H.H.Tolkamp

Hature Conservation Department, Agricultural University, Wageningen

Organism-substrate relationships in lowland streams

IpudooI

Centre for Agricultural Publishing and Documentation

Wageningen - 1980

,y* <3 "3! Communication NatureConservatio n Department211 .

ISBN9 022 0075 96

Theautho r graduatedo n6 Februar y 1981a sDocto r ind e Landbouwwetenschappen atth eAgricultura l University,Wageningen ,th eNetherlands ,o na thesi swit h thesam etitl ean dcontents .

^)Centr e forAgricultura l Publishing andDocumentation ,1980 .

Nopar to fthi sboo kma yb ereproduce do rpublishe d inan y form,b yprint , photoprint,microfil mo ran yothe rmean swithou twritte n permission fromth e publishers. Abstract

Tolkamp, H.H. (1980)Organism-substrat e relationships inlowlan d streams.Agric . Res.Rep . (Versl.landbouwk .Onderz. )907 ,ISB N9 022 007S 96 , (xi)+ 21 1p. ,8 0 tables,4 3 figs.,31 9refs. ,Eng .an dDutc hsummaries , 14appendices . Also:Doctora l thesis,Wageningen .

Afiel d and laboratory studyo n themicrodistributio n ofbotto m dwellingmacro - invertebratest oinvestigat eth erol eo fth estrea msubstrat e inth edevelopmen t andpreservatio no fth emacroinvertebrat ecommunitie s innatural ,undisturbe d low­ land streams isdescribed .Fiel ddat ao nbotto m substratesan d faunawer ecollecte d between 1975an d 1978fro mtw oDutc hlowlan d streams.Substrate swer e characterized by thenatur ean dth eamoun to forgani c detritus and theminera l particlesizes :i n a fieldclassificatio no n thebasi so fth evisuall y dominantparticl e sizes;i na grain-size classificationo nth ebasi so fexac t particle-size analysis inth elabora ­ tory.Substrat epreferenc e for8 4macroinvertebrat especie swa sdemonstrate d using the Indexo fRepresentation . Substrate-selection experimentswer econducte d ina laborator y stream forthre e Trichopteraspecie s (Mioropterna sequax, Chaetopteryx villosa and Seriaostoma per­ sonation) andon eEphemeropter aspecie s (Ephemera daniea). Anexperimen t onth e colonization of artificial substrates inth efiel dwa sals o conducted. From thefiel ddata , several faunal groupscoul db edistinguished , eachgrou p madeu po f specieswit h similar substratepreferences .Detaile d datao nth emicro - distribution inrelatio n tosubstrat eparticl e sizear egive n for26 ,species ,whic h represent thevariou staxonomica lunit stha tcompos e thefauna lgroup s: 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,lif ecycl e and foodpreferences .Fo rsevera l speciessubstrat epreference sma yb edifferen t for different development stageso r indifferen t seasons. Iti sconclude d thatmos t speciessho wdistinc t preferences fora specifi csub ­ strate.Th e small scalespatia lvariatio n insubstrat ecompositio n ofth estrea mbe d isessentia l forth eexistenc eo fman y lowland streammacroinvertebrat e species.

Freedescriptors :substrat epreference ,microdistribution , benthos,macroinvertebrates , particlesize ,detritus ,organi c matter,habita t preference,environmenta l factors, lowland stream, laboratory stream Contents

1 Introduction 1 1.1 General 1 1.2 Purposeo fth einvestigatio n 4 1.3 Hypotheses 5 1.4 Research approach 6

2 Description of the streams 7 2.1' TheSni jdersveerbee k 7 2.2 TheRatumsebee k 11

3 Methods 16 3.1 Fieldprocedur e 16 3.1.1 Selectiono fsamplin g sites 16 3.1.2 Sampling dates 16 3.1.3 Field classificationo fsubstrate s 17 3.1.4 Samplingmetho d 18 3.1.5 Additional collections 20 3.2 Laboratoryprocedur e 20 3.2.1 Sample sorting 20 3.2.2 Substrate analysis 20 3.2.3 Macrofauna analysis 23 3.3 Laboratory experiments 25 3.3.1 Artificial stream channel experiments 25 3.3.1.1 Thestrea m 25 3.3.1.2 Substrates tested 27 3.3.1.3 Experimental design 27 3.3.1.4 Species tested 29 3.3.1.5 Theinfluenc eo fcurren tvelocit yo nsubstrat e selection 29 3.3.2 Rearing channel 30 3.3.3 Experimentswit hTrichopter a 30 3.3.3.1 Case-building experiments 30 3.3.3.2 Grainsiz e analysiso fnatura lTrichopter a cases 31 3.4 Fieldexperiment s 32 3.4.1 Artificial substrate trays 32 3.4.2 Artificial substrates introducedwithou t trays 33 3.4.3 Litterbag s 34 3.5 Dataprocessin g 34 3.5.1 Datastorag e 34 3.5.2 Statisticalmethod s 35

Results 37 4.1 Data 37 4.1.1 Fieldclassificatio no fsubstrat etype s 37 4.1.2 Grain-sizeclassificatio n inth e laboratory 40 4.1.2.1 Substratecompositio n 40 4.1.2.2 Substratetype s 41 4.1.3 Discussion 44 4.1.3.1 Theus eo fth e Indexo fRepresentatio n compared toothe r statisticalmethod s 44 4.1.3.2 The importance ofth ejoin tus eo f H and 10%detritu s classifications 45 4.1.3.3 The influenceo fanima labundanc eo nth e Indexo fRepresen ­ tation 46 4.1.4 Groupingo fsubstrat etype sbase do nspecie scompositio n 47 4.1.5 Groupingo fspecie sbase d onsubstrat epreference s 49 4.1.6 Numberso fspecie san d specimens indifferen t substrate types 56 4.1.7 Fieldexperiment s 58 4.1.7.1 Trays filledwit h artificial substrate 58 4.1.7.2 Particlesize s introducedwithou ttray s 59 4.2 Organism-substrate relationships 60 4.2.1 Outlineo fpresentatio n 60 4.2.2 Autecological datafo rselecte d species 62 4.2.2.1 Lithaxobscuru s (Hagen) (Trichoptera:Goeridae ) 62 4.2.2.2 Sericostomapersonatu m (Spence) (Trichoptera: Sericostomatidae) 68 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: Polycentropodidae) 100 4.2.2.6 Ephemeradanic a (Müller) (Ephemeroptera:Ephemeridae ) 103 4.2.2.7 Nemouracinere a (Retzius) (Plecoptera:Nemouridae ) 114 4.2.2.8 Limniusvolckmar i (Panzer),Elmi saene a (Müller)an d Oulimnius tuberculatus (Müller) (Coleoptera:Elminthidae ) 116 4.2.2.9 Gammaruspule x (L.)(Malacostraca :Amphipoda ,Gammaridae ) 119 4.2.2.10Dicranot aZettersted t sp. (Diptera:Limoniidae ) 128 4.2.2.11 LimnophilaMarquar t spp. (Diptera:Limoniidae ) 132 4.2.2.12Ptychopter aMeige nspp . (Diptera:Ptychopteridae ) 134 4.2.2.13Orthocladiu sva nde rWul p spp. (Diptera:Chironomidae , Orthocladiinae) 13S 4.2.2.14Micropsectr agr .praeco x (sensuTshernowskij )(Diptera : Chironomidae,Tanytarsini ) 137 4.2.2.15Paracladopelm aHarnisc hspp . (Diptera'.Chironomidae , Chironominae) 140 4.2.2.16Prodiames aolivace aMeige n (Diptera:Chironomidae , Orthocladiinae) 142 4.2.2.17Epoicocladiu s flavens (Malloch) (Diptera:Chironomidae , Orthocladiinae) 144 4.2.2.18Chironomida eo fdetritu ssubstrate s 146 Conchapelopiamelanop s (Wiedemann) (Diptera:Chironomidae , Tanypodinae) 146 CorynoneuraWinnert zspp .(Diptera :Chironomidae , Orthocladiinae) 148 Brilliamodest a (Meigen) (Diptera:Chironomidae , Orthocladiinae) 148 Diplocladius cultrigerKleffe r (Diptera:Chironomidae , Orthocladiinae) 149 RheocricotopusThieneman nspp . (Diptera:Chironomidae , Orthocladiinae) 149 Eukiefferiellagr .discoloripe s (sensuMolle rPillot , 1980) (Diptera:Chironomidae ,Orthocladiinae ) 150 Polypedilumlaetu magg . (sensuMolle rPillot ,1979 ) (Diptera: Chironomidae,Chironominae ) 151

5 General discussion 153 5.1 Partielesiz e 154 5.2 Currentvelocit y 156 5.3 Foodcondition s 158

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

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

Abbreviations used in the field classification of substrate types

S = Sand FD = Fine Detritus G = Gravel St = Stable CD = Coarse Detritus Sh = Shifting L = Leaves B = Bare Detritus = CD + L CD/FD = CD with or without FD

Names, phi values and phi indices of grain-size fractions

Frac tiori Phi value Phi index Name of fraction

(mm] <-log2 fraction)

128 - 256 -7 8 cobbles 64 - 128 -6 7 cobbles 32 - 64 -5 6 large pebbles 16 - 32 -4 5 small pebbles 8 - 16 -3 4 coarse gravel 4 - 8 -2 3 medium gravel 2 - 4 -1 2 fine gravel 1 - 2 0 1 very coarse sand 0. 500 - 1 1 1 coarse sand 0. 250 - 0 500 2 2 medium sand 0. 125 0. 250 3 3 fine sand 0.05 0 0. 125. 4 4 very fine sand 0 - 0.05 0 5-10 0 silt and lutum t :0.05 0 mm is used instead of 0.0625

Q M Q index describes the grain-size composition of a substrate by giving the first (Q-), second (median)(H) and third (Q ) quartiles expressed in integer phi values (phi indices). 1 Introduction

1.1 GENERAL

Lowlandstreams ,wit ha strongl yfluctuatin gdischarge ,wate rlevel ,curren t velocity,botto mcompositio nan dvegetatio npattern ,ar ea characteristi c typeo f streamfo rth eNetherlands .A larg enumbe ro fbenthi cmacroinvertebrat e speciesar e restrictedt othi styp eo fenvironmen tan dfor mth echaracteristi c animalcommunit y ofth enatura llowlan dstream . Sinceth e1930 smos t lowland streamsin th eNetherland shav ebee nregulate din connectionwit hlan dreclamatio nscheme so rprogramme saime da tth eimprovemem to f streamhydrolog yt oincreas edrainag ean di nth emor erecen tdecade sals ot olowe r thegroundwate rleve lin vas tareas .Thi s impliesth ereductio no finundation ,pea k flow,erosio nan dsedimen ttransport .T othi sen dmeander sar ecu toff ,bend sar e straightened,th estrea mbe di sdeepene dan dwidened ,th eslop eo fth ebank si sstan ­ dardizedt oa 1: 2o r1: 3profile ,ban kvegetatio ni sremove dan dpath sar econ ­ structedfo rgras smowers ;weir san dbarrage sar eplace da tregula rinterval st o reducesedimen t transportan dretai na minimu mwate r leveli nsumme rfo rirrigatio n purposes.Bank sar eofte nreinforce dwit hconcrete ,nylo nmattin go rwoo dan dsome ­ timesth ewhol estrea mbe di sreinforce dwit hconcret eblocks .Severa lterm sar ein uset odescrib ethes ekin do fphysica lperturbations .Hereafte rth eter mregulatio n willb eused ,t osav eth eter mchannelizatio nfo rstream san drivers.tha thav ebee n regulatedwit hth epurpos eo ffacilitatin gtranspor tb yboat . Regulationstrongl yaffect sth ephysica lcharacteristic so fth estrea msystem , andinvestigation sin th eAchterhoe k (Gardeniers& Tolkamp ,1976 )an delsewher ei n theNetherland s (Heijdeman& va n' tOever ,1976 ;Peter s& Leijten ,1977 ;d eGraaff , 1979)demonstrat etha tth eanima lcommunit ylivin gin regulate d streamsi squit e differentfro mtha tlivin gi nunperturbed ,natura llowlan d streams,a featur efre ­ quentlyreporte di nothe rcountrie sfo rothe rstrea mtype sa swel l (e.g.Wen e& Wickliff,1940 ;Engelhardt ,19S1 ;Stuart ,1959 ;Einsele ,1960 ;Rouyer ,1975) .Th e typicalfaun apresen tin natura l lowlandstream si softe npracticall yabsen tfro m streamstha thav ebee nregulated .Onl yi nstream sregulate din th eol dfashione d way,wher emaintenanc eha sbee nneglecte dsinc eth emajo rregulatio nworks ,ma yth e faunao fth enatura l streamb eabl et osta yo rre-establis h itselfi nplace swher e conditionsar ereturnin gt oth eorigina l state.I nsuc hsemi-regulate d streamsth e faunama yconsis to fa mixtur eo fpond -an dstream-dwellin g species.I nmos tregu ­ latedstreams ,however ,th especie scompositio nresemble stha to fcanals,.ditche san d

1 ponds.Thi s canb e attributed toth echange s thephysica l environmentha sundergone . Levellingdown th espatia l andtempora lvariatio ni ncurren tvelocit ywil l result inmor eunifor m substratepatterns ,whil eth eabsenc eo fban kvegetatio n (treesan d shrubs)whic hwoul d shade thewater ,result s inhighe rwate r temperatures and the developmento fmacrophyte s oreve nmicrophyte swhe ncurren tvelocit y islo wenough . Less allochthonousmateria lwil l enter thestrea m system andalga e andaquati cplant s will replace leavesa s the trophicbasi so f thecommunity .Th e stream system changes fromheterotrophi c toautotrophi c (Cummins et al., 1973). Consequently,majo r changes incommunit y structurewil l result.Fo r eachanima l species it isessentia l thatenvironmenta l factorsar epresen t inth e right extent withinreac ho f theanimal .Comparin gnatura l andregulate d lowland streams,an d noting thedifference s inspecie scompositio no f thecommunitie spresent ,th e impressionbecome s stronger that theenvironmenta l demandso f species characteristic forunperturbe d lowlandstream sar es o specifictha tthe yca nonl yb eme t inver y distinctplace swithi nth e stream.Apparentl y these speciesca nonl yfin d the optimal combinationo fphysica lparameter s ina streamwit hmuc hvariation ,wit h therigh t extento rrang eo f each factor important for their existence (e.g.sub ­ strateparticl e size,curren tvelocity ,food ,oxyge n supply). Many investigationshav ebee ncarrie dou t inDutc hlowlan d streamsdurin g the last twodecades ,mainl y concerning thedescriptio no f thestrea m faunaan 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 l andchemica l qualityo fth e streamsa s related to themacroinvertebrate s have ledt o areasonabl ycomplet epictur eo fth egeographica l distributiono f the benthicmacroinvertebrate s inDutc h lowland streams ando f thedifference s between natural andregulate d streams inth e senseo f thecompositio no f theanima lcommunity . The differences inspecie scompositio nhav eeve nbee nuse d as an instrument tomea ­ sureth edegre eo fregulatio no f alowlan d stream (Tolkamp& Gardeniers , 1977). However,curren tvelocit y isonl yon eo f theparameter s thatma y change after regulationan dn odetaile d information isavailabl eo nth e specific reasons forth e differences inanima lcommunitie sbetwee nnatura l andregulate d streams.Curren t velocity iso fcours eon eo f thereasons ,bu tth edistributio no ffreshwate r animals isals odetermine db y awhol ecomple xo fa larg enumbe ro fphysical ,chemica l and biological factors (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 s et al, 1975;Friber ge tal , 1977). Schmitz (1954)followe dThieneman n (1912)i nth e conceptiontha tcurren tvelocit y and temperaturear e theprimar y factors influencing thedevelopmen t of running-water zoocoenoses.Whitehea d (1935)conclude d that thenatur eo f the streambe d iso fgrea t importance asa facto rdeterminin g thenatur eo fth e fauna,eithe r directly (pro­ viding shelter,suitabl eattachmen t sites)o r indirectly (providing food, influencing thenatur eo fplan t growth,givin g suitableoxyge nconditions) . Thestrea mbotto mi sth eproduc to ftw osource stha tprovid eth ebasi ccom ­ ponents:minera lan dorgani callochthonou smateria l suppliedb ywate ran dair ,an d mineralan dorgani cautochthonou smateria lpresen t inth estrea mbed ,originatin g fromgeomorphologica lconditions .Unde rth e influenceo fth edischarg eregim ean d thefor mo fth estrea mchannel ,interactin g intw omajo rcounte rprocesses ,erosio n andsedimentation ,th ebasi ccomponent sar earrange d insubstrat epattern swit h characteristicpropertie sconcernin gcompositio n (particlesiz ean dnatur eo fminera l andorgani cmatter) , structure (spatialvariations-vertica lan dhorizontal ,stability , packing,porosity )an ddynamic s (temporalchange s instructure) .Becaus eo fth e sortingactivit yo fth ecurrent ,th estructur eo fth estrea mbotto mi sinseparabl y interwovenwit hth evariatio no fth ecurren t (velocity,regime ,turbulence )(Schmitz , 1961;Scherer ,1965) ,resultin g ina constantl yvaryin g (inspac ean dtime )mosai c patterno fsubstrat etypes ,eac hwit hdifferen tenvironmenta lconditions .Grain-siz e compositionma yvar ya tver yshor tdistance san d influence,fo rexample ,th eoxyge n contento fth e interstitialwater ,th eamoun to ftrappe dorgani cdetritus ,th egrowt h ofperiphyto nan dth enumbe ro fcrevices . Cummins &Lauf f (1969)presente da diagra mshowin gth efou rmajo rcategorie so f environmentalparameter s (Fig. 1). Theyemphasize dtha tcurrent ,temperatur ean dcon ­ centrationo fchemica lfactor sma ylimi tth erang eo fhabita ttolerance s (macro- distribution)an dtha t substrateparticl esiz eo rfoo dsuppl yar eprobabl yth emai n microdistributional factors.Althoug hsevera ladditiona lphysica l factorsinfluencin g distributionar eofte nmentioned ,thes ear emostl ydirectl yrelate d toon eo fth e mainfactors :flo wregime ,drought ,spates ,illumination ,suspende dsolids ,proximit y of suitablehabitat 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 dt oth emai nfactor sfood ,curren tan dsubstrate . Ulfstrand (1967)stresse d thepoin ttha tth emos t importantfacto rlinke dwit h substrate isth eprovisio no ffoo di nth efor mo fallochthonou san dautochthonou s matteran dpre yanimals .Thi sagree swit hth evie wo fCunmin s (1975),wh ostate dtha t foodwil lundoubtedl yb e theultimat edeterminan to fmacroinvertebrat edistributio n andabundanc e innon-perturbe drunnin gwaters .Bu th eadde dtha twhe nfoo dcondition s arefavourable ,othe rfactors ,a ssedimen tparticl e size,current ,competitio nfo r spaceo rprédatio nwil ldetermin eth emicrodistributio nwithi na give nsectio no f a stream.Moreover ,foo di spar to fth esubstrat efo ralga lfeeder s (grazers,scrapers ) aswel la sdetritu sfeeder s (shredders,consumers )an dth epresenc ean dabundanc eo f foodsubstance s is influencedby ,fo rexample ,th eparticl esiz e (accumulationo f detritus (Rabeni& Minshall ,1977)) ,sedimen ttranspor t (scouringof fattache d algae), lightcondition s andcurren t (distributiono fdetritus ,growt ho fhydrophytes , bringing foodt ofilte rfeeders) .Th epreferenc eo fpre yorganism sfo rcertai nsub ­ strateo rfoo dtype swil l influenceth edistributio no fthei rpredator s (Ulfstande t al., 1971;Hildre w& Townsend , 1976). Forth ever yreaso ntha tth esubstrat ei sth eresultan to fan dstrongl yinter - SUBSTRATE <- -> FOOD SUBSTANCES PARTICLE (Detritus,prey, SIZE microphytes,etc.)

A

MICRODISTRIBUTION

V V

CURRENTVELOCIT Y OTHERPHYSICA L -CHEMICA L PARAMETERS (e.g.O ,Temp., pH,CaC O FeO)

TURBULENCE andCURREN T

-> :Interaction sbetwee n environmental parameters towhic h agive n benthic species interacts j,: Influenc eo f theenvironmen t ona benthi c specieswhic h results inrecognitio no f thehabita t .;>: Influenc eo f agive nbenthi c specieso n thehabita t

Fig.1 .Genera l relationshipbetwee n environmental parameters and themicro - distributiono fbenthi c streammacroinvertebrate s (afterCummin s8 1Lauff,1969) .

linkedwit ha numbe ro fphysica lfactor san d iso 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 s incurren tvelocit y anddischarg e regimefollowin g streamregulation ,the yma yprov et ob eth emajo rreason sfo rth e differences inspecie scompositio nbetwee nnatura l andregulate d lowlandstreams .

1.2 PURPOSEO FTH EINVESTIGATIO N

Thepurpos e ofth e investigationwa st ogai ninsigh t intoth erol eth e substrate plays inth edevelopmen t andpreservatio no fth emacroinvertebrat ecommunitie s in natural,undisturbe d lowlandstreams .Testin gan dquantificatio no fth erelationship s betweentempora lan dspatia lenvironmenta l factorsa smeasure db ysubstrat echarac ­ teristicsan dth ecompositio no fanima lcommunitie swil l increaseth eknowledg eo f theautecolog yo fsom etypica l lowlandstrea m speciesan dwil lmak e itpossibl et o indicatesom eo fth ecritica lcondition stha tdistinguis hnatura l lowland streams fromothe rwatercourses . Asa basi sfo rpreservatio nan dmanagemen to fthes estream sthi sknowledg ei s indispensablean di twil lcontribut et oth equantificatio no fth elimitin g conditions concerning streamdimensions ,profile ,meandering ,ban kvegetation ,wei rlevel , current speed,maintenance ,effluen tdischarge ,recreatio nan dban kprotection .Ther e isa nurgen tnee dfo r thiskin 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 t substratetype s (e.g.Penna k& va nGerpen , 1947;Thorup ,1966 ;Mackay , 1969;Macka y& Kalff ,1969 ;Ward , 1975;Cummins , 1975). Manyauthor suse d thesubstrat emerel y todescrib e thevariou shabitat sthe yencoun ­ teredan dwer eno ttryin gt oestablis hdifference s inth efauna lcompositio no fth e substratetypes ,bu tdescribe d the streamfaun 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 g speciesdistributio n andsubstrat e composition havebecom enumerou san dman yreference swer egive nb yCummin s (1966),Thoru p (1966) andHyne s (1970a, b). Although aspecie sma ysho wa distinc tpreferenc e fora certai nsubstrat etype , other featuresprevailin g inth esam eplac eo ri nth eneighbourhoo dma ycaus eth e animals totolerat e less-preferred substrates.Cummin s &Lauf f (1969)demonstrate d thisfo rth estonefl y Perlesta placida, insubstrate-selectio n experiments.Variou s authorshav eshow nfo rsevera l speciestha tdifferen t instarsma 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).Ree s (1972)foun da significan trelationshi pbetwee nth ebod ylengt ho f Gammxrus peeudolirrmaeus (Amphipoda)an dth esubstrat eparticl e size inlaborator y experiments,an dWesenberg-Lun d (1943)alread ygav eexample so fsevera l caddisfl y speciestha tus edifferen thouse-buildin gmaterial sdurin g theirdevelopment .Macka y (1977)demonstrate d that Pyenopsyohe soabieipennie (Trichoptera)pupa eburro wi n othersubstrate s thanth e larvaeprefer .Thu sman ybenthic-stream-dwellin gmacro - invertebratesma ynee dsevera l substratetype st ocomplet ethei r lifecycle . Theseobservation s formedth ebasi s forth efollowin ghypothesis : Thedemand so fman ybenthi clowlan dstrea mmacroinvertebrat especie so fth e substrate areo fsuc ha natur etha tthe yca nonl yb eme t ina non-regulate dlowlan dstrea mwit h itstypica l substratecompositio nan dpattern . Twoworkin ghypothese swer eformulate d totes tthi shypothesis : - Manybenthi c lowland streammacroinvertebrat e species show distinct preferences fora specific substrate composition. - Forman y of these species the small-scale spatial variation in substrate compo­ sitiono fth e streambe d isessentia l for their existence.

1.4 RESEARCH APPROACH

Testing ofth eworkin g hypotheses was performed inthre e steps: - Determination ofth emicrodistributiona l patterns of themacroinvertebrate s intw o natural,undisturbe d lowland streams (field investigation). - Determination of substrate preferences of anumbe r ofcharacteristi c lowland streams species insubstrate-selectio nexperiment s ina laboratory stream channel (laboratory experiments). - Determination ofth emacroinvertebrat e colonization of artificial substrates inth e stream bed (field experiments).

This approachwa s chosenbecaus e the interpretation of data from field research only leads to correlations between animal distribution and certain environmental parameters.Experiment s inth e laboratory or the field,o rboth ,ar enecessar y to provide data that canb euse d to test the conclusions derived from the field research. 2 Description of thestream s

The investigationwa scarrie dou ti ntw onatural ,unperturbed ,unpollute d low­ landstreams :th eSnijdersveerbee k (Snijb)an dth eRatumsebee k (Rab).Bot hstream s aresituate di nth eeaster npar to fth eAchterhoe ki nth eprovinc eo fGelderland , wherenatura l streamsar estil lpresen t (Fig.2) .I nbot hstream sth einvestigatio n wasrestricte dt oa sectio no f150 0metres .

2.1 THESNIJDERSVEERBEE K (FIGS.3 AN D 4)

Onlyth efirs t 1500m o fth eSnijdersveerbee ki si na natura lstate .Th edown ­ streampar tha sbee nregulate dan dcontain sonl y stagnantwate ro rn owate ra tal l forth elarges tpar to fth eyear .Th estrea moriginate sa tth ewester nborde ro fth e

Twente kanaal

NLƒ FRG

Ratumsebeek

Willinkbeek Boven Slinge

nijdersveerbee k

Aastrang O ( lOudeIJsse l Nijmegen ^ NL^ FR G

Fig. 2.Stream s inth eAchterhoek .Th eshade dare aindicate s theare awher enatural , unpolluted streamsstil l exist (modified afterGardenier s &Tolkamp , 1976). O 100 200 lig Lil ^XM m 50 150 250

30.0 Bocholt

^m^^^^ thestrea m n ti t l :meadow s ++•»++ + •)• : border NL-FRG

: --"^»x :dr y insumme r -Z- -Zr , farm land 35.0 altitude in m :grave l within 40c m " * road . . hedgerow or forest below the surface

Fig. 3. The Snijdersveerbeek, showing Sections 1-8.

'tertiaryplateau 'i na smal lvalle y approximately3 m belo wth eleve lo fth esur ­ rounding area.I trun si na westerl y directionove rth eslop eo fth eplatea uan d reaches,afte rpassin gth erelativel y steep edgeo fth eplateau ,th efla tare a called 'Pleistocenebasin' .Thi sbasi ni sfille dwit h coarse sandst oa grea tdepth ,whic h givesris et oth eintermitten t charactero fth edownstrea mpar to fth estream . Theuppe rpar to fth estrea mi sfe db yiron-ric h groundwater,whic h continuously seeps intoth estrea mthroug hth ebe dan dbanks .Eve ni nth eextremel ydr ysumme ro f 1976thi sdi dno tstop .Th econtinuou s seepagei sconnecte dwit hth especifi cgeo - morphologicalan dhydro-geologica l characteristicso fth earea :coars e sediments (wind-blownsand san dMiddl ePleistocen e fluviatile sandan dgravel )ar esituate do n Fig.4 .Samplin g sitei nSectio n6 o f theSnijdersveerbeek . heavycla y (teriary 'old' clay),whic hgive sris et oa groundwate r supplyt oth e Snijdersveerbeek froma fairl ylarg ecatchmen t area.Th egroundwate r runsove rth e claythroug hth ecoars e fluviatilesand san dgravel .Wher eth estrea mbe dreache sth e groundwater level,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 s froma 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 y direction,reducin gth epea k flowi nth eactua lstream .Th esmal lamoun to fwate rstil lpermitte dt oflo w through 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 einvestigatio npar to fth estream . Aftera preliminar y investigation (Tolkamp,1975b ;Both ,1976) ,eigh t sections 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 d from2 c mt o3 0cm ,wit ha naverag ei nsumme ro f2-1 0c man di nwinte 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 e current speedwa s5-1 0cm/ si nsummer .I nwinte ri tincrease dt o20-3 0 cm/s,wit hoccasiona l Table 1.Physica l characteristics of theeigh t sections inth eSnijdersveerbee kan d theupstrea m sectiono f theRatumsebeek .

Snijdersveerbe ek 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 Meandering strong 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;C D Veg FD; C D; 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=CoarseDetr i tus; FD=FineD e ;ritus; Veg=Vegetation

higher speedsafte rheav y rainfall.Th etemperatur e regimewa ssimila rt otha to fth e Ratumsebeek.Measurement swer e carriedou tmonthly .Minimu m temperaturesi nwinte r were about 2°C,whil e summer temperaturesvarie dbetivee n1 3C an d1 6C . The streami sshade db ytrees ,brushwood ,hig hgrowin gherb so rhig han dstee p banks,excep tfo roccasiona l short stretches inth efou rupstrea m sectionswher eth e bankvegetatio no rth ebank sha dbee ndamage db ycattl ean dman .I nthes eunshade d places,aquati cvegetatio noccurre d insmal lmosai cpatterns ,mainl y consistingo f Vevoniaa beaaahunga, Mentha aquatiaa, Myosotis palustris andi nSectio n2 als o Glyoeria fluitans. Especiallyth estee pbank swer e coveredwit h livermosses ,amon g them Marohantia polymorpha. Substratevarie dwit h currentvelocit yan dgeologica l conditions.Th epresenc e ofgrave lwa sclearl y linkedwit hth eoccurrenc eo ffluviatil eRhin e deposits.How ­ ever,onl yi nth eSection s4 ,6 an d8 di dgrave l forma majo r parto fth esubstrate . Herei toccurre d overth ewhol ewidt ho fth estrea mbed ,whil ei tsurface donl yin ­ cidentallyi nth eSection s2 ,3 an d5 .Grave l substrateswer emostl y situatedo no r mixedwit h sand.Onl yi nth eSection s6 an d8 di dcla yo rloam y sand formth ebas e forgrave lo rsan d substrates.I nal lsection s except Section7 ,leave san dorgani c detritus formeda majo rpar to fth esubstrat e- accumulate d nearth ebanks ,i npools , againstobstacle sprojectin g fromth ebe di nriffle so rtrappe di nvegetation .Larg e quantitieswer e alsofoun dt ob emixe dwit hth eminera l substrate. Section7 wa sno tinclude di nth eroutin e sampling programmebecaus e thispar t ofth estrea m functioneda sa san d collectionbasin ,whic hwa s redimensionedi n1976 . Thewidt han ddept ho fth estrea m channelwer e enlargedt osuc ha nexten t (andth e trees alongside cut)tha ti nsumme r retentionan devaporatio nwer ehighe r thanth e water supply fromupstream .Thi s causedth edesiccatio no fSectio n8 i nth esummer s followingJun e 1976.

10 2.2 THERATUMSEBEE K (FIGS.5 AN D6 )

Thisstrea mi sfe db ya larg enumbe ro fregulated ,an dmostl yman-mad esmal l tributaries,mainl ysituate di nGermany ,drainin gsom e 1200ha .In th 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) ,th efirs t150 0 m afterth eGerma nborder ,i sstrongl ymeanderin gi nan oak-beec h forest.Th estrea m hasbee nlef t freet ofin dit sow nway ,producin gal ldegree so fmeandering ,althoug h underminedtree stha twoul dobstruc tth eflo wo fth ewate rar eremove db yth eloca l waterboardo r(concerned )farmers . Normallyth estrea mflow sal lyea rround .However ,i nth esumme ro f197 6th e downstreampar tdrie dou tcompletel yan di nth einvestigate dsectio nonl y somepool s remainedwit han occasiona ltrickl efro 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 tin thi ssectio n(1. 5

Mb.O

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

: tributary farm land 45.0 : altitude in

A ^A^ hedgerow or forest ' » m tints Fig. 5.Upstrea m sectiono f theRatumsebeek .Th earrow s indicate theroutin e sampling site (R)an d thesit ewher eartificia l substrates (AS)wer eplaced .

11 Fig. 6. Samplingsit ei nth eupstrea m sectiono f theRatumsebeek .

m/km). Currentvelocit y variedi nsumme r fromver ylo wi npool st o10-1 5 cm/sa t riffles.I nwinter ,pool-riffl e differenceswer e lesspronounce dan dth ecurren twa s 30-40cm/ so nth eaverage ,wit hpeak su pt o10 0cm/ safte rheav yrainfall . Thewidt ho fth estrea mbe dvarie d from1. 5m t o3. 0m .Dept h ranged from0-4 0 cm insumme rt o30-10 0c mi nwinter .Temperatur e variedbetwee n0 Can d5 Ci nwinter , althoughic ewa spracticall y never formed.I nsummer ,temperatur e roset o12-1 6C , with occasionalpeak so f1 9C .Fo rcomparison ,thes edat ahav e been includedi nTabl e 1. Inth einvestigate d sectionth estrea mbe dcut srathe rdee p throughth eland ­ scape,i nsom eplace s2 m o rmor ebelo wth esurfac e level.A strongl y varied rangeo f geological deposits reachth esurfac ei nth estrea mbe d(Bosch , 1967;Kramer , 1972). Fromth eGerma nborde rt osom e2. 5k mdownstrea m lias deposits emerge,especiall yi n theoute rbends .I nthi s area,wher eth estrea mmeander sbetwee nth ehig hfarmlands , localmorain e coversth elia sdeposits .I nsom eplace s thisboulde r clayi scompresse d toa ver yhar d layer.Clayston e banksar eals opresent ,forme d through compressiono f clayan dsan dunde rpressur e inth elia speriod .Ove ra distanc eo fabou t1 k m oligocènecla y reachesth esurfac ei nsom eplace sa swell .I nth einvestigate d section ofth estream ,th esubstrat e consistsfo rapproximatel y 40%o fgrave lan dstone s embeddedi no ro nto po fsan do rclay . Ironconcretions ,resemblin g roughgrave l particles forma nimportan t parto fth eminera l substrate.

12 Thestrea mbe dconsist so fa numbe ro fpool san driffles .Upstrea man ddown ­ streamo fth ehar dbank s (claystone),th eslop eo fth estrea mbe d isles 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 rwit hlarg eamount so fleave s andcoars edetritus .O nth ehar dbank s theslop ei ssteepe ran derosio ntake splace . Hereth ebotto mconsist so fcoars esand ,fin ean dcoars egravel ,iro nconcretions , claystone,cla yan dpebbles .B yth ealternatio no fpool san driffles ,th ewate rrun s stepwisedownstream . Leavesan dorgani cdetritu sfor ma nimportan t substrate inthi sstream .Thi s material isconstantl yblow n intoth e streamfro mth ebank san dca nb e found in variousform so fdegradatio nal lyea rround .I nautum nan dwinte rth e inputo ffres h leafmateria l isgreatest ,whil eth e amountgraduall ydecrease s throughsprin gan d summer.Sometime s largeaccumulation so fleave s formdam s inth 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 esite s sampledi n1977 . Ingeneral ,substrat ecompositio nfluctuate dmarkedl ydurin gth eyear .A sa n illustration,th esurfac eview so fth esamplin gsit e inth eRatumsebee khav ebee n presented foreac hseaso n inFig .7 .I nthi ssectio no fth eRatumsebeek ,whic hi s completely shaded,n oaquati cvegetatio ngrew .

13 Cobbleso r Bricks Branches Water'sedg e Bank Pebbles overhanging water'sedg e

Fig.7 .Substrat emosai c structureo fth estrea mbe d atth eRatumsebee k sampling site for each seasono f1977 .

14 O -O .. o| O O o • .OO• „O O „ O • O o o o ° •o• o- . ' •o •

Sand FineGrave l CoarseGrave l FineGrave l+ Gravel Sand

Älife ? $ ? 9~ „~&>

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

15 3 Methods

3.1 FIELD PROCEDURE

3.1.1 Selection of sampling sites

A representative sampling siteo fapproximatel y 5m lengt hwa schose ni neac h sectiono nth ebasi so fth esubstrat ecompositio nan dvariation .I nth eSection s4 ,5 and6 i nth eSnij ban dth eon esectio ni nth eRab ,th esam e sitewa suse do nal l sampling dates.Thi s givesa nimpressio no fth etempora l substratevariatio nan dan y related changesi nmacroinvertebrat edistribution . Afterth eselectio no fa samplin g site (alwaysworkin gi nupstrea mdirection )a sketchwa smad eo fth estrea mbe d(Fig .7 )an dth estrea mprofile .Th epositio no f thevariou s substrate typesan dth eexpositio no fth esubstrate st oth ecurren twa s thus indicated.Al ldimension swer emeasure dwithou t stepping intoth estream . Places inaccessible fromth ebank swer emeasure d aftercompletin gth esamplin gprogramme .I n eachsketc hth eexac tpositio no fth esample swa sindicate dan dnumbered .Sample s were taken fromal l substrate typespresen ta ta chose n site.Befor e actually taking the samples,th esit ewa sobserve dfo ra whil ean dbotto m faunavisibl eo nth esub ­ stratesurfac e recorded.

3.1.2 Sampling dates

Inth eSnijdersveerbeek ,samplin gwa s carriedou tmonthl y fromSeptembe r197 5 to September 1976an donc eever ytw oo rthre eweek s from September197 6t oApri l 1977. Emphasiswa splace do nth efou rdownstrea m sections;th ethre eupstrea m sectionswer e only sampled incidentally. FromTabl e 2,whic h givesth eseasona lnumbe ro fsample s ineac hsection ,i ti sclea rtha tth enumbe ro fsample si nSectio n8 decrease d after June 1976.Thi swa scause db yth edesiccatio no fth estrea mbe dfro mJul yt oNovembe r 1976a sa resul to fth eenlargemen to fth esand-collectin g sectionupstrea mi nJun e 1976an dth efac ttha tth esumme ro f197 6wa sextremel ydry . Comparedt oothe r sections,Sectio n5 showe d less substrate variation,whic hi s thereaso nfo rth esmalle rnumbe ro fsample s takenthere ;n osample swer e takeni n April 1976.Afte r September 1976,th esamplin g frequencywa s increased,a smentione d above,resultin g ina large rnumbe ro fsample si nautum nan dwinte r thani nsprin g and sumner.O fth esprin g samples,equa lnumber swer e takeni n197 6an d1977 .Onl y the summer sampleswer e almostal ltake ni n1976 ,excep tfo rth efirs t samples from

16 Table2 .Numbe ro fsample s takenI nth eSnijdersveerbee k and theRatumsebee k by season.

Season Weeks Snijdersveerbeek sections Ratumsebeek sections

1 2 3 4 5 6 8 Total 1 4 5 8 Total

Winter 51-52 5 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

1975i nWee k 37,th elas twee ki nsummer . Inth eRatumsebeek ,sample swer e takenever ytw oo rthre eweek s fromJanuar y 1977t oJanuar y 1978.Samplin gdate sar esummarize dpe rseaso ni nTabl e2 .Sample s takeni nthi s streami nJul y 1976,befor eth estrea mdrie dup ,wer eals oincluded . Themor edownstrea mSection s4 ,5 an d8 wer eno tsample do na routin ebasi si n197 7 butth eavailabl edat aclearl yindicat etha tth esubstrat ean dfaun ao fthes esec ­ tionsresembl ethos eo fth eupstrea m sectionstudie di n1977 .

3.1.3 Field Classification of substrates

Substrateso na samplin g sitewer echaracterize db yth edominant-particl esiz e atth esurfac eo fth estrea mbed .Mostl y thisconcerne d combinationso fsevera l particlesize stogethe rwit hsevera ltype so forgani cdetritu si ndifferen tquan ­ tities.Nin eminera l substratecomponent swer edistinguished :Cobble s (Co),Pebble s (P),Coars eGrave l (CG),Fin eGrave l (FG), Gravel (G,a mixtur eo fC Gan dFG) ,Coars e Sand (CS),Fin eSan d (FS),San d (S,a mixtur eo fC San dFS )an dSilt/Lutu m(no t abbreviated).Althoug hn ograin-siz emeasurement swer ecarrie dou ti nth efield ,th e differencesbetwee nth ecomponent s roughlycorrespon dwit hth elimit sgive ni nTabl e 3,combinin gtw ofraction sa ta time ,startin gwit hver yfin esan dan dproceedin g upward from0.0 5mm . Practically everycombinatio no fthes ecomponent swa sfoun di nth etw oinvesti ­ gatedstreams .Mos t samplesconsiste do fa combinatio no ftw oo rmor eo fthes ecom ­ ponents,whic htogethe r formeda substrat e type.Thi swa snote db ymentionin gth e dominant component first,followe db yth eles sabundan t components,e.g .FG+C Go nF S withP .Thi smean stha tth esubstrat emainl y consistedo fFin eGrave lmixe dwit h (less)Coars eGrave lsituate do na bas eo fFin eSan dwit ha noccasiona lPebbl ei nth e substrate.Minera l substratesno tcombine dwit horgani cmateria lwer e indicateda s Bare,i.e .Bar eSan d (BS)o rBar eGrave l (BG).Unstabl eo rshiftin g sand substrates werenote da sShiftin gSan d (Sh.S),whil ecompact ,stabl esan dsubstrate swer enote d asStabl eSan d (St.S). Organicdetritu swa sdistinguishe d inthre etype san da numbe ro fcombination s

17 ofthese : - Leaves (L): accumulation so rlayer so fintac to ronl ypartl y disintegratedleaves , predominantlyo fallochthonou sorigin . - CoarseDetritu s (CD):smalle rpiece so fleaves ,lea fskeletons ,sticks ,fruit s (acorns,beec hnuts) ,bark ,bu dscale s (beech),see d capsules,remain so fhighe r plants, etc. - FineDetritu s (FD):ver y fineorgani cmaterial ,alread yver y disintegrated(e.g . macroinvertebrateexcrements) .Ofte n amorphous,brow ni ncolou ran dfine r than0.0 5 urn. Organic substrateswer e alsodesignate 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 esubstrat ewa sname d CD+L (CoarseDetritu s and Leaves).Whe non eo fthes e typeswa smor eabundant ,th esubstrat ewa sname d after thedominan t typean dth erati obetwee nth etype swa snoted .I nth efollowin g CD+Lo r CDo rL wil lsometime sb ereferre dt oa sDetritu s (D)(e.g .Fig . 12).On eha st obea r inmin d thatthi sdoe sno tinclud eth eFin eDetritu s fraction. FineDetritu swa snoted ,statin gwhethe r therewa smuc ho rlittle .Th eimpres ­ sionobtaine d duringth eactua l sampling aboutth epackin gan dstabilit yo fth e substrate (shiftingo rstable )an dth ecompositio no fth eunderlying ,bu tfro mth e surface invisible,substrat ewa sals oprocesse di nth efiel d classification, includ­ ingdat ao nth eratio so fth eunderlyin g substratetypes .

3.1.4 Sampling method

Since substrateheterogeneit yi sver ymarke di nbot h streams,wit ha stron gal ­ ternationo fsubstrat e types,resultin gi nsmall-scal emosai cpatterns ,a small-scal e samplerwa snecessar yfo rth ecollectio no fsubstrat ean dfauna .Thes emus tb ecol ­ lected togetheri non esampl e sincei ti softe n impossiblet otak ea separat esub ­ strate samplei na certai ntyp ebecaus eo fit srestricte d area.I nstream swit hmor e uniforman dlarge r substrate types separate substratean dfaun a samplesma ywor k satisfactory (e.g.Edwards ,1975 ; Petran, 1977),bu ti tofte nprove dt ob eimpossibl e inth eDutc hsmal l lowlandstreams . A shovel samplerwa sdevised ,fi tt osampl ea tth esam etim ebot h substratean d macroinvertebrateso na smal l scale.Thi s sampler,calle da micro-macrofaun a shovel (Fig.8) ,i smad eo fstainles s steel.I ti s1 0c mwide ,1 0c mhig han d1 5c mlong .O n theto pan da tth erea rar eopening san dthes ear escreene dwit h0. 5m mnylo ngauze . A removablehandle-ba ri sattache dt oth erear .O nth esides ,adjustabl ewing sar e attached,preventin gth eshove l fromdiggin gto odee p intoth estrea mbe dan dmakin g itpossibl et ooperat ewit ha standar d sampling depth.Thi s depthwa s fixeda t3c m inth epresen t investigation.Th ewing ssk iove rth esubstrat eo nbot h sideso fth e shovel. The shoveli spushe d intoth esubstrat ea ta nangl eo fapproximatel y3 0- 4 5C and tiltedbackwards ,bringin gi thorizonta la ssoo na sth edesire d depthi sreached . Fig.8 .Th emicro-macrofaun a shovel.

Attha tmomen tth ewing sar erestin go nth estrea mbottom .I nth esam emovemen tth e shoveli spushe dforwar dthroug hth esubstrat eove ra 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 gsubstrat e andanimal sar erinse dou twit hwater .A mor edetaile ddescriptio no fth emicro - macrofaunashovel ,it sconstructio nan dsamplin gefficienc yi 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 esampled ,whic hyielde d 15-25samples .I n theRatumsebeek ,onl yon esectio nwa s sampled.A naverag eo f6 sample swa stake no n eachoccasion .Th enumbe ro fsample s alwaysdepende do nth enumbe ro fvisibl esub ­ stratetypes .Th esample swer etransporte dt oth elaborator ya squickl ya spossibl e and storeda t2-4° C (3-4hour safte rtakin gth efirs t sample).I na fe w exceptions thesample swer econserve dwit h1 0 %(V/V )formaldehyd ean dstore dt ob esorte d later. Preliminaryresearc h (Both,1976 )showe dtha ti ti sno tpractica lt ous eth e shovelsample ri nlea fpack so rcoars edetritu saccumulations ,becaus ei twil lpus h thesesubstrate sahea do fth esampler ,o rpar to fth eunderlyin gminera lmatte rwil l be includedi nth eorgani csample .Sinc ethi swoul dmak eth einterpretatio no fth e datato ocomplex ,th eorgani csubstrate san dth eunderlyin gminera lmatte rwer esam ­ pledseparately .Th eorgani cmateria lwa ssample db yhand ,b ypushin gth eleave so r coarsedetritu s 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 man are acomparabl et otha tsample db y 2 the shovel (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 2.1.5 Additional collections

A numbero fanimal swer ehand-picke d fromstones ,branches ,aquati c vegetation oran yothe r substrateafte r takingth eroutin e samples.Thes e animalswer e collected inorde rt ochec kwhethe r species dwellingo nsubstrate sno tsample dwit hth eshove l orb yhan dmigh thav ebee nmissed .Th ebody-lengt hmeasurement so fth eanimal s col­ lected thiswa ywer euse di nadditio nt oth edat a fromth eroutin e samplest ocon ­ struct life-historypattern s (especiallyfo rth eTrichoptera) .

3.2 LABORATORY PROCEDURE

3.2.1 Sample sorting

As soona sth esample s arrivedi nth elaboratory ,th esortin gprocedur ewa s started.Thi swa scomplete dwithi n2 4hours ,mostl yo nth esam eday .N osignifican t mortalitywa sobserve d during transportationan dstorage ,excep tfo roccasiona l Baetis nymphs.Thes enymph sar eeasil y injuredi nth eproces so ftransportation .Al l macroinvertebratesvisibl ewit hth enake dey ewer ehand-picke d fromth esample san d storedi n8 0 %(V/V )ethanol .Collectin gth eanimal swa sfacilitate db ydividin gth e sample into somefraction swit hth eai do fa numbe ro fsieves .Fro meac ho fthes e fractions,th eorgani cmateria l thatcoul db ehandle dwit ha pai ro fpincer swa s removed aftercarefu l inspectionfo rmacroinvertebrates ,whic hwer epicke doff .O f theminera lmaterial ,th epebble san dcobble swer e scrutinized individually.Th e finerfraction swer egentl ystirre di nwater ,afte rwhic hth eanimal san ddetritu si n suspensionwer e decanted througha 0. 5m msieve .Thi s processwa srepeate dunti ln o more animals appeared inth esieve ,followe db ysearchin gth eminera lmatte ri nsmal l portionsfo rremainin g animals (strongly clingingo rheav y species,e.g .Elminthidae , Gastropoda,cas ebuilders) . During thisproces sal lth ewate rwa sretained .A ssoo na smos t animalsha dbee n removed,th esil tan dlutu mfractio nwa sbrough t into suspensioni nthi swater , poured througha 0.05 0m siev ean dcollecte di n100 0m lcylinders .Th eanimal s that had slipped throughth e0. 5m msiev ewer epicke dof fth e0.05 0m msieve .Thi s process was repeated severaltime st oremov eth elarges tportion so fth esil tan dcla y fraction. This shouldb edon ebefor edr ysievin gth ecoarse r fractions (Cummins,1962 )sinc e these fineparticle s tendt oclin gt oth ecoarse rone si ndr ycondition san dar e easilymissed .

3.2.2 Substrate analysis

Theparticl e sizeso fth eorgani cdetritu swer eno tdetermined .Th enatur ean d thecompositio no fth eorgani cmateria lwa srecorde d (sticks,fruits ,leaves ,lea f species,etc. )durin g sample sorting,i nadditio nt oth efiel d recordings.Afte rdry -

20 inga t10 5C fo r2 4hour sth eorgani cmateria lwa sweighe dt oth eneares t0. 1g . Aboilin gwater-bat hwa suse dt oevaporat emos to fth ewater ,afte rwhic hth e mineral substratecoarse rtha n0.05 0m mwa sdrie da t105°C .Afte rcoolin gt oroo m temperatureth esubstrat ewa sdivide d intoth efraction so fth eWentwort hscal e (Wentworth,1922 ;Cummins ,1962 ;Hynes ,1970a ) (Table 3).Th eWentwort h classification wasuse dbecaus ei ti spossibl et oconver tth egeometri cparticle-siz eclassification , inwhic heac hparticle-siz e fractioni stwic eth eprecedin gone ,int oa narithmeti c onewit hequa lclas s intervalsb yusin gth eph iscale ,i.e .negativ ebinar ylo go f theparticl e sizei 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 h sievewa sused .Thi sdeviate s fromth eWentwort hclassification ,bu tsinc e thesilt-lutu mfractio nwa s alwaysver y small (mostlyles stha n 2%)i twa sconsidere d unnecessaryt ochang et oa 1/1 6ii mmes h sieve.A mes ho f1/2 0(0.050 )m mi sth elimi t usedi nmor e recentgrain-siz eclassification st oseparat esilt-lutu m fromver yver y finesan d (DeBakke r& Schelling , 1966). Thesampl ewa s sievedo na Ro-Ta pTestin gSiev eShake r (TylerCompany ,Cleveland , Ohio,USA) .Thi s shakermove sth esiev ese ti na horizontal ,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 g timewa s1 5minute s persample ,unles sth esieve sclogged ,i nwhic h casesmalle rportion swer eused . Substrates coarser than4 m mwer ehand-sieve d (8m man d1 6n msieve swit ha circula r mesh),whil e largerparticle swer emeasure d individuallywit ha rul e (thelarges t diametero fth esmalles tprojection) .Th econtent so feac hsiev eo rotherwis edeter ­ mined fractionswer eweighe dt oth eneares t0. 1g . Whenevera referenc ei smad et oa certai ngrain-siz e fraction,th efractio ni s

Table3 .Grain-siz e fractions and theirdefinitio n following theWentwort h classification (afterCummins,196 2an dDoeglas,1968) .

Fraction Phiva l ue Sievemes h Phi index of Nameo f fraction (mm) (-log2 fraction) (mm) fraction(Doeglas)

128-256 -7 rule 8 cobbles 64-128 -6 rule 7 cobbles 32- 64 -5 rule 6 largepebble s 16- 32 -4 16(round) 5 smallpebble s 8-1 6 -3 8(round) 4 coarsegrave l 4- 8 -2 4(square) 3 mediumgrave l 2- 4 -1 2(square) 2 finegrave l 1- 2 0 1(square) Î verycoars esan d 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:use d instead Of0.062 5 nun

21 cumulative %o f grain size fractions 100-

90

80

70-

60

50'

40J

30

20-

10

phivalu e

Fig. 9.Exampl eo fcumulativ e distributiono fgrain-siz e fractions ina sampl e expressed asa percentag e against the-lo g of theparticl e size inm m (phi value). The inset illustrates thecalculatio no fa quartil e indexb y linear interpolation of thecumulativ epercentage s atth eneares t integerph ivalue ,followin gth e formula a/(a+b)= c/(c+d ) ; |c+d|= 1 . referredt ob yth elowe r limit,whic h correspondswit hth esiev emes h that retained the fraction (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= T fo rth e2- 4m mfraction . Itshoul db enote d thatth enegativ e signo fph iunit si splace d aboveth efigure . The fractionfine rtha n0.05 0m mi nth ecylinder swa sdetermine dwit hth epipett e method.Th ecylinder swer e filledu pt oth e1000-m lline ,afte rwhic hth econtent s were resuspendedb yshakin gvigorously .A sampl eo f20.0 0m lwa stake n fromth e centreo fth ecolum nwit ha vacuum-operated ,standar dpipette .Thi s samplewa sdrie d andweighed .Afte r conversiont o100 0m lth eresult so fal lcylinder suse dpe rsampl e wereadde dt othos efo rth esilt-lutu mfractio nobtaine di nth edry-sievin gprocedure . The fractionweight swer e convertedt opercentage so fth etota lminera lweight .

Withth eai do fth ecumulativ epercentages ,th efirs t quartile (Q7ro r(L) , theme ­ dian (Qt-no rM, )an dth ethir dquartil e (Q?ro rQ, )wer e calculatedwit hth efollow ­ ingformula ,derive d fromth ecumulativ e sedimentcurv ewher eth eparticl e sizesar e expressedi nph ivalue s (- log ,o fth eparticl e sizei nmm ) (Fig. 9):

Ki-1 phi. ,wher e i-1 "Ki-1

22 p= 25 ,SO.o r7 5fo rQ 25,Q 5Qo rQ_ s (useda sQ 1,M, ,Q ,whe nrounde doff) ,respective ­ ly K.= cumulativ epercentag eo fth eparticl esiz ewher eth e2 5 %,5 0 %o r7 5 % limit, respectively,i sexceede d

K._1 =cumulativ epercentag eo fth eparticl esiz ebefor eth e2 5I ,5 0I o r7 5 % limit,respectively ,i sexceeded .

Thesequartil evalue sca nals ob ederive d fromth ecumulativ esedimen tcurv e (Morgans, 1956),bu tthi si sles saccurat ean dmore ,tim econsuming . TheQiMjQ ,inde x (Doeglas,1968 )wa scalculate dwit hthes equartil evalues .I n this indexth eph ivalu e0 i sreserve dfo rth efines tcla yfraction ,instea do fth e value 10,an dal lph ivalue s largertha nzer oar esubstitute db yth enex thighes tin ­ tegervalu e (Table 3). Thismean s that,accordin gt othi s system,th efractio ninde x (thesubstitutin gph ivalue )fo rth eparticl e sizescoarse rtha n1- 2m mi scalculate d by takingth enegativ ebinar ylo go fth euppe rlimi to fth efractions ,bu tfo rth e fractionsfine rtha n1 m mthi si sdon ewit hth elowe rlimit .I nfact ,a positiv e fractioninde xi srounde dof ft oth enex thighes tpositiv e integervalu ean da

negativefractio ninde xt oth enex t lowestnegativ e integervalue ,e.g .Q, 5 =-2.1 5

becomesQ 1 =- 3o r3 an dQ so =2.1 5become sM ,= 3 .

3.2.3 Macrofauna analysis

The lowerlimi to fth esmalles tmacroinvertebrate scollecte dwa sdetermine db y twofactors :the yhad t ob evisibl et oth enake dey ean di tshoul db epossibl et o handlethe mwit ha pai ro fpincers .I ngeneral ,animal swit ha bod y lengthsmalle r than1 m mwer eno tcollected .Wheneve rver y smallmidg e larvaewer e observed,thei r smalltube so nth ebotto mo fth esortin gpa nbein gclearl yvisible ,i twa s recorded. Inmos tcase sth elarva ethemselve swer eno tvisibl et oth enake deye ,an dthei r numberswer eno tinclude di nth efina lresults . Identificationo fthes ever y small larvaeshowe dthe mt obelon gt oth eTanytarsini ,mainl y Micropsectra gr. praecox. First instarso fman y faunalgroup sar emisse db ythi smetho do fsorting .Howeve rt o includethes einstar sa swel lwoul dmak ei tnecessar yt oexamin eal lsample sunde ra stereomicroscopeo ra larg emagnifyin gglass .Thi si sver ytim econsumin gan dth e largenumbe ro fsample sdi dno tpermi t this. Animalswer ecollecte dquantitativel y fromth esamples .Onl yi nsample swit h hundredso f(juvenile ) Gammarus orChironomida elarvae ,wer e theseabundan tspecie s counted,afte rremova lo fal lothe rspecie san da representativ epar to fth eabundan t species.T othi send ,th eremainin g samplewa sspli t into4-1 0equa lportions . After identificationo fal lanimal si na sample ,th ecounte dnumber swer e addedt o thecollecte dnumber so fth especie sconcerned .I fi tconcerne dmor e species(e.g . Chironomidae),th erati ofoun di nth ecollecte dnumber swa ssuppose dt ob epresen ti n thenot-collecte dpar ta swel lan di twa suse da sa measur et odivid eth ecounte d

23 numbersove rth especies . Incountin g tube-buildingChironomidae ,th erati obetwee nempt yan dinhabite d tubeswa stake n intoaccount .Empt ycase so fcaddi san ddea dmollusc swer e collected aswell ,bu tthe yar eno tinclude di nth eresults .Sometime shal fspecimen so f Ephemera danica (Ephemeroptera)an d Mieropterna sequax (Trichoptera)wer e found. Theyprobabl yha dbee ncu ti ntw ob yth eshovel .Thes ehal fspecimen swer e considered tob ewhole . Thecollecte dmacroinvertebrate swer ekille dan dpreserve di n8 0I (V/V )ethano l whichwa srenewe d aftersom eday san dagai nafte r identificationo fth ematerial . Tricladidawer e identifiedaliv ean dwer eno tpreserved . Identificationwa s carriedou twit hth emos trecen tkey san ddescription s available (thekey suse dar eliste di na separat eliteratur e list). Identifications carriedou t withkey s thatprove dt ob eou to fdat ewer e redonewit hth elates tke y(e.g . Seri- oostomai personation andNotidobia ciliaris (Trichoptera)larva e identifiedwit hth e keyso fUlme r (1909),Hicki n (1976)an dLepnev a (1964)wer e checkedwit hth eke yo f Wallace (1977),whic h showed thati tconcerne donl yon especies : Seriaostoma personation. As showni nTabl e4 ,th eleve lo fidentificatio nwa sno tth esam efo ral ltaxa . This levelmainl y dependedo nth eavailabilit yo fkeys ,bu ti tals oprove d impossible to identify certainjuvenil e specimens,especiall yo fth eChironomida ean dth e Trichoptera.Whe nther ewa sdoubt ,identification swer echecke db ysevera l Dutch specialists (Simuliidae,drs .J.J.P .Gardeniers ;Chironomidae ,dr .H.K.M .Molle rPillot ; Trichoptera,dr .L.W.G . Higler;Coleoptera ,drs .J .Cuppen) . Larvalan dpupa l iden­ tificationso fsevera lspecie so fTrichoptera ,Ephemeropter aan dPlecopter awer e checkedo nth eadult sb yrearin g themi nth elaboratory : Potamophylax luctuosus, Mieropterna sequax, Chaetopteryx villosa, Seriaostoma personation, Agapetus fusoipes, Lithax obsaurus (Trich.), Ephemera danica, Eabrophlebia fusoa (Ephem.)., Nemoura cinerea, Amphinemura standfussi (Plec). Forth emajorit yo fth especie s (Table 4), body lengtho fal lspecimen swa s measuredi n1 m msiz eclasses .Althoug hmeasurement so fhea d capsulewidth i softe n themos taccurat ewa yt odetermin eth einstar ,thi smetho dwa sno temploye dbecaus e iti sver ytim e consuming.Besides ,th eobjectiv ewa sno tth econstructio no fth elif e historyo fthes e speciesbu tth edeterminatio no fpossibl e differencesi nsubstrat e preferencesbetwee nsmalle ran dlarge r (youngeran dolder )specimens .Bod y lengthi s certainly accurateenoug ht omak e thisdistinction . Bodylengt hwa smeasure dusin gth estereomicroscop ewit hmillimetr e graphpape r underth epetr idis hcontainin gth eanimals .Th edistanc ebetwee nth eanterio r edgeo f thehea dan dth eposterio redg eo fth eabdome nwa smeasured ,excludin g antennaean d caudalappendage sa scerc io rbreathin g tubes.Th elengt ho fcontracte d specimen(e.g . Plecoptera)wa sdetermine d afterbringin gth eanima lbac k intoit s'normal 'position . Curvedanimal s {Gammarus') weremeasure di na standar dposition ,wit ha naverag ebod y curve.Thi s reducedth eabsolut ebod y lengthb yapproximatel y 25°s,givin ga maximu m body lengthfo r Gammarus pulex of1 8mm ;key s state2 4m mfo rth elarges tmales .

24 Table4 .Identificatio n levelfo rmacroinvertebrate san dindicatio no f body lengthmeasurements .

Macroinvertebrate s Body Identificationleve l length measumeasuremenr t Order Family Genus Species/group

Tricladida Oligochaeta Hirudinea Amphipoda X Isopoda Hydracarina Plecoptera X Ephemeroptera X Odonata Heteroptera Trichoptera X x Coleoptera X5 (x) Diptera X Chironomidae X Tipulidae X Dixidae X Ptychopteridae X Simuliidae X Psychodidae X Ceratopogonidae X Culicidae X Stratiomyiidae X X Empididae X x. Tabanidae X Dolichopodidae X Tetanoceridae X X Ephydridae X X Mollusca X Bivalvia X Gastropoda

l:Onlyth ehighe rleve lwa suse dfo rresults ;2 : Eiseniella tetraedra and Stylaria laoustris; 3:Baetidae ;4 :Juveniles ;5 :Onl y larvae;6 :Pupa e

0£fiv eTrichopter aspecies ,hea dwidth ,hea dlength ,cas ewidt han dcas elengt h weremeasure di nadditio nt obod ylength .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

3.3.1 Artifioal stream channel experiments

3.3.1.1 Thestrea m

Substrate-selectionexperiment swer eperforme di na nartificia lstrea mchannel . Thedesig nfollowe dtha to fLauf f& Cunmin s (1964)an dFeldmet h (1970).Th echanne l wasconstructe do fPerspex ,4 2a nwide ,20 0c mlon gan d3 0c mhig h (Fig.10) .Wate r

25 '\AAA1B

Fig. 10.Pla nvie wo f theartificia l stream (measurements in cm). IS= inle tsection ; PKW= permanen t knifewei r (h = 1 8c m );P P= pip eplat e (diam. =4 cm ;h = 1 8c m) ; BP= buffe r plate;S T= substrat e trays (h= 3 cm); AKW= adjustabl eknif ewei r ( h= 0-1 8 cm );C U= coolin gunit ;R = reservoi r (15 01 ) ;P = pump ;F S= filte r section;ER S= en dretainin g screen (mes h= 0. 5m m );SC C= shor t cutcircuit ; streamheigh t= 3 0cm ;strea mwidt h= 4 5c m ;strea mlengt h= 23 0cm .

26 was circulated froma coolin g reservoirwit ha n immersionpum p (maximumcapacit y 300 1/min)tha trelease d it ina smallreservoi r inth estream . Fromher e itflowe d over aknif ewei ran dthroug h a4-cm-thic k tubeplat e (consisting ofpipe so f 4m m inner diameter)befor eenterin g theexperimenta l area ina lamina r flow.A t the endo fth e channel thewate r flowedove r asecon d knifewei r and througha filterbac k intoth e cooling reservoir.Th ewate rwa scoole db ypassin g itthroug ha silver-coated copper spiral filledwit hFreon ,whic hwa s circulated by acompressor .Al l experiments were conducted ata temperatur e of 11C ,th eminimu m temperature thatcoul db e reached with awate rdept ho f 10c man dcurren t speedo f 10cm/ s (themaximu m speed used). Waterdept hwa sregulate db y theheigh to fth edownstrea mweir .Curren t velocity couldb eregulate db y returningmor eo r lesso f thepum p flowdirectl ybac k intoth e reservoir.Ta pwate rwa suse d inal l experiments because itwa so fexcellen t quality. After eachexperiment ,an da t least twice aweek ,th ewate rwa s changed. Sub­ strateswer e introduced in4 0trays ,eac h 10c mx 15c mx 3cm ,i n4 paralle l rows. Itwa spossibl e todivid e thechanne l intw oparalle l channelswit h theai do fa Per ­ spexpartition : tworow so ftray s ineac hchannel .Removabl e screens (1.3m mmesh ) coulddivid e thestrea m into sectionsó fa minimu mo f 2an dmaximu mo f4 0tray spe r section.Upstrea man ddownstrea mo fth eexperimenta l areaa Perspe xplat ewa s laida s abuffe rbetwee n the experimental areaan d theen d retaining screens.Th e surface of theseplate swa s levelwit hth esurfac eo fth e filled substrate traysan d roughened by amonolaye r of 1-2m m sandgrain sglue d toth eplate . Illuminationo fth estrea mfollowe d theoutsid e lightpattern ,durin gth eda y supplemented with time-switch-operated fluorescent daylight lamps.

3.3.1.2 Substrates tested

Substratesuse d inth eexperiment swer eobtaine db y storing allsample s from the Snijdersveerbeek bygrai nsiz eafte r substrate analysis. Inexperiment s allgrai n sizesrangin g from0.05 0t o3 2m mwer eused ,togethe rwit h leafpack s and coarse detritus.Substrate swer e arranged ingrade d serieswithi n eachexperimenta l section ina numbe r of standardposition s according toth emode lpresente d inFig . 11.A test onth e influence ofth e substräte-trayarrangement s showed that for species tested therewa sn o significant difference insubstrat e selection connectedwit h thearrange ­ ment,apar t from the influence ofth ecurren t velocity.

3.3.1.3 Experimental design

All experimentswer ereplicated ,partl y atth e sametim e in2 o r 4paralle l series.Th e finalnumbe ro fexperiment s varied from speciest o species. Substrate selectionwa sassessse d after afixe dperiod ,whic hwa sdetermine d experimentally for eachspecies .Fo rmos t speciesth esubstrat e selection showedn o significant differences after 2,4 ,6 ,8 , 12o r 24hours ,whic hmean t thatal lobservation s couldb emad e

27 II

125 2 2 125 125 2 2 125

250 4 4 250 250 4 4 250

500 8 8 500 500 8 8 500

1 16 16 1 1 16 16 1

II

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

V IV III II ] 2 16 0 © © © 4 2 8 1 8 4 O © © © 1 8 2 4

8 2 125 250 500 1 1 500 250 125

16 4 16 8 4 2 2 4 8 16

Fig.11 .Th emos t commonsubstrat etra y arrangements.Eac h grain-size fractioni s indicatedb yth elowe rlimi to fth efractio n iny mo rm m (125= 0.12 5- 0.25 0mm ; 2=2-4 mm).Wate r runsfro mrigh tt oleft .Arrangement sa- c :Section s Ian dI I haveopposit e arrangements regardingupstrea mo rdownstrea m placemento fth efin e andcoars esubstrates .Section s IIIan dI Var ereplicate so fSection s Ian dII , respectively. SectionV i salternatel y areplicat eo fSection s Ian dII ,rearrange d aftereac h experiment.Arrangemen td :Tw oparalle l streams:4 tray spe rSection s IAan dII Ai nopposit earrangements .III Aan dIV Aar eals oopposit earrangement s andcomparabl ewit h IAan dIIA ,excep tfo rth elea fpack s (circled)place do nto p of theminera l substrate.V Aan dV Bar eopposit earrangements .IB+II Ban dIIIB+IV B areopposit ean dca nb ecompare dwit h Sections Ian dI Ii nArrangement sa-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 swere lef tregularl yi nth eexperimenta lare afo r2 4 hourst ohav ea chec ko nth eselectio nperiod . Specieslik ecase-buildin gTrichopter a thatca nb ehandle dwit ha pai ro fpincer swer eintroduce di nth eexperimenta lare a byplacin gthe mo nto po feac hsubstrat etra yi ndensitie so f2 o r4 animal spe r tray,althoug hdensitie so f3 ,5 ,6 o r8 specime npe rtra ywer euse da swell .Thi s

28 willb eindicate dfo reac hexperimen ti nth eresults . Afterth ese tselectio nperiod ,th eposition so fth eanimal swer erecorde dan d theanimal scollecte db ypickin gthe mof fth esurfac eafte r lightlystirrin gth esub ­ strate in situ. Morevulnerabl e species,lik e Ephemera danioa, were introducedb y placingthe mo nth efille d traysi na smal lpetr idis han dlettin gth enymph s swim awayo fthei row nvolition .Fo rthes e animalsparticle-siz eselectio nwa s determined byremovin gth etray s fromth estrea man dcarefull ybringin gth econtent si na large r traywit hwate ro fth esam etemperature .Th esam eretrievin gproces swa suse dfo r speciesdifficul tt otrac e in situ, e.g.smal l larvaeo f Seviaostoma personatum.

3.3.1.4 Species tested

Experimentswer econducte dwit hsevera l instarso ffou rTrichopter a speciesan d oneEphemeropter a species.Tabl e5 summarize sth especie san dinstars ,includin g possibledifference si ncase-buildin gmateria luse db yth ecaddi s larvae.

3.3.1.5 Theinfluenc eo 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 mtrays .Experiment swer econducte d withsevera lparticle-siz ecombination san dselectio nperiods .Fo rspecie s that showedn osignifican t differencesi nsubstrat e selectionbetwee nupstrea man ddown -

Table 5.Species , instarsan d casebuildin gmateria l insubstrate-selectio n experiments.

Species Instar Length/mm Case-building material Miaropterna sequax F >1 5 mineral (F ;F-l ) F-l 10-15 organic (leaves/detritus) F-2 6-10 (F-2 ;F- l ;F ) 1/2mineral -1/ 2organi c (F-2 ;F- l ;F ) 1/2 pupal (mineral,on een d enlarged Chaetopteryx villosa F >1 0 mineral organic 1/3mineral -2/ 3organi c 1/2mineral -1/ 2organi c 1/2 pupal (mineral,oneen d enlarged) Seriaostoma personatum F 11-14 mineral F-l 8-11 mineral F-2 7-10 mineral F-3 6-7 mineral Ephemera danioa 15-20 15-25 20-25

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

3.5.2 Rearing ohannel

A small rearing channel similart oth elaborator y streamdescribe db yHigle r (1975)wa suse dt oacclimatiz e animalst olaborator y conditionsan dt okee p themi n stockfo rexperiment si nth eartificia l stream described inSectio n 3.3.Wate r tem­ peratures followedth 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-mesh screens dividedth echanne li nsection st okee pth edifferen t species apart,an dscreen so nto pprevente d emerging adults fromescaping . Substratei nal l sections consistedo fa 3 c mthic kmixtur eo fsan dan dgravel ,wit h additional stones and sticks.Fres h leavesan ddetritu s collected fromth eRatumsebee kwer e supplieda s foodan dadditiona l substrate. Illumination followedth eoutsid e lightpattern . Several specieso fTrichoptera ,Ephemeropter aan dPlecopter a (seeSubsectio n 3.2.3)wer e rearedsuccessfull yt oadults .Som e species evenmate d although only Serioostoma personation produced eggsi nth estrea m (thesehatche d later).

3.3.3 Experiments with Trichoptera

Case-buildingmacroinvertebrate s oftenus ematerial s fromth estrea mbe dfo r theircases .Trichopter a formth emajo r groupo fanimal s thatus eminera l and/or organicmateria lt obuil d their cases.Othe r groupsar etube-buildin g Chironomidae and case-building Lepidoptera.Th e(grain-size )compositio no fth ecase smigh ta t leastpartl y reflectth esubstrat e compositiono fthei rhabitat .Th epresenc eo r absenceo fcertai ngrai n sizeso rorgani c substratesmigh tb ea facto r determining thepresenc eo rabsenc eo fcertai ncase-buildin g speciesi na habita to rstream . Caseso ffiv e specieso fTrichopter awer e analysedo nthei r grain-sizecomposi ­ tion.Wit h four species,cas ebuildin g experimentswer e carried out,offerin g several grain sizesan dorgani cmaterial sa sbuildin gmaterials ,whil eth elatte r alsofunc ­ tioneda sfood .Additiona l experimentswer eperforme d inwhic honl y sub-optimalma ­ terialswer eoffered .

3.3.3.1 Case-building experiments

Experimentso nth ecase-buildin g behaviouro ffou rspecie so fTrichopter awer e conductedi ntemperatur ean dphoto-perio d controlled climate cells.Da ylengt h followedth enatura l patternan dtemperatur ewa shel da t1 4C + 1 C .Experiment swit h Mioropterna sequax, Agapetus fusaipes and Lithax obsourus wereperforme di npetr i dishes filledwit hwater .Fo rbuildin g experimentswit h Serioostoma personation, 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 not coloured very finesan d 0.125 -0.25 0 red finesan d 0.250- 0.50 0 whitequart zsan d medium sand 0.500- 1. 0 green coarsesan d 1.0 -2. 0 blue very coarsesan d 2.0 -4. 0 not coloured finegrave l

mlglas sbeaker swer e two-thirdsfille dwit hwate ran daerate dwit hcompresse dai r 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 fleave san dcoars edetritus ,collecte di nth eRatum ­ sebeekan drinse di nta pwater .I norde rt ofacilitat eth erecognitio no fth egrai n sizesuse db yth eanimals ,al lfraction s (rangingfro mver 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 tfo r1 4day so ncoloure d substratesan d showedn oreductio ni nactivity )an dth ein kdoe sno talte rth esurfac e structureo f thegrains .Th egrai nsiz efraction suse dar eliste di nTabl e6 . Foreac hexperiment ,som eo ral lgrai nsize swer eprovide d togetherwit ha fe w freshan dol dbeec hleaves .Larva e (eachi nit sow ndis ho rbeaker )wer e introduced withoutthei rcase so rwit honl yth efron thal fo fth ecase sremoved ,afte rhavin g beenadapte dt oth eexperimenta l conditionsfo ra fe wdays .The ywer e lefti nth e experimentalcell sunti lthe yhad complete dth ebuildin go fthei r finalcase .Thi s wasmostl yreache dwithi n7 day s aftercompletin ga nemergenc ycas e thatwa sbuil d within2- 3day safte r introductionint oth eexperimenta l area.Afte reac hbuildin g experiment,th enumbe ro fgrain si neac hsiz efractio nuse di neac hcas ewa scounte d andth erelativ eproportio no feac hsiz efractio ni nth etota lcas esurfac ewa s calculated.Th emetho duse dfo rthi scalculatio nwil lb edescribe di ndetai lb y Tolkamp& Verdonscho t (tob epublished) .

3.3.3.2 Grainsiz eanalysi so fnatura lTrichopter acase s

Tocompar eth egrain-siz e selectioni nth ecase-buildin g experimentswit hth e compositiono fth enatura lcase sth elatte rwer e analysedfo rthei rgrain-siz ecompo ­ sition.Afte rmeasurin g caselengt han dcas ewidth ,togethe rwit h larvalbod y length, headwidth an dhea d length,case so fwhic h lesstha napproximatel y 5%o fth esurfac e consistedo forgani cmateria lwer ecombine di nclasse so f1 0o rmor efo reac hlarva l instar.Whe nenoug hmateria lwa savailabl eclasse swithi neac h instarwer edistin ­ guishedo nth ebasi so flarva lhea dwidth. Case swit hmor e than 5%organi cmateria l weretreate dseparately .

31 Grain-size analysiswa scarrie dou tafte rdissolvin gth eorgani cmateria lan d salivary secretionb yboilin gth ecase si n30 1 (V/V)H^O ,fo r2 4hours ,followe db y treatingth eremainin gmateria lwit h1 N HC Lan drinsin gwit hwater .Afte rdryin gi n a stovea t11 0C ,1 3grain-siz e fractionswer edetermine db yhan d sieving,usin ga s many sievesa savailabl e (diameter 10cm )wit hopening s of: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 e proportiont oth etota lminera l caseweigt hwa s calculated. Itsrelativ eproportio nt oth esurfac e areao fth ecas ewa scalculate d withth eai do fexperimentall y determined factors (seeTolkam p& Verdonschot ,t ob e published).

3.4 FIELD EXPERIMENTS

Inorde rt ochec ki nth efiel dth eselectio nb yth emacroinvertebrate so fth e grain-sizeo fth esubstrat e severalmethod swer euse dfo rth eintroductio no farti ­ ficial substratesi nth enatura l environment.

3.4.1 Artificial substrate trays

Sincen oexperienc ewit hth eus eo fartificia l substrate samplerswa 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 s studywil lb epublishe d elsewhere (Tolkamp& Verdonschot ,t ob epublished) . Wirebasket sar eonl yfi tfo rrelativel y coarse substrates,sinc e finermaterial s needt ob eintroduce d inclose d containers,e.g .plasti co rti ncan s (Khalaf, 1975). Forth eexperiment s described inthi s subsectiontw osize so fshallo w plastic trayswer eused .Thes e traysmeasure d 13.25c mlengt hx 8 c mwidt hx 3 c mdept han d 18.25c mlengt hx 12.2 5c mwidt hx 3. 5c mdepth ,givin g contentso f31 8c m and 782c m, respectively .Th esmal l trayswer e filledwit h approx.60 0g o fsubstrat e andth elarg e trayswit h approx. 1300g ;al ltray swer e filledt oth ebrim .Al lex ­ perimentswer ecarrie dou ti nApri lan dMa y197 8i na sectio no fth eRatumsebee k with amore-or-les sunifor m gravel-sandsubstrate ,unifor m flowove rth etota lwidt ho f the streambe dan da wate r deptho f5-1 0cm .Tray swer eplace d inth estrea mbe di n rowso fthree ,space d5 0c mi nwidt han dlengt h fromneighbourin g trays. Initially,fo reac hcollectio n date6 smal l trayso feac hgrai nsiz ewer euse d with1 larg e tray,excep tfo rth e8-1 6m mgrai n size,fo rwic h4 larg e trayswer e usedfo rth efirs tse to fexperiments . Lateron ,onl y2 larg e trayswer euse dfo r eachgrai n size,th eamoun to favailabl e substratean dtim et owor ku pal lsample s beingth erestrictin g factors.Smal l trayswer euse da swel l inth elate r experiments, butal lwer e lost duringon eperiod ,bein g removed fromth estrea mb yperson s unknown. Thetray swer edu gint oth estrea mbotto ms otha t theywer e levelwit h it. The substrate fromth estrea mbe dwa ssmoothe dove rth eedge so fth etray san dwha twa s

32 Table7 .Numbe ro fsubstrat e trays foreac hgrai nsiz ean d periodo f colonization inth eRatumsebeek .

Period of Number of traysb y grain 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 • • 1 h 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 ddownstrea mo fth eexperimenta l section.Tray swer e retrieved afterdifferen t periods,rangin g from4 day st o4 week s (Table 7). Animals were sortedi nth elaboratory ,organi cmatte rwa spicke dout ,drie dan dweighe dan d thegrain-siz e compositiono fth eminera l substrate inth etray swa sdetermine dt o establishth eamoun tan dnatur eo flos tan dgaine d substrate.Onl yo ntw ooccasion s wereth etra ycontent swashe d out,i nwhic hcas eth esampl ewa somitted .

3.4.2 Artificial substrates introduced without trays

Dug-intray s filledwit h substrateca nonl yb ecolonize d fromabove .Horizonta l migration throughth estrea mbe do rvertica lmigratio n frombelo wi sprevente db yth e trays,side san dbottoms .Moreover ,th etray s themselvesma yac ta sa nattachmen t sitefo rclingin gan dsuckin ganimal s (e.g.snail san dleeches )an dthe yar egraduall y colonizedb ydiatoms ,bacteri aan dfungi ,trappin g finedetritu s inthei r turn,pro ­ viding foodan dfoothol dfo rman ymacroinvertebrates . Inorde rt oexclud e thesepossibl ydisturbin g influences,severa l grainsize swer e introduced intoth estrea mbe dwit hn ocasin garoun d them.Channel s3 c mdeep ,1 5c m widean d7 5c mlon gwer edu gi nth estrea mbotto man dfille dwit hdrie d substrate; onegrai nsiz ei neac hchannel ,eigh tchannels ,i ntw orow so ffour . Theupstrea mro wcontaine d grainsize so f0.250 , 8.0,4. 0an d0.50 0n man dth e downstreamro wgrai nsize so f1.0 ,16 , 2.0an d0.12 5mm ;th ecoarses t grain sizesi n themiddl eo fth estream ,th efines to nth eedges .Afte ron emonth ,3 sample swer e takenfro meac hgrai nsiz ewit hth emicro-macrofaun ashovel .Th esample swer e sorted inth elaborator yan dth esubstrat e analysed followingth enorma l procedures.Thes e experimentswer ecarrie dou ti nNovember-Decembe r 1978i nth esam esectio no fth e Ratumsebeeka swher eth esubstrat e trayswer e introduced.

33 3.4.3 Litter bags

Leaves forma nimportan t substratefo rsevera l specieso 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 n ratesan dcolonizatio nb y macroinvertebrateso falde r (A),oa k(Q) ,beec h (F)an dpopla r (P)leave s during different incubationperiods. A detaile ddescriptio no fthi s studywil lb epublishe d byTolkam p& Kno l (tob epublished) .

3.5 DATA PROCESSING

3.5.2 Data storage

All fielddat awer eprocesse dwit hth eai do fth ecompute ro fth eAgricultura l Universityo fWageningen .Samplin g dateswer e transformedt oyea ran dwee knumbers . Field classificationo fth esubstrate swa sbinar y codedb yth epresence/absenc eo f the sevenmai ngrain-siz e classesmentione d insubsectio n3.1. 3(th esmalles tan d largestparticl e sizeswer eno tused )an dth epresence/absenc eo fth ethre e detritus classes.Th esubstrat e stabilitywa s recordeda sstabl eo rshifting .Weight so f particle-size fractionswer e roundedof ft oth eneares t gram,sinc ethi s hardly influencesth epercentage so feac hfractio no rth equartil evalue s calculated later. Animalswer e codedb ynumber s (Appendix 1). Length classeswer e indicatedb yth e upper limito fth eclas s (i.e .1- 2m m= 2) , witha separat e codefo rpupa e (99)an d adults(98) . Datawer e storedi ntw odat a filesfo reac hstream .Th efirs t filewit hth edat a ofth esampl e (stream,section ,sampl enumber ,year ,week ,fractio nweights ,fiel d classification,numbe ro fspecies/taxa ,numbe ro fspecimens) .Th esecon d filewit h thedat aconcernin gth especie san dth enumbe ro fspecimen si neac h lengthclass , togetherwit hth esampl e code.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 e file)an db yth ecompute r (fromth especie s file). Afterthes e andothe rchecks ,t oeconimiz eth eprograms ,th esampl e filewa sextende dwit hth e Q-iMiQ,inde xan da binar y filefo rth epresence/absenc eo feac hspecies . Withth eai do fsevera lprograms ,develope di nclos e cooperationwit 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 l classifi­ cations,percentag e occurrencei ndifferen t substrate typesan dWhittaker' s Indexo f Association.

34 3.5.2 Statistical methods

Statisticalmethod suse dfo rtestin g significanceo fcertai n (calculated)dat a areexcellentl y describedi nsevera ltextbooks .Th ebette rpar to fth emethod suse d inthi sthesi sca nb efoun di nEllio t (1977b). Distributiono ftax aove rdifferen tsubstrat etype swa sexpresse da sth eInde x ofRepresentatio n (I.R.)(Hildre w& Townsend ,1976 ) (Table8 )an dstatistica lsignifi ­ cancewa s testedwit hth echi-square d test.Calculatio no fth eI.R .value si sbase d onth enul lhypothesi s (H) thata specie soccur si nal lsubstrat e typesi nequa l densities.H isaccepte dwhe nth edifferenc ebetwee nobserve dan dexpecte d densities isno tenoug ht oyiel dchi-square dvalue sabov eth e5 1level .H isrejecte dwhe n chi-squaredvalue sar ehighe rtha nth e5 $leve li na chi-square d distributiontabl e (e.g.Lindgre n& McElfath ,1970 ,Tabl eII) . WhenH isrejected ,thi s isa nindicatio no funde ro rove rrepresentatio ni n oneo rmor eo fth esubstrat e types.Positiv eI.R .value s indicateove rrepresentatio n andnegativ evalue s indicateunde rrepresentation .However ,difference si nI.R . valueswer eonl yconsidere dt ob esignifican twhe nth evalue sdeviate d2 o rmor e from zero.Onl yvalue soutsid ethi srang e(- 2t o+2 )wer econsidere dt ob eindicativ efo r aversiono rpreference ,respectively ,fo rcertai nsubstrat etypes .A nexampl eo fth e calculationo fth eI.R .value san dchi-square s isgive ni nTabl e8 . Whittaker's (1952)Inde xo fAssociatio nwa suse dt ocalculat eth edegre eo fcom ­ patibilitybetwee nsubstrat etype so nth ebasi so fspecie scomposition .Thi s indexi s calculatedb ysummarizin gth eminimu mpercentage so foccurrenc eo feac hspecie si na seto ftw osample so rsubstrat etypes :

S W= Z min(a. , b-), n=1 1 1 wherea .an db .ar eth epercentage so foccurrenc eo fth ei speciesi nth esample s Aan dB ,an dS i sth enumbe ro fspecie soccurrin gi nbot hsamples .

Table8 .Exampl e forth ecalculatio no fth e Indexo fRepresentatio n (I.R.).

Substrate type Total

I II III Number of samples 20 15 15 50 O= observe d number of species1 120 30 0 150 E= expecte dnumbe r of species 1 60 45 45 150 I.R. value 7.75 -2.24 -6.71 x2 =110.0 0

/ 9 p 2 I.R. = (O- E) // E and x =2 (O- E )/ E n=l where E= thetota l number of species imultiplie db y theproportio no f thesample s ina substrat e type inth etota l seto fsamples.wit hp substratetypes .

35 Clusteranalyse swer e carriedou twit hth eClusta n 1Cprogra mwritte nb y Wishart (1975)tha t ispresen t inth e library files ofth eCompute r Centre.I.R .value swer e useda sra wdat afo rsevera l linkagemethod s todistinguis h groupso fspecie swit h similarpreference so r aversions forcertai nsubstrat e types.Sinc eothe rmethod s testeddi dno t leadt oothe r conclusions,th emetho duse d forpresentin g the results isWard' smetho d ofhierarchica l linkageusin g the error sumo fsquares .

36 4 Results

4.1 DATA

4.1.1 Field classification of substrate types

Forstatistica ltreatmen tth emultitud eo fpossibl ecombination so fth eindivi ­ dualsubstrat echaracteristic shad t ob erestricte dt oa maximu mo f1 4substrat e classes.Thi smean stha tsom etype sdistinguishe di nth efiel dwer ecombine dlate ri n ordert oobtai nsubstrat eclasse s containing enoughsample st oallo wstatistica l treatment. Fourclassificatio nlevel swer eused ,wit h3 (Sor t 3), 5 (Sort 4), 7(Sor t2 )an d1 4 (Sort1 )substrat eclasse s (Fig.12) ,respectively .Appendi x2 give sth enumbe ro f samplesi neac hsubstrat eclas sfo rth eSnijdersveerbee kan dAppendi x3 thos efo rth e Ratumsebeek. Onth efirs tleve l (Sort3 )sample swit hminera lsubstrat ewer e distinguished fromsample sconsistin gmainl yo forgani cmatte r (coarsedetritu sand/o r leaves). Samples classifieda sorgani calway s contained lesstha n15 0g minera lmateria lan d theaverag edr yweigh to fth eorgani cmatte rwa s2 1g pe rsample .Minera lsample sal ­ ways containedles stha n8 g detritu san da naverag eo f90 0g minera lsubstrate .

Sort division criterion 3 Sand Gravel Detritus S/D/FD G/D/FD D/FD

St.S Sh.S S+L S+L S+CD S+L BG G+L/FD G+CD/FD CD/FD L/FD CD+L/FD +CD +CD +FD +FD +FD Fig. 12.Substrat e typesbase do n thefiel dclassificatio no f thesubstrate s atfou r levels (Sorts1 ,2 ,4 ,3) .S -Sand ;G =Gravel ;CD =Coars eDetritus ;L =Leaves ; D=Coars eDetritu s and/orLeaves ;FD =Fin eDetritus ;B =Bare ;St =Stable ;S h= Shifting; += with ; -= without ; /= wit ho rwithout .S+L+C Doccurre d only inth e Snijdersveerbeek (Snijb).S+L+CD+F Doccurre d only inth eRatumsebee k (Rab).

37 Mineralsample swer e distinguished inSan dan dGrave l onth ebasi s ofth edomi ­ nant grainsize s (Subsection 3.1.3).However ,t oobtai na mor e objectivemean s to separate sand andgrave lsubstrates ,th emedia nparticl e sizedetermine d afterdr y sievingwa suse da swell .Sample swit h anegativ emedia nph ivalu e (M,< 0 ,i.e . 50% ormor ecoarse rtha n 1mm )wer e reckoned amonggrave lan dsample swit ha positiv e medianph ivalu e (M,> 0 ,i.e . 50°so rmor e finertha n 1mm ) among sand. This classification caneasil yb e obtained inth e field aswell ,usin g astandar d comparisonsystem .Thi s isa metho d tob e recommended forfutur estudies ,bu t itwa s notuse d inthi sstud ybecaus e the author learnedo f itto o late.Figur e 13give s the quartilepercentag e ofth e samples classifiedwit h thismetho d asGrave lo rsand . Very littleoverla p occursbetwee n the first (CO andth e third (Q,)quartil e values ofGrave lan dSand .Th e twopeak s ineac hquartil e illustrate the correctness ofth e choice fora media nparticl e size of 1m m (M,= 0)a sth eboundary . Comparison of thisdivisio nwit h the field codeshowe d that thepresenc e of arelativel y small proportion ofcoars eparticle s iseasil y over-estimated because the coarsemateria l ismor e abundant atth e surface ofth esubstrat e thandeepe r inth ebottom . These sampleswer e oftencode d asFG+S ,whic hshoul dhav ebee nS+FG .However ,suc h differences arever ydifficul t toquantif y ina classificatio n system,emphasizin g thenee d fora parameter todistinguis h thesesubstrates . On thesecon d classification level (Sort 4), thetw ominera l classeswer efur ­ therdivide d onth ebasi s ofth epresenc e ofCoars e Detritus and/orLeave s intoSan d orGrave lwit h orwithou tCoars eDetritu s and/orLeaves .Togethe rwit h thepurel y organicsubstrat e class ofth e first levelthi sgive s fivesubstrat e classes forthi s classification level. Onth e third level (Sort 2), theminera l classeswer e furtherdivide d into classeswit h andwithou t FineDetritus ,givin g seven classes intotal ,sinc e Gravel substrates combinedwit h CoarseDetritu swithou t Fine Detritus didno toccur . Onth e fourth level (Sort 1), all classeswit h detrituswer e divided into classeswit h orwithou tLeaves ,Coars eDetritu s ora combinatio n ofboth .Thi s isth e first levelwher e the organic class isdivided .O n anyo fth e firstthre e levels a more detailed classification ofth e detritus sampleswa sno tpossibl e since some classeswoul dhav e contained toofe wsamples . For theminera l substrates some theoreticallypossibl e classes hadt ob e combined toobtai nclasse s largeenoug ht ojustif ystatistica l treatment. Inorde rt o include allspecie s except incidental ones it isnecessar y tocombin e at leastsi xsample s in eachsubstrat e class (Tolkamp,t ob epublished) .However ,on esubstrat e class inth e Snijdersveerbeek (S+L+CD)containe d only 3samples .Thi s classwa smaintaine d anyway because itwoul dhav e obscuredpreference s ofsom especie s forS+ Lo rS+CD ,althoug h oneshoul dbea r inmin d thatpossibl e over-representation inthi s three-sample class mustb e considered critically. Inth eRatumsebeek ,severa lclasse s contained less thansi xsamples ,whic hmean s that comparison ofth eresult s ofth etw o streams shouldb emad e ona lessdetaile d level.

38 frequency (%)

60

0-J

frequency(% ) 80

112 3 4 phi index

Fig. 13.Frequenc y distributiono f thefirs t (Q.,)quartil e ,secon d (median)(M d> quartilean dthir d (Q) quartil eove r al"l sample " ~Js "i «--•" nbot --h -stream s Unshaded =Grave lsubstrates •------••;Shade — «.«.-..-d J_ san dsubstrates .

Becauseo fth eus eo fth emedia nparticl esiz e (phivalue )t odistinguis hGrave l andSand ,th efiel dclassification s FineSand ,Coars eSand ,Fin eGrave lan dCoars e 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 eindivid ­ ualspecie san dwhe ncomparin gwit h literaturedat ao nth emicrodistributio no fthes e species. 39 Siltan dlutu msubstrate s only occurred sporadicallyan dwer eno tinclude di n thisresearch .Mi dsubstrate s occurred regularly,bu tthes ewer enormall y accounted fori nth eclasse sS+CD+F Do rS+FD .Mostly i tconcerne da thic k suspensiono ffin e sand,coloure dbrow nb yth eFin eDetritus. Onl y occasionallywer e these substrates blackan danaerobe ,bu tthe nn oanimal swer epresen tan dth esample swer eno tinclude d inth eprogramme . Substrates onlyoccurrin g incidentally (e.g.branches ,tre etrunks ,bricks , kettles,plasti cbags ,bee r tins,aquati cvegetation )wer eno tinclude di 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 gth e microdistributiono fth especie s involved.

4.1.2 Grain-sise classification in the laboratory

4.1.2.1 Substrate composition

The substrate compositiono feac hsampl ewa sexpresse da sth eQiM,Q ,inde x accordingt oDoegla s (1968) (Subsection 3.2.2).Th eexac t 25%,50° san d 7S%quartile s arepresente di nFig .1 4a sth eQiM.Q ,grap ho rsubstrate-characteristi c ofth e streamfo rth eSnijdersveerbeek ,an di nFig .1 5fo rth eRatumsebeek .Th egraph s shouldb erea d frombotto mt oto pa sM ,value s arei na 4 5degre e anglebetwee n abcissaan dordinate ,whil eQ 1 andQ „ar eplotte dbelo wan dabov eth eM ,value , respectively,o fth esample .Thi smean sQ ,an dQ ,shoul db erea d fromth eordinat e (yaxis) ,whil eM ,ca nb erea d frombot h axes. Iti squit eobviou s thatbot h graphsar esimila ran dtha tth eonl y difference betweenth etw ostream s consistso ffewe rdat ai nth eRatumsebeek ,especiall yo nth e coarse (lefthand )side .I tca nb econclude d from this observation thatth etw o streamsca nfunctio na seac hother s twinconcernin gth emineral-substrat e composition. To checkth ereliabilit yo fth eQiM^Q ,grap ha sbein g representative forth esubstrat e compositiono fth estream ,a separat ese to f6 4sample swa stake ni nth eSnijders ­ veerbeek (coveringal lsection swit h6 (Sectio n 7), 8(Section s 1,2 an d3) ,1 0 (Section 5)o r1 2(Section s4 an d6 )samples) .Th eresultin g QiM,Q,grap h(no t presented) fittedexactl y overth egrap ho fFig .14 .I tagai n illustratedth eabundanc e offine ,more-or-les s uniform substrates (M,> 1 )an dth escarcenes so fcoars esub ­ strates,whic hwer e found incidentallyi nth eRatumsebee kan dmore-or-les s restricted *:oStation s6 an d8 i nth eSnijdersveerbee k (thelatte rwa sdr ya tth etim eo fth e check).Fo rbot hgraph si ti sclea rtha tth elarges tnumbe ro fsample swa stake ni n homogeneous,fin esubstrates ,whil eth eothe r samplesar ecompose do fa heterogeneou s mixtureo fcoars ean dfin eparticles .Homogeneou s coarsesubstrate swer ever yscarce . To separate Gravel fromSan d samplesan dSan d fromSil tsample s Doeglas (1968) drewhorizonta l linesthroug hph i= T an dph i= 4 ,respectively .Thi si sth eaccepte d distinctionbetwee nSan dan dGrave l (Cummins, 1962),wher e substrateswit ha media n

40 phivalue s t 5 Ï « Î "d 3J Î . «1

1 •

0

Ï

2^ A,* * A '% A AA A AAA 3 AAAA«a^ A A M A A A 4 ;AA^*A A + 5H V AifA' 4fÄA 6 A' + A

H. (phivalue ) a

Fig.14 .QI MJQO graph f°r theminera l substrate of theSnijdersveerbeek .Th egrap h shouldb erea d frombotto m toto pbecaus eQ andQ areplotte d belowan d aboveth e H value,respectively ,whic h isplotte d ina 4 5degre eangl ebetwee n abcisan d ordinate.

particle size largertha n2- 4m mar eclassifie da sGravel .However ,th eQiM-,Q , graphs illustratetha tespeciall yth eSan dsubstrate s covera wid erang eo fgrai n sizes.Th ecompositio no fth eSan dsubstrat evarie s fromver ywel lsorte d (e.g.222 ) topoorl y sorted (e.g.Ï23 )t over ypoorl ysorte d (e.g.312) .Thu sth ewell-sorte d sandysubstrate sca nb edenominate da spur eSand ,whil eth epoorl y sortedone sar ea combinationo fGrave lan dSand ,wit hSan ddominating .

4.1.2.2 Substratetype s

Todistinguis hsubstrat e typeso nth ebasi so fth egrain-siz e analysisan 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 ,8 o r10 % CoarseDetritu sand/o rLeave s wereconsidere dminera lsamples .Comparin gth eclassification swit heac hother ,thes e

41 phivalu e

V %/ i ,,\ 3 / Ql 2•

1 •

0

Î

2 V V * AAMAM^ A 3 + + A à A^A 4 /SÄÄJ A 4- A AAA A 5 - A

6

M. (phivalue ) a

Fig. 15.Q M Q graph forth eminera l substrateo f theRatumsebeek .Th egrap hshoul d berea d frombotto m toto pbecaus eQ an dQ areplotte dbelo w and above theM value, respectively,whic h isplotte d ina 4 5 15degre eangl ebetwee nabci s andordinate .

ratio's showedtha t2 ,4 ,6 an d8° sadde d little informationt oth e1 1an d10 %divisio n andtha tthi s concerned onlya limite dnumbe ro fsamples .Th elatte rtw opercentage s weremaintained ,expectin gtha tcompariso no fth etw oclassification swoul dyiel d information aboutanimal spreferrin ga combinatio no fminera lan dbetwee n1 an d10 1 organicmaterial .Fo ranimal spreferrin gbetwee n1 an d10 % organicmaterial ,th epre ­ ferencefo rorgani cclasse sa tth eH levelmus t shiftt oth e'mineral 'classe sa t the 101level . Afterthi sseparatio no fth eorgani csamples ,th eminera lsample swer eclassi ­ fiedi nsevera lclassification so nth ebasi so fth eph iinde xo fth efirs tquartil e

(Q1 :Sort 5), themedia n (M,: Sor t6 )an dth ethir dquartil e (Q,:Sor t7 )usin gth e rounded-offquartil evalue s (Doeglas, 1968). Togetherwit hth ethre edetritu s classes

(CD/FD;L/FD;CD+L/FD)thi sgive s1 3classe sfo rQ 1 (7t o3) , Md (7t o3 )an dQ 3( 6 to4 )i nth eSnijdersveerbeek .Appendi x4 give sth enumbe ro fsample si neac hclass . Inth eRatumsebee k lesssample si ncoars e substrateswer etake nan d1 3classe sfo rQ ,

42 (7t o3) , 11fo rM ,( 5t o3 )an donl yeigh tfo rQ 3 (Tt o4 )coul db eseen ,includin g thethre edetritu sclasses .Appendi x5 present sth enumbe ro fsample spe rclass . Severalclasse si nSor t5 t o7 containe donl ya fe wsamples .Thes eclasse swer e not combined furthersinc epreference so fspecie swit ha relativel ylo wabundanc ebu t a specific substrateselectio ncoul db emaske do na less-detaile d levelb yth ecom ­ binationwit h other,no tpreferre d classes.However ,apparen tover-representatio ni n thesesmal lclasse s shouldb econsidere dcriticall ybefor 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 ­ strates7 7differen tQiM^Q ,indice swer ecombine di nsevera lminera lclasse si nSor t 8,als ousin gth eH and10 $organi cmatte rdivisio ni nth esam ethre e organicclasse s (Appendices4 an d 5). InFig .1 6thes esubstrat eclasse sar eindicate di nth e QIMJQ,graph ,whil eth e

M. (phi value) a Fig.16 .Substrat eclasse s inSor t8 projecte d on theQ.MjQ ,grap ho fth e Snijdersveerbeek,xx x indicates theQ.M,Q „inde xo f eachsubstrat eclas s (cf.Appendice s 4an d5) .

43 (XMjQ.,indice s forthes e classes aregive n inAppendice s 4an d 5.However ,whe nmor e thanon e( L,M ,o rQ ,inde xoccurre d ina substrat e class inSor t 8,th e indiceswer e replacedb y anx .On e shouldbea r inmin d thatthi sx doesno tmea ntha t allvalue s canb e filled in.Onl y theph i indices occurring inth eO-M.Q ,grap han d corresponding withth eothe rtw oquartile sar evalid . Classes 1an d 2i nSor t 8ar e the coarsest substrates,characterize db y the median (M,smalle rtha n 3)an d firstquartil e (Q.negativ e andpositiv e forclas s1 and 2,respectively) .I nxx xcod e this ispresente d asxx x andx5 x+ x4x . Inclas s 2, infac txx xshoul db eused ,bu t the onesampl etha tha d anM ,inde xsmalle rtha n5 was asampl e consisting ofa cobbl eplu s a littlebi t ofsan d aspar t ofa detritu s substrate. Classes 3t o6 ar e characterizedb y themedia nparticl e size of 3,2 ,T an d 1, combinedwit h allpossibl enegativ e Q,an dpositiv eQ ~ indices (x3x,x2x ,xïx ,x1x , respectively). Classes 7an d 8ar e characterizedb y amedia nparticl e sizebetwee n1 and 3.Clas s 7ha s anegativ eQ 1 (xxx)whil e class 8ha sa Q 1 between 0an d 1 (1xx).

Inclas s 9,Q 1 andM ,ph ivalue s arebetwee n 1an d 2 (22x). Class 10contain s the 23x substrates.Clas s 11contain sth e 33xsubstrates . Theright-han dpar to fth egrap hwit hM ,value s larger than 3i s formedb y the small amounts ofminera lmatte rpresen t inorgani c substrates andi stherefor e part ofth e classes 12- 14. Comparison ofth e detritus classes inth e field classification with thedetritu s classes inth egrain-siz e classificationusin g the 101 organic detritus levelshowe dtha t thisconcerne d the samesample s inth eRatumsebeek .Thi s confirmsth e correctness ofth e choice ofth e 10°slevel .I nth e Snijdersveerbeek, only small differenceswer epresent ,especiall y concerning the Coarse Detritussamples . Furtherreferenc e toth e H and 10°sdetritu s classificationwil lb emad eb y adding H and 101,respectively ,t o the classificationnumber ,e.g . Sort6 , 10%o r Sort 8, U.

4.1. S Discussion

4.1.3.1 Theus eo fth e Indexo fRepresentatio n compared toothe rstatistica l methods

To check themetho duse dt odetermin e substratepreference ,i.e . the reliability of the Indexo fRepresentatio n (I.R.)a sa too l to assess differencesbetwee n the animalnumber s ondifferen t substrates,severa lmethod swer e studied anduse dinci ­ dentally forcompariso n ofth eoutcome .Cummin s &Lauf f (1969)use dth eprobabilit y values ofth eone-sampl e Kolmogorov-Smirnof (K-S)tes t (DeJonge ,1963 )fo r evaluating theresult s ofthei rexperiment s ina laboratory stream. This test canals ob euse d on fielddata ,bu t iti srathe r time consuming and although itgive s theprobabilit y values indicating the significance ofdifference sbetwee n substrate types,i tdoe s not indicate therelativ e differences insubstrat epreference ,whic hmus tb ecalcu ­ lated orassesse d inanothe rway . Cummins &Lauf f (1969)d othi sgraphically ,bu t

44 usingthei rmetho dn oinformatio nwa sobtaine dtha tcontradicte dth eprobabilit y values obtainedwit hth ecalculatio no fth echi-square dvalue ,whic hmake sth eus eo f theK- S testrathe rsuperfluous .Applicatio no fth eanalysi so fvarianc e (Elliot, 1977,p.108 )t oth efrequencie so faspecie swithi nth esubstrat eclasse si na Sor t didno tgiv ean ysupplementar y informationeither . Allthes emethod s forth ecalculatio no flevel so fsignificanc e andprobabilit y valuesindicat eth esam etendency : formos tspecie sdifference sbetwee nsubstrat e classesexis ta tahighl ysignifican t level,al lindicatin ga distributio no fth e negativebinomia lcontagiou stype .

4.1.3.2 Theimportanc eo fth ejoin tus eo f1 1an d 10%detritu s classifications

Comparing thenumbe ro fsample s inth e1 %an d10 1detritu s classifications (Sort 5-8) inAppendice s4 an d5 show stha t inth eSnij b 68sample s change fromth e3 detritus substratest oth eminera lsubstrates .Thi shappen st o3 3sample s inth e Ratumsebeek.Appendi x6 illustrate swhic hkin do fminera lmateria li scombine dwit h 1-10%organi cdetritu san di ti sapparen ttha t inbot hstream sthi smainl y concerns

substrateswit hQ 1= 2 ,M- ,=3 o r2 an dQ ,= 3 .Onl ya ver ysmal lnumbe ro fsample s incoarse rsubstrate s contain 1-10%organi cdetritu s (CD).Thu sa sa genera l conclusion itca nb estate dtha ta preferenc e shift fromdetritu s tominera lsubstrate s orvic e versaconcerned : - thatthe yhav ea preferenc e forminera lsubstrate s combinedwit h 1-10%organi c detritus,especiall y substrateswhic h arewel lsorte dwit hQ ,= 2 o rmore . - thatthe yhav ea preferenc e forminera lsubstrate swit h lesstha n1 %organi cde ­ tritus;o rfo rorgani csubstrate swit hmor etha n 10% organicdetritus ,whic h concerns onlytw ospecie s inth eRatumsebeek , Amphinemura atandfuasi and Prooladivs, both showingpreferenc e forC Dan dQ ,= 4 i nth e1 %classification ,bu tfo rL an dC Di n the 10%classification . Only Gammarus pulex, Mioropaeatra gr. praecox and Ap8eotrotanypu8 trifasoipennis

showa shif tfro mC Dt osubstrate swit ha negativ eQ 1 (whichconcern s1 6 samplesi n total),togethe rwit ha shif tt o thesubstrate swit hQ ,> 2 .Al lothe rspecie stha t showdifference sbetwee nth e1 % and 10%detritu s classifications shiftt osubstrate s withQ 1= 2 o r3 ,M ,= 2 o r3 an dQ ,= 3 .Thi s concerns thefollowin gtax ai nth e

Snijdersveerbeek:Oligochaeta ,Hydracarina , Palpomyia, Stiotodhironomus3 Polypedilum breviantermatum, Maaropelopia nebutosa and Tanytavsus. Inth eRatumsebee ki tconcerns : Hydracarina,Ampkinemura standfussi, Nemovœa cinerea, Prooladiua, Prodiamesa olivaeea, Epoiooaladius flavens and Paratendipes. Onlytax awit hmor etha n 100specimen s inon e ofth estream s inth etota lspecie s listar ementioned .

45 4.1.3.3 The influence ofanima l abundance onth e Indexo f Representation

Workingwit h the Indexo fRepresentatio n thequestio n arosewhethe r differences inabundanc e ofa specie sbetwee n seasons orinstar swoul d influence theoveral lsub ­ stratepreference smeasure dwit h the index. Ephemera daniaa was selected as test organism since thismayfl y ismuc hmor e abundant init searlie r instars (likemos t invertebrates) and alsobecaus e highdensitie s ofrathe r small individualswer e only found inlat esumme r andearl y autumn. FromAppendi x 7i tca nb e seentha t inth eRatumsebee khig h densities of Ephemera daniaa aremor e or less restricted toanimal s inthei r firstyea r (< 10mm ) whichwer e especially found inOctober .Three-hundre d and teno f the totalo f 482 individualswer e found in 11samples ,whil e the remaining 172animal s occurred in6 2 samples.Two-hundre d andthirt y three ofthes e 310specimen swer epresen t in 8sample s inS+D+FD , 46 in2 sample s inS+F D and 31 in 1sampl e inBS ,illustratin g the clear preference ofthes e smallnymph s forS+D+F Dan dS+FD .Th esampl e inB S (no.142 ) presented anextr adifficult y since the substrate,consistin g ofShiftin g Sandwit h FineDetritus ,wa s classified asSh. S inSor t 2,althoug h thepresenc e ofF Dwa s probablymor e important for E.daniaa. The sample could alsohav ebee n classified as S+FD. Inth eSnijdersveerbeek ,neve rmor e than 20 individuals of E.daniaa occurred in a sample,ye t 183animal s occurred in 13samples ,al lbu t onetake n inSectio n 6.One - hundred and fiftyo fthes e 183wer e present in 7sample s (Appendix 8). Calculation of theI.R .value s for E. daniaa inSor t 2fo rbot hstreams ,excludin g samples containing 10o rmor e specimens,showe d that thehighes t preference forS+D+F Di smaintaine d in both streams (seeTable s 9an d 10). Inth eRatumsebeek ,however ,th esmal lover - representation inS+F Di sreplace db y one forS+ Dan dBG . Inth eSnijdersveerbeek , thepreferenc e forbot h G+Dan dS+ D decreases andi sreplace db y one forBG .Thi s shows that theshif t onlyconcern s the secondarypreference s inbot h streams.Th e highdensit y samples included, thesecondar ypreferenc e is linkedwit h the occurrence ofhig hnumber s ofsmalle r specimens ina fe wsample s and lownumber s of largerspeci ­ mens inman y samples.Withou t thesehig h density samples,th esecondar y preference is linkedwit h lownumber s ofsmal l and largespecimen s ina larg enumbe r ofsamples . High densities of (especially) small Ephemera daniaa nymphs doinfluenc e the distributional pattern asmeasure d by the Indexo fRepresentation . However,n o change inth efavourit e substratewa s seenan dth eonl y conclusion leftfro mthi s excercise istha tsmal lnymph s tend tooccu r inhighe r densities than larger specimens,mainl y inth emos tpreferre d substrate (S+D+FD)i nbot h streams andt oa smalle rexten t in other substrate types.

46 Table9 .Number so fsample san dspecimen so f Ephemera danica Inth eSnijdersveerbee k andth eI.R .value sbefor e (left)an dafte r (right)exclusio no fsample scontainin g more than1 0specimen 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. 3 2.7 - -2.8 9.3 7.7 -0.1 3.5 5.0 0.6 -7.5 -5.4

Italicvalue s ind icate significant over-representation

Table10 .Number so fsample san dspecimen so f Ephemera danica inth eRatumsebee k andth eI.R .value sbefor e (left)an dafte r (right)exclusio no fsample scontainin g moretha n1 0specimen s (highdensit y samples)i nSor t2 .

Substrate type

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

Numbero f 49 47 13 12 9 9 36 28 31 31 10 10 47 47 samples Body length/mm 0-5 50 5 8 4 1 1 126 8 1 1 1 1 4 4 5-10 14 13 20 3 20 20 103 16 20 20 3 3 6 6 10-15 6 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 Total 80 34 43 12 16 16 298 65 42 42 12 12 13 13 I.R. value -4.1 -2.2 1.6-0. 2 -1.5 2.1 21.3 6.5 -4.3 1.6 -2.7 0.5 -9.8 -5.2

Italicvalue sindicat e significant over-representation

4.1.4 Grouping of substrate types based on speai.es composition

Substrateswer ecompare don th ebasi so fth efauna lcompositio no fal l samples in eachsubstrat etyp e (class)in Sor t8 ,10 1usin gWhittaker' sInde xo fAssociatio n (see Subsection3.5.2) .A dendrogra mwa sdraw nusin gth eItopaire dPair-Grou pmetho d usingarithmeti caverage s (UPGMA)(Sneat h& Sokol , 1973),presente dfo rth etw o

47 simili rity (%) 30- (

40

50-

60

70

80

90-

100- Class 13

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

-*- Gravel Coarse Sand -+Coars e Finesan d -*—H 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 (%) 20 -i

30

40

50 -

60

70 -

80 -

90

100 J

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

Substrate CD+L L CD xxx x3x x2x xlx xlx xxx lxx 22x 23x 33x x4x type .... x5x. h »k +7 +- -+• -* si Leaves Coarse Coarse FineGrave l /Coars e Sand FineSan d Coarse Detritus Gravel Gravel

Fig. 18. Dendrogram representing the grouping of substrate types by group averaging in Sort 8,10% in the Ratumsebeek, based on Whittaker's Index of Association.

48 streamsi nFigure s1 7an d18 ,respectively .Bot hfigure ssho wtha tsubstrate s linked bysimila rfauna lcomposition sar eals osimila ri ngrain-siz ecomposition . Inth eSnijdersveerbeek , coarsesubstrate s (Classes1-5 )ar eleas 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 d14) .Coars eDetritu s substrates haveth ehighes taffinit yt oCoars eSan d substrates (Classes6-8) .However ,i nth eRatumsebee ka simila rgroupin goccurre d withsligh tdifferences ,whic har eprobabl ydu et oth elo wnumbe ro fsample si nsom e substratetype s (Classes1 ,2 ,3 ,11 ,12 ,14 )(cf .Appendi x5 ) Althoughth einformatio ntha 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 similarityo fapprox . 70$a scriterion ,a narbitraril y chosenfigure ,i nFig .1 7 for theSnijdersveerbee konl ynin eo fth e1 4origina lsubstrat etype s remain,fiv eo f whichar eGrave lsubstrates .Apparentl yther ear edifference sbetwee nCoars eSan d

(Q1 «1 )an dFin eSan d (Q* >2 )an dbetwee nLeave san dCoars eDetritus ,bu tno ts o muchwithi nFin eSan dan dCoars eSan dsubstrates . Inth eRatumsebee k (Fig.18 )a mor erefine ddistinctio nwithi nFin eSan dclasse s isnecessary ,sinc e22x ,23 xan d33 xemerg ea sseparat eclusters ,whil ethes ear e combinedi non ecluste ri nth eSnijdersveerbeek .Als odistinctio nbetwee nCoars ean d FineGrave li sneeded ,a swel la sth eseparatio no fLeave s fromothe rDetritu s substrates.

4.1.S Groupingof species based on substrate preferences

Severalmethod so fgroupin g (clustering)wer eapplie di norde rt ofin dtax awit h similarsubstrat epreferences .Base do nth eseve nsubstrat e classesi nth efiel d classificationo fSor t2 ,seve nfauna lgroup scoul db edistinguishe db ymanuall y rearrangingth esequenc eo 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), Sand (III),Detritu s (VII),Grave lSan d (II),Gravel/Detritu s (VI),Sand/Detritu s (V) and Gravel/Sand/Detritu s (IV).I nusin gSor t2 ,emphasi si spu to nth esan dsubstrate s (4classes) . Sincesan di sth emos tabundan tsubstrat ei nbot h streams,thi s does representth eactua lsituatio nquit ewell . Appendix9 give sth eI.R .value sfo rth etax afoun dwit hmor etha n2 0specimen s ori nmor etha n1 0sample si non eo fth etw ostreams .Thi sconcerne d8 4taxa ,o f which8 0occurre di nth eSnij ban d7 4i nth eRab .I.R .value s indicatingover-represen ­ tationhav ebee nprinte di nitalic san dthes 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 echi-square d test,no tth eI.R .value sbu tth eactua lnumber shav ebee npresented .Thes etax aar e

49 indicatedwit ha narro w afterth enumbe ro fspecimens . Withineac hfauna lgroup ,th etax ahav ebee narrange d taxonomicallya si n Appendix1 .Eac htaxo nwa splace di na grou po nth ebasi so fth eSnijdersveerbee k data,excep tfo rth etax ano toccurrin gi nthi s streamo rpresen ti nlowe rnumber s thani nth eRatumsebee k (e.g. L-imnephilus lunatue). This grouping emphasizesth e importanceo fCoars eDetritu san dFin eDetritu sfo rth emicrodistributio no fsevera l speciesi n'mineral 'substrates . Gammamis pulex isclassifie dt oth eS/ Dgrou p because ofit sover-representatio ni nDan dS+ Dsubstrate si nth eSnijdersveèrbeek .I nth e Ratumsebeekth eover-representatio noccur s onlyi nDetritu s substrates,indicatin g theimportanc eo fdetritu sfo r Gcomarus. Mosttaxa/specie swit ha preferenc efo r'mineral 'substrate sbesid e detritus substrateshav epreference sfo rSan do rGrave lcombine dwit h detritus (S+D,S+D+FD , G+D/FD),agai nindicatin gth eimportanc eo fdetritus .O nth eothe rhan d othertax a seemt oavoi ddetritu s substratesan doccu rmainl yi nBar e Sando rBar e Gravel,lik e Lithax obseurus and Pisidium. The field classificationgive sa reasonabl y reliablepictur eo fth einfluenc eo f thenatur ean damoun t (roughly)o fth eorgani cmateria li na substrat e type (especial­ lyo nth emos t detailed level,Sor t1 wit h 14classes) . Sort1 i sonl ypresente di n Section4. 2fo rsom eselecte d species.However ,t ogai n insighti nth epossibl e master factor(s)determinin gth esubstrat epreferences ,mor eobjectiv e criteriaar e needed.Bia sdu et oerror smad ei nth efiel d (onlyth esurfac eo fth esubstrat ei s visible)mus tb eminimal .Thi swa salread y reducedb ytakin gth emedia nvalu e zeroa s thedivisio nbetwee nSan dan dGravel ,bu tstil lth etota lparticle-siz e variationo f thesubstrate si shardl y includedi nth efiel dclassification . Withth eai do fWard' s (1963)metho do fhierarchica l linkage,usin gth eerro r sumo fsquares ,incorporate di nth eClusta n1 Cprogra m (Wishart, 1975),tax a occurring withmor e than2 0specimen swer e groupedo nth ebasi so fth eI.R .value si nth e grain-size classificationo fSort s6 an d8 (10°s )an dth efiel dclassificatio no fSor t 2.Compariso no fth eresult so fthes egrouping s showedtha tth egenera ltren di sth e samefo ral lclassification sbu ttha tdifference sd ooccur .Sneat h& Soko l (1973, p. 204)alread y discussedth efac ttha tWard' smetho dma ydivid edens e clustersi na n unacceptablemanner .I nth emateria lo fthi s investigationth edivisio no fth ecluster s wasno tunacceptable ,bu ti tdi dhappe n thatsom epoint si na certai ncluste rwer e nearerth ecentroi do fanothe r clustertha nt oth ecentroi do fthei row ncluster . This especially concernedth etax awit hver ylo wo rver yhig hnumber so fspecimen s giving ratherdeviatian tI.R .values .However ,othe r linkagemethod sdi dno t show moreacceptabl e groupingsan dWard' smetho dwa s retained,bu tonl ya sa mean so f grouping taxawit h similarpreference st ocreat ea startin gpoin tfo rth epresentation . Sort8 ,10° swa sselecte dt orepresen tal lSort s 5-8,becaus ei tinclude sth e totalparticle-siz e variationo fth esubstrate .I ti sa mor e integratedmetho d than Sort 5-7.Th e10 % limitfo rth eorgani cmatte rwa s chosenbecaus ei tgive sa wel lde ­ fineddistinctio nbetwee n organic andminera l substrates,enablin g comparisonswit h

50 Sort 1-4.I twa snecessar yt odistinguis h atleas t 14cluster s togai ninsigh t into thefactor s causing thegrouping . Initially,al ltax aoccurrin gwit hmor etha n2 0specimen swer euse dfo rth e grouping.Thi s concerned 72tax ai nth eSnijdersveerbee k and5 1 inth eRatumsebeek . Theresult s arepresente d indendrogram s (Appendices 10an d 11).I nthes edendrogram s lettercode sfo rGrave l (G),San d (S)an dDetritu s (D)hav ebee ninserte d afterwards onth ebasi s ofanalysi s ofth emai nover-representatio n ofth e specieswithi neac h cluster. Aftercarefu lanalysi so fth ebasi cdat ause d forth eclusterin g (theI.R . values ofeac hspecies )i tbecam eclea rtha tmos t specieswer egroupe dtogethe r on thebasi s ofcorrespondin gpositiv e I.R. values (over-representationo rpreference ) buttha tsom eo fth especie s occurring inver y lownumber swer eclassifie do nth e basis ofsimila rnegativ e orclose-to-zer oI.R . values,thu s influencingth eultimat e average I.R. values.I norde rt oreduc eth einfluenc e ofthes e less abundanttaxa , thebasi s forth efollowin g chapterswa s laidb yusin g onlyth etax aoccurrin gwit h 100o rmor especimen s intotal .Thi s reducedth e listt o4 8taxa ,4 3o fwhic hoccurre d inth eSnij b inthi s abundancean d 26i nth eRab .A s illustratedwit hth e average I.R. values foreac hcluste r (Tables 11an d 12),thre emai ngroup sca nb e distinguished, consisting ofcluster s composed ofspecie swit hpreferenc e forGrave l substrates (Classes 1-6 inSor t 8, 10°s),San dsubstrate s (Classes 7-11) andOrgani c substrates (Classes 12-14). Comparisono fth etw odendrogram s (Figs.1 9an d 20)illustratin g thegroupin g of thespecie so nth ebasi s ofthes e average I.R. values inth etw ostream s shows that speciesbelongin g toon eo fth etw omai ndetritu s clusters inth e Snijdersveerbeek (Fig.19 ,Cluste r6+7+ 4an d3+8+12+14 )ar eals ogroupe d inon eo fth efou rmai nde ­ trituscluster s inth eRatumsebee k (Fig.20 ,Cluste r 14,3+6+11+9 ,4+1 3an d2) . The species inth eSan dan dGrave lcluster s inth eRatumsebee k (Fig.20 ,Cluster s 1+12+5+10an dCluster s 7+8,respectively )als ooccu r inthes ecluster s inth eSnijders ­ veerbeek (Fig. 19,Cluste r 11+1+9+5resp . 2+13+10).Onl ytw ospecie s showa differenc e betweenth estream s inthei rmai ngrouping : Baetis vernus (Taxano .50 )an d Micropter- na sequax (taxano . 128). Bothspecie s aregroupe dwit hth eSan d species inth eSni j- dersveerbeek (Fig. 19)an dwit hth eDetritu s species inth eRatumsebee k (Fig.20) . Considering theI.R . values forthes e species inth esubstrat e types inSor t 8,10 1 (Appendices 12an d 13), itca nb e seentha t Baetis occurred inGrave lan dSan di nth e Snijb (Appendix 12)bu t inDetritu s andGrave l inth eRa b (Appendix 13),suggestin g thatGrave lmigh tb eth emor e important substrate for Baetis vernus. M. sequax isgroupe dwit hth especie spreferrin g Sandsubstrate s inth eSnijb , although iti sover-represente d inGrave lan dDetritu s substrates (Appendix 12).I n theRa b itshowe dpreferenc e inDetritu s substrates (Appendix 13), indicating Detritus asth efavourit e substratetype . InAppendice s 12an d 13,th e I.R. values foral lmor e abundant taxaar epresente d andth e I.R. values indicating over-representationhav ebee noutline d inth esam ewa y

51 Table 11.Th eaverag epositiv e I.R.value sfo reac hcluste r inSor t8,10 %fo r theSnijdersveerbeek .

Cluster Substrateclas s no. 10 11 12 13 14

Gravel Sand Detritus

xxx x5x x3x x2x xlx 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 11.614. 510. 5 EUT] 5 9.0 1.4 4.7 10.0| 9 mm 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 |l2.9| 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. 19 for taxa in each cluster. Boxes indicate groups of taxa with similar substrate preferences.

thecluster si nth eTable s 11an d1 2wer eoutlined .Th etax aar earrange di nth esam e sequencea sth ecluster si nTable s 11an d12 .Fo rsom especie s (Habrophlebia fusea, taxano .48 ;Agapetus fuscipes, taxano .103 ;Limnius volchnavi, taxano .186 ; Epoicoaladius flavens, taxano .283 ; Paratendipes, 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 1i nAppendice s 12an d13 )ar e preferredby ,fo rexample ,th ecaddi sflie s Lithax obscuvus and Agapetus fuscipes, theriffl ebeetle s Elm-is aenea and Limnius volakmari andth emidg elarva e Ovthocladius sp.an d Chaetocladius sp.Th elatte rspecie si sals oover-represente di nDetritu s substrates (Class14) .San d (Classes7-1 1i nSor t8 ,10 1i nAppendice s1 2an d13 )a s thepreferre dsubstrat ei sonl yinhabite db ya fe wspecies ,e.g .th emidge s Pvodiamesa olivacea, Polypedilum breviantennatum. Pvoaladius sp.an d Stictochironomus sp.,th e Diptera Ptychoptera and Palpomyia, watermite s (Hydracarina),Oligochaet aan 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 Sericostoma personatum and Micvoptema sequax, which seemt oprefe rGrave lan dDetritu ssubstrate si nth eSnijb . (Appendix 12).I nth eRa b

52 dissimilarity (squaredeuclidia ndistances )

3000"

2000

1000-

500-

400-

300-

200

100

Clus ter 11 1 13 10 no. Taxa 271 11 217 50 18 280 100 127 40 32 190 277 287 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 20S 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 onth esimilarit y of I.R.values .Cluste r numbers correspond with those inTabl e 11.Tax a numbers refert oth enumber s inAppendice s 1an d 12.Th eletter s S (Sand),G (Gravel)an d D (Detritus)indicat eth emai npreference so f thetax a inth ecluster sbelow .The y wereadde dafte ranalysi so fth ebasi cdat ai nAppendi x12 .

M. sequax prefersDetritu ssubstrate s (Appendix 13). 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 (Tables 11an d12) .Workin gwit haverage ssmal ldifference ssoo n 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 danioa andth eDipter a Lirnnaphila sp.an d Diovanota sp.Compariso no fth edat afro mth eSnij b (Appendix12 ) withtha tfro mth eRa b(Appendi x13 )show stha tspecie spreferrin gSan dan dGrave l

53 Table 12.Th e averagepositiv e I.R.value sfo reac hcluste r inSor t8,10 %fo rth e Ratumsebeek.

Cluster Substrateclas s no. 10 11 12 13 14

Gravel Sand Detritus

x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD 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 6.11 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 17.411. 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. 222. 6 11 0.7 26.1 13 53.213. 4

SeeFig .2 0fo rtax a ineac hcluster . Boxes indicategroup so f taxawit h similar substratepreferences .

substrates inth eSnij bar eals oclustere dtogethe ri nth eRa b (Cluster 1i nbot h streams). Inth eRab ,th epreferenc e forGrave l ismuc h lesspronounced ,however . Thesephenomen awil lb ediscusse d indetai lwhe ndealin gwit h theindividua lspecie s (Section4.2) . Detritussubstrate s (Classes 12-14i nSor t8 ,10° si nAppendice s 12an d 13)ar e preferredb yth elarges tgrou po fspecies ,e.g . thefres hwate rshrim p Gammapus pulsx, twostonefl yspecies , Nemoura cinerea and Amphinemura standfussi, thecaddi s fly Chaetopteryx villosa, thene tspinnin g caddis Plectrocnemia conspersa, thebeetl e larva Helodes sp.an dman yChironomidae ,e.g . Brillia modesta, Eukiefferiella gr. discoloripes and Diplocladius cultriger. Separategroup sar eforme db ysom e individual species,suc ha s Micropsectra gr. praecox. ThisTanytarsin i isstrongl yover-represente d inFin eSan dan dDetritu s substrates inth eSnijb ,whil e itprefer sDetritu ssub ­ stratesi nth eRab . Nemoura cinerea obviouslyprefer sDetritu s substrates inbot hstreams ,a smen ­ tionedbefore ,bu ti nth eRab ,Grave l isals ofavoured ,a phenomeno nsee ni nth e Snijbfo r Amphinemura standfussi. Baetis vermis, Macropelopia nebulosa and Tanytarsus sp.ar eover-represente di nGrave lan dSan dsubstrate s inth eSnij b (Appendix12) . Baetis prefersGrave li nth eSnijb .I nth eRa b itprefer sDetritu s substrates,bu ti t isals oover-represente d onGrave l (Appendix 13). Macropelopia nebulosa and Tanytarsus sp.ar efairl yevenl ydistribute dove rth esubstrat etype s inSor t8 ,10°s ,

54 5000 dissimilarity (squared eucLidiandistances )

3000

2000

500

400

300-

200

100-

Cluster 1 14 no. Taxa 11 271 217 105 287 40 269 128 42 32 no. 38 308 186 48 275 190 249 311 272 283 341 302

Fig. 20. Dendrogram representing the grouping of the 26 most abundant taxa (100 specimens or more) in the Ratumsebeek in Sort 8,10%, based on the similarity of I.B. values. Cluster numbers correspond with those in Table 12.Tax a numbers refer to the numbers in Appendices 1 and 13. The letters S (Sand), G (Gravel) and D (Detritus) indicate the main preferences of the taxa in the clusters below. They were added after analysis of the basic data in Appendix 13.

althoughth eforme rprefer sCoars eGrave l (Class7 )an dth elatte rFin eSan d (Class 10). Thesean dothe rdifference si nspecie spreference sbetwee nth etw ostream swil l bediscusse di ndetai li nSectio n4.2. ,wher e2 6o fth e4 8tax apresente di nAppendice s 12an d13 ,ar edeal twith .Compariso no fth emai ngroup so fspecie shavin gsimila r substratepreference si nth egrain-siz e classificationi nth elaborator yi nSor t8 , 103,(Appendice s 12and 13 )wit hthes egroup si nth efiel dclassificatio ni nSor t2 (Appendix9 ) leadst oth econclusio ntha tmai npreference sca nb 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 d organicdetritus .

4.1.6 Numbers of species and specimens in different substrate types

Somegenera l conclusionsca nb edraw nwhe nconsiderin g numberso fspecie si n each taxonomicaluni t (Table 13),togethe rwit h their average abundance (Table14) . Frombot h tablesChironomida eemerg ea sth emos t abundant groupi nnumbe ro fspecie s aswel la si nnumbe ro fspecimens ,bu tdistinc tdifference si nabundanc ei nth e various substrate typesar epresent .Detritu s substratesar einhabite db yth elarges t numberso fanimals ,predominantl y composedo fTanytarsin i (M.gr . praecox), Gammarus pulex (includedi nOthers) ,Orthocladiina e (severalspecies )an dColeopter a (Helodes larvae)'.The n followS+D+FD ,S+ Dan dS+F Di nthi s sequence,wher e Tanytarsini {M.gr . praecox), G. pulex, Chironominian dOrthocladiina e predominate. G+D/FD comes nextwit hTanytarsini ,Orthocladiina ean d G.pulex. Finallyth ebar eminera l substrates BSan dB Gsho wth esmalles tpopulatio n densities.I nBS ,Tanytarsin ian d G.pulex are still ratherdominant ,bu ti nB Gth enumber so fspecimen s arefairl yequall y distributed overth evariou s taxonomiegroups .Chironomin i occuri nequall yhig hnumber si nSan d substrates combinedwit hDetritus ,whil eOrthocladiina e aremor e abundanti nGrave l substrateswit hDetritu san dPur eDetritu s substrates.Tanypodina ean dTanytarsin i are leastpresen ti nB San dBG .Dipter aar erathe revenl y distributedwhil e Coleoptera areabundan ti nGrave lan dDetritu s substrates.Considerin g thenumbe ro fspecie s foundi neac h substrate type,th edifference s betweenmos tgroup sar eminimal .Onl y Coleopteraan dTrichopter aoccu rwit hmor e speciesi nGravel ,Detritu san dBar eSan d substrates.However ,sinc eth enumbe ro fsample s isdifferen tfo rth evariou s substrate classes,absolut e comparisoni sno tpossible ,althoug hmajo r changesar eno tlikely .

Table 13.Numbe ro f speciesfo rth emai ntaxonomica l groups inth e substrates distinguished inSor t2 i nth eSnijdersveerbeek .

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 Numbero fsample s 87 29 33 53 80 37 63

56 Althoughthes edifference sin anima lnumber sin th e7 substrat etype sin Sor t2 areillustrate dfo rth eSnijdersveerbee ki nTabl e 14,compariso no fth etota lnumbe r ofanimal spe rsubstrat e classthroug hI.R .value s leadst oth esam econclusion san d thesam esequenc eo fabundance sin bot hstream s (cf.Table s7 7an d78) .O fcours eth e heighto fth eI.R .valu ecanno tb etake na sa precis emeasure ,bu tth egenera ltren d issignificant .Th enumbe ro fanimal si slowe rwhe nth eI.R .valu ei slowe r (more negative). Ina stud yo fa smal l woodlandstrea mi nCanada ,Macka y (1969)distinguishe d Sand,Gravel ,Stones ,Leave san dLeaf-Detritu sa ssubstrat etype san dsh efoun dtha t thediversit yan dth enumbe ro fanimal s increasedfro msand ,throug hgrave lan d stonest oleave san ddetritus .Sh eals odemonstrate dtha talthoug h leafan ddetritu s substrateswer eriches tin specie san dnumber s theyar epredominantl y inhabitedb y Dipteraan dtha tgrave lan dston ysubstrate shous emor ePlecoptera ,Ephemeroptera , Trichopteraan dColeoptera .I ngeneral ,difference si nnumber so fspecie san dnumber s ofanimal sfollo wth esam etrend ,showin gan increas e fromsan dthroug hgrave lt o detritus (Pennak& va nGerpen ,1947 ;Ward ,1975 ;Walton ,Reic e& Andrews , 1977). However,thi si sno talway sin th esam esequence ,especiall yin stream swher eston y substratesar escarc eo rcoars esubstrate salway sconsis to fa mixtur eo fstones , gravel,san dan ddetritus ,formin gver ycomple xsubstrates .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 sar eals over ycomplex ,consistin gpredominantl y ofsan dan ddetritus ,occasionall ymixe dwit hgrave land/o rpebbles .Althoug hn o estimationso fanima lbiomas swer emade ,th enumber so fanimal s increase fromBar e Sandan dBar eGrave lthroug hSan dwit hDetritu st oLeave san dDetritu ssubstrates . Thereason sfo rth eoccurrenc eo fexceptionall ylo wnumber so fanimal so ngrave l substrates,compare dt oman y foreignstreams ,i sprobabl y thatth ebar egrave lsub ­ stratesar emostl ysituate di nth emos tunstabl e zoneso fth estrea mbed ,whil eth e

Table 14.Averag enumbe r of specimens In1 0sample s inth esubstrate s distinguished inSor t 2i nth 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 s kindo fsubstrat ei srelativel y smallan dsan dan dsil t transport (scouring)high . Cordone& Kelle y (1961)reviewe d someo fth eolde rpaper so nth edifference si n productionan dstandin g cropo fsan d comparedt omud ,detritus ,gravel ,rubbl ean d vegetation.San d appearedt ob elowes t inproductio nan dstandin g crop,whil e rubble togetherwit h organically enrichedmu dshowe dth ehighes tproduction .Thes e findings are confirmedb ya larg enumbe ro fmor e recentpaper s (Maitland, 1964;Mackay , 1969; Pennak, 1971;Nuttall , 1972;Ward , 1975;Russev , 1977;Petran , 1977;Resh , 1977). Quitter (1969a)discusse dth eeffec to fsan dan dsil t transporto nmacroinvertebrate s andconclude d thatthe ycaus e considerable changesi nth efauna . Increases inth e amounto fsil tan dsan d increaseth einstabilit yo fth erive rbed ,whic h adversely affectsth efaun a (Mackay& Kalff , 1969).

4.1.7 Field expeviments

4.1.7.1 Trays filledwit h artificial substrate

Forstatistica l analysiso fth enumbe ro fanimal san dth especie s caughti neac h substrate trayan dcompariso no fth ecolonizatio no fth egrai n sizes,onl yth edat a ofth e1 4an d2 8day s colonizationperio dca nb eused .I ntabl e 15,th eI.R .value s forth emor e abundant taxaafte r 14day sar egiven .Tabe l1 6give s these data after 28days .Thi s concerned 7an d1 0species ,respectively ,wit h5 o fthe m abundant after bothperiods ; G.pulex, M.gr . praecox, C.melanops, E.octoculata and H.fusca. Only E.oatooulata showa distinc t difference betweenth etw operiods ,whic hi sno tver y surprising since these leecheswer emostl y foundo nth einsid eo fth etray s itself andno to nth esubstrate .Th eleeche swer e also abundantly presento nth eoutsid eo f the trays,bu tthes ewer e discarded. Hdbrophlebia fusoa showedpreferenc e forth e coarserparticl e sizes afterbot hperiods . Gammavus pulex alsodisplaye da clea rpref ­ erence for coarse grainsizes ,whil e Conchapelopia melanops preferred 4an d2 m m grain sizes afterbot hperiods . M.gr . praecox was significantly abundanti n8 an d4

Table 15.Numbe ro f specimens (N)an d I.R. values forth emos t abundant species insubstrat e trays after 14day so fcolonizatio n inth eRatumsebeek .

N Part iclesiz e (lower limi t)/mm 32 16 8 4 2 Gammarus pulex 2034 3.6 9.7 -1.2 0.1 -12.2 Hdbrophlebia fusca 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 ootoculata 15 -1.2 -1.7 0.6 1.7 0.6 Conohapelopia melanops 97 -4.2 -4.0 -4.0 6.3 5.8 Micropsectra gr. praecox 15 0.6 0.6 0.0 0.0 0.0 Italic values indicates i gnificant over-representation

58 Table 16.Numbe ro f specimens (N)an dI.R .value sfo rth emos t abundant species insubstrat etray safte r2 8day so fcolonizatio n 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 Micropseotra gr. praecox 136 -3.6 -0.0 3.8 8.7 1.5 -0.0 -3.4 -3.6 -3.4 Prodiamesa olivacea 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 octoaulata 27 3.5 0.6 0.6 0.0 -1.2 0.0 0.0 -1.7 -1.7 Diaranota 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 fusaa 18 1.4 -0.7 3.5 2.8 -1.4 -1.4 -1.4 -1.4 -1.4

Italicvalue s indicatesignifican t over-representation

mm substrates after2 8days ,althoug h showedn opreferenc e after 14days . Comparing thesedat awit hth edistributio n showni nAppendi x 13fo rth enatura l substrateso fth estrea ma sdetermine dwit hth eshove lsamples ,agreemen ti ssee nfo r some speciesan 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 r finersubstrates ,whic h collect lessdriftin g detritus thanth ecoarse rparticl e sizes.Thes e four substratesar e probablybes tcomparabl et 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 nmore organi 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 Partiole sizes introduced without trays

Onlyon eexperimen to fthi snatur ewa sperformed .Unfortunatel ya spat e occurred duringth eexperimenta lperiod, washin gth efine rsubstrate s awayan dcoverin gth e coarserone swit hmuc h finematerial .Althoug hth esubstrate swer e sampled afterth e setperiod ,analysi so fth egrai nsize so fth esample s showed thata considerabl e changei nparticle-siz e compositionha dtake nplace .Th epopulation so fth esubstrate s showedmuc hmor e resemblancet otha 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 dshoul db egive npriorit y over thosewit hexperimenta l trays.

59 4.2 ORGANISM-SUBSTRATE RELATIONSHIPS

4.2.1 Outline of presentation

Severalspecie sapparentl ydispla ya simila rdistributiona lpattern ,differin g fromtha to fothe rspecie so rgroup so fspecies . (Subsections 4.1.4 and4.1.5J .T o testth ehypothese sstate d inSectio n1. 3 iti sno tnecessar y todea li ndetai lwit h allth especie s listed inAppendice s 9, 12an d 13.Therefor ea selectio no fspecies , representative forth evariou sdistributiona lpattern swil lb ediscusse d indetai lt o illustrate thedifferen tsubstrat epreferences .Emphasi swil lb epu to nth etax a found innumber s largeenoug ht ojustif ystatistica l treatment,especiall y thosewit h more than 100specimen spresen t inth etota lserie so fsample s inon eo fth estream s (Subsection 4.1.5).Thi sconcerne d 48tax aan dfro mthes etax arepresentative s for eachdistributiona lpatter nwer e choseno 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 ,ligh tintensit yo rfoo dconditions )result ­ ingi nsubstrat eselection .

Notal lspecies/tax awer e treatedwit h thesam edegre eo fdetai lbecaus eo flac k ofsufficien tbackgroun d datao rbecaus ethe ywer eonl yidentifie d toa lowtaxonomi e level.Excep tfo ra fe wspecie s- thos emor enumerou s inth eRatumsebee ko rrestricte d totha tstrea m- th edat afro mth eSnijdersveerbee kwil lb euse da sa startin g point.Thi s concernsmor e samplesan dyield smor estatisticall yvali dresults .Th e datafro mth eRatumsebee kwil lfunctio na sa chec ko nth evalidit yo fthos eresult s ina strea mo flarge rdimensions .Attempt swil lb emad e toexplai npossibl ediffer ­ ences insubstrat epreference so f (groupsof )specie sbetwee nth etw ostreams .

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

Life cycle Animalgrowt hi nth etw ostream sstudie di spresente d ina histogram , summarizingbod y lengthi n1-m mclasse sa spercentag epe r fourwee kperiod s (e.g. Fig. 21).I nthes ehistogram s thedat ao fbot hstream sar epresente d together.U pt o 1977,thi sconcern sSnijdersveerbee k dataonly ,an dafte rWee k 15i n 1977Ratumsebee k dataonly .I nth efirs t 15week s of 1977dat afro mbot hstream swer epooled ,bu tno t before comparisono fth ebody-lengt hdistributio nove rth e lengthclasse si nth etw o streamsha dshow ntha tther ewer en osignifican tdifference s inbody-lengt hcompositio n

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

Miarodistvibution I.R.value sfo rth esubstrat etype so fth efou rlevel so ffiel d classification (Sort1 - 4 )wil lb epresente di na dendrogram-lik etabl e (e.g.Tabl e 26)comparabl e toFig . 12,wher eth ename so fth esubstrat etype sar egiven .A tth e topo fthes etable sth esubstrat etype si nSor t3 ar eindicated ,San d (S),Grave l (G) and Detritus (D),whil ea tth ebotto mo feac htabl eth etype si nSor t1 ar eabbrevi ­ ated (seeOutlin eo fsubstrat eclassification ,pag eafte rcontents) :Stabl e (St) Sand,Shiftin g (Sh)Sand ,San d+ Fin eDetritu s (FD), Sand+ Leave s (L),San d+ Coars e Detritus (CD),Bar e (B)Gravel ,o rothe rcombination susin g thesam eabbreviations . Thesetable sca nb ecompare dt oAppendi x2 o r3 ,wher eth enumber so fsample s ineac h substratetyp ear egiven .

I.R. valuesrfo rth esubstrat etype si nth egrain-siz eclassificatio ni nth e laboratoryar epresente dfo rbot h levelso forgani cdetritu s (H and 10%; seeSubsectio n 4.1.2.2)i nSor t5- 8 (e.g.Table s3 7an d 38).Whe nn odifference s insubstrat e preferencebetwee nthes etw olevel swer eobserved ,onl yth e10 1leve li spresente d (e.gTable s 19an d 20). Forsevera ltaxa ,a tabl ei sinclude dgivin gth eI.R . values fordifferen tanima l lengthclasse si nSor t8 , 10% (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 e2 . A discussiono fthes eresult swil lfollo wi nth eligh to fdat afro mth e literature onlif ecycle ,foo dhabit san dhabita tpreferences .

Case building Forth ecase-buildin gTrichoptera ,dat ao nth egrain-siz ecompositio n ofth enatura lcas e (e.g.Fig .22 )wil lb epresented .Whe napplicable ,dat ao ncase - buildingexperiment swil lb ediscusse donl ybriefly ,becaus ethes ewil lb epublishe d inful ldetai lo na late rdat e (Tolkamp& Verdonschot ,t ob epublished) .Th egrain - sizecompositio n (orminera lan dorgani ccomposition )o fthes ecase swil lb ecompare d withth egrain-siz ean dorgani ccompositio no fth epreferre dsubstrat etypes .

Substrate-selection experiments Forth especie ssubjecte dt osubstrate-selectio n experimentsi nth elaborator ystrea m (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 obtainedi nth efield .I nthes efigure sth egrain-siz e fractionsar eindicate db yth e lowerlimi to fth efractions .Grai nsize ssmalle rtha n1 m mar eexpresse di nmicro ­ metresizes ,large rgrain sar eexpresse di nmillimetr esize s (e.g.12 5stand sfo rth e 0.125- 0.25 0m mfraction ;2 stand sfo rth e2 - 4 m m fraction). Forsom especies ,th eselectio no fgrain-siz efraction si nfiel dexperiment s willb ediscussed ,comparin gth eresult swit hthos eo fth efiel dstud yan ddat afro m theliteratur ewhe navailable .

61 4.2.2 Autecological data for selected species

4.2.2.1 Lithaxobscuru s (Hagen) (Trichoptera: Goeridae)

Life cycle Thelif ecycl eo f Lithax obscurus inbot hth eSnijdersveerbee kan dth e Ratumsebeeki ssummarize di nFig .21 .Dat a from197 7ar emainl y fromth eRa ban d earlierdat aar emainl y fromth eSnijb .I nbot hstream spupa ear epresen t fromth e beginningo fDecembe rt oAugust/September ,wit ha pea ki nApril/May ,whic h agrees withth eMay/Jun e flightperio 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 emerged fromearl yApri l tillth een do fMay , andals o fromearl yJul yt omid-August .Sinc eadult swer eno tcollecte d systematically, but only incidentallyi nbot hstreams ,thes eemergenc e dataca 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 ) in- starlarva e occural 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 final instaro ra sa pupa ,bu tpartl y alsoi nearlie r instars.However ,thes ear eon ­ lyth emos tpronounce dpoint si nth elif ecycle ,whic hi sstrongl y dispersed overth e wholeyea rbecaus eo fth elon gfligh tperio dan ddisperse deg ghatching .Anothe r reasonmigh tb etha t larvae thathatc hearl yi nth eyea rgro wfaste r thanlarva etha t hatch latei nautumn ,becaus eo fmor e favourable foodcondition s (periphyton,fin e detritus).

Microdistribution Thismembe ro fth eGoerida e familyoccurre di nbot h streamsmainl y incoars esubstrate s (BG,St. San dG+CD ,Table s1 7an d18) , although over-represen­ tationi sals osee no nC Di nth eRab .Thi s over-representationi sprobabl y causedb y foodscarcity ,sinc e Lithax was onlyfoun di nC Di nsummer ,whe nth eamoun to f detritusi nth emiddl eo fth estrea m (wheremos to fth ecoars esubstrate s occur)i s low.Thi si sals o trueo fperiphyto nproduction ,becaus eo fth eheav yshadin go fth e streambe db yth eban kvegetation . Lithax isa caddis ,wit h feedinghabit squit e similart ovariou sLimnephilida especie san dth eGlossosomatida e (Greniere tal . 1969), feedingo ndetritu san ddiatoms .A sCastr o (1975)an dDougla s (1958)showe d for Agapetus fusaipes, theconsumptio no feac h foodtyp evarie swit hit srelativ e abundance. Theover-representatio ni nSt. Si nSor t1 i spresen ti nbot h streams,bu ti nth e Rabi ti sno tsee ni nan yo fth eless-detaile d classifications.Her eth epreferenc e forSt. Si sobscure di nSort s4 an d2 b ySh. San dS+FD ,tw onot-preferre d substrate types.Thi s illustratesth eimportanc eo fa detaile d classification.I tals o emphasizes thefac ttha ti tma yb ever y importantt odistinguis hbar esubstrate s from substrates mixedwit hdetritus ,an dtha tth enatur ean damoun to fdetritu si sver y important. Fromth egrain-siz eclassification si nbot hstream s (Tables1 9an d20 )i ti s

62 78; nTrfnrillll miwi

77: 49-S2!j

IH!rTTTwJTTT)TTTTTTn

77: *S-«e;

,. ,i IIIHIIHIIIIIIHHINI

77: «1-

«-rfirrfTTTl nïïhm

77: 33-36.

JIIIWTV

77: 25-28- fïïriniu, ^

77; 21-24.,

77: 17-20 Z

T7; 13-16,

77: «*-i2j TTTn-jnflTFL.

77; Ç- 81 co

ÜJ 77: l- 4^ LU •3. CT1HP1

76: »9-S2I O o _^-*TTTfTTT{TÏÏtTR_ CK 76: -s-ta: aLU.

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76; J7-to: (ïïïfTITltTTfTïïl™

76: 33-36] l!Hl!linH(nTL~JTTT>mi

76: 29-32. 1

rrnflTTJl irm N - 2a 1 76: 21-21 rrnJÜII N - 14

76; l7-20: .—min illMINIU—

76; 13-16 1

76: *»-lZ_ nTTH^fT^IH'mTVr^irfu

cm mflïïtP

7S: «s-« W Pïïte

7S: S7-taZ PHI—tnfHBrflïïl

LENGTH CLASS CMM )

Fig. 21.Lif ecycl ehistogram so f Lithax obseurus showingth edistributio n(% )o f larvalbod y length,pupa e (99)an dadult s (98)pe rfour-wee k period.

63 Table 17.I.H .value s for Lithax obsoiœus (N= 451 )i nth efiel d classificationo f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -3.7 8.2 -4.7 I I I 4 -4.7 2.3 -8.3 8.9 1.6 I _J I 2 5.6 -5.0 -6.8 8.9 1.6 -4.7 _J -4.8 1 I r 1 8.1r -1.3 -5.0 -1.5r -4. 5 -1.4 -6.6 -1.9 8.9 -0.2 1.9 -2.7 -3.3 -1.9 st Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L Italicvalue s indicatesignifican t over-representation

Table18 .I.R .value sfo r Lithax obscurus (N= 218 )i nth efiel d classificationo f thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -6.1 9.0 0.8 1 1 1 1 1 1 4 -2.2 -6.8 8.4 3 5 0.8 1 1 1 1 1 1 1 2 -0.5 -3.8 -3.2 -6.0 L 3 5 0.8 1 I 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 -2.1 8.4 -1.1 5.7 -1.0 -0.7 4.1 St Sh FD L CD CD+L CD+FD L+FD B L CD CD L CD+L +FD

Italicvalue s indicate significant over-representation

Table 19.I.R .value s for Lithax obsovœus (N= 451 )i nth 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

phiinde x 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 Sort6,10 % 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 index xxx x5x x3x x2x xlx 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 indicate significant over-representation

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

Substrateclas s

10 11 12 13 14

phi index detritus

6 2 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 Sort7,10 % ------4.6 -1.5 5.6 -6.6-1. 1 5.7 -1.0-0. 7 xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L QlMdQ3 lndex x4x Sort 8,10% 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 indicatesignifican t over-representation

Table 21.I.R . values for Lithax obsourus perlengt h class (A)an d season (B)i nth e Snijdersveerbeek inSor t8,10% .

Length N Subs träte classan d 9lMdQ3 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 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 6-10 283 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 -9 8 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 BSprin g 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 indicatesignifican t over-representation

cleartha t Lithax preferssubstrate swit ha larg eproportio no fth efractio ncoarse r than1- ram2 (Coars eSand ,Q 1 <ï ) .A presentatio no fth edistributiona lpatter npe r lengthclas si nth eSnijdersveerbee k (Table 21A)i nSor t8 ,10 % showstha tth esmal ­ lestspecimen s (1-3mm )ar emainl yfoun do nx2x ,whic hmainl yconcern s sampleswit h Q,= 5 o r4 (cf .Fig . 16).Analysi so fth epreferenc eo fthes esmal llarva ei nSor t 5, 10% (notpresented )showe d thatthe yprefe r( L= 4 . Pupaear epresen to nth etw ocoarses tsubstrat e types (coarsertha nx4x ,especial ­ lyQ i= 7,6 an d5 ;M ,= 7 an d3, base do nlengt hclas spreferenc ei nSor t5, 10 % and Sort6 ,10 %no tpresented) .

65 Theothe r lengthclasse sar efoun do nth etota lrang eo fsubstrat e typeswit h Q-. <Ï an dM , <1 .Thi smean s that Lithax obscurus occursmainl yo ncoars et over y coarsesubstrat ei nsprin gan dautum n (pupaean dearl y instars,respectively )an dca n be foundo nal lothe rsubstrate s forth eres to fth eyear ,a sconfirme db yTabl e21B . Inth eRatumsebee ka simila rpreferenc e ofth esmal l larvae (1-3mm )fo rx2 x was observed,bu tthe yshare d thiswit hxx x .Th elarge r larvaeoccurre 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 san dbranches ,especiall y thoseprotrudin g above thewate r surfacenea rth ebanks .Thi s couldb eobserve d clearly aftera stron g fallo fth ewate r level,bringin gman y attachedpupa eabov e thewate r surface,althoug h thisdi dno thinde rth eemergence ,whic h followedwithi n a fewdays . Theabov edat aagre ewit h theconclusion s ofBeye r (1932)an dGeijske s (1935) thatth eGoerida ebelon gt oth etypica lston efauna .The yar echaracteristi cfo r unpolluted,natura lstream swit ha moderat e tofas tcurrent ,althoug hth esevera l generaselec tdifferen tcurren tspeed s forthei roptima lhabita t (Scott,1958 ;Nielsen , 1942). Thisi sreflecte di nth esiz eo fth eballas tstone so nth eside s ofth ecase , whichincreas efro m Lithax through Silo to Goeva (Wesenberg-Lund,1943 ;Webste r& Webster,1943 ;Grenie re tal. , 1969).

Case building Lithax dbsouvus buildsa cas eo fminera lmaterial .Th ecas ei sa t least6- 7m mlon gan dabou t3 m mwid ei nth efina l instar (Greniere tal ,1969) ,al ­ thoughUlme r (1909)an dLepnev a (1964)reporte da lengt ho f9-1 0mm ,which agrees withou rmeasurements .Th ecas ei sslightl y curvedan dth erea ropenin gi sclose db y amembran ewit ha nexcentri c circular opening.Thi smembran e isalway s coveredwit h somesmal lsan dgrains ,whic hi sa taxonomi echaracteristi c forth egenu s Lithax withinth eGoeridae . Thecas e 'grows'spasmodically ,whereb yth elarv aenlarge sth ecase ,probabl y justbefor ea moult .Thi si sclearl yvisibl e fromth elighte rcolou ro fth enewly - addedfront ,whic hi sstil l free fromattache ddiatom s inth ebeginning .Th ecas e consistso fsan dgrain san di swel l camouflaged (Lepneva, 1964). Thedifferen t instarssho wa differen tpreference ,whic h shifts fromsmal lt o largergrain swit h increasei nlarva lsiz e (Fig.22) .Th eF- 3insta ruse smainl y 0.105- 0.50 0m mgrain san dthi spreferenc e isreplace db yon efo r0.25 0- 2 m mi n thefina linstar .I nth efina linsta rcase sth e1 - 2 m mgrain sar emainl yuse dfo r ballast stoneso nth elatera l sideso fth ecas ean da sca pstone sfo rth epupa lcase . Comparing thegrain-siz epreference so f L.obsaurus forcas ebuildin gwit hth e grainsize spresen t inth esubstrate s init spreferre dsubstrat e typei nth estream s shows thatthe ywil lb eabl et ofin dth esize sneede d inal lsubstrat e typesshowin g over-representation,eve ni nth ecoarses ttype s sincethi s isalway s situatedo nto p offine rmaterial .Lac ko fsuitabl e grainsfo rcas ebuildin gwil lno toccu r inth e preferredsubstrates ,bu ti tma yb eon eo fth ereason sfo rth eunder-representatio n

66 H-F-3-H )•— F-2 •{ *\ Pupae

2 60H m 8. s S soH

—r-T- ' i ' ' 0.5 0.3 oT 0.8 0.9 1.0 head width classes(mm )

Fig. 22.Distributio n(% ) ofgrain-siz efraction si nnatura lcase so f Lithax obsawms. 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. 0

of L.obscurus inth efine rsubstrates .However, i nsubstrate swit hM ,> 1stil l enougho fth esuitabl egrain swil lb eavailable ,an dye tL.obscuru s occursher eonl y sporadically.Thi ssuggest s thatothe rfactor s thanhouse-buildin gmateria lpla ya more importantrol ei ndeterminin g itsdistribution ,e.g . currentvelocit yo r availabilityo ffood .Yet ,considerin g thepreferenc eo f Lithax forth ecoars e substrates (andinseparabl y linkedwit h this,th ehighe r current speeds),it sus eo f relatively largegrain 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 fL.obscurus. Especially theabsenc eo f suitable substratesi notherwis e similarstream s (natural,shaded ,moderat et ofas t flow)i sprobabl yth ecaus eo fth e restrictiono fL.obscurus (andGoerida ei ngeneral ) tostony ,gravell ystreams .

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

Identification Accordingt oBotosanean u (1967), S.pedemontanum isa synony mfo r S.personatum. Inth eNetherlands ,Sericostomatida ear erepresente db ytw ogenera , Sericostoma andNotidobia (Geijskes& Fischer , 1971),o fwhic honl y S.personatum was foundi nthi sinvestigation ,an dthe nonl yi nth eSnijdersveerbeek .Onl yrecently , Wallace (1977)clarifie dth edifference sbetwee n S.personatum and N.ciliaris, making theidentificatio no fth etw ospecie squit esimple .Fro mWallace' swor ki tals o became cleartha tLepnev a (1964)presente dth epronotu mo f S.personatum astha to f N.ciliaris. Adultswer e identifiedwit hMacan' ske y(1973 )afte rrearin gthe mfro m larvaei nth erearin gchannel .

Life cycle Thelif ecycl eo f S.personatum mayvar ygeographically . Iversen (1973) concludedwit hDittma r (19S5)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. 5year s inGrea tBritain .Iverse n (1973)explaine dth eslowe rgrowt hi nDenmar kan dSauerlan d asa neffec to fth elowe rtemperatur efluctuation san dmaxim aan dless-favourabl e foodsupply .I nth eSnij bbot ha 1. 5yea ran d3-yea rlif ecycl ear epossibl ewhe n consideringth edat ai nFig .23 ,givin gbod ylengt ho fth elarva ei ntime .Measure ­ mentso fhea dwidt hindicate dhoweve r thata 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 sfo reac hinstar .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(t ob epublished )hav eestablishe dtha toverwinterin g takesplac ei n theeg gstag ean dth efirs tan dsecon d instari 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-)pupa eoverwinter .Pupa ear emos tabundan t fromApri lt oJune ,whil e adultsemerg e fromJun et oAugus t (cf. Svensson, 1972; Iversen, 1973).

Miarodistribution in the Snijdersveerbeek Sericostoma personatum waspredominantl y foundi nassociatio nwit hcoars edetritus ,excep tfo rth eBar e Gravelsubstrat e (Table 22).Thi si si nagreemen twit hth efoo dpreferences ,sinc e S.personatum isa detritivore (shredder),feedin gmainl yo nleave s (Décamps, 1968), althoughit sgu t doesno tcontai ncellulas e (Bjarnov, 1972),whic h suggeststha tth ebacteri aan d fungiattache dt oleave san ddetritu sar eth emai nfoo d items (Thorup& Iversen , 1974). Togetherwit h detritus,diatoms ,alga ean dfung iar eals oingeste d (Moon,

68 78: 1- 3'. .

77: 49-SZ:

77: 45-48:

77i 41-44!

77: J7-4B!

77: 33-36!

77: Z9-X'.

77: 25- «a:

77: ai-«: 77: 17-20! nnu 77: 13-16: : fTTThr* (TTrflTlïm m. 77: 9-1«: : i *"*' — —^IIIIII||UH'III^.JI i. N- 74 77: ç- B: 60 nm lllirrm irm

LU 77: i- 4: LU 3 —_mrnm »••»•• IHIIMIU-fFT • o 76: 49-sz: o m r '• a: 76: 45-48! ' ' ' "' ' ""'

76: 41-44!

76: 37-48!

76: 33-361 «wflm »rm •tiflTTII'MImt mr

76: 29- 3Z' : rrndinnrtini mi 76: 25-28: mrinnim rrm 76: 21-24 1 76: 17-ZB rniwr-n 1

76: 13-161 mThnfim ^, „ M —v

76: «»-12 ™ ffnW, mntm rr, -m, •m

7é: S- 8

76: 1- 4 HIThlThm m «T»n rr M - 11 75: 49-SZ 1 75: 45-48 11 75: 41-44 l 7S: 37-4B 1

«i-iiTii-iiiiadaaaaaaaaa LENGTH CLASS( MM ) Fig.23 .Lif ecycl ehistogram so f Sericostoma personation showingth edistributio n (%) oflarva lbod ylength ,pupa e(99 )an dadult s (98)pe rfour-wee kperiod .

69 Table22 .I.R .value sfo r Serioostoma personation (N= 346 )i nth efiel dclassificatio n of thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -0.3 2.5 -2.9 1 1 1 1 1 1 1 1 4 -1.3 1.0 2.8 0.4 -2.9 1 I 1 1 1 I 1 I 1 1 2 -0.8 -1.2 3. 0 -1.0 2.8 0.4 -2.9 1 1 I I 1 1 1 1 1 1 1 I 1 I 1 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;,Slack ,1936) ,an dsometime s insectsar eeate na swel l (Dittmar,1955 ;Lepneva , 1964).Thi s iswh yHicki n (1967)classifie d Serioostoma asomnivorous ,althoug hth e percentage ofinsect s isonl yabou t M (Thorup& Iversen , 1974).Sinc ediatom san d algae aremor eabundan to ngrave li nth eSni jdersveerbeek ,th eover-representatio n in BGmigh tb erelate dt othi styp eo ffood ,althoug hthi sca nonl yb e atentativ e conclusion.I nTabl e2 2th epreferenc e forS+CD+ L (I.R.= 4.4 ) shouldb e considered with caresinc ethi sonl yconcern s threesamples . Inth egrain-siz e classification (Table 23)w ese etha t Serioostoma prefersth e gravellysubstrates ,togethe rwit h thedetritu ssubstrates .Th e over-representation inth efine rsubstrate s isprobabl ymainl ydetgrmine db yth epresenc eo fcoars ede ­ tritus,sinc eonl yth eI.R . values forxx xan d 23xincreas efro mth eH toth e10° s sorting. Thever yhig hpreferenc e forcoars esubstrate s isals oclea rfro mth efield -

Table23 .I.R . values for Serioostoma personation (N= 346 )i nth egrain-siz e classificationo f thesubstrate s inth e Snijdersveerbeek.

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 5,10% -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 Sort 6,10% -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 Sort 7,10% - -1.0 -2.1 -1.9 -1.0 -1.9 -2.3 -3.7 6.9 0.6 -1.8 2.8 -4.2 -3.1

Q^MJQ„ index xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L 1 d 3 --x47 x 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

Italic values indicate significant over-representation

70 Table24 .I.R .value sfo r Serioostoma personatum perlengt hclas s (A)an d season (B) Inth eSnijdersveerbee k InSor t8,10% .

Length N Substrate classan d Q index QlMd 3 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 xix 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

Italicvalue s indicatesignifican t over-representation

classificationi nTabl e2 2whe n consideredo na les sdetaile d level.Consideratio no f thepreferenc eo fsevera l lengthclasse si nSor t8 ,10« .(Tabl e24A )show stha tth e smallest (0-5mm )larva eprefe 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 largertha n9 m mdistinctl yprefe rgrave l (x3x,x2x) . Pupaear epre ­ dominantly foundi nxîx . However,al llengt h classessho wpositiv eI.R .value si na tleas t5 substrat e classes,whic h suggests thata wid e rangeo fminera lsubstrate sca nb einhabite db y S.personatum andtha tth epresenc eo fdetritu splay sa nimportan trole .Compariso n betweenseason sshow s (Table 24B)tha tth eanimal sar eabsen t fromth edetritu ssub ­ stratesi nwinte ran dspring ,whe n theyar 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 dtha tthe yca nb efoun dburrowe di nsan d substrateso r undero rbehin dstone swher eth esan di softe nmixe dwit h leaves.The yprefe r these placesbecaus e theyar enight-activ ean dhid edurin gth eday ,a phenomeno nofte n observedi nlaborator yexperiments ,wher e theyburro w immediately duringth eday ,bu t move overth esurfac ea tnight ,althoug h theyma yb eobserve dmovin g overth estrea m bedi nshade dplace sdurin gth eda ya swell .Jone s (1949)an dGeijske s (1935)bot h reported that S.personatum isofte nfoun di nth esam ehabita ta s Ephemera danioa, namelyi ncoars egrave lan dstone snea rth ebanks ,wher eth ecurren ti sslower , but 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 k remainsunexplained ,however . Accordingt oNielse n (1942) S.personation isneve rfoun di nhig hdensities ,bu t thisi scertainl yno ttru efor th eSnijdersveerbeek ,wher eo nsevera loccasion s (when 7 collecting larvaefo rexperiments )mor etha n4 0specimen swer e foundo n10-1 5c m of sandmixe dwit hgrave lt oa dept ho fapprox .5 cm ;a clay/loa mban kprevente d further penetrationbelow .

Case building Accordingt oWallac e (1977), lastinsta rlarva eo f S.personation dwell ina cas ewhic hi s1 3m mlong ,bu tHicki n (1967)an dLepnev a (1964)mentio na cas e lengtho f15-1 6mm .Th ecas ei smad efro m long,narro wgrain sof ,fo rexample ,0.6 5 mmb y0.1 3m m (Nielsen, 1942),whic har earrange di na characteristi cmosai cpatter n ina singl elaye rstuc ktogethe rwit h thick,yellow-brow nsalivar ysecretion .Th e surfacei scompletel ysmooth .Th ecas ei sslightl y curved, especially insmalle r instars-;I ttaper stoward sth erear ,excep ti nth elas tinstar ,fo rwhic hth ecas ei s practicallyparallel-side dbecaus ei ti sn olonge rnecessar yt oenlarg eth ecase ,

—(H F-2 »KF-l—• » -H Pupae

S 50

1 |' I ' | ' I l| • I i | ' I i | ' I ' | ' I ' | • I ' | 'I ' I' I ' I' I ' I' I 1• •I •I • • I• • • T ' • ' •i • • I 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 head width classes (mm) Fig. 24.Distributio n(% ) ofgrain-siz e fractions innatura l caseso f Serioostoma personatvm. 1= 0.05 0- 0.10 5mm ;2 = 0.10 5- 0.15 0mm ;3 = 0.15 0- 0.21 0mm ; 4 =0.21 0- 0.25 0mm ;5 = 0.25 0- 0.35 0mm ;6 = 0.35 0- 0.50 0mm ;7 = 0.50 0- 0.85 0 mm;8 = 0.85 0- 1. 0mm ;9 = 1. 0- 2. 0mm .

72 restrictingth ebuildin g activityt omaintenance .Th erea ren di sclose dwit ha roun d membrane thati sperpendicula rt oth ecas ean dwithi nwhic ha nopenin g formed likea spooli spresent . Analyseso fth egrai nsize suse di nth ecase sshowe da nincreas ei ngrai nsiz e withincreasin g larvalsiz e (Fig« 24).Firs tinsta rlarvae ,reare dfro megg s deposited andhatche di nth erearin gchanne li nth elaborator y fromadult s thatemerge dthere , builda cas eo fgrain ssmalle r than0.15 0m mwithi na day .Goin g fromth einsta rF- 4 toF- 2a decreas e from2 H to0 1wa ssee nfo rth efractio nsmalle r than0.10 5mm , whileth e0.105-0.15 0m mfractio nremaine da tabou t50 1an dth efractio no f0.150 - 0.210m mincrease d from 241t o42«» .Fra nth eF- 2t oth eF instar sth efractio n 0.105- 0.150 decreasedt ozero ,whil eth efractio n0.210-0.35 0m mincrease d significantly. Thepupa l casediffer s fromth elast-insta rcas ei ntha ti tcontain s slightlymor eo f thever ycoars efraction s (upt o2 mm) , especiallyuse dfo rclosin gth ecase .Befor e pupationth ecas ei sextende dwit h largergrain san dattache dt ograve lo reve n stonesi nth estrea mbe d(belo wth esubstrat e surface),afte rwhic hth efron ti s closedwit ha sieve-lik emembran ewit ha centra l clefto fwhic hth eedge sar eben t outwards.Th ecleft si nth efron tan drea rmembran ear esituate dperpendicula rt o eachother . Whennake d finalinsta r larvaeo f S. personation wereoffere dal lgrai nsize s mentionedi nTabl e6 fo rcas ebuilding ,th emediu msan dfractio n (0.250mm )wa s preferred (Experiment1 ,Tabl e 25).Whe n thisfractio nwa s leftout ,th elarva euse d thefine ran dcoarse rsan d fractions (Experiment2 ,Tabl e 25).Whe nfin esan dwa s also leftout ,the ymainl yuse d coarsesan d (Experiment3 ,Tabl e 25),bu ti fthi swa s alsoabsen t (Experiment4 ,Tabl e 25)th elarva ebuil ta nemergenc y caseonl yan dwer e unablet ous ecoarse rgrain so rlea fmateria lfo rcas ebuilding . Comparingth egrain-siz e compositiono fth ecase swit h thato fth esubstrate s preferredb y S.personation inth eSnijdersveerbeek ,n odirec trelationshi pca nb e seen.Al lfraction sneede dfo rcas ebuildin gwil lb epresen ti nth esubstrate .However ,

iti sstrikin gtha tsubstrate swit hQ 3= 2 (0.25 0- 0.50 0mm ) (Table 23,Sor t7 ) are preferred,whic hmean s thatcoars esubstrate s (Sort8 )mus t includea tleas t 251o f the fractions finertha n0.50 0m man dcoarse r than0.12 5mm .

Table 25.Grain-siz ecompositio n (percent)o fcase sbuil t byfina l instarlarva eo f Seriaostoma personation inlaborator y experiments.

Proportion(% ) of grain-size fraction (lowerlevel , mm) incase 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 Experiment 4t 0 Ab Ab Ab

Ab= Grain-siz e fraction absent t:In Experiment 4n ocas ewa sbuil t

73 Substrate-selection experiments Ina firs tserie so fexperiments ,th esubstrat e selectiona tlo wan dhig h currentspeed swa steste dfo rF an dF- 1 instars (theinsta r was onlyroughl ydetermined) .A tbot h currentspeed s these larvae (F, F-1)selecte d thecoarses tparticl e size (16mm) ; particle 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 larvaetha n4 m man d8 mmparticle s (Fig.2 5a an db) , althoughth edifference sar eno tsignificant .Th e sameexperimen t conductedwit hF- 2an dF- 3instar s showed againtha tcurren tdoe sno t influenceth esubstrat eselectio nsignificantl y (Fig.2 4c an d d). 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 wcurren t 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 showed that 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 d thatther ewer en osignifican t differencesi n substrate selectionbetwee ndifferen t instarso f S.personation inlaborator yexperiments . Unfortunatelyn oexperiment swer ecarrie dou twit horgani c substrates.Th eselectio n frequency(% )

40- a

20-

I—I i—' 0- 125 5001 2 4 8 16 125 5001 24 81 6 S 125 5001 2 4 81 6 S

frequency(% ) 40- d

20.

0- I 125 5001 2 4 12 4

Flg. 25.Substrat e selection inlaborator y experimentsb y Seriaostoma personation. Grain-size fractions are indicatedb y thelowe rlimi t in \im(unde r 1mm )an dm m (over 1mm) . S= en d retaining screen.

Figure Instar Body Number of Number of Current no. length experiments larvae per velocity /mm experiment (cm/s) a F ; F-1 8-14 8 16 5 b F ; F-1 8-14 8 32 10 c F-2; F-3 6-10 4 16 5 d F-2; F-3 6-10 8 16 10 e F-1; F-2 7-11 3 32 10

74 phi values î S «3 4

î 3- I Î 2 1•

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ï

2

3- I

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S

6

M (phivalue )

Pig. 26.Compariso no fsubstrat epreference s inth efiel d (unshaded)wit h particle-sizeselectio ni nlaborator y experiments (shaded)fo r Serioostoma personation.

ofth ecoars esubstrate si si nful lagreemen twit hsubstrat epreference sin th e field,a sobserve din th eSnijdersveerbeek ,wher ex3 xan dx2 xsubstrate sar epreferred , forwhic h50 $o rmor eo fparticle sar ecoarse rtha n1 um .Fo rmos to fthes esubstrate s moretha n25 $i scoarse rtha n1 6mm .Th esimilarit yo fth efiel dan dlaborator y studiesi sfurthe rillustrate di nFig .26 ,wher ebot hth esubstrate spreferre di nth e field (basedo nSor t5 t o8 ,10$ )an dth eparticle-siz eselectio ni nth elaborator y experimentshav ebee nprojecte don th eQiM,Q ,grap h (Fig. 14).

4.2.2.3 Micropternasequa x (MacLachlan) (Trichoptera:Limnephilidae )

Life cycle M. sequax hasa clearl yunivoltin elif ecycl ein th eSnijdersveerbee kan d theRatumsebee k (Fig.27) .Larva ewer ecollecte dnumerousl yi nshove lsamples , and alsoin additiona lcollections .Pupa ewer efoun donl y incidentally (11specimen si n total)i nth eshove lsample san dno ta tal lcollecte db yhand ,sinc epupa ear e burrowedi nth esubstrate ,whil elarva emostl yoccu ro nto po fo ri nth euppe rlayer .

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*HI "M" Mi "i*iad a a s a a LEN3TH CLASS ( rn Fig. 27.Lif ecycl ehistogram so fMiaropterna sequax showingth edistributio n(% ) oflarva lbod y length,pupa e (99)an dadult s (98)pe rfour-wee kperiod .

76 Pupaewer e foundfro mMarc h- September ,whic hmigh t indicatea lon g flightperiod . Thiswa sals oconclude db yCrichto n (1971)fo r Stenophylax (= Miavoipterna) 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 rLimnephilus 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 ,th e lastinsta rlarva ebecom e18-1 ran9 long .I nth eSnij ban dRa bthe yreac ho naverag e 20-25nm ,wit hexceptionall y somesmalle rspecimen s (fifthinsta rlarva eo nth ebasi s ofhea dwidt hha da bod y lengthrangin gbetwee n 12.5an d25. 2mm ,se eTolkam p& Verdonschot,t ob epublished) .

Miarodietpibut-ion Inth eRab , M.sequax occurredpredominantl yi ndetritu s substrates andn oover-representatio nwa sfoun do nminera l substrates (Appendices9 an d13) .O f the28 6larvae ,25 2occurre di ndetritus ,8 i ngrave lan d2 6i nsan dwit ha negativ e Q...Th elarva eo nminera l substratewer 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 efo rCoars eDetritu s substratesan dLea fsubstrate si nth eRa bwa s clearly linkedwit hth eseason .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 nleave sar eabundan t (cf.Scott ,195 8fo r Stenophylax spp.). Inspring ,onl y6 animals'*wer efound ;i nwinte r 23.Thes elo wnumber 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 d furthero 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.K .value sfo r Miavoptema sequax (N= 194 )i nth efiel dclassificatio n ofth esubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritusi

3 -2.0 1.2 2.0 I I 1 1 1 1 4 -3.3 0.7 2.1 -0.9 2\0 .1 i 1 1 I 1 1 2 -2.0 -3.1 3.0 -1.5 2.1 -0.9 i.. I 1 11 1 1 1 1 1 1 I 1 1 1 1 1 1 1 0.4 -3.7 -3.1 3.4 -0.4 5.3 -2.0 0.6 2.1 -2.2 1.9 1 -1.5 2.1 2.1 St Sh FD L CD CD+L CD+FD L+FD B L CD CD L CD+L

Italicvalue s indicatesignifican t over-representation

77 Table27 .I.R .value s for Miaropterna sequax (N= 194 )i nth egrain-siz e classificationo fth esubstrate s inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phi index 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 Sort 6,10% -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 QM 0 index xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L 1 d3 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 s indicatesignifican t over-representation

overdifferen t substrate types.Mor e larvae occurredi nSan d (82)an dGrave l(69 ) andno ti nDetritu s (43).I nSor t3 thi s leadst oa preferenc e forDetritu san d Gravelbu tthi spictur ei stotall y differentwhe nconsiderin ga mor e detailedclassi ­ fication (Table 27). Here M. sequax prefers S+CD+Lan dS+L ,followe db yBG ,G+L ,C D andL substrates .I nth egrain-siz e classification (Table 27)thi si sreflecte di n thepreferenc e forxï x (i.e.2Ï2 ,derive d fromSort s5 t o7) , besidesL an dCD .I n

table2 6i tca nb esee n thatth eclassificatio no nth e QIMJQ3 index (Sort 8)seem st o obscureth einfluenc eo fth e separatequartiles .I nSort s5 ,6 an d7 ther ei sa clea r

tendency towardsth esubstrate s with coarse fractions (Q.= 6 ,5 ;M ^= 5 ;Q 3= 5 , 4). Thisi sles sclea ri nSor t8 (x5x ,x4x) . Stillth epresentatio ni nSor t8 wil lb e themos t reliableon e becausei nth e firstsi xclasse si nSor t7 th enumbe ro fsample s

isver y low.Th elo wC \ andM ,value sar ecombine dwit ha hig hQ 3valu ei nth e Classes 2an d5i nSor t8 . Considering thedistributio nbetwee n seasons (Table 28B),minera l substratesar e favouredi nwinter ,sprin gan dsumme ran dorgani cdetritu s substratesi nautumn . The summer dataonl y concernsample s fromth e lastwee ki nsumme r (Week 37). M. sequax was not foundi nth epreviou s 12weeks .Th eautum npreferenc e forLeave si slinke dwit h larvae from 1-10m man dtha tfo rCoars e Detrituswit h 16-20m mlarvae ,whil eth e 10-15m mlarva ear epresen t in22 xan d23 x(combine dwit hdetritus ) (Table 28A).Th e largest larvaeoccu rpredominantl yi nxï xan dx1x ,whil eo fth enin epupae ,eigh t occurredexclusivel yi nsubstrate s coarsertha nxx x (withon especime ni nCD+L) , whichmean s thata tleas t 251o fth egrai n sizesar ecoarse r than1 mm . Preferenceo f thepupa efo ra certai ngrai nsiz ecombinatio ncoul dno tb edemonstrate d signifi­ cantlybecaus eo fth e lownumbe ro fspecimens .I ti sexpected ,however ,tha t sub­ stratespreferre db ylas t instar larvaewil la tleas tpartl y reflect the preference ofth epupae .Thi swil lb eteste di nexperiments .

78 Table28 .I.R .value sfo r Mioropterna sequax perlengt hclas s (A)an dseaso n (B) inth eSnijdersveerbee k inSor t8,10% .

Length N Substrate classan d Q Q3 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 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- 15 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- 20 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- 30 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 B Spring 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

Italic val ues indicates i gnificant over-representation

Mackay (1977)demonstrate dfo rPyanopsyahe soabripennis thatpupa eburro wi n particularsubstrate san dma 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 lshowe dtha tlarva eread 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 yconical ,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 0m mlon g- arefound . M.sequax changesit sbuildin gmateria li nth esam esequenc eNielse n (1942) describedfo rStenaphylax nigrieornis. Juvenile larvaeal lbuil dminera lcases , but later instarsus eleave san dminera lmatte ri nvariou s combinations (Tolkamp& Verdonschot,t ob epublished) .I nth elaboratory ,las tinsta rlarva emainl yuse dth e 0.5-1.0m mparticle sfo rcas ebuilding ,togethe rwit h leavesan d1- 2m msand .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 dcompletel yminera lan dcompletel yorgani ccases ,whil e fifth (F)instar s

79 of cases Instar: F-3 ®

Instar: F-2

15- Instar:F- l 10 n=- _•_ 25 - [-4

20 - Instar: F

10 - nJ ^""n n i n H 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-

80-

70-

60

50 -

40"

30

20 -

12 3 4 5 6 12 3 4 5 6 12 3 A 5 6 123AA6 12AAA6 Substrate offerred

Fig. 28. a: Distribution (%)o f organic and mineral matter in natural cases of Miaropterna sequax for the second (F-3) to the last (F) instar, b: Case building of Miaropterna sequax under experimental conditions in the presence of various grain sizes. 1 = leaves; 2 = 0.125 - 0.250 mm; 3 = 0.250 - 0.500 mm; 4 = 0.500 - 1.0 mm; 5 = 1.0 - 2.0 mm; 6 = 2.0 - 4.0 mm; A = absent.

80 display thesetw oan dal lpossibl e combinationso fleave san dsan d (Fig.28B) .However , pupal casesar ealway scompletel ymineral . Analysiso fth egrai nsize suse db yth edifferen t instarsshowe dtha tth ethir d instaruse dfo r40 1th egrai nsiz e fraction1- 2mm ,an dfo r20 1th efractio n 0.5 -0.8 5mm .Th eremainin g 401wa sdivide dove ral lfine rfractions .Th efourt han d fifth instaruse dsomewha tcoarse rgrain s (0.5- 0.8 5mm ,4 0- 50% ;1- 2mm , 301). Theseratio so fth eparticl e sizeswer epresen ti nth epurel yminera lcase s(Fig . 29A),a swel 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 larger thanthi sbecaus eth ecas ei sextende do nbot hside swit h coarse sandan dgravel .Jus tbefor epupatio nth elarva eattac h1- 4m mgrain st oth efron to f thecase ,completel y closingi tbu tfo rsmal lopening sbetwee nth egrains .O nth e inside,a siev emembran ei smad eo fsalivar ysecretion .Th elarv aturn si no routsid e thecase ,bite sof fth erea rpar tan deventuall yextend s thissid ewit hminera l materialwhe na larg eportio nha dt ob 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 hth eenlarge drea rstil lprotrudin g fromth esurface .I nthi spositio n thene wfron ti sals oclose dwit hcoars esan dan dfin egravel ,sometime seve nattache d tocoars egrave lo rpebbles .Th einsid eo fth efron ti sals ocovere dwit ha membrane . Observationso fpupa ei nthi spositio nwer emad ei nth elaborator yi nth erearin g channel,durin gexperiment si nth eartificia l stream,a swel la si nth efield . Nielsen (1942)alread yoffere da nexplanatio nfo rthi skin do falternatin gcase - buildingbehaviour .Whe n larvaenormall ybuil dminera l cases,th ethic k layerso f leavesi nautum nmigh tpreven tth elarva e fromreachin gth esan dbottom .Whe nthe y normallybuil d leafcases ,i ti spossibl e thatyounge ran dolde r larvaeus ecoars e sandbecaus e leafmateria lma ythe nb escarce .O nth eothe rhan da lea fcas eoffer sa muchbette r camouflagewhe n leafsubstrate sdominat ei nth estream ,an dlikewis efo r aminera l casewhe norgani csubstrate sar escarce .Th enecessit yt obuil da minera l casei nth elas tinstar ,preparin gfo rth epupa l case,probabl y liesi nth efac ttha t prédationo norgani ccase scoul db ehigh ,especiall yi nperiod swit hlo wamount so f organicmaterial .Besides ,organi ccase sar edecompose db ybacteri aan dfung i (Mackay,1972 ;Macka y& Kalff , 1973). Burrowingi nth esubstrat ei sclearl y alsoa protectiv emechanis magains tpréd ­ ationan dpossibl ydrift .I nth erearin gchanne li twa s observed thatcase sdu gint o thesubstrat e completelyo rwit honl yth erea rprotrudin gwer e leftalone ,bu tcase s removed fromth esubstrat ean dpu to nth esurfac ewer e openedb ylarva eo fth esam e speciesan dth epupa e consumed (Gallepp (1974)observe dth esam ephenomeno nfo r Braahyaentrus oooidentalis).

Sxibstrate-seleation experiments Single grain-size fractions Mackay(1977 )performe d experimentswit h P.soabripennis witha 1 6n mpebbl ei nth emiddl eo fth esubstrat e traysan destablishe d thatth elarva eshowe dn ospecia lrespons et oth epebble :n o

81 ie-T-2-M hs F-i M te- Pupae ©

o 50-

'' I' !' I '' I' '' I' I' I' I' I' ' ' I' I' I' '' I' ' ' I' I' I' ' 0.8 1.0 1.2 1.4 1.6 1.8 ®

.2 6°-

0 I • I' i' I' i' I' i ' ' I' I' I' I' I T—r-ri 0.8 1.0 1.2 1.4 1. 1.8 2.0 head width classes(ram ) animalsburrowe ddirectl ybelo wth epebble .I nexperiment swher e M.sequax could choosebetwee n8 particl e sizes,rangin gfro m0.050- 8mm ,th einfluenc eo fa 1 6m m pebbleplace di nth emiddl eo fth etray swa steste di na simila rway .Thi spebbl edi d notinfluenc eth eparticle-siz eselectio no rth epreferenc efo r2 ,4 an d8 m m (compareFigs .30 aan d31b) ,althoug hfine rsubstrate swit ha pebbl eattracte drelativel y moreanimal stha nwithou ta pebble .A similarexperimen twa scarrie dou twit ha beec h leafplace dunde rth epebbl ea swell .Agai nn odifference swer eobserve d (Fig.30 b comparedwit h30 aan d311) . Inal lfollowin gexperiment sth epebbl ewa stherefor e omitted. Iti sinterestin gt onot etha tal lobservation sdon eb yda ylea dt oth esam e result,bu tä 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 gsite san dg oi n searcho ffood ,hous ebuildin gmaterial ,etc .Cummin s (1964)conclude dfo r Pyanapsyahe lepida thatthe yd ono tburro wi nth edark, whic hsuggest stha tth eburro wresponse s arelinke dt ophotoperio di na functiona lway .H eals oconclude dtha tth elarva ed o notburro wwhe nthe ybuild . Giventh echoic ebetwee n0.12 5- 1 6m mparticl esizes , M.sequax preferredcoars e substrates (coarsertha n2 mm )wit hpeak si n1 6m man d4 m m (Fig.30d) .Replacin g particleso f0.12 5m mb ythos eo f3 2mm ,th epreferenc efo rparticle sove r2 m mre ­ mained,bu tth edifference sbetwee nth ecoarse rparticle sar eno tsignifican tan y more (Fig.30e) . Whenparticle so f0.12 5m mar ereplace db yleave s (atra yfille d withbeec h leaves), M. sequax againpreferre d 16an d4 m mabov e8 an d2 m mo rLeave s (Fig. 30f).Whe n 16-mmparticle sar ereplace db yleaves ,th epreferenc eshifte dfro m 16m mt oleave san d8-m mparticle s (Fig. 30g). Ina serie so fexperiment swher eth epreferre dparticl esize(s )wa s (were) omitted,individuall yo ri na combination ,th epreferenc ealway schange dt oth e coarsestparticl esiz epresent .However ,2 ,4 an d1 6m mar epreferre dmor estrongl y than8 mm .Th ecombination soffere dwere :0.05 0m mo r0.12 5mm ,0.25 0mm ,0.50 0m m and1 m mcombine dwit hon ecoarse rparticl esiz e (Fig.31a-g) ,tw ocoarse rparticl e sizes (Fig.31h-j) ,thre ecoarse rparticl esize s (Fig.31k-n )an d4 o r5 coarse r particlesize s (Fig.30 dan de) . Theconclusio nfro mal lthes eexperiment si stha t M.sequax canburro wmor e readilyi n2 ,4 an d1 6m msubstrate s thani 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 garound ,climbin gth escreens ,o rove rth eturne d overtrays ,probabl yi nsearc hfo rmor esuitabl e sites.Th eaversio nfo r8 m mparticle s

Fig.29 .Distributio n(% ) ofgrain-siz efraction si nnatura lcase so f Moroyterrux sequax. a:minera l cases b:case spartl y consistingo forgani cnatter . 1 - 0.105- 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(% )

40

20

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

40 W 20-

0 _Ë Y7A 125 5001 2 4 81 6 S 250 1 2 4 8 163 2 S frequency(% )

40

20-

0- L 5001 2 4 81 6 S L 250 12 4

Fig.30 .Substrat e selectioni nlaborator y experimentsb y Micropterna sequax. Grain-size fractions are indicatedb y thelowe rlimi to f thefractio n in ym (under 1mm )an dm m (over 1mm) . 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 mpebbl e b mixed F >1 5 10 16 + 16m mpebbl e c mixed F >1 5 10 16 idemb ,a tnigh t d mixed F >1 5 29 16 upstream(shaded).downstream e mixed F >1 5 10 16 (unshaded) f mixed F >1 5 10 16 + leafpac k (shaded) g mixed F >1 5 15 16 + leafpac k (shaded)

wasals oapparen ti nexperiment swher eothe rcoars eparticle swer epresen t (Fig.31i , 1 and n). Allexperiment s indicate that M. sequax doesno tprefe rgrai nsize ssmalle rtha n 1mm ,althoug hthe yma yb efoun dher e incidentally. Inman y instances theyar ethe n buildingo rrepairin g theircases .

Mixtures of grain sizes Theparticl e sizes 2,4 ,8 an d1 6mm ,whic happeare dt ob e preferredabov e0.05 0m m- 1m m inal lpreviou sexperiments ,wer e offered together withmixture s (equalamount so fbot hparticl e sizeso nvolum ebasis )wit h0. 5 and1 mm,respectively .I na firs tseries ,th elarva ecoul dchoos efro m 4substrates ,

84 onlyth efou rparticle s sizeso rth efou rmixture s (Fig.32 a- c); ina secon dserie s thechoic ewa s from 8substrates ,namel y thefou rparticl e sizesan dth efou rmix ­ tureswit h 0.5m man d 1mm ,respectivel y (Fig.32d , e). Forth efirs tseries ,i ti sclea rtha tth eattractio no fth epreferre dparticl e sizesa sa substrat e changeswhe nthes eparticl e sizesar emixe dwit h finergrains . Thepreferenc e for2 m mdecrease ddrasticall ywhe nmixe dwit h0. 5m mo r 1mm .Th e preference for1 6mm ,4 m man d 8m m (decreasing inthi ssequence ) (Fig.32a )change d toth esequenc e 4mm , 16m man d 8m m inth 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 man d 16mm ,whic h isa complet ereversio no fth ese ­ quence.A possibleexplanatio n istha tth eaccessibilit y ofth e 8-mm substratein ­ creaseswhe nth e interstices arefille dwit hgrains .Normall y theinterstice s of8 m m areto osmal l for M.sequax toente ran dth e 8-mm grains tooheav yt opus h aside withoutmuc heffort .Fo r 16-mmparticle s iti sno tnecessar y andfo r4-m m particles iti sobviousl yn oproble m topus hasid e thegrains .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 e the 16-mmgrain s areto 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 coarse grainsma yrol lasid eeasie rwhe n thefin egrain s areremoved .Particl e sizes smaller than 1m mar eno tpreferre d (Fig. 30),possibl ybecaus ethe yoffe rto omuc h resistance anddeman dto ogrea ta neffor tfo rpenetration . Fromth eexperiment s discusses above,i ti sclea rtha t 1m m canstil lb euse db y parto fth epopulation ,whic hmean s thatth eresistanc e ofthi sparticle s sizei sno t insurmountable (Fig. 31b),whil e in0. 5 mman dsmalle rparticles ,th eanimal shardl y burrowa tall ,sho wn opreferenc e andkee pmovin garoun d (Fig.31c) . Inth esecon dseries ,i nwhic h thelarva eha d thechoic ebetwee nth e fourbar 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 h 0.5m 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 serieso fexperiment swit h M.sequax indifferen t casetype swa s conducted: animalswit h an 'almost'pupa lcase ,alread yclose do non e sidewit h coarsegrain s (seesubsectio no ncas ebuilding),th eso-calle dhal fpupae ; animalswit ha minera l case;an danimal swit h apartl ymineral ,partl y organic case (mixedcases)(se e table5) . Halfpupa epreferre d thethre ecoarses tgrai nsize s (Fig.32f )withou t any preference fora specifi cgrai nsize .Thi s agreeswit h thedistributio n inth efiel d ofth e largest larvaean dpupae ,whic hpreferre d substrateswit h at least 251coarse r than2 mm .Al lothe rcas e typesshowe d thesam epreferenc e aspreviou s experiments (Fig.32g ,h) , although larvaewit h aminera l casepreferre d 8m m afterth e first choice of 16mm . Inth epreviou s experiments larvaewit hmixe d caseswer e always

85 used,an di ti slogica l thatth esam epreference s for1 6an d4m mwer e found.Th e difference between larvaewit hminera lan dmixe d casesca npossibl yb eexplaine db y thestronge rpenetratin g abilityo flarva ewit hminera l cases.Partl y organic cases aremore easilydamaged .O nth eothe rhand ,th eanimal si nminera l casesma yb e closert opupation ,becaus e animalswit hpartl y organic cases stillhav et oreplac e the organicmateria lb yminera lparticles . A serieso fexperiment swit h larvaewit hminera lan dmixe d caseso nsubstrate s consistingo fa monolaye ro f2 ,4 ,8 o r1 6m mgrain so na bas eo f0. 5m man d1 mm

frequency (%)

60 H

40-

20-

0J i i • 50 250 1 2 A A S+B

60_| freq.(%) IgTk

40-1 d

20"

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 Mk 60- freq.(%)

40- g

20- • oJ n12 5 n50 0 1 A 4 A A S+B 50 250 1 2 A 8 S+B 125 500 1 2 A 8 16 S+B

60~| freq. (%)

40-' j

20- • 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

60- freq.(%) .

40-

20-

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

86 (Fig.32 ian dj) , respectively,showe d thatth epreferenc efo r1 6m man d4 m mremain s forbot hcas e types,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 penetrating abilityo flarva ei nminera l casesma ycaus eth epreferenc efo r4 mm . Larvaei n1 6m mwer emostl ypresen to nth ebase ,no to ronl yhal fburrowe d beneath the 16m mgrains ,whil e thosei n4 m mha dcompletel y disappeared fromview .

Differences between instars Aserie so fexperiment swit h larvaeo fdifferen tag eo n substrateso f0.12 5- 1 6m mshowe d thatth epreferenc efo r1 6m mi ssimila ri nal l instars studied (.Fig.32k :F-2 ;Fig .321 :F-1 ;Fig .30 d: F) .F- 1an dF- 2insta r larvaewer ever y activean 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 t speedo nth esubstrat e selectiono f the larvaeshowe d thatth epreferenc eo flas tinsta r larvaei sno tinfluence db yth e current (Fig- 30d).Younge r larvae (F2),however ,positivel y selectedth edownstrea m substratesa thig h currentspee.d s (10cm/s ) (Fig.32m) .

Leafpaaks as siibstrate placed on a mineral base Offering M.sequax alea fpac k(beech ) ina smal l 12m mmes hbasket ,place do nto po fth e0.12 5m msubstrate ,togethe rwit h theminera l substrates 0.125- 1 6mm ,F- 2insta r larvaepreferre dth elea fpack s (Fig.33a ,b) , whileth eanimal sar ever y activea ssee nb yth elarg enumbe ro f screenanimals .Offerin g these larvaea 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 selectioni nlaborator y experimentsb y Mioropterna sequax. Grain-size fractionsar eindicate db yth elowe r limito fth efractio ni n um (under1 mm )an dm m(ove r1 mm) . S= en dretainin g screen;B = botto mo freverse d tray (shaded);A = absent . Figure Case Instar Body Numbero f Number of Note no. type 1ength experiments larvae per /mm experiment a mixed F > 15 5 16 4 and 8m m absent b mixed F > 15 5 16 2,4an d8 m mabsen t c mixed F > 15 5 16 1,2,4 and8 m m absent d mixed F > 15 1 16 4,8 and 16m mabsen t e mixed F > 15 1 16 2,4 and8 m m absent f mixed F > 15 1 16 2,4an d 16m mabsen t g mixed F > 15 1 16 2,8an d 16m mabsen t h mixed F > 15 5 16 4m m absent i mixed F > 15 4 16 4m m absent i mixed F > 15 5 16 4 and8 m m absent k mixed F > 15 14 16 8m m absent 1 mixed F > 15 35 16 16m m absent m mixed F > 15 5 16 8 and 16m m absent n mixed F > 15 4 16 2m m absent

87 onth escreen s (Fig.33c) .F- 1insta r larvaewit hmixe d cases (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 n4 m mi s preferred (Fig.33e) ,whil ei nsection swithou ta lea fpac kan dth esam eminera l substrates (Fig.33f) ,2 an d4 m mar eselecte dwit ha muc hhighe rnumbe ro fscree n animals.F- 1insta r larvaeo n1- 8mm ,eac hprovide dwit ha lea fpack ,preferre dth e leafpac ko n1 m man dther ewer en osignifican tdifference sbetwee nth eothe r leaf packso rth eminera l substrate (Fig. 33g). Giventh echoic ebetwee n1- 8mm ,th e fractionso f2 ,4 ,an d8 m mar eequall y chosenwit h largenumber s ofanimal so nth e screens (Fig. 33h). Ina nexperimen twher e 0.125- 1 6m mparticle swer emixe dwit h coarse detritus (smallpiece so fbeec h leaves) M.sequax showedn osignifican tdifference si ngrain - sizeselectio n (compare Figs.33 ian d30d) ,indicatin g thatth eselectio no f1 6an d4

frequency (%) 60-

40-

20

0 2 4 8 16 2 4 8 16 S 2 4 8 16 S 2 4 8 16 S + + + + 500 + +1+ + frequency (%)

40-

20-

0 2 4 8 16 S 248 16 •S 248 16 S 2 4 8 16 S frequency (%) i J 40-

20-

0 - __ rzL 2 4 8 16 S 2 4 8 16 S• on 500 on 1 frequency (%)

40-

20-

1 rLH o- 125 500 1 2 4 8 16 S 125 500 1 2 H 8 16 S 12 4 8 S mmsubstrat eis- area lpreferenc efo rthes eparticl e sizeswhe n foodcondition sar e favourable,bu tFigs . 33a,d ,an de indicat etha twhe n foodcondition s (leafpacks ) aremor e favourableo nothe rsubstrat e types,foo di sth emai nselectio ncriterion . Concludingi tca nb estate dtha t M.sequax prefers leafpack s aboveminera lsub ­ strates.However ,whe n leafpack sar eabsen tthe yclearl yprefe rcoars eparticl e sizes (coarsertha n2 mm) ,i nparticula r1 6- 3 2m man d4- 8mm .Th efractio n8-1 6m m is lesspreferred ;thi smigh tb erelate dt oth epenetrabilit yo fth esubstrate .N o significantdifference swer eobserve di nsubstrat eselectio nbetwee nth ethre e last larvalinstars . Comparisonwit hth edistributio ni nth efiel d (Table27 )show s that substrates witha larg eproportio naroun d8-1 6m m(Q -o rM ,= 4 ) ar eavoided ,bu twhe nmos to f thesubstrat ei scoarse rtha n8-1 6m m(Q 3= 4 ) th esubstrat ema yactuall yb eprefer ­ red.Th esimilarit yi nsubstrat epreference s foundi nth efiel dan dth elaborator yi s furtherillustrate di nFig .34 ,upo nwhic hbot hth eparticl 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 ,101 )hav ebee nprojecte do nth eQiM,Q 3graph . Thusth eresult so fth elaborator yexperiment sconfir mth esubstrat epreference sob ­ servedi nth efield ,especiall y concerningth eshif to fpreference s fromdetritu s substratesi nautum n- whe ndetritu si sabundan t- t ocoars eminera lsubstrate si n winteran dsprin g- whe ndetritu s substratesbecom e lessabundan tan di tform sa mor e integratedpar to fth eminera l substrates.Th epreferenc eo fF- 1 instar larvae (10-15

Fig.32 .Substrat eselectio n inlaborator y experimentsb y Mioropterna sequax. Grain-size fractions areindicate db y thelowe rlimi to f thefractio n in ym (under 1mm )an dm m (over 1mm) . S= en d retainingscreen . FigureCas e InstarBod y Number of Numbero f Note no. type length experiments larvaepe r /mm experiment a mixed F > 15 16 16 b mixed F > 15 10 8 mixtureswit h0. 5m m mixed F > 15 2 16 mixtureswit h0. 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 e 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 ro n0. 5m m j 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-

40

20-J

O" 125 5001 2 4 81 6 S 5001 2mi x + L frequency(% ) "! d^ 40H l%t 20- D 25u0 1 2 500 1 2 4 S 5001 2 4 + + + + frequency(% )

40-| g

20

0 12 4 8 S 125 50012 4 81 6 S + + ++ ++ + + CD

Fig. 33.Substrat e selection inlaborator y experiments by Miovopterna sequax. Grain-size fractions areindicate d byth elowe r limit ofth efractio n in um (under 1mm )an dm m (over 1mm) .L = leaves; S= en dretainin g screen;C D= coarse detritus.

Figure Case Instar Body Number of Numbero f Note no. type length experiments larvaepe r /mm experiment a mixed F-2 6-10 5 32 leaf pack (shaded)o n0.12 5m m b mixed F-2 6-10 5 32 leaf pack (shaded)o n0.12 5m m c mixed F-2 6-10 5 16 mixture of0.5+1+2+ 4 mm d mixed F-l 10-15 5 16 leaf pack (shaded)o n0.25 0m m e mixed F-l 10-15 5 16 leaf pack (shaded)o nal l f mixed F-l 10-15 5 16 g mixed F-l 10-15 4 8 leaf pack (shaded)o nal l h mixed F-l 10-15 4 8 i mixed F >1 5 3 16 all mixed withC D

mm)fo rsan d substrates (Table 28)coul dno tb e confirmed inexperiment s (Fig.33d - k), buti ti sproblabl yexplaine db y thepresenc e ofcoars edetritu s inth esan d substrate,althoug h iti sles stha n 10%.

90 phi values î S Q 3 4

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3

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5

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

A.Z.2A Chaetopteryxvillos 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 g channel,emergenc estarte d mid-Octoberan dcontinue dtil learl yDecember ,whic hagree swit hth epea ki nNovembe r reportedb ySvensso n (1972),althoug hh estate da tota lfligh tperio d frommid - Septemberunti lJanuary .Decamp s (1968)ofte nfoun dadult si nth esnow .Hicki n (1967) gavea shorte rperiod : onlyth 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 y fast,partl ybefor ewinte rwhil e parto fth eegg soverwinters .I nMay ,firs tinsta r larvaeca nb estil lfound .Earl y hatched larvaeoverwinte ri nth efirs to rsecon d instar (Dittmar,1955 )an dstar t

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'°H!1c1lu1^r"l01'^9-!a33ï!Siy3ïlS im !_rNG'r' - :;L.ASS ( M"i) Fig.35 .Lif ecycl ehistogram s of Chaetoptevyx villosa showing thedistributio n (%) oflarva lbod y length,pupa e (99)an d adults (98)pe r four-week period.

92 growingagai ni nApri l (Elliot,1971) ,althoug h inth eSnijdersveerbee k thisseem st o beearlie r (Fig.35) .Ellio t (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 m longan d 3m mwide . Insumme rth elarva 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 di nth epresen tresearch ,a sgrowt hwa sstil lobserve d in 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 g inal l directions (aso-calle dshodd y case).Startin gfro mth efourt h (F-1)instar ,minera l matter isuse dalso .I nth efift h (F)insta rminera lmatte r isofte nth eonl ybuildin g materialwit hperhap ssom esmal lpiece so flea fmateria la tth erea rend . Fromth edat ao fth eSnijdersveerbee k thistendenc y isals 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 h indicates thatmimesi sma ypla ya nimportan trole ,a salread yreporte d for M.sequax. Ch.villosa uses leafan dminera lmateria li nal linstars ,althoug h thefirs tthre einstar sus e relativelymor eorgani cmateria lan dth elas ttw oinstar smor eminera lmatter .O fth e mineralmateria lther ewa sa significan tpreferenc e forth e 1-2m man d0. 5 -0.8 5 mm fractions inth elas tinstars ,wit ha decreas eo fth estil lfine rfraction swit hin ­ creasing instar (Fig.36) . Similarchange sfro mvegetabl e tominera lmatte rhav ebee nobserve dfo rman y memberso fth eLimnephilida e familyan dhav ebee ndescribe db yCummin s (1964)an d Mackay (1977)fo r Pyanopsyche spp.Fro mresearc ho n Potamophylax latipennis byZint l (1976)an do n Lepidostoma hirtum byHansel l (1972; 1974)i ti sclea rfo ra t least thesetw ospecie s thata chang ei nbuildin gmateria lan dstyl e isno tbase do n environmentalfactor sbu to na comple xo fendogenou s factors.Ellio t (1971)conclude d theopposit efo r Ch.villosa. He correlated thechang efro morgani ct ominera lbuildin g materialafte rth ethir d instarwit ha migratio no fth e larvafro mvegetabl et o mineralsubstrates .Th e latterphenomeno ni sals oobserve d inth epresen tstudy , althoughi twa sno tdirectl y linkedwit h theinstars ,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 e thepupa lcase sfro m M.sequax, butar esmalle ran dofte nstil lcontai nsom eorgani cmaterial .A similar closingsyste mi sused :th elarv aclose sth efron twit h 1-2an d 2-4m mgrains ,open s therear ,sometime sremove sth eorgani cmateria lan dextend s thecas ewit hminera l matter ifnecessary ,burrow sperpendicularl y intoth esubstrat e andclose sth ene w frontwit hmateria la thand .Th egrai nsize suse dfo rclosin gbot hend svar yfro m 0.5 -8 mm .

93 -F-2 ik F-l »| Re­ nest Pupae

-S 60-

I 'I ' ' 'I ' ' I' '' I ' I ' I ' I ' I' I' I MM '' I ' I ' I' I' I ' I 0.5 0.7 0.9 1.1 1.3 1.5 1.7 head width classes (mm)

Fig.36 .Distributio n (%) ofgrain-siz e fractions innatura lcase so f Chaetoptevyx 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 (1971J statedtha tth eadult sar equit ecapabl eo fflyin gint oth ewin d (atnight ,i nupstrea mdirectio nt ocompensat e fordriftin 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 r larvaei nth edownstrea msection s confirmElliot' s observationo nth epresenc eo fa colonizatio ncycl e (Müller, 19S4).

Microdistribution Inal lsubstrat e classifications, Ch.villosa obviouslyprefer sth e organicsubstrate s (Table2 9an d 30), althougha sligh tpreferenc efo rcoars eminera l substrates (Gravelan dDetritus )ca nb eobserve da swell . FromTabl e 31A,givin gth eI.R .value sfo ral llengt hclasses ,i ti sclea rtha t thepreferenc efo rorgani csubstrate si sprimaril y causedb yjuvenil e larvae (maximum length7 mm) . Larger larvae (12-20mm )prefe rminera lsubstrate swit hQ- ,< T an d preferablyM , È T (coarsertha n1 mm). Animalso fth elengt hClas s 8- 1 1m mwer emos tabundan ti nCoars eDetritus ,bu t

94 Table29 .I.R .value sfo r Chaetopteryx villosa (N= 386 )i nth efiel d classification of thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -8.7 1.7 13.2 1__ I— I 4 -7.2 -4.9 0.2 2.7 13.2 _J —i I 2 -6.0 -4.1 -0.4 -6.0 0.2 2.7 13.2 I r_1 _ 1 r r_ l r 1 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 . valuesfo r Chaetopteryx villosa (N= 386 )i nth egrain-siz e classificationo fth esubstrate s inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phiinde x detritus

6 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 xxx x5x x3x x2x xïx xlx xxx lxx 22x 23x 33x CD L CD+L QlMdQ3 indeX x4x Sort8,10 % 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 sindicat e significant over-representation

theyhav ealread ypartl ymove dt oth ecoars eminera lsubstrate swher eth elarges t larvaear efound .Pupa ewer eexclusivel y foundi nminera lsubstrat ewit ha preferenc e

forM ,betwee n2 an d8 m m(ph i= 3 an d2 )o rx3x ,x2 xsubstrat e (Q1 andM• ,< Ï ) .I n leafpack shardl yan y Ch.villosa larvaewer e found. Similarpreference swer eprobabl ypresen ti nth eRatumsebeek ,bu tthi scoul dno t be testedfo rth evariou s instarsb ylac ko fsufficien tmateria l (only6 0specimens) . Consideringth edistributio nbetwee nseasons ,Tabl e31 Bshow stha ti nwinte ran d springth ehighes tpreference sar efoun di nCoars eDetritus ,i nadditio nt owhic hi n winter onlynegativ eI.R .value sar efoun di nminera l substrates.I nsprin g therei s alsoover-representatio ni nxx xan dx4x/x5 x (M,resp .7 an d4) . Insumme rth eprefer ­ encei ssolel yfo rminera 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 Table 31.I.R .value s for Chaetopteryx villosa perlengt hclas s (A)an dseaso n (B) inth eSnijdersveerbee k inSor t8,10% .

Length N Subs träte classan d Q index QlMd 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 indicates i gnificant over-repre sentation

theseseasona ldifference swit h thedifference sbetwee nth evariola sinstar sshow sa remarkableconformit y inth edistributiona lchange sunde rth einfluenc eo flarva l size (age). Ch.villosa seemst ob ever ywel l adaptedt oth eseasona l changes inth e abundance ofsubstrat e typesan dfoo dresource s (coarsedetritus) . Chaeptopteryx isa detritivor e andth elarva eus e theenzyme spectinas ean d xylanaset obrea kdow nvegetabl ematte r (Bjarnov, 1972).Dittma r (1955)foun dtha t thelarva eoccu ri ncombinatio nwit hmacrophytes ,wher e theyfee do ndetritus , filamentous algaean ddiatoms ,althoug hthe yals opredat e onchironomid san dcaddi s larvae.I nth erearin gchannel ,Ch.villos awa softe nobserve d feedingo ncases , larvae orpupa e (mostlythos ewit hstil lsom eorgani cmateria l inthei rcases )o fit s ownspecies . Inwinter ,whe ndetritu s isabundan ti nth estreams ,th e larvaear esmal lan d theybuil dorgani ccase san dinhabi tdetritu s substrates onwhic hthe yfeed .Durin g springan d intosummer ,whe ndetritu s substratesbecom emor escarc eth e larvaegro w andmov et ominera l substrates,althoug hthes ewil lstil lcontai nenoug horgani c material,o rwil lb esituate d inth eneighbourhoo d ofdetritu s substrates,t oprovid e food,whic h isconsume da tnigh t (personalobservation) . Insumme ran dearl yautum n detritussubstrate sar ever yscarc ean dthi smigh t formpar to fth eexplanatio nfo ra possiblerestin gperio d inthi stim eo fyear .Apar tfro mth eobservatio nb yPetra n (1977), Kamler& Riede l (1960)als ofoun d Ch.villosa tob eth eonl y thrichopteran occurring indesiccatin g sections ofa stream . lilies (1952)state d forCh.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 s isno tcompletel yknown , but itprobabl yoccur smainl y inth esmalle r (uppercours etype )streams .Sinc e

96 Ch.villosa isa neurythermou san dmoderatel y rheophilous limnephilidi toccur si n quietplaces ,i npool so fsmal lstream so rstagnatin g largerstream swher e temperature 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, H.interpunotatus) andh ethough ttha t Ch.villosa mightb ecol dstenothermous .Th e observationsmad eb yth eothe rabov ementione d authorsan db yth edat afro mth e presentresearc hd ono tconfir mthis . Inhi sstud yo nth eemergenc epattern so fvariou s insectsi nth eBreitenbach , lilies (1978)foun da contradictio ni nth eemergenc eo fth emayfla y Baetis verrats and Ch.villosa, whichh eattribute dt oquantitativ ean dqualitativ e changesi nsubstrat e mosaicpattern si nth einvestigate d streamsectio n (the greenhouse) .Afte ranalysin g severalfactor s (temperature,food ,wate r level)h esuppose d thatth etempora l variabilityi nsubstrat epattern s (betweenyears )wa sth eonl ypossibl e factor responsiblefo rth ereciproca l abundanceo f Ùh.villosa and B.vermis, assumingtha t theyhav eopposit ehabita t (substrate)preferences .Th edat ao fth epresen tresearc h supportlilies 'assumption . Ch.villosa clearlyneed smor e thanon esubstrat etyp et o completeit slif ecycl ei na stream ,whil e Baetis vermis largelyprefer sth e(sheltere d placesof )ver ycoars eminera l substrates togetherwit hth esan d+ detritu s substrates (Appendix 12).Th elatte ri 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 elarva ear egrowin gfast ,an dcoars eminera lsubstrate si nsumme ran d autumnfo rrestin gan dpupation .I ti sver y likelytha ttempora lsubstrat evariatio n playeda rol ei nth egreenhous ewher eth eemergenc eo fthes especie swa srecorde db y lilies (1978).Whe nsan dan ddetritu ssubstrates ,perhap s togetherwit hsom elarg e stones,ar epresen ti nspring ,thi shabita twil lb efavourabl efo rB.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 s dominate,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 r larvaewit hvariou scas etype s (Fig.37) .Al lexperiment s lasted8 o r2 4 hours.Thi sgav en odifference si nsubstrat eselection .Afte r1 4hour sth edistribu ­ tiono fth elarva ei nth edar kwa srecorde da swell .Th elatte rresult swil lno tb e presented.I ngenera lth emai npreference s seenb 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 g screenso ra tth eedge so fth eexperimenta larea ,wher ethe ywer e obviouslyi nsearc hfo rmor esuitabl esubstrate so rfood .Th eresult so fth eexperi ­ mentswit hCh.villos aar esummarize di nFig .37 . Inal lexperiment swher ea leafpac kwa spresen to non eo rmor eo fth eminera l substrates,leave swer eth epreferre d substrate typefo ral lcas etype s (Fig.37a ,b ,

97 frequency (%)

a 40-

20- y A% m s 0-J D m, V 125 500 1 2 4 8 16 S 12 4 8 S 125 500 1 2 4 8 16 S + + + + i frequency (%) 40-

20

0-1 i—t 1 é2. n=A 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S + + L L frequency (%)

40- g M 20- 1 0 D D r^D 125 500 1 2 4 8 16 S 2 4 8 16 S 125 5001 2 4 8 16 S

frequency (%) 40-| j

20

0 D 125 500 1 2 4 8 16 S 2 4 8 16 S • 12 4 8

frequency (%) 40-

20- i

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

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

98 e,f ,i ,m , o), exceptfo rlarva ewit hhalf-pupa l cases,whic hpreferre dminera l substrates i.e.4 an d8 m m(Fig .37c) .Togethe rwit ha preferenc efo rleaves ,th e (partly)minera l casetype sselecte dparticl e sizescoarse r than2 mm ,wit ha distinc t preferencefo rthes eminera lparticle swhe n leafpack swer eabsen t (Fig.37 gan dj) . Larvaewit hhalf-pupa l casesals 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 c cases,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 ecoul dchoos ebetwee nal lgrai nsize s from 0.125- 1 6mm ,th epreferenc ewa s clearlyfo rth ecoarses tparticl e sizes,wher e1 6 mman d2m mwer e selectedmostl yb yth elarva ei nminera lcase s (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 esize s(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 hcase s 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 e size (shadedare ai nFig .37 man do) . Larvaei norgani ccase ssho wa simila rselectio no fth elea fpack sbu tno t

Fig.37 .Substrat e selection inlaborator y experimentsb y last (F)insta rlarva e of Chaetopteryx villosa.Grain-size fractions areindicate db y thelowe rlimi to f thefractio n in pm (under 1mm )an dm m (over1 mm) . L= leaves ;S = en dretainin g screen. (1/2- 1/ 2 :1/ 2organic , 1/2mineral ) 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 0.125m m b organic 5 16 leaf pack on all substrates c ipupa l 1 16 leaf pack on 0.125m m d Jpupa l 3 16 e mineral 4 16 leaf pack on 0.125m m 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 0.125m m i 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 all substrates 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 0.5m m

99 linkedt oth eminera lsubstrate ,whil eth eselectio no fth etw ocoarses tgrai nsize s isles spronounce d (Fig.37b) . When theselarva ehav eth echoic ebetwee na monolaye r ofsevera lgrai nsize son a bas eo f2 mm ,togethe rwit ha lea fpac kon 2 mm , therei s nodistinc tpreferenc efo ran ysubstrat e (Fig.37p) .Whe nplace do n0. 5mm ,4 m man d 16m mar eselected ,whic hindicate s thatno tonl yth esurfac eo fa substrat ei s importantfo rselectio no fburrowin g sites,bu tals oth ecompositio no fth eunderlyin g material. Fromal lthes eexperiment si ti sclea r thatfo r Ch.villosa leafpack s formth e mostpreferre dsubstrate ,afte rwhic hcoars eparticl esize s largertha n2 m mar e favoured,especiall y1 6mm .Th eselectio no flea fpack sca nb esee nfo ral llarva l casetypes ,bu tth epreferenc efo rminera lsubstrat ei shighe rfo rlarva ewit hpartl y orcompletel yminera lcase s thanfo rlarva ewit hpurel yorgani c cases.Larva ever y closet opupatio nsignificantl yprefe r coarseminera lsubstrates ,whic h agreeswit h thefiel dstud y (Table 31a: 16-20m mlarvae) .A nadditiona lobservatio ni stha t larvae foundon th efou r finestsubstrate swer e oftenbuildin go rrepairin g their caseso rstartin gt obuil d theirhalf-pupa l case.Som eo fth ehalf-pupa eeve nclose d theircas edurin gan experiment ,whic hmad ei tnecessar yt oreplac ethem .

Field experiments with artificial substrates Inth eRatumsebee kvariou sgrai nsize s wereoffere dfo rcolonization .Thes e artificial substrateswer e collected after1 4 and2 8days .I nthes e (spring)experiment s Ch.villosa occurredwit h9 larva ei nth e replicateso f5 substrat e types after1 4days ;6 o fthes e larvaeoccurre di n3 2m m (Table 32).Afte r2 8days ,wit h9 substrat e types,4 2larva ewer e found, 18o f whichoccurre din 3 2m m(Tabl e 32). This clearly indicates that Ch.villosa preferred thecoarses tgrai nsiz eabov eth efine rsubstrate s (see Table 16).Moreover ,8 m mwa s avoidedafte rbot hperiod san da simila rexplanatio na stha tgive nfo rM.sequax might be applicable,namel yth eimpenetrabilit yo fthi sgrai nsize .

4.2.2.5 Plectrocnemiaconspers a (Curtis) (Trichoptera:Polycentropodidae )

Miarodistribution Pleotroanemia aonspersa isth eonl ynet-spinnin gTrichopter aspecie s foundi nreasonabl enumber si nth eSnijb .I nth eRa bonl ya fe windividual swer e

Table 32.Numbe ro f Chaetopteryx villosa larvae inartificia l substrate inth eRatumsebee k inApril/Ma y 1978afte r1 4an d 28day so fcolonization .

Dayso f Numbero f larvaeb 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 Hydropsyehe angustiperniis, Lype reduota and Tinodee waeneri wereonl yfoun d incidentally. T.waeneri wasonl yfoun di nth eRa b andneve ri nshove lsample sbu talway so nlarge rstones . Inth eSnij bth edistributio no f Pleotroanemia oonaperaa isrestricte dt oth e detritus substrates,especiall yC Do rL .Th ecombinatio no fC Dan dL i sno tpreferre d althougha sligh tover-representatio n occurred (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 sa mino rover-representatio ni nth efines tminera l substrate (33x),whic hresemble smu do rfin esan dwit h finedetritus .Coars e substrates areonl y inhabitedb yfe wp . oonaperaa larvae,probabl ybecaus eth ecurren ti s too fastan dbecaus esan dan dpebble sar eno tlyin g looselypacked ,whic hwoul doffe r dwelling sites,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. Pleotroonemia oonaperaa mainlyoccur si nrelativel y coldupstrea 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 h faster currents (rapids,riffles )bu tthe nalway si nsheltere dplace sunde r stones.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 l zonationo fPolycentropodidae ,wher e P.oonaperaa isreplace d by Polyoentropue flavomaoulatua (cf.Nielsen ,1942 )i nth edownstrea m sections.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 e toleranceo fsevera l specieso fPolycentropodida e isver y important inlongitudina l zonationan dtha tthi si sdirectl y linkedwit hthei rventilatio n behaviourfo rth eoxyge nintak e (Philipson, 1978). Pleotroonemia oonsperea prefers substrate typeswher epre ydensit yi shig h

Table33 .I.R .value s for Pleotroonemia oonspersa (N= 233 )i nth efiel d classificationo fth esubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -4.4 -6.4 16.7 1 I 1 1 I 4 -6.0 0.2 -6.3 -2.2 — 1 16.7 _J I— I I 1 2 -6.2 -1.4 3.1 -2.2 -2.2 I -6.3 16.7 1—'—i I r n l I I 1 I I i I l I 1.6 -1.9 -1.1 -6.3 -1.1 5 -1.1 7 1 1.7 1 4.6 -4.1 -1.4 -0. 3.7 12.4 12.8 St Sh FD CD CD+LCD+F D L+FD CD CD CD+L

Italicvalue s indicatesignifican t over-representation

101 Table34 .I.R .value sfo r Pleetrocnemia conspersa (N= 233 )i nth egrain-siz e classificationo f the substrates inth eSnijdersveerbeek .

Substrateclas s

10 11 12 13 14

phi index detritus

7 6 5 4 3 2 1 1 2 3 4 CD L 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 13.2 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 12.5 1.1 QlMdQ3 index XXX x5x x3x x2x xïx xlx XXX lxx 22x 23x 33x CD L 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.aonspersa isa 'si tan dwait 'predato r (Hildrew& Townsend , 1976)tha tcatche sit sfoo db ya characteristic ,bu tirregular ,ne tconsistin go fa smalldwellin g tube (e.g.unde ra stone )tha texpand sa tbot hend st ofor ma funnel - shapedcatchin g area.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 species inhabiting slow-runningwate r (Wallace,Webste r& Woodall , 1977). Iti s colouredbrow nb yattache ddetritu sparticles ,which wa sregularl y observedi nth e rearingchanne lwher e P.oonepersa started spinningnet sa ssoo na si twa s introduced. Insmal lstream sth enet sma ycove rlarg esurface sgivin gth eimpressio ntha tth e streami sovergrow nwit hfung io rsom ekin do fthrea d forming bacteria (cf.Wesenberg - Lund. 1911). P.aonspersa consumesal lanimal sdriftin go rswimmin g againstth ene t andtrappe di ni t(Dittmar ,1955 ;Edington , 1968),bu tespeciall ymicro-Crustace aan d insect larvaear eeate n (Nielsen, 1942).Townsen d& Hildre w (1978)foun dtha tal l instarsea tstoneflie san dchironomids ,bu tth esmalle r larvae consumemor emicro - crustaceaan dth elarge r larvaemor 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 (Winterboum, 1978), althoughi 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 y functionstatisfactor yi nslow-runnin gwaters ,sinc e theyar e damagedb yhig hcurrent s (Edington, 1968). Thismake si timprobabl e that Pleatrocnemia isdependan to ndrif tfo rit sfoo dsupply .Mor e likely,animal s swimmingagains tth e net formth emai npre y organisms (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 f P.oonspersa topre ydensity ,whic hmean stha tsubstrat epreference so f thepre ywil ldetermin eth edistributio no f P.oonspevsa (Hildrew& Townsend , 1977). Inth eSnijb ,detritu ssubstrate swere th emos tdensel ypopulate dsubstrate s (especially chironomids),whic hexplain swh y P.oonspersa prefersthes esubstrates .Moreover ,t o beabl et obuil da net , P.oonspevsa needssubstrate stha tprojec tfro mth estrea m bed,suc ha sstones ,leafpack san dstick s (CD).Thes ewil lb eth esite swher eon e shouldfin d P.oonsperaa larvae,an dth edat apresente dabov efull yconfir mthi sfo r theSnijdersveerbeek .

4.2.2.6 Ephemeradanic a (Müller) (Ephemeroptera:Ephemeridae )

Population density E.danioa wasfoun di n10 7o fth e38 2sample s inth eSnijdersveer ­ beekwith 43 6specimens .Th enymph sonl yoccurre di nth eSection s4 ,5 ,6 an d8 (32 5 samples): in60 1o fth esample si nSectio n6 ;i n4S Io fth esample si nSectio n5 ;i n 141o fth esample si nSectio n8 ;an di n10 Vo fth esample si nSectio n4 . Inth eRatumsebeek ,50 4specimen swer efoun di n8 0sample s (outo fa tota lo f 195).Compariso no fth edensity -pe rsurfac euni treveal stha tthi si smuc hhighe ri n theRa btha ni nth eSnijb :6.2 2 and4.0 7 specimens,respectively ,pe rsampl eo f15 0 cm ,givin g41 4an d27 1pe rsquar emetre. Compare dwith th 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 ea sreporte dfo rth erelate dEphemerida e nymph Hexagenia limbata: 266 (Lyman,1955 )an d75 8pe rsquar emetr e (Neave,1932) . Theyar ehowever ,much highe rtha nth efigur eNeedha m (1917/18)presente dfo r E.simians, 32pe rsquar emetr eo rHun t (1953)gav efo r Hexagenia limbata, 127-365 persquar emetre ,wit ha naverag eo f15 3pe rsquar emetre .Zimmerma ne tal . (1975) showedtha tth edensitie so f H. 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). Theyquot eHudso n& Swanso n (1972),wh o statetha tmigratio ni smos tintensiv ei npopulation so fmore tha n10 0specimen s persquar emetre. Thes edat ao nage-correlate ddensit yar econfirme dfo r E.danioa in thispresen tresearch ,whic hshow sth esam epatter n (Table9 an d 10,Subsectio n 4.1.3.3.)

Life oyole Inth etw ostream sunde rinvestigation ,th elif ecycl eo f E.danioa appearedt ob ebivoltin e (Fig.38) ,whic hi si nagreemen twit hdat aknow nfro mothe r areas (Landa,1968 ;Sowa ,1975b ;Svensson ,1976 ,1977) ,althoug hsom eauthor sfoun d 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 yaccepte dtha t E.danioa isunivoltin ean dillustrate dthi s withth efac ttha tsh ehardl yfoun dnymph si nJuly .Considerin gth estrea m (the Schwechat,i nAustria )sh einvestigated ,i ti smor e likelytha tthes edat aar e unreliablebecaus eo fth ecrud esamplin gmetho duse dan dth ejoinin go fsample sfro m

103 _^JIl[lvTfTTTl_^_

77, 37-40 r-JTrTTTTrfTnïïÏÏVTTv^, _ 77; J3-36 Jfc

77: &-3Z

77; Ä-29

77; 13-16

77: Ç- a:

CO S j

Q 76: -9-SZ^ o :

P^ 76: "5-4 8 _" a.

76: "1-44

T r 76: 37-to .-n-rrTTHlïï 'hT >-T1

76; J3-36 1 -^TTTÏÏÏÏP—

76. Z9-32

76:

FTP fînrw, rrrr^ 76: 1 76: \7-za~z IUI rmrm (TTTi ™ 76: 13-10: r i ! i ! i rn 1 ! i (TTTi nrn rrrn nrn

76: S-IZ ~\ : friTTlThTy! 1 .TTTI r, —. 76; 5- 8^

76; i- 4: . H>_ _^MII!l'k-_ _^, _ 75; •"9-52 „. rnïïHl ^TTTW.,

75; •»s-4 8 ;

75: 41-41 : JTTfr rm rrm

75: 37-4« P n

•niii'i-i^i^adaaaaaaaassiiüaaüiiisisi

...ENGT!- CL.ASS ( tfMl Fig.38 .Lif ecycl ehistogram so f Ephemera daniaa showingth edistributio n(% ) of nymphalbod y lengthan dadult s (98)pe rfour-wee kperiod .

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 t and distinction betweenmale s andfemale sfo rolde rnymphs )t oexclud ewit hcertainl y thepresenc e of univoltine specimensbu t theirpresenc eseem shardl y likely.Som eo fth ever y large nymphs found inautum nmigh t spendthre eyear s inth e streamhavin gmisse dth e previousemergenc eperiod ,althoug h iti sals opossibl etha tthe yhav e grown faster duringth elas tsumme rtha nmos tother so fth esam eag ebecaus eo fextremel yfavour ­ ablefoo dconditions .I nth eAchterhoek , E.danioa emerges fromth een do fMa yunti l theen do fJun e (Weeks21-26) ,afte rwhich th efirs tyoun gnymph s arefoun d inAugust . They areb ythe nalread y startingo nthei rsecon do rthir dmoult .I nth eautum nther e isa perio do f fastgrowth ,whil e inth ewinte r growth isretarde d (cf.Thibault , 1971;Sowa ,1975 ;Svensson ,1977) .Th epresenc eo fver ysmal lnymph s fromAugus t into May indicatestha ta tleas tsom eo fth eegg so rbatche so fegg shav eretarde dhatching . Thelo wnumbe ro fsmal lt oaverag esize dnymph s inth eRa b inth esprin go f 1977 andth elarge rspecimen s inth eautum nan dwinte r 1977-1978migh tb e theresul to f thedesiccatio no fpart so fth estrea m inth esumme ro f 1976.Earl yhatche dnymph s mayno thav esurvived ,leavin gonl yth eoffsprin go fth e 'resting'eggs ,whic h is probablymuc hsmalle r innumbe rtha ntha to fearl yhatche d eggs,considerin g the ratiobetwee nth enumbe ro fsmal lnymph s inWee k 37-40an dthos eappearin g afterWee k 45.

Mcrodietrïbution The fieldclassificatio no fth esubstrate s shows clearly thati n bothstream sth ehighes tpreferenc e isfo rS+CD+E D inSor t 1 (Tables 35an d36) . Secondly,G+CD/F Dan dS+C Di spreferre d inth eSnijb . Inth eRa b onlya sligh t preference forG+ Lan dS+F Dwa s established.Detritu s substrateswer ealway s avoided (onlyon especime nwa scaugh ti na leafpac kan dthi sconcerne d anymp h readyt o emergefro mth estrea man dprobabl yo nit swa y toth ewate r surface).Analysin g Tables 35an d 36a tles sdetaile dclassificatio n levels reveals that Ephemera danioa prefersSan dfa rabov eGrave l inth eRab ,bu t inth eSnij bGrave l ischose nquit e often,althoug halway s lesstha nSand ,excep t inSor t3 . Inbot hstreams ,minera l substratesmixe dand/o rcovere dwit h Coarse andFin e Detritusar ealway spreferred .Thi s agreeswit hth epreliminar y conclusions drawnb y Tolkamp& Bot h (1978),althoug hsom edifference sca nb e seen.However, th eresult so f thelaborator yanalysi sshowe dtha tsom esample s includedi nth eS+F Dsubstrat e in thepreliminar y classification infac 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 d classificationa ttha tmoment .Anothe r reasonfo rdifference s inth epreference s foundthe nan d laterma yhav eresulte d fromth efac ttha tth e periodJanuary-Apri l 1977wa sno t included inth epreliminar y data,whic hmean stha t especiallyth esmalles tan d largest specimenswer eunder-represente d inth earrange ­ mento fth epreliminar y results.Thi s canhav e considerable influenceo nth etota l

105 Table 35.I.R .value sfo r Ephemera danica (N= 436 )i nth efiel dclassificatio no f thesubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Det ritus

3 2.1 2.7 -7.5 I 1 1 1 1 4 -4.9 9.0 -0.1 5. 0 -7.5 _J 1 1 2 -5.4 -0.5 2.7 9.3 -0.1 5 0 -7.5 1 I I 1 1 I 1 1 1 1 1 1 -4.3 1 -3.7 -4.0 -0.5 -3.0 4.8 0.9 10.3 0.4 1 -1.3 6.6 -5.3 -3.3 St Sh FD L CD CD+LCD+F D L+FD -0.B1 L CD CD L CD+L

Italicvalue s indicate significant over-representation

Table36 .I.R .value sfo r Ephemera daniaa (N= 504)i nth efiel d classificationo f thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Detritus

3 9.7 -5.1 -9.8 i 1 1 1 1 1 1 4 -2.9 18.3 -4.3 -2.7 -9.8 I i 1 1 1 1 I 1 1 2 -4.1 1.6 -1.5 21.3 -4.3 -2.7 -9.8 1 i i 1 1 I 1 "1 r i 1 1 1 1 1 1 1 1 -2.2 -3.9 1.6 -1.0 24.2 -0 4 -4.3 1.5 -3.4 -3 3 -9.1 -2.0 St Sh FD -1.6 -1.0 CD+L CD+FD L+]" D B L CD CI L CD+L L CD +FD

Italicvalue s indicate significant over-representation

results,becaus enymph so fdifferen t sizes showdifferen t substrate preferences (Tolkamp& Both , 1978). Tables3 7an d3 8giv eth eI.R .value sfo rth egrain-siz e classifications.I n bothstreams ,th ehig hpreferenc efo rC Dsubstrate s (Class1 4o r12 )a tth eH detritus levelmove st oth efin eminera l substratesa tth e10° slevel ,whic h indicates that thisconcern sSan d substrateswit h 1-10% organic detritus.Th edistributiona l pattern seeni nth efiel dclassificatio ni srepeate di nSort s 5-8:i nth eSnij bther ei spre ­ ferencefo rQ 1 =2 ,M d= 3 an dQ 3= 3 ,see ni nSor t8 a s22 xan d23x ;bu tals ofo r moregravell y substratewit hQ 1 =5 ,M d =3 ,2 ,o rÏ an dQ ,= 2 (Sort s 5-7),see ni n Sort8 a sx3x ,x2 xan dxïx .I nth eRatumsebeek , Ephemera daniaa prefersth ewel l sortedmaterial swit hQ 1,M ,an dQ 3= 3 ,althoug hQ ,= 3 an d4 ,M ,= 2 an dQ ,= 3 o r 4i sals o favoured,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 (M,= 1 o rmore )wit h less than 50% gravel (Q1 =4,3) ,whil ei nth eSnij b

106 Table 37.I.R .value sfo r Ephemera danioa (N= 436 )i nth egrain-siz e classificationo f thesubstrate s Inth eSnijdersveerbeek .

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 1 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 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 -3.3 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 -3.0 Sort7,10 % - -1.1 -3.4 -2.1 -1.1 -1.7 -1.5 -4.6 4.2 5.1 0.9 -3.2 -5.3 -3.3 inde x XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L Ws x4x 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 -3.0 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 -5.3 -3.3

Italicvalue s indicate significant over-representation

Table38 .I.R . valuesfo r Ephemera danioa (N= 504 )i nth egrain-siz e classificationo fth esubstrate s inth eRatumsebeek .

Substrateclas s

9 10 11 12 13 14

phiinde x detritus

CD CD+L

Sort5,1 % -1.0-1. 0-3. 5 2.4 7.1 -3.0 0.4 -2.8-4. 4 -l.i 12.4 -8.8-1. 7 Sort5,10 % -1.0-1. 0 -3.5 2.1 9.0 -2.5 0.4 -2.7 2.7 10.9 - -3.3 -9.1-2. 0 Sort6,1 % -1.6-1. 4 -3.2 -3.0-2. 0 2.0 2.0 -0.4 - 12.4 -8.8-1. 7 Sort6,10 % -1.6-1. 4 -3.2 -3.2-2. 0 1.3 5.7 10.4 - -3.3-9. 1-2. 0 Sort7,1 % -1.6-0. 8-8. 3 9.8 -0.4 12.4 -8.8-1. 7 Sort7,10 % -1.6-0. 8-8. 9 16.2 8.6 -3.3-9. 1-2. 0 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD CD+L Ws x4x Sort8,1 % -1.6-1. 4-3. 2 -3.0-2. 0 2.0 10.1 -2.8-4. 8 0.5 -1.6 12.4 -8.8-1. 7 Sort8,10 % -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

Italicvalue s indicatesignifican t over-representation

Gravelsubstrate s (M,=Ï o rless )wit h lesstha n 501San d (Q,= 2 )ar eals opreferred . Calculationo fth eI.R . valuesfo rsevera l lengthclasse so f E.danioa nymphsi n Sort5 fo rth eRatumsebee k leadst oth econclusio ntha tth eover-representatio ni n

substrateswit hQ 1= 4 (Tabl e38 )i scause db ynymph so f5-2 0n man di nQ 1= 3 b y nymphso f0-1 0 mil.Th e latter (lengthclas s 1-10)ar eals oresponsibl e forth epref -

107 erencei nQ ,= 3 ,whil eth elarges t specimens (20-27mm )prefe r especially Q1 =2 . Consideringth emedia n grain size (Sort6 )hardl yan ydifferenc e between length classesca nb esee ni nth eRatumsebeek , although 10-20m mnymph s havea stronge r preferencefo rM ,= Ï o r1 tha n2 o r3 . Inth eQ ,classificatio n (Sort7 )onl yth esmal lnymph s (0-10 mm), especially the smallestone s (0-5mm) , preferbot hQ ,= 3 an dQ ,= 4 ;th elarg e specimens favour onlyQ_ ,= 3 .Thes e differences betweenyounge ran dolde rnymph s returni na condense d

Table 39.I.R .value s for Ephemera daniaa perlengt h class (A)an d season (B)i n the Snijdersveerbeek inSor t8,10% .

Length N Subs träte class and Q M Q index

and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Season XXX x&x 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 - 15 116 -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 - 20 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 - 27 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

Italic values indicate si gnificant over- representation

Table 40. I.R. values for Ephemera daniaa perlengt h class (A)an d season (B)i n theRatumsebee k inSor t8,10% .

Substrateclas s andQ„M,Q „inde x Length N 1 d3 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 1 519 8 -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 12.1 -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 val ues indicate si gnificant over- representation form inSor t 8 (Table 40A).Th epreferenc e forxx xan d33 x iscause db y 0-10m m nymphs;fo r23 xb y 0-5 mmand 15-27m m animals andth esligh tover-representatio ni n x1xb yanimal so f 5-20m m length.I tshoul db enote dtha t 10-15n mnymph sprefe rx1 x

substrates (Q1 = 5,4 ,Ï ;M d = 1; Q 3 =3) . Analysiso fth eSnijdersveerbee k data forth enympha l sizeclasse so f Ephemera inSor t8 (Table39A )confirm sth epreliminar y conclusionspreviousl y drawnfo rpar t ofth edat a (Tolkamp& Both , 1978).Large rnymph sprefe rgravell y substrates:20-2 7 rannymph sar emostl y found inx3 xan d 15-20ran nymph s inx1x ,althoug hals oi nsan d (22x)wit hdetritus .Smalle rnymph soccu r ingrave la swel la s insan d :0- 5 mm nymphsespeciall yi nxT xan dx3 xsubstrate s and5-1 5m mnymph s inbot h22x ,23x , 33xsubstrate swit hdetritu s andi nx3 xan dx2 xsubstrates .Fro mal lothe rclassi ­ fications (Sort5-7 )th esam epictur eemerged . Comparisono fth eI.R .value s forth esevera lnympha l sizeclasse si nSor t2 (notpresented )wit hth edirectl y comparablepreliminar y resultsdoe s showsom edif ­ ferences,fo rreason smentione dearlier . Betweenseason sth edistributiona lpatter nfollow sth epreference so fth emor e abundant lengthclasse 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 e shifts tomor egravell y substrates insumme r (xTx,x3x )whe nespeciall y thesmal lnymph s areabundant .I nautum nthi sdistributiona l patternremains ,althoug ha sth enymph sgro wa shif tbac k tosan dca nb eobserved . Inwinte rth epreference s aremor e or lessequall ydistribute d overgrave lan dsand . Inth eRab ,a simila rchang eo fpreferenc e from sandt omor ecoars e substrates aftersprin g ispresent ;althoug hsubstrate s ascoars ea sth eone spreferre d inth e Snijb showedn oover-representation , theywer ever y scarce inth eRa banyway . Theseshift s inpreferenc e coincidewit 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 dspatia ldistribution .I nth eSnijb ,Grave l isoriginall ypresen t in thestrea mbotto mbecaus eo fth efluviatil egrave ldeposit san d itoccur sove rth e totalwidth o fth ebed ,bar eo rcovere dwit ha laye ro f sando rdetritus .I nth eRab , Gravel ispresen t infa rsmalle rquantitie s andi tofte nconsist so firon-condensates , formed inth estream ,an daccumulation so fth eheavie rmateria l remaining after erosiono fbank sand bed .Th eRa b streambe d ismuc hwide ran dth emaximu m current speedsar emuc hhigher .I nth eRab ,th egrave l ismor eo rles s restrictedt oth e riffleso rth emiddl eo fth ebed ,place swher eth ecurren t ishighest .San dan d Detritussubstrate s aremor eabundan t inth epool san dalon g thebanks . Since E.danica nymphsprefe rminera l substratescombine dwit hdetritu s (especial­ ly finedetritus) ,which occu 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 ,which isswep t awayb y thecurrent .Moreover ,als o thefin e sandingeste d forit sbacteria l growth (Zimmerman &Wissing ,1978 )i sabsen there . Summarizing thedat apresente d above itca nb e statedtha t Ephemera danica pre­ fers substrateswit ha t least 251,an dpreferabl y 751fine r than0. 5mm ,o r25 1 coarser than4 m mbu t finertha n 32mm ,althoug hfo rth elatte ri sno tcertai nbecaus e ofth e limitednumbe ro fsample s inthi s substrate type.Th e importanceo fth epre ­ senceo ffin edetritu s incombinatio nwit hminera l substrates isbes t illustrated in themos tdetaile d field classification,an dth eknowledg etha tth e finesan dsub ­ strates inSor t8 contai n largeamount so ffin edetritu s confirms thisver ywell . Thisrelationshi pwit h finedetritu swil lcertainl yb e linkedwit h E.danica's feeding habits,sinc e iti 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 f inorganic sediment forth emicrobia l growtho n it (Zimmerman &Wissing , 1978). Ephemeridaear ecalle d 'mud-eaters' (Bengtsson,1924 ;Hunt ,1953) , althoughi t hast ob eoxyge nric hmud (Wautier& Pattee ,1955 ;Eriksen ,1963a ,b ; 1964;1966 ; 1968),whic hemphasize s thefac ttha tdetritu s feeders isprobabl y abette rdescription . Although Ephemera isa eurythermou sgenu s (Percival& Whitehead , 1926;Kamler , 1966), E.danioa occurs instream swit hles shig htemperatur e fluctuations than 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 san d largerstream s (Foxe t al, 1934;Molle rPillot ,1971) . Percival &White ­ head (1926)foun donl y few E.danica inmud andthe yoccurre dpredominantl y insand y streamsi nth esubstrate swit hth ecoarses tfractio nbetwee n0.0 5 and1. 0m m (651 coarse sand,2 1fin esan dan d 11silt) .Th e abundance of E.danioa decreasedwit ha n increasing amounto fsil tan dcla y (finertha n0.0 5 mm),whil enymph sneve rmigrate d toneighbourin g substrateswit h ahighe rsil tcontent . E.danioa lives inth ebotto m insmal ltunnels ,whic har eburrowe dwit hthei r strong front legsan dmandible 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 tostic kcoarse r grainstogethe ri n order toobtai na stabl etunne l structure.Eastha m (1939)suggeste d thatth epreferenc e of E.danioa forcertai nsubstrate smigh tb edetermine db y thenee d fortunnel s of somepermanency ,eas yt omak e andeas y toleav ean dpermittin g anaxia lwate rcurren t without thetunne lwall scollapsing .A highsilt/cla y contentmigh tb e detrimental becauseth eparticle s canobstruc tgil lmovemen t andclo g them,preventin gprope r respiration. Mostauthor sreportin go nsubstrat epreference so f Ephemera danica givea sth e characteristichabita tth esan dsubstrat e inth e current (Geijskes,1935 ;Pleskot , 1953; Collins, 1971), thequiete rplace snea rth ebank swit hmud o rcla y fractions (Percival& Whitehead , 1926;Beyer ,1932 ;Dittmar, 1955), the shelteredplace s in stony-gravellybottoms ,wher e finegrave l (Percival& Whitehead , 1930), sand,mu d and detritus (Sowa,1975a )accumulate ,o rcoars esubstrate snea rth ebanks ,wher eth e

110 current isslac k (Jones,1949) .Thes edat aagre ewit h those found inth eRatumsebee k andth eSnijdersveerbeek , althoughth eresult so fthes e investigations emphasizeth e importanceo fth epresenc eo forgani c detritusan dfin esand .

Substrate-aeleation experiments A serieso fexperiment swa sconducte dt oestablis h the effecto fcurren tvelocit y onth esubstrat e selectiono f Ephemera daniaa. Sub­ stratesrangin g from0.05 0m mt o8 m mwer e offereda thig h (10cm/s )an dlo w( 5cm/s ) currentvelocities ,an dsubstrat eselectio nwa sdetermine d after 24hours .Th enymph s were introduced intoth estagnan t streamo neac hgrai nsiz ei ndensitie so f1 ,2 o r4 pertray .Afte rintroductio nthe 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) .Wit ha stron g currentsignificantl ymor enymph swer e foundo nth e downstream screensan dburrowe d inth edownstrea m substrates,mor eo rles s independant- lyo fgrai nsiz e (Fig.39b) .Wit ha slo wcurren t thiseffec ti sno tnotice d(Fig . 39d).-Thi slead st oth econclusio ntha tfo ra lo wcurren tvelocit y thesubstrat e selectiono f Ephemera isvoluntary ,bu tfo ra hig hcurren tvelocit yenforced .Fig . 39cshow stha t E.daniaa prefers 2-4m mgrains ,an dthi spreferenc e decreasest obot h coarseran dfine rparticl e sizes,wit hth eexceptio no f0.05 0- 0.12 5mm . 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 o1 ,0.12 5 and1 6m mshowe dover-representation .N osignifican t differenceswer epresen tbetwee n thetw oexperiments .Whe nmixe dwit hfin ean dcoars edetritus ,practicall y thesam e substrate selectionwa sfoun d (Fig.39f) ,indicatin gtha tth epresenc eo ffoo dsub ­ stancesdi dno tinfluenc eth esubstrat e selectioni nthes eexperiments . Experimentswit h2 ,4 ,8 an d1 6m mgrain smixe dwit h0. 5o r1 m m (Fig.39 han d 39i)showe dtha t E.daniaa hasn osignifican tpreferenc e foran yo fthes emixtures . Particle sizes8 m 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 gth efou rcoars eparticl e sizeswit h0. 5m mo r1 m msan dlevel sdow nth e differences insubstrat e selection,althoug h8 m mseem st obecom emor eaccessible . Ina serie so fexperiment swher eonl ytw oo fth epreferre d substrateswer e offered, E.daniaa 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 5m m (Fig.391) .Also ,a nexperimen t was startedwher egrain so f0.12 5- 1 6m mwer emixe dwit h approximately one-third 0.050n msubstrate .Th eexperimen t showedtha tmixin gwit h thisver y finesan d strongly levelleddow nth edifference s betweenth edifferen t grainsizes ,althoug hove r40 1o f thenymph sdi dno tburro wbu tsa to nth escreens ,whil e 10%die 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 s andcar ewa s takentha ti nfollowin g experimentswel lfed ,fres hnymph swer eused .

111 Experiments withtw osiz e classeso f E.danioa (15-20m man d20-2 5mm )wer econ ­ ducted,givin g them choicebetwee n 1,2 ,4 an d8m mparticle s coveredwit ha thi n layero f0. 5m msan dan dbar e1 ,2 ,4 an d8 m msubstrate .Larg e nymphspreferre d 2m m and8 m man dn oinfluenc eo fth e0. 5m mcoverin gwa snotice d (Fig.39m) .Smalle r nymphs displayedth esam egrain-siz e selection (Fig.39n )bu tthe y differed fromth e largernymph si nthei r strongpreferenc efo rbar eparticl e sizes comparedwit hth e coveredone s (Fig.39 oan d 39p). Comparedwit hth eresult so fth efiel d investigationth epreferenc eo flarg e Ephemera nymphsfo rgravell y substrates isthu s confirmedb yth eselectio no f2- 4m m particles inth elaborator y experiments.Th e(les sdistinct )selectio no fsmalle r particles sizes also agreeswit hth eoccurrenc e infine r substrates (22x,23x )i nth e

frequency (%) 60-

40-

20-

0- 50 250 12 4L 8 n US DSDBUB 50 250 12 4 8 S • DSDBUB frequency (%)

40-

20- I '

125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S 125 500 1 2 4 8 16 S + ++ + ++ + + CD frequency (%) 75 60

40-

20-

0 248 16 248 16 2 16 S 125 16 S • 50 125 S + + + + + + + + 1 500 frequency (%) 75

60-J m n op

40- n M 20- lu 1 1248 •S 1248 S +- + - + 500 + + 500 + 500 500

112 phi values î 5 Q 3 4• T Md 3 •

Î 2

1•

0.

î•

2 <

3•

4-

6- V +" V A' 6 + A

U. (phivalue ) a Fig.40 .Compariso no fsubstrat epreference s inth efiel d (unshaded)wit h particle-sizeselectio ni nlaborator y experiments (shaded)fo r Ephemera danica.

Fig.39 .Substrat eselectio ni nlaborator y experimentsb y Ephemera danica. Grain- sizefraction s areindicate db yth elowe rlimi to f thefractio n in pm (under1 mm ) andm m (over1 mm) . S= en dretainin gscreen ;D S= downstrea m screen ;D B- down ­ streamburrowed ;U B= upstrea mburrowe d (fig.d) ;C D- coars edetritus . Figure Body Number of Number of Current Note no. length experiments nymphs per 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 e 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 h1. 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 m+o 20-25 2 24 5 bare(unshaded),coveredwit h 0.5 n+p 15-20 2 24 5 mm (shaded)

113 field.Th edifference s seenbetwee n largean dsmal lnymph s inth eexperiment s with mixtureso fparticle s sizes agreewit h thedifference si npreferenc e seenbetwee n thesenymph si nth eRatumsebeek ,wher eth e largenymph s occurpredominantl yi nfine r substrate (23x),whil e smallernymph s preferred coarser substrates. Conclusionsdraw n from thefiel d researchar ethu s confirmedb yth elaborator y experiments,a sillustrate di nFig . 40,i nwhic hparticle-siz e selectioni nth e experimentsi sprojecte do nth e QIMJQ? graphtogethe rwit h the substrate preferences seeni nSort s 5-8, 10%.Th enymph s select2- 4mm , 16-32m man d0.125-0.25 0m mpar ­ ticlesi nth e laboratory.Thes eparticl e sizes correspondwit h theQ ,an dM ,particl e sizeso fth e substrates selectedi nth e field.

4.2.2.7 Nemouracinere a (Retzius) (Plecoptera:Nemouridae )

Microdistribution Inth eSnijdersveerbee kth epopulatio no f Nemoura cinerea was rather small andonl y15 5specimen swer epresen ti n2 6samples .I nth e Ratumsebeek, 2896specimen swer e caughti n8 7samples .I nbot h streams,th ehighes tnumber s were presenti nlea fpacks .Thi si sclea ri nbot hth e fieldclassificatio n (Table 41)an d thegrain-siz e classification, although only Sort8 ,10 %i spresente d (Table42) . Over-representationals o occurso nver y coarse substrates inth e Ratumsebeek. Thispreferenc ei sonl y seeni nth ewinte r season (Table 42B),whic hi sb yth ewa y theonl yperio dwhe nthi s substrate classi spresent ,an di tconcern sal llengt h classes (i.e.1- 3an d3-6 ) (Table 42A),althoug hrelativel ymor e small (0-3mm ) specimenswer e foundo nminera l substrate (Classes2 an d4- 7i nSor t 8)tha n larger (3-6mm )ones .Thi si si ncompariso nwit hth e totalnumbe ro feac h length class. The only statistical clue forthi s statement liesi nth e small difference betweenth e I.R.value s forth e1- 3m mlengt h classi nx5x ,x4 xan dLea f substrates,th eadditio ­ naloccurence so fpositiv e I.R. valuesi nx2 x andxï x substratesan dth e less negative valuesi nth eothe rminera l classes comparedt olengt h class3- 6mm .

Table41 .I.R .value sfo r Nemoura cinerea (N= 2896 )i nth efiel dclassificatio no f thesubstrate s inth eRatumsebeek .

Sort Sand ravel Detritus

3 -28.1 -1.9 44.2 1 1 1 1 i 1 4 -20.2 -19.6 4.5 -11.8 44.2 1 1 1 1 1 1 1 1 2 -15.6 -13.8 -5.7 -19.1 1 -11.8 44.2 1 1 4.5 1 1. 1 1 1 1 1 1 1 1 1 i 1 -6.2-16. 9 -13.8 -3 .9 -4.7 -4.6-19. 2 -1.7 4.5 -3.9-11. 1 -8.5 53.7 -4.7 St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L +FD

Italicvalue s indicate significant over-representation

114 Table42 .I.R .value s for Nemoura cinerea perlengt hclas s (A)an d season (B)i n theRatumsebee k InSor t 8,10%.

Length N Substrateclas s andQ M 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 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.S -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

Italic values Indicatesignifican t over-representation

Foral llengt hclasses ,preferenc ei salway shighes tfo rleaves .I nsprin gan d autumnth edistributio ni smainl y restrictedt othes e leafpacks ,whil ei nsumme rth e preferencei shighe rfo rL+CD ,althoug hth eI.R .value s shouldb econsidere dscep ­ ticallysinc eonl ytw osample swer etake ni nthi s substrateclas si nsummer ,onl yon e ofwhic hcontaine d N.cinerea (12specimens) ,agains t fouro fth ete nsample si n winteri nLeave s (16specimens) .Th edat afo rth eSnijdersveerbee k haveno tbee npre ­ sentedbecaus eo fth ever y strongresemblanc et oth eRatumsebee kdata ,wit hth e exceptiontha tover-representatio ni nlea fpack s occurredi nbot hseason s (winteran d spring)i nth eSnijdersveerbee k only.Similarit yi nresult swa sals osee nfo rth e lengthclasse si nth eSnijdersveerbeek , althoughsligh tover-representatio nwa s found inC Dan dCD+ Li nsprin gfo rlarg e (6-10inn )specimen swhic hi sprobabl yth eresul t ofth edisappearanc eo flea fpack si nspring . Semovœa cinerea nymphsar eherbivorou san dfee dmainl yo nvegetabl ematte ra s detritusan ddea dleaves ,althoug hthe yals oinges tmos s tissuean dalgae ,dependan t onth eabundanc eo fth evariou sfoo dtype spresen t (Hynes,1941) .Thu si ti sno t surprisingt ofin da stron g relationshipo fthes estonefl ynymph st odetritu ssub ­ strates,a fac treporte db ysevera lauthor s (Geijskes,1935 ;Dittmar , 1955). N.cinerea iswidel ydistribute di nEurop e (ubiquist)an doccur si nvarious , strongly-differing biotopes,suc ha strickle s fromsprings ,lowlan dstream san d rivers.I ti sals ofrequentl y foundi nlittora l zoneso fpond san dlake s (Brinck, 1949; Hynes,1941) .However ,i nth eNetherland si ti sonl yfoun di n(slowly )runnin g wateran di smos tabundan ti nsmal lwoodlan d streams,whic h oftendesiccat ei nsummer . The lifecycl eo f N.cinerea iswel ladapte dt olif ei nlea fpack san dsummer-dr y streams (Bontenbale tal. , 1979).I nth estud yarea ,th elif ecycl eo f N.cinerea is clearlyunivoltine ,wit hgrowt hi nautumn ,winte ran dspring ,whe n leafpack sar e abundant.Adult sfl yfro mearl yApri lan dcontinu et od os owel l intoJune ,an dfirs t

115 instarnymph sar epresen tfro mAugus tt oFebruary ,althoug hmos tnymph shatc h latei n autumn (October/November).Thi smean 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 Limniusvolckmar i (Panzer),Elmi s aenea (Müller),an dOulimniu stuberculatu s (Miller) (Coleoptera:Elminthidae )

Microdistribution Limnius volckmari occurredi nth eSnijdersveerbee kwit h2 7speci ­ mens (larvaean dadults )i n1 1samples ;42 3specimen s (larvaean dadults )wer e found 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 withQ 1 <2 (2- 4mm )sho wover-representatio n (Table44) . Elmis aenea wasfoun di n4 0sample si nth eSnijdersveerbee k(13 3specimens )an d in2 9sample si nth eRatumsebee k (53specimens) . E.aenea showeda simila rpreferenc e as L. volckmari, butwa srestricte dt oGrave lsubstrate sonl y (Table 45).Again ,th e distributionwa ssimila ri nbot hstreams .Th ehighe rpreferenc efo rcoarse rsubstrate s than L. volckmari showedi sespeciall yclea ri nSor t 5-8,10°6 ,wher eonl yth ecoarses t substratessho wsignifican tover-representation . Elmis aenea avoidsclasse s4 ,6an 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 tuberculatus showsth esam epreference sa s L. volckmari withth ehighes tpreferenc efo rClas s5 i nSor t8 ,101 .Onl y2 5larva e and2 3adult swer efoun di n2 8sample si nth eRatumsebeek .Larva eshowe dn osignifican t

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

Sort Sand Gravel Detritus

3 -4.2 15.7 -8 3 i 1 1 1 I 1 4 0.1 -6.6 11 8 0 -8 3 I 11 1 1 1 1 2 2.2 -4.0 -1.5 -6.7 11 8 11 0 -8 3 i 1 1 I r~ 1 1 1 1 1 1 1 1 1 I 1 1 -2.8 -4.0 - -1.5 -1.1 -2.2 -5.7 -3.0 8 -0.8 11.9 -2.1 -7 7 -2 6 1 5.2 11 St Sh FD L CD CD+L CD+FD L+FD B L CD CD L CD+L +FD

Italic values indicat e significant over-repr esentation

116 Table44 .I.R .value s for Limnius volakmari (N = 42 3) i nth egrain-siz e Classificationo fth esubstrate s inth eRatumsebeek , including thedistinctio n betweenlarva e and adults inSor t8,10% .

Substrateclas s

10 11 12 13 14

phi index detritus

6 CD CD+L

Sort 5,10% 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 index xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L W3 x4x Sort 8,10% 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 indicatesignifican t over-representation

Table45 . I.R. values for Elmis aenea (N= 133)i nth efiel dclassificatio no fth e substrates inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 -7.3 11. 6 -2.8 l 1 1 1 I 4 -4.9 -5.5 13.3 1.2 -2.8 I 1 I 1| 1 I 2 -4.1 -2.9 -3.4 -4.3 1.2 -2.8 13.3 1 _J I 1 1 1 - 2.4 -3.4 -2.9 -1.7 -2.8 -1.0 -3.8 -2.0 13.3 1.6 1 0|4 -0.5 -2.J 3 -2.0

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

Italicvalue s indicatesignifican t over-representation

preferencealthoug hcoarse rsubstrate syielde dmor epositiv eI.R .value s thanth e finersubstrates .Adult swer esignificantl yover-represente di nClasse s2 an d5o f Sort8 ,101 .I nth eSnijdersveerbee k only2 adult so f O.tubevaulatua and2 3larva e were caughti n1 1samples .Thes e larvaeonl yoccurre di nsubstrate s coarsertha n class7 i nSor t8 ,10 %whic hi ssimila rt oth eresult sfo r L.volehncun. inth eRatumse ­ beek (seeAppendi x9) . Theseresult sconfir mtha tth ecommo nnam efo rthi sgrou po fbeetles ,'riffl e beetles'i swel lchosen .Thi snam e indeed indicatesthei rpreferre dhabitat .Thes e verysmal lbeetle sca nwithstan dver y strongcurrent s (Dittmar,1955 ;Dorie r& Vaillant,1955) .The yattac hthemselve st oth esubstrat ewit hthei rsprawling ,large - clawed legs.Th elarva ear ever ywel lstreamline dan dsom especie s (.e.g. Elmis aenea)

117 Table46 .I.R .value s for Elmis aenea (N= 133 )I nth egrain-siz e classification of thesubstrate s inth eSnijdersveerbeek , including thedistinctio nbetwee n larvae andadult s inSor t8,10% .

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

Sort5,10 % 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 Sort6,10 % 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 XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L QlMdQ3 index 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.S 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 indicates i gnificant over-repre sentation

cansea lof fth eventra l sideo fthei rbod ywit hnumerou s hairy spines,producin ga tightgri po nth esurfac e (Hynes, 1970a). Elminthidaear emos tconmo no nsmal l stonesan dgrave li nmoderatel y swift waters (Percival& Whitehead , 1929;Jones , 1949), sometimes coveredwit hdens e algal growth (Berge tal , 1948;Jones , 1951).Comparin gth edistributio no f E.aenea and L.volakmari asshow ni nTable s4 3an d45 ,i ti sclea r thatth epresenc eo fdetritu s ismor e importantfo rL.volakmari thani ti sfo rE.aenea. L.volokmari hasequa l preferencesfo rBar eGrave lan dGrave l+ Coars eDetritus ,whil e E.aenea stronglypre ­ fersBar eGrave l (andPebbles) .Thi spreferenc eo f L.volehnar-L forcoars e substrates withdetritu sdoe sno tsho wi nan yo fth egrain-siz e classifications (Table44) , whichmean s thatth eamoun to ftrappe d detrituswa ssmalle rtha n 1 % ofth esampl e weight.Thi semphasize sth eimportanc eo fusin ga fiel dclassificatio n togetherwit h agrain-siz e classification.Th eimportanc eo fdetritu sfo r L.volckmari wouldhav e beenobscure di nth egrain-siz eclassification ,an dth edifferenc ebetwee n E.aenea and L.volokmari, withpreference s forver y coarsegrave lan dmediu m gravel,respectively , wouldhav ebee nunnotice di nth efiel d classification. Ofcours eon eshoul dbea ri nmin d thati nth egrain-siz e classifications o calledminera l samples (Classes 1-11) stillma ycontai nu pt oU or10 %detritus , although thismainl y concerns sampleswit hQ .5 2 (cf .Subsectio n 4.1.3.2). Rabeni& Minshall (1977)showe dtha t1-3. 5m msubstrate scollecte dmor edetritu stha n coarser orfine r substratesan dtha tth epresenc eo fdetritu sma yb eth eprimar y reason responsiblefo rinsec tcolonization .Th erelationshi pwit hminera l substratesremains , however,sinc eth enatur eo fth eminera l substrate determinesth eamoun to fdetritu s trappedi nth einterstices .

118 Egglishaw (1964,1969 )conclude dtha tth edistributio no f Esolue parallelopipedus, anothermembe ro fth eElminthida e isstrongl ycorrelate dwit hth epresenc eo fdetritus , althoughthi swa smor e important forth eadult stha nfo rth elarvae .Edward s (1975) showedtha t Esolus •parallelopipedus hasa simila rdistributio n as Limnius volekmari. Larvaeo f E.parallelopipedus showedn o correlationwit 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 study areno tsufficient ,however ,t ojustif yth estatis ­ ticaltreatmen to flarva ean dadult sseparately .Th eI.R .value s forlarva ean d adultsi nTabl e4 4an d4 6shoul donl yb econsidere da sindicative ,sinc eth e differences areno tsignificant . Iti sno tpossibl et ogiv ean ydetaile dresult so fth eseasona ldistributio no f Elnris aenea sincemost animal s (82o fth etota lo f 107)wer ecaugh ti nsprin g and showeda substrat epreferenc esimila rt oth edistributio npresente d inTabl e50 .I t isnoteworth y thati nsunnie ra sligh tover-représentâ tio ni ssee ni nC Da swel l (5 specimenso fth e 21).A similarobservatio nwa smad e for Lithax obsourus insumme r (seeSubsectio n4.2.2.1 )an dthi smigh tb erelate dt oth eavailabilit y offoo d (algae anddetritus ) (Jones,1951 ;Hynes , 1961). Limnius volohnari occurred inhighes tnumber s insummer ,autum nan dwinter ,bu t inal lseason sClas s 5(Tabl e44 )wa spreferre d (xïx).Onl y insprin gwa s ahig 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 l larval instarsexcep tth e firstma yb epresen t throughoutth eyea r (Holland,1972) .Th epopulatio n foundwil lmostl yb e amixtur e ofyounge ran dolde r larvaean dadults .

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

Life cycle Inth eSnijdersveerbee k andth eRatumsebee k allsize so f G.pulex are present inal lseason s (Fig.41) .Reproductio n takesplac 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 r andearl ysprin g (Weeks 41-16)ther e isa restin g period,afte rwhic hjuvenile s appearagai ni nabundance .Adult sdi eprobabl y inJune - July,whic hwoul dexplai nth edecreas ei nlarg especimen s (above9-1 0 mm)i nthi s period (Fig.41) . The annualtemperatur e fluctuations ofth estrea mar ecomparabl ewit hthos e foundb yHyne s (1955)(varyin g from5-15° Cmostly) ,an di tseem sprobabl e thatth e lifecycl eo fG.pule xi sals oi naccordanc ewit htha tdescribe db yHyne s (1955).Rou x (1970)describe d acontinuou s reproductiono f G.pulex infou rstream swit hver ysmal l annualfluctuation s intemperatur e (between 10an d 15°C)an dals otha ta restin g period inreproductio noccur s inautum ni n streamswit ha stron g seasonal fluctuation ofth ewate rtemperatur e (lesstha n5° Ci nwinter ,mor etha n15° C insunmer) .Th e

119 77= «9-52

77; «5-4B.

77; J7-40

77; J3-36

77: 29-32

77: 25-28 _JÏÏ!ÏÏÏÏWTK.

77: 21-24 —nnfïïïKrn—

fïïïtïïïL____

_~j>ur>lliM»i m H^iinr

W ":

76: "9-5Z

76: «5-18 _jniiriiwT»»-T»—

rrrWTTTTITTTTm-^TT-

—JTTrfTHïTTTfTÏÏW-,

-T-T»TTTI—ITÏÏTTTTfTITmn— 76: i7-2Q mm

76: 13-16: P» - -M1

76: <*-'2

76; s- a

75: 19-Sz

75: *5-48

rïïnTTn-rfTTTTT^T-^____

75: J7-40

LEN3TI- CLASS ( r"i) Fig. 41.Lif ecycl ehistogram so f Gammarus pulk? showingth edistributio n (%) ofanima lbod y lengthpe r four-weekperiod .

120 lattercycl e iscomparabl ewit hth eobservation so fHyne s (1955),wh ofoun d that breeding sloweddow n inSeptembe r andstarte d againi nDecember .H e foundtha t species born insprin g reachmaturit y inJul y andAugust ,bree d through September,res tunti l December/Januar y andbree dagai nthroughou t spring.The ythe ndie ,whic hcause sa decrease innumber s inJune/July .Specimen sbor n later insumme roverwinte ra s juveniles andreac hmaturit y inMarch ,afte rwhic hthe ybree dunti lJun ean dthe n probablydie .Hyne s statedfo roverwinterin g specimens aperio do fabou t 7month s to mature (T=5-10°C )an dfo rsunnie rgrower s aperio do f 3-4month s (T= 10-15°C). Roux (1970)suggeste d thatth ereproductiv e rhythmfoun db y several authorsi s duet oa synergeti c influenceo fwate r temperature andda y lengths.Nilsso n (1974) showedtha ttemperatur e isth edeterminin g factor forgrowt ho f G.pulex andRou x (1975)demonstrate d thattemperatur e affects thetim ebetwee nth emoults . Iversen& Jessen (1977)foun di nRol dKild etha tbreedin g isinsignifican t orabsen t inwinte r and thatth ene wgeneratio nappear s inMarch-April ,bu ti smos t abundant insummer . Growtho fjuvenile s isslightl y reduced inwinter .The yobserve d thatpar to fa gene ­ rationsurvive sunti l thethir d summer,whic hgive sa maximu m ageo ftw oyears .The y contribute thedifference swit hth eresult so fHyne s (1955)t oth e lowersumme r temperatures inRol dKilde .I nth etw oDutc h lowlandstream sn o indicationo f a reducedbreedin go rgrowt hwa sobserved ,whic h confirms theconclusion s ofRou x (1970)an dHyne s (1955).

Miovodistvibution Gammxrus pulex isth emos tdominan t species inbot hstream sre ­ gardingth enumbe ro fsample s inwhic h itoccurred : in28 2o fth e 382sample s inth e Snijb and in15 4o fth e 195sample s inth eRab . Inth eRa b itwa s alsoth emos t dominant species innumber s (9958specimens )wherea sthi swa s M. gr. praecox inth e Snijb (20138specimens) ,followe db y G.pulex (11125specimens) . G.pulex occurred in practically allsample s inth eupstrea m sections inth eSnij b and itbecam e less frequent inth emor edownstrea m sections.Thi s isprobabl y connectedwit h itstendenc y tomov eupstrea m (Meijering,1972 )an dwit hth e increasing substrate heterogeneity. Basedo nth efiel dclassification "o fth esubstrate s (Sort 1-4),G.pulex shows a significantpreferenc e fordetritu s substrates (Table 47an d 48), especially for CoarseDetritus .Thi s isconfirme db y thegrain-siz e classifications (Table49) . Therei sals oa clea rover-representatio ni nSan dsample smixe dwit hCoars eDetritu s and/orLeave s inth eSnijb ,whil eGrave lwit hLeave s isals opreferre d inth eRab . Comparing thiswit hth egrain-siz e classifications itca nb e seentha tther e isonl y

a slightpreferenc e forQ 1 =Ï wit h 11organi cmatte ran dQ 1 =Ï an d2 an dM ,« •6 with 10% organicmatter . Inth eRa bonl ya littleover-representatio nfo rQ ,= T i s seen (I.R.= 3.2),bu tthi s concerns 1sampl es oi t isno t reliable.Th epreferenc e inth eSnij bfo rrathe rfin esubstrate swit ha coars e topfractio ni sals oclea rfro m Sort8 ,10 1wher exx xcontain smos tanimal s afterdetritu s substrates.Fro mth e slightshiftin go fth epreference s fromdetritu ssubstrate s tominera l substrates with1-10 1organi cmatte r inSort s 5-8,1» »t o 10% (Table 49), iti sapparen ttha t

121 Table 47. I.R. values for Gammarus pulex (N= 11125) inth efiel d classification of thesubstrate s inth e Snijdersveerbeek.

Sort Sand Gravel Detritus

3 0.1 -41.9 56.9 1 I 4 -25.9 30.2 -39.5 56.9 I I -16.5 2 -27.2 -4.6 52.6 -3.0 -39.5 -16.5 56.9 I 1 L ~\ i 1 1 r i. 1-15.1 -24.7 -4.6 9.2 53.5 14.5 -6.1 5.2 -39.5 -5.9 -15.6 35.2 32.4 34.2 St Sh CD CD+L CD+FD L+FD CD CD CD+L

Italic values indicate significant over-representation

Table 48. I.R.value s for Gammarus pulex (N= 9918) inth efiel d classificationo f the substrates inth eRatumsebeek .

Sort Sand Gravel Detritus

3 -50.7 -28.5 103.2 1 | i 1 4 -43.2 -27.5 -28.0 -8.4 103.2 1 1 | 1 1 1 1 1 1 2 -39.4 -17.8 -15.6 -23.0 -28.0 -8.4 103.2 1 1 1 | 1 | II 1 l 1 ! 1 1 1 1 1 -25.5-30. 9-17. 8 -7 1 -14. 1 -10.4-18. 3 -10.6 -28.0 S. 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 ievalue sindicat e significant over-representation

Table49 . I.R. values for Gammarus pulex (N= 11125)i nth egrain-siz e classificationo fth esubstrate s inth eSnijdersveerbeek .

Substrateclas s

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

phiinde x detritus

CD CD+L

Sort5,1 % -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 Sort6,10 % -5.4 3.7 -10.2 -22.4 -23S -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 CD+L QlMdQ3 index XXX x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD x4x Sort8,1 % -13.4 -22.8 -23.8 -20.2 -13.9 -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 -1.2 12.9 -10.5-8. 6-12. 2-7. 5 55.3 32.0 35.5

Italic values indicate significant over-representation

122 mineral substratescombine dwit hdetritu sar eals oselecte da sa habitat .A preferenc e forGrave lwit hLeave si nth eRa b (Table 48)i ssee ni nSor t 8, 10%i nth epreferenc e forxx xsubstrate . Divisiono fth edistributio nove rsubstrate s into lengthclasse si nSor t5 show s thatth esligh tpreferenc efo r0 ,= T (H detritus level)an dT an d2 (10 1detritu s level)i nth eSnij bi scause db ysmal l specimens (1-6mm )tha tprefe rsubstrate swit h atleas t25 s»o fth egrain s coarsertha n1 m m (seeTabl e 50A,Sor t8 ,Classe s6 an d 7).Th epreferenc e forM ,» Ï i scause db yanimal s from6 t o1 8iim ,an despeciall y theone sfro m15-1 8mm .Tabl e50 Aillustrate s furtherfo rth eSnij b thatth esmalles t specimens (1-3mm )ar emos tabundan ti nC Do rCD+L ,whil e largerspecimen s (16-18inn ) aremor e abundanti nCD+ Lo rL .Thi s shifti npreferenc ebetwee nth ethre etype so f detritusoccur s gradually fromC Dthroug hL t oCD+ L fromsmal lt olarg e animals.I n theRa bexactl yth esam eshif tfro mC Dt oCD+ Lwa sobserved .Th epreferenc efo rQ ,= Ï appearedt ob ecause db ysmal l (1-3mn )animals ,an dfo rG+ Li nth efiel dclassi ­ ficationb y3- 6m manimals . Insunme rth epreferenc efo rdetritu ssubstrate ssee ni nal lothe r seasons shiftst o'mineral 'substrate si nSor t8 ,10 1 (Table 50B).Thi s shifti sno tpresen t inSor t8 ,1 1whe nC Dshow sth ehighes tI.R .values ,indicatin g thatpurel y detritus substratesar emor escarc ei nsunmer ,forcin gth eanimal st ob econten twit hth e combinationo fminera l substratewit hsmal l amountso fdetritus . Specieso fth egenu s Gcarmarusca nb ecalle daspec tdeterminin gi nman y lowland streams,mountai nstream san dals oslo wflowin griver s (ofgoo dwate rqualit yan d withenoug h inputo forgani cmaterial) .Ofte non eca nspea ko f Gammarus streams (Meijering,1971) .Als oth echoic eo fth e Garnnarus groupfo rth esecon dbes twater -

Table 50.I.R . values for Garrmxrus pulex per lengthclas s (A)an d season (B)i nth e Snijdersveerbeek inSor t8,10% .

Length N Substrateclas san d Q„M.Q index 0 1a o class • and 1 1 2 2_ 3 34 54 6 5_ 7 6 8 79 180 11 12 13 14 Season xxXXxX x5 xx5 x3x x x3x2xx xîx2xx xlxlx xxx xxl lxx x XX22Xx 23lxxx 33x CD L CD+L x4x A 0 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- 1 2133 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- 1 8 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 indicatesignifican t over-representation

123 qualityclas s inth esyste mo fMolle rPillo tfo rth eassessmen to fth ewate rqualit y oflowlan d streams (MollerPillot ,1971 )i sconnecte dwit h this.Meijerin g (1971) suggestedt ocal l G.pulex the 'commonfreshwate r shrimp'an d G.fossarum the 'stream freshwatershrimp' ,base do nthei rdifferin gpreference s forslowe ro r fastercurren t velocities ando nth emor e limited distributiono f G.foesarum. Gammärids areprobabl y themos tcommonl yknow n inhabitantso fdetritu s substrates,wher e theyma y occurver y abundantly. G.pulex isa detritivor ewhic h feedsmainl y onth 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 o feedso na varie d assortmento fdetritus ,includin g living anddea 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 was found abundantly indetritu sbu t alsoo nfo rexampl ea drowne d rabbit. Inth e laboratory G.pulex fedreadil y onan y deadanima ltha thappene d tob e inth erearin g channel (e.g. Ephemera danisa nymphs andpupa eo f M. sequax), oftenfeedin gtogethe rwit h M.sequax larvaeo nth elatter' s prey. The abundanceo f G.pulex indetritu s substrates asdemonstrate d above,i sdeter ­ minedb y itspreferenc e for leaves (andassociate dmicroflora )a sfood ,a swel l asb y itspreferenc e forsheltere d siteswit hrelativel y slow flow (e.g.Badcock ,1949 ; Albrecht, 1953;Hynes ,1954 ,1970a ,p . 146;Meijering , 1972;Franke , 1977). Fooda swel l asprotectio nca nbot hb e found indetritus/lea fpack sbu tals ob y the (secondary)selectio no fcoars eminera l substrateswher e current isreduce d inth e crevicesan d interstices,especiall ywhe nals osom edetritu s istrapped .Ree s (1972) foundfo r G.pseudolimnaeus apreferenc e for 16-32m m substrate andh e alsodemonstrate d a significantrelationshi pbetwee nth ebod y lengtho f G.pseudol-inmaeus and theparticl e sizeo fth esubstrate .I nles spreferre d substrates,th eoxyge n consumption increased, whichh eexplaine d asbein g theresul to f theabsenc e ofth e 'properparticl esiz e stimulus' (cf.Eriksen , 1963a). Meijering (1972)state d that G.pulex isrestricte dt o thezone stha tar ealmos tcurren t free,behin d andunde rstone swhe nth ecurren t velocityo fth emai nwate rbod y ishigh . Differences insubstrat epreferenc ebetwee ndifferently-size d specimenswer e observedb yman y authors,wh omainl y looked fordifference s ingrai nsize so fminera l substrates,an dno t fordifference sbetwee norgani csubstrates .Petra n (1977)foun d thesmalles t specimenso f G.fossarum moreabundan ti nfin esubstrate s (M,=0. 6 mm) and largerspecimen smor e abundant incoars emateria l (M,= 24. 5an d 26rim )i nth e fieldsamples ,wit hsimila rdifference s inartificia l substratesplace d inth estream . Probably theavailabilit yo fspac e isth emai nreaso nfo rthes edifferences .Whe n intersticesbetwee nstone sar eto o small tooffe rshelte r for larger animals,onl y smallone swil lb epresen t (Whitehead, 1935). Thedifferen tpreference s of larger andsmalle r G.pulex inth eSnij ban dRa b can

124 onlyb eexplaine dwit hspac e asth e selectionmechanism . Itcoul dver ywel lb e the explanationfo rth eover-representatio no fonl ysmalle rspecimen s inminera l substrates (Table 50A)bu t itdoe sno tcove rth edifference sbetwee nth ethre eorgani c substrates types.Her e theabilit yt ofee d onth e substratemigh tb e important aswel l asth e carryingcapacit yo fth esubstrat e types involved (Nilsson& Sjöstrom , 1977).Juve ­ nilegammarid softe nfee do nth e faeceso fth eolde rone s (Hynes,1954) ,an dthe yma y feedo nfin edetritu s aswell .Fro mfiel dobservation s iti sclea rtha tcoars e detritussubstrate s containmuc hmor efin edetritu s thanlea fpacks ,whic hmigh t explainth epreferenc eo fsmal l G.pulex forCD .Large ranimal sdwel lmor eo nLeave s or thecombinatio no fC Dan dL ,bu t theobserve d differencebetwee nth emediu man d largersize danimal sremain spuzzling . Differences infoo dpreference s betweenanimal so fdifferen t sizecoul db e an explanation.Especiall ywhe n foodpreference so fmediu man d largersize d animals overlap,competitio nfo rfoo dan dspac ewil ldetermin eth ebalanc e assoo na sth e carryingcapacit yo fth esubstrat e isapproache d fora populatio no fa certai nsiz e class composition (Nilsson& Sjöstrom , 1977). Morelikely ,however ,th edifferenc e inpreferenc ebetwee nmedium-size d and larger-sized animals isinheren t toth eorgani c substrate.Lea fpack sdisappea r in thecours eo fwinter ,sprin gan d summeran dar egraduall y incorporated inth ecoars e detritus substratesa ssmalle rfragments .Medium-size d specimens are especially abundant inwinter ,whe n leafpack s are stilldominant .A stim egoe son ,th eanimal s growan dmov ewit hth e (remainso fthe )leave s toth eC Dsubstrate .

Field expérimenta Inth eRatumsebee kth ecolonizatio nrat efo r G.pulex ofth e 8n m and4 m mgrai nsiz eappeare d tob eth e samea sNilsso n &Sjöstro m (1977)foun d in HöjeA (Fig.42) ,althoug hther eth ecolonizatio n started sooner,probabl ybecaus e of a strongerdrif trat ecompare d toth eRatumsebeek . Foral lothe rgrai nsize sth e numbero fobservation s isto osmal lt ojustif yan yconclusions . Tables 51 and 52giv eth enumbe ro f G.pulex for6 siz e classes after 14an d2 8 days colonization,respectively . Iti sapparen t thatsmalle r specimenscoloniz emuc h fastertha nlarge rones ,a phenomeno nwhic hagree swit h anotherobservatio nb yNilsso n & Sjöstrom (1977),wh o explained thisa sbein grelate dt oth epresenc eo feac hsiz e class inth edrift ,whic h ishighes t forth esmalles t sizes.Summarize dove ral lsiz e classes,th epreferenc eo f G.pulex after 28day scolonizatio ndecrease s inth e sequence 8,4 ,1 6an d 32m m (SeeSubsectio n 4.1.7,Tabl e 16).Lookin g atsiz e classes (Table53 )animal s smallertha n6 m mdetermin e thepreferenc e for8 an d4 nm ,an dth e larger individuals,whic har epresen t insmalle rnumbers ,th epreferenc e for 16an d 32mm .This illustrates thatavailabilit y ofinterstitia l spacema y influence the sizegrou po f Gœmcœue thatwil l inhabitth e substrate (cf.Whitehead , 1935). Comparisono fthes eexperimenta ldat awit h thoseo fth efiel d investigation without including thedetritu s substrates leads tosom e interestingconclusions . Table 54give sth eI.R .value s forSor t6 , 101i nth eRab ,an dcomparin g thesewit h

125 Table 51.Numbe ro f Gammavus pulex intw oartificia l substrate trays inth e Ratumsebeek after 14day so fcolonization .

Length class Particlesiz e (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- 1 5 31 43 21 - - 95 15- 1 8 6 3 1 - - 10

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

Lengthclas s Particlesiz e (lowerlimlt)/m m Total /mm 32 16 8 4 2 1 0.5 0.25 0.125 1- 3 234 329 529 595 97 1 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- 15 66 75 2 - - 1 - - - 144 15- 18 8 5 ------13

Table 53.I.R .value s for Gammavus pulex intw oartificia l substrate traysi n theRatumsebee k after2 8day so fcolonization .

Lengthclas s Particlesiz e (lower limit)/mm

32 16 8 4 2 1 0.5 0.25 0.125 1-3 2.5 9.2 22.4 28.0 -7.3 -14.0 -14.0 -14.0 -13.8 3-6 -2.8 12.2 47.2 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 2.0 -1.2 -1.2 -1.2 -1.2 -1.2 -1.2 -1.2

Italicvalue s indicates i gnificant over--representatio n

theI.R .value sfo rth esam e sizeclasse si nth eexperiment si nTabl e5 3reveal s that the resultsonl ypartl y agree.Smal l individualsmainl y colonizeth ecoars eartificia l substratean dar eals opresen ti nth eshove l samples takeni ncoars esubstrate . However,large r specimensonl ycoloniz eth ecoarses t artificial substrates,bu tar e nearly absenti nth ecoars e shovel samplesan dabundan ti nth efin e sandsubstrates , whichar eofte nmixe dwit h 1-10% organicdetritus . Comparedwit h Sort6 ,11 ,whic hmean s that thenonl yminera l sampleswit h less than \%organi c detritusar eincluded ,th epreferenc eo fth esmalle r individuals hardly changes,indicatin g thatthi si sa tru e selectiono fth eminera lparticles .

126 2200 - A

1800-

/ / / 1600 - /

/ 1200- / / / / ,' / / 800- / / / / , / / 400- // _ /' y i i i i 1 14 21 28 colonization time (days)

Flg.42 .Colonizatio nrat eo f Garnmarus pulex inartificia l substrates inth efield . A)accordin g toNilsso n& Sjöströ m (1977) y= 75. 4x +113. 1 ;r = 0.99 7 ;N = 5 ; P <0.00 5 B)i n8 m msubstrat e inth eRatumsebee k y =77. 6x -654. 6 ;r = 0.95 6 ;N = 5 ;P <0.0 1 C)i n4 m msubstrat e inth eRatumsebee k y = 59.8 x - 402.9 ; r = 0.954 ; N = 6 ; P < 0.005

Table54 .I.R .value s for Gammarus pulex inth eminera l classeso f Sort6,10 % inth eRatumsebeek .

Total Median particlesiz e (M.)/mm d 16 8 4 2 1 0.5 0.25 0.125 Numbero fsample s14 8 1 4 4 18 14 19 67 21

Lengthclass/m m N 1-3 1176 -2.8 3.9 11.2 -0.7 0.5 7.7 -5.2 -3.9 3-6 919 -2.5 -0.2 3.8 0.7 2.9 3.4 -2.1 -3.6 6-9 212 -1.2 -2.4 -2.4 1.8 -0.2 2.6 -2.0 2.0 9-12 131 -0.9 -1.4 -1.9 1.3 -3.5 0.8 -2.3 6.6 12- 15 t 39 3 1 3 8 24 15- 18t 6 2 4

Italicvalue s indicatesignifican t over-representation t:actua lnumbe ro fspe c imensbecaus e nosignifican t over-representation

127 However,fo rth elarge rspecimen sth epreferenc e shifted from0.12 5 urnt o 2ran an d 0.5mm ,becaus e all sampleswit h 1-10%organi c detrituswer eno w included inth e detritus samples (comparewit hAppendi x 6,o nshiftin g of samples inclasses) .How ­ ever,th erelativ edifferenc ewit h small-sized individuals remains.Obviously , larger-sized G.pulex dono t selectth e substrate forit sgrai nsiz ebu tfo rth e amounto favailabl e food (detritus,leaves) .

4.2.2.10 DicranotaZettersted t sp. (Diptera:Limoniidae )

Identification Dicranota larvaear e easily recognisable Limoniidae larvaewit h5 pairs ofventra lpseudopods .The ywer eonl y identified togenu sbecaus en oke ywa s available forth e identification ofth e larvae andn o adultswer e foundo rreared . AlthoughHenni g (1968,vol.11 )mentione d onlyon epossibl e species forEurop e (0.bimaaulata), Mendl (1978)give s another species forth elowlan dare a {D.guerini). Which species isfoun d inth eAchterhoe k streams isuncertain ;perhap s theybot h occurthere .

Life cycle Hennig (1968,p .420 )state s thatLimoniida eprobabl yhav e 4larva l instars liketh eTipulidae ,t owhic h they are closely related.Accordin g toLev y (1919) Dicranota himaculata pupates inFebruary ,althoug hh ewa sunabl e to rearth e pupaet oadults .Pomeis l (1953)als ostate dtha t Dicranota larvae arever yhar dt o keep alive inth elaboratory .Mend l (1973)foun d twofligh tperiod s inth eBreiten ­ bach (April/Ma y andSeptember/October ) andh e concluded that therear e 2 generations ayear .Fro mth edat ai nFig .4 3i ti sclea rtha ti nth eRatumse - andSnijdersveerbeek , Dicranota has indeed twogeneration s ina year .Althoug hn o adultswer e caught the first flightperio dwil lb e aroundwee k 13-16 (April)an dth e second inwee k 33-36 (August/September) ,whic hcorrespond swit hth eobservation s ofMend l (1973).

Microdistribution Dicranota occurredwit h 209 specimens in 108sample s inth eSnijders ­ veerbeek,an dwit h 74specimen s in4 3sample s inth eRatumsebeek . Inth efiel dclassi ­ fication (Sort 1)i nth eSnijdersveerbee kth eI.R .value s indicate significant over- representation inS+C D andSh. S (Table 55),whil en o significantpositiv e I.R. values occurred inan yothe rsan dsubstrat eexcep t thosewit h finedetritus .Positiv e I.R. values alsooccurre d inB Gan dG+CD . Inth eRatumsebee k significantpositiv e I.R. valueswer eonl y found inB G andG+C D (Appendix9) . Dicranota presents anic e exampleo fth edifference s thatca nb e foundwhe n using different levels offiel d classifications (Table 55).I nSor t 3wit h only 3 substrate classesn o significantover-representatio ni spresen t (all I.R. values be­ low 2.0). InSor t 4,wit h 5classes ,over-representatio ni spresen t inSan dwithou t CoarseDetritus ,whic h shiftst oS+L/C D inSor t 2 (with 7classes) ,whil e theSan d classeswithou tC Donl ygiv emoderate ,not-significan t I.R. values. InSor t 1,th e mostdetaile d classification,wit h 14classes ,th e abovementione dpreference swer e

128 Ifc om 77: «9-S2 ITTTÏTTTVmftTïl

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77: 37-«

77: 33-36.

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77: 2S-Z8

77: Z\-2A inn

HIK 77- 13-1* ~* nm HmrnlTnif^x

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76: «S-*8

76: 41-

76: J7-*>! nrn nm firn 76: 33-36

76: «-32

76: ZS-28

76: Z1-Z-*

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il nm 76: Ç- B

76: 1- il mninUm 7E: «9-SZ

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rprrfTÎTfTTTÎTÏÏI ~*.

LENGTH CLASS (IUI ) Fig.43 .Lif ecycl ehistogram so f Dicranota sp.showin gth edistributio n(% ) of larvalbod y length per four-week period.

129 Table 55.I.E .value s for Dioranota spp. (N= 209 )i nth efiel d classificationo f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 1.1 0.5 -2.6 I ~~1 4 2.3 -1.0 oU -0.1 -2.6 I 2 1.7 1.8 2.8 -3.5 0.6 -0.1 J.e _l I I 1 1 1 0.4 2.2 1.8 0.3 2.9 1.1 -2.7 -2.5 0.6 -1.3 0.7 -0.9 -2.7 -0.4 St Sh FD CD CD+LCD+F D L+FD CD CD CD+L

Italicvalue s indicatesignifican t over-representation

found,whic hagre ewit hth eresul to fSor t2 ,bu tindee dgiv emor edetaile dinforma ­ tion.Stabl e Sandi sno tpreferred ,whil eo fth eS+ Dsamples ,C Di sth emos t important andth ecombinatio nwit hCoars ean dFin eDetritu si sles spreferred . Consideringth egrain-siz e classificationfo rDiaranota inth eSnijdersveerbee k (Table56 )i ti sobviou s fromth edifference sbetwee nth e1 1an d10 % classification thatsubstrate swit h less than 1 % coarseorgani cmatte rar epreferre d above substrates with 1-10%CD ,althoug hthi sonl y concernsth efine rsan dsubstrate s (Q,> 2 )an dno t thecoars e substrateswhic hmostl yhav e less than 1 % detritus anyway.Onl yth esub ­ strateswit hQ 1 =T sho wa nincreas ei nI.R .value s going fromH to10 % CD,bu tthi s onlyaffect sth epictur e fromSor t8 i nClas s7 (xxx),whil eClas s5 (xïx )i sun ­ altered.A tth esam e timehowever ,th eI.R .value si nth efin e substrates (0,> 2 )

Table 56.I.R . valuesfo r Dioranota spp. (N= 209 )i nth egrain-siz eclassificatio n ofth esubstrate s inth eSnijdersveerbeek .

Subs träte 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 % -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 Sort6,10 % -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 33x CD L CD+L 9lMdQ3 index XXX x5x x3x x2x xlx xlx xxx lxx 22x 23x 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 indicates i gnifi cant over-repre sentation

130 decrease,resultin gi nvalue s smallertha n2. 0i nSor t8 ,10$ ,indicatin gtha t Dioranota preferssubstrate swit hles stha nH CD.Fro mth edrasti cshif to fover - representationi nSor t5 betwee n1 an d10 $an dth erelativel yunaltere dI.R .value s inSor t6 an d7 ,th econclusio nmus tb edaw ntha tth eQ 1 isespeciall yimportan ti n connectionwit hth eamoun to fCoars eDetritu spresent .Furthermor ei tca nb econclude d that Dioranota dwellspreferabl yi nFin eSan dsubstrate s (Q,> 2 )wit honl ysmal l amountso fC Dan di nFin eGrave lsubstrate s (Q1 =ï ;M ,= Î). Inth e10 $classifi ­ cationth epreferenc efo rFin eSan di sles spronounce dan dhighe rfo rFin eGravel / CoarseSand .I nth eRatumsebeek , Dioranota alwayspreferre dth ecoarse rsubstrate s (Classes1 ,3 ,4 ,5 i nSor t8 ,10$ :xxx ,x3x ,x2x ,xïx )wit hth ehighes tover-repre ­ sentationi nxTx ,correspondin gt oth edistributio ni nth eSnijdersveerbeek . Fromth eresult so fth efiel dexperiment spresente di nSectio n4.1. 7(Tabl e16 ) iti sclea rtha t Dioranota occurredmainl yi nth e0. 5- ran1 grai nsiz efractio n(ph i index=1) , butals oi nth efraction s1- 2an d0.2 5- 0.5 0mm ,whic hcorrespond swit h themedia ngrai nsiz eo fth exT xsubstrates . Analysiso fth edistributio no fdifferently-size danimal si nthre elengt hclasse s showedn osignifican tdifferences ,althoug hsmal llarva eoccurre dpreferabl yi nxïx , 33xan dxx xsubstrates ,whil elarge rone spreferre d23 xan 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 sshowe dn osignifican t preferencea tall ,althoug hthe ymostl yoccurre di nth esam esubstrate sa sth eothe r sizes. Since Dioranota iscarnivorous ,predatin gmainl yo nChironomida ean dOligochaet a (Levy,1919 ;Wesenberg-Lund ,1943 ;Hynes ,1961 )on emigh texpec ta relatio nbetwee n thedistributio no fpre yorganism san dDiaranota. Whenthes eresult sar ecompare dwit h thedistributio no fOligochaet a (i.e.Tubificidae )th epreferenc ei nSor t8 ,10 $fo r23 x and33 xcorrespond swit htha to fth eOligochaet afo rthes esubstrates .Als oman yChiro ­ nomidae larvaesho wpreference sfo rth esam esubstrate sa s Diaranota (seeAppendi x12) . Amor edetaile dstud yo fthi srelationshi p includinggu tconten tanalysi swil lb eneces ­ saryfo restablishin grelationship sbetwee nth edistributio no f Diaranota andit s

Table57 .I.R . valuesfo r Diaranota spp.pe rlengt hclas s (A)an d season (B)I n theSnijdersveerbee k inSor t8,10% .

Length N Substrate classan d Q,M.Q_ index class 1 d o 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 65 0.8 -1.9 1.4 -1.1 4.6 -2.0 2.5 -1.4 -1.9 0.5 3.8 -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 values indicatesignifican t over-representation

131 foodanimal s sincepossibl epre ywa sabundan ti nal lsubstrat etypes . Theabov epresente d datao nth emicrodistributio n partly agreewit h earlier data,althoug h thesecove ra wid e rangeo fsubstrates .Geijske s (1935)state d that Limoniidaean dTipulida ebelon gt oth emu dfaun aa swel la st oth edetritu s fauna, buttha t Diaranota occursi nsand ybottoms .Thi s agreeswit hth eobservatio no f Petran (1977)wh ofoun d that Diaranota prefers fine substrates.Edward s (1975)caugh t Diaranota specimensi nsite swit ha nabundanc eo ffin e substrates enrichedwit h organicmatte ran dfoun d less specimenswit h increasing current speedan dcoarse r medianparticl e size,whic h agreeswit hEgglishaw' s (1969)conclusion .However ,Jone s (1951)reporte d that Diaranota and Limnophila occur among stonesan dcoars egrave li n slackwate rnea rth ebanks .Althoug h thesedistributiona l dataar eno tcontradictory , it illustrates that Diaranota occursi na wid e rangeo fsubstrates ,varyin g from fine sandan dmu dt ocoars egrave lan dstones ,preferabl y combinedwit h finedetritus . Thispictur e alsoemerge sfo rth eSnijdersveerbeek ,wher e sand substrates combined with fineo rcoars edetritu sar epreferred ,althoug h Diaranota isabsen ti nsample s with largeamount so fcoars edetritus . Miall (1893)foun d thatpupa eneve r liveunde rwater ,bu ttha t theymigrat et o dampplace s aboveth ewate r surface,e.g .bank so rsan dridge si nth estrea mbed . This agreeswit hth epresenc eo f Diaranota inespeciall yth esample s thatwer e taken from innerbend san dsan dbank si nth eSnijdersveerbeek .Mend l (1978)note d that D.guerini dwellsi nstream san dsmal lrivers ,bu ttha t D.bimaaulata isfoun dwithi n thedirec t reacho fth ewate r surfacei nth edam pbank so fthes ewate r types.Thi s emphasizesth enecessit yt oidentif yth egenu st ospecie s levelan dth eabove-cite d differences inpreferre dhabita tmigh tb erelate dt odifferen tspecies .

4.2.2.11 LimnophilaMarquar t spp. (Diptera:Limoniidae )

Miarodistribution Althoughfou rdifferen t Limnophila specieswer e distinguished (Appendix1 :tax ano' s 197,198 ,19 9an d208 )th eidentificatio n remaineduncertai n andi tma yhav econcerne dmor especies .Fro mth edistributio no f Limnophila inth e Snijdersveerbeek (Tables6 2an d63 )i tca nb esee ntha t Limnophila prefersbot h Gravelan dSan dsubstrates .Tabl e5 8show s that especiallybar esubstrate s (without CDo rL )ar einhabited ,whic hi sals oapparen t fromth edecreas eo fth epositiv eI.R . valuescomparin gth eU and10 % classification inTabe l 59,excep tfo rClas s7 i n Sort8 .Sinc ei tconcern s several species,i ti spossibl e thatth epreferenc efo r CoarseGrave lan dFin eSan drefer st odifferen tspecies .Thi s cannotb eteste d since 342o fth e38 5specimen swer e classifieda son etaxon ,th egenu s Limnophila, which may concern several species,whil eth eremainin g4 3larva ebelonge dt oth eothe r threetax a( 9t o Limnophila sp.a ,1 t oLimnophil a sp.b an d3 3t o Limnophila gr. fusaipennis). Inth eRatumsebee k only6 2specimen swer e foundan dthes e occurredmainl yi n BareSan d substrates (Appendix 9). Inth egrain-siz e classificationa preferenc efo r

132 Table58 .I.R .value sfo r Lirrmophila spp. (N= 385)i nth efiel dclassificatio no f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 2.6 1.1 -6.2 I I 4 3.8 -0.4 2.2 ^.2 -6.2 _1 i I 2 3.1r Ü* 2.7 -2.7 L -1.2 -6.2 I L_ + 1 I , i 1 1.5 3.2 2.2 4.2 r0. 2 1.7 -3.4 0.9 2.2 -1.0 -0.8 r-2. 6 -4.7 -3.3

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

Italicvalue s indicatesignifican t over-representation

Table59 .I.R . valuesfo r Limnophila 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 Q index Ql"d 3 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 + 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

Italicvalue s indicate significant over-représentâtio n + :onl yon e specimenno t measured.N oI . R.value s calculated

xlx,xx xan d1x xwa spresent ,whil en oover-representatio nwa ssee ni ncoars esub ­ strates.Tabl e5 9present sth eI.R .value sfo r4 lengt hclasse s (and1 unmeasure d specimen) (Table59A )o f Limnophila andthos efo rth eseason s (Table 59B)i nth e Snijdersveerbeek.Thes edat asho wtha tth edistributio no fth elarva ei sdifferen ti n summeran dautum ntha ni nwinte ran dspring .Th elatte rseason sar eth eonl yperiod s withman y larvaei ncoars esubstrates :mos t larvaeoccu ri nClasse s7 an d1 0i n summeran dautumn .Lookin ga tthi sdistributio nfo reac hlengt hclas sshow s that smallerlarva e (0-8mm) ,whic har emor enumerou stha nlarge r ones (7:3),determin e theoveral l (total)distributio nsee ni nTabl e 59C.Lik eth esmalle r larvae,large r ones (8-20mm )occurre di npracticall y every substrate type,bu tpreferabl yi nth e finersubstrates .

133 According toLev y (1919) Limnophila iscarnivorous ,lik e Dioranota and Pedicia, and they dwellpreferabl y inmu d anddetritu s substrates. Inexperiment swit harti ­ ficial substrates Petran (1977)foun dtha tLimoniida ean dTipulida eprefe r fine­ grainedsubstrate s asChironomida ean dTubificida e do,expeciall y inth eslowe r running sectionso fth estream .Thi sma yb e apredator-pre y relationship. Jones (1949)foun d Limnophila betweenstone s andcoars e gravelan d according to Geijskes (1935)th eLimoniida ebelon g toth emu dan ddetritu s fauna,a sd oth eTipuli ­ dae.Althoug h Limnophila did occur inSan d+ Leaves ,th edat afro mth eSnijdersveer ­ beekan dth eRatumsebee khardl y supportth epossibilit y that Limnophila dwells in detritus substrates.The yprefe r FineSand ,whic h ismostl y combinedwit h FineDetritu s (mud),bu tthe yals ooccu r insevera lcoarse r substrate types.Thi s emphasizesth e dangero fgeneralizin g fromdat aconcernin g families orgroup s ofspecie s andth e needt o identify toth emos t detailedlevel .

4.2.2.12 PtychopteraMeige nspp . (Diptera: Ptychopteridae)

Miorodistribution Inth eSnijdersveerbee k Ptyohoptera occurredmainl y insand ysub ­ strateswit h astron gpreferenc e forS+FD ,whic h canals ob edescribe d asmud ,althoug h iti soxygen-rich ,a t leasta tth e surface.Othe r substrates inth e fieldclassifi ­ cationwer e alla combinatio nbetwee nC D and/orF Dan dSand ,althoug h especially the FDplaye d an important role (Sort2 ,Tabl e60) . Inth egrain-siz e classificationth e finest substrates arepreferre d (Table61) . Only asmal lshif t inpreferenc e fromClas s 12 (CD)t o 11 (33x)i sobserve dwhe n comparing the H and 101classifications ,indicatin g thatth e amounto fcoars e detritus isno tver y important.Th e fineorgani cmaterial ,whic h isprimaril y apar to f finer substrates,play s amor e important role aswa s seeni nth e field classification. According toWagne r (1978)th e larvae andpupa eo f Ptyohoptera occur inloosel y packed,sof t substrates thatar e enrichedwit horgani cmud .There ,the y feedo n organicmatter .The yburro wperpendicula r inth e substrate,breathin g through their long,retractibl e siphon,whic hextend s toth ewate r surface.Th emaximu m lengtho f thesipho ndetermine s themaximu mwate rdept htha t canb e tolerated (forlonge r periods).Thi s isprobabl ywh y Ptyohoptera wasno t found inth eRatumsebeek ,sinc e thisstrea m isofte nto odee p inth epool s andth ecurren t isto ostron g inth e shallowerplaces . Geijskes (1935)classifie d Ptyohoptera as atypica lmud-species , liketh e Tubificidae, Sialis andChironomidae . Ptyohoptera occurmainl y inwater swit ha leniticcharacter ,wher e theyca ntolerat epollutio nquit ewel l (Berg,1948 ;Zitek - Zwyrtek, 1971;persona lobservation). Mos t species live inseepin g springs and spring-swamps,bu tthe y alsooccu r inslowl y running streams (Thomas,1977a ,b) . The literaturecite dconfirm s theobservation smad e inth eSnijdersveerbeek ,wher e Ptyohoptera areespeciall yrelate d toth e substrateswit hmuc hdetritus ,presen t in quietpart so fth e stream.

134 Table60 .I.R .value s for Ptyohoptera sp. (N= 251 )i nth efiel dclassificatio no f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 7.7 -7.1 -4.1 i 1 1 I _! I 4 3.8 7.4 -6.8 -2.5 I 1 i -4.1 i 1 I I 2 -0.2 7 6.5 -6.8 -2.5 -4.1 I | i 1 1 1 1 1 1 1 -2.5 2.9 1.6 3. 0 1.5 4.8 4.8 -6.8 0.0 -2.9 -2.3 -3.r 3 -1.2

St Sh FD L CI CD+L CD+FD L+FD B L CD CD L CD+L

Italicvalue s indicatesignifican t over-representation

Table61 .I.R . valuesfo r Ptyohoptera sp. (N= 251 )i nth egrain-siz eclassificatio n ofth esubstrate s inth eSnijdersveerbeek .

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 1 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 Sort5,10 % -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 Sort6,1 % -0.8 - -2.0 -3.7 -4.1 -3.5 -3.5 -1.8 6.0 6.1 - 3.3 -3.2 -0.7 Sort6,10 % -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 Sort7,10 % - -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 XXX x5x xlx XXX lxx 22x 23x 33x CD L CD+L 9lMdQ3 index x3x x2x xlx 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 s indicate significant over-représentâtio n

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

Microdistribution Orthooladius occurredi n3 1sample swit h63 1specimen si nth etw o mostdownstrea msection s( 6an d8 )i nth eSnijdersveerbeek ;th eothe r1 1specimen s werefoun di n1 sampl ei nSectio n4 .Accordin gt oMolle rPillo t (personalcommunica ­ tion)i tconcern sa tleas ttw odifferen t species,althoug hn ospecifi cspecie sname s areknow nyet . Inth eRatumsebeek ,onl ythre especimen swer efound ,eac hi na différen tsample . Inth eSnijb , Orthoaladius showeda distinc tpreferenc efo rGrave lsubstrate scom ­ binedwit hDetritu s (Table62 ,Sor t 2), especiallyLeave s (Table62 ,Sor t 1),i nth e

135 Table62 .I.R .value s for Orthoaladius spp. (N= 642 )i nth efiel dclassificatio n of thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 -16.4 24.0 -3.3 _L_ I , I I I 4 -13.1 -9.9 -0.6 43.5 -3.3 I _J I I I -11.1 -7.0 -4.1 -9.4 -0.6 43.5 -3.3 l -^-1 i l_ 1 I 1 1 -9.3 -6.1 -7.0 3.2 -6.r 1 -2.3 -8.4 -4.3r -0. 6 79.9 4.7 2.5 -3.9 -4.3 St Sh FD L CD CD+LCD+F D L+FD B L CD CD L CD+L

Italicvalue s indicatesignifican t over-representation

Table63 .I.R . values for Orthoaladius spp. (N= 642 )i nth egrain-siz eclassificatio n ofth esubstrate s inth e Snijdersveerbeek.

Substrateclas s

10 11 12 13 14

phiinde x 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 lndex xxx x5x x3x x2x xîx xlx xxx lxx 22x 23x 33x CD L CD+L W3 x4x Sort8,10 % -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 efo rx3 x(i.e .53x ) in thegrain-siz e classification (Table63 ,Sor t 5-8).Comparin gth epreferenc ei nSor t 5-7, 101wit hth epreferenc ei nSor t8 ,10 1 (Table 63],th epreferenc efo rQ ,= 5 (Sort5 )an dM ,= 3 (Sor t6 )i sals osee ni nth epreferenc efo rx3 xi nSor t8 , emphasizingth eimportanc eo fth ecoars egrains .However ,th eQ ,seem st ob eles s important sinceth eover-representatio n seeni nSort s5 an d6 i sdivide d overQ ,= Ï-3 inSor t7 . Orthocladiinae larvaean despeciall y generarelate dt o Orthoaladius (e.g.

EuorthoaladiuSs Rheorthoaladius3 Syriarthoaladius and Triahoaladius) areregarde da s typicalfo rth eston yhabita ti nrunnin gwate r (e.g.Nietzke ,1937 ;Thienemann , 1954). Orthoaladius larvaebuil d loose tubeso nstone s (Geijskes,1935) . Orthocladiinae larvaear emor erheophilou san dmor e abundanto nstone san dvegetatio ntha nChirono - minae (Thienemann,1954 ,Lindegaard , 1972).Cummin s (1972)state dtha t Orthocladiinae

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 Micropaeatra larvaewer edistinguishe di ntw olarva lgroups : M.gr . praecox andM. gr . trivialis, thelatte rhavin ga muc hlonge rspin eo nth e in­ nercorne ro fth eantenna lbase .Undoubtedl yth e praecox groupconsist so fsevera l species,bu tfo rfurthe ridentificatio nn 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 weak current , whereth etube so fforme rgeneration sma yhav eforme dtic klayers .The yals ooccu ri n vegetationan dsheltere dplaces ,wher ethe yals obuil d longsan dtube s (Lindegaard, 1972). Inth eSnijb , M.gr . praecox isth emos tnumerou sspecie so fal lmacro-inverte ­ bratesfound ,whil ei ti sth esecon dmos tnumerou son ei nth eRab .I nbot hstream si t occurspredominantl yi ndetritu ssubstrate s (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 n 10%organi cmaterial ,becaus eth e preferencei sonl ysee ni nSor t5 , 10%(Tabl e 65).Th eimportanc eo fdetritu si s illustratedb yth eincreas eo fI.R .value si n23 xan d33 xsubstrate si nSor t8 ,1( H andth edecreas ei nC Dcomparin gwit hth eU classification.Thi scorrespond sver y wellwit hsimila rchange si nI.R . valuesi 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 eclassification ,wit honl ymino rpreference s forSan d+ C Do rL an dF Dsubstrates ,whic hcorrespond swit hth e23 xan d33 xsubstrate s inSor t8 ,101 .

Table64 .I.R . valuesfo r Micropsectra gr. praecox (N= 20138 )i nth efiel d classificationo f thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 4.8 -53.7 64.7 1 1 1 1 1 r 4 -38.0 51.4 -63.0 -2.8 64.7 1 | 1 I 1 2 -55.6 20.3 -11.5 74.6 -63.0 -2.8 64.7 i I 1 i 1 I 1 1 1 1 1 1 1 1 1 1 1 1-46. 1-31. 3 20.3 - 10.7 -6.1 -1.6 84.5 -1.5 -63.0 26.6 -18.4 -10 7 90.7 8.9

St Sh FD L CD CD+L CD+FD L+FD B L CD CI) L CD+I

Italicvalue s indicate significantove r -representation

137 Table65 .I.R .value sfo r Miaropseatra gr. praecox (N= 20138 )i nth egrain-siz e Classificationo f the substrates inth e Snijdersveerbeek.

Substrateclas s

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

phi index detritus

CD L CD+L

Sort 5,1% -7.3-16. 2-47. 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 -44.8-46. 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 3-25. 2 S7.S - 25.8 88.6 4.5 Sort 7,1% - -7.3-10. 3-14. 5-7. 3-14. 4-17. 6-37. 5 -A9.S -13.4 23.4 57.8 93.9 5.1 Sort 7,10% - -7.3-16. 1-14. 5 -7.3-14. 4-17. 6-37. 5-33. 0 -9.3 34.2 25.8 88.6 4.5 Q,M 0 index xxx x5x x3x x2x xîx xlx xxx lxx 22x 23x 33x CD L CD+L 1 d3 o -- x4x Sort 8,1% -22.7 -31.4 -43.0-28. 5-29. 4 -28.4-13 5-33. 6-9. 4-23. 7 20.1 57.8 93.9 5.1 Sort 8,10% -22.8 -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

Italic values indicate significant over-representation

Lindegaard (1972)remarke d thati ti sstil luncertai nwhethe rth elarva efound inth ebotto mbelon gt oth esam e speciesa 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 e thisi sals o different from thepreference s observed inth eRatumsebeek . Further investigationo fth elarva l material frombot h streamsmigh t revealtha ti tdoe sconcer n different species. The combinedmateria l frombot h streams shows that Miaropseatra gr. praecox has twomai n flightperiods :on ei nMarch-Apri l (Weeks9-16 )an don ei nAugust-Septembe r (Weeks 33-40) (Fig.44) . Differently sized larvaeo 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 e Detritusi nspring ; iti sno ts odensel ypopulate d inan yothe r season.I nsummer ,whe npur e detritus substratesar erar ei nth estream ,minera l substrate combinedwit h detritusi spre ­ ferred,whil ei nautum nan dwinte rth emai npreference s arefo rLeave san dsecondl y forSand/Mu d+ Detritu s (Table 66B).I nth eRatumsebeek , small larvae (0-5mm )prefe r CDo rCD+ L (insummer) ,whil e larger larvae (5-10mm )occu rmainl y inCD+ Lo r23 x (+ detritus).Th epreferenc efo r23 xan d33 xsubstrate sb ylarge r larvaei 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 e datawit hth egrain-siz e selectioni nth efiel d experiments (Tables1 5an d16 )show s that aftera perio do f1 4day so fcolonization ,th elarva e

138 — iiiiriMlllfTnUr,

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«i-n,ii,'WHS:j ia LENGTH CLASS( IT » Fig.44 .Lif ecycl ehistogram so f Micropseotra gr. praecox showingth edistributio n (%)o flarva lbod y lengthan dpupa e (99)pe rfour-wee k period.

139 Table 66.I.R .value s for M-icropsectra gr. praecox per length class (A)an d season (B)i nth e Snijdersveerbeek inSor t 8,10%.

Length N SubE träte class and Vd Q3 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 1846 -7.3 -12.4 -2.6 -11.0 -83 -10.2 24.4 -13.7 38.0 -5.7 33.3 -9.4 -13.0 1.5 1-5 9499 -16.3 -18.3 -23.9 -20.2 7.4 -18S -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 53.6 41.4 2.3 11-20 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 -11.9 -7.5 -10.8 -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 -12.9 -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 13.9 26.4 21.2 -9.1 653 1.4

Italic values i ndicate si gnificant over- representation + :N o I.R. val uesc alcul ated

arepresen ti nequall yhig hnumber si nal lgrai nsizes ,whil e theyar eover-represente d inth e4 m man d8 m mfraction s after2 8days .I ti shighl y likely thatthi 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 fM. gr . praecox inthes e coarse-mineralparticl e sizes.

4.2.2.15 ParacladopelmaHarnisc hspp . (Diptera:Chironomidae ,Chironominae )

Miarodistribution Twospecie so f Paracladopelma werefoun di nbot hstreams : P.laminata and P. oamptolabis. 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 , 185specimen 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 y identified.Th edistributiona lpatter nwa sth esam ei nbot h streamsfo r both speciesconsiderin gth efiel d classification (Table 67), althoughth enumbe ro f animalsi srathe rlo wfo rstatistica lanalysis .Bot hspecie s showth ehighes tprefer ­ encefo rS+ED ,followe db yBar eSan dsubstrate s (Sh.San dSt.S) .Th esmal llarva e preferS+C D togetherwit hS+ED . InSor t8 ,10 1som edifference sbetwee nth etw ospecie s appear (Table68) . P.oamptolabis dwellspreferabl yi n1x xsand ,an dalthoug h P.laminata occurredi nthi s substrate,i tpreferre d 23x.Smal l Paracladopelma larvaewer e foundpredominantl yi n ibex,wher eals osom eo fth elarge rlarva eo fth etw ospecie swer efound . Thetw ospecie sonl y sporadicallyoccurre d togetheri nth esam esample :o fth e

140 in co in m •<* CM •* co + rH H H CM CM H iH CM 1 1 1 1 U o lil i m«« rH m in CM <1< rH 3 •J CM CM CM +» i i i •1* CM CM CM Tf •H ri H co t- 0) III I +» a a O u O iH i-l H u co e» H t» O 1 1 1 O 1-1 CM CM CO 0) CM 01 a III I u H O CM' CM 1 1 1 in co o co non O O H o iH j i-i o H' rH I I I O i i I O Mi CM O M> a> CO H M co O h H Mt O t"3 O o m CO• CM• *M i" co t m co •O 1 1 1 i O r-t O O u a o Tf Ci O 00 Co 0 * ^*^ *^ •+j rt < O• •H H Oj CM H lO o> 1 1 1 M Q CM co m H H t- co Ol 00 •«O •»-> o+ CM O H CM .H o o ^3 CD •H u 1 1 1 a i-i co 1» » (• CM 01 + H « CM 0) e a o' o' d rH I« d M u i i i 1 O H O +» m t» io oo a I I en a a a 0 CO CD CO o •H u O H • I•X N3• •H o •H 1 H O O •P H d CM O CO O +«> o> +> +> a |CM a h j H H O H 0 Iri CM ^ Ci CM h H CO O h a Q • • • • a. |CO P. •H Pu CX «O »-H Ml o I« CM H CM Ï-H ï-H i u I I I 1 «WH 1-1 u s K X CM i-s A • • • 0 •H un iir *• I» CO ^H ^ H IXIK sa ta 0 CO cy •o Mi CO O rH •p •o co •S e • • • ci « A •p «JHH a s iH CM ^o ta CO 1 1 d o I (3 •H «H 0> CM •* m •H ag, sa il a 0 co 2 m S 0 o •H co E •H 01 'ti l--i •o •o a a > •H •9 V *-* -i-S Q 5 o S1« m o •8 « § +> ,S Ö 0 •w s; IH a s 1•i i i-«i g g y rH rH « a CO a t t»' OM S +» CJ r-i to • . Ö 0 > g ESH Rj OH fx, E-" u o •H H a iH A M rH t- Ol 00 « • H t- 01 a a 0 O o o> +> es O O o 01 H EH a m co CM M EH S co co CM

141 19sample swit h P.laminata present,onl y three samples alsocontaine d P.oamptolabis. This couldb e ecological segregation,on especie s excluding theothe rb y somemechan ­ ism,e.g . foodcompetition .Mor e likely,th edifference s insubstrat epreferenc epla y a role inseparatin gth etw ospecies : P.laminata preferring finersubstrate s than P.aanptolabis, althoughmor edetaile d information isneede d toconfir mthis .

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

Microdistribution Prodiamesa olivaaea iswit h itswhit ebod y andlon gblac kparalabia l hair-tuftson eo fth emos t easilyrecognisabl eOrthocladiina e larvae.I twa squit e numerous inth eSnijdersveerbee k (950specimen s in 105samples )an dth eRatumsebee k 240specime ni n2 8 samples),givin g anaverag eo f 8-9 specimenpe rsampl e inbot h streams. A directrelationshi pwit hdetritu sin combinatio nwit hSan dsubstrate si s apparent inbot hstreams ,whic h is illustrated forth eSnijdersveerbee k inTabl e6 9 forth efiel dclassification .Her e themai npreferenc e isfo rS+CD+FD ,wit h amino r over-representationi nS+CD+L .Th epreferenc e ispresen t through all fourclassifica ­ tionlevels ,excep t forth esligh tover-representatio n inlea fpack s (118specimen s in3 4samples) .Th epreferenc e forS+CD+F D is apreferenc etha t isrepeate d inth e grains-size classification,whic h isno t always so,a sdemonstrate d forsom eo fth e detritus-preferringChironomida e (seeSubsectio n4.2.2.18) . InSor t5-8 ,H themai n preference is forC D substrate (Table 70), followedb yth e finestminera l substrate inal lclassification s exceptSor t 6, indicating thatsubstrate spreferre db y Prodiamesa containmor etha n 1°sCD . Inth e 10°&classification sth epreferenc eha s shiftedfro mC Dt oth e finestminera lsubstrates ,whic hmean s that P.olivaaea occurs predominantly inver yFin eSan dsubstrate s combinedwit h 1-101coars eorgani cdetritus . As demonstrated inAppendi x 6,thes ear eals oth esubstrate swit hth e largestamount s offin eorgani cdetritus . The slightover-representatio ni nLeave s isconstan t inbot hth e 1 % and10° s classifications,indicatin gtha t itconcern s leafpack swithou tmuc hminera lmatter . Inth efiel dclassificatio nfo rth eRa bth epreferenc ewa shighes t forS+L+F Dan d S+FDfollowe db yS+CD+FD . Inth egrain-siz e classification thepreference swer eprac ­ tically identicalwit hthos e seenfo rth eSnijb ,excep t forth e facttha t inth eRa b Class 9 (22x)wa smainl ypreferre d inbot hth e H and 101classifications ,whil ede ­ tritus substrates showedn oover-representatio ni nan yclassification .However ,an increase inth eI.R .value s forth efines tminera l substratesoccurre d inth e 10% classification,togethe rwit ha decreas e ofth e I.R. values inCD ,indicatin gtha t sampleswit h 1—10%C Dan dcontainin g P.olivacea weremaske d inth e H classifications. Thedistributio no fdifferentl y sized larvae inthre e lengthclasse s (0-6,6-1 0 and 10-17mm )showe dn o differences insubstrat epreference .No rwer e therean ysea ­ sonalvariation s inth edistributiona lpatter nove rth esubstrates .I nth efiel d experiments (Table 16), a selectiono fth e 4m mparticl e sizewa s seen.Probabl y the

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

Sort Sand Gravel Detritus

3 13.3 -15.4 -2.8 1 1 1 I 4 -11.6 33.8 -14.0 -6.8 -2.8 I _l 1 i— 1 I r -2.5 1.9 41.6 -14.0 -6.8 -2.8 -12.0 I i r 1 _l_ 1 1 1 1-10. r7 J-5. 8 -2.5 -1.1 3.7 -2.0 46.9 -0.r5 -14.0 -3.3 1-6. 0 -6.2 3.6 -5.0r

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

Italicvalue s indicatesignifican t over-representation

Table70 .I.R . values for Prodiamesa olivaoea (N= 950 )i nth egrain-siz e classificationo fth esubstrate s 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 % -1.6 -4.3 -11X) -93 -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 Sort 6,1% -1.6 - -4.7 -7.2 -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 -32 24.4 - 6.5 3.3 -5.3 Sort7,1 % - -1.6 -2.2 -32 -1.6 -3.2 -3.9 -8.1 -123 -122 5.1 32.9 3.3 -5.4 Sort7,10 % - -1.6 -3.5 -32 -1.6 -3.2 -3.9 -8.1 -11.9 8.2 14.5 6.5 3.3 -5.3

QjMdQ3 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 21.8 13.7 6.5 3.3 -5.3

Italicvalue s indicates i gnificant over-representation

sameexplanatio na sgive nfo rth eover-representatio no f M.gr . praecox inthi s grain-sizefractio napplies ,namel yth ehig hamoun to fdetritu strappe di nth e4m m fraction. Geijskes (1935)an dNietzk e (1937)assigne d Prodiameda olivaoea toth e 'mud- inhabitants', a grou po fspecie sconsistin go f Mioropseotra praecox, Polypedilum laetum, Polypedilum pédestre, Polypedilum conviction, Ablabesmyia geijskesi, Chironomus, Macropelopia, Pseotvotanypus andothers ,a communit yals odescribe 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 ssubstrates .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 t inLea fsubstrate s andles s inth efines tsan d (mud),althoug hth e largestnumber so f M. gr. praecox and P.olivaaea alwaysoccurre d inth esam erang eo fsubstrate s (Class9-1 3 inSor t8 , 10°6),wit hth eonl ydifferenc e inth emainl ypreferre d type (Leavesan d23 xSand , bothi ncombinatio nwit hFin eDetritus) . Inth eRatumsebeek , Mioropseotra gr. praecox occurredmainl y inth eC Dsubstrates ,whil e P.olivaaea waspredominantl y found in22 x Sand (Class 9). However,al lreference san dth eresult s frombot hstream s reported here indicate that P.olivaaea prefers soft substrates,consistin go fFin eSan dan d FineDetritu s (mud)wit habundan tCoars eDetritus ,whic h ispresen t inplace swit ha weakcurrent . P.olivaaea isa free-livin gdetritivor e that isver ywel ladapte dt o live inth esan dhabitat ,wher e iteat sth esan d formicro-organism s (Bryce,1960) . Iti sa neducate dgues stha t itwil lals oconsum e largeamount so ffin edetritus .

4.2.2.17 Epoicocladius flavens (Malloch) (Diptera:Chironomidae ,Orthocladiinae )

Miarodistribution The lifecycl eo f E.flavens and itsassociatio nwit h Ephemera daniaa (Ephemeroptera)ha sbee nexcellentl y describedb ySvensso n (1976).H efoun d lesstha n 2%o fth etota lnumbe ro f E. flavens larvae free inth esubstrate ;th eres t was associatedwit h Ephemera daniaa nymphs. Inth eSnij ban dth eRab ,th esecon dt ofourt h instar larvae (longertha n 1mm ) were always found insample scontainin g E.daniaa nymphs,bu t since thenumbe ro flar ­ vaeo nth e livenymph swa sno tdetermined , iti sno tpossibl e tosa ywhethe rsom e occurred freeo rwhethe r allwer e attachedt o E.daniaa. Inth eSnijb ,onl yfou r E.flavens larvaewer e found (with43 6 E.daniaa nymphs inth e samples). Inth eRab , however,13 0larva eoccurre dtogethe rwit h 504 E.daniaa nymphs,althoug h inal l samplescontainin g E.flavens larvaeonl y 190 E.daniaa nymphswer epresent .Thi sgive s a rather lowinfestatio nratio r(0.26)o nth etota l averagean d isstil l low (0.68) whenonl y considering the samplescontainin gbot hlarva ean dnymphs . Comparisono fth edistributio no f Epoicocladius flavens inth eRa bwit h thato f Ephemera daniaa shouldgiv ea simila rdistributio n ifth elarva echoos ethei rhost s atrandom . Ifthe yprefe r largernymphs ,a differenc e inth etota l distribution shouldb e found,bu tagreemen twit htha to fth elarge rnymphs . Inth efiel dclassificatio n (Table 71) E.flavens showsa clea rpreferenc e for S+CD+FD,wit ha muc hlowe rpositiv eI.R .valu e inS+L+FD .Thi s agreesver ywel lwit h thepreferenc eo f E.daniaa (Table 36),especiall y sinceth eover-representatio ni n S+FDan dG+ L iscause db y the6-1 5 mm sizeclas s andlarge rspecimen sar emor eo r less retrictedt oS+CD+FD . Inth egrain-siz eclassificatio n (Table 72)th epreferenc e of E. flavens inSor t 8,10° sagree sbes twit htha to fth e largest E. daniaa nymphs (Table 40). The sameshift so fpreferenc e existbetwee nth e H and 101classification . Analysiso fthes edat afo reac hnympha lsiz eclas s shows againtha t E.flavens follows the largest E.daniaa nymphs.Difference sbetwee nTabl e 72an dTabl e 38ca nb e relatedt oth epresenc eo fman ysmal lnymph s (seeTabl e 40).Althoug h23 x ispreferred ,

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 i 1 1 1 1 1 4 -3.8 10.6 0.3 -1.8 -5.4 I 1 1 i 1 1 1 1 2 -3.6 -1.3 -0.8 12.3 0.3 -1.8 -5.4 I I I 1 II 1 1 1 1 1 1 1 1 1 1 ~~1 1 -2.1 -3.1 -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 D L+FD B L CD CD L CD+L +FD

Italicvalue s indicate significant over-representation

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

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

phiinde x detritus CD CD+L

Sort5,1 % 2.9 -1.2-1. 8 2.5 -2.6-0. 8-1. 2-2. 2-2. 6-0. 8 10.8 -4.0-2. 0 Sort5,10 % 2.9 -1.2-1. 8 2.3 -2.9-0. 7-1. 2-1. 8 8.9 -1.8 - -1.8-4. 8-1. 6 Sort6,1 % -0.8 0.2-1. 6-1. 3 1.5 0.5-4. 3 1.4 - 10.8 -4.0-2. 0 Sort6,10 % -0.8 0.2-1. 6-1. 4 1.5 0.1-3. 1 14.4 - -1.8-4. 8-1. 6 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 lnde x xxx x5x x3x x2x xlx xlx xxx lxx 22x 23x 33x CD L CD+L

E.flavens occurred(o n E.danioa nymphs)i nal lgrai nsize sfro mClas s4-1 0i nSor t8 , 101wit ha nadditiona lthre elarva ei nClas s2 (x5x ,x3x) .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 y5 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 elegs ,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 gca nb econclude do nth edis ­ tributiono f E.flavens pupae. 145 4.2.2.18 Chironomidaeo fdetritu s substrates

Ofth e2 0Chironomida e species foundwit hmor e than10 0specimen s during this investigation,th efollowin g7 showe da majo rpreferenc efo rCoars eDetritu s and/orLea fsubstrate si nbot hth efiel dan dth egrain-siz eclassification s (Appen­ dices9 ,1 2an d 13): 253/254 Conehapelopia (metanope) 269 Corynoneuraspp . 272 Brillia modesta 275 Diploeladiua aultvigev 277 Rheoevieotopua spp. 279 Eukiefferiella gr. diseolovipea 310 Polypedilum laetvanagg . Comparisono fAppendi x9 wit hAppendice s 12an d1 3show s thatpreference 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 Conehapelopia, inth egrou po fspe ­ ciesoccurrin gmainl yi naquati cvegetatio no r(les sabundant )o nstones .Geijske s (1935)mentioned ,amon gothers , Bvillia, Corynonevœa, Rheoerieotopus and Limnophye s forth edetritu shabitat .Fo rdetaile dnote so nth eecolog yo fthes especies , the paperb yLindegaar d (1972)ca nb econsulted .Sinc eth eclassification s Sort2- 4an d Sort5- 7d ono tad dan yvita l informationon th esubstrat epreference so fthes e species,onl ySor t1 an dSor t8 wil lb epresented . (Table7 3an dAppendice s1 2 and 13).

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

Mierodistribution Conehapelopia larvaecanno tb eidentifie dt ospecie s levelwhe n thepupa lthoraca lhorn sar estil l absent.Sinc eal llarva ean dpupa etha tcoul db e identifiedt ospecie sleve lwer e C.melanopa, all Conehapelopia larvaewer e considered tobelon gt othi sspecies . Conehapelopia isth eonl yTanypodina epreferrin gDetritu s substrates above mineral substrates (cf.Appendice s9 ,1 2an d13) . Althoughrelativel ymor 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 ,U withSor t8 ,10° s(Tabl e74 ) showsan increas eo fth eI.R .value si nmos to fth eminera l substrates,togethe rwit h anincreas ei nth eorgani c substrates.Thi s indicates thata tleas tpar to fth epopu ­ lationlive si nminera l substrateswit h 1-10%organi cmatter .However ,thi s doesno t concerndifferen t instars sinceanalysi so fth edistributio no fdifferen t length classesreveale dn osignifican tdifference si ndistribution .

146 O ri r-l I I I

o cnco^iososcoosos XI rHCsCsC^lO^COOS j c-a co c\a ri iô co CM

co o •p CJ M^n I ri CO ri m u ON'»*»*«« o oeo*cocoi»oocD u i i i i i i i

J I il cxi MI I j CO 00 ri Os Q) Os CO có CO Mi n^Nio^ion« 2 •aH u t- h co ri Co CO Cv ^tl + OOCOHi-icOCOin •P J I I I I I I •H 9) Os co CO r-| C\J to M h O 8 1-1 r-i ri O P •H a nnsiTiiiFiio CD O N O 0) lO co O fn •H co + HBlON^OHO •o eo eq IH T-I rt r* ci Q I I I I H H H s. U III 1-1 • a M K rH N co co co oo a a d> co 0 o eo o N • N• c•o •O a OsOHNrHriirHOO co xi co i i 1 1 U I I I I a si o o o M S) « e e» n CO o £M eo »n « rH H CO a •O n> i i 1 1 1 0 •I a onNnnioHM! o a h •H a u I I I I I I t-i a o O eo c~ rH ^ji in •P •o •a 8 a »e -o H •* •* riNNN p •H a O -H 1 I 1 1 1 1 a e» •H a o co - eo K o> ce t- en eo o co O J I II II o ce 0) M 0 H co N N O eo rH SH •H p. •p ,a iR i i i i 0, a •tfeor»r-coen*'e>» o u -P u o X CD •* o o eo o 1«1 a TfTt"in'j''5icoo^' I co a H i o »l I I I I I I H i h •H IK eo eo N N o co t< O •O i i i i i i V i > a co O a a, ,41 co en e» c» rH eo 0> a «»»»"»ons P 1 K rH iH O O M rH +> ta i i i i i H H i t-s«i §ö i i i i i i i a • i-i a 00 CD M n ^ n o a g IM co o •uH •p IM rH rH O H CO IXIX •* eo N rH rH H u iH n +- s o tu •H a 5g M £X«* CA a > o o •* O in oo co a •H M »H • «0 0 co S ca CD -CS o O • u w i'R8 N IN rH rH O l-l •H oi a m o ce o 1 1 1 1 1 1 CO O Ci) +S -ji -J» CJ -ji S o si • "H O • ii 1 4 l-l Q) a ö S „S +* -t * . « 3 O l-l 3 r^STSr-lrJCO'ÇH, H o B* S* H • S«» a S Ss Q 3 S O H. ri • O S« o a co m tî ^1 rH rH rH t» u a* • O • • . rC • • •p t- - > 0 fH o a n co« o o» 60 ri a ri u 0) M « -H coenNinint»o>o a •• XI h h U •hH E1 p3 Pa a a o lnCOt»t»NC-r»rH p 0. 3 3 TH a a H et a o CO CO

147 Lindegaard (1972)mentione d that Conohapelopia livesprimaril yo n Elodea veg­ etationi nplace swher eth ecurren ti sweak .H eassume d that Eukiefferiella and Criootopus species,whic hals ooccu ri nthi shabitat ,wil lb eth emai nfoo dorganism s forth epredator y Conohapelopia larvae.I nth etw oinvestigate dDutc h streamsan yo f thespecie sdwellin gi nth edetritu shabita tmigh t servea sfoo dfo r Conohapelopia. However,onl ya nanalysi so fth egu tcontent sca nclarif ythi si ndetail . Inth etw ostream s studied, Conohapelopia wasfoun dwit hal llarva l sizespresen t duringth ewhol eyear .N osignifican t differencesi nsubstrat epreferenc ewer e seen betweenlarva eo fdifferen t size (1-5an d5-1 0mm) . Preferencefo rC Dwa spresen ti n allseason sbu thighes ti nsprin gan dsumme r (Table 74).I nwinte rpreferenc efo ral l Detritus substrateswa sequall yhig han dshare dwit h FineSan dwit hDetritu s (33x). Inautum nSan dsubstrate swer e favoured afterCD+L . Inth ecolonizatio n experimentso fsevera lgrain-siz e fractionsi nth eRa b (Tables1 5an d16 ,Subsectio n 4.1.7), Conohapelopia preferredth e2 an d4 m mfraction s afterbot hcolonizatio nperiod s (like Maoropelopia nebulosa, anotherTanypodina e larva). Moredat ao nth econdition soccurrin g inth eartificia l substratesi nth efiel dar e necessaryt oexplai nthi spreference .

CorynoneuraWinnert zspp . (Diptera:Chironomidae ,Orthocladiinae )

Microdistribution Thegenu s Corynoneura wasrepresente db ya tleas ttw ospecies : C.minuta and C. eoutellata. C.minuta correspondst oth e Corynoneura sp.I Io fLindegaar d (1972)an d C.soutellata resembleshi ssp . I. Treateda tth egeneri c level,thi smixtur eo fspecie s showeda clea rpreferenc e fororgani csubstrates ,especiall yCoars eDetritu so rLeaves .I nth eSnij bonl ya slightover-representatio noccurre di nS+ Lan dG+ L(Tabl e 73). Inth eRa b Corynoneura occurredpredominantl y inlea fpacks .Ber ge tal . (1948)an dLindegaar d (1972)foun d Corynomeura mainlyi nvegetatio nwher e detritusi softe nabundant .

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

Miorodistribution B.modesta isth emos t common Brillia species found,an dth eonl y onei nth eRab .I nth eSnijb ,anothe rspecie swa spresen ti nlo wnumbers : B.longifuroa (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 s9 ,1 2an d13) . Inbot h streams,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%o fal l larvaewa spresen ti non eo fth ethre eorgani c substratesi nSor t8 ,10°s .Onl y3 5 larvaewer e foundi nth eminera lsubstrates .I nth efiel dclassificatio n thiswa s 901 forth edetritu ssubstrate san dth e4 2remainin g larvaeoccurre di nth eminera l

148 substratescombine dwit hC Do rL . Inth eRab ,onl ythre e larvae (21)di dno toccu ri nth edetritu ssubstrate si n anyclassification .Thes edat aemphasiz etha torgani csubstrate s formth especifi c habitato f Brillia. Geijskes (193S)foun dthe mmainl ybetwee n leaves,bu tals oi n moss,detritu san dalgae .Ber ge tal . (1948)foun d Brillia betweenbeec hleave si na slowrunnin gspring .Hyne s (1970a)mentione dtha t Brillia isa wood-eatin gspecies , whichagree swit hth eobservation sb yN.H .Anderso n (personalcommunication )tha t Brillia dwellsmainl y incoars edetritu ssubstrate swit ha lo to fdecayin gwoo d present. Iti spossibl etha tthi sconcern sa differenc e inth e Brillia 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 efoo dsource .

Diplocladiuscultrige rKie fe r (Diptera*.Chironomidae ,Orthocladiinae )

Microdistribution Thisfree-livin gOrthocladiina ewa s foundi nbot hstreams ,wher e itoccurre d inth 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 cultriger predominantly invegetatio ntogethe rwit h Eukiefferiella species.Thi scombinatio ni s alsoapparen tfo rth eLea fsubstrat e inth eSnijb ,althoug hsom edifference s remain concerningth esecondl ypreferre dsubstrate . D.cultriger 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 e concluded that D.cultriger isa sprin gspecies . Alllarva llengt hclasse sdistinguishe d (1-4nm ,4- 6n man dlarge rspecimens )showe d similarsubstrat epreference s inal lseasons .

RheocricotopusThieneman nspp . (Diptera:Chironomidae ,Orthocladiinae )

Microdistribution Onlyo na fe woccasion swer e Rheocricotopus larvaeidentifie dt o species level,an dthe ntw ospecie swer erecognized : R.dorieri and R.fuscipes, the latterprobabl ybein gth emos tabundan ton e (MollerPillot ,persona lcommunication) . However,al l Rheocricotopus spp.wer etreate da tth egeneri clevel . Rheocricotopus wasextremel yabundan t inlea fpacks ,wit hsmalle rnumber s in CoarseDetritu ssubstrate s anda fe wspecimen so nstone scombine dwit ha fe wleave s (Table 73).Thi s isa distributio nquit esimila rt otha to f Eukiefferiella gr. disaoloripes. The sameincreas ei nI.R .value so fth epreferre ddetritu s substrate (Leaves)an ddecreas eo fI.R . valuesi nth e 'mineral'substrate s isobserve di n comparingSor t8 ,H andSor t8,101 .I nSor t 5-7als oover-representatio nwa s seeni n thecoarses tminera lsubstrate ,bu tthi sconcerne donl yon esampl e (seeAppendi x4) . Thienemann (1954,p .629 )gav ea sth echaracteristi cbiotop efo r Rheocricotopus theslower -o rfaster-runnin griver san dstreams ,an deve nsprings ,i nlowland san d

149 middleo rhig hmountai n areas,mostl ybetwee nplant sbu tals oo nstones ,eve ni n pollutedstreams . Lindegaard (1972)mention s that Rheoariootopus fusaipes isa sprin g forma s all specimens occurred fromMarc ht oMa ywit ha maximu mi nApril .I nth eSnij ban dth e Rabth elarva ewer e alwayspresen twit hmaximu mdensitie s inspring ,autum nan d winter,indicatin g thati tconcern smor e generationsa yea ro ra mixtur eo fspecies . Rh. eff usus isknow nt ohav ethre egeneration s during springan dsumme r (Lindegaard, 1972).

Eukiefferiellagr .discoloripe s (sensuMolle r Pillot,1980 ) (Diptera:Chironomidae , Orthocladiinae)

Miarodistribution This greenOrthocladiina e larvawa squit e abundanti nth eSnijders ­ veerbeek,bu twa sfoun donl y incidentally inth eRatumsebeek .I tprove dt ob ea tru e representativeo fNietzke' s (1937)plants-stone s groupa si tpreferre d detritusan d gravel substrates (Table 73):G+L ,C Dan dL i nSor t1 .I nSor t8 ,onl yC Dan dL wer e preferredan dn o'mineral 'substrates ,indicatin g thato fth ecombinatio ngravel - leaves,th eleave swer emor e important.Th eI.R .value si nth eC Dan dL classe si n Sort8 increase d fromth e1% t oth e10 % classificationwithou tan yincreas ei nth e I.R. valuesi nth e'mineral 'classes ,whic h indicates thatdetritu s sampleswit honl y 1-10%organi cmateria lar eno tth epreferre d substratefo r Eukiefferiella gr. disaoloripes. This result correspondswel lwit hth eobservation so fThieneman n (1936,p .50 ) asreporte db yBer ge tal . (1948),wh ofoun d that Eukiefferiella larvaedeman d good oxygencondition si nfast-runnin gwater ,wher e they dwellbetwee n algaean dmos so n stones.Ber ge tal . (1948)als o found themo nstones .Th ereaso nfo rth esmal l populationo f E. gr.disaoloripes inth eRatumsebee k isno tknown . Eukiefferiella verralli larvae(include di nth e disaoloripes group)fee do n detritusan dalthoug hthe yar erheobiontic ,the yar emos t abundant inplace sno t exposedt oth estronges t current (vegetation)wher e detritus accumulates (Lindegaard, 1972).Thi s typeo fdistributio n corresponds closelywit h thato f Eukiefferiella gr. disaoloripes inth eSnijdersveerbeek . E. gr.disaoloripes ispresen t throughoutth eyear ,wit ha minimu m innumber si n summeri nth eSnijdersveerbeek .Pupa ewer e foundi nMarch ,an dprobabl yth efligh t periodwil lb eth esam ea sLindegaar d (1972)reported :Marc h- Jun ean dincidentall y duringth ewhol e summer,sinc e small larvaewer emos t abundant fromOctobe rt oDecem ­ beran dlarg e larvae fromFebruar yt oApril .

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

Identification P.laetum isa Polypedilum speciestha tca nb eeasil yconfuse dwit h P.pedestve. Allmateria lwa schecke dwit hth emos trecen tke y(Molle rPillot , 1979) andman y identificationswer echecke db yMolle rPillot . Miarodistpibution 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 y occurred predominantly indetritu s substrates,showin ga simila rdistributio na s Conohapelopia melanops. Leaves,C Dan dS+CD+ Lwer emostl ypreferre d (Table 73),whic hagree swit h Hynes' (1970a)statemen t that Polypedilum belongst oth ewood-eaters ,althoug hh edi d notspecif yth especies . Inth efiel dclassification ,a mino rover-representatio nwa s seeni 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 indicates thatsubstrate 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 san d vegetation. Breakdowno fth epreference st otw olarva llengt hclasse s (Table76A )show s that thepreferenc efo r3Ï xresult s fromth esmalle r larvae (0-5mm) , although thesesho w aneve nhighe rpreferenc efo rLeaves .Large r larvae (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

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% -1.7-3. 2-5. 5-10. 3 19.0 -6.2-2. 1-8. 2 -9.4 -2.5 - 5.7 22.4 -0.5 Sort 5,10% -1.7-3. 2-5. 7-10 3 17.7 -6.4 6.8 -8.9 -105 -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 - 5.7 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 Sort 7,1% - -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 5-3. 4 14.7 24.2 -4.4 Q<,M.,Qoinde x xxx x5x x3x x2x xîx ilx xxx lxx 22x 23x 33x CD L CD+L 1a 3 -- 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 indicatesignifican t over-representation

151 Table76 .I.R .value sfo r Polypedilum laetum agg.pe r lengthclas s (A)an d season (B)i nth eSnijdersveerbee k inSor t8,10% .

Length N Substrateclas s andQ,M.Q _ index 1d 3 class and 12 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 35+ 18+ 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 22.5 -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 s indicate significant over-representation + :Actua l numbersar egiven .N o I.R. valuescalculate d

Seasonally therear eals odifference s (Table 76B).I nspring ,Detritu s substrates werepreferred ,whil ei nautum nmos t larvaeoccurre di nxl x Gravelan dDetritus .I n sunmer,onl yminera l substrates showove r representation,whil ei nwinte r Coarse Gravel (xSx,x4x )i spreferre d togetherwit hDetritus .Thi s clearly indicates that theautumn-winter-sprin g generationha sothe rpreference s thanth esumme rgeneration . A fact thatmigh tb econnecte dwit hth eavailabilit yo fth epreferre dsubstrates . Insummer ,whe ndetritu s substratesar escarce ,th egeneratio nspend sa muc h shortertim ei nth estream .I nautum nan dwinter ,whe ndetritu s substratesar eabun ­ dantbu tlarva lgrowt hi sminimal ,th eyoun g larvaeprefe rminera l substrates,whil e inspring ,a perio do ffas tgrowth ,the yobviousl ymov et odetritus .

152 5 General discussion

As demonstratedi nSubsectio n4.1.5 .an delucidate dfo rsevera lspecie si n Subsection 4.2.2,mos tmacroinvertebrat e speciesar estrongl y relatedt ocertai n substratetype s composedo fminera lo rorgani cmateria lo ra combinatio no fboth . These results supportth ehypothesi s thatman y lowland-stream specieshav edistinc t substratepreferences ,ofte nwit hnarro wrange s concerningth epreferre d particle size (combinations).Th eresult s concerningth especie s dealtwit hi ndetai lhav e alreadybee ncompare dwit h literature datai nSubsectio n4.2. 2an di ngenera l agree witho rgiv eadditiona lo rmor edetaile d informationo nth esubstrat epreferences . Oneshould ,however ,kee pi nmin d thatrelationship swit h certain substrate typeso rparticl e sizes,conclude d fromover-representatio ni nthes e substrates,ar e notnecessaril yth eresul to fpreference sfo rth esubstrate .Preferenc e impliesth e activechoic eo f'optimal 'condition sb yth eanimals ,an dconclusion s about substrate preference shouldtherefor eb ebase do nlaborator y experimentsi ncombinatio nwit h fielddata .I ti sno tpracticable ,however ,t operfor m laboratory experiments testing thesubstrat eo rparticle-siz e selectionfo ral lspecie spresen ti na stream . Oftenpreferenc ewil lno tb eaime da tth esubstrat e compositiono rth eparticl e sizeitself ,bu ta t(th ecombinatio nof )othe r factorsprevailin gi ntha tparticula r habitatan dperhap son eshoul dspea ko fhabita tpreferenc e rather thano fsubstrat e preference,especiall ywhe nonl yfiel ddat aar eavailabl ean dth esubstrat ei si n factuse da sa descripto ro fth ehabitat .Current ,foo dan doxyge ncondition sar eal l strongly relatedt oth esubstrat econdition san dth esubstrat ei stherefor ea nout ­ standingparamete rt odescrib ea habitat .No tonl ybecaus ei tcatche sth eey ean di s easiert odescrib eo rmeasure ,bu tals obecaus ei tusuall y reflectsth econdition s prevailingi nth eperio dbefor esampling . Thepresenc eo fa specie si na habita ti sth eresul to fit sbahavioura l response toth eenvironmenta l conditionsprevailin go nth espo t (Meadows& Campbell , 1972). Cummins (1975)state d thatth erelationshi po fth emicrodistributio nan dabundanc e ofmacroinvertebrate swit hvariou s specificphysical-chemica l parametersma yb eo f onlya nindirec tnature .Th eanima ldistribution sma yactuall yb econtrolle db ysom e otherfactor ,whic h itselfi smor edirectl y relatedt oa physical-chemica lparameter . Substrate composition,o rth erang eo fparticl esize spresen ti na habitat ,i s determinedb yth ecurren t (velocity,flo wregim ean dturbulence) ,whil e thesear e alsoresponsibl efo rth eamoun to faccumulate d organic detritus,th egrowt ho fmacro - phytesan dth eoxyge nsupply .Thu si ti spossibl e thata relationshi pbetwee nth e microdistributiono fa specie san dth esubstrat ei si nfac tcontrolle db yth ecurren t

153 velocity orth e amount offoo d (detritus)present .However ,o nth ebasi s ofth e knowledge ofth ecorrelatio nbetwee nvariou s specificparameter s and the substrate it ispossibl et o indicate foreac h specieswhic hparamete rwil lb e responsible for the selectiono fa certai nsubstrat etype . Themos t importantmechanism s seen inSubsectio n 4.2.2.ar e eitherdirectl y linked toth e substrate,becaus e itrestrict s or enhances thepossibilitie s for burrowing,attachin g (clinging,sucking) ,hidin g or theprovisio no fth emateria l necessary forcas e ortub ebuilding ,o r indirectly,becaus e of factors associated with substrate conditions,e.g .microbial ,alga l ordetrita l food,o rpre y density, current-velocity,-regim e and-turbulenc e and oxygen supply. Insummar y itca nb e stated thatth e three factorsmainl y responsible forsubstrat e selection are: particle size,curren t velocity and food conditions,a s also illustrated inth e diagrampresente db yCummin s &Lauf f (1969) (Fig. 1).O f course these factors are ofteno fa combine d influence andno teasil y separated,bu t itwil lb epossibl e to illustratethei r individualroles .

5.1 PARTICLE SIZE

Species reacting directly to substrateparticl e size canb e found especially among the species dwelling oncoars e substrates,wher e the surface is largeenoug h to allow attachment and clinging (Simulium) orsmoot h enought o allow sucking (Anaylus) orth e sealing offo fth eventra l sideo fth ebod y (Elm-is larvae).Althoug h these relationshipswit h coarse substrates are inseparably connectedwit hhighe r current velocities,thes e species areno t foundo n fine substrateswit h similar (high) currents.Coars eminera l substrates are comparable tomacrophytes ,branche s orob ­ jectsa splasti cbags ,kettles ,bottles ,etc. ,whic hal lhav e incommo ntha tth e surface area islarg e andsmooth . Other species distinctly related to theparticl e size ofth e substrate are those that ingest theminera l substrate inorde rt o collect the attachedmicrobia l andalga lgrowth .Thi swa s demonstrated for severalOligochaet ab yJuge t (1979),wh o showeda positiv e correlationbetwee n the ingestedparticl e size,th epresenc e of theseparticl e sizes inth e substrate and thewidt h ofth e intestines.Thi sma yb e one ofth e reasonswh y the smallOligochaet a (mainlyTubificidae ) aremostl yrestric ­ ted toth e fine substrates,whil e the larger Eiseniella dwells incoarse r substrates (Appendices 9an d 12), since the former feeds ondetritu s andmu d (smaller than 0.13 mm (Juget,1979) )whil e the latter feeds onbacteri a and diatoms scraped from larger sandgrain s (0.3-1.3mm )o r filamentous algae (Ward, 1976). Ephemera danioa couldb e anexampl eo fsuc ha relationshi p aswell ,sinc e Ephemeridae areknow nt o ingest largeamount s ofinorgani c sediment,togethe rwit h theirmai n food source,fin e detritus and the associatedmicrobia l growthan d seston. Itwa s demonstrated that the distributiono f Ephemera danioa is linkedwit h thepresenc e of finedetritu s inth e substrate,an d theconclusio nmigh t followtha tth e factor foodwil lb e an important

154 selectionmechanis mfo rEphemera danioa. However,Erikse n (1963)demonstrate dfo r E.similans thatth etolerabl eamoun to ffin eminera lmateria l thatma yb epresen t is limitedbecaus eo fit sdetrimenta l effecto nth eoxyge nconten to fth eintersti ­ tialwater .Fo rE.simulons theoxyge nconten to fth einterstitia lwate rreache sth e criticalvalu eo f1.2 0mg/ 1whe n8-10 1o fth esubstrat e consistso ffin e sand (0.125-0.25ran).0 Unde rthes econdition s iti snecessar y thatth 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 snecessar yt oglu e largerparticle s togethert oobtai n a stabletunne l structure (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 d that Ephemera danioa needs substrateswit henoug h fineorgani c detritust ofee don ,bu tcoars e enoughi nminera lparticle-siz e compositiont 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 tnot-to omuc ht oclo gth egill so fth enymphs . Iti sver y likely thatothe rburrowin g speciesar erelate dt oth eparticle-siz e compositiono fth esubstrat ei na simila rmanner .Th eselectio no fparticula r sub­ stratesfo rpupatio nb ylas t instar larvaeo f M.sequax couldb ecause db yth efac t thatsubstrat e compositioni srelate dt ocurren tvelocit yan doxyge n supply. Pupae areunabl et omigrat et omor e suitableplace swhe ncondition s change.T osurviv ei t istherefor e obligatoryt oselec tsite swher e suchchange sar eleas t likely.Th e aggregationo fth epupa eo f Lithax obsaurus, Agapetus fusaipes and Fotamophylax luo- tuosus onstone san dbranche sprojectin g fromth estrea mbed ,ofte nnea rth ebanks , isprobabl yth eresul to fth esam ephenomenon . Other species showinga direc t relationshipwit hth eparticl e sizear ethos e thatus eth eminera lan dorgani cmateria lfo rcas ebuildin go rtub e formation.I t wasdemonstrate di ncas ebuildin g experiments that Seriaostoma personation uses mainly0.25-0.5 0m mgrain sfo rit scas ean dtha tth erang eo fmaterial s thatca nb e used liesbetwee n0.12 5m man d1. 0mm .Thi smean s that Seriaostoma personation will needa substrat eo fwhic ha considerabl e proportion fallswithi n thisgrai nsiz e range,althoug hi ti sno tknow nye twha tth eminimu mamoun t shouldbe .Furthermore , Seriaostoma personatum dwellspreferabl y incoars e substrates,whic hmean s thatth e case-buildingmateria lha st ob efoun damon gth esmalle r fractionsan dtha tth e substrate selectioni srelate dt osom eothe r factor,whic hi sprobabl yth epresenc e ofCoars eDetritus ,a sdemonstrate d before,an da moderat et ofas t current velocity. Thecaddi s larvae Lithax obsourus and Agapetus fusaipes bothprefe r gravelly substrates,wher ethe y liveo nto po fstone sor ,whe nth ecurren ti sver y strong, behindstones .The ybot hus eminera lmatte rt oconstruc t theircases . Agapetus fusaipes usesgrain-siz e fractions ranging from0.25-0.8 5m mi nth eF- 3instar ,bu t thisgraduall yshift st o0.5-0.8 5m man d1- 2m mfraction si nth eF- 1 instar,an d mainlyth e1- 2m mfractio ni nth efina l instaran dth epupa lcase .Comparin gth e

155 distribution of Agapetue fuseipes inth eRatumsebee kwit h theparticle-siz e selec­ tion forcas ebuilding ,i ti sclea rtha t selectiono f 1-2m mgrain s inth e final andpupa l stage isrelate d toth epresenc e ofthi s fraction inth eunderlyin g material.Substrate swit h amedia nparticl e size ranging from0. Sm m to 2m m are clearlypreferre d (M,= Î and 1,respectivel y ;Appendi x 13),togethe rwit hver y coarsesubstrate s (x5x,x4x) , forwhic hQ ,varie s around 0.5mm .Thi smean s that enoughsuitabl e grainswil lb epresen t forth e (largely)fina l instar larvaean d pupae onthi s substrate.Smalle r larvaeus e relativelymor e smallgrain s and they occurpredominantl yo nfine r substrates than larger larvae.A similar conclusion applies to Lithax obseurus (cf.Tabl e21) .

5.2. CURRENT VELOCITY

Since substrate andcurren t are two inseparably connected factors (Schmitz, 1961; Scherer,1965 )i t isver y difficult todistinguis hwhethe r the individual factors or theircombinatio ndetermin emacroinvertebrat epreferences ,althoug h the latter ismos tprobable .Th e current isresponsibl e for thevariatio n of thegrain-siz e compositionove rver y shortdistance s (mosaicpattern s and longitudinal substrate bands). The current influences,fo rexample ,th e oxygenconten t ofth e interstitial water,th eamoun to ftrappe ddetritus ,th enumbe r ofcrevice s andth e growtho f periphyton.Togethe rwit h the interactionsbetwee nvolum e of flowan d channeldimen ­ sions,th ecurren t isresponsibl e forth e zonation inth e substrate composition from headwate r todelt ao r fromsprin gt o confluence,whereb yth emedia nparticl e size andth ecoarsenes s of the detritus decrease (Behning, 1928;Beyer ,1932 ;Pennak , 1971; Cummins,1975) .Accordin g toUlfstran d (1968)th edirec t effecto fth e current onth e faunal distributionha softe nbee nover-estimated ,especiall y for animals living inrunnin gwate rbu t dwelling outo f the current,dependan t asthe yma yb e on oxygenan d foodsupply . The substrate compositiono fth e streambotto m isdetermine db y the interaction oferosio nan d sedimentation.Thi s principle isuse db yman y authors (e.g.Cummins , 1975)t odistinguis h threemai n zones instream s andrivers ,whic h are alsopresen t inlowlan d streams:erosiona l (riffleswit h coarse substrate andhig h current velocities),depositiona l (poolswit h finesubstrat e and lowcurren tvelocities )an d intermediate zones (withgravel-san d substrate andmoderat e current velocities). Although significant differences insubstrat e composition andcurren tvelocit y form themajo rdifference sbetwee nthes e zones,Cummin s (1966)stresse s that thefood - chainbase s are alsodifferent : inerosiona lhabitats , 'Aufwuchs'o rperiphyto n predominates asth emajo r food source,whil e indepositiona l habitats the input of detritus acts assuch .Al l thesefactor s are of influence onth e faunal composition ofthes e zones.Accordin g toCummin s (1975)eac h zone ischaracterize db y aspecifi c benthic fauna,whic h ingenera l ismor e or less restricted to itsenvironmen tb y morphological,physiologica l andethologica l adaptations (Hora,1936 ;Ambühl ,1959 ;

156 Pleskot,1961 ;Jaa g& Ambühl ,1963 ;Bournaud ,1963 ;Scherer ,1965 ;Cummins , 1972; Uhlmann, 1975). Threefauna lgroup sca nb edistinguished : - Faunao fth eerosiona lzone ,whic hca nattac hitsel ft oth esubstrat eb ysuckin g (Anayolus), clinging (Simulium) oravoi dth ecurren tb yflattenin g (Eeptagenid) or dwellingi ncrevice s (Gamnarus) orwhic hhav especiall y adaptedcase senablin gthe m towithstan dth ecurren t (Goeva) • - Sprawling,climbin g (Habrophlebia, Limnephilidae)o rburrowin g {Ephemera, Ptyohop- teva) faunao fth edepositiona l zone,ofte nwit ha mechanis mt oavoi d foulingo fth e respiratorysurface s (Caenis, Ephemera). Mud-chiroromidsar eals ofoun di nthi szone . - Faunaofte nmor eo rles srestricte dt oth eintermediat e zone,dwellin gi nmoderat e flowan dburrowin gi nsand-grave lsubstrate s (Ephemera, Mioropterna, Serioostoma). Themor ecomple xsubstrates ,compose do fvariou scombination so fth eorgani can d mineralcomponents ,for mth emajo rpar to fth estrea mbottom ,especiall yi nlowlan d streams,wher emos tsubstrat etype sar ecompose do fsan dcombine dwit hdetritus ; coarsesubstrate sar eneve rabundant . Inth eSnijdersveerbee kan dth eRatumsebee kmos tsubstrate ssample dwit hth e shovelwer esituate di na relativel ymoderat ecurren ti nth eintermediat eo rdeposi ­ tionalzone ,excep tfo rBar eGravel ,Bar eSan dan dlea fpack s againstobstacle si n thecurrent . Onlya fe wspecie swer e significantlyover-represente di nth etw ominera lsub ­ stratesdirectl yexpose dt oth ecurrent .Th especie s foundi nBar eGrave lwer eal l welladapte dt oliv ei nstronge rcurrent so nth esurfac eo fth esubstrat e (Baetis Verrais, L-ithax obsaurus, Agapetus fusoipes, Etmie aenealarvae , Rheotanytarsus spp.), burrowingi ni t {Mioropterna sequax, L-imnophilaspp . ,Sericostoma personation, Eiseniella tetraedra) orlivin gi nexistin gcrevice san dinterstitia l spaces (Amphinemura standfuse-i, Limniue volokmxri, Elmis aeneaadults) .Mos to fthes espe ­ ciesfee do nperiphyto nan ddetritus ,wit hit sassociate dmicrobia lgrowt h (scrapers orgrazers) .Onl y L-imnophila 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 texposur et oth ecurren tunles s theyposses s special adaptations (Hynes,1970a) . Habrophlebia fusaa needsa well-oxygenate dhabitat ,bu ti ti sa ver ypoo r swimmer.It spreferenc efo rlea fpack san dcoars edetritu san dlea faccumulation si s thereforeno tsurprising ,sinc ethes esubstrate softe naccumulat eagains to 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 dth ecurrent .Onl ywhe n G.pulex issmall ,ca ni tdwel li nth e intersticeso fcoars eminera lsubstrates . Current,i ncombinatio nwit hsubstrat eparticl e size,i sals oresponsibl efo r substratestabilit yan dma ythu sinfluenc especies 'microdistribution .I twa sdemon -

157 stratedb ysevera l authorstha t instable substratesar epoo r habitats (Petran, 1977), only inhabitedb yOligochaet aan dsom eChifonomida especies .I nth eRatumsebee kan d theSnijdersveerbee kth esam e conclusionwa s reached.I nshiftin g sand,onl yOligo ­ chaeta (mainlyTubificidae) ,Chironomida e [Polypedilum bveviantennatwn, Stiotoohiro- norrus, Prodiamesa olivacea), someothe rDipter a {Ptyahopteva, Palpomyia, Limnophila), Hydracarinaan dPisidivm showed over-representation,whil e onlyOligochaeta , StictochironomuSj Polypedilum breviantennatum and Pisidivm showedpreferenc efo r thissubstrate . Transporto ffin eminera lmateria l (siltan dsand )b yth ecurren t resultingi n scouringo fmor e stable substratesma yals ob eresponsibl efo rth eabsenc eo fspecie s fromsubstrate snormall ypreferred .O nman y occasions,especiall y afterperiod so f highdischarge , Agapetus fusoipes couldno tb efoun di nit susua lhabita to fCoars e Gravelo ro nstones ,bu twa si thidde nunde rth estone so ri nfine r substrates.Th e preferenceo f Simulivm forCoars eDetritu san dLeave sma yals ob elinke dt o the scouring effectso ftransporte d sando nth egrave l substrate,forcin gth elarva et o movet oplace swher eth ecurren ti sstron g enought oprovid e sufficient foodt othei r filtering cephalic fans,bu tslo wenoug ht ob efre eo fminera l particles.Thes e conditionsca nb efoun do nto po fdetritu s accumulationso rstone san dbranche s(o r plants),whic hprojec t intoth ewate r column,bu tar ehig henoug h aboveth estrea m bed itself.

5.3 FOOD CONDITIONS

Provideda wid e rangeo fothe r factorsi ssuitable ,th epresenc eo fdetritu sha s probablya stronge r influenceo nth emicrodistributio no fmos tmacroinvertebrate s thanan yothe rfactor .Althoug h fooda sa facto rwa sno tstudied ,mos ttax acoul db e relatedt oth esubstrate s theypreferre db ythei r foodpreference s andfeedin ghabits . Cummins (1972,1975 )develope da theor yabou tth erelationshi p between locomotion, feeding,growth ,respiratio nan dselectio no fphysical-chemica lparameter si ndeter ­ miningmacroinvertebrat edistributio nan dabundance .I nhi sflo w scheme Cummins (1975)distinguishe dmacro -an dmicro-movements .Macro-movement s include rapidmigra ­ tionan ddrif t inducedb ya sub-optima lphysical-chemica l environment.Animal s leave placeswher eth efactor s likecurrent ,substrate ,temperature ,oxyge nan dligh td o notmee t theirneeds .The y also leavewhe n food conditionsar eba do rcompetitio ni s too strong.Havin g foundth eoptima l combinationo fphysical-chemica l conditions, micro-movements leadt ohabita t selection.Thes emovement s startwit h orientation towards current directionan dturbulence ,whil eth eultimat e habitat selectioni s largely determinedb yth enature ,particl e sizean damoun to favailabl e food.Thi s theoryput smor eweigh to nth eimportanc eo ffoo dfo rth eultimat e selectiono fth e habitatwithi na give nsectio no fa strea m thati schose no nth ebasi so fothe r factors.However ,whe n sufficient foodo fa suitabl e compositiont osuppor ta populatio n isavailabl e ina strea m section,othe r factorswil l determineth edetaile dmicro -

158 distributionalpatter no fmacroinvertebrates .The nsubstrat eparticl e sizei s possiblyth emai nfactor . Comparisono fth emicrodistributiona l patternso fsevera lspecie si nth eRatumse - beekwit hthos ei nth eSnijdersveerbee k providesa nic e illustrationo fthi s theory. TheSnijdersveerbee k has small dimensionsan da larg e inputo fallochthonou s organic material thati sdistribute dove rth ewhol ewidt han dlengt ho fth estream .Thi s createsa situatio nwher efo rfin eo rcoars eparticl e detritivoresan dthei rpredators , sufficient foodo fsuitabl eparticl e sizeswil lb eavailabl e throughoutth estream . TheRatumsebeek ,however ,i slarger ,als owit ha larg e inputo fallochthonou s organic matter thati smainl ydistribute d alongth emargin so fth estrea mbe dbecaus eo fth e muchstronge rcurren tvelocities ,especiall y afterperiod so fheav y rainfall.Thi s restrictsth ebul ko fth eavailabl e detritust oth efine rsubstrate s alongth ebanks , accumulated againstobstacle si nth emiddl eo fth estreambed ,trappe di nth einter ­ sticeso fcoars e substrates,o rcovere dwit htransporte dminera lmaterial .Onl y after extendedperiod swit ha lo wdischarg ewer e accumulationso fleave san dcoars e detritus foundi nth emiddl eo fth estrea mbed ,i ndeepe rpools .I nCummins ' (1972) terminology thepool san dth emargin so fth estrea mar eth emacro-depositiona l zones,whil eth e accumulationsi nth ecurren t formth emicro-depositiona lpockets . Inth eSnijdersveerbeek ,th epracticall y overall favourable foodcondition smak e itpossibl efo rth emacroinvertebrate s toselec t theirhabita to nth ebasi so ffac ­ tors likesubstrat eparticl e size,curren tvelocity ,oxyge ncondition san dproximit y of substratesneede dfo rcas ebuilding .I nth eRatumsebee k foodcondition sar eles s favourable,a tleas ti nth emiddl eo fth estreambed ,forcin gth eanimal st ob econ ­ tentwit h lesspreferre dphysical-chemica lcondition s infavou ro favailabilit yo f food.Severa l exampleso fthi snegativ e influenceo fth eabsenc eo fsuitabl e foodo n themicrodistributio no fmacroinvertebrate s were already indicatedi nSubsectio n 4.2.2.Perhap sth ebes texample sar eforme db yth edifference si ndistributiona l patternso f Ephemera danioa, Mioropterna sequax and Serioostoma personation. The lattercaddis-fl y specieswa sno tfoun di nth eRatumsebee ka tall ,althoug hth e grain-size composition selectedb ythi s specieswa sabundantl ypresent..Apar t from macrodistributionalfactors ,on eo fth ereason sfo rit sabsenc ei nth eRatumsebee k couldver ywel lb eth eabsenc eo fth eprope r combinationo fsubstrat ean dfoo di nth e samehabitat . Ephemera danioa andMioropterna sequax show smallbu tdistinc t differencesi n micro-distributioni nth etw ostreams .I nth eRatumsebeek , M.sequax occursmainl yi n Detritus substrates,whil ei twa smor eo rles s evenly distributed over Sand+ Detri ­ tus,Bar eGrave lan dDetritu s (Sort2 ,Appendi x 3)i nth eSnijdersveerbeek . Eventhi s preferencefo rBar eGrave li nth eSnijdersveerbee k fitsth etheor y sinceth eanimal s inBar eGrave lar estil lwithi neas yreac ho fDetritu s substrateso rhav en ofurthe r needo ffoo d (pupae).I nth eRatumsebeek ,Bar eGrave l substrateswer e restrictedt o theerosiona l zonean donl yher ecoul dpupa eb efound ,whil e inth eSnij bth eBar e Gravelals ooccur si nth eintermediat e zonewher eth ecurren ti smoderate . E.danioa

159 occurredi nbot hstreams ,mainl yi nth eSan d+ Coars ean dFin eDetritu ssubstrates , buti tshowe da muc hnarrowe rdistributio nove rth estreambe di nth eRa bi nth efiel d classification. (Sort2 ,Appendi x 9). Inth egrain-siz e classifications (Tables3 7 and38 )th edifference si npreferre d substrate compositionwer e evenmor epronounced . Inth eSnijb ,th enymph soccurre di nequa ldensitie si nGrave lan dFin eSan dsub ­ strates,whil ethe ywer e restrictedt oCoars eSan dan dFin eSan di nth eRab . Fromthes edat ai tma yb econclude d thatespeciall yth especie s showingdiffer ­ encesi nmicrodistributiona lpattern sbetwee nth etw ostream s inhabitth einter ­ mediate zonewit hgravel-san d substratesan 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 y species,whil eth eintermediat e zonei s rarebecaus e coarsesubstrate sar emor e less restrictedt oth echanne lpar twher eth e maincurren ti spresent . Thedat aon th emicrodistributio no fth eindividua l speciesi nSubsectio n4.2. 2 clearlydemonstrat e thatspecies 'substrat epreference sar estrongl y linkedwit h their feedinghabit san dfoo dpreferences .Table s7 7an d7 8illustrat efo rbot h streamsth erelationshi pbetwee nfeedin gmechanis man dmajo r foodtyp efo rth efou r functionaltrophi cgroup s (Cummins,1973 )an dth edistributio nove rth esubstrat e typesdistinguishe di nSor t2 (Appendi x9) . Scrapersan dgrazers ,feedin g largelyon periphyto nan dfin eorgani cmatte rwit h itsassociate dmicroflora ,prefe rGrave lan dBar eSan dsubstrates .Thi s concerns,fo r example, Lithax obscurus andAgapetus fusoipes, dwellingon Grave lan dBar eSand , Hydrophilidae,Elminthida ean d Dryops spp.dwellin gon Gravel ,an d Pisidium, occur­ ringmainl yo nBar eSan dan d+ Fin eDetritus . Species feedingo ncoars eorgani cdetritu san dleave s (shredderso rcoars e particulatedetritivores )ar epredominantl y foundi nDetritu s substrateso rminera l substrates combinedwit hdetritus .However ,difference si nmicrodistributio nbetwee n thespecie s remainan dthes ear eprobabl yno tcause db ydifference s infoo dprefer ­ enceo rfeedin ghabi tbu tb yfactor s likesubstrat eparticl e sizean dcurren tvelocity . MostLimnephilida elarva e(e.g .Mioropterna sequax, Chaetopteryx villosa, Potamophy- lax luatuosus, Halesus radiatus and Glyphotaelius pelluoidus andals o Serioostoma personation prefer substrateswher e coarsedetritu si spresen ti nsufficien tamounts . S.personation prefers Sand+ Detritu ssubstrate sbu toccur si nCoars eDetritu ssub ­ strateswhe ni ti ssmal l (Table 24). Whenyoung ,bot h M.sequax and Ch.villosa preferLeaves ,bu tmov et ominera l substratescombine dwit hdetritu swhe n theyar e older (Tables2 8an d31) . H.radiatus and P.luatuosus and G.pelluoidus wereonl yfoun d insmal lnumbers ,bu tthe yar edistinctl yassociate dwit hDetritu s substrates,i nth e larvalstag ea tleast .Pupa eo f Potamophylax luatuosus wheremostl y foundo nth e undersideo flarg estones ,branche so rlogs .Thes epupa ehav ea cas eo fcoars esan d and finegravel ,whil eth elarva ehav ea lea fcas eu pt oth efina linstar ,whe n they

160 Table77 .I.R .value s forth etrophi cgroup s inth eSnijdersveerbee k inSor t2 .

Trophicgrou p Substrateclas s andsubstrat 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 11.1 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 Miaropseatra 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 indicatesignifican t over-representation

Table78 .I.R . valuesfo r thetrophi c groups inth eRatumsebee k inSor t2 .

Trophic group Substrateclas s and substrate type

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.pulex -20.5 -15.8 -1.1 -21.0 -1.0 -16.3 55.0 Shredders excluding and G.pulex -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 Collectorsexcludin g M. gr. praecox -16.0 -7.3 -6.9 2.3 -16.1 -8.7 38.2 Mioropseatra 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 indicatesignifican t over-representation startbuildin ga minera lcase ,probabl yfo rprotectio n inth epupa lstag eagains t predatorsan dshredders .Th e leafcas eo f P.luatuoeus isquit esimila rt otha to f G.pellucidus. Thesecases ,wit hthei rroun dpiece so fbeec h leaves forma 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 s feedingo nCoars eDetritu san dLeave s arepredominantl y foundi n thepur eDetritu s substrates,e.g .Tipulida e and Helodee larvae. Gammarus pulex is themos tabundan t shredder inbot hstream san dprefer sbot hpur eDetritu s substrates (largerspecimens )an dSan d+ Coars eDetritu s (smallerones ) (Table 54). Plecoptera nymphs [Nemoura cinerea and Amphinemura standfusei) preferDetritu ssubstrates , although A.standfuesi isals oover-represente do nBar eGravel ,wher e itprobabl y feedso nth eattache d finedetritu san ddiatom s (Dittmar,1955 ;Madsen ,1974) .Coars e Detritus feederssee mt oavoi d substrateswher e largeamount so fFin eDetritu sar e present,eve nwhe nCoars eDetritu si sabundant ,whic h isillustrate db y thestrongl y

161 negativeI Rvalue si nth eClasse s1 ,2 an d4 i nTabl e77 . Collectors,feedin go nfin eparticulat e organicdetritu s (fineparticl edetriti - vores)b yfilterin g (Simuliion spp., Rheotanytarsus spp.,man yOrthocladiina e species) ordeposi tfeedin g (Ephemera danioa, mostChironomin ian dTanytarsin i species)dwel l preferablyi nminera 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 d inSectio n5.2 . Simulium spp.an dRheotanytarsus spp.ar eknow nt ooccu rabundantl yo ngrave lsub ­ stratesu pt over yhig hcurren tvelocitie s (Hynes,1970a )and ,indeed ,smal lnumber s were foundi nbar eminera l substrates,bu t Simulium occurredpredominantl y inCoars e Detrituso rlea fpack s thatwer eofte nsituate di na goo dcurren tbu thighe rabov e thestreambed ,wher e therei smuc h less scouringb ytransporte d sand. Rheotanytarsus spp. preferredSan d+ Coars eDetritu s substratesbu twer e alsofoun do nBar e Gravel andi nCoars eDetritus . MostOrthocladiina e species (e.g. Eukiefferiella spp., Brillia spp., Corynoneura spp., Diploaladius oultviger, Rheooriootopua spp.prefe rCoars eDetritu so rLeaves , andth especie scompositio nfoun dhere ,correspond s quitewel lwit htha tgive nfo r vegetationb yLindegaar d (1972).Thes e species feedher eo nth etrappe d FineDetritu s andattache dalga lgrowth . Orthooladiua feedsstrictl yo ndiatom san di ti stherefor e not surprisingt ofin di tmainl yo ngravell y substrateswher e theydwel li ntube s attachedt oth eminera lsubstrat e (Lindegaard, 1972).Perhap s thisan dsimila r speciesshoul db ecalle d scraperso rgrazers . Prodiamesa olivaoea isa fre e livingOrthocladiina e speciesdwellin gpreferabl y inSan dwit hCoars ean dFin eDetritus ,th esam ehabita tpreferre db y Mioropseotra gr. praeoox, whichagree swit hth eobservation sb yMarlie r (1951)an dLindegaar d (1972).However , M.gr .praeoox showsa wide rdistributio ntha n Prodiamesa olivaoea sincei ti sals oabundantl ypresen ti npur eDetritu s substratesan dS+ED .Othe r Tanytarsinispecie s showquit edifferen t substratepreferences ,e.g . Cladotanytarsus forBar eSan dan dGrave l+ Detritus ,whil e Tanytarsus ourtioornis prefers Gravel+ Detritusbu ti sover-represente d inmos tothe rsubstrat e types exceptBar eSand . MostChironomin i larvaeprefe rth esubstrate s consistingo fa mixtur eo fSan d andDetritus ,althoug hsom especie sar eals oabundan ti npur e Detritus substrates {Polypedilum laetum, Phaenopseotra). Somespecie swer e evenfoun di nshiftin gsan d substrates (Stiotoohironomus, Polypedilum breviantennatwn, Paraoladopelma spp.), whichmigh t indicatetha tthes especie sca nals ofee do nth emicrobia l growtho nfin e mineral substrates,o rdiatom spossibl ypresen ti nthi shabitat . Epoioooladius flavens, achironomi dlivin gphoreticall yo n Ephemera danioa, feedso nth edetritu spassin gove rth emayfl ynymph swit hth eaxia lcurren t generated byth egil lmovements .I toccur si nth esam e substratea spreferre db y Ephemera danioa, whichfeed so nth esam ematerial ,namel ySan d+ Coars ean dFin eDetritus . Anothermayfl y feedingo nFin eDetritu si s Habrophlebia fusoa, whichwa sonl y found inth eRatumsebeek .Her ei toccurre dpredominantl y inLeave so rCoars eDetritu s+

162 Leaves,wher eFin eDetritu san dattache dmicrobia lan dalga lgrowt hi sabundant ,bu t whereth eleave soffe ra goo dprotectio nagains tth ecurrent . Baetia isa bette r swimmer,feedin go nth esam emateria lbu tdwellin go nBar eGrave lo rSand. +Detritu s inth eSnij ban di nlea fpack si nth eRab . Predatorsar emor eevenl ydistribute dove rth edifferen tsubstrat etype stha n anyothe rtrophi cgroup .The ypredominat ei nSan dwit hCoars ean dFin eDetritus , but areals oover-represente d inal lothe rsubstrat etype sexcep tfo rBar eSan dan dBar e Gravel.Withi nthi sgroup ,th edifference sbetwee nth eindividua l speciesar econsider ­ able. Pleatroonemia aonspevea prefersDetritu ssubstrates ,whil e Hycbopeyche angusti- pennis, theothe rne tspinnin g caddis,occur smainl y inGravel .The ybot hfee d onanimal s (largelyChironomidae )driftin gi no rswimmin g againstthei rcapturin g nets.O fth eTanypodinae , Maoropelopia nebulosa prefersSan dwit h FineDetritus ,San d withCoars ean dFin eDetritu san dGrave lwit hCoars eDetritus ,a distributio nsimila r totha to fApsectrotanypus tvifaseipennis. Conahapelopia melanopsprefer sDetritu s substratesan d Prooladins and Zawelimyia Sandwit hDetritu san dDetritus .Thes e preferencesclosel yagre ewit hth ehabita tdescriptio nan dspecie scombination s given byLindegaar d (1972). Otherpredaciou sDipter alarva e (e.g. Lvmophila, Dicranota, Palpomyia) are moreevenl ydistribute dove rSan dan dGrave l substrates,althoug hdifference sbetwee n thetw ostream sca nb eobserved .Detaile danalysi so fpredato rgu tcontent swoul db e necessaryt olin kpredato r densityan ddistributio nt opre ydistribution ,althoug h forsom epredator sa positiv erelationshi pbetwee npre ydensit yan dpredato rabundanc e wasdemonstrate d (e.g.fo r Pleotroanemùx aonspevea; Hildrew& Townsend , 1976). AlthoughTable s7 7an d7 8illustrat eth emai npreference so fth etrophi cgroups , theyd ono tgiv ean yinsigh ti nth ecommunit y structurewithi na substrat etype .T o thisend ,th erelativ eproportio no feac htrophi cgrou pwithi neac hsubstrat etyp e mustb econsidere d (Tables7 9an d80) . Theni tca nb esee ntha tscraper san dgrazer s

Table79 .Percentag eoccurrenc eo f thetrophi c groupswithi n thesubstrat e types inSor t 2i nth e Snijdersveerbeek.

Trophicgrou p Substrate class and substratetyp 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 Ganmarus pulex 29 17 47 13 13 11 24 22 Collectors excluding M.gr . pvaeoox 29 18 22 18 48 35 24 25 Mieropsectra gr. praecox 21 56 23 62 4 38 40 40 Unknown 1 + - - 1 + + + N= 100 % 3956 4129 55631087 7 3256 4825 177655037 1

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

163 Table80 .Percentag eoccurrenc e of thetrophi c groupswithi n thesubstrat etype s inSor t2 i nth eRaturasebeek .

Trophic group Substrate class and substral e type 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 Shredders excluding G.pulex and 2 1 16 2 3 1 6 5 N. cinerea Gammarus pulex 22 30 20 28 23 40 53 42 Nemoura cinerea 13 + 11 3 27 1 13 12 Collectors excluding M. gr. praecox 30 31 21 34 17 15 18 22 Miaropsectra gr.praecox 5 21 17 19 6 14 7 9 Unknown + + - 1 + + 1 + N = 100 % 2384 671 617 2993 2040 790 13989 23484

+ :les s than 0.5 % - :zer o

areonl ypresen ti nconsiderabl enumber si nBar e Sandan dGrave l substrates,whil e predators forma mor eo rles sconstan tproportio no fth epopulatio n (5-10°s)i nal l substrate typesexcep tDetritu s substrates,wher eth eextremel y highnumber so f G.pulex andM. gr. praecox resulti na lo wpercentag eoccurrenc eo fth epredators . Shreddersar edominate db y Gatrmarus inth eSnijdersveerbee kan d G.pulex and M.gr . praecox inth eRatumsebeek .Wit hth eexceptio no fthes e species,shredder sar e mostabundan ti nBar e Gravel (Amphinemura standfussi, Miaropterna sequax and Chaetop- teryx villosa, andDetritu ssubstrate s (Amphinemura standfussi, Chaetopteryx villosa and Helodes). Collectorspredominat ei nnumber si nal lsubstrat e types,whic hi s mainlycause db yth ehig hnumber so fChironomidae .Expresse di nbiomass ,thes e figures wouldprobabl yb emor ei nfavou ro fth eshredders ,which ar ei ngeneral ,muc hlarge r thanth ecollectors .Fro mTable s7 9an d80 ,whic h showth epercentag e occurrenceo f thefou rtrophi cgroups ,i ti sclea rtha tgrave lobviousl ypresent sth emos t favour­ ablecondition sfo ra heterogeneou s trophic structure,offerin g suitable foodcondi ­ tionst oal ldifferen ttrophi c levelso fth estrea mcommunity .I nthes etable sth e dominant specieshav ebee ntreate d separately,t oillustrat eth eproportio no fth e otherspecie si nth egroup so fth eshredder san dcollectors .

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 cmacr oinvertebrat e species occurring inth eSnijdersveerbee kar edistribute d unevenly overth evariou s substrate types, whichar ecompose do fminera lmatter ,organi cdetritu so ra combinatio no fboth .A specieswa sconsidere dt oprefe ra substrat e typewhe ni twa spresen ti nsignificantl y highernumber s thano no ri nothe r substrate types.O fth e8 4specie spresen twit ha totalnumbe ro f2 0specimen so rmore i non eo fth etw ostreams ,o rpresen ti nmor e than1 0samples ,4 2wer eover-represente di nonl yon eo fth eseve nsubstrat e types distinguished (Sort2 ,Appendi x 9). Nineteenpreferre d detritus substrates,1 3grave l (3Bare Gravel ,1 0Grave lmixe dwit hDetritus )an d1 0were mos t abundanti nsan d( 2 inBar eSand ,1 i nSan dwit hCoars eDetritu san d7 i nSan dwit hCoars ean dFin e Detritus).I ngeneral ,preference so fspecie sfo ra certai n substratetyp e observed inth eSnijdersveerbee kwer econfirme di nth eRatumsebeek .Som especie s showed small differencesi nsubstrat epreference s betweenth estreams ,bu tthes ecoul db eexplaine d onth ebasi so fdimensiona l differences betweenth estream s (Section5.3) . Substrateswer eclassifie d insevera l substrate typeso nth ebasi so ffiel d observations (Subsection 4.1.1),laborator y analysiso fth egrai nsize san dth e nature (andparticl esize )o fth eorgani c detritus (Subsection4.1.2.2) . 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 . These groupswere similari nbot hth efiel dan dlaborator y grain-size classifications.O na mor edetaile d level,th efiel d classificationdemon ­ stratedth eimportanc eo fth epresenc eo rabsenc eo ffin ean dcoars edetritu san d leavesi ncombinatio nwit hminera lsubstrates ,withi nthes emai nsubstrat e types,fo r themicrodistributio no fth emacroinvertebrates .Th eclassificatio no nth ebasi so f grain sizesdetermine di nth elaborator y emphasizedth erol eo fminera l particle-size compositiono nth emicrodistributio no fth emacroinvertebrates . Substrate compositioni sstrongl y relatedt ofoo dconditions ,curren tvelocit y andoxyge nconditions .Thes eparameter sar eclosel y relatedan dchange si nth e

165 physical environmentwil l influence them concurrently. Coarse substrates generally occur inplace swit hhighe r currentvelocities ,wher e oxygen saturation ishig han d the amountso ffin e organic detritus are low. Fine substrates occur togetherwit h low currentvelocities ,accumulation s of finean d coarse organic detritus andofte n less favourable oxygenconditions . Current velocity, oxygenconten t and the amount ofde ­ tritus are intermediatewher e substrates consisting ofa mixtur e of finean d coarse sediments are found. Leafpack s forma special habitatwher e oxygencontent ,curren tvelocit y and amounto f finedetritu sma yvar y considerably, depending onthei rpositio n inth e streambed . Ifaccumulate d against obstacles projecting from the streambe d (e.g. branches and stones), conditionswil lb e similar to those incoars eminera l sub­ strates; ifaccumulate dnea r thebank s oro n thebotto m ofpools , conditions willb e similar to those infin eminera l substrates. Because animalmicrodistribution s are strongly related to theminera l and organic composition of the substrate,th e substrate composition isa nexcellen t parameter to classify species habitats or community biotopes.Thi s principle has successfully been usedb yman y of the earlyworker s on stream ecology (e.g.Thienemann , 1912;Beyer , 1932; Geijskes,1935 ;Nietzke , 1937;Ber g et al., 1948;Marlier , 1951;Dittmar , 1955) andha sno t lost its importance since.

6.2 SUBSTRATE PATTERNS

Forman ymacroinvertebrat especie s dwelling in lowland streams,no t only the substrate,curren to r food conditionsprevailin g inthei r habitats arenecessar y for their existence,th eproximit y ofothe rhabitat s isals o essential.Th e heterogeneous environment ofnatura l lowland streams forms thebasi s for theheterogeneou s macro- invertebrate community.The y canoccu r inth e samebiotop ebecaus e ofth e spatial variation of environmental conditions. The characteristic lowland-streamcommunit y is formed by a largevariet y of specieswit hquit e different habitat preferences.Man y authors have demonstrated that themosai c substrate patterns,th e alternation of riffles andpool s and the occurrence oferosiona l anddepositiona l sites innatura l streams are themai nreason s for the existence of theheterogeneou s stream community (e.g. lilies, 1952;Schmitz ,1961 ; Cummins, 1966), becausemos t species occurring ina streamdwel l indistinctl y defined habitats,a sdemonstrate d inth eprecedin g chapters. Reice (1974)state d that sedimentparticl e size isprobabl y anorganizin g factor instream-communit y dynamics and that different community levelprocesse s canb e expected to increase their rates inproportio n to the spatial heterogeneity and stability of their environment. % Malmqviste t al. (1978)conclude d inthei r studyo f the influence of detritus on thedistributio no f thebottom-anima l communities that environmental heterogeneity and substrate stability areth e twomos t important variables influencing thecommuni -

166 ty. Detritus asa foo d sourcema yno tonl y influence the species composition but also thestructura lmodificatio no fth ebottom . Rabenian dMinshal l (1977)performe d experimentswit hartificia l substrates in poolsan driffles ,concludin g that themaximu manima l densities they foundwer e posi­ tively correlatedwit hth eamoun t oftrappe d coarse organic detritus.Thei rconclu ­ sionstha tdetritu s isth emos t important factor influencing themicrodistributio n of insects,an dtha t substrate structure and grainsiz edetermin e thedistributio n of thedetritus ,i s inagreemen twit hEgglishaw' s (1964, 1968, 1969). Theimportanc e oforgani c detritus forrunning-wate r communitiesha sbee 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 same time,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).Detritu s forms an integralpar to f the streambottom . Itma y coverth eminera l substrateo rvic eversa , orma yb emixe dwit h it.I nit svariou s stages ofdegradatio n from leaves to fine- detritusparticle s itfunction s as afoo d source aswel l asa nattachmen t site. It also forms an important componento fsubstrate s largely consisting ofminera lparticles . Itloosen sminera l substratepacking ,increase sporosit y and thus thepenetrability . Mineral substrates always formth ebas e fororgani cmatter .Mosse s growo n solid objects anddetritu s and leavesar edeposite d onth ebotto m and gettrappe 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).Roote d aquaticplant s canofte nb e regarded asa separate habitat,lik efloatin g ones,bu t there isofte na combinatio nwit h trapped detritus (Higler,1977 ;Mackey , 1976, 1977). Theconcurren tpresenc eo f severalnot-preferre d substrate types togetherwit h thepreferre d typema yb eessentia l for thesurviva l ofcertai n specieswhe ncondi ­ tionsar eunfavourabl e inthei rpreferre d habitat.Place swit h arelativel y lowcur ­ rentvelocit y andmor e stable substrates,e.g .behin d obstacleswher edetritu s can accumulate,for mrefuge s forman y species living inplace s thatbecom eunstabl e or offer too little fooda t timeso fhig hdischarge . Ephemera danica nymphsmov e from gravelly substrates inth emiddl eo f the streamt o sandwit h finedetritu snea r the banks andbehin dobstacle swhe nth ecurren tvelocit y increases inwinter ,whic h increases the instability ofth egrave l substrates and reduces theamoun to ffoo d (Subsection 4.2.2.6). Similarly, gravelly substrateswit hman y intersticeswil l form a refuge forman y species,protectin g themagains t thecurren tan d thus forming a reservoir fromwher eothe r substrates canb e stocked againwhe ncondition s improve (Mackay, 1969). Speciesma ynee d different substrate typesbecaus e theynee d othergrai n sizes ormaterial s tobuil d theircase stha nar epresen t inthei rpreferre d habitat (e.g.

167 manyTrichoptera ,suc ha s M.sequax, Ch.villosa, P.luctuosus). Pupaenee dplace swher e theywil lb eassure do fsuitabl eprotectio n againstpredator san do fcontinuin g good oxygenconditions .The y cannotdefen d themselvesno rchang e theirpositio n should conditionsdeteriorat e (e.g.M.sequax, Ch.villosa, L.obsourus, A.fusaipes). Mackay (1977)demonstrate dfo rPyonopsyahe soabripennis thatpupa e seemt ob eburrowe d only insubstrate swher ea considerabl e proportiono fgrave lo f4- 8m man d8-1 6m mi s present,whil eth elarva eprefe rorgani c substrates.Sh esuggeste d thatth eexten to f theseparticl e sizesavailabl efo raestivatio nan dpupatio nma yeve n limitth eabun ­ danceo fthi s species.Man yTrichopter a species normally dwelling inorgani c sub­ stratespupat ei nsite swher e theyca nattac h their casest osom esoli d object,suc h as logs,branches ,sticks ,cobbles ,bricks ,kettles ,e.g .Halesus radiatus, Glypho- taelius pelluaidus. Other species,normall y occurringi ngravell y substrates,bu t ofteni nplace s sheltered fromth edirec t forceo fth ecurrent ,mov et ostone so r branchéssituate di nmuc h stronger currentst opupat e (e.g. Lithax obsaurus, Agapetus fusoipes). Here theyca nb eassure do fa goo doxyge nsuppl ywhil eth echanc e ofbein g smotheredb ytransporte d sedimenti sminimal .Becaus epupa l casesar efirml y attachedt oth esubstrat e theyar eno tswep tawa yb ystron g currents.Larva ema y avoid these sitesbecaus e theywoul d havet oexpen dto omuc h energy justt owithstan d thecurren t (Bournaud, 1974). Somespecie s evenchang ethei r case-building material priort opupation ,whe n their larvalcase sconsis to forgani cmaterial ,probabl yt oobtai nbette r protection againstpredator san dshredders .Thi si sexpeciall ys owhe npupatio n takesplac ea t theen do fspring ,whe ndetritu s substrates become scarcer.Cummin s (1964)demonstra ­ tedthi sfo rPyonopsyahe lepida, andi nth eRatumsebee k Potamophylax luetuosus isa good exampleo fthi smateria lan dhabita t change.Bot h Misropterna eequax and Chaetoptevyx villosa demonstratea simila r changei nsubstrate s preferred during their development.Comparin g lifecycle ,substrat e preferences,foo dhabit san dcas e buildingo fthes etw olimnephili dcaddis-fl y species,onl yon econclusio nca nfollow : they showsimila r substrate,foo dan dhabita tpreferences ,an dthe ybuil d similar cases.But ,thei r comparabledevelopmen t stagesar eno tconcurrent ,whic hmean sthe y preferth esam ehabitat sa tdifferen t timeso fth eyear ,s ocompetitio nwil lb e minimal.Thes e species forma remarkabl e exampleo fspatia lan dtempora l ecological segregation.I nsumme ran dautumn ,whe n Ch.villosa hasreache d itsfina l instaran d isi na restin g stageo ri sa pupa ,juvenil e M.sequax larvaeappear .A tthi stim e Ch..villosa ispresen ti ngrave l substrates,whil e M.sequax dwellspredominantl yi n detritus.I nautum n some Ch.villosa larvaeca nals ob efoun d inCoars eDetritus . Untilth efirs twee ko fOctobe r this concerns larvae justbefor epupation ,whic hwer e probably consuming their lastmeal sbefor e closing their cases. M.sequax larvae occurring inCoars eDetritu si nautumn ,wer eonl y foundafte rth esecon dwee ko f October,whic hmean sth etw ospecie sar eseldo m found togetheri nth esam e substrate. Inwinte ran dspring ,whe n M.sequax larvaear efull y grown,the ymov et ominera l substratest obuil da minera l casean dburrow ,whil e feedingo nth ecoars e detritus

168 present inthes esite so r inth eproximity .A t the sametim ejuvenil e Ch.villosa larvaedwel lpredominantl y inthei rorgani ccase s inCoars eDetritu ssubstrates .Onl y insprin gan d summerd othe ymov et ominera l substratesan dbuil d (partly)minera l cases,bu tb ythe n M.sequax hasalread ypupate do remerged .Thes etw ospecie sfor ma pairtha tcoul db ecalle dth eEuropea nequivalen to fth especie s studiedb yCummin s (1964): Pyonopayahe lepida and P.guttiger. Thesetw o Pyanopeyahe species areals o spatially separateda ttime swhe nthe yoccu rtogethe ri na stream . P.lepida showsth e samechange sin case-buildin gmateria lan d substratepreferenc ea s M.sequax.

6.3 EFFECTO FREGULATIO N

Themai ngoa lbehin dth epresen tresearc hwa st odemonstrat e thatth e limitation ofman ybenthi cmacroinvertebrat e speciest onatura lo rsemi-natura l lowlandstream s (andth eabsenc eo fthes especie sfro mregulate d streams)i sstrongl yconnecte dt o thedifference s insubstrat ecompositio nan dheterogeneit ybetwee nnatura lan d regulatedstreams .I na stud yo nth emicrodistributio no fbenthi cmacroinvertebrates , theamoun to fmateria l thatha st ob e analysedma y soonbecom eto omuc ht odea lwit h inth etim eavailable .Therefor e itwa sno tpossibl et o includesom eregulate dstream s inth eresearch . However,give nth edistinc tsubstrat epreference sdemonstrate db ymos tspecie s andknowin gtha tman yo fth esubstrate s found innatura lstream sd ono toccu ro rar e muchles sabundan tin regulate dones ,th econclusio ni sobviou stha tth esubstrat e compositionma yb ea nimportan tparamete rresponsibl efo rth edifference s inbenthi c faunalcomposition .Th estrea mbotto mo fnatura llowlan dstream sconsist so fa larg e varietyo fsubstrates ,alternatin g inspac ean dtim ei nminera lparticle-siz ecom ­ positionan dth eamoun tan dnatur eo forgani cdetritu sunde rth e influenceo fcurren t velocityan dth efor mo fth estrea mbed .Th epresenc eo fthes emosai cpattern si s essentialfo rth eexistenc eo fth echaracteristi cmacroinvertebrat e community in lowlandstreams . Mostmacroinvertebrate s livingin thes e streamsoccu r incharacteristi chabitat s withinth estrea mbed ,wher econdition sconcernin gth eavailabilit yo fsuitabl efoo d substances,particl esiz eo fth eminera lsubstrate ,curren tvelocit y andoxyge n supplyar eoptimal .B yfa rth elarges tnumbe r isdetritivor eo rherbivore ,feedin go n theallochthonou sdetritu soriginatin gfro m thevegetatio no nth ebanks . Somespecie s canus eth e leavesalmos t immediatelyafte rthe yhav eentere dth estrea msystem , othersdepen do nmicrobia l activityt oconver tth eleave s intomor edigestibl e components (mostmacroinvertebrate s dono tposses s cellulase)o ro nth eactivit yo f othermacroinvertebrate s tobrea kdow nth eleave st osmalle rparticle s (faeces,fin e detritus,coars edetritus) ,ofte nver yric h inmicro-organisms . Theabundanc eo fth evariou sdegradatio nstage so fth eallochthonou sorgani c matter inth estrea mhabitat si sstrongl ycorrelate dwit hth ecurren tvelocit yan d

169 theminera l particle sizes. Current isresponsibl e forth e constant redistribution of the detritus over the streambe d andove r thevariou s substrate types. Coarse mineral substrates,ofte nsituate d inhighe r currents,wil l trapbot h fine and coarse detritus inth e interstices. Fineminera l substrates aremor e abundant when current velocities are lower,alon g thebank s and in front ofan d behind obstacles and ininne rbends . These areth eplace swher emos t of the coarse and finedetritu s accumulations canb e found.Whe n currentvelocitie s are lowthroughou t the stream, intim e of lowdischarge , the areawit h detritus accumulations can extend over thewhol e streambed , although this concernsmainl y the fine detritus,becaus e whole leaves orpart s ofthe m are lessabundan t inth e stream system inthes e periods (late spring, summer and early autumn). It is essential thatdetritu s canaccumulat e insheltere d places,becaus e it forms thebasi so f theheterotrophi c foodwe b of a lowland stream. Inthes e places thedetritu s canb ebroke ndown ,partl y to smaller particles,whic h are transported toothe rplaces ,an dpartl y digested.Withou t these accumulation sites the stream would soonb e swept cleano fdetritu s andbecom e devoid of itsmai n food source. Moreover,th e accumulationo fver y thick layers of finedetritu s (mud)i nwhic h anaerobic conditions would occurwithi n a short distance below the surface,a s often seen inregulate d streams,i sprevente d by the constant sequence of allochthonous input,accumulatio n in sheltered places,degradatio nb y fungi,micro-organisms , macroinvertebrates andmechanica l reduction of theparticl e sizeb y shredders and the interaction of current andminera l particles,an d the constant redistribution of the organicparticle sb y the current. Iti stherefor e essential thatpool s and riffles aremaintaine d in additiont o streammeanders . Bothmechanism s areuse db y the stream toexpen d itsenerg y and toredistribut e itsbotto mmateria l and transport itswast e downstream,wher e itca nb ebroke n down further indepositiona l habitatswit h their characteristic fauna (large,slo wriver s and lakes and ponds). Many of thedifference s inspecie s compositionbetwee nnatura l and regulated streams canb e explained on thebasi s of changed environmental conditions as aconse ­ quenceo f the enlarged dimensions and the discharge regimeo f the stream. These changes concern the formo f the streambed , thewate r depth,th e degree ofmeandering , the alternation of riffles andpools , the frequency of spates and droughts,th e light intensity reaching thewate r surface,th e current velocity, theminimu m andmaximu m water temperature and their fluctuations,th eparticle-siz e compositiono f the sub­ strate and the inputo fallochthonou s material.Minera l substrate composition of the streambottom , currentvelocit y and thenatur e andorigi no f the organic detritus are themajo rhabita t parameters that change.Erosiona l and intermediate zones disappear, togetherwit h theassociate d fauna.Lea fpack s and coarse (leaf)detritu s substrates areno tpresen t and of courseneithe r isth e faunaassociate dwit h these allochthonous organic substrates. Fineminera l substrates combinedwit h fineorgani c detritus form themos t abundant substrate inregulate d streams,togethe rwit h large fields of macrophytes. The fine detritus doesno toriginat e from thebreak-dow n of leafmateria l

170 fromallochthonou s sources,bu tfro mdecayin gmicrophyte s andmacrophyte sproduce d inth estrea m itself.Fluctuation s intemperatur e andoxyge nregim ear emuc hgreate r inregulate d streamsbecaus eo fth edirec texposur et oth esunligh t andth e resulting increase inprimar yproduction .Th eamount so ffin edetritu s accumulatingpe runi t areaar eals omuc h largerbecaus ecurren tvelocitie s arekep tlo wb yweir s atregula r distancesalon gth estream san db yth eextremel yhig hstorag ecapacitie so f (enlarged) streamchannels . Theregulate d sandcollecto r (Section 7)i nbetwee nth etw onatura l sections in theSnijdersveerbee k formsa nexampl eo fsuc hchanges .Thi s sectionrun sparalle lt o a roadan dha sfunctione d asa sandcollecto r for2 0years ,afte ra serie so fthre e smallpool sbetwee nSection s 4an d 7wer e filled in.However ,unti l 1976i t consisted ofa smal lstrea mchanne lwithi nth ewide r streambed ,wher e currentan d substrate resembled thato fSectio n6 ,excep tfo ra poo la tth edownstrea men do fSectio n7 thatwa sapproximatel y 20m longan d 3m wide .Th ewate r left this sectionthroug ha culvert.Unde rth ewate rwork s schemeo fth e landreclamatio nfo rAalten ,plan swer e madet oregulat eth eSnijdersveerbee k downstreamo fSectio n6 .O n thebasi so fth e occurrenceo fsevera lrar emacroinvertebrat especie s inthi sstrea man despeciall y in thedownstrea msection s itwa s agreedtha tthi spar to fth eplan swoul dno tb e carriedout .Sectio n8 i s inhabitedb y the largestnumbe ro f species ofal ldifferen t sections,som eo fth especie soccurrin gonl y inthi s section,e.g . Goeva pilosa, Atkripeodes oineveus, Hydropsyahe augustipennis (Tolkamp, 1975b).Mic ht oth esurpri ­ seo feveryone ,includin g localfarmers ,th esan dcollecto rwa s regulated anyway in thesumme ro f 1976.Withi ntw odays ,th etree swer e cut,th e trunksremoved ,an dth e sectionwidene d from3 t o 7m wit ha slop eo f1 :1 an dth ebottom-leve llowere d80 - 100cm .Th ewidt ho fth ewate r inth ebe d increased from5 0t o 165c 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 d flowthroug hth eculvert ,a situatio ntha toccurre d forth e firsttim ei nlat eDecember ,whic hmean stha tSectio n8 wa sdr y inthi speriod .Th e summero f 1976wa s extremelydry ,bu t inth efollowin gyear s the same situation occurred forshorte rperiods . The substrateo fth eregulate d sectionconsiste d ofa unifor mlaye ro ffin e sands (233,334 )mixe dwit ha larg eamoun to ffin edetritus .N omacrophyte s have grownther e since 1976an d thedetritu sprobabl ycam e fromth eupstrea msections . Occasionally somegrave lwa spresen t inSectio n8 ,bu talway scovere dwit h athic k layero fsan dan dfin edetritus . Thefaun apredominatin g inth eregulate d section isver ydifferen t fromth e other,natura lsection so fth estream .Appendi x 14compare s thespecie san dthei r numbersfoun d in5 shove l samples insan dan d gravel substrates and4 han d samples of leafpack s inSectio n6 ,wit h 2handne t samples inSectio n7 .I nth e regulated section, with itssand/mu dsubstrate ,onl ya fewspecie sar epresen t thatals ooccu r inth e upstream sections,whil ethei r abundances arequit edifferent .Heteropter a andOdonat a wereonl yfoun d insmal lnumber so rno t atal l inth eupstrea mo rdownstrea msections ,

171 norwer e themajorit y ofth eChironomida e species found inth e sand collector (cf. Appendix 9). Itca nb e concluded thatchangin g a stream into alon gnarro wpon d by regulationresult s inth edestructio no f the stream fauna and the settlement of a pond orditc hfauna .

172 Summary

A lowland streamca nb edistinguishe d fromothe r typeso f streamsb y itsstrong ­ lyvaryin gdischarge ,wate r level,curren tvelocity ,botto mcompositio nan dvegetatio n pattern.A largenumbe ro fbenthi cmacroinvertebrat e species arerestricte d tothi s typeo fenvironmen t andfor mth echaracteristi c animal communityo f thenatura l lowland stream. A largenumbe ro fphysica l factorsdirectl y influence thedistributio no fmacro - invertebrates overth evariou shabita ttype s thatca nb e found ina stream . Current velocity,substrat ecompositio nan d thenatur ean damoun to f foodar e themos t importantones . Chapter 1,th e introduction,deal swit h therelationshi pbetwee n these factors andthei r influenceo nth estrea mecosystem .A s astartin gpoin t for investigations intoth erol e thesubstrat eplay s inth edevelopmen t andpreservatio no fth emacro - invertebratecommunitie s innatural ,undisturbe d lowland streams,tw oclosel y related workinghypothese swer e formulated: - Manybenthi c lowland streammacroinvertebrat e species showdistinc tpreference s fora specifi c substratecomposition . - Forman y ofthes e speciesth esmall-scal e spatialvariatio n insubstrat ecomposi ­ tiono fth estrea mbe d isessentia l forthei rexistence . Theresearc hwa scarrie d out intw ounperturbe d lowland streams,th e Snijders­ veerbeekan dth eRatumsebeek .Thes etw o streams aredescribe d inChapte r2 . InChapte r 3,Sectio n 3.1 themetho duse d toclassif y substrates inth e field on visualcharacteristics ,th e selectiono fth esamplin g sites and themetho do f sampling substratean dmacroinvertebrate s atth e sametim ewit hth emicro-macrofaun a shovel aredescribed . InSectio n 3.2 adetaile ddescriptio n isgive no f theprocedure s car­ riedou t inth e laboratory: collectionan d identificationo f themacroinvertebrates ; particle-size analysiso fth e substrate;an ddeterminatio no fth enatur ean d amount oforgani cdetritus .Sectio n3. 3 treatsth emethod suse d inth e laboratoryt otes t theresult so fth efiel d study:performin g substrate selection experiments for several macroinvertebrate species ina laboratory streamchannel .Sectio n 3.4 dealswit hth e methodsuse dt o studyth ecolonizatio no fartificia l substrates inth e field. In Section3.5 ,th emethod suse d forstatistica l analysis of the collecteddat a are described. InChapte r 4,Sectio n 1th eresult so f the field studyar egiven .O n thebasi s ofth efiel d classificationo fth e substrates,eac hsampl e isclassifie d to asub ­ stratetyp echaracterize d by therati obetwee nth edominan tminera l (e.g.gravel ,

173 sand andorgani c (e.g.leaves ,coars e detritus,fin edetritus ) components. Four classification levels areused . Comparison ofthes e levels illustrates that iti s important tomak ea distinction betweenminera l andorgani c substrates,betwee n coarse and fineminera l substrates,betwee n coarse and fine organic substrates and between thevariou s combinations of these types (Fig.12) . Fromth eparticle-siz e analysis inth e laboratory of theminera l components of the samples,th e substrate characteristic (Q..M,Q,graph ) isdetermine d forbot h streams (Figs. 14an d 15). Several substrate types aredistinguishe d using the first, second (median)an d third quartile,o r their combination, inth eQ-|M,Q ,inde x (Appendices 4an d 5). Substrates consisting ofmor e than 10% (U ina parallel classification) organic detritus are distinguished as separate types: coarsedetritus , leaves and thecombinatio n ofthes etwo . Thepreferenc e of a species foron e ormor e substrate typeswa s indicated by the Indexo fRepresentation . Thismetho d gave satisfactory results andwa smor e convenient thanothe r statistical methods (Subsection 4.1.3.1). The importance ofth e jointus e ofth e two classification levels for the organic material is illustrated inSubsectio n 4.1.3.2. Itwa s demonstrated that ahig h abundance of a species {Ephemera danioa, amay ­ fly)ma y influence the totalmicrodistributiona lpatter n over thevariou s substrate types,becaus e juvenile animals aremor enumerou s thanolde r ones, although this does not influence the specific substrate preference asmeasure db y the Indexo f Represen­ tation (Subsection 4.1.3.3). Although only smalldifference s inth e totalnumbe r of species between the substrate types are found,th e differences are largerwhe n the specimens are considered pertaxonomi euni t (Tables 13an d 14;Subsectio n 4.1.6). Inal l substrate types, chironomidmidg e larvae are dominant interm s ofnumbe r of species andnumbe r of specimens.However ,ther ear e distinct differences between thevariou s sub-families. Substrate types consisting ofpurel yminera l material (bare sand,bar e gravel) are poorest inspecimens ,bu tno t in species. Bare gravel,fo r example,i sriches t in species,followe d by detritus substrates.Bar e gravel shows themos t evenly balanced distribution of thenumbe r of specimens over thevariou s taxonomieunits . InSubsectio n 4.1.4 clustering of the 14 substrate types (characterized by the (LMiQ,index )o nth ebasi s of the species composition and the relative abundance of eachspecie spe r substrate type demonstrates that the faunal composition differs strongly amongth e gravel substrates. It is also shown that there are differences between coarse sand,fin e sand,leave s and coarse detritus,an d thatwithi n these types thedifference s are lesspronounced . For themai n substrate types,onl y small differences are foundbetwee n thetw o streams (Figs. 17an d18) . InSubsectio n 4.1.5 the grouping of the species on thebasi s of their substrate preference(s)i sdescribed . The grouping isdon eusin g the field classification (Appendix 9)an dth e grain-size classification of the substrates (Appendices 12an d 13). Several species appear tohav e similar substrate preferences,makin g it

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 s of thefauna lgroups ,whic hmainl y showdistinc tpreference s forgravel ,san do r a combinationo fthes e twotypes . InSectio n4. 2 detailed datao n substratepreferenc e arepresente d for2 6tax a fromth evariou staxonomi eunit srepresentin g the species composing the faunal groups.Mechanism s leading to substrate selectionan d eventualdifference s insub ­ stratepreferenc ebetwee ndifferen tdevelopmen t stageso f anorganis mar ediscussed . Theresult so fth e analysiso fth e fielddat aar ecompare dwit hdat a fromth e literature and,fo ra restricte dnumbe ro f species,wit h the resultso fsubstrate - selectionexperiment s inth e laboratory andcolonizatio n experiments inth e field.I t isshow ntha t it isnecessar y tous e adetaile d substrate analysis forth e assessment of the substratepreference so f individualspecies . Theresult s forth e individual species arediscusse d inChapte r 5,emphasizin g therol eo fth emai nfactor s thatdetermin eth e substratepreference s (particlesize , currentvelocity ,an d food conditions). InChapte r 6,th econclusion s concerning theworkin ghypothese s formulated in Chapter 1ar ediscussed : - Mostbenthi cmacroinvertebrate s arerelate d tocertai n substrate types.Thre emai n groups canb e distinguished, composedo f specieswit hpreference s forcoars e mineral substrate (gravel),fin eminera l substrate (sand)an dorgani cmateria l (leaves or detritus),respectively .Th eparticl e sizeo fth eminera l componento fth e substrate aswel la sth enatur e and amounto fth eorgani cdetritu s influence themicrodistri ­ butiono fmos to fth e investigated species.Factor s related toth e substrate,suc ha s foodavailability ,oxygen -an d current conditions,ar eals oimportant . - Variousmacroinvertebrat especie snee d several substrate types atth e sametim eo r consecutively tob e ablet omaintai nthemselve s ina lowlan d stream.Change s infoo d supplyo r food selection,a swel l asalteration s incase-buildin gmateria l (for caddis flies)o r inth eproportio no f factorsrelate d toth e substrate,suc ha s currentvelocit y (forth emayfl y Ephemera decnioa) make thisnecessary . Ifa specie sprefer svariou s substrate types,thes epreference s dono toccu ra t thesam emomen t (seasonaldifferences )o ra tth e samedevelopmen t stage. Thealteratio n insubstrat e composition,change s inflo wregim ean d thechange d nature andorigi no fth e foodwe bbasis ,ar eth emos t important reasons forth e differences infauna lcompositio nbetwee n thecommunitie s ofnatura l and regulated lowlandstreams .Becaus ecurren tvelocit y directly affects the substrate composition, andstrea mhedgerow s aredirectl y related toth e structureo f the foodwe b inth e stream (leavesar eth ebasi c food), iti sessentia l thatno tonl y the hydrological consequences ofhydrologica l operations inth estrea m areconsidered ,bu tals oth e effectso nth estrea mecosystem . This implies thatth enatura l currentregim emus tb e maintained and thathedgerow s and forests along thebank smus tno tb e cleared tomak e wayfo r inspectionpaths .

175 Samenvatting

Laaglandbekenvorme nee nvoo rNederlan d karakteristiek beektype,gekenmerk t dooree n grotedynamie ki nafvoerfrequentie ,waterstand , stroomsnelheid,bodemsamenstellin ge n vegetatiepatroon.Vel ebenthisch e diersoorten,voornamelij k behorendto td emacro ­ fauna,kome n alleeno fbi jvoorkeu ri ndi tmilieutyp e voore nvorme n daarmeed eken ­ merkende dierlijke levensgemeenschapva nee nongestoord e laaglandbeek. Voord everspreidin gva nmacrofauna-organisme nove rd everschillend e habitat- typenwelk eme ni nee nbee kka naantreffe n (microdistributie) zijnee naanta l fysische milieufactorenva nbelang ,waarva nd estroomsnelhei dva nhe twater ,d esamenstellin g vanhe tsubstraa te nd eaar de nd ehoeveelhei dva nhe tvoedse ld ebelangrijkst e vormen. Ind einleidin gi nhoofdstu k 1word t ingegaano pd esamenhan g tussend efactore n end einvloe dva ndez e factoreno phe tbeekecosysteem . Hetdoe lva nhe tonderhavig e onderzoek ishe tverkrijge nva ninzich ti nd ero l died esamenstellin ge nd evariati eva nhe tsubstraa t spelenbi jhe tontstaa ne nin - stand-blijvenva nd evoo rongestoord e laaglandbeken karakteristieke macrofauna- levensgemeenschap.Di ti sverva ti ntwe e samenhangende hypotheses: - Veelbodembewonend e laaglandbeek-macrofaunasoortenvertone n duidelijke voorkeuren vooree nspecifiek e substraatsamenstelling. - Voorvee lva ndez e soorteni sd ekleinschalig e ruimtelijke variatie insubstraat ­ samenstellingva nd ebeekbode m essentieel voorhu n(voort)bestaan . Het onderzoekwer dverrich t intwe e ongestoorde laaglandbeken,d eSnijdersveer ­ beeke nd eRatumsebeek ,welk ebeschreve nworde ni nhoofdstu k2 . Paragraaf3. 1beschrijf td ewijz ewaaro p substrateni nhe tvel dwerde n gekarak­ teriseerd,d eselecti eva nd ebemonsteringsplaatse ne nd emethod eva ngelijktijdig e bemonsteringva nsubstraa te nmacrofaun ame td emicro-macrofauna-schoffel . Paragraaf3. 2gaa ti no pd everwerkin gva nd emonster s inhe tlaboratorium ,he t uitzoeken,conservere ne ndeterminere nva nd emacrofauna ,d ekorrelgrootteanalys eva n het substraate nd ebepalin gva nd ehoeveelhei d organische stofi niede rmonster . Inparagraa f3. 3zij nd emethodieke n beschrevenwaarme ed eresultate nva nd e veldinventarisatie inhe tlaboratoriu mwerde n getoetst doorhe tverrichte nva nsub - straatselectieexperimenteni nee nlaboratoriumstroomgoo tvoo r diverse macrofauna- soorten. Paragraaf3. 4geef td emethod e toegepast voord ebestuderin gva nd ekolonisati e vani nhe tvel d aangeboden substraten, zogenaamde kunstmatige substraten, terwijl paragraaf3. 5d ewiskundige verwerkingva nd everzameld e gegevensweergeeft .

176 Inparagraa f4. 1 wordend emethodisch e resultatenva nhe tveldonderzoe kbespro ­ ken.O pgron dva nd eveldclassificati eword t iedermonste r ingedeeldbi jee nsub ­ straattype,gekarakteriseer d doord everhoudin g tussend e inhe tvel d herkenbare dominantemineral e (bijvoorbeeld grind enzand )e norganisch e (bijvoorbeeld blad, grovedetritu se n fijnedetritus )componenten .Hierbi jworde nvie rclassificatie ­ niveausgebruikt ,welk edoo ronderling evergelijkin ghe tbelan g illustrerenva nhe t makenva nonderschei d tussenmineraa l enorganisc h substraat,tusse ngro fe n fijn mineraal substraat,tusse ngro fe nfij norganisc h substraate ntusse nd edivers e combinatiesva ndez e substraten (fig.12) . Opbasi sva nd ekorrelgrootteanalys e vand emineral edele nva nd emonster s isd e substraatkarakteristiek voord ebeid ebeke nopgestel d (fig. 14e n 15)e nworde ne r diverse substraattypenonderscheide nme tbehul pva nhe teerste ,tweed e (mediaan)e n derdekwartie lo fhu ncombinati e ind eQ.jM-|Q,-inde x (appendix4 e n 5), waarbijsub ­ stratenbestaand eui tmee rda n 10$ (11i nee nparallell e indeling)organisch e detritus alsapart etype sworde nonderscheide n ingrov edetritus ,bla d end ecombinati e van beide. Erword t aangetoond datd egekoze nmethod eo md evoorkeu rva nee norganism evoo r eeno fmee r substraattypent eherkenne ndoo rmidde lva nd e 'Indexo f Representation', goedvoldoe t invergelijkin gme tander e statistischemethode n (paragraaf 4.1.3.1). Hetbelan gva nhe tgebrui kva nd ebeid eclassificatie-grenze n voorhe t organisch materiaalwer dgeïllustreer d inparagraa f 4.1.3.2.Teven sword t aangetoondda thog e dichthedenva nee nsoor t {Ephsmewa danica, eenhaft )we lhe talgehel everspreidings ­ beeldove rd edivers e substraattypen kanbeïnvloede nomda t juvenielediere nveela l talrijker zijnda noudere ,maa r datd eme tbehul pva nd e 'Indexo fRepresentation ' aangetoonde specifiekevoorkeu rhierdoo rnie tword t gemaskeerd (paragraaf 4.1.3.3). Hoewel erte naanzie nva nhe ttotaa l aantal soorten slechtsgering e verschillen tussend e substraattypenwerde ngevonden ,blijke n ergroter everschille nwannee rd e aantallen soortene nindividue nnie tal stotaa lmaa rpe rtaxonomisch e eenheidworde n beschouwd (tabel 13e n 14,paragraa f 4.1.6).Hierbi jblijk t datchironomide n (mugge- larven)zowe lwa tbetref the taanta l soortenal she taanta l individuen inall esub ­ straattypendomineren ,waarbi j erechte rduidelijk everschille nbestaa n tussend e diverse subfamilies.Substraattype nbestaand eui tpuu rmineraa lmateriaa l (kaal zand, kaalgrind )zij nhe tarms taa n individuen,maa rnie t aansoorten .Kaa lgrin d is zelfs hetrijks taa nsoorten ,gevolg d doordetritussubstraten . Kaalgrin d isteven s het substraattype datd emees t evenwichtigeverdelin g vanhe taanta l individuenove rd e diversetaxonomisch e eenhedent e ziengeeft . Inparagraa f4.1. 4 wordtdoo rmidde lva nee nclusterin gva nd e 14doo rd e QIMJQJ indexgekarakteriseerd e substraattypeno pbasi sva nd esoortensamenstellin g end e talrijkheidva n iederesoor tpe r substraattype aangetoondda td e faunistische samen­ stellingva nd edivers e grindsubstratenonderlin g sterkverschilt .Teven skom tnaa r vorenda te rverschille n zijn infaunistisch e samenstelling tussengro f zand,

177 blad engrove-detritussubstrate n maar datbinne ndez e substraattypend e verschillen minder groot zijn.Tusse n debeid ebeke nwerde n slechts geringeverschille n ind e hoofdtypengrind , zand endetritu s gevonden (fig. 17e n18) . Inparagraa f 4.1.Sword td e groepering vand e soorteno pbasi s vanhu n substraat­ voorkeurbeschreven .Dez ewer d zoweluitgevoer d opbasi s vand e veldclassificatie (appendix 9)al so pbasi sva n dekorrelgrootteclassificati e van de substraten (appen­ dix 12e n13) . Diverse soortenblijke ndezelfd e substraatvoorkeur(en)t ehebben ,zoda the tmo ­ gelijk iso m faunistische groepen teonderscheiden ,el kme t eenbepaald e substraat­ voorkeur.E rkom tnaa r vorenda tee n gedetailleerde substraatanalyse niet terug te vinden is ind evoorkeure nva n de groepen soorten,di eveela l reageren ophe tonder ­ scheid grind, zand,detritu s ofee ncombinati eva n dezehoofdtypen . Paragraaf 4.2 behandeldvoo r 26soorten ,vertegenwoordiger s van genoemde faunis­ tische groepen,verdeel d over dedivers e taxonomische eenheden,d e gedetailleerde substraatvoorkeuren,waarbi j ingegaanword t op demechanisme n die leiden totsub ­ straatselectie eneventuel everschille n invoorkeu r onder invloed vanhe tontwikke ­ lingsstadiumva nhe t organisme.D e resultatenva n deanalys e vand e veldgegevens wordenvergeleke nme t de literatuurgegevens en,voo r eenbeperk t aantal soorten,me t deresultate nva n laboratoriumexperimenten enkolonisatieexperimente n met kunstmatig substraat inhe tveld . Erblijk tda t hetvoo r devaststellin g van de substraatvoor­ keurva n individuele soortenwe lbelangrij k iso m een zo gedetailleerd mogelijke sub­ straatanalyse tehanteren . Paragraaf 4.4 geeft eenoverzich tva n debelangrijkst e resultatenva nd eveld - experimenten. Inhoofdstu k 5volg t de geïntegreerde discussieva nd e hiervoor gepresenteerde resultatenvoo r de individuele soorten,waarbi j denadru kword t gelegdo pd ehoofd ­ factorendi ed e substraatpreferentie bepalen,namelij k korrelgrootte, stroomsnelheid envoedsel . Inhoofdstu k 6worde nd e conclusies gegeven aand ehan d van de eerder gestelde hypotheses:

1. Demeest ebodembewonend emacrofaunaorganisme n zijn gerelateerd aanbepaald e sub­ straattypen.Dri ehoofdgroepe n kunnenworde nonderscheiden ,bestaand eui t soortenme t eenvoorkeu rvoo r respectievelijk grofmineraa l substraat (grind), fijnmateriaa l substraat (zand)e norganisc h substraat (blado f detritus). Zowel de korrelgrootte van demineral e componentva nhe t substraat alsd e aard end ehoeveelhei d vanhe t organischmateriaa l beïnvloeden demicrodistributi e van demeest eonderzocht eorganis ­ men.Hierbi j spelen tevensme t het substraat gerelateerde omstandigheden zoals voedselaanbod, zuurstofgehalte en stroomsnelheid eenrol . 2. Diverse soortenmacrofaun a hebbenmee r substraten tegelijkertijd of in successie nodigo m zicht ekunne nhandhave n inee n laaglandbeek. Hierbij spelen zowelwijzi ­ gingen inhe tvoedselaanbo d ofd evoedselkeuz e eenrol ,al swisselinge n inhe t

178 materiaalgebruik tvoo rhuisjesbou w (bijkokerjuffers )o fgewijzigde ,aa nhe t substraat gerelateerdefactore nal sd estroomsnelhei d (bijvoorbeeldvoo rd ehaf t Ephemera danioa). Wanneeree nsoor tmee rsubstrate nprefereert ,blijk tn a gedetailleerdeanalys e 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 t lichtva nd everschille ni nfaunistisch e samenstellingva nd elevensgemeenschappe nva nnatuurlijk ee ngereguleerd elaagland ­ bekenleid tto td econclusi eda td ewijziginge ni nsubstraatsamenstellin gtesame nme 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 .Ctoda t de stroomsnelheiddirec tva ninvloe d iso pd esubstraatsamenstelling ,terwij lbeek - begeleidendehoutopstande ndirec tgerelateer d zijnme td eopbou wva nhe tvoedselnet - werk ind ebee k (blad isbasisvoedsel) ,i she tva nwezenlij kbelan gda te rbi jd e planningva nhydrologisch eingrepe ni nhe tbeekecosystee mnie tallee nme td ehydro ­ logischeconsequentie sword tgerekend ,maa roo kme td ehydrobiologische ,hetgee nim ­ pliceertda the tnatuurlij kstromingsregie mmoe tworde ngehandhaafd ,terwij ld e beekbegeleidendebosse ne nhoutwalle nnie tmoete nwijke nvoo rschouwpaden .

179 Appendices

Appendix 1.Macroinvertebrat e species and taxa found inth eSnijdersveerbee k and theRatumsebeek . 0 :taxo nno tconsidere d forcalculatio no fnumbe r ofspecie s 00 :taxo nno t considered assuch ; identificationuncertain ; perhapsno taquatic . 4 3 :taxo n3 i spar to f theoverlappin g taxon4 ,althoug h itma yb ea wel l defined species.Taxo n 3i salway s considered asbein g included inth e overlapping taxon4 . Nomenclature followsth ekey suse d foridentificatio n (see Identification References).Whe nonl y agenu snam e isstated , itma yconcer nmor etha non e species (spp.). unless all specimens areexpecte d tobelon g toon especies , but thespecie snam e isunknow n (sp.). Numeral taxacode s areuniqu e forthi sresearc h andwer euse d forcompute r analysiso f thedata .

Tricladida: 4 3 Polycelis tenuis (Ijima) 4 Polyoelis Ehrbg. spp. Dendrocoelum laatewn (Müller) Oligochaeta: 11 Oligochaeta spp. 11 12 Tubificidae spp. 11 13 Naididae spp. 11 14 Lumbriculidaespp . 18 Eiseniella tetraedra (Savigny) 19 Stylaria laeustris (L.) Hirudinea: 21 Erpobdella ootooulata (L.) 22 Erpobdella testaoea (Savigny) 23 Glossiphonia eomplanata (L.) 25 Helobdella stagnalis (L.) 28 Theromyzon tessulatum (Müller) Malacostraça:Crustacea: 32 Garrmarus pulex (L.) 33 Gammarus roeselii (Gervais) 35 Asellus aquatious (L.) 36 Asellus meridianus Racovitza Hydracarina: 38 Hydracarinaspp . Araneae: 39 Argyroneta aquatica (Clerck) Plecoptera: 40 Amphinemura standfussi Ris 42 Nemoicra cinerea (Retzius) Ephemeroptera: 47 Ephemera daniea Müller) 48 Habrophlebia fusoa (Curtis) 49 Centroptilum luteolwn (Müller) 52 50 Baetis vernus Curtis 52 51 Baetis mutious (L.) 52 Baetis Leach,spp . 53 Paraleptophlebia submarginata (Stephens)

181 56 Caenis horaria (L.) 57 Caen-is robusta Eaton Odonata: 59 Zygoptera spp. 61 Aeshna mixta Latreille 63 Somatoahlova aratioa Zetterstedt 74 Ceriagrion tenellum (Villers) Hemiptera: 0 75 Corixinae larvae spp. 76 Velia caprai Tamaninl 77 Notoneota glauca L. 81 Notoneota viridis Delcourt 83 Gewis gibbifer Schummel 84 Sigara striata (L.) 85 Sigava falleni (Fieber) 86 Sigara distinota (Fieber) 87 Sigara lateralis (Leach) 88 Sigara semistriata (Fieber) 93 Hesperocorixa sahlbergi (Fieber) 96 Nepa rubra (L.) 97 Bydrometra stagnorum (L.) 98 Gerris najas (De Geer) Trichoptera: 99 Hydropsyohe angustipennis (Curtis) 100 Plectrocnemia oonspersa (Curtis) 101 Lype reduata (Hagen) 103 Agapetus fusoipes Curtis 105 Lithax obsourus (Hagen) 107 Goera pilosa (Fabricius) 109 Serioostoma personation (Spence) 0 112 Halesus Stephens spp. 113 Halesus digitatus (Schrank) 114 Halesus tesselatus (Rambur) 116 Lirnnephilus auricula Curtis 117 Halesus radiatus interpunotatus (Zetterstedt) 118 Potamophylax rotundipennis (Brauer) 122 Potamophylax luotuosus (Piller &Mitterpacher ) 0 125 Potamophylacini spp. 126 Enoicyla pusilla (Burmeister) 127 Chaetopteryx villosa (Fabricius) 128 Miaropterna sequax MacLachlan 130 Hydatophylax infumatus (MacLachlan) 131 Lirnnephilus sparsus Curtis 132 Lirnnephilus extrioatus MacLachlan 133 Anabolia nervosa Curtis 134 Glyphotaelius pellucidus (Retzius) 135 Lirnnephilus lunatus Curtis 136 Lirnnephilus rhombicus (L.) 0 142 Limnephilidae spp. 143 Bereodes minutus (L.) 0 144 Leptoceridae spp. 145 Mystaoides longicornis (L.) 146 Athripsodes ainereus (Curtis) 147 Athripsodes aterrimus (Stephens) 148 Athripsodes bilineatus (L.) 149 Molanna angustata Curtis Megaloptera: 0 152 Sialis Latreille spp. 153 Sialis lutaria (L.) 154 Sialis fuliginosa Pictet Coleoptera: 150 Coelostoma Brul spp.

182 151 Agàbus paludosus (Fabriclus) 155 Agdbus Leach larvae spp. 157 Agàbus bipustulatus (L.) 158 Platambus maaulatus (L.) 160 Ilybius Er. larvae spp. 163 Noterus Clairville spp. 165 Laccophilu8 Leach spp. 168 Hydroporus Clairville spp. 169 Colymbetus fusaus (L.) 170 Stiototarsus duodeaimpustulatus Fabriclus 172 Haliplus Latreille spp. 173 Hydrophilidae spp 174 Helophorus aquatious L. 175 Helophorus Leachspp . 176 Limnebius Leachspp . 178 Hydrophilidaespp .larva e 179 Anacaena limbata (Fabriclus) 180 Anacaena globulus (Paykull) 181 Laooobius Erchs.spp . 181 182 Laooobius sinuatus Motsch/ striatulus (Fabriclus) 183 Gyrinus substriatus Stephens 184 Dryops01 .spp . 185 Elmis aenea (Müller) 186 Limnius volakmari (Panzer) 187 Oulimnius tuberoülatus (Müller) 189 Oohthebius Leach. spp. 190 Helodes minuta L. larvae 191 Chaetharthria seminulum Herbst 192 Megastemum boletophagum Mrsh. Diptera: 193 Tipula L. spp. 193 194 Tipula gr. lunata sensuTheowalt,195 7 193 195 Tipula gr. pruinosa sensuTheowalt,195 7 193 196 lamatotipula Matsumuraspp . 198 197 Limnophila Marquartsp .a 198 Limnophila Marquartsp p 198 199 Limnophila gr. fusoipennis sensuTolkamp ,197 6 200 Pedioia Latreille 202 Gnophomyiasubg . Leiponeura sensuHennig ,196 8 203 GnophomyiaOsten-Sacke nspp . 204 Elephantomyia Osten-Sackenspp . 205 Dioranota Zetterstedt 198 208 Limnophila Marquartsp .b 210 Anopheles Meigenspp . 215 214 DixaMeiße nspp . 215 Dixagr . maoulata sensuDisney,197 5 216 Bezzia Klefferspp . 217 Palpomyia Megerlespp . 218 Palpomyia tibialis Meigen 219 Simulium erythrooephalum DeGee r 220 Simulium latipes Meigen 221 Simulium aureum Fries 222 Simulium gr. ornatum Meigen 0 223 Simulium Latreillespp . 224 Simulium brevioaule Dorier& Grenie r 225 Psyohoda Latreillespp . 225 226 Periooma Walkerspp . 0 227 Simulium naturale Davies 231 Beris Latreillespp . 232 Dixella Dyer& Shanno nspp . 233 Tabanus L.spp . 234 HaematopodaMeige nspp .

183 236 Aphrosylus Walker spp. 238 Bibionidaespp . 239 Hemerodromia Meigen spp. 240 Ephydridae spp. 241 Ptyohoptera Meigen 242 Tetanoceridaespp . 243 Osmylus fulvioephalus (Scopoli) (Neuroptera) 244 Macropelopia Thienemannspp . 244 245 Maoropelopia nebulosa (Meigen) 248 Apsectrotanypus trifasoipennis (Zetterstedt) 249 Proaladius Skusespp . 250 Teichomyza Marquet spp. (Ephydridae) 251 Hydraena excisa (Coleoptera) 00 252 Coleoptera larvae spp. 253 cf.Conohapelopia sensuMolle rPillot , 1978 253 254 Conohapelopia melanops (Wiedemann) 256 Zavrelimyia Fittkauspp . 258 Metrioonemus van derWul p spp. 260 Clinotanypus nervosus (Meigen) .0 263 Orthocladiinae spp. (juv.) 0 264 Chironomini spp. (juv.) 265 Criootopus (Criootopue) van derWul p 266 Criootopus bioinotus (Meigen) 268 Orthooladius van derWul p spp. 269 Corynoneura Winnertzspp . 270 Thienemanniella Kiefferspp . 271 Prodiamesa olivaoea (Meigen) 272 Brillia modesta (Meigen) 273 Odontomesa fulva (Kieffer) 274 Brillia longifuroa Kieffer 275 Diplooladius oultriger Kieffer 276 Nanooladius Kieffer 277 Rheooriaotopus Thienemann 278 Pseotrooladius Kiefferspp . 279 Eukiefferiella gr. disooloripes sensuMolle rPillo t 1980 280 Chaetooladius Kiefferspp . 281 Eukiefferiella brevioalcar (Kieffer) 282 Eukiefferiella olaripennis (Lundbeck) 283 Epoioooladius flavens (Malloch) 285 Limnophyes Eatonspp . 0 286 Tanytarsini spp 287 Mioropseotra gr. praecox sensuTshernowski j 288 Tanytarsus ourtioornis (cf.Mothers ) 289 Mioropseotra gr. trivialis sensuTshernowski j 290 Tanytarsus vande rWul p spp. 291 Stempellina Bausespp . 292 Cladotanytarsus Kiefferspp . 293 Rheotanytarsus Bausespp . 294 Paratanytarsus Bausespp . 296 Chironomus Meige nspp . 297 Glyptotendipes Kiefferspp . 298 Diorotendipes gr. notatus sensuMolle rPillot , 1979 0 299 Paracladopelma Harnisch spp. 300 Cryptoohironomus Kieffer spp. 301 Paracladopelma camptolabis agg.sens uMolle r Pillot, 1979 302 Paratendipes Kiefferspp . 303 Miorotendipes gr. ohloris sensuMolle rPillot,197 9 306 Phaenopseotra Kiefferspp . 307 Paracladopelma laminata agg.sens uMolle rPillot,197 9 308 Stictochironomus Kieffer 310 Polypedilum laetum agg. sensu Moller Pillot, 1979 311 Polypedilum breviantennatvm Tsl^rnowskij

184 312 Polypedilum gr. nubeculosum sensu Tshernowskij 312 313 Polypedilum gr. oonviotum sensu Tshernowskij 314 Hydrobaenus pilipes (Malloch) 277 315 Rheoorieotopus ct.dorieri sensu Pankratova, 1970 0 317 Dlptera pupae spp. 0 318 Chironomini pupae spp. 0 319 Orthocladiinae pupae spp. Mollusca 321 Planorbarius oovneus (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 Physa fontinalis (L.) 340 Anaylus fluviatilis Müller 341 Pi8-idiwn C.Pfei f fer spp. 342 Sphaerium Scopol! spp. Various: 343 Sisyra Burmeister spp. (Neuroptera) 344 Lepidoptera spp. 345 Hyàrobius fusoipes L. (Coleoptera) 346 Unknown Orthocladiinae larva (Diptera) 198 351 Limnobiidae spp. (Diptera) 00 352 Coleoptera spp. 354 Helooharu8 lividue Forst. (Coleoptera) 277 355 Rheocricotopu8 gr. fusoipes sensu Thienemann, 1944 (Diptera) 0 356 Diptera spp. 0 357 Pupae ofunknow norde r 0 358 Tanytarsini pupae spp. (Diptera) 184 359 Dryaps luridus Er.(Coleoptera ) 0 360 Ironoquia dubia (Stephens)exuviu m (Trichoptera) Pisces: 361 Gasterosteus aauleatus (L.) 362 Pungitius pungitius (L.) 363 Noemzoheilus barbatulus (L.) Cyclostomata: 364 Lampetra planeri (Bloch)

185 Appendix2 .Numbe ro f samples ineac hsubstrat e class inth efiel dclassificatio n of thesubstrate s inth eSnijdersveerbeek .

Sort Sand Gravel Detritus

3 202 117 63 1 1 i 1 1 1 1 4 116 86 80 37 63 1 I 1 1 1 1 1 1 1 2 87 29 33 53 80 37 63 1 1 1 1 1 1 1 | 1 1 1 1 1 1 ""1 1 53 34 29 8 22 3 42 11 80 9 28 18 34 11

St Sh FD L CD CD+L CD L B L CD CD L CD +FD FD L

Appendix3 .Numbe ro f samples ineac hsubstrat eclas si nth efiel dclassificatio n of thesubstrate s inth eRatumsebeek .

Sort Sand Gravel Det ritus

3 107 41 47 1 1 1 1 1 1 1 4 62 45 31 10 47 I 1 1 r 1 1 1 2 49 13 9 36 31 10 47 1 1 1 1 1 1 1 1 1 1 1 r 1 1 1| 1 1 29 20 13 1 8 3 29 4 31 l 9 5 38 4

St Sh FD L CD CD+L CD L+FD B L CD CD L CD+L +FD +FD

Appendix4 .Numbe ro fsample s ineac hsubstrat eclas s inth egrain-siz e classificationo f thesubstrate s inth eSnijdersveerbee k (N= 382) .

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

Sort 5,1% 1 9 59 47 12 13 20 35 38 6 - 81 47 14 Sort 5,10% 1 11 62 52 13 14 24 39 76 16 - 26 35 13 Sort 6,1% 1 - 9 27 25 24 22 25 82 25 - 81 47 14 Sort 6,10% 1 1 11 28 26 25 23 26 101 66 - 26 35 13 Sort 7,1% - 1 2 4 1 4 6 32 73 113 4 81 47 14 Sort 7,10% - 1 5 4 1 4 6 32 77 169 9 26 35 13

XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L QlMdQ3 index x4x Sort 8,1% 10 29 23 24 22 22 31 35 21 17 6 81 47 14 Sort 8,10% 11 32 24 25 23 23 3D 39 31 45 16 26 35 13

186 Appendix 5.Numbe ro f samples ineac hsubstrat eclas s inth egrain-siz e classificationo f thesubstrate s inth eRatumsebee k (N- 195) .

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

Sort 5.1% 1 2 14 25 25 9 2 7 29 1 - 32 42 6 Sort 5,10% 1 2 14 26 28 12 2 12 46 5 - 5 38 4 Sort 6,1% - - 1 4 4 17 14 17 54 4 - 32 42 6 Sort 6,10% - - 1 4 4 18 14 19 67 21 - 5 38 4 Sort 7,1% ------1 5 67 41 1 32 42 6 Sort7,10 % ------1 5 74 63 5 5 38 4 inde x XXX x5x x3x x2x xlx xlx XXX lxx 22x 23x 33x CD L CD+L Ws x4x Sort 8,1% 1 4 4 17 14 17 21 7 26 3 1 32 42 6 Sort 8,10% 1 4 4 18 14 19 25 12 33 13 5 5 38 4

Appendix 6.Numbe r of samples shifting fromorgani c substrates tominera l substrateswhe nchangin g thelimi t from 1% t o1 0% organi cmatter . 'Shifted'sample s shownpe r phi index (class)fo rQ (Sort 5),M (Sort6 ) andQ 3 (Sort7) .

CD L CD+L phi index

Snijb 6543211234

1% 81 47 14 10% 26 35 13 2351144 381 0 - Shift 55 12 1211111 19 41- - 3 15 6 5

Rab

1% 32 42 6 10% 5 38 4 -133-5 17 4- ---1-2 13 17- Shift 27 4 2 722 4

187 Appendix7 .Numbe r ofspecimen so f Ephemera daniaa inhig h density samples inth e Ratumsebeek for5 lengt h classes inSor t2 .

Sample Year Week Numbero f Sort2 Body length/mm no. specimens class 0-5 5-10 10-15 15-20 >2 0

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

Appendix8 .Numbe ro f specimenso f Ephemera daniaa inhig hdensit y samples inth e Snijdersveerbeek for 5lengt hclasse s inSor t2 .

Sample Year Week Numbero f Sort2 Body length/mm no. specimens class 0-5 5-10 10 15-20 >2 0

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

Ratumsebeek Taxa Taxa name Snijdersveerbeek

Substrate class Substrate class 2 3 4 5 2 5 S+FD S+D S+D+FD BG S+FD S+D S+D+FD BG I. 18 Eiaeniella 80 ------99 Hydropayche 11 103 Agapetus 8 47 211 4.S -3.2 -1.8 -5.9 5.3 10.7 -6.6 105 Lithax 150 55 218 -0.5 -3.8 -3.2 -6.0 8.4 3.5 0.8 107 Goera 11 146 Athripsodee 2 10- 2-2 0.-2 1.-3 -1.-0 -2.-0 -1.-3 10.2- -2.-3 175 Helophorua 10 181 Laooobius 11 184 Dryope 19 1 1 •» - - : ~ : ~ 1 185 Elmia 40 29 53 -1.7 -1.9 -0.3 -2.2 7.4 -1.0 -0.8 186 Lirmiue 11 92 423 2.2 -4.0 -1.5 -6.7 11.8 11.0 -8.3 187 Oulimnius 11 28 48 2.9 -1.8 -1.5 -3.0 4.8 -0.3 -2.5 233 Tabanus 28 24 31 -0.3 -0.7 0.5 1.4 -1.8 4.3 -1.3 268 Orthocladius 32 3 3 * 1 1 1 303 Microtendipes 1 14 50 -2.-7 -0.-7 -1.5 -2.1 -1.8 21.s- -2.-9 :i. 47 Ephemera 107 81 504 -4.1 1.6 -1.5 21.3 -4.3 -2.7 -9.8 50 Baeti.8 45 27 103 -3.1 -2.6 -2.2 -3.0 1.6 -1.9 7.7 109 Serioostoma 125 198 Limnophila 155 39 62 3.9 0.9 0.7 -1.0 -0.6 -0.1 -3.4 245 Maaropelopia 59 27 87 -3.0 6.7 -1.0 8.5 -3.2 -1.6 -2.4 248 Apseatrotanypus 39 1 1 •* 1 288 Tanyt.ourtiaornis 22 ------290 Tanytarsus 27 6 96 -4.9 0.6 -2.1 38.2 -3.9 -2.2 -4.4 292 Cladotanytarsus 16 1 6 3.7 -0.6 -0.5 -1.1 -1.0 -0.6 -1.2 296 Chironomus 14 8 23 -2.4 -1.2 -1.0 4.7 -1.4 -1.1 1.0 II. 11 Oligochaeta 132 116 491 2.S 5.2 -0.6 4.5 0.1 0.2 -9.0 38 Hydracarina 54 25 102 1.1 2.0 -1.3 4.9 -3.0 -1.9 -2.5 96 Nepa rubra 12 202 Gnophomyia 12 2 22 0.2 -1.2 14.9 -2.0 -1.9 -1.1 -2.3 205 Dicranota 106 43 74 -0.8 -1.3 -1.3 -3.2 8.2 2.7 -1.4" 217 Palpomyia 126 68 159 2.5 -0.2 0.6 0.3 2.3 2.4 -6.0 239 Uermrodromia 34 241 Ptychoptera 85 249 Prooladiue 34 26 152 -6.0 -1.3 1.1 16.6 -4.9 -2.1 -3.2 264 juv.Chironimini 12 271 Prodiameaa 105 28 240 -1.5 10.3 -2.1 12.3 -6.2 -3.5 -7.1 283 Epoiaocladins 3 29 130 -3.6 -1.3 -0.8 12.3 0.3 -1.8 -5.4 299 Paraaladopelma 16 6 30 4.5 -1.4 -1.2 -1.5 -2.2 -1.2 0.3 301 P. oairptolabis 28 1 1-* 1 307 P. Zamtnata Id 9 16 3.0- 0.-9 -0.-9 -1.7 0.-9 -0.-9 -2.-0 300 CryptoohironomuB 6 20 34 1.5 2.5 -0.5 1.1 -0.2 -1.3 -2.9 302 Paratewdipes 15 21 110 1.4 -2.7 0.9 9.7 -4.2 -2.4 -4.4 308 Stictoahironomue 84 51 210 8.3 -0.5 -1.5 0.4 -3.7 -1.2 -4.3 311 P.breviantennation 179 48 203 8.3 -1.8 -2.1 -3.3 3.8 -0.1 -6.4 341 Pieidium 78 83 328 11.4 1.5 1.0 -3.4 -3.6 2.2 -8.0 IV. 128 Mioropterna 92 54 286 -6.7 -3.9 -3.6 -6.0 -5.6 -3.8 22. J 280 Chaetocladiue 27 15 32 -2.5 -1.8 2.9 0.0 -1.4 -1.3 3.3 293 Rheotanytarsus 1 l* 1 ------V. 4 PolyceliB 18 31 -2.4 -1.4 -0.4 -0.7 -1.8 -1.3 6.1 23 Glossiphonia 21 32 11 14* 3 3 3 1 6 32 Gammarus pulex 282 11125 154 9918 -39.4 -17.8 -15.-6 -23.0 -28.0 -8.-4 Z03.2 36 AeelluB meridian. 32 58 -3.6 -2.0 -1.0 3.5 -1.7 -1.1 4.0 135 Limn, lunatus 7 -1.3 -1.1 -1.1 0.6 -1.2 e.3 -0.9 17 61 -3.2 -2.0 7.3 2.0 -2.8 -1.8 2.4 155 larvae Agabus 55 134 -5.3 -1.3 0.7 2.2 -4.7 1.7 8.7 1 1* 1 160 larvae Ilybius 20 -2.1 -1.2 3.3 0.1 -2.1 0.1 3.1 3 3-1- 1- - - 2- - - 256 Zavrelimyia 42 105 -4.5 0.0 4.0 5.9 -4.3 -1.0 2.e 10 16 -2.0 -1.-0 -0.-9 3.5 -1.-0 -1.-0 1.-1 285 Limnophyes 0.5 -1.3 1.0 -1.7 -0.2 -0.7 2.0 20 41 -2.3 -1.7 0.1 2.0 -1.0 -1.5 2.9 287 Microps.praecox 223 20138 -55.6 20.3 -11.5 74. e •63.0 -2.8 64.7 82 2111 -18.1 0.2 0.5 9.2 -11.4 0.4 19.2 289 M. trivialis 15 47 -3.3 -1.9 0.5 -1.2 0.7 3.3 306 Phaenopsectra 19 67 -3.9 -1.6 -3.5 -2.6 7.2 17 30 -2.4 -1.4 -1.2 0.6 -1.7 -0.4 4.8 313 Pol. gr .oonvictum 16 22 3 6 9 -" - - 1 2 3 - 3 VI. 40 Amphinemura 42 408 -7.9 -5.6 -5.3 -7.3 4.6 -4.1 21.4 26 313 -7.5 -4.6 3.3 -7.6 -3.4 -4.0 17.1 127 Chaetopteryx 95 386 -6.0 -4.1 -0.4 -6.0 0.2 2.7 13.2 27 60 -2.6 -1.0 -1.7 -1.5 -0.2 -1.2 5.9 180 -4naffaena 53 -2.6 -1.5 -2.1 -1.6 -2.1 10.1 1.8 1 1 » - - 1 VII. 21 Erpobdella oato. 41 74 -3.2 -1.8 0.9 -1.5 -2.3 -2.0 7.9 42 Hemoura cinerea 87 2896 -15.6 -13.8 -5.7 -19.1 4.5 -11.8 44.2 Habrophlebia 74 727 -7.3 -6.1 2.7 -6.0 -6.0 -4.5 21.7 100 Plectrocnemia 8 9 * 2 3 1 3 117 Hateeus radiatus 4 4 •* - - 1 - 3 122 Potamophylax luct. 15 30 -2.-8 -0.-7 -1.2 -1.-1 -2.-2 -1.-2 7.0 190 larvae Helodes 33 207 -7.1 -3.5 7.3 -5.4 -5.6 -3.0 16.4 193 Tipula 7 14 1.3 -1.0 -0.8 2.8 -0.9 -0.9 -1.8 220 Simulium 8 12 -1.7 -0.9 1.9 -1.5 0.1 -0.8 3.0 225 Peychodidae 4 4 -t- 2 1 1 254 Conchapelopia 18 47 -3.4 -1.-8 -1.-5 -1.3 -2.-4 -0.-3 8.2. 263 juv.Orthocladiinae 15 2 7 -1.3 -0.7 -0.6 -0.3 -1.1 -0.6 3.3 269 Corynoneura 33 225 -7.4 -3.9 -3.2 -6.5 -5.5 -3.1 22.5 272 Brillia modeeta 28 151 -6.2 -3.2 -2.3 -5.1 -4.9 -2.4 18.5 274 B. longifuraa 1 1 •» 1 275 Diplocladius 44 366 -8.-8 -4.-7 -3.-6 -7.-6 -4.-5 -2.-7 24.6 277 RheocricotopuB 43 1177 -16.8 -8.9 -6.8 -14.5 -12.7 -7.4 51.2 279 Eukiefferiella 3 6 -1.2 -0.6 -0.5 -1.1 -1.0 -0.6 3.8 310 Polyped.taetum 1 1 •» 1 318 pupae Chironominl 17 74 -4.-1 -2.-2 -1.-9 -0.-5 -2.-9 -0.-9 9.3 A h M H a> O -p M -m o •H 3 0> CM 01 CM 0> •H roH TJ O M CrM- CO >01 C A h 0) -P O Q. Q. S •o < -H •r-ï

h

•S a a p 3 C >H oi ^r co co o ro m O) H CM CM CM CO o t» •* o O CM iH CM 1-1 T* CM CM « +> « « u •a u o s o CO M h -H O CM f CO CO 00 iH o o c« CM CM CM CM CM CM CO CM 3 O t> ß a -p 0) m

t-l CM C- +> - - -P -P iH H iH H eo CD CD •H O • m ho a> a 3 •H rH cd O. cd ^ ja Dl 3 > 3 o o O to m to -P J3 CO in Ol -H P CM CM CM O t-i u P O Q O O in oi CM +JiHU H a u a o m Ol d> a at c CO Ol CM CM CM h g rH h o rH CM CO H ri O O O o CO CO CO CO CO CB -P c~ CO iH Ol in CO CO o -a CM CM CM CM CM O O •o -

c o * AV d) p p o O. U P H o, o ci 0 U C H C < M H fi

190 V M K a i- •p a T X e Ci it 4 •H C « 0 d 9 d a c p •H 4) «a A h P •p « « •H s « O •H ! c a 1« o 0 Ü a ja a p« •p p 0 0«) ci p d •O h *h< a 0) «O, 3 •H •a O a a h •H d • +> m e d n h p 0 O) o d o» m A J3 TJ te r» n •P CN CM i-i O m SN •p n o CD A d •P HS i•S o *o P >> M « 0) H n a O »H ~ a A d P «M o 0 h DO •8 ffi O 00 s>> a -p O O •aH co CO CO CO •p d -l « CN 0) m i-H O 9) V •H > TJ tH S d T3 in a. -H h d M CO 'T O o to o CN CN CO h W O 0 h a A O m CO I p O 00 CO o o u » CN CO M a '•v >> 0 0 •O 0) h a a CO CO 13 •o a H O 00 a o n o n Q a A 03 5» ^« O m CO <0 00 H 00 0) o H m 0) CN CN CN CN CO CO rti-t l« h « 3 o X H p n •H K h •o O O s r-l P AV o »P m a. •i 0 3 a. 3 a .-I < a -" o

191 Appendix 12. I.R. values for the 43 most-abundant taxa (more than 100 specimens) in the Snijdersveerbeek in Sort 8,10%.

Taxa Taxa name Substrate class no.

QM O index

x5x x4x

18 Ezseniella tetraedra 5.0 5.3 6.7 15.4 8.9 -2.0 -3.3 -5.6 -2.8 -3.9 105 Lithax obs cunts 5.0 4.3 2.0 6.2 1.3 7.5 2.5 -6.7 -4.4 -3.6 185 Elmis aenea 15.4 5.S 2.6 -0.9 7.3 -0.4 -3.4 -4.0 -2.4

268 Orthocladius -1.3 -1.6 51.9 2.2 1.8 -2.2 0.0 -3.8 -4.7

280 Chaetocladius -3.2 -4.8 -4.7 11.8 14.5 10.5 -4.4 0.0 \_26.1

50 Baetis vernus 18.4 -2.7 -3.6 -1.8 1.5 -0.9 -3.5 -2.1 4.9 -3.2 -3.4 -4.6 -2.9 245 Macropelopia nebulosa 1.1 -2.4 2.1 2.6 -2.9 11.1 -3.9 -4.8 6.5 0.8 -2.9 -5.4 -3.7 -4.4 -4.1 -5.9 -1.7 -3.9 -5.3 -3.6 290 Tanytarsus 7.4 3.5 -3.5 4.0 -5.5 18.7 264 Chironomini spp.(juv.)

11 Oligochaeta -1.2 -0.0 -3.2 5.2 -1.3 8.5 6.7 -2.6 -3.9 5.5 38 Hydracarina -1.9 -2.3 -1.9 5.7 4.7 1.9 -1.4 0.5 -1.3 -2.1 47 Ephemera danica -2.4 -2.4 6.4 2.3 2.1 0.5 -5.5 6.0 5.4 0.9 -3.2 -5.4 -3.3 109 Sericostoma personation -3.2 -0.7 3.3 3.9 1.8 2.5 -2.9 -1.9 1.0 -2.0 2.8 -4.2 -3.1 128 Micropterna sequax -1.1 0.7 0.9 0.4 5.5 -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 1.9 -1.8 2.5 0.2 5.2 -2.8 -4.8 -3.3 205 Dicranota -0.4 -2.0 0.5 0.1 5.5 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 0.8 -3.9 5.2 -0.9 6.2 5.8 -2.2 -1.5 241 Ptychoptera -2.7 -3.5 3.7 -3.6 -2.1 1.5 -1.3 8.6 1.2 11.6 0.7 -3.3 -1.2 248 Apsectrotanypus trifascip. -1.7 3.6 2.5 -2.6 2.0 -1.7 -1.7 2.0 2.3 0.4 -1.5 2.5 -0.8 249 Procladius -2.0 -2.6 2.0 -2.7 -1.6 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 -0.8 -3.0 -0.5 5.9 1.7 0.7 5.5 3.9 308 Stictochironomus -2.8 -3.5 2.4 -1.3 -1.5 -1.4 7.2 9.3 2.9 0.8 -3.8 -4.8 -3.0 341 Pisidium -2.6 -3.0 2.7 -1.8 0.7 6.5 -0.6 2.5 0.1 7.7 -3.7 -2.3 -2.0

271 Prodiamesa olivacea 6.6 -7.1 -7.3 -7.3 -7.3 9.2 21.8 13.7 6.5 3.3 -5.3 6.7 -7.5 -3.4 -0.7 0.7 5.5 16.9 15.9 -1.2 -6.3 -3.8 311 Polypedilwi breviantennat. -29.8 -32.3 -29.4 -1.5 29.5 30.1 25.8 88.6 4.5 287 Micropsectra gr. praecox -11.6 -22.3 -22.7 -20.8 -14.4 -8.6 -12.2 -7.5 65.5 32.0 35.5 32 Gammarus pülex 0.9 2.1 2.0 -0.9 -0.7 -4.0 -5.3 -3.8 27.7 -3.6 -3.6 127 Chaetopteryx villosa 1.9 -1.8 -3.7 -2.4 -3.1 -4.9 -6.0 -3.6 31.9 10.7 -2.9 220 Simutium latipes 4.0 1.1 1.7 -2.2 2.7 -6.6 -2.1 -4.3 18.8 -1.3 -0.8 293 Rheotany tarsus 40 Amphinemura standfussi -5.8 -6.9 -3.9 -3.0 32.3 -2.9 42 Nemoura cinerea -3.3 -4.3 -2.2 -1.1 31.8 -1.0 269 Corynoneura -3.3 -2.8 -4.0 14.5 22.5 -0.3 272 Brillia modesta -5.3 -5.6 -4.0 10.4 30.7 16.7 275 Diplocladius cultriger -1.0 -3.8 -5.2 -2.6 -0.2 18.1 11.7 310 Polypedilum laetum -2.2 -9.5 -5.8 -5.6 14.7 29.2 -4.4

277 Rheocriaotopus -7.7 -9.3 -8.2 -8.6 -6.7 8.5 64.3 0.2 -6.5 -10.7 -10.5 -12.4 -7.5 31.1 62.6 -2.9 279 Eukiefferiella gr. disaol. -7.3 -10.9 -6.5 54.3 18.4 18.9 190 Helodes larvae -1.4 -3.4 -3.5 1.4 13.Z 12.5 1.1 100 Plectroonemia conspersa -2.8 -2.9 -1.8 0.0 1.8 -1.5 5.9 10.8 0.7 155 Agabus larvae -3.8 -0.3 -2.6 -1.9 -0.2 -1.2 16.1 2.2 5.8 254 Conchapelopia melanops -1.2 -2.7 -2.2 -1.2 -0.9 14.3 5.3 -2.0 318 Chironomini pupae spp. Italic values indicate significant over-representation Boxes indicate groups of taxa with similar over-representation

192 Appendix13 .I.R .value sfo rth e2 6»oat-abundan t taxa(»or etha n10 0specimens )i nth eRatumsebee ki nSor t8,10% .

TaxaTax anaa e Substrateclas s

x5x x4x

103 AgapetuB fueaipee -1.0 9.9 1.3 0.4 10.8 30.2 -1.4 -1.4 -5.6 -3.8 -2.3

10S Lithax obaauruß 4.S 0.3 2.1 6.2 5.9 2.S -2.1 -3.4 -5.9 -3.8 -1.9 5.7 -1.0 -0.7 186 Limniue volchnari 7.4 2.8 S.9 4.9 14.e 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 Stictochironomua -1.0 -2.1 -1.6 -2.4 -1.6 -2.5 7.3 1.1 S.9 -1.3 -2.3 -2.3 -3.6 -1.1 311 Polypedilum breviantennat. -1.0 -2.0 -2.0 3.3 4.0 -1.1 3.3 -2.1 S.6 -2.3 -1.8 -2.3 -5.8 -1.5 341 Pieidiien 0.3 -2.2 -0.3 -0.8 -1.3 -2.3 3.2 0.9 10.8 -0.4 -0.8 -2.2 -7.2

47 Ephemera danica -1.6 -1.3 -3.2 -3.3 -2.0 1.3 12.2 -2.7 -1.0 6.6 10.9 -3.3 -2.0

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 0.6 38 Hydracarina -0.7 -0.8 -1.5 -2.4 -2.0 -3.2 2.S -1.3 4.3 7.0 -1.6 -1.6 -4.2 6.2 249 Procladius -0.9 -1.8 -1.8 -3.5 -3.0 -2.8 -3.7 -2.1 4.8 18.3 3.« -2.0 -5.4 7.9 283 Epoiooaladius flavens -0.8 0.2 -1.6 -1.4 1.5 0.1 -1.9 -1.8 -1.5 19.1 -1.8 -1.8 -4.8 -1.6 -0.8 -1.5 -1.5 -3.2 -2.8 -1.8 6.3 0.1 1.3 9.9 -0.5 0.1 -4.4 -1.5 302 Paratendipes -1.1 -2.2 -2.2 -4.7 -4.1 -2.6 -3.4 -2.8 37.3 5.3 e.o 271 Prodiamesa olivacea -1.5 4.1 -0.8 0.2 -0.6 -2.3 -2.5 -3.5 -1.6 9.6 -1.5 90 Baetie vernua 17.3 -7.7 -4.5 -2.3 -6.3 -10.1 -9.8 -22.0 -8.5 53.7 -4.7 42 Nemoura cinerea -1.3 0.6 -2.5 -3.0 -3.7 -4.1 -5.6 -7.0 -4.6 -2.8 -2.8 17.8 6.9 40 Amphinemura BtandfuBsi -4.0 -5.3 6.6 -1.4 -3.6 -1.0 1.8 -5.9 0.0 -10.5 -4.9 -0.6 16.1 17.4 48 Habrophlebia fusoa -0.9 -1.8 -1.8 -3.7 -3.0 -2.7 -5.1 -2.9 -2.0 -2.0 18.2 9.6 272 Brillia modeata -3.8 -4.4 128 Miaropterna eequax -1.2 -2.0 -2.0 -4.9 -3.4 -3.4 -4.1 -3.7 -6.7 -4.4 -2.7 20.6 16.2 2.8 -1.0 -2.1 -1.6 -4.1 -3.9 6.4 -5.2 -3.7 -2.3 14.6 13.0 -0.1 190 Helodes larvae -4.3 -4.8 1.6 -4.9 -7.7 -2.4 -5.3 -2.0 0.9 2.3 64.9 -10.9 26.8 287 Miaropeeotra gr. praecox -6.0 -4.4 3.2 -4.5 -19.8 -17.3 -12.7 -33.9 -19.3 -13.8 160.5 49.2 22.6 32 Garrmarue pulex -16.1 -23.0 -0.1 -2.2 -1.7 -4.6 -3.5 -3.7 -6.2 -3.9 -2.4 1.4 24.3 -1.7 269 Corynoneiœa -1.4 -2.0 -2.4 -3.6 -2.2 -4.5 -5.4 -4.8 -7.7 -4.1 -3.1 -2.1 27.9 0.5 275 Z>tpZoöladtua ewîtrtg'ei' -4.5 -6.6 277 RheocricotopuB -8.5 -10.1 -12.2 -14.0 -1.7 S3.2 13.4

Italievalue sindicat esignifican tover-representatio n Boxesindicat egroup so ftax awit hsimila rover-representatio n

193 Appendix 14.Compariso n of the faunal composition of the Sand (S),Grave l (G)an d Leaf (L)substrate s inth enatura l sectiono f theSnijdersveerbee k (Section 6)wit h thato f theSan d andFin eDetritu s (S+FD)substrat e inth eregulate d section (7) downstream of Section 6.

Section6 Section7

Taxon S+FD

Lumbriculidae 1 Eiseniella tetraedva 3 20 Gammarus pulex 7 4 27 1 Hydracarina 2 3 1 6 Ephemera daniaa 46 32 2 Pleatroanemia oonspersa 2 10 Agapetus fuscipes 1 Lithax obsaurus 15 1 Serioostoma personatum 22 22 Halesus radiatus 1 1 Potamophylax rotundipennis 1 1 Chaetopteryx villosa 1 Mioropterna sequax 4 5 2 Agabus sp. 3 2 Dryops sp. 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 Hemerodromia sp. 1 Maoropelopia nebulosa 3 12 Apseotrotanypus trifasaipennis 10 28 Prooladius sp. 2 127 Conchapelopia melanops 9 4 8 Zavrelimyia sp. 2 1 Orthocladiinae 2 3 Chironomini 1 7 Orthoeladius sp. 1 Corynoneura sp. 2 1 41 Prodiamesa olivaaea 8 1 3 Brillia modesta 1 57 Brillia longifuroa 5 Diplooladius cultriger 24 Rheooriootopus sp. 4 2 76 Eukiefferiella gr. disooloripes 1 13 56 Limnophyes sp. 2 Mioropseotra gr. praecox 105 3 102 67 Tanytarsus aurticornis 3 Rheotanytarsus sp. 10 Paratanytarsus sp. 2 Paratendipes sp. 1 Stiatoohironomus sp. 4 7 Polypedilum breviantennatum 15 5 2 Polypedilum gr. conviotum 1 358 Chironomidae pupae 1 12 Pisidium sp. 5 1 1 Lepidoptera 1 1

194 Appendix 14 (continued)

Taxon Section 6 Section 7

SGL S+FD

Somatoehlora arotioa 4 Caenis hovaria 7 Corixidae larvae 3 Notonecta vivides 1 Sigava striata 78 Sigava falleni 51 Sigava distinota 1 Sigava lateralis 13 Sigava falleni/longipalis 47 Hespevoaovixa sahlhevgi 4 Ilybius larvae 2 Laaoophilus sp. 1 Stiatotavsus duodeaimpustulatus 2 Diavanota sp. 2 Cviootpus sp. 12 Pseotvooladius sp. 3 Tanytavsus sp. 481 Cladotanytarsus sp. 119 Chivonomus sp. 26 Glyptotendipes sp. 48 Cvyptoohivonomus sp. 34 Miovotendipes gr. ohlovis 21 Polypedilim nubeaulosum 6 Lymnaea auvioulavia 33 Mystaoides longiaovnis 1

Number of taxa 37 26 27 38

195 Identification references

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197 Lepneva,S.G. ,1964 .Faun ao fUSSR ,Trichopter aVol .II ,no .1 .Larva ean dpupa e ofAnnulipalpia .Zool .Inst .Acad .Sc .USSR ,Ne wSerie sno .88 ,Israe lProgra m Sc.Translat. ,Jerusalem , 1971:63 8p . Lepneva,S.G. , 1966.Faun ao fUSSR ,Trichopter aVol .II ,no .2 .Larva ean dpupa e of Integripalpia.Zool .Inst .Acad .Sc .USSR ,Ne w Seriesno .95 ,Israe lProgra m Sc.Translat. ,Jerusalem , 1971:70 0p . Macan,T.T. , 1973.A ke yt oth eadult so f theBritis hTrichoptera .Sc .Publ . Freshwat.biol .Ass .28 :15 1p .+ photo's . Tobias,W. ,1962 .Di eGehäusebaute nde rKöcherfliege n (Trichoptera)unte r Berücksichtigung derbi s 1961erschienene nLiteratur .Mimeograph :12 6p . Ulmer,G. , 1909.Trichoptera .Süsswasserfaun aDeutschland sHef t 5/6, In:A .Braue r (Ed.). Fischer,Jena :32 6p . Wallace, I.D., 1977.A ke y toth elarva ean dpupa eo f Sericostomapersonatu m (Spence) andNotidobi aciliari s (Linné) (Sericostomatidae,Trichoptera )i nBritain . Freshwat.Biol .7 :93-98 . Coleoptera Bertrand,H. , 1972.Larve se tnymphe sde sColéoptère s aquatiques duglobe ,ave c tableauxd edéterminatio nde sgenres .Paillart ,Paris :80 4p . Drost,B .& M . Schrijer,1976 .Waterkeve r tabel.Jeugdbondsuitg. ,Amsterdam : 201p . Freude,H. ,K.W .Hard e& G.A .Lohse ,1971 .Di eKäfe rMitteleuropa's ,Ban d 3,1-41 . Goecke& Evers ,Krefeld . Holland,D.G. , 1972.A ke yt oth elarvae ,pupa ean dadult so fth eBritis hspecie s ofElminthidae .Sc .Publ .Freshwat .biol .Ass .26 :5 8p . Klausnitzer,B. ,1977 .Bestimmungstabelle n fürdi eGattunge n aquatischer Coleopteren-LarvenMitteleuropas .Beitr .Ent. ,Berli n27 :145-192 . Diptera (general) Bertrand,H. , 1954.Le s insectesaquatique sd'europ eBd .2 .Encyclop .Entomol .31 , Paris: 547p . Hennig,W. , 1968.Di eLarvenforme n derDiptere nT . I, II,III .Akademi eVerla gBerli n 184p. ,45 8p .an d62 8p . Johannsen,O.A. , 1934.Aquati cDiptera ,Par t 1,2 ,3 ,4 :Par t 5b yL.C .Thomson , Entomol.Reprin t Specialists,Unchange d reprint 1969 (1st), 1977 (4th)o f original papers in '34,'3 5an d '37.95 , 74,102 ,56 ,9 8p .resp . Tolkamp,H.H. , 1976.Determinatietabe l voorhe tbepale nva nfamilie ,geslach te n somszelf ssoor tde rEuropese ,i nhe twate rlevend eDiptera-larven . Mimeograph Nat.Cons .Dept .Agric .Univ .Wageningen :7 4p . Dixidae Disney,R.H.L. ,1975 .A ke y toth eBritis hDixidae .So .Publ .Freshwat .biol .Ass . 31:7 8p . Simuliidae Davies,L. , 1968.A ke y toth eBritis h specieso f Simuliidae (Diptera)i nth e larval,pupa l and adult stages.Sc .Publ .Freshwat .biol .Ass .24 :12 6p . Tipulidae Theowald,Br. ,1957 .Di eEntwicklungsstadie nde rTipuliden ,insbesonder ede r West-PaläarktischenArten .Tijdschr .Ent .10 0 (2): 195-308. Culiaidae Mohrig,W. ,1969 .Di eCulicide nDeutschlands ,Untersuchunge n zurtaxonomie ,biologi e undÖkologi ede reinheimische n Stechmücken.Parasitolog . Sehr.Reih e18 :26 0p . Chironomidae Brundin,L. ,1948 .Uebe rdi eMetamorphos ede r SectioTanytarsaria e connectentes (Dipt.,Chir.) . Arkiv förZoolog iBd .41 A (2):1-2 2 +7 Tafeln . Fittkau,E.J. , 1962.Di eTanypodina e (Diptera,Chironomidae) .(Di eTribu s Anatopyniini,Macropelopiin iun dPentaneurini) .Abh .Larvalsyst .Insekten , AkademieVerlag ,Berlin :45 3p . Hirvenoja,A. ,1973 .Revisio nde rGattun gCricotopu svo nde rWul pun d ihrer Verwandten (Diptera,Chironomidae) .Ann .Zool .Fennic i 10:1-363 .

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211