa ssee ni ncoars esub strates.Tabl e 59present s the I.R. values for4 lengt hclasse s (and1 unmeasure d specimen) (Table59A )o f Lirnnophila and thosefo rth eseason s (TableS9B )i nth e Snijdersveerbeek.Thes edat asho wtha tth edistributio no fth e larvaei sdifferen ti n summeran dautum ntha ni nwinte r andspring .Th e latterseason sar eth eonl yperiod s withman y larvae incoars esubstrates :mos t larvaeoccu ri nClasse s7 an d 10i n summeran dautumn .Lookin ga tthi sdistributio n foreac hlengt hclas s showstha t smaller larvae (0-8mm) ,whic har emor enumerou stha nlarge rone s (7:3), determine theoveral l (total)distributio nsee ni nTabl e 59C.Lik e thesmalle rlarvae ,large r ones (8-20mm )occurre d inpracticall y everysubstrat e type,bu tpreferabl y inth e finersubstrates .

133 Accordingt oLev y (1919) Limnophila iscarnivorous ,lik e Dieranota and Pedicia, andthe ydwel lpreferabl y inmu dan ddetritu s substrates.I nexperiment swit harti ficialsubstrate sPetra n (1977)foun dtha tLimoniida ean dTipulida eprefe rfine grainedsubstrate sa sChironomida ean dTubificida edo ,expeciall y inth eslowe r runningsection so fth estream .Thi sma yb ea predator-pre y relationship. Jones (1949)foun d Limnophila betweenstone s andcoars egrave lan daccordin gt o Geijskes (1935)th eLimoniida ebelon g toth emu dan ddetritu s fauna,a sd oth eTipuli dae.Althoug h Limnophila didoccu ri nSan d+ Leaves ,th edat afro mth eSnijdersveer beekan dth eRatumsebee khardl y supportth epossibilit y that Limnophila dwells in detritussubstrates .The yprefe rFin eSand ,whic h ismostl ycombine dwit hFin eDetritu s (mud),bu tthe yals ooccu ri nsevera lcoarse rsubstrat etypes .Thi semphasize sth e dangero fgeneralizin gfro mdat aconcernin gfamilie s orgroup so fspecie s andth e needt oidentif yt oth emos tdetaile dlevel . t

4.2.2.12 PtychopteraMeige nspp .(Diptera :Ptychopteridae )

Microdistribution Inth eSnijdersveerbee k Ptychoptera occurredmainl y insand ysub strateswit ha stron gpreferenc efo rS+FD ,whic hca nals ob edescribe da smud ,althoug h iti soxygen-rich ,a tleas ta tth esurface .Othe rsubstrate s inth efiel dclassifi cationwer eal la combinatio nbetwee nC D and/orE Dan dSand ,althoug hespeciall yth e EDplaye da nimportan trol e (Sort2 ,Tabl e60) . Inth egrain-siz eclassificatio nth efines tsubstrate s arepreferre d (Table61) . Onlya smal lshif t inpreferenc efro mClas s 12 (CD)t o 11 (33x)i sobserve dwhe n comparingth eH and10 %classifications ,indicatin g thatth eamoun to fcoars e detritus isno tver yimportant .Th efin eorgani cmaterial ,whic hi sprimaril y apar to ffine r substrates,play sa mor e importantrol ea swa s seeni nth efiel dclassification . Accordingt oWagne r (1978)th elarva ean dpupa eo f Ptychoptera occuri nloosel y packed,sof tsubstrate stha tar eenriche dwit horgani cmud .There ,the yfee do n organicmatter .The yburro wperpendicula r inth esubstrate ,breathin gthroug hthei r long,retractibl esiphon ,whic hextend st oth ewate rsurface .Th emaximu m lengtho f thesipho ndetermine sth emaximu mwate rdept htha tca nb etolerate d (forlonge r periods).Thi si sprobabl ywh y Ptychoptera wasno tfoun di nth eRatumsebeek ,sinc e thisstrea mi softe nto odee p inth epool s andth ecurren ti sto ostron g inth e shallowerplaces . Geijskes (1935)classifie d Ptychoptera asa typica lmud-species , liketh e Tubificidae, Sialis andChironomidae . Ptychoptera occurmainl y inwater swit h a leniticcharacter ,wher ethe yca ntolerat epollutio nquit ewel l (Berg,1948 ;Zitek - Zwyrtek,1971 ;persona lobservation) .Mos t species livei nseepin g springsan d spring-swamps,bu tthe yals ooccu ri nslowl yrunnin g streams (Thomas,1977a ,b) . The literaturecite dconfirm sth eobservation smad e inth eSnijdersveerbeek ,wher e Ptychoptera areespeciall yrelate dt oth esubstrate swit hmuc hdetritus, presen ti n quietpart so fth estream .

134 Table60 .I.R .value sfo r Ptyehoptera sp.( N= 251 )I nth efiel dclassificatio no f thesubstrate si nth eSnijdersveerbeek .

Sort Sand Gravel Detritui3

3 7.7 -7.1 -4.1 i 1 1 1 1 1 4 1 7.4 -6.8 -2.5 -4.1 3.8 i i 1 1 1 1 2 0.2 1 As 6.5 -6.8 -2.5 -4.1 1 J7 i I i 1 i ii 1 1 1 r i 1 1 1 1 -2.5 2.9 1.5 4.8 4.8 -6.8 -2.31 -3.3 -1.2 1.6 3.0 0.0 -2.9 St Sh FD CD+LCD+F D L+FD B CD L CD+L L CD Italic values indicat esignifican t over-representation L CD

Table61 .I.R .value sfo r Ptyahoptera sp.( N 251)i nth egrain-siz eclassificatio n ofth esubstrate si nth eSnijdersveerbeek .

Substrateclass '

8 9 10 11 12 13 14

phi index deti•itu s

7 6 5 4 3 2 Ï 1 2 3 4 CD L CD+L

Sort5,1 % -0.8 -2.0 -5.7 -5.2 -2.1 -0.9 5.2 -1.0 8.4 9.6 _ 3.3 -3.2 -0.7 Sort 5,10% -0.8 -2.3 -5.4 -5.2 -0.2 -1.1 4.1 -1.3 6.4 11.6 - 0.7 -3.3 -1.2 Sort 6,1% -0.8 - -2.0 -3.7 -4.1 -3.5 -3.5 -1.8 6.0 6.1 - 3.3 -3.2 -0.7 Sort 6,10% -0.8 -0.8 -2.3 -3.4 -3.9 -3.6 -2.1 -2.0 5.4 6.3 - 0.7 -3.3 -1.2 Sort7,1 % - -0.8 -1.2 -1.6 -0.8 -1.6 -2.0 -3.9 -5.1 5.3 9.5 3.3 -3.2 -0.7 Sort 7,10% - -0.8 -1.8 -1.6 -0.8 -1.6 -2.0 -3.9 -4.0 4.7 11.1 0.7 -3.3 -1.2 xBx x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L QlMdQ3 index XXX x4x Sort8,1 % -2.6 -3.7 -3.9 -3.5 -3.5 -1.4 2.4 -1.0 9.5 2.0 9.6 3.3 -3.2 -0.7 Sort8,10% ' -2.7 -3.5 -3.7 -3.6 -2.1 -1.6 1.5 -1.3 8.6 1.2 11.6 0.7 -3.3 -1.2

Italicvalue sindicat esignifican tover-representatio n

4.2.2.13 Orthocladiusva nde rWul pspp . (Diptera:Chironomidae ,Orthocladiinae )

MiorodistTibution Orthoaladius occurredi n3 1 sampleswit h63 1 specimensi nth etw o mostdownstrea msection s( 6an d8 )i nth eSnijdersveerbeek ;th eothe r 11 specimens were foundi n1 sampl ei nSectio n 4.Accordin g toMolle rPillo t (personalconmunica - tion)i tconcern sa tleas ttw odifferen t species,althoug hn ospecifi cspecie sname s areknow nyet . Inth eRatumsebeek ,onl ythre especimen swer e found,eac hi na differen tsample . Inth eSnijb , Orthocladius showeda distinc tpreferenc e forGrave lsubstrate s com binedwit hDetritu s (Table62 ,Sor t 2), especiallyLeave s (Table62,.Sor t 1), inth e

135 Table62 .I.R .value sfo r Orthoaladius spp. (N= 642 )i nth efiel d classification of thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -16.4 24.0 -3.3 I I I I 4 -13.1 -9.9 -0.6 43.5 -3.3 _J I I 2 -11.1 -7.0 -4.1 -9.4 -0.6 43.5 -3.3 _l L__ 1 ' ' -8.4 -4.3 -0.6 79.9 r 4.7 2.5 -3.9 -4.3 1 -9.3 -6.1 -7.0 3.2 -6.1 -2.3 St Sh FD CD CD+LCD+F D L+FD B CD CD CD+L

Italicvalue s indicatesignifican t over-representation

Table63 .I.R . values for Orthocladvus spp.( N= 642 )i nth egrain-siz e classification ofth esubstrate si nth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phi index detritus

CD CD+L

Sort5,10 % -1.3-2. 7 28.7 4.3 -4.7 0.1 -6.4-6. 7-11. 3 -5.0 - 0.1 -3.8-4. 7 Sort 6,10% -1.3-1. 3-4. 3 1.2 49.4 2.2 1.8 -2.8-12. 2-10. 4 - 0.1 -3.8-4. 7 Sort7,10 % -1.3-2. 9-2. 6-1. 3-2. 6 0.9 4.5 0.8 2.7 -3.9 0.1 -3.8-4. 7 L CD+L QlMdQ3 index XXX X5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD x4x Sort 8,10% 1.3 -1.6 51.9 2.2 1.8 -2.2-8. 1-6. 7-7. 2-8. 7-5. 0 0.1 -3.8-4. 7

Italicvalue s indicate significant over-representation

fieldclassification ,an dthi scorrespond st oth epreferenc e forx3 x (i.e.53x )i n thegrain-siz eclassificatio n (Table63 ,Sor t 5-8).Comparin g thepreferenc ei nSor t 5-7, 10$wit hth epreferenc ei nSor t8 ,10 1 (Table 63),th epreferenc e forC s= 5 (Sort5 )an dM ^= 3 (Sor t6 )i sals osee ni nth epreferenc e foric3 xi nSor t8 , emphasizingth eimportanc eo fth ecoars egrains .However ,th eQ ,seem st ob eles s importantsinc eth eover-representatio n seeni nSort s5 an d6 i sdivide dove rQ ,= Î-3i nSor t7 . Orthocladiinae larvaean despeciall ygener arelate dt o Orthoaladius (e.g. Euorthooladiu8j Rheorthoaladius, Syrwrthooladins and IviohoaladiuB) areregarde da s typicalfo rth eston yhabita ti nrunnin gwate r (e.g.Nietzke ,1937 ;Thienemann , 1954). Orthooladius larvaebuil dloos etube so nstone s (Geijskes,1935) . Orthocladiinae larvaear emor erheophilou s andmor eabundan to nstone san dvegetatio ntha nChirono - minae(Thienemann ,1954 ,Lindegaard , 1972).Cummin s (1972)state d thatOrthocladiina e

136 aremor eabundan ti nerosiona l zones,whic hagree swit hit sdistributio ni nth eSnij b asfa ra sth egravell y substratesar econcerned .I nsand ysubstrate s (e.g.Bar eSand ) Chironominaear emor eabundan t (Subsection4.1.6 ,Tabl e14) .

4.2.2.14 Micropsectragr .praeco x (sensuTshernowskij )(Diptera :Chironomidae ,Tany - tarsini)

Microdistribution Micropsectra larvaewer edistinguishe di ntw olarva lgroups : M.gr . praecox and M.gr . trivialis, thelatte rhavin ga muc h longerspin eo nth ein nercorne ro fth eantenna lbase .Undoubtedl yth epraecox groupconsist so fsevera l species,bu tfo rfurthe r identificationn okey swer eavailable . The Micropsectra larvaebuil dver y longtube so fsan dan ddetritus .The ynormal lyar epresen ti nan do nth euppe rlaye ro fth ebotto mi nplace swit ha wea kcurrent , whereth etube so fforme rgeneration sma yhav eforme dtic klayers .The y alsooccu ri n vegetationan dsheltere dplaces ,wher e theyals obuil dlon gsan dtube s (Lindegaard, 1972). Inth eSnijb , M.gr . praecox isth emos tnumerou s specieso fal lmacro-inverte brates found,whil ei ti sth esecon dmos tnumerou son ei nth eRab .I nbot hstream si t occurspredominantl y indetritu s substrates (Appendix 9). Inth eSnijb ,th epreferenc e isabou tequa lfo rLeave san dS+CD+FD ,wit hS+F Dan dG+ La ssecondl ypreferre dsub strates (Table 64).Thi sG+ Lsubstrat ei nfac tconcerne drathe rfin esan dcombine d withsom ecoars emateria l (Q1 =3 )wit h lesstha n10 * organicmaterial ,becaus eth e preferencei sonl ysee ni nSor t5 ,10 * (Table 65).Th eimportanc eo fdetritu si s illustratedb yth eincreas eo fI.R .value si n23 xan d33 xsubstrate si nSor t8 ,10 * andth edecreas ei nC Dcomparin gwit hth e1 *classification .Thi s correspondsver y wellwit hsimila rchange si nI.R .value si nSor t5 ,6 an d7 (Tabl e65) . Inth eRab , M.gr .praecox wasmos tabundan ti nth eC Dsubstrat ei nbot hth e fieldclassificatio nan dth egrain-siz e classification,wit honl ymino rpreference s forSan d+ C Do rL an dF Dsubstrates ,whic hcorrespond swit hth e23 xan d33 xsubstrate s inSor t8 , 10*.

Table 64.I.R . values for Micropsectra gr. praecox (N= 20138 )i nth efiel d classification of thesubstrate s inth e Snijdersveerbeek. Detritus

CD+L

Italicvalue s indicatesignifican t over-representation

137 Table65 .I.H .value sfo r Micropseotra gr. praecox (N= 20138 )i nth egrain-siz e classificationo fth esubstrate si nth eSnijdersveerbeek .

Substrateclas s 1 2 3 4 5 6 7 8 9 10 11 12 13 14

phi index detritus

76543211234 CD L CD+L

Sort 5,1% -7.3 -16.2 -17.6 -45.7 -23.3 -12.0 -7.6 -33.6 -22.8 20.1 - 57.8 93.9 5.1 Sort 5,10% -7.3 -19.0 -44.8 -16.6 11.1 -8.3 -4.7 -33.4 25.7 30.1 - 25.8 88.6 4.5 Sort 6,1% -7.3 — -2L7 -29.7 -35.5 -28.5-29.4 -31.0 -31.5 -12.1 - 57.8 93.9 5.1 Sort 6,10% -7.3 -7.0 -24.0 -26.3 -33.8 -29.4 -3.6 -29.8 -25.2 37JS - 25.8 88.6 4.5 Sort 7,1% - -7.3 -10.3 -14.5 -7.3 -14.4 -17.6 -37.5 -49.8 -13.4 23.4 57.8 93.9 5.1 Sort 7,10% - -7.3 -16.1 -14.5 -73 -14.4 -17.6 -37.5 -33.0 -9.3 34.2 25.8 88.6 4.5 M Q-.1d JQ3 O index xxx— -x5x x3x x2x xïx xlx xxx Ixx 22x 23x 33x CD L CD+L x4x Sort 8,1% -2£7 -31/4-43. 0-28. 5-29. 4-28. 4-13. 9-33. 6 -9.4-23. 720.1 57.8 93.9 5.1 Sort 8,10% -225-29. 8-32. 3-29. 4 -3.6-27. 2-11. 7-33. 4 -1.5 29.5 30.1 25.8 88.6 4.5 Italic values indicate significant over-representation

Lindegaard (1972)remarke d thati ti sstil luncertai nwhethe rth elarva e found inth ebotto mbelon gt oth esam especie sa sth eone si nth evegetation .Th esam e reasoning appliest oth edifference s foundi nth eSnijb ,wit htw oquit e different substrate types (leafpack san dS+CD+FD )preferred ,whil ethi si sals odifferen t from thepreference sobserve di nth eRatumsebeek .Furthe r investigationo fth elarva l material frombot hstream smigh trevea ltha ti tdoe sconcer ndifferen tspecies . Thecombine dmateria lfro mbot hstream s shows that Mioropseotra gr. praecox has twomai nfligh tperiods :on ei nMarch-Apri l (Weeks9-16 )an don ei nAugust-Septembe r (Weeks33-40 ) (Fig.44) . Differently sizedlarva eo f M.gr . praecox showedn odifference s insubstrat e preference,bu tbetwee nth efou rseason s differences indistributio nwer e seen (Table 66A). Inth eSnijdersveerbeek , M.gr .praecox onlyprefer sCoars eDetritu si nspring ; iti sno ts odensel ypopulate di nan yothe r season.I nsummer ,whe npur e detritus substratesar erar ei nth estream ,minera l substrate combinedwit hdetritu si spre ferred,whil ei nautum nan dwinte rth emai npreference sar efo rLeave san dsecondly . forSand/Mu d+ Detritu s (Table 66B). Inth eRatumsebeek , small larvae (0-5mm )prefe r CDo rCD+ L (insummer) ,whil elarge rlarva e (5-10mm )occu rmainl yi nCD+ Lo r23 x( + detritus).Th epreferenc efo r23 xan d33 xsubstrate sb ylarge rlarva ei smainl y seen inwinter ,whil ei nautum nmos t larvaear efoun di nCD+L ,althoug hn osample swer e takeni nth eC Dsubstrat ei nautum nan dwinter ,makin g interpretationo fth edat a difficult. Comparisono fthes edat awit hth egrain-siz e selectioni nth efiel d experiments (Tables1 5an d16 )show s thatafte ra perio do f1 4day so fcolonization ,th elarva e

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1-MTil i 11*13:1 ia LENGTHCLAS S(MM ) Fig. 44.Lif e cyclehistogram so f Moropseotra gr. praecox showingth edistributio n (%)o flarva lbod y lengthan dpupa e (99)pe rfour-wee kperiod .

139 Table66 .I.R .value s for Miaropsectra gr. praecox perlengt hclas s (A)an d season (B)i nth eSnijdersveerbee k inSor t8,10% .

Length N Substrateclas san dQjM.Q o index class and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Season xxx xBx x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L x4x A 0 1846 -7.3-12. 4 -2.6-11. 0 -83 -10.2 24.4 -13.7 3S.0 -5.733.3-9. 4 -13X) 1.5 1-5 9499-16. 3-18. 3-23 5 -20.2 7.4 -185-11. 0-21. 7 -6.8 11.7 17.8 -9.9 94.7 3.7 6-10 8789-15. 7-20. 4-22. 8-18. 4 -9.0-16. 7-17. 5-21. 7-12. 6 35.2 11.8 S3.6 41.4 2.3 11- 2 0 3 + 99 1 + Total 20138-23. 8-29. 8-32. 3-29. 4 -3.6-27. 2-11. 7-33. 4 -1.5 29.5 30.1 25.8 88.6 4.5 B Spring 2249 -5.4-10. 1 -9.4-U S -7.5-10 5-13. 2 -6.5 -7.7 -1.3-4. 7 87.8 -14.1-10. 4 Summer 3663-11. 3-13. 3-16. 2 -9.0 -7.4-18. 3 2.3 -123 -10.0 '48.3 23.1 -8.9 - Autumn 7013-14. 5 -6.7-14. 8-19. 0 24.6 -0.6 -5.1-21. 4-11.8-18. 2 7.2 -7.1 66.6 18.0 Winter 7213-15. 1-22.0.-215-17. 0-21. 4-17. 5-11. 4-23. 0 13a 26.4 21.2 -9.1 65£ 1.4

Italicvalue s indicate significant over-representation + :N o I.R. valuescalculate d

arepresen ti nequall yhig hnumber si nal lgrai nsizes ,whil ethe yar eover-represente d inth e4 m man d8 m mfraction safte r2 8days .I ti shighl y likelytha tthi si sno ta preferencefo rth eminera lparticl esiz ebu tfo rth edetritu s trappedbetwee nth e mineralgrains .Mor edat a (e.g.measurement so fth eamount so ftrappe ddetritus )mus t begathere dt ob eabl et oexplai nth eover-representatio no f M. gr. praecox inthes e coarse-mineralparticl esizes .

4.2.2.15 ParacladopelmaHarnisc hspp . (Diptera:Chironomidae ,Chironominae )

Microdistribution Twospecie so fParacladopelma wer efoun di nbot hstreams : P.laminata andP . aamptolabis. However,onl yth elarva elonge rtha n2 m mwer e identifiedt o specieslevel ,becaus edifference sbetwee nth especie swer eno tconstan ti nth e smallerspecimen . Inth eSnijdersveerbeek ,18 5specimen swer e found,6 4o fwhic hcoul dno tb e identifiedt ospecie s level.O fth e4 7larva efoun di nth eRatumsebeek ,onl y 17coul d becompletel yidentified .Th edistributiona lpatter nwa sth esam e inbot hstream sfo r bothspecie sconsiderin gth efiel dclassificatio n (Table 67), althoughth enumbe ro f animalsi srathe rlo wfo rstatistica lanalysis .Bot hspecie ssho wth ehighes tprefer encefo rS+FD ,followe db yBar eSan dsubstrate s (Sh.San d St.S).Th esmal l larvae preferS+C Dtogethe rwit hS+ED . InSor t8 ,10 1som edifference sbetwee nth etw ospecie sappea r (Table68) . P.aamptolabis dwellspreferabl yi n1x xsand ,an dalthoug h P.laminata occurredi nthi s substrate,i tpreferre d23x .Smal l Paracladopelma larvaewer efoun dpredominantl yi n xxx,wher eals osom eo fth elarge rlarva eo fth etw ospecie swer efound . Thetw ospecie sonl ysporadicall yoccurre dtogethe ri nth esam esample :o fth e

140 J * n Tf CQ •J in co in in a+ rH rH rH CM a+ CM H rH CM u i i i 1 u 1 1 1 I »M * «H 01 in CM ^ rH co 3 3 j CM CM CM 1" •P j CM CM CM •* •P 1 1 1 1 •H 1 1 1 1 h •rrit H CD t» en +> 00 Ol H t» •P • • • a> 0 a O ri H H• Q o O H CM CM' O o 1 1 1 o 1 1 1 1

m en CM en in CD o CD Q CO O H o cq CM CO o' i i i i

co r» CM I-I XI . 0 - . 2 - 1 JA CO .4 0 H •J H O H H 0 CM H Mt O tO O i i 1 0 A a> 00 H CO co X CD •>« in oo M EO CM O n> N• «« •• CM o H' O o 1 1 1 > i a CO Tl* *J1 **l •0" ri oo » co 0) H jï H O H' H 13 rH Ol CM rH LO 1 1 1 1-1 1 •H EaH 00 W ri rH Ö X l> CO o> 00 CQ + NOri' CM .N OOK) oó o 1 1 1 a> ri J3 t- o t- CM •p X •* CM Ol 0) a H a+ o• o> o • rH• a IX OH> • O• O o 1 1 1 1 •H 1 1 ' in t- LO CO a 68 Kl CO CD CD en a a 0 O |rH 0 O » iH• IS• . tO• •H rH IX H • O• • O o• •H o •P 1 1 •p at ta CM o co O •P X rl <& ri en •p •P ICM a •4 HrtO i-i a0 ri 1« CM O CM CM o 1 1 i co 0 1 1 1 n 00 o WHQ CM u X HCl O rH h O o. a |CO h IS•. C•O T-•H Ml t» •H X 1« CM• H* •CM CO tt0 t-^ rn o 1 1 1 1 h •o U «IWri t-1 u 1 X X rjl t" CO CM u J= 0> !~i •H uniTf V CQ Ml LO rH U5 IXIX CM' O' CM' CO > CO 1 1 1 > 0 0 •o Ml CD O rH •p ey IX •* CM •* CO +> ci -SÖ •o 1 X a s eEl a WHM O T-^ rH IX H rH rH CM C+Q> 1 1 Üm 1 1 1 1 Ü co ti Ö CL, a 0 >-i 43 Q •H oo X Or-1 S •P 0 CD O > a Ui Öj BH EH 0 EH BH BH' S H U EH •H •H 0) H H rH ta rH l> en en .Q H t» 01 d 3 •p m c o o en •p o o en en M E-, « 3 CO Cl CM M EH EH C 1 co eo CM

141 19sample swit h P.laminata present,onl ythre esample sals ocontaine d P.camptolabis. Thiscoul db eecologica lsegregation ,on especie sexcludin gth eothe rb ysom emechan ism,e.g .foo dcompetition .Mor elikely ,th edifference si nsubstrat epreferenc epla y arol ei nseparatin gth etw ospecies : P.laminata preferring finersubstrate s than P.camptolabis, althoughmor edetaile d informationi sneede dt oconfir mthis .

4.2.2.16 Prodiamesaolivace a (Meigen)(Diptera :Chironomidae ,Orthocladiinae )

Micvodistribution Prodiamesa olivacea iswit h itswhit ebod y andlon gblac kparalabia l hair-tuftson eo fth emos teasil yrecognisabl eOrthocladiina e larvae.I twa squit e numerousi nth eSnijdersveerbee k (950specimen s in10 5samples )an dth eRatumsebee k 240specime ni n2 8samples) ,givin ga naverag eo f8- 9 specimenpe rsampl ei nbot h streams. A directrelationshi pwit hdetritu s incombinatio nwit hSan dsubstrate si s apparent inbot hstreams ,which i sillustrate d forth eSnijdersveerbee k inTabl e6 9 forth efiel dclassification .Her eth emai npreferenc e isfo rS+CD+ED ,wit ha mino r over-representationi nS+CD+L .Th epreferenc e ispresen tthroug hal l fourclassifica tionlevels ,excep tfo rth esligh tover-representatio ni nlea fpack s (118specimen s in3 4samples) .Th epreferenc efo rS+CD+E Di sa preferenc etha ti srepeate di nth e grains-sizeclassification ,whic hi sno talway sso ,a sdemonstrate d forsom eo fth e detritus-preferringChironomida e (seeSubsectio n4.2.2.18) . InSor t5-8 ,1 1th emai n preferencei sfo rC Dsubstrat e (Table 70), followedb yth efines tminera l substrate inal lclassification sexcep tSor t6 ,indicatin gtha tsubstrate spreferre db y Prodiamesa containmor etha n1 4CD .I nth e10 1classification sth epreferenc eha s shiftedfro mC Dt oth efines tminera lsubstrates ,which mean stha t P.olivacea occurs predominantlyi nver yFin eSan dsubstrate scombine dwit h1-10 1coars eorgani cdetritus . Asdemonstrate di nAppendi x6 ,thes ear eals oth esubstrate swit hth elarges tamount s offin eorgani cdetritus . Thesligh tover-representatio ni nLeave s isconstan ti nbot hth e1 1an d10 1 classifications,indicatin gtha ti tconcern slea fpack swithou tmuc hminera lmatter . Inth efiel dclassificatio nfo rth eRa bth epreferenc ewa shighes tfo rS+L+F Dan d S+FDfollowe db yS+CD+FD .I nth egrain-siz eclassificatio nth epreference swer eprac tically identicalwit hthos esee nfo rth eSnijb ,excep t forth efac ttha ti nth eRa b Class9 (22x)wa smainl ypreferre d inbot hth e 14an d 104classifications ,whil ede tritussubstrate sshowe dn oover-representatio ni nan yclassification .However ,a n increasei nth eI.R .value s forth efines tminera lsubstrate soccurre di nth e10 4 classification,togethe rwit ha decreas eo fth eI.R . values inCD ,indicatin gtha t sampleswit h1-10 4 CDan dcontainin g P.olivacea weremaske d inth e 14classifications . Thedistributio no fdifferentl ysize dlarva ei nthre elengt hclasse s (0-6,6-1 0 and10-1 7mm )showe dn odifference si nsubstrat epreference .No rwer ether ean ysea sonalvariation si nth edistributiona lpatter nove rth esubstrates .I nth efiel d experiments (Table 16),a selectio no fth e4 m mparticl esiz ewa sseen .Probabl yth e

142 Table69 .I.R .value sfo r Prodiamesa olivaoea (N= 950 )i nth efiel d classification ofth esubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritu s

3 13.3 -15.4 -2.8 1 1 1 1 4 -11.6 33.8 -14.0 -6.8 -2.8 , 1 1 1 1 1 -i 2 -12.0 1 1 1 -2.5 1.9 41.6 -14.0 -6.8 -2.8 I L • i i 1 1 1 II 1 i i 1 —1 1 1-10. 7 -5.8 -2.5 - -2.0 -0.5 1.1 3.7 46.9 -14.0 -6. 2 3.6 -5.0 -3.3 -6.0 St Sh FD L CD CD+LCD+F D L+FD B CEI L CD+L L CD Italicvalue s indicate significant over-representation

Table 70.I.R .value sfo r Prodiamesa olivaaea (N= 950 )i nth egrain-siz e classificationo fth esubstrate s inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14 phi index detritus

2 3 4 CD CD+L Sort5,1 % -1.6-4. 3-11X ) -9.9-5. 5 -4.1-6. 6-7. 6 -5.6 4.4 - 32.9 3.3 -5.4 Sort5,10 % -1.6-4. 9-10. 6-10. 4-5. 7-4. 4-5. 7-7. 3 22.7 13.7 - 6.5 3.3 -5.3 Sort6,1 % -1.6 - -4.7 -13. -7.6-7. 0-7. 1-6. 9 -103 -1.4- 32.9 3.3 -5.4 Sort6,10 % -1.6-1. 6 -5.2-7. 0-6. 9-7. 1-7. 3-7. 1 -3.2 24.4 - 6.5 3.3 -5.3 Sort7,1 % -1.6 -2.2 -32 -1.6 -3.2-3. 9-8. 1-12. 3-12. 2 5.1 32.9 3.3-5. 4 Sort7,10 % -1.6 -3.5 -32 -1.6-3. 2-3. 9-8. 1-11 5 \2 14.5 6.5 3.3 -5.3 QlMdQ3 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L x4x Sort8,1 % -5.0-7. 6-7. 3 -7.0 -7.1 -6.3-7. 5 -7.6 -4.3 -3.6 4.4 32.9 3.3 -5.4 Sort8,10 % -5.2-7. 7 -6.6-7. 1 -7.3 -6.5-7. 3 -7.3 9.2 21£ 13.7 6.5 3.3 -5.3 Italicvalue s indicatesignifican t over-representation

sameexplanatio na sgive nfo rth eover-representatio no f U.gr . praecox inthi s grain-size fractionapplies ,namel yth ehig hamoun to fdetritu s trappedi nth e4m m fraction. Geijskes (1935)an dNietzk e (1937)assigne d Prodiameda olivaaea toth e'mud - inhabitants',a grou po fspecie s consistingo f Mioropseotra praecox, Polypedilum laetum, Polypedilum pédestre, Polypedilum oonvictum, Ablabesmyia geijskesi, Chironomus, Mzcropelopia, Pseatrotanypus andothers ,a communit y alsodescribe db yLindegaar d (1972),wh ogive sa neve nlonge rlis to fspecie si nthi shabitat .Jone s (1951)foun d P.olivaoea mainlyi nsand-mud-detritu s substrates.Marlie r (1951)describe dth e Mioropseotra preaoox community,wher e Prodiamesa olivaoea ison eo fth epredominan t species.

143 Inth eSnijb , M.gr . praecox occurredmos tdominan ti nLea fsubstrate san dles s inth efines tsan d(mud) ,althoug hth elarges tnumber so f M.gr . praecox and P.olivaoea alwaysoccurre di nth esam erang eo fsubstrate s(Clas s9-1 3i nSor t8 , 101),wit hth eonl ydifferenc ei nth emainl ypreferre dtyp e(Leave san d23 xSand , bothi ncombinatio nwit hFin eDetritus) .I nth eRatumsebeek , Mieropsectra gr. praecox occurredmainl yi nth eC Dsubstrates ,whil e P.olivaoea waspredominantl yfoun di n22 x Sand(Clas s 9).However ,al lreference san dth eresult sfro mbot hstream sreporte d hereindicat etha t P.olivaoea preferssof tsubstrates ,consistin go fFin eSan dan d FineDetritu s(mud )wit habundan tCoars eDetritus ,whic hi spresen ti nplace swit ha weakcurrent . P.olivaoea isa free-livin gdetritivor etha ti sver ywel ladapte dt o livei nth esan dhabitat ,wher ei teat sth esan dfo rmicro-organism s (Bryce,1960) . Iti sa neducate dgues stha ti twil lals oconsum elarg eamount so ffin edetritus .

4.2.2.17 Epoicocladiusflaven s(Malloch )(Diptera :Chironomidae ,Orthocladiinae )

Microdistribution Thelif ecycl eo f E.flavens andit sassociatio nwit h Ephemera danica (Ephemeroptera)ha sbee nexcellentl ydescribe db ySvensso n(1976) .H efoun d lesstha n 2%o fth etota lnumbe ro f E.flavens larvaefre ei nth esubstrate ;th eres t wasassociate dwit h Ephemera danica nymphs. Inth eSnij ban dth eRab ,th esecon dt ofourt hinsta rlarva e(longe rtha n1 mm ) werealway sfoun di nsample scontainin g E.danica nymphs,bu tsinc eth enumbe ro flar vaeo nth eliv enymph swa sno tdetermined ,i ti sno tpossibl et osa ywhethe rsom e occurredfre eo rwhethe ral lwer eattache dt o E.danica. Inth eSnijb ,onl yfou r E.flavens larvaewer efoun d(wit h43 6 E.danica nymphsi nth esamples) .I nth eRab , however,13 0larva eoccurre dtogethe rwit h50 4 E.danica nymphs,althoug hi nal l samplescontainin g E.flavens larvaeonl y19 0 E.danica nymphswer epresent .Thi sgive s arathe rlo winfestatio nrati o(0.26 )o nth etota laverag ean di sstil llo w(0.68 ) whenonl yconsiderin gth esample scontainin gbot hlarva ean dnymphs . Comparisono fth edistributio no f Epoicocladius flavens inth eRa bwit htha to f Ephemera danica shouldgiv ea simila rdistributio ni fth elarva echoos ethei rhost s atrandom .I fthe yprefe rlarge rnymphs ,a differenc ei nth etota ldistributio n shouldb efound ,bu tagreemen twit htha to fth elarge rnymphs . Inth efiel dclassificatio n(Tabl e71 ) E.flavens showsa clea rpreferenc efo r S+CD+FD,wit ha .muc hlowe rpositiv eI.R .valu ei nS+L+FD .Thi sagree sver ywel lwit h thepreferenc eo f E.danica (Table36) ,especiall ysinc eth eover-representatio ni n S+FDan dG+ Li scause db yth e6-1 5m msiz eclas san dlarge rspecimen sar emor eo r lessretricte dt oS+CD+FD .I nth egrain-siz eclassificatio n(Tabl e72 )th epreferenc e of E.flavens inSor t8 ,10 %agree sbes twit htha to fth elarges t E.danica nymphs (Table40) .Th esam eshift so fpreferenc eexis tbetwee nth e1 1an d10 1classification . Analysiso fthes edat afo reac hnympha lsiz eclas sshow sagai ntha t E. flavens followsth elarges t E.danica nymphs.Difference sbetwee nTabl e7 2an dTabl e3 8ca nb e relatedt oth epresenc eo fman ysmal lnymph s(se eTabl e40) .Althoug h23 xi spreferred ,

144 Table71 .I.R .value sfo r Epoioooladius flaVens (N= 130 )i nth efiel dclassificatio n ofth esubstrate si nth eRatumsebeek .

Sort Sand Gravel Detritus

3 4.0 -0.6 -5.4 I— _l I 4 -3.8 10.6 0.3 -1.8 -5.4 r _J I I I I -3.6 -1.3 -0.8 12.3 0.3 -1.8 -5.4 I , I , , I 1 I 1 1 I 1 -2.1 -3.1 -l[3 -0.8 -0.6 -1.4 13.3 2.0 0.3 0.4 -2.0 -1.8 -4.8 -1.6 St Sh FD L CD CD+LCD+F DL+F D B CD CD L CD+L +FD

Italicvalue sindicat esignifican tover-representatio n

Table72 .I.R .value sfo r Epoioooladius flavens (N= 130 )i nth egrain-siz e classificationo fth esubstrate si nth eRatumsebeek .

Substrate! clas s

1 2 3 4 5 6 7 8 9 10 11 12 13 14

phi index detritus L CD+L 7 6 5 4 3 2 Ï 1 2 3 4 CD -4.0 -2.0 Sort5,1 % 2.9 -1.2 -1.8 2.5 -2.6 -0.8 -1.2 -2.2 -2.6 -0.8 10.8 -4.8 -1.6 Sort5,10 % -1.2 -1.8 2.3 -2.9 -0.7 -1.2 -1.8 8.9 -1.8 -1.8 2.9 -4.0 -2.0 Sort 6,1% -0.8 0.2 -1.6 -1.3 1.5 0.5 -4.3 1.4 10.8 -4.8 -1.6 Sort 6,10% -0.8 0.2 -1.6 -1.4 1.5 0.1 -3.1 14.4 -1.8 Sort7,1 % -0.8 -0.2 -3.8 -0.1 2.9 10.8 -4.0 -2.0 Sort7,10 % -0.8 -0.2 -4.3 9.6 -0.2 -1.8 -4.8 -1.6 23x 33x CD L CD+L xBx x3x x2x xïx xlx XXX Ixx 22x QlMdQ3 index XXX x4x -0.8 10.8 -4.0 -2.0 Sort8,1 % -0.8 0.2 -1.6 -1.3 1.5 0.5 -1.9 -2.2 -3.4 •2.1 -1.8 -1.8 -4.8 -1.6 Sort8,10 % -0.8 0.2 -1.6 -1.4 1.5 0.1 -1.9 -1.8 -1.5 19.1

Italic values indicate significant over--representation

E. flavens occurred (on E.danioa nymphs)i nal lgrai nsize sfro mClas s4-1 0i nSor t8 , 101wit ha nadditiona lthre elarva e inClas s2 (x5x ,x4x) .Sinc eonl y5 pupa ewer e foundi nth eshove lsamples ,n oreliabl estatemen tca nb emad eo nthei rdistribution . Alllarva lsiz eclasse sshowe dth esam edistributiona lpattern ,wit hth emai npreferenc e forClas s1 0(23x) . Althoughonl yS E. flavens pupaewer ecollecte di nth esubstrat esamples ,man y E.danioa nymphswer efoun dwit hth eremain so fpupa ltube sattache dt oth esternu m betweenth emiddl e legs,ofte no nbot hsides ,indicatin gtha ttw opupa eha dbee n attached.Sinc eth epupa lstag eonl ylast sa fe wdays ,the yar eeasil ymisse dwit ha samplingfrequenc yo fonc ei ntw oweeks .Hence ,nothin g canb econclude do nth edis tributiono f E.flavens pupae. 4.2.2.18 Chironomidaeo fdetritu s substrates

Ofth e2 0Chironomida e species foundwit hmor e than10 0specimen s during thisinvestigation ,th efollowin g7 showe da majo rpreferenc efo rCoars eDetritu s and/orLea fsubstrate si nbot hth efiel dan dth egrain-siz e classifications (Appen dices9 ,1 2an d 13): 253/254 Conahapelopia (melanops) 269 Coxnjnoneura spp. 272 Brillia modeeta 275 Diploaladius aultvigev 277 Rheoavicotopus spp. 279 Eukiefferiella gr. disaolovipes 310 Polypediltm laetumagg . Comparisono fAppendi x9 wit hAppendice s 12an d1 3show stha tpreference sfo r sando rgrave lsubstrate si nth efiel dclassificatio nar eno tsee ni nth eminera l classesi nth egrain-siz eclassifications .Thi s indicates thatdetritu si smor e importantfo rthes especie s thanminera lmatter .Al lspecie s listedabov ewer e mentionedb yLindegaar d (1972)a sspecie swit hvegetatio na sthei rspecifi chabitat . Nietzke (1937)classifie d thesespecies ,excep t Conahapelopia, inth egrou po fspe ciesoccurrin gmainl yi naquati cvegetatio no r(les sabundant )o nstones .Geijske s (1935)mentioned ,amon gothers , Bvillia, Covynonewa, Rheoavicotopus and Limnophyes forth edetritu shabitat .Fo rdetaile dnote so nth eecolog yo fthes e species,th e paperb yLindegaar d (1972)ca nb econsulted .Sinc eth eclassification s Sort2- 4an d Sort5- 7d ono tad dan yvita l informationo nth esubstrat epreference so fthes e species,onl ySor t1 an dSor t8 wil lb epresented . (Table7 3an dAppendice s 12an d 13). .

Conchapelopiamelanop s (Wiedemann) (Diptera:Chironomidae ,Tanypodinae )

Miavodistribution Conahapelopia larvaecanno tb eidentifie dt ospecie s levelwhe n thepupa lthoraca lhorn sar estil labsent .Sinc eal llarva ean dpupa etha tcoul db e identifiedt ospecie sleve lwer e C.melanope, all Conahapelopia larvaewer e considered tobelon gt othi sspecies . Conahapelopia isth eonl yTanypodina epreferrin g Detritus substrates above mineralsubstrate s (cf.Appendice s9 ,1 2an d13) .Althoug h relativelymor e larvae were foundi nS+ Dan dG+ Dtha ni npur eDetritu s substrates,th edensitie spe rsampl e weremuc hhighe ri nth elatter .Compariso no fSor t8 ,1 1wit hSor t8 ,10 1 (Table74 ) showsa nincreas eo fth eI.R .value si nmos to fth eminera l substrates,togethe rwit h anincreas ei nth eorgani csubstrates .Thi s indicatestha ta tleas tpar to fth epopu lationlive si nminera l substrateswit h1-10 1organi cmatter .However ,thi sdoe sno t concerndifferen t instarssinc eanalysi so fth edistributio no fdifferen t length classesreveale dn osignifican tdifference si ndistribution .

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147 Lindegaard (1972)mentione dtha t Conahapelopia livesprimaril yo nElodea veg etationi nplace swher eth ecurren ti sweak .H eassume dtha t Eukiefferiella and Criaotopus species,whic hals ooccu ri nthi shabitat ,wil lb eth emai nfoo dorganism s forth epredator y Conahapelopia larvae.I nth etw oinvestigate dDutc hstream s anyo f thespecie sdwellin gi nth edetritu shabita tmigh tserv ea sfoo dfo r Conahapelopia. However,onl ya nanalysi so fth egu tcontent sca nclarif ythi si ndetail . Inth etw ostream sstudied , Conahapelopia was foundwit hal llarva lsize spresen t duringth ewhol eyear .N osignifican tdifference si nsubstrat epreferenc ewer e seen betweenlarva eo fdifferen tsiz e (1-5an d5-1 0mm) . Preference forC Dwa spresen ti n allseason sbu thighes ti nsprin gan dsumme r (Table 74). Inwinte rpreferenc e foral l Detritus substrateswa sequall yhig han dshare dwit hFin eSan dwit hDetritu s (33x). Inautum nSan dsubstrate swer efavoure dafte rCD+L . Inth ecolonizatio nexperiment so fsevera lgrain-siz e fractionsi nth eRa b (Tables1 5an d16 ,Subsectio n 4.1.7), Conahapelopia preferred the2 an d4 m mfraction s afterbot hcolonizatio nperiod s (like Maoropelopia nebulosa, anotherTanypodina e larva). Moredat ao nth econdition soccurrin gi nth eartificia lsubstrate si nth efiel dar e necessaryt oexplai nthi spreference .

~~CorynoneuraWinnert zspp . (Diptera:Chironomidae ,Orthocladiinae )~~

Utorodietribution Thegenu s Corynoneura wasrepresente db ya tleas ttw ospecies : C.minuta and C.scutellata.C.minuta correspondst oth e Corynoneura sp.I Io fLindegaar d (1972)an d C.soutellata resembleshi s sp.I . Treateda tth egeneri clevel ,thi smixtur eo fspecie sshowe da clea rpreferenc e fororgani csubstrates ,especiall yCoars eDetritu so rLeaves .I nth eSnij bonl ya slightover-representatio noccurre di nS+ Lan dG+ L (Table 73).I nth eRa b Corynoneura occurredpredominantl yi nlea fpacks .Ber ge tal . (1948)an dLindegaar d (1972)foun d Corynomeura mainlyi nvegetatio nwher edetritu si softe nabundant .

~~Brilliamodest a (Meigen)(Diptera :Chironomidae ,Orthocladiinae )~~

Microdistribution B.modesta isth emos tcommo n Brillia speciesfound ,an dth eonl y onei nth eRab .I nth eSnijb ,anothe rspecie swa spresen ti nlo wnumbers : B.longifuraa (19specimens) . Bothspecie soccurre di nth esam esubstrat e types.I nal lsubstrat eclassifi cations B.modesta showedpreferenc efo rDetritu s substratesi ngeneral ,an dfo r Leavesi nparticula r (Table7 3an dAppendice s 9,1 2an d 13). Inbot hstreams ,CD+ L wasth esecon dpreference ,followe di nth eSnij bb yC Da sth ethir dchoice .Considerin g theactua lnumber so f Brillia modesta larvaei nth eSnijdersveerbeek ,92 1o fal l larvaewa spresen ti non eo fth ethre eorgani csubstrate si nSor t8 ,101 .Onl y3 5 larvaewer efoun di nth eminera lsubstrates .I nth efiel dclassificatio nthi swa s90 $ forth edetritu ssubstrate san dth e4 2remainin g larvaeoccurre di nth eminera l

148 Substratescombine dwit hC Do rL . Inth eRab ,onl ythre elarva e (21)di dno toccu ri nth edetritu ssubstrate si n anyclassification .Thes edat aemphasiz etha torgani csubstrate sfor mth especifi c habitato f Brill-La. Geijskes (193S)foun dthe mmainl ybetwee nleaves ,bu tals oi n moss,detritu san dalgae .Ber ge tal . (1948)foun d Bvillia betweenbeec hleave si na slowrunnin gspring .Hyne s (1970a)mentione dtha t Bvillia isa wood-eatin gspecies , whichagree swit hth eobservation sb yN.H .Anderso n (personalcommunication )tha t Bvillia dwellsmainl yi ncoars edetritu ssubstrate swit ha lo to fdecayin gwoo d present.I ti spossibl etha tthi sconcern sa differenc ei nth e Bvillia species,sinc e B.modesta showeda distinc tpreferenc efo rLea fsubstrate swithou tmuc hdetritu si n thefor mo fsticks ,bark ,fruit so rdecayin gwood .Mor elikel yi sth eassumptio ntha t itconcern sa nadaptatio nt oth emost-readily-availabl e foodsource .

~~Diplocladiuscultrige rKieffe r (Diptera:Chironomidae ,Orthocladiinae )~~

Mievodistvibution Thisfree-livin gOrthocladiina ewa sfoun di nbot hstreams ,wher e itoccurre di nth eRa bmainl yi nLea fpack san dwit hequa lpreferenc efo rLea fpack s andCD+ Li nth eSnij b (Table 73).Lindegaar d (1972)foun d Diplocladius aulteigev predominantlyi nvegetatio ntogethe rwit h Eukieffeviella species.Thi scombinatio ni s alsoapparen tfo rth eLea fsubstrat ei nth eSnijb ,althoug hsom edifference sremai n concerningth esecondl ypreferre dsubstrate . V.oultvigev wasmos tabundan ti nautumn ,winte ran dspring .I nsumme ronl yver y smallnumber swer efoun di nbot hstreams ,whic hagree swit hth edat aan dreference s Lindegaard (1972)presented .H econclude dtha t V.oultvigev isa sprin gspecies . Alllarva llengt hclasse sdistinguishe d (1-4nm ,4- 6m man dlarge rspecimens )showe d similarsubstrat epreference s inal lseasons .

~~RheocricotopusThieneman nspp .(Diptera :Chironomidae ,Orthocladiinae )~~

Mievodistvibution Onlyo na fe woccasion swer e Rheooviootopus larvaeidentifie dt o specieslevel ,an dthe ntw ospecie swer erecognized : R.dovievi and R.fusoipes, the latterprobabl ybein gth emos tabundan ton e (MollerPillot ,persona lcommunication) . However,al l Rheooviootopus spp.wer etreate da tth egeneri clevel . Rheooviootopus wasextremel yabundan ti nlea fpacks ,wit hsmalle rnumber si n CoarseDetritu ssubstrate san da fe wspecimen so nstone scombine dwit ha fe wleave s (Table 73).Thi s isa distributio nquit esimila rt otha to f Eukieffeviella gr. disoolovipes. Thesam eincreas ei nI.R .value so fth epreferre ddetritu ssubstrat e (Leaves)an ddecreas eo fI.R . valuesi nth e 'mineral'substrate s isobserve di n comparingSor t8,1 1an dSor t8,101 .I nSor t5- 7als oover-representatio nwa ssee ni n thecoarses tminera lsubstrate ,bu tthi sconcerne donl yon esampl e (seeAppendi x4) . Thienemann (1954,p .629 )gav ea sth echaracteristi cbiotop efo r Rheooviootopus theslower -o rfaster-runnin griver san dstreams ,an deve nsprings ,i nlowland san d

149 middleo rhig hmountai nareas ,mostl ybetwee nplant sbu tals oo nstones ,eve ni n pollutedstreams . Lindegaard (1972)mention stha t Rheocriaotopus fuscipes isa sprin gfor ma sal l specimensoccurre dfro mMarc ht oMa ywit ha maximu mi nApril .I nth eSnij ban dth e Rabth elarva ewer ealway spresen twit hmaximu mdensitie si nspring ,autum nan d winter,indicatin gtha ti tconcern smor egeneration sa yea ro ramixtur eo fspecies . Rh.effusus isknow nt ohav ethre egeneration sdurin gsprin gan dsumme r (Lindegaard, 1972).

~~Eukiefferiellagr .discoloripe s (sensuMolle rPillot ,1980 ) (Diptera:Chironomidae , Orthocladiinae)~~

Microdistribution Thisgree nOrthocladiina e larvawa squit eabundan ti nth eSnijders - veerbeeè,bu twa sfoun donl yincidentall yi nth eRatumsebeek .I tprove dt ob ea tru e representativeo fNietzke' s (1937)plants-stone sgrou pa si tpreferre ddetritu san d gravelsubstrate s (Table73) :G+L ,C Dan dL i nSor t 1.I nSor t8 ,onl yC Dan dL wer e preferredan dn o 'mineral'substrates ,indicatin gtha to fth ecombinatio ngravel - leaves,th eleave swer emor eimportant .Th eI.R .value si nth eC Dan dL classe si n Sort8 increase dfro mth e1 1t oth e10 1classificatio nwithou tan yincreas ei nth e I.R.value si nth e 'mineral'classes ,whic hindicate stha tdetritu ssample swit honl y 1-10%organi cmateria lar eno tth epreferre dsubstrat efo r Eukiefferiella gr. discoloripes. Thisresul tcorrespond swel lwit hth eobservation so fThieneman n (1936,p .50 ) asreporte db yBer ge tal . (1948),wh ofoun dtha t Eukiefferiella larvaedeman dgoo d oxygencondition si nfast-runnin gwater ,wher ethe ydwel lbetwee nalga ean dmos so n stones.Ber ge tal . (1948)als ofoun dthe mo nstones .Th ereaso nfo rth esmal l populationo f E. gr. discoloripes inth eRatumsebee ki sno tknown . Eukiefferiella -oerralli larvae(include di nth e discoloripes group)fee do n detritusan dalthoug hthe yar erheobiontic ,the yar emos tabundan t inplace sno t exposedt oth estronges tcurren t (vegetation)wher edetritu saccumulate s (Lindegaard, 1972).Thi styp eo fdistributio ncorrespond sclosel ywit htha to fEukiefferiella gr. discoloripes inth eSnijdersveerbeek . E. gr. discoloripes ispresen tthroughou t theyear ,wit ha minimu mi nnumber si n sunmeri nth eSnijdersveerbeek .Pupa ewer e foundi nMarch ,an dprobabl yth efligh t periodwil lb eth esam ea sLindegaar d (1972)reported :Marc h- Jun e andincidentall y duringth ewhol esummer ,sinc esmal llarva ewer emos tabundan t fromOctobe rt oDecem beran dlarg elarva efro mFebruar yt oApril .

~~150 Polypedilumlaetu magg . (sensuMolle rPillot ,1979 )(Diptera :Chironomidae , Chironominae)~~

Identification P. laetum isa Polypedilum speciestha tca nb eeasil yconfuse dwit h P.pedestre. Allmateria lwa schecke dwit hth emos trecen tke y(Molle rPillot , 1979) andman y identificationswer echecke db yMolle rPillot . Miarodistribution P. laetum wasonl yfoun donc ei nth eRab ,downstrea mo fth einvesti gatedstrea msection .I nth eSnijb ,larg enumber so flarva ewer e found.The yoccurre d predominantlyi ndetritu ssubstrates ,showin ga simila rdistributio na s Conahapelopia melanops. Leaves,C Dan dS+CD+ Lwer emostl ypreferre d (Table 73),whic hagree swit h Hynes' (1970a)statemen ttha t Polypedilum belongst oth ewood-eaters ,althoug hh edi d notspecif yth especies . Inth efiel dclassification ,a mino rover-representatio nwa ssee ni nBar eGravel , butthi sappeare dt ob ea distinc tpreferenc efo r3Ï xsubstrates,.whic hi sconclude d fromTabl e 75.Moreover ,thi sconcerne donl yon esampl ewit h15 0specimens .Th ein creaseo fth eI.R .value si nC Dan dL substrate s indicatestha tsubstrate smainl y consistingo forgani cmateria lar epreferre dan dno tth ecombinatio nwit hSand .Thi s agreeswit hth esubstrat ewher eBer ge tal . (1948)foun d P.laetum: onstone sand ' vegetation. Breakdowno fth epreference st otw olarva llengt hclasse s (Table76A )show s that thepreferenc efo r3Ï xresult sfro mth esmalle rlarva e (0-5 mm), althoughthes esho w aneve nhighe rpreferenc efo rLeaves .Large rlarva e (5-8mm )mainl yoccu ri nDetritu s substratesan da numbe ro fno tmeasure d larvaepreferre dCoars eSan d (xxx).

~~Table75 .I.R . values for Polypedilum laetum agg.( N= 1125 )i nth egrain-siz e classification of thesubstrate s inth eSnijdersveerbeek .~~

~~Substrateclas s~~

~~10 11 12 13 14~~

~~phi index detritus~~

~~CD CD+L~~

Sort 5,1% -1.7-3. 2-5. 5-10. 3 19.0 -6.2-2. 1-8. 2 -9.4 -2.5 - S.7 22.4 -0.5 Sort5,10 % -1.7-3. 2-5. 7-10. 8 17.7 -6.4 6.8 -8.9-10 5 -5.6 - 14.7 24.2 -4.4 Sort6,1 % -1.7 - -4.8 -13 -5.0-6. 3 10.6 -7.4-11. 4 -6.4 - S.7 22.4 -0.5 Sort 6,10% -1.7-1. 7-4. 1 -2.0-5. 2-6. 5 10.0 -7.6 -8.4 -8.6 - 14.7 24.2 -4.4 Sort7,1 % -1.7-2. 4 -3.4-1. 7-2. 9-4. 2-2. 9 -2.4-12. 6-1. 4 5.7 22.4 -0.5 Sort 7,10% -1.7-2. 0 -3.4-1. 7-2. 9-4. 2-2. 9 -3:0-11. 3-3. 4 14.7 24.2 -4.4 QlMdQ3 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD CD+L x4x Sort 8,1% -5.4-2. 2 -4.5-6. 3 10.6 -7.9 -3.9 -8.2-7. 9-5. 4-2. 5 5.7 22.4 -0.5 Sort 8,10% -5.7-2. 2 -4.7-6. 5 10.1 -8.1 2.4 -8.9-9. 5-5. 8-5. 6 14.7 24.2 -4.4

~~Italicvalue s indicate significant over-representation~~

~~151 Table76 .I.R .value sfo r Volypedilvm laetum agg.pe rlengt hclas s (A)an d season (B)i nth eSnijdersveerbee k inSor t 8,10%.~~

Length N Substrate clas s andQ,M . Qg index class 1 0 and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Season XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L x4x A 0 53 35t 18t 1-5 919 -5.1 -0.8 -3.7 -6.1 12.7 -7.3 -0.2 -8.0 -8.5 -4.7 -4.8 8.9 28.0 -4.9 6-10 153 -2.1 -2.7 -2.8 -1.6 -3.0 -3.0 -0.4 -2.9 -3.5 -2.6 -2.5 13.5 11.8 0.8 Total 1125 -5.7 -2.2 -4.7 -6.5 10.0 -8.1 2.4 -8.9 -9.5 -5.8 -5.6 14.7 29.2 -4.4 B Spring 459 -2.4 -2.9 0.5 -4.9 -5.5 -4.9 -6.6 -6.5 -5.5 -5.5 -2.4 13.5 34.8 -3.7 Summer 122 -2.1 -1.4 -0.7 0.2 -2.0 -3.4 10.5 -0.2 -2.4 -0.2 -2.7 3.6 - - Autumn 452 -3.8 -4.1 -3.0 -4.9 22. S -3.1 0.7 -7.2 -6.7 -2.3 -1.9 7.2 5.0 -2.4 Winter 92 -1.7 10.1 -2.9 -1.9 -2.0 -2.2 -1.1 -0.4 -3.0 -2.0 -1.4 4.3 3.2 -1.0

~~Italicvalue sindicat e significant over-representation t :Actua l numbers aregiven .N o I.R. values calculated~~

Seasonallyther ear eals odifference s (Table 76B).I nspring ,Detritu s substrates werepreferred ,whil ei nautum nmos t larvaeoccurre d inxl xGrave l andDetritus .I n sunnier,onl yminera l substrates showove rrepresentation ,whil e inwinte r Coarse Gravel (x5x,x4x )i spreferre d togetherwit hDetritus .Thi s clearly indicates that theautumn-winter-sprin g generationha sothe rpreference s thanth esumme rgeneration . A facttha tmigh tb econnecte dwit hth eavailabilit yo fth epreferre dsubstrates . Insummer ,whe ndetritu ssubstrate sar e scarce,th egeneratio nspend sa muc h shortertim ei nth estream .I nautum nan dwinter ,whe ndetritu s substrates areabun dantbu tlarva lgrowt hi sminimal ,th eyoun glarva eprefe rminera l substrates,whil e inspring ,a perio do ffas tgrowth ,the yobviousl ymov et odetritus .

~~152 5 General discussion~~

As demonstratedi nSubsectio n 4.1.5. andelucidate d forsevera l speciesi n Subsection 4.2.2,mos tmacroinvertebrat especie s are strongly relatedt o certain substrate types composed ofminera l ororgani cmateria lo ra combinatio no fboth . These results support thehypothesi s thatman y lowland-stream specieshav e distinct substratepreferences ,ofte nwit hnarro wrange s concerning thepreferre d particle size (combinations).Th eresult s concerning thespecie s dealtwit h indetai lhav e alreadybee ncompare dwit h literaturedat ai nSubsectio n4.2. 2 and ingenera l agree witho rgiv eadditiona l ormor edetaile d informationo nth esubstrat epreferences . One should,however ,kee p inmin d thatrelationship swit h certain substrate typeso rparticl e sizes,conclude d fromover-representatio ni nthes e substrates,ar e notnecessaril y theresul to fpreference s forth esubstrate .Preferenc e impliesth e active choiceo f'optimal 'condition sb yth e animals,an dconclusion s about substrate preference shouldtherefor eb ebase do nlaborator yexperiment si ncombinatio nwit h fielddata .I ti s notpracticable ,however ,t operfor m laboratory experiments testing thesubstrat eo rparticle-siz e selection foral lspecie spresen ti na stream . Oftenpreferenc ewil lno tb e aimeda tth esubstrat ecompositio no rth e particle size itself,bu ta t(th ecombinatio n of)othe rfactor sprevailin gi ntha tparticula r habitatan dperhap s oneshoul dspea ko fhabita tpreferenc e rather thano f substrate preference,especiall ywhe nonl y fielddat aar eavailabl e andth esubstrat ei s in factuse d asa descripto ro fth ehabitat .Current ,foo d andoxyge ncondition s areal l strongly related to thesubstrat econdition s and thesubstrat ei stherefor ea nout standingparamete rt odescrib ea habitat .Not .onl ybecaus ei t catches theey ean di s easier todescrib e ormeasure ,bu tals obecaus e itusuall y reflects the conditions prevailing inth eperio dbefor esampling . Thepresenc eo fa specie si nahabita t isth eresul to fit sbahavioura l response toth e environmental conditionsprevailin go nth espo t (MeadowsS Campbell , 1972). Cummins (1975)state d thatth erelationshi po fth emicrodistributio n and abundance ofmacroinvertebrate swit hvariou s specificphysical-chemica l parametersma yb eo f onlya nindirec tnature .Th e animaldistribution sma yactuall yb e controlledb ysom e otherfactor ,whic h itselfi smor edirectl y relatedt oa physical-chemica l parameter. Substrate composition,o rth erang eo fparticl esize spresen t ina habitat ,i s determinedb yth ecurren t (velocity,flo wregim ean dturbulence) ,whil e thesear e alsoresponsibl e forth eamoun to faccumulate d organicdetritus ,th egrowt ho fmacro - phytesan dth eoxyge nsupply .Thu si ti s possibletha ta relationshi pbetwee nth e microdistribution ofa specie s and thesubstrat ei si nfac tcontrolle db y the current

153 velocityo rth eamoun to ffoo d (detritus)present .However ,o nth ebasi so fth e knowledgeo fth ecorrelatio nbetwee nvariou sspecifi c parameters andth esubstrat e iti spossibl et oindicat efo reac hspecie swhic hparamete rwil lb eresponsibl efo r the selectiono fa certai nsubstrat etype . Themos t importantmechanism s seeni nSubsectio n 4.2.2.ar eeithe r directly linkedt oth esubstrate ,becaus e itrestrict so renhance s thepossibilitie sfo r burrowing,attachin g (clinging,sucking) ,hidin go rth eprovisio no fth emateria l necessary forcas eo rtub ebuilding ,o rindirectly ,becaus e offactor s associated with substrate conditions,e.g .microbial ,alga lo rdetrita l food,o rpre y density, current-velocity,-regim ean d-turbulenc e andoxyge n supply. Insummar y itca nb e statedtha tth ethre e factorsmainl y responsiblefo rsubstrat e selectionare : particle size,curren tvelocit yan dfoo d conditions,a sals o illustrated inth e diagrampresente db yCummin s& Lau f (1969) (Fig.1) . Ofcours e these factorsar e ofteno fa combine d influencean dno teasil y separated,bu ti twil lb epossibl et o illustratethei r individualroles .

~~5.1 PARTICLE SIZE~~

Speciesreactin gdirectl yt osubstrat eparticl e sizeca nb efoun d especially amongth especie sdwellin go ncoars esubstrates ,wher e thesurfac e islarg eenoug ht o allowattachmen tan dclingin g (Simulium) orsmoot h enought oallo w sucking (Anaylue) orth esealin gof fo fth eventra lsid eo fth ebod y (Elmis larvae).Althoug h these relationshipswit h coarsesubstrate s areinseparabl y connectedwit hhighe r current velocities,thes e speciesar eno tfoun do nfin e substrateswit h similar (high) currents.Coars eminera l substrates arecomparabl e tomacrophytes ,branche so rob jectsa splasti cbags ,kettles ,bottles ,etc. ,whic hal lhav e incommo ntha tth e surfaceare ai slarg ean dsmooth . Otherspecie sdistinctl y relatedt oth eparticl e sizeo fth esubstrat ear e those thatinges tth eminera l substrate inorde rt ocollec t theattache d microbial andalga lgrowth .Thi swa sdemonstrate d forsevera lOligochaet ab yJuge t (1979),wh o showeda positiv e correlationbetwee nth eingeste dparticl e size,th epresenc eo f theseparticl e sizesi nth esubstrat ean dth ewidt ho fth eintestines .Thi sma yb e oneo fth ereason swh yth esmal lOligochaet a (mainlyTubificidae ) aremostl yrestric tedt oth efin esubstrates ,whil eth elarge r Eieeniella dwells incoarse r substrates (Appendices9 an d12) , sinceth eforme r feedso ndetritu s andmu d (smaller than0.1 3 mm (Juget,1979) )whil eth elatte r feedso nbacteri aan ddiatom s scraped from larger sandgrain s (0.3-1.3mm )o rfilamentou s algae (Ward, 1976). Ephemera danica couldb e anexampl eo fsuc ha relationshi pa swell ,sinc eEphemerida e areknow nt oinges t largeamount so finorgani csediment ,togethe rwit h theirmai n food source,fin e detritusan dth eassociate dmicrobia l growthan dseston . Itwa sdemonstrate d thatth e distributiono f Ephemera daniaa islinke dwit hth epresenc e offin e detritus inth e substrate,an dth econclusio nmigh t followtha tth efacto r foodwil lb ea nimportan t

154 selectionmechanis mfo r Ephemera danioa. However,Erikse n (1963)demonstrate dfo r E.similans thatth etolerabl eamoun to ffin eminera lmateria ltha tma yb epresen t islimite dbecaus eo fit sdetrimenta leffec to nth eoxyge nconten to fth eintersti tialwater .Fo r E.eimulans theoxyge nconten to fth einterstitia lwate rreache sth e criticalvalu eo f1.2 0mg/ 1whe n8-10 1o fth esubstrat econsist so ffin esan d (0.125-0.250mm) . Underthes econdition si ti snecessar ytha tth eburro wremain si n opencontac twit hth estrea mwater .I nthi seven ta certai n (small)amoun to fver y fineparticle s (silt,lutum )i s necessaryt oglu elarge rparticle stogethe rt oobtai n a stabletunne lstructur e (Eastham,1939) .However ,th eamoun to fver yfin eparticle s mustno tb eto ohigh ,becaus eth egil lmovemen to fEphemer ama yb eobstructed .Thu s itca nb econclude dtha t Ephemera danioa needssubstrate swit henoug hfin eorgani c detritust ofee don ,bu tcoars eenoug hi nminera lparticle-siz ecompositio nt oallo w a good interchangeo foxyge nbetwee nth einterstitia lwate ran dth estream ,o rwit h a largeenoug hproportio no ffin eparticle s (smallertha n0.0 5mm )t omak eth esub stratesticky ,bu tno tto omuc ht oclo gth egill so fth enymphs . Iti sver ylikel ytha tothe rburrowin gspecie sar erelate dt oth eparticle-siz e compositiono fth esubstrat ei na simila rmanner .Th eselectio no fparticula rsub stratesfo rpupatio nb ylas tinsta rlarva eo f M.sequax couldb e causedb yth efac t thatsubstrat ecompositio ni srelate dt ocurren tvelocit yan doxyge nsupply .Pupa e areunabl et omigrat et omor esuitabl eplace swhe ncondition schange .T osurviv ei t istherefor eobligator yt oselec tsite swher esuc hchange sar eleas tlikely . The aggregationo fth epupa eo f Lithax obeaurue, Agapetue fusaipee and Potamophylax luatuosus onstone san dbranche sprojectin gfro mth estrea mbed ,ofte nnea rth ebanks , isprobabl yth eresul to fth esam ephenomenon . Otherspecie sshowin ga direc trelationshi pwit hth eparticl esiz ear ethos e thatus eth eminera lan dorgani cmateria lfo rcas ebuildin go rtub eformation .I t wasdemonstrate di ncas ebuildin gexperiment stha t Seriaostoma pereonatum uses mainly0.25-0.5 0m mgrain sfo rit scas ean dtha tth erang eo fmaterial stha tca nb e usedlie sbetwee n0.12 5m man d 1.0mm .Thi smean stha t Seriaostoma pereonatum will needa substrat eo fwhic ha considerabl eproportio nfall swithi nthi sgrai nsiz e range,althoug hi ti s notknow nye twha tth eminimu mamoun tshoul dbe .Furthermore , Seriaostoma pereonatum dwellspreferabl yi ncoars esubstrates ,whic hmean stha tth e case-buildingmateria lha st ob efoun damon gth esmalle rfraction san dtha tth e substrateselectio ni srelate dt osom eothe rfactor ,whic hi sprobabl yth epresenc e ofCoars eDetritus ,a sdemonstrate dbefore ,an da moderat et ofas tcurren tvelocity . Thecaddi slarva e Lithax obeaurus and Agapetue fusaipes bothprefe rgravell y substrates,wher ethe yliv eo nto po fstone sor ,whe nth ecurren ti sver ystrong , behindstones .The ybot hus eminera lmatte rt oconstruc tthei rcases . Agapetue fusaipes usesgrain-siz efraction srangin gfro m0.25-0.8 5m mi nth eF- 3 instar,bu t thisgraduall yshift st o0.5-0.8 5m man d1- 2m mfraction si nth eF- 1instar , and mainlyth e 1-2m mfractio ni nth efina linsta ran dth epupa lcase .Comparin gth e

155 distributiono f Agapetua fusaipes inth eRatumsebee kwit hth eparticle-siz eselec tionfo rcas ebuilding ,i ti sclea rtha tselectio no f1- ran2 grain s inth efina l andpupa lstag ei srelate dt oth epresenc eo fthi sfractio ni nth eunderlyin g material.Substrate swit ha media nparticl esiz erangin g from0. 5m mt o2 m mar e clearlypreferre d (M,= Ï an d1 ,respectivel y ;Appendi x 13),togethe rwit hver y coarsesubstrate s (x5x,x3x) ,fo rwhic hQ 3varie s around0. 5mm .Thi smean stha t enoughsuitabl egrain swil lb epresen tfo rth e(largely )fina l instar larvaean d pupaeo nthi ssubstrate .Smalle rlarva eus erelativel ymor e smallgrain san dthe y occurpredominantl yo nfine rsubstrate s thanlarge rlarvae .A similar conclusion appliest o Lithax obseurus (cf.Tabl e 21).

~~5.2. CURRENT VELOCITY~~

Sincesubstrat ean dcurren tar etw oinseparabl yconnecte d factors (Schmitz, 1961; Scherer,1965 )i ti sver ydifficul tt odistinguis hwhethe rth eindividua l factorso rthei rcombinatio ndetermin emacr oinvertebrat epreferences ,althoug hth e latteri smos tprobable .Th ecurren ti sresponsibl efo rth evariatio no fth egrain-siz e compositionove rver yshor tdistance s (mosaicpattern san dlongitudina l substrate bands).Th ecurren tinfluences ,fo rexample ,th eoxyge nconten to fth einterstitia l water,th eamoun to ftrappe ddetritus ,th enumbe ro fcrevice san dth egrowt ho f periphyton.Togethe rwit hth einteraction sbetwee nvolum eo fflo wan dchanne ldimen sions,th ecurren ti sresponsibl efo rth ezonatio ni nth esubstrat e compositionfro m headwate rt odelt ao rfro msprin gt oconfluence ,whereb yth emedia nparticl e size andth ecoarsenes so fth edetritu sdecreas e (Behning,1928 ;Beyer ,1932 ;Pennak , 1971; Cumnins,1975) .Accordin gt oUlfstran d (1968)th edirec t effecto fth ecurren t onth efauna ldistributio nha softe nbee nover-estimated ,especiall yfo ranimal s livingi nrunnin gwate rbu tdwellin gou to fth ecurrent ,dependan t asthe yma yb eo n oxygenan dfoo dsupply . Thesubstrat ecompositio no fth estrea mbotto m isdetermine db yth einteractio n oferosio nan dsedimentation .Thi sprincipl ei suse db yman y authors (e.g.Cummins , 1975)t odistinguis hthre emai nzone sin.stream san drivers ,whic har eals opresen t inlowlan dstreams :erosiona l (riffleswit hcoars esubstrat ean dhig hcurren t velocities),depositiona l (poolswit hfin esubstrat ean dlo wcurren tvelocities )an d intermediatezone s (withgravel-san d substratean dmoderat e currentvelocities) . Althoughsignifican tdifference si nsubstrat e compositionan dcurren tvelocit yfor m themajo rdifference sbetwee nthes ezones ,Cummin s (1966)stresse s thatth efood - chainbase sar eals odifferent :i nerosiona lhabitats , 'Aufwuchs'o rperiphyto n predominatesa sth emajo rfoo dsource ,whil ei ndepositiona lhabitat sth einpu to f detritusact sa ssuch .Al lthes efactor sar eo finfluenc eo nth efauna l composition ofthes ezones .Accordin gt oCummin s (1975)eac hzon ei scharacterize db ya specifi c benthicfauna ,whic hi ngenera li smor eo rles srestricte dt oit senvironmen tb y morphological,physiologica lan detiologica ladaptation s (Hora,1936 ;Ambühl , 1959;

156 Pleskot,1961 ;Jaa g& Ambühl ,1963 ;Bournaud ,1963 ;Scherer ,1965 ;Cummins , 1972; Uhlmann, 1975). Three faunalgroup sca nb edistinguished : - Faunao fth e erosional zone,whic hca nattac hitsel ft oth esubstrat eb ysuckin g (Anayolus), clinging (Simulivm) oravoi dth ecurren tb yflattenin g (Heptagenia) or dwellingi ncrevice s (Gammarus) orwhic hhav especiall y adaptedcase senablin g them towithstan dth ecurren t (Goera). - Sprawling,climbin g (Habrophlebia, Limnephilidae)o rburrowin g (Ephemera, Ptyohop- tera) faunao fth eoppositiona lzone ,ofte nwit ha mechanis mt oavoi d foulingo fth e respiratory surfaces (Caenis, Ephemera). Mud-chiroromidsar eals o foundi nthi szone . - Faunaofte nmor eo rles srestricte dt oth eintermediat e zone,dwellin gi nmoderat e flowan dburrowin gi nsand-grave l substrates (.Ephemera, Mioropterna, Serioostoma). Themor ecomple xsubstrates ,compose do fvariou s combinationso fth eorgani can d mineral components,for mth emajo rpar to fth estrea mbottom ,especiall yi nlowlan d streams,wher emos tsubstrat e typesar ecompose do fsan dcombine dwit hdetritus ; coarsesubstrate s areneve rabundant . Inth eSnijdersveerbee kan dth eRatumsebee kmos t substrates sampledwit hth e shovelwer e situatedi na relativel ymoderat ecurren ti nth eintermediat eo r deposi- tional zone,excep tfo rBar eGravel ,Bar eSan dan dlea fpack s againstobstacle si n thecurrent . Onlya fe wspecie swer e significantly over-representedi nth etw ominera lsub strates directly exposedt oth ecurrent .Th especie s foundi nBar eGrave lwer eal l well adaptedt oliv ei nstronge r currentso nth esurfac eo fth esubstrat e (Baetis Vernus, Lithax obsourus, Agapetus fusoipes, Elmis aenealarvae , Eheotanytarsus spp.), burrowingi ni t (Mioropterna sequax, Limnophila spp. ,Serioostoma personation, Eiseniella tetraedra) orlivin gi nexistin g crevicesan dinterstitia l spaces (Amphinemura standfussi, Limnius volokmari, Elmis aeneaadults) .Mos to fthes espe ciesfee do nperiphyto nan ddetritus ,wit hit sassociate dmicrobia lgrowt h (scrapers orgrazers) .Onl y Limnophila ispredacious . Becauseth ecurren tbring sth eoxyge nan dth efoo dt oth eanimals ,th ecurren t velocityi nth estrea mma yb eextremel y importantfo rspecies 'microdistribution ,bu t mostanimal swil lavoi ddirec t exposuret oth ecurren tunles s theyposses s special adaptations (Hynes,1970a) . Habrophlebia fusoa needsa well-oxygenate d habitat,bu ti ti saver ypoo r swimmer. Itspreferenc efo rlea fpack san dcoars edetritu san dlea faccumulation si s thereforeno tsurprising ,sinc e these substratesofte naccumulat e againsto rbehin d obstaclesi nth emai ncurrent ,bu tprotec tth eanimal s inside.Th esam eprincipl e appliest o Gammarus pulex, whichi sals oa poo rswimme rwithou t special attachment mechanismst owithstan d thecurrent .Onl ywhe n G.pulex issmall ,ca ni tdwel li nth e intersticeso fcoars eminera lsubstrates . Current,i ncombinatio nwit h substrateparticl e size,i sals oresponsibl efo r substrate stability andma ythu sinfluenc e species'microdistribution . Itwa sdemon - 157 stratedb ysevera lauthor stha tinstabl esubstrate sar epoo rhabitat s (Petran,1977) , only inhabitedb yOligochaet aan dsom eChironomida e species.I nth eRatumsebee kan d theSnijdersveerbee kth esam econclusio nwa sreached .I nshiftin g sand,onl yOligo chaeta (mainlyTubificidae) ,Chironomida e (Polypedilwn breviantennatum, StiatoaMro- norms, Prodiamesa olivacea), someothe rDipter a (Ptychoptera, Palpomyia, limnophila), Hydracarinaan d Piaidivm showedover-representation ,whil eonl yOligochaeta , SUatooMeonomua, Polypedilwn breviantennatum and PisUivm showedpreferenc efo r thissubstrate . Transporto ffin eminera lmateria l (siltan dsand )b yth ecurren tresultin gi n scouringo fmor e stablesubstrate sma yals ob eresponsibl e forth e absenceo fspecie s fromsubstrate snormall ypreferred .O nman yoccasions ,especiall y afterperiod so f highdischarge , Agapetua fuaoipee couldno tb efoun di nit susua lhabita to fCoars e Gravelo ro nstones ,bu twaswi thidde nunde rth estone so ri nfine rsubstrates .Th e preferenceo f Simulivm forCoars eDetritu san dLeave sma y alsob elinke dt oth e scouringeffect so ftransporte dsan do nth egrave l substrate,forcin g the larvaet o movet oplace swher eth ecurren ti s strongenoug ht oprovid e sufficient foodt othei r filteringcephali cfans ,bu tslo wenoug ht ob efre eo fminera lparticles .Thes e conditionsca nb efoun do nto po fdetritu saccumulation so rstone s andbranche s(o r plants),whic hprojec tint oth ewate rcolumn ,bu t arehig henoug habov eth estrea m beditself .

~~5.3 FOODCONDITION S~~

Provideda wid erang eo fothe rfactor si ssuitable ,th epresenc eo fdetritu sha s probablya stronge rinfluenc eo nth emicrodistributio no fmos tmacr oinvertebrate s thanan yothe rfactor .Althoug hfoo da sa facto rwa sno t studied,mos ttax acoul db e relatedt oth esubstrate sthe ypreferre db ythei rfoo dpreference s and feedinghabits . Cummins (1972,1975 )develope da theor yabou tth erelationshi pbetwee nlocomotion , feeding,growth ,respiratio nan dselectio no fphysical-chemica lparameter si ndeter miningmacroinvertebrat edistributio nan dabundance .I nhi s flowschem eCummin s (1975)distinguishe dmacro -an dmicro-movements .Macro-movement s includerapi dmigr a tionan ddrif tinduce db ya sub-optima lphysical-chemica lenvironment .Animal s leave placeswher eth efactor slik ecurrent ,substrate ,temperature, oxyge n and lightd o notmee tthei rneeds .The yals oleav ewhe nfoo dcondition s areba do rcompetitio ni s toostrong .Havin gfoun dth eoptima lcombinatio no fphysical-chemica lconditions , micro-movementslea dt ohabita tselection .Thes emovement s startwit h orientation towardscurren tdirectio nan dturbulence ,whil e theultimat ehabita t selectioni s largelydetermine db yth enature ,particl esiz ean damoun to favailabl e food.Thi s theoryput smor eweigh to nth e importanceo ffoo dfo rth eultimat e selectiono fth e habitatwithi na give nsectio no fa strea mtha ti schose no nth ebasi so fothe r factors.However ,whe nsufficien tfoo do fa suitabl ecompositio nt osuppor ta po p isavailabl ei na strea msection ,othe rfactor swil ldetermin e thedetaile dmicro -

158 distributionalpatter no fmacr oinvertebrates .The nsubstrat eparticl e sizei s possibly themai nfactor . Comparisono fth emicrodistributiona l patternso fsevera l speciesi nth eRatumse - beekwit hthos e inth eSnijdersveerbee k providesa nic e illustrationo fthi s theory. TheSnijdersveerbee k hassmal l dimensions anda larg einpu to fallochthonou s organic material thati sdistribute d over thewhol ewidt h and lengtho fth estream .Thi s createsa situatio nwher e forfin eo rcoars eparticl e detritivores andthei rpredators , sufficient foodo fsuitabl eparticl e sizeswil lb eavailabl e throughout the stream. TheRatumsebeek ,however ,i slarger ,als owit ha larg e inputo fallochthonou s organic matter that ismainl y distributed along themargin so fth estrea mbe dbecaus eo fth e muchstronge rcurren tvelocities ,especiall y afterperiod so fheav y rainfall.Thi s restricts thebulk 'o fth eavailabl e detritust oth e finersubstrate s alongth ebanks , accumulated againstobstacle si nth emiddl eo fth estreambed ,trappe di nth e inter sticeso fcoars e substrates,o rcovere dwit htransporte dminera lmaterial .Onl y after extendedperiod swit ha lo wdischarg ewer e accumulationso fleave s andcoars e detritus foundi nth emiddl eo fth estrea mbed ,i ndeepe rpools . InCummins ' (1972)terminolog y thepool s andth emargin so fth e stream areth emacro-depositiona l zones,whil e the accumulationsi nth ecurren t formth emicro-depositiona lpockets . Inth eSnijdersveerbeek ,th epracticall y overall favourable foodcondition smak e itpossibl e forth emacroinvertebrate st oselec tthei rhabita to nth ebasi so ffac tors likesubstrat eparticl e size,curren tvelocity ,oxyge ncondition s andproximit y ofsubstrate sneede d forcas ebuilding .I nth eRatumsebee k foodcondition sar eles s favourable,a tleas ti nth emiddl eo fth estreambed ,forcin g theanimal st ob e con tentwit hles spreferre dphysical-chemica l conditionsi nfavou ro favailabilit yo f food.Severa lexample so fthi snegativ e influenceo fth eabsenc eo fsuitabl e foodo n themicrodistributio n ofmacroinvertebrate s werealread yindicate d inSubsectio n 4.2.2.Perhap s thebes t examples areforme db yth edifference si ndistributiona l patternso fEphemera danioa, Mioropterna sequaxan d Seriaostoma personation.Th e lattercaddis-fl y specieswa sno t foundi nth eRatumsebee ka tall ,althoug h the grain-size compositionselecte db ythi sspecie swa sabundantl ypresent .Apar tfro m macrodistributionalfactors ,on eo fth ereason s forit sabsenc ei nth e Ratumsebeek couldver ywel lb e theabsenc eo fth eprope r combinationo fsubstrat ean d foodi nth e samehabitat . Ephemera danioa and Miaropterna sequax showsmal lbu tdistinc tdifference si n micro-distribution inth etw ostreams .I nth eRatumsebeek , M.sequax occursmainl yi n Detritus substrates,whil e itwa smor eo rles sevenl ydistribute d overSan d+ Detri tus,Bar eGrave lan dDetritu s (Sort2 ,Appendi x3 )i nth eSnijdersveerbeek .Eve nthi s preference forBar eGrave l inth eSnijdersveerbee k fits thetheor ysinc e the animals inBar eGrave lar estil lwithi neas yreac ho fDetritu s substrateso rhav en o further needo ffoo d (pupae). Inth eRatumsebeek ,Bar eGrave l substrateswer e restrictedt o theerosiona l zonean donl yher ecoul dpupa eb efound ,whil ei nth eSnij b theBar e Gravelals ooccur s inth eintermediat e zonewher e thecurren t ismoderate . E.danioa

159 occurredi nbot hstreams ,mainl yi nth eSan d+ Coars ean d FineDetritu ssubstrates , buti tshowe da muc hnarrowe rdistributio nove r thestreambe di nth eRa bi nth efiel d classification.(Sor t2 ,Appendi x 9). Inth egrain-siz eclassification s (Tables3 7 and38 )th edifference si npreferre dsubstrat ecompositio nwer e evenmor epronounced . Inth eSnijb ,th enymph soccurre di nequa ldensitie si nGrave l andFin eSan dsub strates,whil ethe ywer erestricte dt oCoars eSan dan dFin eSan di nth eRab . Fromthes edat ai tma yb econclude dtha tespeciall yth especie s showingdiffer encesi nmicrodistributiona lpattern sbetwee nth etw ostream s inhabitth einter mediatezon ewit hgravel-san dsubstrate san dmoderat et olo wcurren tvelocitie si n theSnijdersveerbee kan dth edepositiona l zonewit h sand-detritus substratesan dlo w currentvelocitie si nth eRatumsebeek .I nth eRab ,th eerosiona l zonecontain sth e rightsubstrat ecompositio no fsan dan dgravel ,bu tothe r factors likecurrent , turbulencean dfoo dar eunfavourabl efo rman yspecies ,whil e the intermediate zonei s rarebecaus ecoars esubstrate sar emor e lessrestricte dt oth echanne lpar twher eth e maincurren ti spresent . Thedat ao nth emicrodistributio no fth eindividua lspecie si nSubsectio n 4.2.2 clearlydemonstrat etha tspecies 'substrat epreference s arestrongl y linkedwit h theirfeedin ghabit san dfoo dpreferences .Table s7 7an d7 8illustrat e forbot h streamsth erelationshi pbetwee nfeedin gmechanis m andmajo r foodtyp efo rth efou r functionaltrophi cgroup s (Cummins,1973 )an dth edistributio nove r thesubstrat e typesdistinguishe di nSor t2 (Appendi x 9). Scrapersan dgrazers ,feedin glargel yo nperiphyto nan d fineorgani cmatte rwit h itsassociate dmicroflora ,prefe rGrave lan dBar eSan dsubstrates .Thi sconcerns , for example, Lithax obscurus and Agapetua fueoipee, dwellingo nGrave lan dBar eSand , Hydrophilidae,EMinthida ean d Dryops spp.dwellin go nGravel ,an d Pisid-ivm, occur ringmainl yo nBar eSan dan d+ Fin eDetritus . Speciesfeedin go ncoars eorgani cdetritu san dleave s (shredderso rcoars e particulatedetritivores )ar epredominantl yfoun d inDetritu s substrateso rminera l substratescombine dwit hdetritus .However ,difference s inmicrodistributio nbetwee n thespecie sremai nan dthes ear eprobabl yno tcause db ydifference si nfoo dprefer enceo rfeedin ghabi tbu tb yfactor s likesubstrat eparticl e sizean dcurren tvelocity . MostLimnephilida elarva e(e.g . Mioropterna sequax, chaetoptevyx villoea, Potamophy- lax luatucsus, Baleeus radiatue and Glyphotaeliue pellucidua andals o Sericostoma pevsomtm prefersubstrate swher ecoars edetritu si spresen ti nsufficien tamounts . S.persomtm prefersSan d• Detritu ssubstrate sbu toccur si nCoars eDetritu ssub strateswhe ni ti ssmal l (Table 24).Whe nyoung ,bot h M.sequax and Ch. villoea preferLeaves ,bu tmov et ominera lsubstrate scombine dwit hdetritu swhe nthe yar e older (Tables2 8an d 31). E.radiatus and P.luctuosus and G.pellucidus wereonl yfoun d insmal lnumbers ,bu tthe yar edistinctl yassociate dwit hDetritu s substrates,i nth e larvalstag ea tleast .Pupa eo f Potmophylax luctuosue wheremostl y foundo nth e undersideo flarg estones ,branche so rlogs .Thes epupa ehav ea cas eo fcoars esan d andfan egravel ,whil eth elarva ehav ea lea fcas eu pt oth e finalinstar ,whe nthe y

~~160 Table77 .I.H .value s forth etrophi c groups inth eSnijdersveerbee k inSor t2 .~~

~~Trophic group Substrateclas san dsubstrat etyp e~~

1 2 3 4 5 6 7 BS S+FD S+D S+D+FD BG G+D/FD D/FD Predators -11.8 4.5 3.5 12.9 -10.3 4.3 4.8 Scrapers/Grazers 3.3 -3.0 -6.9 -7.8 ll.n 5.9 -6.7 Shredders excluding G.pulex -17.5-11. 8 -4.4-14. 2 -6.2 -0.6 52.2 Gammarus pulex -27.2 -4.6 52.6 -3.0-39. 5-16. 5 56.9 Collectorsexcludin g M. gr. praecox -32.4 -7.1 4.6 5.0 -21.0 13.9 47.7 Micropseatra gr. praecox -55.6 20.3 -11.5 74.6 -63.0 -2.8 64.7 Total -36.1 -9.3 1.5 1.3-20.5 14.2 58.7

~~Italic values indicate significant over-representation~~

~~Table 78.I.R .value sfo r thetrophi c groups inth eRatumsebee k inSor t2 .~~

~~Trophic group Substrateclas san dsubstrat e ityp e~~

1 2 3 4 5 6 7 BS S+FD S+D S+D+FD BG G+D/FD D/FD Predators -4.0 0.5 1.8 10.1 -4.2 -2.2 -1.4 Scrapers/Grazers 8.8 -5.2 -2.9-11. 0 11.8 14.4 -11.5 Shredders excluding G.pülex -20.5 -15.8 -1.1-21. 0 -1.0 -16.3 55.0 Shredders excluding G.pulex and -13.8 -7.8 7.3 -9.0 -9.1 -6.4 32.2 N. cinerea Gammarus pulex -39.4 -17.8-15. 6-23. 0 -28.0 -8.4 103.2 Nemoura cinerea -15.6 -13.8 -5.7-19. 1 4.5 -11.8 44.2 Collectors excluding M.gr . praecox -16.0 -7.3 -6.9 2.3 -16.1 -8.7 38.2 Micropsectra gr. praecox -18.1 0.2 0.5 9.2 -11.4 0.4 19.2 Total -15.4 -10.3 -3.6 -2.5 -12.7 -4.1 37.1

~~Italicvalue s indicate significant over-representation~~

startbuildin ga minera lcase ,probabl yfo rprotectio ni nth epupa lstag eagains t predatorsan dshredders .Th e leafcas eo f P.luctuosus is quitesimila rt otha to f G.pellucidus . Thesecases ,wit hthei rroun dpiece so fbeec hleave sfor ma nextremel y goodcamouflag ei nlea fpack san dar eon eo fth efines texample so fth eabilit yo f Trichopterat oadap tthei rcase st othei renvironment . Otherspecie sfeedin go nCoars eDetritu san dLeave sar epredominantl yfoun di n thepur eDetritu ssubstrates ,e.g .Tipulida ean d Helodes larvae. GammaruB pulex is themos tabundan tshredde ri nbot hstream san dprefer sbot hpur eDetritu ssubstrate s (largerspecimens )an dSan d+ Coars eDetritu s (smallerones )(Tabl e 54). Plecoptera nymphs (Nemoura cinerea and Amphinemura standfueei) preferDetritu ssubstrates , although A.etandfusei isals oover-represente do nBar eGravel ,wher ei tprobabl y feedso nth eattache dfin edetritu san ddiatom s (Dittmar,1955 ;Madsen ,1974) .Coars e Detritus feederssee mt oavoi dsubstrate swher elarg eamount so fFin eDetritu sar e present,eve nwhe nCoars eDetritu si sabundant ,whic hi sillustrate db y thestrongl y

161 negative IRvalue si nth eClasse s 1,2 an d4 i nTabl e 77. Collectors,feedin go nfin eparticulat eorgani cdetritu s (fineparticl edetriti - vores)b yfilterin g (Simulium spp., Rheotanytarsus spp.,man yOrthocladiina e species) ordeposi tfeedin g (Ephemera daniaa, mostChironomin ian dTanytarsin i species)dwel l preferably inminera lsubstrate s combinedwit hdetritus .Substrate s devoido fdetri tusar eno tavoide db ymos to fthes especies ,bu tthe yar ecertainl yno tpreferre d exceptfo rth especie sdwellin gi nShiftin gSan da smentione di nSectio n5.2 . Simulium spp.an d Rheotanytarsus spp.ar eknow nt ooccu rabundantl yo ngrave lsub stratesu pt over yhig hcurren tvelocitie s (Hynes,1970a )and ,indeed ,smal lnumber s werefoun di nbar eminera lsubstrates ,bu t Simulium occurredpredominantl y inCoars e Detrituso rlea fpack stha twer eofte nsituate di na goo dcurren tbu thighe r above thestreambed ,wher ether ei smuc hles sscourin gb ytransporte d sand. Rheotanytarsus spp.preferre dSan d+ Coars eDetritu ssubstrate sbu twer eals ofoun do nBar e Gravel andi nCoars eDetritus . MostOrthocladiina e species (e.g. Eukiefferiella spp., Brillia spp., Corynoneura spp., Diploaladius oultriger, Rheooriaotopus spp.prefe rCoars eDetritu so rLeaves , andth especie scompositio nfoun dhere ,correspond s quitewel lwit htha tgive nfo r vegetationb yLindegaar d (1972).Thes especie s feedher eo nth etrappe dFin eDetritu s andattache dalga lgrowth . Orthooladius feeds strictlyo ndiatom san di ti stherefor e notsurprisin gt ofin di tmainl yo ngravell y substrateswher ethe ydwel li ntube s attachedt oth eminera lsubstrat e (Lindegaard, 1972).Perhap sthi s andsimila r speciesshoul db ecalle dscraper so rgrazers . Prodiamesa olivaaea isa fre elivin gOrthocladiina e speciesdwellin gpreferabl y inSan dwit hCoars ean dFin eDetritus ,th esam ehabita tpreferre db y Mioropseatra gr. praeaox, whichagree swit hth eobservation sb yMarlie r (1951)an dLindegaar d (1972).However , M.gr . praeaox showsa wide rdistributio n than Prodiamesa olivacea sincei ti sals oabundantl ypresen t inpur eDetritu s substrates andS+FD .Othe r Tanytarsinispecie ssho wquit edifferen t substratepreferences ,e.g . cladotanytarsus forBar eSan dan dGrave l+ Detritus ,whil e Tony tarsus aurtiaornis prefers Gravel+ Detritusbu ti sover-represente d inmos tothe rsubstrat etype sexcep tBar eSand . MostChironomin i larvaeprefe rth esubstrate s consistingo fa mixtur eo fSan d andDetritus ,althoug hsom especie sar eals oabundan t inpur eDetritu s substrates (Polypedilum laetum, Phaenopseatra). Somespecie swer eeve nfoun di nshiftin g sand substrates (ßtiatoohironorms, Polypedilum breviantennatum, Paraaladopelmaspp.) , whichmigh t indicatetha tthes especie s canals ofee do nth emicrobia l growtho nfin e mineralsubstrates ,o rdiatom spossibl ypresen ti nthi shabitat . Epoiaooladius flavens, achironomi dlivin gphoreticall yo n Ephemera daniaa, feedso nth edetritu spassin gove rth emayfl ynymph swit hth eaxia lcurren t generated byth egil lmovements .I toccur si nth esam esubstrat ea spreferre db y Ephemera daniaa, whichfeed so nth esam ematerial ,namel ySan d+ Coars ean dFin eDetritus . Anothermayfl yfeedin go nFin eDetritu si sHabrophlebia fusaa, whichwa sonl y found inth eRatumsebeek .Her ei toccurre dpredominantl yi nLeave so rCoars eDetritu s+

162 Leaves,wher eFin eDetritu s andattache dmicrobia l andalga lgrowt hi sabundant ,bu t where theleave soffe ra goo dprotectio n againstth ecurrent . Baetia is. abette r swimmer,feedin go nth esam emateria lbu tdwellin go nBar eGrave lo rSand. + Detritus inth eSnij ban di nlea fpack si nth eRab . Predators aremor eevenl y distributed over thedifferen t substrate types than anyothe rtrophi cgroup .The ypredominat ei nSan dwit hCoars e and FineDetritus ,bu t areals oover-represente di nal lothe r substrate types exceptfo rBar eSan dan dBar e Gravel.Withi nthi sgroup ,th edifference s betweenth e individual species areconsider able. Pleotroonemia conspevaa prefersDetritu s substrates,whil e Hydropeyahe angustipennis, theothe rne tspinnin g caddis,occur smainl yi nGravel .The ybot h feed onanimal s (largelyChironomidae )driftin gi no rswimmin g againstthei r capturing nets.O fth eTanypodinae , Maovopelopia nebulosa prefers Sandwit h FineDetritus ,San d withCoars ean dFin eDetritu s andGrave lwit hCoars eDetritus ,a distributio n similar totha to fApsectrotanypm tvifaaaipermis. Conehapelopiamelanops prefer sDetritu s substratesan d Proaladius and Zawel-imyia Sandwit hDetritu s andDetritus .Thes e preferences closelyagre ewit h thehabita tdescriptio n andspecie scombination s given byLindegaar d (1972). Otherpredaciou sDipter a larvae (e.g. Limnophila, Dicranota, Palpomyia) are moreevenl ydistribute d overSan dan dGrave l substrates,althoug hdifference s between thetw o streamsca nb eobserved .Detaile d analysis ofpredato r gutcontent swoul db e necessaryt olin kpredato r density anddistributio n topre ydistribution ,althoug h forsom epredator sa positiv erelationshi p betweenpre ydensit y andpredato r abundance wasdemonstrate d (e.g.fo r Vleatvoonemia coneperea; Hildrew& Townsend , 1976). AlthoughTable s7 7an d 78illustrat eth emai npreference so fth etrophi cgroups , theyd ono tgiv ean y insight inth econmunit ystructur ewithi na substrat etype .T o thisend ,th erelativ eproportio no feac htrophi c groupwithi neac hsubstrat etyp e mustb econsidere d (Tables7 9an d 80)..The ni t canb e seentha tscraper s and grazers

~~Table79 .Percentag eoccurrenc eo f thetrophi c groupswithi nth esubstrat etype s inSor t 2 inth e Snijdersveerbeek.~~

~~Trophic group Substrate class andsu b stratetyp e Total~~

1 2 3 4 5 6 7 BS S+FD S+D S+D+FD BG G+D D/FD Predators 8 6 5 6 9 7 3 5 Scrapers/Grazers 8 1 1 1 13 4 1 2 Shredders excluding G.pulex 5 1 3 1 13 5 9 5 Gamnarus pulex 29 17 47 13 13 11 24 22 Collectors excluding M.gr . praecox 29 18 22 18 48 35 24 25 Micvopsectra gr. praecox 21 56 23 62 4 38 40 40 Unknown 1 + - - 1 + + + N= 100% 3956 4129 5563 10877 3256 4825 177655037 1

~~+ :les stha n0. 5 % - :zer o~~

~~163 Table 80. Percentage occurrence of the trophic groups within the substrate types in Sort 2 in the Ratumsebeek.~~

~~Trophicgrou p Substrate class and substrat etyp e Total~~

1 2 3 4 5 6 7 BS S+FD S+D S+D+FD BG G+D D/FD Predators 7 10 9 10 5 4 2 4 Scrapers/Grazers 21 6 7 3 19 24 1 6 Shreddersexcludin g G.pulex and 2 1 16 2 3 1 6 5 N. cinerea Gamnarus pulex 22 30 20 28 23 40 53 42 Nemoura cinerea 13 + 11 3 27 1 13 12 Collectorsexcludin g M.gr . praecox 30 31 21 34 17 15 18 22 Micropsectra gr.praecox 5 21 17 19 6 14 7 9 Unknown + + - 1 + + 1 + N= 10 0 % 2384 671 617 2993 2040 790 13989 23484

~~+ :les stha n0. 5% - :zer o~~

are only present in considerable numbers in Bare Sand and Gravel substrates, while predators form a more or less constant proportion of the population (5-10%) in all substrate types except Detritus substrates, where the extremely high numbers of G.pulex and M. gr. praecox result in a low percentage occurrence of the predators. Shredders are dominated by Ganmarus in the Snijdersveerbeek and G.pulex and M. gr. praecox in the Ratumsebeek. With the exception of these species, shredders are most abundant in Bare Gravel (Amphinemura atandfusai, Micropterm aequox and Chaetop- teryx villosa, and Detritus substrates (Amphinemura standfusei, Chaetopteryx villosa and Helodes). Collectors predominate in numbers in all substrate types, which is mainly caused by the high numbers of Chironomidae. Expressed in biomass, these figures would probably be more in favour of the shredders, which are in general, mich larger than the collectors. From Tables 79 and 80, which show the percentage occurrence.of the four trophic groups, it is clear that gravel obviously presents the most favour able conditions for a heterogeneous trophic structure, offering suitable food condi tions to all different trophic levels of the stream community. In these tables the dominant species have been treated separately, to illustrate the proportion of the other species in the groups of the shredders and collectors.

~~164 6 Conclusions~~

~~Thedat apresente di nth epreviou s chaptersprovid ea sufficien tbasi sfo r acceptingth etw oworkin ghypothese s concerning substrate compositionan dsubstrat e patterns (Chapter1 ,Sectio n1.3) .~~

~~6.1 SUBSTRATE COMPOSITION~~

Itha sbee ndemonstrate d thatmos tbenthi cmacroinvertebrat e species occurring inth eSnijdersveerbee kar edistribute dunevenl y overth evariou s substrate types, whichar ecompose do fminera lmatter ,organi cdetritu so ra combinatio no fboth .A specieswa sconsidere d toprefe ra substrat e typewhe ni twa spresen ti nsignificantl y highernumber s thano no ri nothe rsubstrat e types.O fth e8 4specie spresen twit ha totalnumbe ro f2 0specimen so rmor ei non eo fth etw ostreams ,o rpresen ti nmor e than1 0samples ,4 2wer eover-represente d inonl yon eo fth eseve nsubstrat e types distinguished (Sort2 ,Appendi x 9). Nineteenpreferre d detritussubstrates ,1 3grave l (3Bar eGravel ,1 0Grave lmixe dwit hDetritus )an d1 0wer emos t abundanti nsan d( 2 inBar eSand ,1 i nSan dwit hCoars eDetritu san d7 i nSan dwit hCoars ean dFin e Detritus). Ingeneral ,preference so fspecie sfo ra certai nsubstrat e typeobserve d inth eSnijdersveerbee kwer e confirmedi nth eRatumsebeek . Somespecie s showed small differencesi nsubstrat epreference s betweenth estreams ,bu tthes ecoul db eexplaine d onth ebasi so fdimensiona l differences betweenth estream s (SectionS.3) . Substrateswer e classifiedi nsevera l substrate typeso nth ebasi so ffiel d observations (Subsection 4.1.1),laborator y analysiso fth egrai nsize san dth e nature (andparticl e size)o fth eorgani c detritus (Subsection 4.1.2.2). Considering thedistributio no fth emacroinvertebrate sove rth esubstrat e types,thre emai n groupso fspecie scoul db edistinguished ,wit hpreferenc efo rcoars eminera l substrates (Gravel),fin eminera l substrates (Sand)an dorgani c substrates (Leaveso rCoars e Detritus),respectively .Thes e groupswer e similari nbot hth efiel dan dlaborator y grain-size classifications.O namor edetaile d level,th efiel dclassificatio ndemon stratedth eimportanc eo fth epresenc eo rabsenc eo ffin ean dcoars edetritu san d leavesi ncombinatio nwit hminera lsubstrates ,withi nthes emai n substrate types,fo r themicrodistributio no fth emacroinvertebrates .Th eclassificatio no nth ebasi so f grainsize sdetermine d inth elaborator y emphasizedth erol eo fminera l particle-size compositiono nth emicrodistributio no fth emacroinvertebrates . Substrate compositioni sstrongl yrelate dt ofoo dconditions ,curren tvelocit y andoxyge nconditions .Thes eparameter sar eclosel y relatedan dchange si nth e

165 physicalenvironmen twil l influencethe mconcurrently .Coars esubstrate s generally occuri nplace swit hhighe rcurren tvelocities ,wher e oxygensaturatio ni shig han d theamount so ffin eorgani cdetritu sar elow .Fin esubstrate soccu rtogethe rwit hlo w currentvelocities ,accumulation so ffin ean dcoars eorgani cdetritu san dofte nles s favourableoxyge nconditions .Curren tvelocity ,oxyge nconten tan dth eamoun to fde tritusare intermediat ewher esubstrate s consistingo fa mixtur eo ffin ean dcoars e sedimentsar efound . Leafpack sfor ma specia lhabita twher eoxyge ncontent ,curren tvelocit yan d amounto ffin edetritu sma yvar yconsiderably ,dependin go nthei rpositio ni nth e streambed .I faccumulate dagains tobstacle sprojectin g fromth estrea mbe d(e.g . branchesan dstones) ,condition swil lb esimila rt othos ei ncoars eminera lsub strates;i faccumulate dnea rth ebank so ro nth ebotto mo fpools ,condition swil lb e similart othos ei nfin eminera lsubstrates . Becauseanima lmicrodistribution sar estrongl y relatedt oth eminera lan dorgani c compositiono fth esubstrate ,th esubstrat ecompositio ni sa nexcellen tparamete rt o classifyspecie shabitat so rcommunit ybiotopes .Thi sprincipl eha ssuccessfull ybee n usedb yman yo fth eearl yworker so nstrea mecolog y (e.g.Thienemann ,1912 ;Beyer , 1932;Geijskes ,1935 ;Nietzke ,1937 ;Ber ge tal. , 1948;Marlier , 1951;Dittmar ,1955 ) andha sno tlos tit simportanc esince .

~~6.2 SUBSTRATEPATTERN S~~

Forman ymacroinvertebrat especie sdwellin gi nlowlan dstreams ,no tonl yth e substrate,curren to rfoo dcondition sprevailin gi nthei rhabitat sar enecessar yfo r theirexistence ,th eproximit yo fothe rhabitat si sals oessential .Th eheterogeneou s environmento fnatura llowlan dstream sform sth ebasi sfo rth eheterogeneou smacro - invertebratecommunity .The yca noccu ri nth esam ebiotop ebecaus eo fth espatia l variationo fenvironmenta lconditions . The characteristic lowland-streamcommunit yi sforme db ya larg evariet yo f specieswit hquit edifferen thabita tpreferences .Man y authorshav edemonstrate d that themosai c substratepatterns ,th ealternatio no friffle san dpool san dth eoccurrenc e oferosiona lan ddepositiona lsite si nnatura lstream sar eth emai nreason sfo rth e existenceo fth eheterogeneou sstrea mcommunit y (e.g.lilies ,1952 ;Schmitz , 1961; Cummins, 1966),becaus emos t speciesoccurrin g ina strea mdwel li ndistinctl ydefine d habitats,a sdemonstrate di nth eprecedin gchapters . Reice (1974)state dtha tsedimen tparticl e sizei sprobabl ya norganizin gfacto r instream-communit ydynamic san dtha tdifferen tcommunit y levelprocesse sca nb e expectedt oincreas ethei rrate si nproportio nt oth espatia lheterogeneit yan d stabilityo fthei renvironment . Malmqviste tal . (1978)conclude di nthei rstud yo fth einfluenc eo fdetritu so n thedistributio no fth ebottom-anima lcommunitie s thatenvironmenta l heterogeneity andsubstrat estabilit yar eth etw omos t importantvariable s influencingth ecommuni -

166 ty. Detritus asa food sourcema yno tonl y influence thespecie s compositionbu t also thestructura lmodificatio n ofth ebottom . Rabenian dMinshal l (1977)performe d experimentswit hartificia l substrates in pools andriffles ,concludin g thatth emaximu manima l densities they foundwer eposi tively correlatedwit h theamoun to ftrappe d coarse organic detritus.Thei rconclu sions thatdetritu s isth emos t important factor influencing themicrodistributio n of insects,an d that substrate structure and grainsiz edetermin e thedistributio n of thedetritus ,i si nagreemen twit hEgglishaw' s (1964, 1968, 1969). The importance oforgani cdetritu s forrunning-wate r communitieshas bee ndemon stratedb ynumerou s authors (e.g.Sprules ,1947 ;Schwoerbel ,1961 ;Cummins ,1962 , 1964, 1966;Thorup ,1966 ;Macka y& Kalff , 1969;Lindegaard , 1972;Fische r &Likens , 1973; Williams &Hynes , 1974;Lindegaar d &Thorup ,1975 ;Hildre w &Townsend , 1976). At the sametime ,th e influenceo nth emicrodistributio n alsoreceive d asmuc hatten tion (e.g.precedin g referencesplu sMinshall ,1967 ,1968 ;Kaushi k &Hynes ,1968 , 1971; Cummins,1973 ;Hyne se t al., 1974;Bolin g et al., 1975). Detritus forms an integralpar to fth e streambottom . Itma y cover theminera l substrateo rvic eversa , orma yb emixe dwit h it.I nit svariou s stages ofdegradatio n from leaves tofine - detritusparticle s itfunction s asa foo d sourcea swel l asa nattachmen t site.I t also formsa n important componento fsubstrate s largely consisting ofminera lparticles . Itloosen sminera l substratepacking ,increase sporosit y andthu sth epenetrability . Mineral substrates always formth ebas efo rorgani cmatter .Mosse s growo n solid objects anddetritu san dleave s aredeposite d onth ebotto man dge ttrappe d inth e mineral substrate,althoug hth enatur e andparticl e sizeo fth etrappe d detritus depend onth eparticl e sizeo fth eminera l substrate (Minshall &Minshall ,1977 ; Williams &Mundie , 1978). Rooted aquaticplant sca nofte nb eregarde d asa separate habitat,lik efloatin gones ,bu tther e isofte na combinatio nwit htrappe d detritus (Higler,1977 ;Mackey , 1976, 1977). The concurrentpresenc eo f severalnot-preferre d substrate types togetherwit h thepreferre d typema yb e essential forth esurviva lo fcertai nspecie swhe ncondi tionsar eunfavourabl e inthei rpreferre d habitat.Place swit ha relativel y lowcur rentvelocit y andmor e stablesubstrates ,e.g .behin d obstacleswher edetritu s can accumulate,for mrefuge s forman y species living inplace s thatbecom eunstabl eo r offerto o littlefoo da ttime so fhig hdischarge . Ephemera daniaa nymphsmov e from gravelly substrates inth emiddl eo fth e streamt o sandwit h finedetritu snea rth e banks andbehin dobstacle swhe nth ecurren tvelocit y increases inwinter ,whic h increases the instabilityo fth egrave l substrates andreduce s theamoun to f food (Subsection 4.2.2.6).Similarly ,gravell y substrateswit hman y intersticeswil l form a refuge forman y species,protectin g themagains tth ecurren tan dthu sformin g a reservoir fromwher eothe r substrates canb e stockedagai nwhe ncondition s improve (Mackay, 1969). Speciesma ynee d different substrate typesbecaus e theynee dothe rgrai nsize s ormaterial s tobuil d theircase s thanar epresen t inthei rpreferre dhabita t (e.g.

167 manyTrichoptera ,suc ha s M. sequax, Ch.villosa, P.luotuosuB). Pupaenee dplace swher e theywil lb eassure do fsuitabl eprotectio nagains tpredator san do fcontinuin ggoo d oxygenconditions .The ycanno tdefen dthemselve sno rchang ethei rpositio nshoul d conditionsdeteriorat e(e.g . M.sequax, Ch.villoea, L.obsourus, A.fusaipes'). Mackay (1977)demonstrate dfo r Pyonopsyohe soabvipennis thatpupa esee mt ob eburrowe donl y insubstrate swher ea considerabl eproportio no fgrave lo f4- 8m man d 8-16u mi s present,whil eth elarva eprefe rorgani csubstrates .Sh esuggeste dtha tth eexten to f theseparticl esize savailabl efo raestivatio nan dpupatio nma yeve nlimi tth eabun danceo fthi sspecies .Man yTrichopter aspecie snormall ydwellin gi norgani csub stratespupat ei nsite swher ethe yca nattac hthei rcase st osom esoli dobject ,suc h aslogs ,branches ,sticks ,cobbles ,bricks ,kettles ,e.g . Halesus radiatus, Glypho- taelius pellucidus. Otherspecies ,normall yoccurrin gi ngravell ysubstrates ,bu t ofteni nplace ssheltere dfro mth edirec tforc eo fth ecurrent ,mov et ostone so r branchéssituate di nmuch stronge rcurrent st opupat e (e.g. Lithax obscurus, Agapetus fusoipes). Herethe yca nb eassure do fa goo doxyge nsuppl ywhil eth echanc e ofbein gsmothere db ytransporte dsedimen ti sminimal .Becaus epupa lcase sar efirml y attachedt oth esubstrat ethe yar eno tswep tawa yb ystron gcurrents .Larva ema y avoidthes esite sbecaus ethe ywoul dhav et oexpen dto omuch energ yjus tt owithstan d thecurren t (Bournaud,1974) . Somespecie seve nchang ethei rcase-buildin gmateria lprio rt opupation ,whe n theirlarva lcase sconsis to forgani cmaterial ,probabl yt oobtai nbette rprotectio n againstpredator san dshredders .Thi si sexpeciall ys owhe npupatio ntake splac ea t theen do fspring ,whe ndetritu ssubstrate sbecom escarcer .Cummin s (1964)demonstra tedthi sfo r Pyonopsyahe lepida, andi nth eRatumsebee k Potamophylax luotuosus isa goodexampl eo fthi smateria lan dhabita tchange .Bot h Uiavoptevna sequax and Chaetopteryx villosa demonstratea simila rchang ei nsubstrate spreferre ddurin g theirdevelopment .Comparin glif ecycle ,substrat epreferences ,foo dhabit san dcas e buildingo fthes etw olimnephili dcaddis-fl yspecies ,onl yon econclusio nca nfollow : theysho wsimila rsubstrate ,foo dan dhabita tpreferences ,an dthe ybuil dsimila r cases.But ,thei rcomparabl edevelopmen tstage s areno tconcurrent ,whic hmean sthe y preferth esam ehabitat sa tdifferen ttime so fth eyear ,s ocompetitio nwil lb e minijiial.Thes especie sfor ma remarkabl eexampl eo fspatia lan dtempora lecologica l segregation.I nsumme ran dautumn ,whe n Ch.villosa hasreache dit sfina linsta ran d isi na restin gstag eo ri sa pupa ,juvenil e M.sequax larvaeappear .A tthi stim e Ch.villosa ispresen ti ngrave lsubstrates ,whil e M.sequax dwellspredominantl yi n detritus.I nautum nsom e Ch.villosa larvaeca nals ob efoun di nCoars eDetritus . Untilth efirs twee ko fOctobe rthi sconcern slarva ejus tbefor epupation ,whic hwer e probablyconsumin gthei rlas tmeal sbefor eclosin gthei rcases . M.sequax larvae occurringi nCoars eDetritu si nautumn ,wer eonl yfoun dafte rth esecon dwee ko f October,whic hmean sth etw ospecie sar eseldo mfoun dtogethe ri nth esam esubstrate . Inwinte ran dspring ,whe n M.sequax larvaear efull ygrown ,the ymov et ominera l substratest obuil da minera lcas ean dburrow ,whil efeedin go nth ecoars edetritu s

168 presenti nthes esite so ri nth eproximity .A tth esam etim ejuvenil e Ch.villosa larvaedwel lpredominantl y inthei rorgani ccase s inCoars eDetritu s substrates.Onl y insprin gan d summerd othe ymov et ominera l substratesan dbuil d (partly)minera l cases,bu tb ythe n M.sequax has alreadypupate do remerged .Thes etw ospecie sfor ma pairtha tcoul db e called theEuropea n equivalento fth especie sstudie db yCummin s (1964): Pycnopsyehe lepida and P.guttiger. Thesetw o Pyanopeyahe speciesar eals o spatially separated attime swhe n theyoccu r togetheri na stream . P.lepida showsth e samechange si ncase-buildin gmateria l and substratepreferenc e as M.sequax.

~~6.3 EFFECTO FREGULATIO N~~

Themai ngoa lbehin dth epresen tresearc hwa st odemonstrat e thatth e limitation ofman ybenthi cmacroinvertebrat especie st onatura lo rsemi-natura l lowlandstream s (andth eabsenc eo fthes especie s fromregulate d streams)i sstrongl yconnecte dt o thedifference si nsubstrat e composition andheterogeneit ybetwee nnatura lan d regulated streams.I na stud yo nth emicrodistributio no fbenthi cmacroinvertebrates , theamoun to fmateria l thatha st ob eanalyse dma ysoo nbecom eto omuc ht odea lwit h inth etim e available.Therefor e itwa sno tpossibl et oinclud e someregulate d streams inth eresearch . However,give nth edistinc t substratepreference sdemonstrate db ymos t species andknowin gtha tman yo fth esubstrate s found innatura lstream sd ono toccu ro rar e muchles sabundan ti nregulate dones ,th econclusio n isobviou stha tth esubstrat e compositionma yb ea nimportan tparamete rresponsibl efo rth edifference si nbenthi c faunal composition.Th estrea mbotto mo fnatura l lowland streamsconsist so fa larg e varietyo fsubstrates ,alternatin gi nspac ean d time inminera lparticle-siz e com position and the amountan dnatur eo forgani c detritusunde rth einfluenc eo fcurren t velocityan dth efor mo fth estrea mbed .Th epresenc eo fthes emosai cpattern si s essential for theexistenc eo fth echaracteristi cmacroinvertebrat e communityi n lowlandstreams . Mostmacroinvertebrate s living inthes e streamsoccu ri ncharacteristi chabitat s withinth estrea mbed ,wher econdition sconcernin gth eavailabilit yo fsuitabl efoo d substances,particl esiz eo fth eminera lsubstrate ,curren tvelocit yan doxyge n supplyar eoptimal .B yfa rth elarges tnumbe ri sdetritivor eo rherbivore ,feedin go n theallochthonou s detritusoriginatin g from thevegetatio no nth ebanks . Somespecie s canus e the leavesalmos t immediately afterthe yhav eentere d thestrea msystem , othersdepen do nmicrobia l activityt oconver tth e leaves intomor e digestible components (mostmacroinvertebrate s dono tposses s cellulase)o ro nth eactivit yo f othermacroinvertebrate st o breakdow nth eleave st osmalle rparticle s (faeces,fin e detritus,coars edetritus) ,ofte nver yric hi nmicro-organisms . Theabundanc eo fth evariou sdegradatio n stageso fth eallochthonou s organic matteri nth e streamhabitat si sstrongl ycorrelate dwit hth ecurren tvelocit yan d

169 theminera lparticl e sizes.Curren t isresponsibl e forth e constant redistribution of thedetritu sove rth estrea mbe dan dove r thevariou s substrate types. Coarseminera l substrates,ofte nsituate d inhighe r currents,wil l trapbot h fine and coarse detritus inth e interstices.Fin eminera l substrates aremor e abundantwhe n current velocities arelower ,alon gth ebank san di nfron to fan dbehin d obstacles and ininne rbends . These areth eplace swher emos to fth e coarse and finedetritu s accumulations canb e found.Whe ncurren tvelocitie s are lowthroughou t the stream, intim e of lowdischarge , theare awit hdetritu s accumulations canexten d over thewhol e streambed , although thisconcern smainl y the finedetritus ,becaus ewhol e leaveso rparts o fthe m are lessabundan t inth e stream system inthes eperiod s (late spring,summe r and early autumn). Iti sessentia l thatdetritu s canaccumulat e insheltere dplaces ,becaus e it formsth ebasi so fth eheterotrophi c foodwe bo f alowlan d stream. Inthes e places thedetritu sca nb ebroke ndown ,partl y tosmalle rparticles ,whic h are transported toothe rplaces ,an dpartl ydigested .Withou t these accumulation sites the stream would soonb e sweptclea no fdetritu s andbecom e devoid of itsmai n foodsource . Moreover,th eaccumulatio no fver y thick layerso f finedetritu s (mud)i nwhic h anaerobic conditionswoul doccu rwithi na shortdistanc ebelo wth e surface,a s often seen inregulate d streams,i sprevente db y the constant sequenceo f allochthonous input,accumulatio n insheltere dplaces ,degradatio nb y fungi,micro-organisms , macroinvertebrates andmechanica l reductiono fth eparticl e sizeb y shredders andth e interaction ofcurren t andminera l particles,an d theconstan t redistribution of the organicparticle sb yth e current. Iti stherefor e essential thatpools and riffles aremaintaine d inadditio nt o streammeanders .Bot hmechanism s areuse db y the stream toexpen d itsenerg y andt oredistribut e itsbotto mmateria l and transport itswast e downstream,wher e itca nb ebroke ndow n further indepositiona l habitatswit h their characteristic fauna (large,slo wriver s and lakes and ponds). Many ofth edifference s inspecie scompositio nbetwee nnatura l and regulated streams canb e explained onth ebasi s ofchange d environmental conditions asa conse quenceo fth eenlarge d dimensions and the discharge regimeo f the stream. These changesconcer nth e formo fth e streambed ,th ewate rdepth ,th edegre e ofmeandering , thealternatio no friffle san dpools ,th e frequency of spates anddroughts ,th e light intensity reaching thewate r surface,th ecurren tvelocity , theminimu m andmaximu m water temperature and their fluctuations,th eparticle-siz e compositiono fth e sub stratean d the inputo fallochthonou s material.Minera l substrate composition of the streambottom ,curren tvelocit y and thenatur e andorigi no fth eorgani cdetritu s are themajo rhabita tparameter s thatchange .Erosiona l and intermediate zones disappear, togetherwit hth eassociate d fauna.Lea fpacks and coarse (leaf)detritu s substrates areno tpresen t ando fcours eneithe r isth e faunaassociate dwit hthes e allochthonous organic substrates.Fin eminera l substrates combinedwit h fineorgani c detritus form themos t abundant substrate inregulate d streams,togethe rwit h large fields of macrophytes.Th efin edetritu s doesno toriginat e fromth ebreak-dow n of leafmateria l

170 fromallochthonou ssources ,bu tfro mdecayin gmicrophyte san dmacrophyte sproduce d inth estrea m itself.Fluctuation s intemperatur ean doxyge nregim ear emuc hgreate r inregulate dstream sbecaus eo fth edirec texposur et oth esunligh tan dth eresultin g increase inprimar yproduction .Th eamount so ffin edetritu saccumulatin gpe runi t areaar eals omuc hlarge rbecaus ecurren tvelocitie sar ekep tlo wb yweir sa tregula r distances alongth estream san db yth eextremel yhig hstorag ecapacitie so f (enlarged) stream.channels. Theregulate d sandcollecto r (Section7 )i nbetwee nth etw onatura lsection si n theSnijdersveerbee kform sa nexampl eo fsuc hchanges .Thi ssectio nrun sparalle lt o a roadan dha sfunctione da sa sandcollecto rfo r2 0years ,afte ra serie so fthre e smallpool sbetwee nSection s4 an d 7wer efille d in.However ,unti l 1976i tconsiste d ofa smal lstrea mchanne lwithi nth ewide rstrea mbed ,wher ecurren tan dsubstrat e resembledtha to fSectio n6 ,excep tfo ra poo la tth edownstrea men do fSectio n7 thatwa sapproximatel y 20m longan d3 m wide .Th ewate rlef tthi ssectio nthroug ha culvert.Unde rth ewate rwork sschem eo fth elan dreclamatio nfo rAalten ,plan swer e madet oregulat eth eSnijdersveerbee kdownstrea mo fSectio n6 .O nth ebasi so fth e occurrenceo fsevera lrar emacroinvertebrat especie s inthi sstrea man despeciall yi n thedownstrea msection si twa sagree dtha tthi spar to fth eplan swoul dno tb e carriedout .Sectio n8 i sinhabite db yth elarges tnumbe ro fspecie so fal ldifferen t sections,som eo fth especie soccurrin gonl y inthi ssection ,e.g . Goera pilosa, Athripsodes oineveus, Hydropsyahe ccugustipennis (Tolkamp,1975b) .Muc ht oth esurpri seo feveryone ,includin gloca lfarmers ,th esan dcollecto rwa sregulate danywa yi n thesumme ro f 1976.Withi ntw odays ,th etree swer ecut ,th etrunk sremoved ,an dth e sectionwidene d from3 t o7 m wit ha slop eo f 1:1 an dth ebottom-leve llowere d80 - 100cm .Th ewidt ho fth ewate ri nth ebe d increased from5 0t o16 5c man dth ewate r levelha dt o increasedfro m2 5c m (inth epoo lbefor eth eculvert )t o 105c mbefor e onedro po fwate rcoul dflo wthroug hth eculvert ,a situatio ntha toccurre dfo rth e firsttim ei nlat eDecember ,whic hmean stha tSectio n8 wa sdr yi nthi speriod .Th e simmero f 1976wa sextremel ydry ,bu t inth efollowin gyear sth esam esituatio n occurredfo rshorte rperiods . Thesubstrat eo fth eregulate dsectio nconsiste do fa unifor mlaye ro ffin e sands (233,334 )mixe dwit ha larg eamoun to f finedetritus .N omacrophyte shav e grownther esinc e 1976an dth edetritu sprobabl ycam efro mth eupstrea msections . Occasionally somegrave lwa spresen ti nSectio n8 ,bu talway scovere dwit ha thic k layero fsan dan dfin edetritus . Thefaun apredominatin g inth eregulate dsectio ni sver ydifferen tfro mth e other,natura lsection so fth estream .Appendi x1 4compare sth especie san dthei r numbersfoun di n5 shove lsample s insan dan dgrave lsubstrate san d4 han dsample so f leafpack s inSectio n6 ,wit h2 handne tsample s inSectio n7 .I nth eregulate dsection , with itssand/mu dsubstrate ,onl ya fe wspecie sar epresen ttha tals ooccu ri nth e upstreamsections ,whil ethei rabundance sar equit edifferent .Heteropter aan dOdonat a wereonl yfoun d insmal lnumber so rno ta tal li nth eupstrea mo rdownstrea msections ,

171 norwer e themajorit yo fth eChironomida especie s found inth e sand collector (cf. Appendix 9). Itca nb e concluded thatchangin g astrea m intoa lon gnarro wpon db y regulationresult s inth edestructio no fth e streamfaun a andth e settlemento f a pondo rditc hfauna .

~~172 Summary~~

A lowland streamca nb e distinguished fromothe rtype so fstream sb y itsstrong lyvaryin gdischarge ,wate r level,curren tvelocity ,botto mcompositio nan dvegetatio n pattern.A largenumbe r ofbenthi cmacroinvertebrat especie s arerestricte d tothi s typeo fenvironmen t and form the characteristic animalcommunit yo fth enatura l lowland stream. A largenumbe r ofphysica l factors directly influence thedistributio no fmacro - invertebrates over thevariou s habitat types that canb e found ina stream . Current velocity,substrat e composition and thenatur ean damoun to ffoo dar eth emos t important ones. Chapter 1,th e introduction,deal swit hth erelationshi pbetwee nthes e factors andthei r influenceo nth e stream ecosystem.A s astartin gpoin t for investigations intoth erol e the substrateplay s inth edevelopmen t andpreservatio no fth emacro - invertebrate communities innatural ,undisturbe d lowland streams,tw oclosel y related working hypotheses were formulated: - Manybenthi c lowland streammacroinvertebrat e species showdistinc t preferences fora specific substrate composition. - Forman y ofthes e species the small-scale spatialvariatio n insubstrat ecomposi tiono fth e streambe d isessentia l forthei r existence. The researchwa s carried out intw ounperturbe d lowland streams,th eSnijders veerbeekan d theRatumsebeek .Thes e twostream s aredescribe d inChapte r2 . InChapte r 3,Sectio n 3.1 themetho duse d toclassif y substrates inth e fieldo n visualcharacteristics ,th e selectiono fth e sampling sites andth emetho do f sampling substrate andmacroinvertebrate sa t the sametim ewit hth emicro-macrofaun a shovel aredescribed . InSectio n 3.2 adetaile d description isgive no fth eprocedure scar riedou t inth e laboratory: collection and identification ofth emacroinvertebrates ; particle-size analysis ofth e substrate;an ddeterminatio n ofth enatur ean damoun t oforgani c detritus.Sectio n 3.3 treats themethod suse d inth e laboratoryt o test theresult s ofth e field study:performin g substrate selectionexperiment s for several macroinvertebrate species ina laboratory streamchannel .Sectio n3. 4 dealswit hth e methodsuse d to study the colonization ofartificia l substrates inth efield . In Section3.5 ,th emethod suse d forstatistica l analysis ofth ecollecte ddat aar e described. InChapte r 4,Sectio n 1th eresult so fth e field studyar egiven .O nth ebasi s ofth efiel d classification ofth e substrates,eac hsampl e isclassifie d toa sub strate type characterized by therati obetwee nth edominan tminera l (e.g.gravel , 173 sandan dorgani c (e.g.leaves ,coars edetritus ,fin edetritus )components .Fou r classificationlevel sar eused .Compariso no fthes e levels illustrates that iti s importantt omak ea distinctio nbetwee nminera lan dorgani csubstrates ,betwee n coarsean dfin eminera lsubstrates ,betwee ncoars ean dfin eorgani c substrates and betweenth evariou s combinationso fthes etype s (Fig. 12). Fromth eparticle-siz e analysis inth e laboratory ofth eminera lcomponent s of thesamples ,th esubstrat e characteristic (Q..MdQ,graph )i sdetermine d forbot h streams (Figs.1 4an d 15). Severalsubstrat e typesar edistinguishe dusin gth efirst , second (median)an dthir dquartile ,o rthei r combination,i nth eQiM-tQ ,inde x (Appendices4 an d 5). Substrates consistingo fmor etha n 104 (14i na paralle l classification)organi cdetritu sar edistinguishe da sseparat etypes :coars edetritus , leavesan dth ecombinatio no fthes etwo . Thepreferenc eo fa specie sfo ron eo rmor e substrate typeswa s indicatedb yth e Indexo fRepresentation .Thi smetho d gavesatisfactor y resultsan dwa smor e convenient thanothe rstatistica lmethod s (Subsection 4.1.3.1). The importanceo fth ejoin tus e ofth etw oclassificatio n levels forth eorgani c material is illustrated inSubsectio n4.1.3.2 . Itwa sdemonstrate dtha ta hig habundanc eo fa specie s (Ephemera danioa, amay fly)ma yinfluenc eth etota lmicrodistributiona lpatter nove rth evariou s substrate types,becaus ejuvenil eanimal sar emor enumerou s thanolde r ones,althoug h thisdoe s not influenceth especifi csubstrat epreferenc ea smeasure db y the Indexo fRepresen tation (Subsection 4.1.3.3). Althoughonl ysmal ldifference s inth etota lnumbe ro f speciesbetwee nth e substratetype sar efound ,th edifference s arelarge rwhe nth especimen s are considered pertaxonomi euni t (Tables 13an d 14;Subsectio n 4.1.6). Inal l substratetypes , chironomidmidg e larvaear edominan t interm so fnumbe ro f species andnumbe ro f specimens.However ,ther ear edistinc tdifference sbetwee nth evariou ssub-families . Substratetype sconsistin go fpurel yminera lmateria l (baresand ,bar e gravel)ar e poorest inspecimens ,bu tno t inspecies .Bar e gravel,fo rexample ,i sriches t in species,followe db ydetritu s substrates.Bar egrave l showsth emos tevenl ybalance d distributiono fth enumbe ro fspecimen sove rth evariou staxonomi eunits . InSubsectio n4.1. 4 clusteringo fth e 14substrat etype s (characterizedb yth e QHMJQ, index)o nth ebasi so fth e speciescompositio nan dth erelativ e abundanceo f eachspecie spe rsubstrat e typedemonstrate s thatth efauna l compositiondiffer s stronglyamon gth egrave lsubstrates .I ti sals oshow ntha tther ear edifference s betweencoars e sand,fin esand ,leave san dcoars edetritus ,an d thatwithi n these typesth edifference sar eles spronounced .Fo rth emai n substratetypes ,onl y small differencesar efoun dbetwee nth etw ostream s (Figs.1 7an d18) . InSubsectio n4.1. 5th egroupin go fth e specieso nth ebasi s ofthei r substrate preference(s)i sdescribed .Th egroupin g isdon eusin gth e field classification (Appendix9 )an dth egrain-siz eclassificatio no fth e substrates (Appendices 12an d 13). Several speciesappea rt ohav e similarsubstrat epreferences ,makin gi t

174 possiblet odistinguis hfauna lgroups ,eac hwit ha certai nsubstrat epreference .I t isclea rtha ta detaile d substrateanalysi s isno treflecte d inth epreference so f thefauna lgroups ,whic hmainl y showdistinc tpreference s forgravel ,san do ra combinationo fthes etw otypes . InSectio n4. 2 detailed datao nsubstrat epreferenc ear epresente d for2 6tax a fromth evariou staxonomi eunit srepresentin g thespecie scomposin gth efauna l groups.Mechanism s leadingt osubstrat e selectionan deventua ldifference s insub stratepreferenc ebetwee ndifferen tdevelopmen tstage so fa norganis mar ediscussed . Theresult so fth e analysiso fth efiel ddat aar ecompare dwit hdat a fromth e literature and,fo ra restricte dnumbe ro fspecies ,wit hth eresult so fsubstrate - selectionexperiment s inth elaborator yan dcolonizatio nexperiment s inth e field.I t isshow ntha ti ti snecessar y tous ea detaile dsubstrat eanalysi s forth eassessmen t ofth esubstrat epreference so f individualspecies . Theresult sfo rth e individual species arediscusse d inChapte r 5,emphasizin g therol eo fth emai nfactor stha tdetermin e thesubstrat epreference s (particlesize , currentvelocity ,an dfoo d conditions). InChapte r 6,th econclusion sconcernin gth eworkin ghypothese s formulated in Chapter 1ar ediscussed : - Mostbenthi cmacroinvertebrate sar erelate dt ocertai nsubstrat etypes .Thre emai n groups canb e distinguished,compose dof'specie swit hpreference sfo rcoars eminera l substrate (gravel),fin eminera l substrate (sand)an dorgani cmateria l (leaveso r detritus),respectively .Th eparticl e sizeo fth eminera lcomponen to fth esubstrat e aswel la sth enatur ean damoun to fth eorgani cdetritu s influenceth emicrodistri - butiono fmos to fth e investigated species.Factor srelate dt oth esubstrate ,suc ha s foodavailability ,oxygen -an dcurren tconditions ,ar eals oimportant . - Variousmacroinvertebrat especie snee d several substratetype sa tth esam etim eo r consecutively tob e ablet omaintai nthemselve s ina lowlandstream .Change s infoo d supplyo rfoo d selection,a swel l asalteration s incase-buildin gmateria l (for caddis flies)o r inth eproportio no ffactor srelate dt oth esubstrate ,suc ha s currentvelocit y (forth emayfl y Ephemera daniaa) makethi snecessary . Ifa speciesprefer svariou s substratetypes ,thes epreference s dono toccu ra t thesam emomen t (seasonaldifferences )o ra tth esam edevelopmen tstage . The alteration insubstrat e composition,change s inflo wregim ean dth echange d nature andorigi no f thefoo dwe bbasis ,ar eth emos t importantreason sfo rth e differences infauna lcompositio nbetwee nth ecommunitie so fnatura lan dregulate d lowlandstreams .Becaus ecurren tvelocit ydirectl yaffect sth esubstrat ecomposition , andstrea mhedgerow sar edirectl yrelate d toth estructur eo fth efoo dwe b inth e stream (leavesar e thebasi c food), iti sessentia l thatno tonl y thehydrologica l consequenceso fhydrologica loperation s inth estrea mar econsidered ,bu tals oth e effectso nth estrea mecosystem .Thi s implies thatth enatura lcurren tregim emus tb e maintainedan dtha thedgerow san d forests alongth ebank smus tno tb ecleare d tomak e wayfo r inspectionpaths .

~~175 Samenvatting~~

Laaglandbekenvorme nee nvoo rNederlan dkarakteristie kbeektype ,gekenmerk tdoo ree n grotedynamie k inafvoerfrequentie ,waterstand ,stroomsnelheid ,bodemsamenstellin ge n vegetatiepatroon.Vel ebenthisch ediersoorten ,voornamelij kbehoren d totd emacro fauna,kome nallee no fbi jvoorkeu ri ndi tmilieutyp evoo re nvorme ndaarme ed e ken merkendedierlijk elevensgemeenscha pva nee nongestoord e laaglandbeek. Voord everspreidin gva nmacrofauna-organisme nove rd everschillend ehabitat - typenwelk eme ni nee nbee kka naantreffe n (microdistributie)zij nee naanta l fysische milieufactorenva nbelang ,waarva nd estroomsnelhei dva nhe twater ,d esamenstellin g vanhe t substraate nd eaar de nd ehoeveelhei dva nhe tvoedse ld ebelangrijkst e vormen. Ind einleidin g inhoofdstu k1 word t ingegaano pd esamenhan g tussend e factoren end einvloe dva ndez efactore np phe tbeekecosysteem . Hetdoe lva nhe tonderhavig eonderzoe ki she tverkrijge nva n inzicht ind ero l died esamenstellin ge nd evariati eva nhe t substraat spelenbi jhe tontstaa ne n in- stand-blijvenva nd evoo rongestoord elaaglandbeke nkarakteristiek emacrofauna - levensgemeenschap.Di t isverva ti ntwe esamenhangend ehypotheses : - Veelbodembewonend elaaglandbeek-macrofaunasoorte nvertone nduidelijk evoorkeure n vooree nspecifiek esubstraatsamenstelling . - Voorvee lva ndez esoorte ni sd ekleinschalig eruimtelijk evariati ei nsubstraat samenstellingva nd ebeekbode messentiee lvoo rhu n (voort)bestaan. Hetonderzoe kwer dverrich ti ntwe eongestoord e laaglandbeken,d eSnijdersveer beeke nd eRatumsebeek ,welk ebeschreve nworde n inhoofdstu k2 . Paragraaf3. 1 beschrijftd ewijz ewaaro p substrateni nhe tvel dwerde ngekarak teriseerd,d eselecti eva nd ebemonsteringsplaatse ne nd emethod eva ngelijktijdig e bemonsteringva nsubstraa te nmacrofaun ame td emicro-macrofauna-schoffel . Paragraaf3. 2 gaat ino pd everwerkin gva nd emonster s inhe tlaboratorium ,he t uitzoeken,conservere ne ndeterminere nva nd emacrofauna ,d ekorrelgrootteanalys eva n hetsubstraa te nd ebepalin gva nd ehoeveelhei dorganisch e stofi niede rmonster . Inparagraa f3. 3 zijnd emethodieke nbeschreve nwaarme ed eresultate nva nd e veldinventarisatie inhe t laboratoriumwerde ngetoets tdoo rhe tverrichte nva nsub - straatselectieexperimenteni nee nlaboratoriumstroomgoo tvoo rdivers emacrofauna - soorten. Paragraaf3. 4 geeftd emethod etoegepas tvoo rd ebestuderin gva nd ekolonisati e vani nhe tvel daangebode nsubstraten ,zogenaamd ekunstmatig esubstraten ,terwij l paragraaf3. Sd ewiskundig everwerkin gva nd everzameld egegeven sweergeeft .

176 Inparagraa f4. 1worde nd emethodisch e resultatenva nhe tveldonderzoe kbespro ken.O p grondva nd eveldclassificati e wordt iedermonste ringedeel dbi j eensub straattype,gekarakteriseer d doord everhoudin g tussend e inhe tvel d herkenbare dominantemineral e (bijvoorbeeld grind enzand )e norganisch e (bijvoorbeeld blad, grove detritus en fijnedetritus )componenten .Hierbi jworde nvie rclassificatie niveaus gebruikt,welk edoo ronderling evergelijkin g hetbelan g illustrerenva nhe t makenva nonderschei d tussenmineraa l enorganisc h substraat,tusse n grofe nfij n mineraal substraat,tusse n grofe nfij norganisc h substraate ntusse nd edivers e combinaties vandez e substraten (fig.12) . Opbasi sva n dekorrelgrootteanalys e vand emineral e delenva n demonster s isd e substraatkarakteristiek voord ebeid ebeke nopgestel d (fig.1 4e n 15)e nworde n er diverse substraattypenonderscheide nme tbehul pva nhe teerste ,tweed e (mediaan)e n derdekwartie lo fhu ncombinati e ind eQ..M,Q,-inde x (appendix4 e n 5), waarbij sub stratenbestaand eui tmee r dan 101 (H inee nparallell e indeling)organisch e detritus alsapart e typesworde nonderscheide n ingrov edetritus ,bla d end ecombinati e van beide. Erword t aangetoond datd e gekozenmethod e omd evoorkeu rva n eenorganism e voor eeno fmee r substraattypen teherkenne ndoo rmidde lva nd e 'Indexo f Representation', goedvoldoe t invergelijkin gme t andere statistischemethode n (paragraaf 4.1.3.1). Hetbelan g vanhe t gebruikva nd ebeid e classificatie-grenzen voorhe t organisch materiaalwer dgeïllustreer d inparagraa f 4.1.3.2.Teven sword t aangetoond dathog e dichtheden vanee nsoor t (Ephemcœa danioa, eenhaft )we l hetalgehel everspreidings beeldove r dedivers e substraattypen kanbeïnvloede nomda tjuveniel e dierenveela l talrijker zijnda noudere ,maa r datd eme tbehul pva nd e 'Indexo f Representation' aangetoonde specifiekevoorkeu r hierdoornie tword t gemaskeerd (paragraaf 4.1.3.3). Hoewel erte naanzie nva nhe t totaal aantal soorten slechts geringe verschillen tussend e substraattypenwerde n gevonden,blijke ne rgroter everschille nwannee rd e aantallen soorten enindividue nnie t alstotaa lmaa rpe rtaxonomisch eeenhei dworde n beschouwd (tabel 13e n 14,paragraa f 4.1.6).Hierbi jblijk tda tchironomide n (mugge- larven)zowe lwa tbetref the taanta l soorten alshe taanta l individuen inall esub straattypen domineren,waarbi j er echterduidelijk everschille nbestaa ntusse nd e diverse subfamilies. Substraattypenbestaand e uitpuu rmineraa lmateriaa l (kaalzand , kaal grind) zijnhe t armstaa n individuen,maa rnie t aansoorten .Kaa lgrin d is zelfs hetrijks t aan soorten,gevolg d doordetritussubstraten . Kaalgrin d isteven she t substraattype dat demees t evenwichtigeverdelin g vanhe t aantal individuenove rd e diverse taxonomische eenhedent e ziengeeft . Inparagraa f 4.1.4 wordt doormidde lva nee nclusterin gva nd e 14doo rd e Q^O^ indexgekarakteriseerd e substraattypen opbasi sva nd e soortensamenstelling end e talrijkheidva n iedere soortpe r substraattype aangetoond datd e faunistischesamen stellingva nd edivers e grindsubstraten onderling sterkverschilt .Teven skom tnaa r vorenda t erverschille n zijn infaunistisch e samenstelling tussen grof zand,

177 blade ngrove-detritussubstrate nmaa rda tbinne ndez e substraattypend everschille n mindergroo tzijn .Tusse nd ebeid ebeke nwerde n slechtsgering everschille n ind e hoofdtypengrind ,zan de ndetritu sgevonde n (fig.1 7e n18) . Inparagraa f4.1. 5 wordtd egroeperin gva nd esoorte no pbasi sva nhu nsubstraat voorkeurbeschreven .Dez ewer dzowe luitgevoer do pbasi sva nd eveldclassificati e (appendix9 )al so pbasi sva nd ekorrelgrootteclassificati eva nd esubstrate n (appen dix 12e n13) . Diversesoorte nblijke ndezelfd esubstraatvoorkeur(en )t ehebben ,zoda the tmo gelijki so mfaunistisch egroepe nt eonderscheiden ,el kme tee nbepaald e substraat voorkeur.E rkom tnaa rvore nda tee ngedetailleerd e substraatanalysenie tteru gt e vindeni si nd evoorkeure nva nd egroepe nsoorten ,di eveela lreagere no phe tonder scheidgrind ,zand ,detritu so fee ncombinati eva ndez ehoofdtypen . Paragraaf4. 2 behandeldvoo r2 6soorten ,vertegenwoordiger sva ngenoemd efaunis tischegroepen ,verdeel dove rd edivers etaxonomisch e eenheden,d e gedetailleerde substraatvoorkeuren,waarbi j ingegaanword to pd emechanisme ndie leidento tsub straatselectiee neventuel everschille n invoorkeu ronde r invloedva nhe tontwikke lingsstadiumva nhe torganisme .D eresultate nva nd eanalys eva nd eveldgegeven s wordenvergeleke nme td eliteratuurgegeven sen ,voo ree nbeperk t aantal soorten,me t deresultate nva nlaboratoriumexperimente ne nkolonisatieexperimente nme tkunstmati g substraati nhe tveld .E rblijk tda the tvoo rd evaststellin gva nd esubstraatvoor keurva n individuelesoorte nwe lbelangrij k iso mee nz ogedetailleer dmogelijk esub straatanalyset ehanteren . Paragraaf4. 4 geeftee noverzich tva nd ebelangrijkst eresultate nva nd eveld - experimenten. Inhoofdstu k5 volg td egeïntegreerd ediscussi eva nd ehiervoo r gepresenteerde resultatenvoo rd eindividuel esoorten ,waarbi j denadru kword tgeleg do pd ehoofd factorendie d esubstraatpreferenti ebepalen ,namelij kkorrelgrootte ,stroomsnelhei d envoedsel . Inhoofdstu k6 worde nd econclusie s gegevenaa nd ehan dva nd eeerde rgesteld e hypotheses:

1. Demeest ebodembewonend emacrofaunaorganisme nzij ngerelateer daa nbepaald esub straattypen.Dri ehoofdgroepe nkunne nworde nonderscheiden ,bestaand eui tsoorte nme t eenvoorkeu rvoo rrespectievelij kgro fmineraa l substraat (grind),fij nmateriaa l substraat (zand)e norganisc hsubstraa t (blado fdetritus) .Zowe ld ekorrelgroott e vand emineral ecomponen tva nhe tsubstraa tal sd e aarde nd ehoeveelhei dva nhe t organischmateriaa lbeïnvloede nd emicrodistributi eva nd emeest eonderzocht eorganis men.Hierbi j spelenteven sme the t substraatgerelateerd eomstandighede nzoal s voedselaanbod,zuurstofgehalt ee nstroomsnelhei d eenrol . 2. Diversesoorte nmacrofaun ahebbe nmee rsubstrate ntegelijkertij do fi n successie nodigo mzic ht ekunne nhandhave ni nee nlaaglandbeek .Hierbi j spelenzowe lwijzi gingeni nhe tvoedselaanbo do fd evoedselkeuz eee nrol ,al swisselinge n inhe t

178 materiaal gebruiktvoo rhuisjesbou w (bijkokerjuffers )o fgewijzigde ,aa nhe t substraat gerelateerdefactore nal sd estroomsnelhei d (bijvoorbeeldvoo rd ehaf t Ephemera dan-ùca). Wanneeree nsoor tmee r substratenprefereert ,blijk tn agedetailleerd e analyse vand egegeven sda tdez e ind erege lnie to phetzelfd etijdsti pvoorkome n (seizoens verschillen)o fda tverschillend eontwikkelingsstadi averschillend e substraattypen prefereren.

Beschouwingva ndez econclusie s inhe tlich tva nd everschille ni nfaunistisch e samenstellingva nd elevensgemeenschappe nva nnatuurlijk e engereguleerd e laagland bekenleid tto td econclusi eda td ewijziginge ni nsubstraatsamenstellin g tesamenme t hetgewijzigd estfomingsregie me nd eaar de nherkoms tva nd ebasi sva nhe tvoedsel - netwerkal sd ebelangrijkst eoorzake nvoo rdez everschille nzij naa nt ewijzen .Omda t de stroomsnelheid directva ninvloe d iso pd esubstraatsamenstelling ,terwij lbeek - begeleidendehoutopstande ndirec tgerelateer d zijnme td eopbou wva nhe tvoedselnet - werk ind ebee k (blad isbasisvoedsel) , ishe tva nwezenlij kbelan gda te rbi jd e planningva nhydrologisch e ingrepeni nhe tbeekecosystee mnie t alleenme td ehydro logischeconsequentie sword tgerekend ,maa roo kme td ehydrobiologische ,hetgee nim pliceertda the tnatuurlij k stromingsregiemmoe tworde ngehandhaafd ,terwij ld e beekbegeleidendebosse ne nhoutwalle nnie tmoete nwijke nvoo rschouwpaden .

~~179 Appendices~~

Appendix 1.Macroinvertebrat especie san d taxa found inth eSnijdersveerbee k and theRatumsebeek . 0 :taxo nno tconsidere d forcalculatio no fnumbe ro f species 00 :taxo nno tconsidere d assuch ; identificationuncertain ;perhap sno taquatic . 4 3 :taxo n3 ispar to f theoverlappin g taxon4 ,althoug h itma yb e awel l defined species.Taxo n3 i salway sconsidere d asbein g included inth e overlapping taxon4 . Nomenclature follows thekey suse d foridentificatio n (see Identification References).Whe nonl y agenu snam e isstated , itma yconcer nmor etha non e species (spp.),unles s allspecimen s areexpecte d tobelon g toon especies , but thespecie snam ei sunknow n (sp.). Numeral taxacode s areuniqu efo rthi sresearc h andwer euse d forcompute r analysiso f thedata .

Tricladida: 4 3 Polyoelis tenuis (Ijima) 4 Volyoelis Ehrbg. spp. 9 DendrocoeVum laateum (Müller) Oligochaeta: 11 Oligochaetaspp . 11 12 Tubificidaespp . 11 13 Naididaespp . 11 14 Lumbriculidae spp. 18 Eiseniella tetraedra (Savigny) 19 Stylaria laeustris (L.) Hirudinea: 21 Erpobdella oatoaulata (L.) 22 Erpobdella testaaea (Savigny) 23 Glossiphonia aomplanata (L.) 25 Helobdella stagnalis (L.) 28 Theromyzon tessulatum (Müller) Malacostraca Crustacea: 32 Gammarus pulex (L.) 33 Gammarus roeselii (Gervais) 35 Asellus aquations (L.) 36 Asellus meridianus Racovitza Hydracarina: 38 Hydracarina spp. Araneae: 39 Argyroneta aquatioa (Clerck) Plecoptera: 40 Amphinemura standfussi Ris 42 Nemoura cinerea (Retzius) Ephemeroptera 47 Ephemera danica Müller) 48 Habrophlebia fusoa (Curtis) 49 Centroptilum luteolum (Müller) 52 50 Baetis vernus Curtis 52 51 Baetis mutiaus (L.) 52 Baetis Leach, spp. 53 Faraleptophlebia submarginata (Stephens)

181 56 Caenis hovaria (L.) 57 Caenis robusta Eaton Odonata: 59 Zygopteraspp . 61 Aeshna mixta Latreille 63 Somatoohlora aratioa Zettersted t 74 Ceriagrion tenellum (Villers) Hemlptera: 0 75 Corixinae larvaespp . 76 Velia oaprai Tamanini 77 Notoneota glauaa L. 81 Notoneata viridis Delcourt 83 Gerris gibbifer Schununel 84 Sigava striata (L.) 85 Sigara falleni (Fieber) 86 Sigara distinata (Fieber) 87 Sigara lateralis (Leach) 88 Sigara semistriata (Fieber) 93 Hesperooorixa sahlbergi (Fieber) 96 Hepa rubra (L.) 97 Hydrometra stagnorum (L.) 98 Gerris najas (DeGeer ) Trichoptera: 99 Hydropsyohe angustipennis (Curtis) 100 Pleotroanemia aonspersa (Curtis) 101 Lype reduota (Hagen) 103 Agapetus fusoipes Curtis 105 Lithax obsaurus (Hagen) 107 Goera pilosa (Fabricius) 109 Serioostoma personation (Spence) 0 112 Halesus Stephensspp . 113 Halesus digitatus (Schrank) 114 Halesus tesselatus (Kambur) 116 Limnephilus auricula Curtis 117 Halesus radiatus interpunotatus (Zetterstedt) 118 Potamophylax rotundipennis (Brauer) 122 Potamophylax luotuosus (Piller& Mitterpacher ) 0 125 Potamophylacinispp . 126 Enoioyla pusilla (Burmeister) 127 Chaetapteryx villosa (Fabricius) 128 Mioropterna sequax MacLachlan 130 Hydatophylax infumatus (MacLachlan) 131 Limnephilus sparsus Curtis 132 Limnephilus extriaatus MacLachlan 133 Anabolia nervosa Curtis 134 Glyphotaelius pelluaidus (Retzius) 135 Limnephilus lunatus Curtis 136 Limnephilus rhombious (L.) 0 142 Limnephilidaespp . 143 Bereodes minutus (L.) 0 144 Leptoceridaespp . 145 (L.) 146 Mystaoides longicornis Athripsodes oinereus (Curtis) 147 (Stephens) 148 Athripsodes aterrimus Athripsodes bilineatus (L.) 149 Curtis Megaloptera: Molanna angustata 0 152 Sialis Latreillespp . 153 Sialis lutaria (L.) 154 Pictet Coleoptera: Sialis fuliginosa 150 Coelostoma Brulspp .

182 151 Agabus paludosus (Fabriclus) 155 AgabusLeac hlarva espp . 157 Agabus bipustulatus (L.) 158 Platambus maaulatus (L.) 160 Ilybius Er.larva espp . 163 Noterus Clairvillespp . 165 Laooophilus Leac hspp . 168 Hydroporus Clairvillespp . 169 Colyrribetus fusaus (L.) 170 Stiototarsus duodeoimpustulatus Fabricius 172 Haliplus Latreillespp . 173 Hydrophilidaesp p 174 Helophorus aquations L. 175 Helophorus Leachspp . 176 Limnebius Leachspp . 178 Hydrophilidaespp .larva e 179 Anaaaena limbata (Fabricius) 180 Anaaaena globulus (Paykull) 181 Laaoobius Erchs.spp . 181 182 Laooobius sinuatus Motsch/ striatulus (Fabricius) 183 Gyrinus substriatus Stephens. 184 Dryops Ol.spp . 185 Elmis aenea (Müller) 186 Limnius volohnari (Panzer) 187 Oulimnius tuberoülatus (Müller) 189 Oohthebius Leach.spp . 190 Helodes minuta L.larva e 191 Chaetharthria seminulum Herbst 192 Megasternum boletophagum Mrsh. Diptera: 193 Tipula L.spp . 193 194 Tipula gr. lunata sensu Theowalt,1957 193 195 Tipula gr. pruinosa sensu Theowalt,1957 193 196 lamatotipula Matsumura spp. 198 197 Limnophila Marquart sp. a 198 Limnophila Marquart spp 198 199 Limnophila gr. fusoipennis sensu Tolkamp, 1976 200 Pedieia Latreille 202 Gnophomyia subg. Leiponeura sensu Hennig, 1968 203 Gnophomyia Osten-Sacken spp. 204 Elephantomyia Osten-Sacken spp, 205 Dioranota Zetterstedt 198 208 Limnophila Marquart sp. b 210 Anopheles Meigen spp. 215 214 Dixa Meißen spp. 215 Dixa gr. maculata sensu Disney,1975 216 Bezzia Kieffer spp. 217 Palpomyia Megerle spp. 218 Palpomyia tibialis Meigen 219 Simulium erythrooephalum De Geer 220 Simulium latipes Meigen 221 Simulium aureum Fries 222 Simulium gr. ornatum Meigen 0 223 Simulium Latreille spp. 224 Simulium breviaaule Dorier & Grenier 225 Psyahoda Latreille spp. 225 226 Periooma Walker spp. 0 227 Simulium naturale Davies 231 Berts Latreillespp . 232 Dixella Dyer& Shanno nspp . 233 Tabanus L..spp . 234 HaematopodaMeige nspp .

183 236 Aphrosylus Walkerspp . 238 Bibionidaespp . 239 HemerodromiaMeige nspp . 240 Ephydridaespp . 241 Ptyohoptera Meigen 242 Tetanoceridaespp . 243 Osmylus fulvioephalus (Scopoli)(Neuroptera ) 244 Maoropelopia Thienemannspp . 244 245 Maoropelopia nebulosa (Meigen) 248 Apseotrotanypus trifasoipennis (Zetterstedt) 249 Prooladius Skusespp . 250 Teiohomyza Marquetspp .(Ephydridae ) 251 Hydraena exoisa (Coleoptera) 00 252 Coleopteralarva espp . 253 cf.Conohapelopia sensuMolle rPillot ,197 8 253 254 Conohapelopia melanops (Wiedemann) 256 Zavrelimyia Fittkauspp . 258 Metrioonemus vande rWul pspp . 260 Clinotanypus nervosus (Meigen) ,0 263 Orthooladiinaespp .(juv. ) 0 264 Chironominispp .(juv. ) 265 Criaotopus (Criootopus) vande rWul p 266 Criootopus bioinotus (Meigen) 268 Orthooladius vande rWul pspp . 269 Covynoneura Winnertzspp . 270 Thienemanniella Kiefferspp . 271 Prodiamesa olivaoea (Meigen) 272 Brillia modesta (Meigen) 273 Odontomesa fulva (Kieffer) 274 Brillia. longifuroa Kieffer 275 Diplooladius aultriger Kieffer 276 Nanocladius Kieffer 277 Rheooriootopus Thienemann 278 Pseotrooladius Kiefferspp . 279 Eukiefferiella gr. disaoloripes sensuMolle rPillo t198 0 280 Chaetooladius Kiefferspp . 281 Eukiefferiella brevicalcar (Kieffer) 282 Eukiefferiella alaripennis (Lundbeck) 283 Epoiaoaladius flavens (Malloch) 285 Limnophyes Eatonspp . 0 286 Tanytarsinisp p 287 Mioropseotra gr. praecox sensuTshernowski j 288 Tanytarsus aurtioornis (cf.Mothers ) 289 Mioropseotra gr. trvoialis sensuTshernowski j 290 Tanytarsus vande rWul pspp . 291 Stempellina Bausespp . 292 Cladotanytarsus Kiefferspp . 293 Rheotanytarsus Bausespp . 294 Paratanytarsus Bausespp . 296 Chironomus Meigenspp . 297 Glyptotendipes Kiefferspp . 298 Diorotendipes gr. notatus sensuMolle rPillot ,197 9 0 299 Paraeladopelma Harnischspp . 300 Cryptochironomus Kiefferspp . 301 Paraoladopeltm eamptoldbis agg.sens uMolle rPillot ,197 9 302 Paratendipes Kiefferspp . 303 Miorotendipes gr. ohloris sensuMolle rPillot,197 9 306 Phaenopseotra Kiefferspp . 307 Paraoladopelma laminata agg.sens uMolle rPillot,197 9 308 Stiotoohironomus Kieffer 310 Polypedilim laetum agg.sens uMolle rPillot ,197 9 311 Polypedilum breviantennatum Tsbernowskij

184 312 Polypedilum gr. nubeoulosum sensuTshernowski j 312 313 Polypedilion gr. aonviatvm sensuTshernowski j 314 Hydrobaenus pilipes (Malloch) 277 315 Rheoariaotapus ct.dorieri sensu Pankrat ova , 1970 O 317 Diptera pupae spp. O 318 Chironomini pupae spp. O 319 Orthocladiinae pupae spp. Mollusca: 321 Planorbarius aorneus (L.) 323 Gyraulus albus (Müller) 325 Anisus leuoostoma (Millet) 327 Lymnaea peregra t.ovata (Müller) 328 Lymnaea trunaatula Müller 330 Lymnaea palustris (Müller) 331 Lymnaea aurioularia (L.) 332 Lymnaea glabra (Müller) 338 Thysa fontinalis (L.) 340 Aneylus fluviatilis Müller 341 Pisidium C.Pfeiffer spp. 342 Sphaerium Scopol! spp. Various: 343 Sisyra Burmeister spp. (Neuroptera) 344 Lepidoptera spp. 345 Hydrdbius fusaipes L. (Coleoptera) 346 Unknown Orthocladiinae larva (Diptera) 198 351 Limnobiidae spp. (Diptera) 00 352 Coleoptera spp. 354 Heloaharus lividus Forst. (Coleoptera) 277 355 Rheoariaotapus gr. fusaipes sensuThienemann ,194 4 (Diptera) 0 356 Dipteraspp . 0 357 Pupae ofunknow norde r 0 358 Tanytarsini pupaespp . (Diptera) 184 359 Dryops luridus Er. (Coleoptera) 0 360 Ironoquia dubia (Stephens)exuviu m (Trichoptera) Pisces: 361 Gasterosteus aauleatus (L.) 362 Pungitius pungitius (L.) 363 Noemaaheilus barbatulus (L.) Cyclostomata: 364 Lampetra planeri (Bloch)

~~185 Appendix7 .Numbe ro f specimenso f Ephemera daniaa inhig h density samples inth e Ratumsebeek for5 lengt hclasse s inSor t2 .~~

~~Sample Year Week Number of Sort 2 Bodjr leng t h/mm no. specimens class 0-5 5-10 10-15 15-20 >: 20~~

55 1977 19 15 4 1 2 12 60 1977 21 10 4 1 1 2 6 106 1977 35 26 4 26 109 1977 35 32 1 32 129 1977 40 38 4 32 6 130 1977 40 29 4 11 18 133 1977 40 26 4 14 12 142 1977 43 14 1 13 1 146 1977 43 78 4 31 42 5 164 1977 49 31 2 4 17 8 1 1 176 1978 03 11 4 2 9 Total 310 167 105 14 5 19

~~Appendix8 .Numbe ro f specimenso f Ephemera danica inhig h density samples in the Snijdersveerbeek for 5lengt h classes inSor t2 .~~

~~Sample Year Week Numbero f Sort 2 Body length/mm no. specimens class 0-5 5-10 10-1S1 15-20 >:~~

35 1976 04 14 2 8 4 83 1976 34 20 20 86 1976 37 10 3 2 8 90 1976 37 10 4 5 5 95 1976 43 14 4 2 3 8 1 97 1976 43 15 6 1 5 9 98 1976 43 12 2 1 5 5 1 103 1976 45 12 4 2 7 3 121 1977 03 20 3 4 8 7 1 122 1977 03 11 1 1 5 3 1 1 126 1977 03 10 5 3 4 3 147 1977 12 19 4 2 7 8 2 155 1977 15 16 3 1 7 4 4 Total 183 41 66 54 18 4

188 Appendix 9. I.R. values for the main taxa in Sort 2 for the Snijdersveerbeek and the Ratumsebeek. Italic values Indicate significant over-representation. Sam = number of samples in which the taxon occurred, n = number of specimens. B * Bare, S = Sand, G = Gravel, D = Coarse Detritus / Leaves, FD - Fine Detritus. Boxes indicate the main substrate preferences of faunal groups: I : Gravel, II: Gravel / Sand, III: Sand, IV: Gravel / Sand / Detritus, V: Sand / Detritus, VI: Gravel / Detritus, VII: Detritus.

~~Taxa Taxa name Snijdersveerbeek~~

~~Substrate class Substrate class~~

~~2 3 4 2 3 4 5 6~~

~~n S+FD S+D S+D+FD S+FD S+D S+D+rD B0 0+D~~

I. 18 Eieeniella 80 311 -5.7 -4.9 -4.2 -5.7 18.6 3.4 -5.4 11 27 -2.5 -1.4 -1.5 -1.9 5.2 2.7 -1.2 103 AgapetuB 8 13 * 4 - - - 6 1 2 47 211 4.9 -3.2 -1.8 -5.9 5.3 10.7 -6.6 105 Lithax 150 451 5.6 -5.0 -4.8 -6.8 8.4 1.6 -4.7 55 218 -0.3 -3.8 -3.2 -6.0 8.4 3.5 0.8 107 Goera 11 14 -0.1 -1.0 -1.1 -1.4 2.4 2.3 -1.5 - _ - - « - m « - 146 Athripsodes 2 2 * 1 1 10 22 0.2 1.3 -1.0 -2.0 -1,3 10.2 -2.3 175 Helophorus 10 39 0.0 -0.-6 -1.-8 -2.-3 -1.-8 7.8 -0.-2 181 Laacobius 11 28 0.3 -0.8 -1.6 -2.0 1.7 3.8 -1.7 _ _ _ _ _ - _ _ . 184 Dryopa 19 30 -2.2 -1.5 -1.0 -1.1 1.9 5.3 -0.9 1 1 + - - - - . - 1 185 Elmis 40 133 -4.1 -2.9 -3.4 -4.3 13.3 1.2 -2.8 29 53 -1.7 -1.9 -0.3 -2.2 7.4 -1.0 -0.6 186 Lirmiua 11 27 -0.1 -1.4 -1.5 -1.9 5.2 0.2 -2.1 92 423 2.2 -4.0 -1.5 -6.7 11.8 11.0 -8.3 187 GuHmnius 11 25 -0.7 -1.4 -1.5 -1.9 6.5 -0.9 -2.0 28 48 2.9 -1.8 -1.5 -3.0 4.8 -0.3 -2.9 233 Tabanus 28 40 * 7 6 5 10 3 5 4 24 31 -0.3 -0.7 0.5 1.4 -1.8 4.3 -1.3 268 Grthocladius 642 -11.1 -7.0 -4.1 -9.4 -0.6 43.5 -3.3 3 3 •+ 1 1 1 - - - -2.-9 303 Aticrotendipea 2 -»• — - - 2 - - - 14 50 -2.7 -0.7 -1.5 -2.1 -1.8 22.5 47 Ephemera 107 436 -5.4 -0.5 2.7 9.3 -0.1 5.0 -7.3 81 504 -4.1 1.6 -1.5 22.3 -4.3 -2.7 -9.8 50 Baetia 45 250 -1.6 -1.1 7.2 -4.9 8.7 -2.1 -6.3 27 103 -3.1 -2.6 -2.2 -3.0 1.6 -1.0 7.7 109 Sericoatoma 125 346 -0.8 -1.2 3.0 -1.0 2.8 0.4 -2.9 . _ ------3.-4 198 Limnophila 155 385 3.1 2.2 2.7 -2.7 2.2 -1.2 -6.2 39 62 3.9 0.9 0.7 -1.0 -0.6 -0.1 -3.2 -2.4 245 Mxcropelopia 59 401 -8.8 14.6 -0.5 7.0 -7.3 11.9 -6.3 27 87 -3.0 6.7 -1.0 8.5 -1.6 1 1 248 Apsectrotanypua 39 102 -4.8 -1.0 -2.0 8.2 -4.6 6.4 0.5 1- " - - - - - 288 Tanyt. curticornie 22 48 -3.3 1.8 -0.1 1.7 -1.6 3.4 0.4 0.6 -3.9 -2.2 -4.4 290 Tanytarsus 27 374 -8.4 6.5 -5.0 17.4 -8.4 13.1 -7.5 6 96 -4.9 -2.1 16.2 -0.6 -1.2 292 Cladotanytareua 16 90 7.4 -1.1 -2.8 -3.3 -3.0 5.5 -3.9 1 6 3.7 -0.6 -0.5 -1.1 -1.0 -1.4 1.0 296 Chironomus 14 92 -4.6 -2.6 -2.8 5.7 -3.9 9.4 1.2 8 23 -2.4 -1.2 -1.0 4.7 -1.1 2.5 5.2 -0.6 4.5 0.1 0.2 -9.0 III. 11 Oligochaeta 132 383 -2.7 5.9 6.9 4.9 -3.4 0.8 -5.8 116 491 -1.3 -3.0 -1.9 -2.5 38 Hydracarina 54 125 0.5 -0.5 1.3 3.3 -2.8 0.5 -1.5 25 102 1.1 2.0 4.9 96 Hepa rubra 12 32 5.8 -0.9 -1.7 -2.1 -1.4 1.1 -2.3 . _ ------1 3 5 2 22 0.2 -1.2 14.9 -2.0 -1.9 -1.1 -2.3 202 Gnophomyia 12 21 •» 4 - 2 6 43 74 -0.8 -1.3 -1.3 -3.2 6.2 2.7 -1.4' 205 Dioranota 108 209 1.7 1.8 2.8 -3.5 0.6 -0.1 -2.6 -0.2 0.6 0.3 2.4 -6.0 217 126 317 -2.9 0.6 -0.8 8.9 -0.4 -1.2 -3.2 68 159 2.5 2.3 239 Hemerodromia 34 91 -2.8 1.9 -1.4 4.6 -0.2 -0.3 -0.8 ------241 Ptyohoptera 85 251 -0.2 7.8 3.7 6.5 -6.8 -2.5 -4.1 _ ------152 -6.0 -1.3 1.1 16.8 -4.9 -2.1 -3.2 249 Proaladius 34 142 -5.2 1.3 -2.7 17.6 -4.3 -2.1 -2.4 26 264 juv.Chironimini 12 119 25.2 -3.0 -2.9 -2.8 -5.0 -3.4 -2.9 _ _ ------28 240 -1.5 10.3 -2.1 22.3 -6.2 -3.5 -7.1 271 Prodiamesa 105 950 -12.0 -2.5 1.9 41.6 -14.0 -6.8 -2.8 29 130 -3.6 -1.3 -0.8 22.3 0.3 -1.8 -3.4 283 Epoiaoaladiue 3 4 -1.0 -0.6 -0.6 3.3 -0.9 1.0 -0.8 6 30 -1.4 -1.2 -1.5 -2.2 -1.2 0.3 299 Parae Xadope Ima 16 64 -2.3 11.0 6.2 -1.6 -2.3 -2.5 -3.3 4.5 1 1+ 1 301 P.oamptolabis 28 69 5.« 7.5 -0.4 -3.1 -3.8 -2.2 -2.5 - - - - - 9 16 3.0- 0.9 -0.9 -1.7 0.9 -0.9 -2.0 307 P. taminata 19 52 2.1 6.1 -2.1 0.7 -2.1 -0.5 -2.9 20 34 1.5 2.5 -0.5 1.1 -0.2 -1.3 -2.9 300 Cryptoahironamus 18 -2.0 -1.2 5.2 4.8 -1.9 -1.3 -1.7 21 110 1.4 -2.7 0.9 9.7 -4.2 -2.4 -4.4 302 Paratendipes 15 84 -4.2 -0.2 -2.7 16.8 -4.2 -0.8 -3.2 51 210 8.3 -0.5 -1.5 0.4 -3.7 -1.2 -4.3 308 Stictochironomus 84 268 1.8 6.6 2.7 5.4 -4.7 -2.4 -6.5 48 203 8.3 -1.8 -2.1 -3.3 3.6 -0.1 -6.4 311 P.breviantennatum 179 1247 0.1 13.7 2.3 16.8 -13.7 -4.4 -7.7 83 328 11.4 1.5 1.0 -3.4 -3.6 2.2 -8.0 341 Piaidium 78 225 6.1 5.3 -1.8 0.5 -3.1 -3.0 -4.1 54 286 -6.7 -3.9 -3.6 -6.0 -3.6 -3.8 22.2 IV. 128 Micropterna 92 194 -2.0 -3.1 3.0 -1.5 2.1 -0.9 2.0 15 32 -2.5 -1.8 2.9 0.0 -1.4 -1.3 3.3. 280 Chaetooladiua 27 346 -8.1 -4.5 7.0 -6.6 1.2 12.0 3.0 1 1* 1 293 Rheotanytaraus 70 612 -2.4 -4.5 12.0 -6.1 3.3 -4.8 2.7 - - - - 18 31 -2.4 -1.4 -0.4 -0.7 -1.8 -1.3 6.1 V. 4 Polycelis 12 20 2.6 -0.4 -0.6 -1.7 -2.1 -1.4 2.6 11 14• • 3 3 3 1 23 Gloesiphonia 21 32 1.0 1.0 0.1 -0.7 -1.8 -1.8 2.1 - - 154 9918 -39.4 -17.8 -15.6 -23.0 -29.0 -8.4 103.2» 32 Gammaru8 putex 282 11125 I--27.: 2 -4.6 52.6 -3.0 -39.5 -16.3 56.9 58 -3.6 -2.0 -1.0 3.5 -1.7 -1.1 4.0 36 AselluB meridian. 32 61 -3.2 -2.0 7.3 2.0 -2.8 -1.6 2.4 135 Limn, tunatuß -1.3 -1.1 -1.1 0.8 -1.2 6.3 -0.9 17 7 15 1 1» 1 155 larvae Agabus -5.3 -1.3 0.7 2.2 -4.7 1.7 8.7 ------55 134 3 3* 1 2 160 larvae IZybiue -1.2 0.1 -2.1 0.1 3.1 15 20 -2.1 3.3 -1.-0 -0.-9 3.5 -1.-0 -1.-0 1."1 -4.3 -1.0 10 16 -2.0 256 Zavrelimyia 42 105 -4.5 0.0 4.0 5.9 2.6 -1.0 -1.5 -0.7 20 41 -2.3 -1.7 0.1 2.0 2.9 285 LimnophyeB 4 0.5 -1.3 1.0 -1.7 -0.2 2.0 -11.4 82 2111 •18.1 0.2 0.3 9.2 0.4 19.2 287 Microps.praecox 223 20138 -35.6 20.3 -11.5 74.6 -63.0 -2.8 64.7 289 M.trivialis 15 47 -3.3 -1.9 0.5 2.5 -1.2 0.7 3.3 0.6 -1.7 -0.4 4.8 -2.6 17 30 -2.4 -1.4 -1.2 306 Phaenopsectra 19 67 -3.9 -2.3 -1.6 6.5 -3.5 7.2 6 9 - 1 2 3 3 313 PoZ.gr.eonvictum 16 22 •+ - 3 3 4 4 5 3 - - - -3.4 -4.0 27.2 26 313 -7.5 -4.8 3.3 -7.6 VI, -5.6 -5.3 -7.3 4.6 -4.1 21.4 40 Amphinemura 42 408 -7.9 27 60 -2.6 -1.0 -1.7 -1.3 -0.2 -1.2 S.I -4.1 -0.4 -6.0 0.2 2.7 13.2 127 Chaetopteryx 95 386 -6.0 1 1- + - 1 -1.6 -2.1 10.1 1.8 - - - - - 180 Anacaena 13 53 -2.6 -1.5 -2.1 7.9 41 74 -3.2 -1.8 0.9 -1.5 -2.3 -2.0 VII. 21 -11.8 Erpobdella octo. 87 2896 -15.6 -13.8 -5.7 -19.1 4.5 44.2 42 -3.1 -3.1 -4.6 -5.0 -3.6 23.4 Nemoura cinerea -5.4 74 727 -7.3 -«.1 2.7 -6.0 -6.0 -4.5 21.7 48 Habrophlebia 2 3 1 3 -2.2 16.7 8 9* 100 Plectrocnemia 88 233 -6.2 -1.4 3.1 -2.2 -6.3 - - 1 - 3 -1.6 4 4» 117 Haleaue radiatus -1.4 -0.9 -0.4 -2.0 7.8 -1.1 -2.2 -1.2 14 27 -2.1 13 30 -2.8 -0.7 -1.2 7.0 122 -3.0 Potamophylax luat, -7.1 -3.S 7.3 -5.4 -5.6 18.4 -11.0 -13.0 0.4 51.4 33 207 190 larvae Helodes 79 1054 -15.0 -8.7 -4.8 14 1.3 -1.0 -0.8 2.8 -0.9 -0.9 -1.8 -1.3 1.4 -0.7 7 193 Tipula 37 46 -2.6 -0.8 0.0 3.8 -0.9 1.9 -1.5 0.1 -0.8 1.0 -4.7 8 12 -1.7 220 Simulium -6.4 -4.8 -5.1 -6.5 -3.9 28.4 1 1 25 302 4 4» 2 225 Payahodidae -2.2 -1.3 -0.6 -1.1 0.8 0.7 3.5 -1.3 -2.4 -0.3 8.2. 15 21 18 47 -3.4 -1.8 -1.3 254 Conohapetopia -4.4 2.3 1.4 -4.3 0.0 13.6 -0.6 86 257 -7.4 7 -1.3 -0.7 -0.6 -0.3 -1.1 3.1 263 2 juv.Orthocladilnae '1 155 30 •+ 7 2 4 1 12 1 3 -6.5 -3.5 -3.1 22.S 35 225 -7.4 -3.9 -3.2 269 Corynoneura -1.5 -2.7 -5.4 -1.4 24.0 -3.1 -4.9 -2.4 84 388 -8.9 -4.3 151 -6.2 -3.2 -2.3 18.1 272 Brillia modeeta -6.5 -9.2 -4.2 37.8 28 1 50 433 -9.9 -5.7 -3.8 1* 274 B. longifurca -1.0 -1.5 -1.4 6.7 1 -7.6 -4.» -2.7 24.6 12 19 -2.1 0.5 -1.3 366 -8.8 -4.7 -3.6 275 Diplocladius -4.6 -2.4 -1.2 17.6 44 -7.4 SI.2 S3 244 -4.2 -4.3 -2.6 -16.8 -8.9 -6.8 -14.5-12. 7 277 Rheocricotopua 43 1177 3.8 119 1288 -16.1 -8.9 -3.0 -10.0 -10.6 3.5 45.6 -0.6 -0.5 -1.1 -1.0 -0.6 279 3 8 -1.2 1 Eukiefferiella -4.5 -13.5 -12.2 17.1 44.6 97 1489 -18.2 -10.4 1• » 310 Polyped. laetum -11.5 0.2 -7.3 1 -2.9 -0.9 9.3 76 1125 -14.0 -4.2 21.7 26.7 -4.1 -2.2 -1.9 -0.5 318 pupae Chironomini 17 74 68 174 -5.5 -2.3 2.8 0.4 -4.1 3.5 7.5 O M O) N O

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~~191 Appendix12 .I.R .value sfo rth e4 3most-abundan t taxa (moretha n10 0specimens )i nth eSnijdersveerbee ki nSor t8,10% .~~

~~TaxaTax anam e Substrateclas s no.~~

~~x5x x4x~~

18 Eiaeniella tetvaedra 5.0 5.3 6.7 13.4 8.9 -2.0 -3.3 -5.3 -4.4 -5.6 -2.8 -3.9 -3.5 -3.3 105 Lithax obscunts 5.0 4.9 2.0 6.2 1.3 7.3 2.5 -0.3 -5.4 -6.7 -4.4 -3.6 -3.5 -2.4 185 Elmis aenea 13.4 5.9 2.6 -0.9 7.1 -0.4 -3.4 -3.4 -3.3 -4.0 -2.4 -1.3 -2.1

~~268 OrthocladiuB -1.3 -1.6 51.S 2.2 1.8 -2.2 -8.1 -6.7 -7.2 -8.7 -5.0 0.0~~

~~280 ChaetoaladiuB -3.2 -4.8 -4.7 11.6 14.5 10.5 -4.8 -5.9 -5.1 -6.4 -3.8 -4.4~~

50 Baetie vermis 0.7 18.4 -2.7 -3.6 -1.8 1.5 -0.9 -3.5 -2.1 4.9 -3.2 -3.4 -4.6 -2.9 2.6 -2.9 11.1 -3.9 -4.8 6.5 0.8 -2.9 -5.4 -3.7 245 Macropelopia nebulosa -2.5 1.1 -2.4 2.1 -3.3 7.4 -4.4 -4.1 3.3 -3.5 4.0 -5.9 -5.5 IB.7 -1.7 -5.3 290 TanytœesuB 264 Chironominispp.CJuv. ) -1.8 -3.2 -2.7 -2.8 -2.7 -2.7 26.1 -2.9 -3.1 -2.4 -1.3

11 Oligochaeta -1.2 -0.0 -2.1 -3.2 -3.1 -1.5 -3.2 3.2 -1.3 8.5 6.7 -2.6 -3.9 3.3 38 Hydracarina -1.9 -2.3 0.8 1.3 -2.4 -2.4 -1.9 3.7 4.7 1.9 -1.4 0.5 -1.3 -2.1 47 Ephemera danioa -2.4 -2.4 6.4 2.3 2.1 -2.8 0.5 -5.5 6.0 5.4 0.9 -3.2 -5.4 -3.3 109 Seriooatoma personation -3.2 -0.7 3.3 3.9 1.8 1.6 2.5 -2.9 -1.9 1.0 -2.0 2.8 -4.2 -3.1 128 Micropterna eequax -1.1 0.7 -0.9 0.4 3.3 0.7 -0.2 -3.6 -0.7 0.0 -2.2 1.6 2.0 -0.2 198 Limnophila -2.7 2.6 -1.5 -0.4 3.7 0.8 1.9 -1.8 2.5 0.2 5.2 -2.8 -4.8 -3.3 205 Diaranota -0.4 -2.0 0.5 0.1 3.5 0.7 1.7 -2.4 -0.5 1.9 1.4 -0.6 -2.8 -0.4 217 Palpomyia -1.0 -0.5 -0.2 -0.4 -0.7 -1.2 0.8 -3.9 3.2 -0.9 6.2 3.8 -2.2 -1.5 241 Ptyahoptera -2.7 -3.5 -3.7 -3.6 -2.1 -1.6 1.5 -1.3 8.6 1.2 11.6 0.7 -3.3 -1.2 248 Apeectrotanypua trifaacip. -1.7 3.6 -2.5 -2.6 2.0 -2.1 -1.7 -1.7 2.0 2.3 0.4 -1.5 2.5 -0.8 249 Proolodiua -2.0 -2.6 -2.0 -2.7 -1.6 -2.9 0.9 -3.5 14.6 4.5 -0.8 -2.8 -0.6 -2.2 256 Zavrelimyia -1.7 -2.6 -1.4 -2.6 -1.3 -2.1 -0.8 -3.0 -0.5 5.9 1.7 0.7 3.3 3.9 308 Stiatoahironomus -2.8 -3.5 -2.4 -1.3 -1.5 0.5 -1.4 7.2 9.3 2.9 0.8 -3.8 -4.8 -3.0 341 Piaidivm -2.6 -3.0 -2.7 -1.8 0.7 0.9 6.3 -0.6 2.3 0.1 7.7 -3.7 -2.3 -2.0

~~271 Prodiameaa olivaoea -5.2 -7.7 -6.6 -7.1 -7.3 -6.5 -7.3 -7.3 9.2 21.8 13.7 5.5 3.3 -5.3 311 Polyped-ilum brev-iantennat. -5.8 -7.1 -6.7 -7.5 -3.4 -0.7 -0.7 0.7 5.3 16.9 15.9 -1.2 -6.3 -3.8~~

~~287 Micropaectra gr. praecox -23.8 -29.8 -32.3 -29.4 -3.6 -27.2 -11.7 -33.4 -1.5 29.5 10.1 25.8 88.6 4.5~~

~~32 Garmarua pulex -11.6 -22.3 -22.7 -20.8 -14.4 -1.2 | 12.9 1-10.5 -8.6 -12.2 -7.5 55.3 32.0 35.5~~

127 Chaetopteryx villoea 0.9 2.1 2.0 -0.9 -0.7 -1.1 -1.5 -5.8 -4.0 -5.3 -3.8 27.7 -3.6 -3.6 220 Simulium latipea -1.9 -1.8 -3.7 -2.4 -3.1 -0.5 -5.6 -5.6 -4.9 -6.0 -3.6 31.9 10.7 -2.9 293 Rheotanytar8ua -4.0 1.1 1.7 -2.2 2.7 -4.9 8.4 -7.8 -6.6 -2.1 -4.3 18.8 -1.3 -0.8

40 Amphinemira atandfussi -1.1 4.3 1.7 -2.1 -1.1 -2.1 -5.4 -6.4 -5.8 -6.9 -3.9 -3.0 32.3 -2.9 42 Vemoura ainerea -2.1 -3.1 -3.1 -2.9 -2.4 -2.4 -3.5 -4.0 -3.3 -4.3 -2.2 -1.1 31.8 -1.0 269 Corynoneura 0.3 -3.9 -3.9 -3.3 -2.8 -4.6 -3.9 -5.8 -3.3 -2.8 -4.0 14.5 22.5 -0.3 272 Brillia modeata -3.5 -5.5 -3.9 -5.1 -4.9 -5.1 -5.8 -6.5 -5.3 -5.6 -4.0 10.4 30.7 16.7 275 Dipioaladiua cultriger -2.7 -1.0 -0.9 -3.5 -1.2 0.1 -2.2 -4.4 -3.8 -5.2 -2.6 -0.2 18.1 11.7 310 Polypedilum laetum -5.7 -2.2 -4.7 -6.5 10.0 -8.1 2.4 -8.9 -9.5 -5.8 -5.6 14.7 29.2 -4.4

~~277 Rheocriaotopus -3.1 -6.3 -7.7 -5.0 -5.3 -7.3 -9.3 -10.7 -8.2 -8.6 -6.7 8.5 64.3 0.2 279 Eukieffertella gr. diaool. -0.3 -9.9 -6.5 -7.3 -6.8 -9.4 -10.7 -12.3 -10.5 -12.4 -7.5 31.1 62.6 -2.9~~

~~190 Helodes larvae -7.3 -10.9 -6.5 54.3 18.4 18.9~~

100 Pleotroonemia conspevsa •2.6 -4.0 -2.5 -2.9 -2.1 -2.9 -1.4 -2.8 -3.4 -3.5 1.4 13.3 12.5 1.1 155 Agabue larvae •1.5 -2.8 -2.9 -2.3 -2.5 -2.5 -1.8 -3.4 0.0 1.8 -1.5 5.9 10.8 0.7 254 Conahapelopia melanops •2.3 -3.8 -0.3 0.0 -1.9 -3.4 -2.6 -4.3 -1.9 -0.2 -1.2 16.1 2.2 5.8 318 Chironominipupa espp . •1.8 -1.2 -2.7 -1.6 0.5 -1.7 -1.6 -3.7 -2.2 -1.2 -0.9 14.3 5.3 -2.0

~~Italicvalue sindicat esignifican t over-representation Boxesindicat egroup so ftax awit hsimila rover-representatio n~~

~~192 Appendix 13. I.R.value s forth e2 6most-abundan t taxa (more than 100specimens )i nth eRaturnsebee ki nSor t 8,10%.~~

~~Taxa Taxa name Substrate class~~

~~1 2 3 4 5 6 7 8 9 10 11 12 13 14~~

~~Va U3 Index Detrltui XXX X5x x3x x2x xïx xlx XXX lxx 22x 23% 33x CD L CD+L x4x~~

~~103 Agapetus fusovpes -1.0 9.9 1.3 0.4 10.8 10.2 -1.4 -1.4 -5.6 -3.8 -2.3 -2.3 -5.8 -2.1~~

~~105 Lithax obecurus 4.6 0.3 2.1 6.2 5.9 2.6 -2.1 -3.4 -5.9 -3.8 -1.9 5.7 -1.0 -0.7 186 Limnius volokmari 7.4 2.8 5.9 4.9 14.6 2.0 3.9 -3.9 -6.0 -4.9 -2.7 -2.1 -7.6 -2.6~~

217 Palpomyia -0.9 3.2 1.5 3.2 -0.4 -0.1 1.5 1.7 2.0 0.4 -2.0 -2.0 -5.4 -1.8 308 Stictoohironomus -1.0 -2.1 -1.6 -2.4 -1.6 -2.5 7.3 1.1 5.9 -1.3 -2.3 -2.3 -3.6 -1.1 311 Polypedilwn breviantennat. -1.0 -2.0 -2.0 3.3 4.0 -1.1 3.3 -2.1 5.6 -2.3 -1.8 -2.3 -5.8 -1.5 341 Pieidium 0.3 -2.2 -0.3 -0.8 -1.3 -2.3 3.2 0.9 10.S -0.4 -0.8 -2.2 -7.2 -2.6

47 Ephemera daniaa -1.8 -1.3 -3.2 -3.3 -2.0 1.3 12.2 -2.7 ' -1.0 6.6 10.9 -3.3 -9.1 -2.0 0.6 11 Oligochaeta -1.6 2.8 -2.2 -1.7 2.3 -3.3 -0.3 -1.0 8.9 8.1 -0.2 -3.6 -9.0 -4.2 6.2 38 Hydracarina -0.7 -0.8 -1.5 -2.4 -2.0 -3.2 2.5 -1.3 4.3 7.0 -1.6 -1.6 -2.0 -5.4 7.9 249 Pr*ocladiu8 -0.9 -1.8 -1.8 -3.5 -3.0 -2.8 -3.7 -2.1 4.8 16.3 3.6 -1.8 -1.8 -4.8 -1.6 283 Epoiooaladius ftavena -0.8 0.2 -1.6 -1.4 1.5 0.1 -1.9 -1.8 -1.5 19.1 1.3 -0.5 0.1 -4.4 -1.5 302 Paratendipee -0.8 -1.5 -1.5 -3.2 -2.8 -1.8 5.3 0.1 9.9 -2.3 -6.7 -0.9 271 Prodiamesa olivacea -1.1 -2.2 -2.2 -4.7 -4.1 -2.6 -3.4 -2.8 17.3 5.3 6.0 -1.6 -1.6 9.6 -1.5 50 Baetia vernua 0.6 -1.5 4.1 -0.8 0.2 -0.6 -2.3 -2.5 -3.5 -2.6 -9.9 -7.3 -8.5 53.7 -4.7 42 Nemoura cinerea -3.8 17.3 -7.7 -4.5 -2.3 -6.3 -10.1 -9.8 -22.0 -4.6 -2.8 -2.8 17.8 6.9 40 Amphinemura etandfusei -1.3 0.6 -2.5 -3.0 -3.7 -4.1 -5.6 6.6 -7.0 -4.9 -0.6 6.8 16.1 17.4 48 Habrophlebia fusca -1.4 -3.6 -1.0 -4.0 -5.3 1.8 -5.9 0.0 -10.5 -2.9 -2.0 -2.0 16.2 9.6 272 Brillia modesta -0.9 -1.8 -1.8 -3.7 -3.0 -3.8 -4.4 -2.7 -5.1 -6.7 -4.4 -2.7 20.6 16.2 2.5 128 Mioropterna eequax -1.2 -2.0 -2.0 -4.9 -3.4 -3.4 -4.1 -3.7 -5.2 -3.7 -2.3 14.6 13.0 -0.1 190 Helodes larvae -1.0 -2.1 -1.6 -4.1 -3.9 -4.3 -4.8 5.4 -2.0 0.9 2.3 64.9 -10.9 26.8 287 Miaropseotra gr. praecox 1.6 -6.3 -4.9 -7.7 -2.4 -6.0 -4.4 -5.3 -33.9 -19.3 -13.8 160.5 49.2 22.6 32 Gammarue pulex 3.2 -13.9 -4.5 -19.8 -17.3 -16.1 -23.0 -12.7 -3.7 -6.2 -3.9 -2.4 3.4 24.3 -1.7 269 Corynoneura -0.1 -2.2 -1.7 -4.6 -3.5 -4.5 -5.4 -4.8 -7.7 -4.1 -3.1 -2.1 27.9 0.5 275 Diploaladina oultriger -1.4 -2.0 -2.4 -3.6 -2.2 -4.5 -6.6 -12.2 -8.0 -14.0 -8.9 -5.5 -1.7 53.2 13.4 277 Rheoariootopus -1.2 -4.9 -4.1 -10.0 -8.5 -10.1

~~Italic values indicate signifie ant ove r-representati on Boxes indicate groups of taxa w ith sin liar over-repr esentation~~

193 Appendix14 .Compariso no f thefauna l compositiono f the Sand (S),Grave l (G)an d Leaf (L)substrate s inth enatura l sectiono f the Snijdersveerbeek (Section6 )wit h thato f theSan dan dFin eDetritu s (S+FD)substrat e inth eregulate d section (7) downstreamo f Section6 .

~~Section 6 Sectie~~

~~Taxon S G L S+FD~~

Lumbriculidae 1 EisenieVla tetraedra 3 20 Gammarus pulex 7 4 27 1 Hydracarina 2 3 1 6 Ephemera danioa 46 32 2 Pleatroanemia aonspersa 2 10 Agapetus fusoipes 1 Lithax obsourus 15 1 Sevicostoma personation 22 22 Udlesus vadiatus 1 1 Potamophylax rotundipennis 1 1 Chaetopteryx villosa 1 Micropterna sequax 4 5 2 Agabussp . 3 2 Dryopssp . 1 Elmis aenea 1 1 2 Helodes minuta (larvae) 2 27 Tipula sp. 2 2 1 Limnophila sp. 2 5 Bezzia sp. 1 1 Palpomyia sp. 2 7 98 Hemerodromiasp . 1 Maoropelopia nebulosa 3 12 Apsectrotanypus trifascipennis 10 28 Prooladius sp. 2 127 Conehapelopia melanops 9 4 8 Zavrelimyia sp. 2 1 Orthocladiinae 2 3 Chironomini 1 7 Orthocladius sp. 1 Corynoneura sp. 2 1 41 Prodïamesa olivaaea 8 1 3 Brillia modesta 1 57 Brillia longifuraa 5 Diplooladius oultriger 24 Rheocriootopus sp. 4 2 76 Eukiefferiella gr. diseoloripes 1 13 56 Limnophyes sp. 2 Miaropseatra gr. praecox 105 3 102 67 Tanytarsus ourtioornis 3 Rheotanytarsus sp. 10 Paratanytarsus sp. 2 Paratendipes sp'. 1 Stiatoahironomus sp. 4 7 Polypedilum breviantennatum 15 5 2 Polypedilum gr. aonviatum 1 358 Chironomidaepupa e 1 12 Pisidium sp. 5 1 1 Lepidoptera 1 1

~~194 Appendix 14 (continued)~~

~~Taxon Section6 Section7~~

~~SGL S+FD~~

Somatoehlora avatiaa 4 Caenis hovavia 7 Corixidae larvae 3 Notoneota vivides 1 Sigava striata 78 Sigava falleni 51 Sigava distineta 1 Sigara lateralis 13 Sigava falleni/longipalis 47 Hespevoaovixa sahlbergi 4 Ilybius larvae 2 Laaoophilus sp. 1 Stiototavsus duodecimpustulatus 2 Dioranota sp. 2 Cviootpus sp. 12 Pseatvoaladius sp. 3 Tanytarsus sp. 481 Cladotanytavsus sp. 119 Chivonomus sp. 26 Glyptotendipes sp. 48 Cryptoohironomus sp. 34 Miovotendipes gr. ohlovis 21 Pplypedilwn nubeeuloswn 6 Lymnaea auricularia 33 Mystaaides longiaornis 1

~~Numbero ftax a 37 26 27 38~~

~~195 Identification references~~

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196 Tolkamp,H.H. , 1975.Tabe l voorhe tonderschelde nva nd ewaterpissebedde n (Isopoda) inAsellu s aquaticuse nA .meridianus .Mimeograp hNat .Cons .Dept .Agric . Univ.Wageningen , 1p . Zool.Museu m Amsterdam, 1969.Gammarus-tabe l (3rd.Ed.) : 8p . Plecoptera Hynes,H.B.N. , 1941.Th etaxonom y andecolog y ofth enymph so fBritis hPlecopter a with noteso n theadult san d eggs.Trans .R .ent .Soc .Londo n91 :459-557 . Hynes,H.B.N. , 1963.Th egill-les snemouri d nymphso fBritai n(Plecoptera) . Proc. R. ent.Soc .Londo n (A)38 :7'-76 . Hynes,H.B.N. , 1977.A ke y toth eadult san dnymph so f theBritis h Stoneflies (Plecoptera). Sc.Publ .Freshwat .biol .Ass .1 7 (3rd.Ed.) : 92p . lilies,J. , 1955.Steinfliege node rPlecoptera .Tierwel tDeutschland s43 :15 0p . Ephemeroptera Buck,H .S iH .Merz ,1976 .Baëti s Schüssel (Larven).Landesanst .Gewässerkund e Baden-Württemberg: 17p . Kimmins,D.E. ,1972 .A revise d key toth eadult so fth eBritis hspecie so f Ephemeropterawit hnote so nthei recology .Sc .Publ .Freshwat .biol .Ass .15 : 75p . Macan,T.T. , 1979.A ke y toth enymph so fBritis h specieso fEphemeroptera . Sc.Publ .Freshwat .biol .Ass .2 0 (3rd.Ed.) : 79p . MüllerLiebenau , I.,1970 .Revisio nde reuropäische nArte nde rGattun gBaëti sLeach , 1845 (Insecta,Ephemeroptera) .Gewässe ru .Abw .48/49 :21 4p . Schoenemund,E. ,1930 .Eintagsfliege node rEphemeroptera .Tierwel tDeutschland s19 : 214p . Odonata Dutmer,G . &F .Duijm , 1974.Libellen .Tabelle nvoo rd eNederlands e imago'se n larven.Jeugdbondsuitg. :5 6p . Heteroptera Cobben,R.H .& H .Molle rPillot ,1960 .Th elarva eo fCorixida ean d anattemp t toke y thelas tlarva l instaro f theDutc hspecies . (Hemiptera,Heteroptera) . Hydrobiologia 16 (4): 323-356. Macan,T.T. , 1976.A revise dke y toth eBritis hwate rbug s (Hemiptera,Heteroptera) . 2nd ed.,Sc .Publ .Freshwat .biol .Ass .16 :7 7p . Nieser,N. ,1968 .D eNederlands ewater -e noppervlaktewantsen .Wet .Med .KNN V77 : 56p . Magaloptera and Nenroptera Elliot,J.M. , 1977.A ke y toBritis h freshwaterMegalopter a andNeuroptera . Sc.Publ .Freshwat .biol .Ass .35 :5 2p . Trichoptera Edington,J.M. , 1964.Th etaxonom yo fBritis hpolycentropodi d larvae(Trichoptera) . Proc.Zool .Soc .Londo n143 :281-300 . Edington,J.M . &R .Alderson ,1973 .Th etaxonom yo fBritis hPsychomyii dlarva e (Trichoptera).Freshwat .Biol .3 :463-478 . Geijskes,D.C .& F.C.J .Fischer ,1971 .Ee nnieuw enaamlijs tva nd eNederlands e Trichopterame t eenfaunistisch eliteratuurlijs tvana f1934 .Entomol .Ber .31 : 235-244. Grenier,S. ,H .Décamp s& J .Giudicelli ,1969 .Le slarve sd eGoerida e (Trichoptera) del a fauned eFrance .Taxonom y etEcologie .Annls .d eLimnologi e5 (2) : 129-161. Hickin,N.E, ,1967 .Caddi s larvae.Hutchinson ,London :47 6p . Hildrew,A.G .& J.C .Morgan ,1974 .Th etaxonom yo f theBritis hHydropsychida e (Trichoptera).J . Ent. (B)43 :217-230 . Hiley,P.D. , 1972.Th e taxonomyo f thelarva eo fth eBritis h Sericostomatidae (Trichoptera).Entomol .Gazett e23 :105-119 . ,„,,.... •> Hiley,P.D. , 1976.Th e identificationo fBritis hlimnephili dlarva e(Trichoptera) . Systematic Entomol.1 :147-167 .

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~~211 Stellingen~~

~~1.D evoo rlaaglandbeke n karakteristieke kleinschalige afwisselingva nsubstraat - typen isva n levensbelangvoo rd ebodembewonend eorganismen .~~

~~2.D ebeschikbaarhei d vanvoedse l isva ngroter e invloedo pd ehabitatselecti e doormacro-evertebrate n dand e substraatsamenstelling.~~

3.He t aangeven van substraatvoorkeuren doorhe tprocentuel e aandeel vanee nsoor t binnenee nmonste r tevergelijke nme td esubstraatkarakteristieke n isnie tgeoor loofd. L.Kdwards , 1975.Doctora l thesis,Univ .Salford .

4.He t lijktonvoldoend e bekend tezij nda tbeekregulati e leidt totafnam eva n deruimtelijk e entemporel e afwisseling vansubstraattype n endaarme eto tuitroei ingva nd evoo rbeke nkarakteristiek e benthische levensgemeenschappen.

~~5.Beke n stromen.~~

~~6.He t verdient aanbeveling deter mmacrofaun anie t tegebruike nvoo rmacro - evertebraten.~~

~~7.He tbelan gva nbeekbegeleidend e bossene nhoutwalle n voord ebenthisch elevens gemeenschappen bestaat niet alleenui t deleverin g vanschadu w envoedsel .~~

~~8.He tverdien t aanbeveling debeekkarakterinde x verder teonderbouwe n tenbehoev e vanmilieueffectrapportage . J.J.P. Gardeniers& H.H .Tolkamp ,1976 .~~

9.Da t volgens de 'Kaartva nd ebiologisch e kwaliteit vand ewaterlope n inBelgië ' bekenme t eengoed ekwalitei t slechtsvoorkome n ind eArdenne n isnie tuitsluiten d eengevol gva nwaterverontreinigin g inhe toverig e deelva nBelgië .

~~'Kaartva nd ebiologisch ekwalitei t vand e waterlopen inBelgië' . Instituutvoo rHygiën e enEpidemiologie ,Brussel,1979 .~~

10. Standaardisatie vanhe tdeterminatienivea u isgee nvoorwaard evoo r harmonisatieva nbiologisch e waterkwaliteitsbeoordelingssystemen. 11. Demat ewaarme eme n zich inzet voorhe t voortbestaan van eendiersoor t heeft minder temake nme t zijnmat e vanbedreig d zijndan 'me t zijn aaibaarheidswaarde.

~~12. Deovereenkoms t tussen eenpromotieplechtighei d end ebalt sva nkemphane ngaa t verderda nhe t dragenva nee nprachtkleed .~~

~~Proefschrift vanHarr yH .Tolkam p Organism-substrate relationships inlowlan d streams. Wageningen,6 februar i1981 .~~