University of the Pacific Scholarly Commons
University of the Pacific Theses and Dissertations Graduate School
1972
The ecological life history and feeding biology of Batillaria zonalis (Bruguière)
Robert Bruce Whitlatch University of the Pacific
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Recommended Citation Whitlatch, Robert Bruce. (1972). The ecological life history and feeding biology of Batillaria zonalis (Bruguière). University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/416
This Thesis is brought to you for free and open access by the Graduate School at Scholarly Commons. It has been accepted for inclusion in University of the Pacific Theses and Dissertations by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. 'l'HE 'l!:COI..OOICJ.L L!F'E HISTORY AND F'E'.;."!UNC BIOUX:Y OF'
JU;'l'ILY.ARJA &lli\tJJ! ( ERUGUIERE) I I
A Thesis
! r l Uni YEl1'lli ty of the Pacific: j
In 1-'"atial F'l:tlfillment
~tar of Science
--~--. This thesis, written and submitted by
Robert Bruce Whitlatch is approved for recommendation to the Committee on Graduate Studies, University of the Pacific.
Department Chairman or Dean:
Thesis Committee:
/4Mt tfl~· Chairman
w.. j)/1 f~
Dated'------I would sincerely Uke to thank Dr, Steven Obt'el:m helpful suggestions a;Jd constant encouragement that he gave me dur:lne all phases of this roseat)(lh and JTI\f two year stay at the Pae:!.fie Marine Station, He ahrays "madel'' time to listen to my problee am was will~ ing to generate itlformat:l. ve diacnss:l.orus to solve them, I wish to tha..'lk !lim for the use of the \lang computer and his program U bra.:cy • . aids that made analyzing the data much easier, I am grateful for the s\lggestions that D't'S, E,H, Smith, W,J3, Gladfelter, and J ,A, Blake made concerning this manuscript, Dr, R,G, Jo!L'!Son gave info:t'lilative suggestions. eoneernirlg the initial stages of the resea'X!h on the feooing biology of the g-<~Stropods, duri¥1g Jil\l'll'.ll.:r.y 1971! A•. ~:, Hajek for her unpublished de;ta an the trem- a.tooe parasi.tes of ~-11:!J£l:ias and S, Ho.ffman for hls help in photo·· gntph:!.ng a!W. printi:r.g many of the figures, Ann-·""'las it trudging through the Jl!lU'Shes and typir;g the :manuscr'i pt or tnl.G it cm.rulll!!l-m,:x and ~rine • • • ohe wh PAGE ACKNOWLEDGE!o!ENTS 111 • • • •• . . ~ • • • • • • • • • • •• LIST OF TA1J1..ES • • • • • • • • • • • • • • • ~ • • • • • • • • • LIS1' OF FIGURES, • • • • • • • • • • • • • • • • • • • • • • • • ix I INTRODUC'I'It\N • • • • • • • • • • • • • • • • • • • • • • • • • • l , HAlliTAT. ·' , • • • - • • • 8 • • • • • • • " ...... ' . METHODS AND !fill. TEIUALS. , • • • • • • • 19 I GENERAL BIOLOGY, , , 20 • • • • • • • • ' . • • • • • DISPERSIO!\l ...... • • • • ~ 8 ' . 0 • • " • • . ' • • • • • GROl/Tl! , , • 0 • ;a • • • • • . ' . -D " . . ' • • • ' . ' . • • I }larked Individual Animals . ' . . ' ••• I REPRODUGTION AN'u RECRUIT!1ENT , • " , I PREDA'I'OHS AND PARASITES 0~' ~'l;M.i'!.11\. , , , , , , , , , ., , , • PO'P.ULATION ABUNDANCE Al'lD AGJ\J-S'l'RUC'TURE , • • • • • Walker Creeka Station..'! 1, 2. ani :; , , •• , • , , , , , , 67 Stations 4 and 5 , c tl .. .. • • 68 l~illert.om Millert.ons . . ~ • • • ' . 93 Selecttv:l.ty , • • 93 • • • • . '. "' 0 $ • " • • . . ' 95 • • 95 SPECIES :UJVJ,;HSI1'Y, , , , , . ' • • v STABILI1~ IN NATURAL ECOSYSTEMS, , , , • • • • 109 GENERAL FAC1'0RS LIIUTING THE GROWTH OF POPu:t.ATit1NS , ' . . • • • 11.5 Environmental Preclictab111ty, , • , , , , , , • • • , , , • 116 Predictability of Food., , • • • •• . . . " • • • • . . . .. 117 Salt Marsh Anil!la.1 Feeding St.rategies. and. Community Stab- .llity, ••••• ~ • • . ~ .. . ? • • Sl.Jlt!MARY • , $ ~ • • • • • • • • • • • e ~ • • • • • • • ' . LITERA'l'URE CITf'J'J , • • to • .J $ •• ~ • • • Ill " • • • • • APPENDIX A - ESTII1ATES OF' THE NEGATIVE BIN011IAI, PARii~IETJt"R k, • • - APPENDIX B - ESTIMA'flJS OF MEAN CROW!llNG AND PATCHINESS , , , • • I 1 LIST OF TABLES TABLE PAGE I, Percentages of Total Marsh Area Between Successive Con• tour Intervals , , • , , , • e • • • e e e • • • • • • • 7 II. Distribution of Marsh Plitnts in the Tomales Bay Salt l~arsh. • • ,• • • • • 1o • • • • • • • to ,0 lfl • • • • • * !l 8 III. Neasuremants of Surface Sediment and Wa·ter Temp&mtuxes ------in the Sampling Areas of ~lalker Creek ani Millerton, ' ' 9 IV, Cx' a Coefficient of Aggregation, Walker Creek , , , , , , )1 v. ex• a Coefficient of Aggregation, Millerton, :• • , , , , , 32 VI, Variance/mean Ratios, Walker Creek • • • • • :n VII, Va:d.ance/mean Ratios, H:tlJ.erton, , • • • • • • • • • • ' . )4 ; VIII, J at Walker ~'r'eek and Millert-on, • ,. • a & . ' 57 IX, Density }::Sti!o.ates of Juveniles Settling on tho Wallter Creek and Millerton Salt !l.arshes , , • , • • . ' . • • • x. Chi-square Analysis of the Sex Rat:l.os of Bat11J,g!.ri.;}.. • • • XI, Number and Percentage of Snails Stu•vi ving Desiccation at Nine Time Intervals • • • • • • • • • • • • • • ' • • 71 ; A·I. Estimates of the Negative.Binomial k for R"'ti}J,arl~. ' Station 1, Walker Creek,.,-, • • • • • • • • • • • • • • 132 A-II, Estimates of the Negative Bino1uial k for~~~. Station 2 0 Walker Creek, , , , , • • • 133 A-III, Estimates of the Negative Binomial It for Batill'"x::j,~, Station 3. Walker C:t·eelt, , , , , e " o 11 t1 e O· 11 " .e • 111 A-IV, Estimates of the Negative Binomial k for ~i!ll~. • • • 1:35 A-V. Esti!liates of the Negative Binomial k for Bat"JJ,.alj.a• Station 5, Walker Creek, • , , , • • • • • • 0 ~ • • • • 136 A~VI, Estimates of the Negative Binomial k for~~~. Station 1, Mlllerton , , • • , , , , • , • • , • , ' . . 137 A-VII, Estimates of the Neg- Station 2, Millerton • , , , , , • • • • • • • 0 • • • • 138 Station 3, Millerton , , • , , , • • • 139 A-IX. Estimates of the Negat1 ve Bin01nial k fo:r ~·p~l)JJ,J'_ia, Station 4, Mil~erton • , • , , , • • • · A-X, Es'c5.mates of the Negative Binomial k for ;r.-a~rla • Station 5, Millerton , , , , , , , , , , • , , , , • , , J.IH 1, Walker Creek, , • , , • • , • , , , • • , , , , , • , 147 ·B-II, Moment Estimates of Mean Crowding arrl Patchiness, Station 2, Walker Creek, , • , • @ • ft ~ • o • • o • e • ¢ • o Q 148 l:l-III, ~Joment Estimates of !1ean Crowding and Patchiness, Station. 3, Walke.r Creek, • , , B•IV, Homent F..stir~ate:;:: of Mean Cr~ding v.r.JJ. l'atehh1css, Stat:l.on ...... ' - . . 4, Walker Creek, , , • • • o • o • o ~ e • • ~ . e • ~ * • B-V, Hommrt Estinw.tes of Mean Crowding andPatehiness 0 Station 5o Walker Creek, , , , e ~ • • & t & e c • • • w • • o • 1.51 B·VI, Moment Estimates of Mean Crowding and Patchiness. Station 1, Millerton , . . ' . viii 13-VII, Mome!rt Estimates of 11ean Crowding and Patch1ne.'!ls 0 Sta.tlon 2 • Millerton , ~ • e • • • • o e i • • • a ~ • . • t • e • B-VIII, Moment Estimates of !1ean Crowding and Patchiness, Station :), Millerton , • -· • • • • • • • • • • • • • .• • • • 0 • 13-IX. Moment Estimates of Naan Crowding aoo Patchiness, Station 4 1 Millerton • 9 • • • ~ • • • • • 0 • • • • • . • • • • • 1.5.5 B-X, Mora-:~nt F.sti!\la.t~?.s oi' Mean Cr 5. M:l.llerton , e 11 ' • 8 • • • • ~ • • ~ • • ~ • • ~ ~ • ll-XI. Monu:mt EstiP~ates of Mean Crowding and Pateh:tne:ss, Station 6• Millerton • • • • • • • • ' ~ • • • 8 ~ • • 8 • • • • LIS'!' OF FIGURES FIGURE PAGE 1, Map of Tomales Bay, Oa.J.ifornia, _Depicting the Locations of the Salt Marshes Studied , , , , , , ~ ...... ~ . 10 2, Dlagramma.tic ~la.p of the Millerton Salt. Marsh lr.dicating the Position.~ of the Sampling LocaJ~ties , , , , • , , , , • . ' 11 the Positions of the Sampling Localities , , • , , o • e • • l2 4, D:lagxammatic l'!8.p of Millerton Salt Marsh Showing the Distribution of Different Plant Assemblages, •• , • • • • • 13 5, Diagrammatic ~la.p of Walker Creek Salt Marsh Shmring. the Dist:;:1.1mt:! .. on cf Different Pl:;u~t Ac:t>crablages, • , , , 14 • • • • - 6, ll';d;;:.r .and !lpr·&Y' Substra:t.e ~l'emper<~.tur.,s Taken At Walhr - C:r·eek, Station ), on December 160 197'0 , , , • , , , • • • • 15 ? , Water Temperature~:~ Taken at Walker Creek and Millerton Salt Ma:r:shes Ba-tween January 1971 and Ap:rll 1972. • • • 16 8, Average Monthly Air Temperatures Between Januaey 1971 arld May 1972 Compared with the 4-year J4onthly Mean 'fempera- tures, 1? • • • • • • • • • • • • • • • • • • • • • • • • • • • !' 9. Rair.f'all Occurring Betneen Ja.nuary 1971 and Yuay 19'12 Compe;red ;;;; with 4-year Grand. Monthly l1e.-.n F-airJfa.ll, , .;; .• • • • • • • • lB - 10, ·Histograms Showing the Frequency Illilices and RelaHve Dem;Hies Wa.J.ker Creek and Millerton • , , , ••• 23 11, F.stirnates. of Patchiness for .~i!.U.ll~.tl£!., St.ation 1 0 Walker C:r:eek. · , ~ • • , • It • • It • , If 6 • " " • * • • • • 0 • •• 35 ',,J.ko Creek, • • • • • • • • • • • • • • • • • • • • • • • • • • • 36 13. F.stima.tes of'. Patchiness . for ~:Ullm.!!, StaUon 3, Walker Creek, • • • • • • • • • • • • • • • • • • • • • • • • • • • 37 14, Size-frequency Distrtbutlons of Ba.tlllari!l, StaUonl, Walker Creek • • • • • • • • • • • ·• • • • • • • • • • • • • L~.J. 15. S!ze~f:requency Distributions of ~:till~:ri!!:o Station2, Walker Creek • • • • • • • • • • • • • • • • • • • • • • • • 42 16, Size-frequency Distributions of~. Station :3, Walker Creek • • • • • • • • • • • • • • • • • • ·• • • • • • 43 I - 17. Size-frequency Distributio~~ of Jl2.J;U..~J!, Sts.tion 1;., Walker Creek • • • • • • • • • • • • • • • • • • • • • • • • lj4 1,8, Size-frequency Distributions of J~;!;jJlru;M~, Stat:l.on 5o Walker Creek, lj_? • • • • • • • • • • • • • • • • • • • • " • • • • • • .19. Size....,freq tteney Distr:l.butlo:ms oi: l'"'lt~ll~"'i?:,. Station 1, Millert::-n, 46 • • • • • • • • • • • • • ' ' ' • • • • • • • • • 20, Size-frequency Di.st:t"lbutions of ll!J.tHla.r:ll!o Station 2, Millerton, • • • • • • • • • • • • • • • • • • • • • • • • • In 21. Size-frequency Distribut:!. on.~ o:f llati:!..l.a..~. St.o"ltion ), Millerton, • • • • • • • • • • • • • • • • • • • • • • • • • ~ 22. Size-fre~uency Distributions of ~.ler1a 0 Station4, - ;;;: Millerton, • • • • • • • • .- . • • ' • • • • • • • ! • • • • 49 23. Si.Zf;-f:reqmmc:r Distri buttons of ~.iUJJ1.'1j,,s;,, . Station. . 5t Millerton, • • • • • • • • • • • • • • • • • • • • • ' • • • .50 24, Siz e-frt:..oq uenoy Distributions of m:li11.1J!.ru.' Station 6, l'lille:don, • • • • • • • • • • • • • • • • • • • • • • • • • 25. Ford~Walford Plot of tha Shi:fta in the Modes of S:tze~ Dat.,..'\ , frequeney Distrl.butions and Hark Recapture 11 .. • • • • 52 xi 26. Age !'lotted in Yea.rs for J.lMID.~ Derived Frcll! the Ford~ Walford Equation , , , • , • • • • • • • • • • • • • • • • • .5J 27, Size~frequency llistrlbutions o:f Copulating SMils from !JI'alker. Creek and Millerton, , . , , . , , , , , , . . . ~ . . . . • • • 60 28, Scatter Diagram ShO'ning the Relatlcmship Between 1-engths of Copulating Males and Copulating Females, , , , , • • • • • • 61 29. Histograms of Sex.Ratios of ~]J]_'f.ia from Walker Creek and e 9 9 II 9 9 Millerton. •• • e • • '" •- 30, Size-frequency Distributions of ll!l:.i,illalj£ Infected with Lar11al Trematodes :f:r.'om Walker Creek and Nillerton , ; • , , , , , , 6.5 31. ·Percentages of M~ Infected llith •rrematode Pa.:rasites From Walker Creek and Millerton, , , , , , , • 66 • " " !!I • • • - 72 ~~ Walker Creek. • e • Cl " •• e •. ·- -: • • -" _CI,, •. 6- f> . ~ . . . ~ . 73 34. Est.i.mates of Population Abundance of ll!J..tillar1~ 0 Station 3, Walker Creek , , , • e • e • • ' • • • • • o e e • ' • ~ ~ • 74 35, l'opulaU.on Structure of }latillarilj,, Station 1, ~Talker Creek, , ?'5 36, Population Structure of lJi!ti;!,lil,:ria.~ Station 2. Walker Creek. , 76 3'?. Poptd.ati.on. Structure of ~.illatll!.t .Statton 3, Walker Creek, , 7'? )8, Estimates of the PopulationAbund.ance of J'AJ.:iUlarla. Stations 4 a.nd 5, Walker Creek. e • "' • • . • .- , • e ••• 78 Creek. • • e • t • 79 40, Estin1ates of the: Population Abundance. of J!l..ttll~. Station • fl ;J ; 41, Estimates of the Population Abundance of Bat,:l.llaru~ Station 81 2, Millerton , 0 f • • • • t * • & • • • • • • • • • • • • • 42, Estimates of the Population Abundance.of ~tillaria, Station 3, l'-1illarton • • •. e • • • • • • • • e • • ~ • • • • • • • • , 4:3 •. Population Structure of, Ba.tillarj.§., Sta.tian 1, Millerton • • • 83 44, Population Structure of Jlatillarla, Station ?. , Millerton • • • 84 45, Population St:r.uctu:r:e of Batillar:l.i!.• Station 3, Mlllerton , , , 85 46. Estimates of the Population Abundll.rlce. of Ea11Uari.if!.• Stations 4, 5, and. 6 • !Ullerton , • , , , . , , , , , , • , • • • • • • 86 Population St:r.u.cture of ~ill;~&~ll.& Stations 4, 5, 60 Miller- ii I ton • • tl • tl • • • Ill $ • • 8'? I • e ~ ~ • 8 e • ~ ~ e • • • • • • i 48, j • • • • • • Cl 89 50. Population Structure of~. Walker Creek (Pooled Data frorr; the Tidal Creeks ami Marsh Ponds), • • • • • • • • 90 51, Populat:lon Structure of B~.• Millerton (Pooled Data :t"rttm the Tidal Creeks and ~larsh Ptmds) , , , , , , • , , • • 91 !)2, Size-frequency Distributions of 50 Randomly Sa,mpled Diatoms T~(en from the Guts of ~-~lAri~, , , , , , • , , , , , , 53, S,.ze•:frequency Dist:ribut ions of 50 Rand.omly SaJllpled. Diatom.o;~ Taken From the Guts of . Cer:j,~!!Jil-it~· ., , . , , , . , •. , , , • , , , , 99 54, Size-frequency Di.stri'but.ions of 100 Handomly Saw:pled Dlatoms li'r()lll a Sediment Core CollectecJ. at Walker Creek , • . . " . . 100 55, 1~.near Reg:resslon Analysis of. Shell Lerlgths Plotted Against xiU and .Qerltl)idea., September 28, 1971 • , , , , , , , , • • • , 101 56, Linear Regression Analysis of' Shell Lengths Plotted Agalnst Average Diatom. Length Obtained from. the. Guts of l?J!.~J,.~ and ~~~idea, April 8, 1972. , , , , • , , • , , ••• • • 101 Station A, Millert~n , • • • • • • e • • • • v • e • • • • • 102 ------Station B. M:l.llerton • , . " . ' ...... ~ ••• 103 y:), Estimates of the A'bundance of' Cerithidea and ~ti:Uari<\ 0 Stations A and B, Hillerton. • • • , , , • • • • , • • • • • INTRODUCTION Ther•' is considerable specmla.tion concerning the relationship of spt'H'lie~; diver.dty to oornmunity stability, JJ of atability i.n rv:~.tural communi ties is considered 'by some ecologists to be one of the pri~~ry objectives of community ecology (see Woodwell and ______.i.._.ea=l....,ly dist.tnet s_ttlliis_c:t:plinEJs_wi±.hln- -eeolc~gy-a-l'!.d-biC!grGogra.ph.r--EHai-rs·-ton,,,---- .!l.t, .11.1,, 1968). 'l'he hypothee;is of a positive correlation between stability and species d.:l.versity is 11.n old one, It originated. :l.n non:rigorous obse:t"ll~:· t:l.onal evldence but has been repeat.edly affirmed as vnlid :l.n ecological 11 terature, Only a few attempts have beari rnad.e to actually test "th-e ple~dty t.o the stahi.lity of a community (Hai.rston, et £11,, 1968: Hurd, li'ul:ther st,udJ.es relating cr.mmu:rrl.ty stahiUt,r to species d1ve:csity tn:e needed, cal COi!ll\lunity are demographic characterlst:l.cs of componen:t species :popu- mation on in . must be ava.Uable, Life histm:·y patterns reflect evolved characterlstics concernod with .th<> ability of a species to persist in a given envlrmm«nt.. 1'hus 0 for er.2,mple, SloOOdk:ln and Sanders (1969) hypothesi~::e th<•t environ- nmnl:..al U!lpredictahl.lit)• will result in sclectton for completely differ<>nt sets <)f ada.pt.s. t:l.l.:ms than either regularly fluctuating or cormtant erwi:ron- fl10t'rt~J •. · Paina (1969, 1966) provides evidence that certain "ke.vstone" !Jayton ( 19'11) on the basis of controlled experllilents in rJckJ!· intel:tidal ha'b1tats suggests that the distributhm and abundance of many of the component species is p:rt!ditlbble :from intemetiorlll between them, and, more interestingly, that events affecting larval stagEs in the plankton have no bearing on community organization of the adult ox·ganisms comprising the benthic COUIAIU ty, In the present study, aspeotlil of the ecologi.ca.l life history of ----~------Batillarla .!!.Q.r.aj,i,s_ (Brugiere) !>.as been investigated for a period of two years, Trends in population dynamics and aspects ef its biology in two salt marsh loealiHes are described, Results of studies on thl!l feeding I~ (an "eeolog;.t'-'al ~>-qliivalent" o:f 1:/i!,j;i.. JJ.~~ (Hacdow.tld• 1969} arld th;:;:l.r interaetion with t1.iatom.s l.:t"e 'l:epo:rt.oo. w:\.th l:."e:ference to t'l.nld··re.~ctlr{:e part.i= J '··~ testing eyllOthesea about diversH:y and stability in salt lJ! Although these lmsio theoretical questions. ca.'l.nct be tumwe1.'ed ;,n thirn :!.a believed to .have ehC~:ro.cterlstics fat'lilita.ting testing of' specific hypotheses about couunity dynamics, •@i HABITAT The salt marshes occurring along the Pacific Coast of N~rth America exhibit both geological and flo~lst1c chaneteristics that separate coastal plain hll.s restricte aooent 011 this coast, 'l'he floras of these marshes a.:ry~ characteti.zed i:Jy r.elll.ti vel:! few 11!:l.b11. no~th of San Fr Tomales :na:r ls 12.6 miles long with an average depth of 10,6 :feet $11,t I!I~~Jan lowE~r low watl!lr (Johru;on, 196.5). The tid ~-gur!ls 2 aultl. 3. Ths 11alke:r .C1·eek salt JWl:lllh .. is located at the lii>Outh of l1alker C:r~elc (lat. 38"12"48H lone, 122°55'30u) practices introoueed by EuropeaM in the mid"'ninetoenth century (Ilaetwyler, 1965). Macdonald (1969) not®d that a characteristic zonation pattern occurs :l.n hcific Coas'fr salt ~aarshcs il'i which the lower Unit of salt mro:sh vegetation CC.:tTesponds 'lfi th the MJ:Jflf, that part of the intert:ldal 1!:0!10 wilieh is e:Jr:f!~;soo at least o!'!ee every 21~ hours. Using this :l.nfoo:'llllll'tion, he divid~:d tidal slltll!lergenees frequently last lol'lger than 6 hounr and are never I J in 'bt1th ~.ar;::hes. Theae creeks usually lie below m.Mll' and not. only lack I veget,ati,;,n (o:lgM> such as ~ and IlL!iJ) ·5- different plant aaseablagea on the man~hes. The sampling areas of MillertOl'l and. lialke.'l:' Crt!ek salt u.rohes 11.1'6 divided ir.to two typesl salt mamh pans and tidal ~eks. Sampling = aroo.s 1 0 2, and 3 at the Millerton marsh and 3. 4, and 5 at lfa.!lter Ct'C'Ilk are ~~~a.rsh parw. The pollds are depres!!lions a.pp:ro~tely J-5 «::111 in depth el.li'T.'Ounded prillil!.:d.ly by ~. The pMs va:ry in dimendon. The largef.lt is a1~Jl'L'Cxiruttely 15 m lang alld 3 11 li:l.d.e while the runv.llf.,st :l.s ----- = 2 111 long and 1. 5 m ll'id.e. Suplir~g etations 4, .5. aril. 6 at Mi:J.le:ct.on and 1 and 2 at Walker Cree!< are tidal creeks which M.:!!ect. the marsh .. liill"~a !l.l:fJ quite tmi:fc;:rm. !~et~suremelits taken Dect>,mlJ IM!!! !i!#J:'ch 19/'2 sh® a VJ.rlat:hm of le~&.s tl~.n i;h:;:ee d~g!:e'IIIJ rt:l!l?it.:tg:rad!l J I · A dai.ly cycle fJi' i:Gl!lp I -6- I ~ 1 Table I, Percentage of i~ot.a.l salt marsh area (excluding tida.l creeks) 1-'-~~~~~~~----'be"'~'-"t.,.w"e~er~l~s~u~ccJ)_~slye_c_Qnt_oJtr_:i.nter ------·------Elevation above MLLli (ft,) li'alker Creek 14:i.l1erton. ------n---~--·__..._,-====:::::.::======:::::: __.__, 4,00 6,0 - 6.5 22,82 .5.0 - .5. 5 4.5 .• 5,0 4,0 - 4.5 1,44 ------·--:--·------/ ·------~-- " ~'otal are::\ of" marsh 1i x 103 110,71 ----~------··------···· Total area o:f:' t:i.da.l c-reeks m2 x J.O 3 7.64 = J il T~bl~ II, Distribution cf marsh pants ~.n the Tomales ll'!l-Y salt m.-'lr.shes (adapted from Ha~donald. 1967). Walker Creek Millerton I!istiehl.i§. SJ<1AAi~ (L.) Green =--- Cotula .Q.Q_ro.ni~:oi19.lil!! L. t . Fr.s.n.O,:en;l..?, ~·nd.i:folia Cham, and Schi. [email protected]:!A sa. 1'1:J.l:IA "'-·l!:,:gea , I ~ !::tl.l'le~ Nutt. Distiehl:!s .§.J~i_ca:t&<, (L,) Green ~d s;.a:~"'nOii.~~ (Less.) Gray Franke!rl.a Ju:. ! ~ornia ~o:!,fie; Standley Grindeli! .$ll!ll ! '. I ) ii.JJ.~rg.v,,rtll!. c.f, lJL;.r:tna \L• G:dseb, L'ill.:!l~ ~~!li!. (Leas,) Gra;y- 1 Trirlo,;;hi.n ;rm.i;i~~:,a L. S~~:Ucor;rl.@. Jiil~ific!\ Standley I 7&ste:rn ~ ~rgulari% r~·, marlna (L.) Griseb, f'r2.1£0loahin !iarlti ma ( L,) Algae Enteromo~ spp, 1!l.'& sp. 1 1 I i I I :· II I 1':: 'IIIII~ I ' I ' I i : 1: I 11!1 I'· H ·Iii; 'I: ·JI· !l"·HI pi. !FIII.llll I Table III. Measurements of su:ti'ace sedi.lllent a!ld water ttm~per.ttures (in °C) i~n the sampling areas of Walker Creek and Millerton, --·-- Walker c-reek Millerto!'l Water Sedime_nt liater_S_ediment Date Station Temp, Temp, StaUcm Temp, Telnp. ------~--... ------...------·-- Deeeltlt't!'.r 16, 1970 1 14.0 13.5 1 14,6 14,0 2 '• 1:3~2 1:3.8 2 14,:3 1,5,0 :3 15,1 15.0 3 13,0 13,8 _,_,_ __~ Octo1;,er 28. "'0'/'1J....- •• 1 .1.),0 15.2 1 14.8 1),0 - 2 14.2 14,0 2 14,8 ).j •.5 - :3 13,8 14,0 3 14,6 1.5,0 4 15.5 15,0 4 15,2 1,5,1 5 15.3 15.0 5 15.5 15.5 6 15,0 15.0 _, ____ --... msr.-- ... ----- ~ "' March 16. 1972 1 ]2,0 12.0 1 n.o J2.1 2 12,8 )2,0 2" 12,0 12.,0 "- "' - :3 12,5 12~8 :3 ll.5 l2,0 - 4 1),,0 1).5 ;~, 13,2 l;J,O <; i1-t,2 ~ l),O 5. 13,0 1.2,8 6 13,1 12,6 ..,_ ...__ ___ ._..... ____ ·----.. -- ... -~,_,....- Fi!!;l.t"l:'!li l. Hap of T"'w.al~.~ MYt ~~~------~------1 N ____j_, ______._L ______...... ~----J--·----·--·-· 1 1•.•.?·>a t:.. ,J;::.·-" I 12~)"Ll.c.Y--~- :::~ li'ig~n~ 2, m. . / / " I I / N , / / / / ! I , !r I I I ~ , I I I I == I I ,I (J I =o I I I! I I I I 1- - - J I - ~ ·-- - 200 '----:-·'--- ft. - ~ = Fi.g"U"t'!S 3 ' })iagr. -12- I -~ \-\ \ \ j \ 2 3 0...___-:-:- _ __::5_90 ft. ------Figura 4, Diar;.;::ilnn.ati.e: l~il'l:fl of Ni:n.,Tt.on salt '"!l.l~Jh uhcwing the distrl.bu Uon of d:i.:fftn:'<'lnt· plant aesemblages (Macdonald. 1967), Horlzont.al hatc•hill.g"' !i"E!>!!:!:l'J'~J.l!< :ntii~,'I.;[Ul assemblagl'!l t o bl:i.q ue imtchi nr,~i:~;j,J~l9.~2,:!!/I4w~>:~.:Oi1-!!11 :!:'lor~~., -13- I - ~ 0 __200 _. ft. _ .. ______, __ j. I \ \ 0 _..500 ft. - Figure 6. · Wate:e· ~JJl upper sun"lt.:r;:t~'e ti!l!llpersture!l\ takcm at 'l!a.lker t'xaek. Stai!;i<:~n 3, o?; !l 0 0. 0 0 0 0 0 0 0 0 [') ...... U1 L -- s.: - ~- (j) -- 0 0 E 1- 0 0 0 0 0 0 0 0 ()) t------~~-----·~ l- 0 0 0 C\l ..... C\l Jo l .J8:j.OM ll'icy::~e ?\ llate:::: tempOXIi'.tt11.'@~1 'Gake!l at. tlalker C:t'eek (") am Millerton (o)---~alt }iitt:C~h.~t; em t~:tt.m}.-;li~g fu'\~es from J&.nuaey, l97l to Apx:·1lt 19721; l'lea.suroa;uent!l tc the rlt'. Fi{;la:!':e 8. Av®:t'agc !i!Ol\th:t::i air ttll!lp,p.rntures (~ "" Wk"dmtll!l li.ve:ragi!ll Gil "' $l.W~x:r·t~ge~ V &.i idY~lWrut:i, if.\V~t'f'r.i!?~f5(11) 1Je';;.~"ti:\'lt'ii~:J. J.(;~tu~:.c.;r 19·7.1 ~:v;li t~y .1972 ([email protected]$~~f~ ~·i th ( ""'·-) ·i;.hc.~ :ftti.tl~"'Y~Mt.r Yi.~iil'ilhly ~~~n air ternpe:ra;t.·ur~., ~te fz.. e:a~t rt'aci:t'"i.. ~ Na:rine 5tat:tfln0 Dillon Il61J..::h, Cali:!:"o:mi<~-. -1?- 2 <{ 2~ (J)...... LL - -~ 0 0 z . 0 ; • j Vl I i' <{ ) r:::: CJ) ) ...... 2 0 j-, L.-·-'---, .,.!- --L------l-'._'- -- 0 0 0 0 0 (', <( e LL 1------'"""'-.....~ .z 4111-0 I tf) r <( - ! <( _... L.-- ..- --1 ~ (\J ( 'LII) IIDJ.U[D?::J After a. pt'l!lluina:ey sampling s\lrlfey in llecemoor 19'70, changes in the abundance of I!!~ in the salt ~hes were stud1.!!!d 'by periodic = supling cf selooted study areas chosen as chu"aeteristlc habitats of the snails, In thu itdtial stages of the sampling prog.ra.~t~~ three study u·ea.s I Samples were taken 'IIith a eo:d.ng deviee !llll.de cr.f pol,yrley1 ohlortde pipe that watt 10,16 ell! in diruneter am l2 em long. Rend0111 mel!l!pUng GENERAL BIOireY ~~ ~ (B:ruguiere) • a style-bearing aesogastropod, is the only rep:r.esentat:!. ve of the genus foU!Xl on the California coast of North America. J:t is the most C011Spieuous mem bcr o:f the epi:f'a.Ul'la at the lii! Creek a.nd the Millerton salt maxshes and is presently krumn to occur from ~------':;::::: :::::ht:o::::_::::::t:;:;:;_::::::::~~::::~-96-o-')_. __ ~ probably !nt:r.cdueed into 'l'omales Ba:ll' as ea.rly as 19.28 when 'the first expt.r imel'ltal .sots of ~,!l~l~~ ~were pll!.ntw in the bay. However, Bo;met (1935) S1U"Veyi11g a sb.1.p.ment o:f. oyst~:U' spat at Elkho:L'n Slough :l.n ~lost e;,f tb"' 1s·tu.d:i.e1.~ r.lAM.ling ~ith .~t..:lJ.li:ll;i:i are conom.'Tied Hith taxc:mr;my - ( I.l.sehke) ~!hile cOMidel.'able att.~mti<.m !'.as beer1 paid to ecological studie?> o:f' ee:ttai.r, other Pa.rxtf:i.e e..w. for a. re·llie.w) • ~.tiJl;},;da l'-.as rece:l.ved little stv.tly although it i.s vm:;; gatiol".t> em the i1tpG()ies are Aoo•t~ (1936) etholog.i.eal study of a. Japallese popuJ.aUmt a:.'ld H;;cedo1m.ld 9 s (1.967) ;..;m~ve'y of populat:l.ans in several sa.lt GENERAL DISTRIBUI'ION OF llATII!J,ii.~JlL\ ~~ AT WA!K!'Jl CREEK AND MILLERTON SA:Ll' ~!ARSHES In a general su:rvey of Walker Cl:reelt and Millertou ;::alt marshes in Detlember 1970, the distribution of llatiJlmA was found to coineid.e with the lower limit" af the salt marsh vegetation, The a'bl!nda.nce of the srmil g:t'eatly dimin:ished above MliHii, of lw.bitats on both salt m:l."shes in 01.'\i.er to obtain an idM. of the gona:r.al tl.istrl bution of ~. The areas sanrpled were d_:l vldl!ld as follows 1 A. YJ<:.rsh pc)OOS -- depressloxts on the nwrsh covered by wa;ter on lim outgoing tide, B. 'l'id.l!.l oreeks ~~ creek."! bisecting the sur.tlwe of the Ina:t Fift;r :r.ar,tk>m corfm Jfe:t'® t.a.kf•!l in eac:h of the subd.i~.. clcns at both salt !'>l!l.l'.":>hes. The I'< t.requ~m:y index (the proportion of t.he total sample11 col1eetoo :tn wh:l.eh the spoc:!.oo we-re present) a,nd in tem.<: of :l."elati ve a bti!tdance. The It tla!l be coMluded. i'l'om Figure 10 that the abun.:hmees and frequency indiee«.> of lill.:!JJ.lm~. :foll.ow s>o co!'IS:istant pattern at both salt ma:r.ehes, The e;:reatest snail densitiel! were fmrE' Probably the ujor factor effectil'lg the distribution of~ at both salt lllM'Shes is exposure. !n the u.rsh ponds, the snails ua covered by a thin layer of water even on an ebb tide, and in the tidal creEks the snails are normally covered by water at least onoe every l2 hours, The vegetation zones, hO!fever, are characterized b.r shorter periods of sui:aergenee and longer periods of exposure ( Cha:pi~mn 1 196o), Another factor effecting the distrlbut! on of. the snail 'f!!!il:Y oo the nay congregate in areas with favorable nutritional characteristics, pcll!slbly areas cO!ldt!.eive to J.arge 'banthie diatom popUlations, It has ooen observed that llatil::L~ feeds ol".ly whe..'l it :l.s covered by nater and will withdraw into its shell when exposed, Figure 10. Histo~ shwing the :frequent:',/ irdices and relAtive densit:j.cs o:f Jk!,.ll,)J,";;DA ~c~1~ at di:fferent salt Jl1l.:t'Sh habitats t;t Walker Crt;ek and Millerton, oo.ta collect~ December • 1970. !lelatlw densities based upon 10,16 em cor~. -2)- . CREEKS l r r,'_~·· :------•---M-U_D___ F_L_A_T __ ~. '' ("' ·~------~"L------______, SALICORNIA Millerton K+ .. - -~~ r--! fi...... ,.-,...,.,.~~. ..,.,1 ... ·.·-... ·. PONDS .!' ~ j___ CF MUD-F=-LAT ------11-·------ll----·-·-- SAUCORNIA ~-----·-- ---' ,______. __ • .-J 1 0 10 ° F--requency Abundance DISPERSION The spatial dispeJ:sion, the decrl.ption of the pattern of d:!.st.rlbu tion of animals in space, is thaught to have ecological significance, Since the pattern of spatial dispersion of a partictdar speeies will affect the frequency distrlb.ttions of num'OOrs .in samples, analysis of dispersion r.IEJ.Y' also suggest e.lte:cmtive methoos for analyzing sa.mple data, The1.-e are three general patterns of spatial dispersion for a ~Sing._.l::_e__ _ species populationa 1. FandOlll--the probability of occurrence of an organism is equal at aey point in an area, and the poeition of other organiSllls of ths same species doss not affect the position of tha.t individual. 2. J.gg!'&{',"ated or contagious--the probability of an orgal'lism ooeul'Ting at tl'tf:Y poin!G is var:table, and. the o:;:ganisr4B t~oo to ooou:r. in clumps. This mey oocu:r if indi·l:!.dmlls ars r.ttraeted to ea.eh e-Ither or if T\l!SI.l~IX'(:O~S .are patchily dist:d but.f.de and the organisms tend to congreg&te in a;roo:s r.•f lrl.gh :resource availab.'l.Uty. :3, Even or nega:tively contagioW!l~~the probt> bility of an org:r;.l'liZll! <'!Ccurrlng at e.ey point S.s varlll.ble, and the organialW tend to be over·"{U.Sp!IXIS This type of !tlt~pe:rn:.on occurs i:n sagebrush where ohem1.oal. seereticms i'rw. the roots of pJ,t;;nts repel other plants (!1uller. ~ f\1,, 1965), The Pc.isson dist:dbution !ms ~n used to test the dev.l.at.io-n of samplirt..g data from t.he :!:'<>ndCI!ll C1M!~ s1r1ee t.h® varlanee in this d1s'cl'i 'bution ls eq_u."'l to the !llean. Agg:regated. ox elumpoo t:'J.zt:ribut:lcms have varlance-to.. mean ratios in elttless of unity1 while eV@l'lly dist:dootoo organisms have ratios less: t.han one. Green ( 1966) hll£ X'tlVlewoo a num l>s:r. o±' tho moo.sures fxf non~:ml".J.omnfA>S :l.rt spatial dt:;rt:d.b.:Uoru; ani!. bas po:!.nt~ out tlmt m"'!l7 of totaln1ll'l.ber of imivid.ualrs sampl Evans (1954) have shown that the variancrto-~~~ea.n ratio increases with increased SIIJi!ple size, Green (1966) proposes a new measure that has none of the aforanentioned defects and is eas;r to calculate for large l!.lllowrts of data. Applications of ·this coefficient to the data cf Jl§.t11}Wa (Tables IV and V) at both salt l!lll.nlhes shau consistent aggregation at Walker Cree.'< and oeea.s:l.oMl aggrag&tion at-Millerton,- Si\\iUarresu:rts are expressed using the var:!.an~e-to'"ll!ean ratios (Tables 'II and VII). A number of dist:rlbutions which describe contagion are available to the eXperimenter. It must be remembered that these models are useful onl:1 in that they provide measures of aggregation a;ld changes in aggregation, Southwood (1967) has pointed out that it is "unst:n:md to attempt to analy:r.e t.he det.... ns of the biol<>gieal proo!!sses involv~o.>d in genera.t1ng a distrl.o 'bi.!ticm from the JMi.thematiea.l mooel(s)". He e"Jneluded. that in l!'i.ost t:t>see the biologi.cal significance of the p!t:l:'ll.lllete:m of various distrlb>;tions is unclea..r. Various matheJ'Illl.tical models of aggregation have been l'oeviewed by Aru;eMO!! (1950) and Evans (1953), l'hese inel~.d(l the ThoraaH, Neym&n types A, B0 and c. and tho l'olya•Aeppll distrlbutions. One of 'the most oor,lmon·= l.r usoo ll!athema:!;ieal !llcdels is exp-.:•essed by the !legative b:l.m>lnial distrl· bution (BUss and Fisher. 1953). Many contagious iMeet :populations ~:;twlled. have b~>en exp:<>essro by th<> negative 'M.noru.al. dist:r.ibut;:l.on (Bliss and Owen. 19581 Harco11rt, 1965). Obreooki (1968) has fitted thin diat:cl but:!.cm to popt!l~tio!lll of the bivalve. :.\:m~ti,lJJJ, ~. and the 8Jllphi:pOO.• .l!19llllfZ~. !!Jl:Il.bj,l'l~E.I.'IJL~•• ~'h'IJ orlg:irJr41 anrl simplest. solution (Fisher. 191H) for esM.m:1.t:!.r,g t.h<.~ lt is eltpressed as1 The variance of k tor this estimate is given b.T• . s2 ,. (m + F.h/k The mathematical properties of the negative binomial distribution are sueh that as k approaches infinity and p approaches zero (p"" m/k) 0 the variance and. mean equal unity, and the distrlbuUon conve:t'ges to the Poisson distrt- f-----·mt-t<~n-;-Ir-ICbooomes zero0 the nee;a,tlve-Dinom1al-di~rtbution converges to a logarlthlllie ae:cies (li'ishe:r0 ~ aJ,. 1 1943). Small values of k, therefore, indicate aggregation. Bliss and Fisher (1953) describe goodness of fit tests to the negative binomial distribution provided by Anseombe (19.50) 'based on the .second and third mOl\lents of the d5.strl1:mtion. Eva.ns ( 19 53) provides a chart for most accurate 1:or v·,Jrtous Gombinations of' the mean a11d the k estimate. q>he results o:f the est:l.J!V:ttes of the neg/Zi;l~i ve 'blnomia.l para.meter k and the goodness of fit for Bgtil~a are presented in Appendix A. All the dates :for the sampling stations ttt Walker Oraek fit the distri bution, Of the sampling stations at Millerton, however, Station 1 is the only locality that ecooiflten:tl;r fits the distrlbuUon; the trthe:r.:s Es'ti.1nates of the :tmrruneter li: using the lll!l.rlmv.m l:lkelihood method dese:rctlr of the mow>nt estimates, Since the ma:dmtlli! ll.kelihood estimate :l.s very 1aborioruJ to calculate. only ome sample locality at each r.tarsh rms estimated, most cases. Ancoombe (19.50) has shown that the ef±'iciency of the moment solution varles £or. d.if'!erent combinations of s!IJIIple density and k, Anscombe (1950) a~.JII~t.el:s and Henson (1959) have concluded that the negative binordai dist:i:ibtft:l:on can arise in at least four different I~ situa.tionsa (1) In populat.ion."i: with constant birth, death and immigra tion rates; (2) ln contagion where the occurrence of one individual or event increases the probability that another ir.dividual or event will. occur1 (:3) in heterogeneous Poisson sampU1;g where the mean of a Poisson dist11.- sampling where if a proportion of' individuals in a population po..".lsess a certain cha.racter, the num 1>-::.1' of samples in excess of k, th&t must be taken to obtain k ind.ividua.ls with this character will have a negative binomial distrlbutiori where the number of oolol'lies of o:rg3llisw.s are distributed as a. Poisson distdbution, but the ntmlbe:r of 1ndivi.du.als per colony follows a logarlthlliic sarles. Of the poss:ihle explanation underlying the negative binor~ial distribu= tion oi' ~•t;Ula:d.i:!.t (4) does not apJ,JlYt and (1) cannot be tested with the available infonnation on the species. An explanation of why ~'l,tillari,i exhibits contagion may be rela·ted to the second situation, Information oollcoted ~-n August, 1971, on the spatial distribution of benthic diatom population.'S shO'..rP.'J.. that the spooies were very patchily d:l.stri buted within Lloyd (1967) suggests that a new measure of a.ggregat.ion called "m•mn population a'bu1'lilance, · Two criteria muet be :fulfilled before estimates of crowding and patchiness are appl:!.ed1 (l) the a~ls must live in a. .. relatively continuous habitat, and (2) the orgru1isms must be :(:ree- :::;= r.toving al'ld non-territorial, . Both of these apply to populations of Baiillaria (see Population Abundanee section}, Lloyd (1967) postulates that each anilllal bas a typical area that it moves ino called the ambit o:f the individual, The nllllloor of other am;nalll particular individual, Lloyd defines the pa:ra!ileter "mean crowding" ]XItchiness (mean c'W!I:d.ing/llioon dens:!. t!") taeasm:e.."l hco.J many times as c:rowdoo .on the e,verage an individ'Ul).l is as it would r:.,. if the papulation were distributed :m11domly, The negative binomial P<•=et0r Jc o1;ta:1.M biologl Ca.l meaning H' the underlying distribution of abundance :i.s negative binOlld.al, Lloyd shows that "mean crowding", (m)* "' m 4· m/k and. patelll.ness. (m/m)* = 1 + 1/k, Lloyd ( 1967) hypothesizes tlmt one C'.ll\!l ll.'.le his estima:tes of mean populat:l.mm wtthout studying the h!divid'Ul).l tmteh:JS separ;1te:ty, If• fo:r e:r.ample, an inex·ea,..;e in the mean dem;ity caused 'by a dens:!. ty-independent :pntchea of locally high and low densities, 'l~herefore, mean de:Mity and mean crowding will increase but patchi1wss (pt1.tchiness in this ca.sa is t.ha ratio. (tl; + 1) /r.1 9 since the llldiv.l.d:.ml baing et~ooidered w&.s left out in rlef:l.lling llle* but wall included in the calculation of m) • whieh is tile rat:!.o changes in patchiness to be associated with demity-i!Ylapendent mortality and nata.llty. If mcrtallty is (ler.sity-dependent ( eg, heavier in patches of high density when c011pared to patches of low deMity), 111* willdecrease more than m, and patchiness will decrease. If1 on the other ham, there is a deMit)'-dependent increase in numbers, and the ine:r.easl!lS are depressed ~-----!-n-:pa.-tches-c:f'-l'-~gh-deraai-ty.-t-hen---m-n--1-11--incre~u~n.=!-:tess----th.an-m~-Lloyd* states that in this case it is il!lpossi bla to determine which direetion patchiness will change, In most cases. however, one does not have density co:nto~US o:f' entire populations, but merely two independent sets of random C..a!i!ples taken at d.ift~ent ti~tes, I,:toyu (1967. yaga 22, fl'igure 8) gives a figure and the opex:ation of' densi ty~governing factors are ooelll.'rlng, If'• on the o-ther hand~ x- dec:t'ea.Ses as *x .inerea.ses0 centrlpet {aggra,gaticm or ecntaglon) acr:o.flll:.an:l.ed by detlSit:y""iiisturbing factors are Eatil!;lltes of "ll~::asl crowding'' and :p,.'!.tch.tnsss with thei:r stantlA:r. a:T.'O p:eest~nted in Appendix B where k is ol.Jt.ainei.l using the lll0!110l:rt esti~;ates, CO!llp.!!.risons of clmnges in pateh:tn.ess wl th ret~pect t~:~ ch~ in relative incr~~.e!.'\ in most o:f' the !!larnpl:l.ng looaliUcs, Acconiing to Lloyil.0 s models. t!l.ts r«sult. indicates eelt'•rifug,'tl ~lfJ\'I'l!ll®l't~ (disperz.al) alld op!li' the kt,i]Jerla populations and clearly aore dl!l.ta on the. ecology of the species is neceesar,y to arrive at a testable interpretation of the rooults. '"' - Lloyd's models relatiDg clwlges. in .patchiness and. crowding with ~ density attempt to attribute biological meaning to statistics describing dispersion. The major problem with this aodel is that in the absence of add:l.tional.informa.tion about the population 'being stlXiied, ecnellll!ions 1nesa and abundance cannot be derived. Obrebsid (personal_commun:l.ca. tion) points out that Lloyd does not consider the effects of size of the organiau in his model. A pOpulation made up of' a :fl'!llf large organisms lllay ' be more crotlded than one COlllposed of man;y .S!Iialler animals. In single l speeies populations containing difi'erent-sized organi.SJIIS (as aost do), · ubits anil.. the effects o:£ crowding will depend. on particular eon..+"igun~tions jI ·of size distribution. Thus, sDller ani!llall'l could be more "crowded~ if they occur with larger ai:ti.mals than with the same number of s.imilar-sized individuals. In such instances relations between patchine.'ls and abun:lance. changes in particular size (age) groups could be of use in interpreting population changes using Lloyd8s statistics. At this point appropriate models have not been developed. Table IV. ex; a coefi1cient ot aggregation. Vallter Criaek. Station 1 Station 2 Station 3 S·,t.ationI 4 Station S - Date A B A B A B A I B A B 1-19-71 0.03'736 o.o1279 0.02140 0.00797 o.03212 0.00234 2- 3-71 0.01439 0,00967 o.o13;6 o.oo610 0.02238 0,00271 2-16-71 0.02793 0,01866 0.02793 0.00912 0.00553 0,00335 3- .5-71 0,011~12 0.01166 0,03354 0,00675 0,00703 0.00290 3-1'7-'71 o.Ol566 0,01057 0,03483 0,00755 0,00296 0,00322 ~~ 8-11 0.01'(06 0,00728 o.o14l8 0,00678 0,00767 0.00342 4-21-71 0.01805 0.01032 0,02,566 0.00376 0,00765 0,00208 5'0 21-71 0,03.536 0,00?21 0,02.576 0,00667 .0.01053 0,00327 I ~ 6= 9-71 0,01134 o.oo505 0,0:3106 0,00228 o.o16B1 0,00280 ... I I 6-25.,.71 0,02616 0.00442 0,02626 o.ooz46 0,00812 0,00308 I 7• 9-71 0.03388 0,00661 0,03383 0,00386 0,00848 0,00386 ! 7-23-71 0.15501. 0,00534 0,09423 0.00394 0,00730 0,00334 - I 9-:n-n 0,04610 0,02689 0,05874 0,01249 0,018!18 0.00711 0,0~36 0,01429 0,03200 0,01866 10- 5-(1 0.24667 0,22662 0.04701 o.oo649 0.0.5114 o.oo478 o.o28i68 o.ou66 0.03984 0,00872 ___ .,.. ___ ..., 11-15-71 ------______o.07875 o.oo617 0.0186.5 0.00372 o,o48J,~6 o.oo6lo 0.018?2 o.oo:ns 1- 7~?2 0.26464 O,Olll19 0.06254 0,00_518 0,05168 0.00598 0.02677 0,00209 J~ 8-?2 ------<>!!>-- 0.06140 0,01175 0.01.519 0,00770 o.o22;59 0.02223 0.01496 0.010?2 4-21-?2 ------_.. _____ 0,19523 0.01079 0,04167 o.oo64? o.o22;38 0.1)0271 0,00553 0,003:35 6-16-72 ------o.o1681 o.oozao 0,01805 0.01032 o.o:31p6 o.oo228 0,01848 o.oo711 2 s /m - 1 A C . .. x "' l',x-1 B • upper value for rt>.lldomness at a • 0.05 given b,y Green (1966) b,y thll :ri~lation r 2 . ~-a (N - 1 d.t.) C .. N-1 ~-a Nm - 1 liiilllllllml·l 1 11 · . 1111 1111 ll'i'l . ;I .. 1 ··~ ! l.::r ·"llll_ !1-111 ;Ill "" I i I Table v. ex' a coefficient of aggregation. Millert•~n I Station 1 Station 2 Station 3 :~tation 4 Station 5 Date A :a A B A B AI B A B 1-14-71 0.02605 0,00814 0.01094 0.00570 o.033B4 0,00938 2- 6-71 0.02255 o.oo338 0,00450 o.oo606 o.oo504 0.00290 2-l?-71 0.019:32 0,00270 o.oo,56B 0,00583 0,00}52 0,00474 :3- 6-71 0.01734 o.oo302 o.oo596 0,00096 0,00242 0,00266 J-19-71 0,01068 0,00285 0,00831 0,00669 0,03871 0,00785 4- 9-71 0,01220 0,00398 0,00163 0,00785 0,00155 0,01229 4-21-71 o.o321J8 0,00419 0,001}74 0.01017 0,01030 0,00973 5-21-71 0.07854 0,00610 0,00512 0,00998 0,00666 0.01175 0,00620 ~ 6-10-71 0,11474 0.,00622 0,00497 0,00866 0,00958 I 6-21~-71 0,04850 0.00793 0,01357 0,01416 0,01070 0,01024 ?- 8-71 0,06417 0,00906 0,00888 0,03237 0,01086 0,22664 I ?-22-71 0,02666 0,00801 0,13666 0,06610 0,02182 0,07211 I · ..,. 9-19-71 0,01832 0,00886 0,01618 0,04666 0,01246 0,()2614 o,o1i~74 0.01636 ... 0,02794 0.01072 10-10-71 0,01950 0,00443 0,04198 0,01496 0,02294 0,00778 0,0!1,;()6 0,01290 : 0.05724 0,01289 11-16-71 0,07048 0,00404 0,05699 0,00973 0,00876 0,00782 0,06'182 0,01588 0,13279 0,00805 1- 5-72 0,08816 0,00423 0,02264 0.01666 0,01824 0.01072 0,021786 0,01133 0,03108 0,01010 3- 7-72 0,02027 0,00435 0,00724 0.02993 o,Ol385 o.oo872 0,01131+5 0,00125 0,04170 0,01934 4-20-?2 0,02780 0,01125 0,03693 0,02087 0,00433 0,01249 o,o:ta25 0,01424 0,02469 0,032:37 6-15-72 0.04850 0,00793 0,1)666 o.o6610 0,02182 0,0?210 0.01!3.56 0,01412 0,00474 0.01023 ,...._.....__ 1 I A•C"' tli-m I X ~X- 1 I. I B • XZ upper value for randO:nness at a • 0,05 given by Green (1966) by the ¥·elation ~-a (N - 1 d,f,) N-J. c .. Nm-1 ~-a ll'illl 'IIIIIIWII ii I'll 1111 I' I ' 1'1'1:" 11111'111 ,,, ''I -:n- Table VI, Variance/mean ratios, Walker Oreelt, ~ ~- --- Date Station 1 Station 2 Station 3 Station 4 Station 5 ~ -- 1-19-71 5.67 5.28 22,81 2- 3-71 ).36 4.12 14,05 2•16-71 2.72 5.86 3.62 ~ 3- 5-71 2.92 8.75 4,84 3•17•71 3.35 8,35 2,46 4- 8-71 4,?2 4,32 4.56 4-21-71 3.78 6,83 6,84 5-21•71 8.78 11,83 6,11 . 6-9-71 4.56 22,62 10.50 21~,13. 6...zs-n 10,39 5.18 - . 7- 9-71 9,10 17.34 4.48 7-23-71 4?.04 24.95 4.47 9-21-71 3.72 8,46 5.12 10,42 3.72 10- 8-71 2.48 8,24 17.98 4.90 6,43 11-15-71 ----- 37.52 20.15 14,67 21,24 1- 7-72 :n.52 81,?8 13,6o 14.80 ~ ------3- 8-72 ----- 9.29 4.13 2.37 3,20 ~ ., ___ 4•21-72 .. 29.70 11,21 3.81 2.53 6-16-72 ----- 9.11 1?.34 5.21 4,84 - A test of significance of deviation from unity given ~ Lloyd (1967) asa -?- -C (q-1} l·rx with (q-1) d,f. Table VII, Variance/111ean ratios, Millerton, ~ ~ -- ~ ~ Date Stat10l'l 1 Station 2 Station 3 Station 4 Station 5 Stat1on6 "- 1•14-71 6,08 4,04 6,72 2- 6·11 ll,6o 2,18 3.76 2-178 ?1 9.9:3 2 • .54 2.50 =- - 3- 6-71 10,12 2,17 2,44 3-18-71 6,94 2.97 8,)2 4- 9-71 4,87 1.:33* 1•20* 4-21-71 13,28 1,74* 2,68 5-21-71 21.42 0,82* 1,90 -- 6-10-71 :30.26 1.89 2.3:3 6-24-71 10.70 2.52 2,66 - 7- 8-71 12,23 J,64 1.76 7·22-71 6,28 4,28 1,48* 9-18-71 4,28 1,55* 1,96 2.71 3.11 1,08* 10-10•71 1.96 5.44 5.68 6,13 8,04 2,86 11-16-11 28 •. 70 10,29 2.78 9.1;,7 27.16 7.8? 1- 5-12 YJ-,06 4,07 3.70 4,90 5.88 9.91 "'~ ~ 3- 1-12 8,')8 1,00* 3.52 2,52 4,42 1 • .58 --- - 4-20-72 4,92 '),80 1.55* 2,26 2,21 4.94 4,10 6-15=72 ?.62 3.76 . i .76 1,02* 1.58 A test of significance of deviation :f"rom t.tnity given by Lloyd (1967) 2 hi x2 ~ {q-1) s /i with (q~l) d,f, *Values n l.J.. 0 L() cd 0 ~. -- <( LL <\J X/X ~ Figilre 12, Estimat.es of patchiness '!: 2 standard erro...-s fer l3at:l.llaria. between Febl."'..P..ry, 1971, and June, 19'72 1 Station 2, Walker Creek, 1 <( _I.L ____ 0 0 <( LL lO~------~------~------·-L------~------~ C0 N X/X "' ;=;= R"'= - -- II! I I i ~ ~ •~ Figure 13, Eztimaites o~ patchiness !2 standard e:rrors for Bati41arla j between February, il971 and June, 1972, Station 3. Walker Creek, ~ i I <( LL 1------c______~ -~------~--[----'=---- 0 0 <( -+- ---- J ~ I' ~ {j)...- ~ ...... - , --~ --!-- <( --!-- _..._--- -+- LL lO (\J X/X "' GROWTH CClllpa.ritlons of the a:nrwal growth rates of Batilj.aria. were studied to detemine if' gro-.rth :rates differed at the two salt ma.rshes, Wilbur and Owen (1967) ha.ve reviewed the lllethods far measuring growth in aolluscs. The three procedures eOJmllonly applicable to gast:rcpod popula• tiollS are (1) measuring the distances between successive annuli on t.he opercullllll ax counting shell annuli, (2) mrking aeasured individual animals i------c---c--~~------c---··------and rgea.surtng at subsequent intervals, (3) following shifts in sUe• frequency modes corresponding to different age groups per unit time, Since Batilla.rta. exhib1 ts no annuli on the shell r:r opercu1Ull1 the latter two methods were used., Shifts in the M¢es of Size-tngyeney Distrtbut~ Figures 14-24 illustrate the size-frequency distributions of ~tilla:rla, for the different aampling stations at Walker Creek IU'A Miller- ton marshes. The data follw the usual polyllloda.l distribution.<; eh.araeter- istie of animal populations :made up of several distinct age-groups, At Stations 4 and. 6 at Walker Creek and Station 3 at Millerton in May-June, juveniles form a well•defined mode at about 0,3 u, the first year anillla.ls at 0,7 a, and the second year indivldua.ls at 1,) llll!t, Thi:rd and fourth year animals were insufficient :l.n nlllllbe:r to give rtse to distinguishable modes, When the animals reach aoout 20 u, the age- groups merge into a single, generally normal distribution due to a decline in the growth rate, By plotting the shifts :l.n the lllodes of the size~frequenc-.f distri butions for both marshes at one year {Lt) e.gain. butions in the next year (Lt+l), a straight line is prcdueed from which the !mean annual growth of an a.rd:mal of aey given size is est:l.mated. (Figure 25). This is the well-known Ford-Walford plot. dieclll'lsed. by Hancock -39- (1965) al'lli is described by the equation I Lt+l • Lt (1 • e•k) + Lae·k p= where Lt • length at tue t, Lt+l • length 1 year later, La • theo:zoetieal I maximum size to which the animal can grow, represented by the intercept I of the Ford-Wal:fo:rd plot with the 45' line, k • a constant which des cribes the rate at which the growth rate of the~ animal decreases with age, e .. the base of natural logarithms. The equation was estimated as ---- by linear regression analysis of the data. The theoretical maximum size of 42.:3 mm given by the regression equation is a little greater than the IIIBXilllum recorded length o:f :36.8 u. Knight (1968) hae shwn that limH.ed. illportance .should be attached to the La values :f'rO.!ll. the equation and suggesta that La should probably be called "average maximum siu". Values of Lt and Lt+l for the two .marshes show no sigr.ifieant differences in the growth rate for the two populations of PgtUJ,eria. when an analysis of covariance was applied to the data. In May 1971 appro:x:l.mately 800 snails at each marsh were marked w1 th adhesive tags covered by epOxY resin. The snails were returned to their \ respective looa.lities. Eight individuals at Millerton am two ind1v:l.dual3 at Walker Creek were recovered in May 1972. The shell lengths at the initial time of marking (Lt) are plotted against the lengths at the time of' recapture (Lt+l) in Figure 25. Comparisons of the Ford•lifal:rord plots in .F'igu:t"e 2.5 ehmr no significant differences in the growth rates o:f lll3.rked ani.ma.ls with the growth rates of tha snifts in the modes of the size~irequeney distributions, Both methc$; of' estimating the annual growth rate o:f' Ba,tillarta. give similar results, suggesting that the Fo:rd•lial.fozd equation give:l!l a fairly true estimate of growth rate for the snail. Based on the assump tio~ that the young settle at l u 1 FigUre 26 shows a c:~onventional growth curve where shell-length obtained fi'Olll the Fo:rd-lialfozd equation is plotted against age in years. Figuxtl 14. Size""frequeney distributions of J3atil.laria Station l, Walker Creek. 0 WALKER CREEK -1 20 ·. 14-1-71 19-IV-71 24-VI-71 10 ! ~20 I ;f. 16-11-71 21-V-71 '23-VII-71 ~ ;, u c: 10 20{ 16-111-71 9-VI-71 21-IX-71 ,r'l 10 L 10 20 30 10 20. 3d 10 20 30 Shell-length (mm) , I' 1 1111 1r i1111m1··1 1 11 ill , I I. I''i 1"'1''1"'I "'1"1'1fill I ' ''I' F:l.gure 1.5. Size~:f~ueney distributions of ~t.illariae Station 2, Walker Creek, WALKER CREEK. :2 14-1-71 15-XI-71 I 1- 10 1-- ' ;:_ 20 16-11-71 :24-VI-71 7-1-72 1 r I, ~ 16-111-71 :23-VII-71 8-111-72 ' 20r ~ 10r ~ c «J :J 0" GJ L. LL 20 19-IV-71 21-IX-71 21-IV-72 10 20 21-V-71 11-X-71 16-;Vi-72 10 ' 30 20 30 Shell-length (mm) :li"-gur~' 16. Size·frequ~m:y dist:ributlo:r.s of BIJ,tilJilr!a, Station 3, Walker Creek. ~-- -1;)- WALKER CREEK-3 20 14-1-71 9-Vl-71 15..XJ-71 10 - - ~- ~- - c 20 16-11-71 24-Vl-71 7 10 ! ,_, nl ~--- I IJHffll [1111 Ill hw, ---1~111/.IIIL ~ t 20 I' 16-1:1-71 ~ 23-VII-71 8-111-72 i 10 ~ ~ •--'! II "'lJ ::>" 0"" '-" I "- [ 20 19-IV-71 21-IX-71 20-IV-72 10 20 21-V-71 11-X-71 16-Vl-72 = 10 20 30 10 20 30 Shell-length (mm) 10 20 30 F1g\n:e 17, Size-frequency distributions of' Ba.tilla.rls. Station 4, Walker Creek, ' . -~--...,;;------44- WALKER CREEK-4 20 21.:rx-71 7-1-72 10 • ~0 .e., 11-X-71 8-111-72 >. u c <1.> 5-10 Q). L LL 20 15-XI-71 16-VI-72 10 10 20 30 10 20 30 Shell-length (mm) Figure 18.; Size-frequency distributions of Bat.illaJ:i!J,, Station 5, Walker Creek. WALKER CREEK-5 I I 20 21-IX-71 10 ...... 20 ...... -!- 11-X-71 8-111-72 >. u c (J) 10 ::J 0" Q) l.... lL 20 15-XI-71 16-V.I-72 10 10 20 30 10 20 30 Shell-length (mm) Figure 19, ·. Size•frequeney distributions of Batillari!j,, Station 1, Millerton. MILLERTON- t 20 18-1-71 10.VI-71 16--XI-71 1 20 17-11-71 25-VI-71 5-1-72 ]Ill_ 18-111-71 22-VII-71 7-111-72 :lk.. 20 21-IV-71 19-IX-71 20-IV-72 10 20 21-V-71 10-X-71 15-VI-72 10 30 20 30 20 30 20 Shell-length (mm) ; 1· Figure 20, Size•frequ 20 18-1-71 10-VI-71 ·16-XI-71 10 20r 17-11-71 ·-T·A 25-VI-71 f____ m~5-1--72 4 • 0 ~~~ 20 [ 22-VII-71 7-111-72 10 20 , 21-IV-71 19-IX-71 20-IV-72 10 20 21-V-71 107<-71 15-VI-72 W..U.LLL1JJ.LJ::U.WCU,U.D.~ 20 30 10 20 30 10 20 30 Shell-length (mm) Figo.l:."a 21. Siza~frequency dis-tributions of Jl;,j,tillari!h Station 3. Millerton, .------:---:=-.. --- MILLERTON-3 18-1-71 6NI-71 16-XI-71 -=;- 25-VI-71 5-1-72 ~20 t 18-111-71 22-VII-71 7-111-72 »u "~10 <1> .... --- u. ~ 20 21-IV-71 19-IX-71 20-IV-72 10 20 21-V-71 10-X-71 15-VI-72 10 20 30 30 30 Shell-length (mm) ;:::::_ ~gure 22, Size-frequency distributions of Batillaris• Station 4, Millerton, MILLERTON-4 20 19-IX-71 7-111-72 10 2G• ·- -·-n "- I. 10-X-71 [20-'V-72 -- 10 ~~_.....rf t- >, cu (J ::Jcr 20 ilJ 16-XI-71 15-VI-72 L LL. - 10 20 5-1-72 10 10 20 30 Shell-length (mm) Figure 23. · Size-frequency distributions of lla.tlllarla,0 Station 5, Millerton. -.50- MILLERTON -5 20 7-111-72 10 i n • 20 10-X-71 20-IV-72 10 ~ ~ . n, . 0 nnf n., ~ nM » u c:: Cli ::l g 20 tt 16-XI-71 '15-VI.:/2 10 20 5-1-72 10 10 20 30 Shell-length (mm) Figure J?.~t,ii Size~frequeney distributions o:f' Eatilll!.ria0 Station 6 0 j Millerton. ------ -51- MILLERTON-6 20 18-IX-71 7-111-72 10 20 10-X-71 20-IV-72 10 16-XI-71 15-VI-72 10 20 5-1-72 10 L----~·~~~~~ 10 20 30 10 20 30 Shell-length (mm) ~~- ~-~~--~-- -- ' Figure 25. Ford-Walford :Plot of shell-length at time t (L_,) on the abscissa and shell-length at one year later (!,t._ ) on the ordinate. l I • data from eize"fi'equency modes in 1971 and 1972 for Walker Creek; I 0 "' data from size-frequency modes in 1971 and 1972 for l<'.illerton; A .. data from ma.'t'k·reeapture experiment at Walker Creek; A .. data. from 1 mark-recapture experiment at Millerton. -52- 50r 40 30 E E ..--20 ...... + _J . 10 10 20 30 40 50 .. Figure 26, Shell.,length derl ved from the Fom-Wal:t'o:rd equation fitted in Figure 25, plotted against age in years, It is assUJIIed that the juveniles settle at 1, 0 lll!il, -5.3- 40 • • • • ----. 30 E E ..c +-' ~20 -(() I (() ..c ll) 10 = 2 4 6 8 10 Age (yrs) REPRODUC'l'ION AND f!ECRUI'l'MENT RecOl.'ds (Habe, 1944r A.'llio 0 1963) eonfim that the early life history of B.s.tillmi!. is ver'l! similar to .that of Cerlthidila o1!.J.l;f;!'£1ltS\o a closely :related species, as postulatoo by Macdonald (1969). Copulating pa.ir.s o:r. :Bc.til.l2,tla were observed frolll ~larch to June in both 1971 and 19'?2, with the greatest number occurring during the early part of May. Table VIII shows the ntW.ber of copuJ.at:l.r.g pa1.~of_the __s_M_'i_l_B ___ I 2 . per m at ·Walker Cree.lt and Millerton for four sampling dates in the 19?2 bz:eeding season. Ulli'o:rtunately, there were fe n'Ulllber of' egg ll'~lses laid by a single female, Allill1als did not dcpc.sit egg masses in the labo:mtory, and only fom: e'gg masses were founii in the field, The egg strings lrere fou."ld on the subl.~tra.te or on pieces o:f del'.d. and. deea.:;.- Although copulating snails were found in the tidal creeks at both marshest no egg massea were oooerved. in tr..a.t habitat. The egg n1a.:sses laid in t.he creeks could be washed away with an outgoing tid.e, The fertilized eggs are laid in strands 1-2 em long encase-l within a sheath COl~post.>d of sn1i- lilent and fee;;;.l particles. The eggs appoo:r to be white when they are :fi:t'llt = The four egg masses studied had an ave-rage length of 12.5 mm, The avllrage size of a.n .i!ld1 vid.u;;,l egg was o.z !llllt and only one egg was in each per mm of egg cas~. Attempts were ~lade to culture. two of the egg ntasses in the lal:>O:ratory, but afi;.er eight dz.:rs. a.ll the eggs d:'~ed. Habe (19~~) reports that liJ .. f.'tc~r a brief' planktonic phaseo the veU~rs settle. In vieu o:f the la.rge n11111ber of copulating pain of snails observed at both l'IIUIShes a:.nd the small ftlllllber of egg masnes found, it is possible t.hat attachment of. the aub!!tmte 11ay not be the general case with 1ll;,t111etil!t egg masses. Egg masses laid i_; on Zostma• for example, may 'be easily washed away with the tides. Examination of gonad smears in Fellruaey 19'72 showed maturity (aotile spe:rm ant\ fully developed eggs) to occur at ail approldmate sb:e of 1:3.0 in which only individuals greater than 1).0 u were observed copulating. Figure 27 shows the aize-i'requeney distributions of copulating pairs of ~tillaria. from Walker Creek and tlillerton llllm!lhes in the 1972 breeding season. The results indicate that only infl..ivlduals greatel: than two years of s,ge (see Grmrth Section) are reproductively aetive. Cor•parative analysis using Kolmogo:rov-Sldmoy I'IOll~pamt~~etrlll statistiez CJ.f the ;si2:e•fl:'eg_uency distributions at both mal"Sl:es :shows no rlif:f'erenr.:es in the size dist:ct'bu~ tiol'IS of copulating inil.i viduals 'betwew sampling periods in the breeding season and in salt marsh localities. Figure 28 shows a seatte:t-dia.graa or the rela.tionsh.ip between lengths of copulating l!ll).les and lo;mgths c'f eopulatir.g females. Linear regression analysi.s shows there is a sig'!!i£1- ca.nt corxelation (MS regression/~lS devi;r.tions (18df) "' 28.38; :M;S deviatioM/ MS within (18df) "' 3.36) where larger felfllllla.-: copulate with larger males. No hypothesi~ about the significance of this result r~ come to mind at this time. Unfortlm!i.tely, only one female was seen depositing em egg lllll.l:;s in th!l field. Ccnseq_ueritJ.:y. there is no indication W'h!lther or not reproductive potent1~.1, as measured 'by the mwber o:f egg masses produced, decreases Phillips (1969) studyi~C-~g Dieaptba.il!!. aeg;ro.t~'il. :f'oll!lll. that rep-~uct:l.ve potential did. not decrease vith age. Loosanci'f' (1954) found no reduction in egg production in oysters and clams estimated to be between 30 and 40 years old.. Although the sexes are. separate and the.males are distinguished b.r a penis, it :l.s.diffieult to sex the animals while they are alive. It is a f'omidable task to cause the a.l'liMl to extrude its body frOI!l the shell to ratios :f'x'Ol!l gonsd smears was obtained, snit the results are sUilllllarlzed in Table IX and Figure 29. Analysis of the data. using the l..'hi·square test showed no significant diffe-rences of. the sex ratios frOIIl umty in all cases. Settlement oi' juveniles o:f' Ba,t:l.lla.rlft was f"irst noticed in the samples population.~ as :l.ril.ividw.ls 1-2 nm in length. The ave:rage dens:!. ties o:f' the juveniles at the different sampling stations in June 1971 are giv~n in Table X. Juveniles were present only :l.n the :marsh ponds, No young indh'i.dusls settled in any of ·the tidal creeks, Tho faet tha.t no juveniles settled in the t:I.Cls.l creaks my be an indication that the mic:roenvironments of' the creeks an much more severe than th011e o:f the M:n;h :;;;ooos. The water, The tldal creek. on the other band, usually dra.ins completely on an outgoing tide and 1nay be exposed for periods of 10 hours or longer. (The sallie pattern of recndtment was observed by Hat::donald, (1967) in lrl.s sampling of the ll!Eir8hes in 1966), Table VIII, Estimates of the abundance of copulatil!g pai:rs of ~till~!· at Walker Creek and Milletton in the 2 19'72 breeding season (nUlllbers per m ), ------·-··----·----·---·--- Walker Creek Millerton ...... --... -==-======-=-·-- -·· _,_. .... --.:-- March 8, 197Z • 2,2 ~!arch s. 1912 •· 1,8 March 21, 1972 - o,:; March 23, 1972 - o.o Ap:ri1 7, 1972 - 1.5 April 6, 1972 - 2,6 May 5t 1972 - 6,3 Hay 5. 1972 - 7.0 May 16, 1972 - J.J May 1.2, 1972 - 2.5 .; 0,1 June ·~ June 1, 1972 1 0 1972.., c.o __ __ = • ·- -58- I ! ' Table !X, Density estimates of juveniles settling on the Walker Creek and l1illerton salt marshes. June, 1971. Numbers/10,16 ca core t 95% confidence liuLtts, ------·------Ydllerton Station 1 3,05 t 1.:n Station 1 9.21 t 6.25 Ste.tion 2 11,21 t 4,64 Station 2 1,6o t 1.15 Station 3 0,00 t o.oo Station 3 0.45 t 0.32 Table x. Chi-square analysis o! the sex ratios of_;Una;tl.§._.:fr=o,...m'------ Walker Creek and Millerton. Data collected September 1971. NUlllber of Males Number of Females Walker Creek 13 19 Ponds 38 Millerton ,, Creeks 33 33 o.ooO** Ponds 1.5 18 ------= Fi!W.t·e 27; Size-fteque:ncy dist:rli:r.ztions of copulating snails from li'allte:c Cl.•e.ek and. ·Millerton dutin.g fotL"t' sa.Japling date'.i!l in the 1972 bre<~ding seasor1, 1 ------ WALKER CREEK MILLERTON 15. e-m-72 8.-ill-72 ! I I 5 I 15 r 21-ill-72 r 23-DI-72 •!------~--1------1 5 c"' ·c:E 0 l m -0 t 15 ~ 7-IV-72 6-IV-72 z::1 5 15 5-V-72 5-V-72 5 ~---,---U~~~--~30 ~---1~0~ rrllJL20 30 10 20 Shell-length (mrn) Figure 28f;c Seatter di~gram shol "- r0 ...--. • o E •• • C\J ...__.E •••• .c +-' ()) •••e€t®QI c • @f) CD - I •• _cG.l til oO-- 0 0 0 (Y) (\.] ..- (WLL!) L!+6U8J-JI8YS JJ F3,gl!l'e 29. 1;; His·tog:r:ams of' sex ratios of' llil,:till_~ From MHle:r.ton ar:d Walker Creek, September 1971, WALKER C:REEK 10 .!!! c E ·c: c 10 -0 ~ .a __L~·- 0 38 0 :J L------~--1--;;;;l~ Cl. 10. N=36 1/1 10 MILLERTON -- 10 -,() N= 33 tD 0 !D .. 0. N=33 . - ,.. 1/1 (/) " 0 -- -~c 10 - 0 0 - ~ '- - QJ .a 10 E :J -- z IJ Q N=15 0 ::J 0 Cl. 0.N=18 ·rta& 1/1 10 0 10 --20 30 Shell- length (mm) PREDATORS· AND. PARASIT!m OF .llll\:IL~ Although Macdonald (1967) suggests that possible predators of: Batillal'ia. might include different species a£ shore birds, on nine separate surveys throughout the study no shell fragments were f'ow:ld in biro droppings collected at both salt marshes. Predation by' gastropods is probably negligible as onl;f one shell found out of more than ~.ooo eJCalllined was drilled by' snails, other possible predators may include crabs, although they were never observed preying upon the snails. and bottom fishes which enter the marsh tidal creeks on incoming tides, During the course of the laboratory observations o:f' Bat.illar.l.!!,, in:f'estationB of trP.ma.tode parasites were :found in the gonads and digestive glarrls of the snails. Normally, the :female gona.d is lobular and yellow, and the male gonad :l.s a murky white-yellmr color~ 'b.tt whAn he.avl:ty infeetcl with parasites, the gonadal region."> become gmy, Microscopic observa- tions of heavily infected gonads revealed no eggs or spe:r:m in the hlllix, Some ce:rean.ae and rediae were found in the digestive diverticula. but these were not abundant as those inhabiting the gonadal reg:l.on, I lihen the eercaria.e a.:t'e !lll'Ltu:re, their eyespots and the region where the digestive cecae develop are pigmented, 'l'he ee:rea.rls.e !lave tails wh ..i.eh are finned both dc>rsally and la.t~r.ally. These char&.cter:l.stics .make 'them 1 distinguisheble m.embe1.'S of the t:cemat,Me order Opisthorchlida a.nd family i Hste:ro:p.hy-ldae (Holliman, 1961), I aJll umble to nv:~ke a positive collf'irma.- t:!.on o:f the parasite species, although it can oo tentathe]Jf identified as lli.ll!mnl~.!Wi. ji r..a11.J:OD!:tc!\. (Martin. 1972). In attel,!pting to quantify levels o:t' partu.lltio infestation of the snails, cor~s were ohl:~ined in ~-;ay 19/'2 from ooth salt !llal'Shes (-this =~=~~~~~~~~~~~==-c--- ~------~------=-====--c study wa.s done in conjunction ltith A, E, Hajek in May 1972). Analysis of the Patilla;ia collected at both marshes showed an average of 1,75% trema tode infestation, The length-frequency distributions (Figure :;o) of' the sampled snails indicate no parasitism evident in snails less tl'.an 1.5 em .in length, The infestation levels definitely a.re skewed toward larger individuals, In a second sampling of both mlll."Shes only individuals greater than_ 2,0 em were collected in random cores and e:xa.mined i"or Creek and 35% were infected at Millerton, Chi-square analysis showed no significant differences in the infestation levels at. the two :marshes (-1- ... 0,2718, df 1), All individuals greater than :;.o em were inf'ected (Figure 31), Since samples were obtained only during ll'.ay 1972 ai!:d since only one l:!.m.ina:ry in nature. Martin (1955) :l.n studying seasonal tremate tion levels of' Q(:.rlilJ.19...$& Si!:lifoW,ca concluded that though infec'.:iom of different species of trematodes fluctuate in abundance seasorm.llJrt the total level o:f infestation was quite constant, 'l'he presence of high infestation by trematodes in older snails indicates that rec:ruitment account for a dispropt.r.r.tionate amount. of egg production .in the Jlo:pula.tiou, r-- ~------~------~------~· F:l.~ JO. S!za-!'req.uenC".{ S.istrlhrUcms of 20 :random ~>El.ll:ple>..<> of Jl!!t:·· 2,].1&;ri!l. ·;oclleeted May, 19'/2 at Walker Creek and Nillerton, :?arasitl•lled snails indicated by darkene-.i portion o:f' di:;;-trib;;tion. WALKER CREEK ~----~------~-jn-1----~-~·------?·· I I MILLERTON - - . ----- "" I - rr~ ,.... --- Shell-length (mm) ~--.- Figu:t"$ 31~. Percentages of J3Atil1~ infected with trematode parasite..<; from/( ) .Walker Creek and (0) .Millerton salt marshes, Samples collected l'.a:r 1972. -66- 100 u (1) +-' ...... ~ 60 c ;;--0 20 0 2.0-2.5 3.0-3.5 4.0-4.5 Size-class (em) POPULATION ABUNDANCE Al'fD AGE-BTRUCTtlRE Sequential cbanges in abundance were CCIIIIpared using 95% confidence 111111ts for the estimate ·of the mean. Walker Cre§1 StatigM 1. 2, and , These sarapl1.ng stations are located .in the marsh-pond area. Station l (Figure 32) shows a relatively stable population abtmdanoe 1----~~~~~~fn~~~~..ranua:ey l97l.-to AugustJ.~?l wr-tn a general increase ·in nU!llh!!rs of J3atillaria. in June-August. This increase can be traced to tho recruitment of the 1971 age-group of snails that settled on the marsh. In August 1971 large MOunts of Zostm were washed into the marsh, and unusually large quantities of this eel gTaSs were deposited at this s&lllpling station. The Z~~. rems.ined in this area for the next nine months and slowly decos:posed. When the large quantity of Zostera appear&l., the:r:e was n sharp deeline in the number of ll:t!.illla;ia, Ul'til virtually no snails were present in the core samples taken between October 1971 and June 1972. Station 2 (li':l.gure 33) sho-lfs a sharp increase :l.n the abundance .of snails :l.n June-July of 1971 indicating the settlement of the new 1971 age-group. The increase in nlll!lber was restricted to the :summer months (June~August), and the abundance of .snails quickly stabilized to approximately the same density- that occurred before the settlement of juveniles. Although Station 3 is located :l.n the same general area, no settlement of juveniles was evident in the samples, The am~nces of l;latillarla were relatively stable (Figu,re 34) througho•xl; the entire sampling period td.th a general deeline taking plac~ in the llW!!lller months, -68- The population age•strueture for the three stations is quite coMtant (Figures 35-37). The settloent of &·,new year class in June 1971 is evident at Stations 1 and 2 while the average shell· length at Station 3 is quite stable throughout the sampling period. Wa.lkgr Creeka sta,t.icms 4 and 5 . Both of these sampling sites are located in tidal creeks, In both localities abundances were quite stable (Figure 38), however, there was a sharp increase in numbers in December 1971 and Janua...-y 1972, Increased amounts of ~ and Enteromo~ upon which Batillaria CO!lllllonly browses were noticed during this period which ~~~&y be a possible explanation for the dramatic increase in the number of the snails, AMl ysis o.f' the age-structure (Figure 39) of the tidal creeks also shows relative stability between times, Mill~rtgnt Stations l. 2, and 1 All of these sampling loca::'..ities are located in marsh ponds, There was a general trend in all of the sites where a relatively stable population level was maintained tb:roughout the srunpling period (Fig" ures 40-42), J.. gradual reduction in number during the sUJlllller months of 1971 (June-september) was noted in all of the sites. In April- )!ay 1971 a large amount of sand was deposited at Station 1 and com- p1etely filled in the marsh pond, Although there was a gradual decline in nUIIIber after the sudden accretion of sediment, the abundances of aniMls remained quite stable, Figures 43-4·5 show the changes in the age•strueture of the ponds, The decrease in the shell-length in June-August reflect the settlement of the 1971 age-group. -69- Millerton 1 §tati!ltlS 4, 5· and 6 . · All of these localities are tidal creeks, Comparative analysis of these sampling stations shQif rema:t'kable. stability over the saapling period in abundances, nUIIIbers of animals, and age-structure of the animals (Figures 46 and 47). ' Ccmparative analysis of the estimates of abundances and popula• tion age-structure of ]atiJla;i~ at the different sampling sta- variability, The results indicate, however1 large and relatively stable population size, Variability in abundances and population age-structure between and within sampling localities may be caused by two factors, (1) Recruitment of BaUlla.ria is restricted to the protected marsh pond.s et both salt marshes (see Reproduction Section), Although recr1J1t- · ment is restricted to the llla:rsh-pond areas, t.here is also a. great deal of varlability in the recruitment between marsh-pond stations (ses Table IX Reproduction ani Recruitment Section), Local physical and I biological conditions rr>.ay have a great deal of effect on the j settlement of the new age-group of snails (Phillips, 1969). In all the tidal creeks sampled at both salt' marshes, no juveniles were observed, (2) ~tillaria is very mobile, By e:x:tendir.g its foot and u.sing the surface tension of the water, the snails ean flcmt. Although attempts to quantifY this response proved fruitless, individuals of all sizes were co;nmonly seen floating in the tidal creeks and marsh ponds at WaJ~er Creek and Millerton, The snails eom!llonly feed upon the epiphytic diatoms occurring on ;zostera and ~. It has been observed that literally hl!l1dreds of animals -70- browse on these clUIIIps of algae, As the tide comes in, the algae begin to float with the snails still attached, The algae, present only at the Walker Creek salt marsh, cOIIIl!lonly are seen floating in the tidal creeks with a large nWIIber of Batillarla attached, Analysis Of mark-recapture experiments in December 1970 and May 1971 indicates that over 7% of the marked individuals moved out of a one square meter area within seven days after release, ponds for both salt marshes, In analyzing the population age- structure of both marshes a definite trend is produced, In all cases, the tidal creeks are inhabited by larger individuals, Figures 50 and 51 show that no individuals less than 0,3 em were found in the tidal creeks. The miero•enviro111110ntal conditions of the tidal creeks may be too severe for the juveniles since they are.commonly exposed for longer periods of time than the marsh ponds, Laboratory studios confim that juveniles (individuals less than 0,5 om) are very sensitive to desiccation (Table XI). The older animals are not a.~ sensitive and may migrate into the Udal creeks as they become older,. Table xr. Number and percentage of snails of different size groupings s~viving desiccation at nine time periods (each experiment initially contained 2.5 ~nimals). Time in o.o - o.; cm 0.5- 1,0 C!ll 1.0 - 1,5 em 1, 5 • 2,0 Clll 2.0.- 2.5 Clll 2. 5I- Clll Ho•..tr:s Not'l % No. % No. % No. % ro· % No. % I l2 21 84 2.5 100 25 100 2.5 100 :25 100 25 100 I I ' I 24 2 8 2:3 92 2.5 100 25 . 100 :~.5 100 25 100 I I 48 0 0 20 80 24 96 24 96 '25 100 2.5 100 1 * I '72 0 0 21 84 24 96 2.5 100 :~.5 100 '. 25 100 ' I I 120 0 0 10 40 20 80 2:3 92 24 96 2.5 100 I I 168 0 0 8 , :32 21 84 23 92 :~.5 100 25 100 I 24-::l 0 0 :3 12 . 1.5 60 20 80 J~4 96 25 100 I . ' I I 480 0 0 0 0 7 28 17 68 r·~:3 92 24 96 no 0 0 0 0 0 0 2 8 8 :32 1:3 52 - ,, I II' 11111111 i Ill :1 I I iii : I :Ill li' ' I II' 'II' 'II' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-- Figure~32, Estimates ef the population abundance of B!!.tilla.ril! zontJ.lis, Sta"j;ion 1, Walker Creek, showing mean and 95% confidence 1il'llits, Averages based upon 10,16 em core, ' '" ~·" •"•'"'""-'' _ .., ' ---~--~----··•-·-··-··--·-''"'"-.....u-.-~•..,.o..• -----~~w ,, ,, "!! I' I!' 30 l I I I if) ~I 0 E WALKER CREEK-'1 ·c 20 0 ..,._ ~ I z 10~ l l ld t I t I t • • I A S 0 N D J)_____ F_ M A M J J J F M A M ..J J 1971 1972 I i. , . 'I I'' 1111111111 I Ill '!I I II !'I !Ill ''' Ill' ::'1 I '11"'11' i ' . Figu:re ;13, Estinw.tes of the population abundance of .l\atillaria zona;!.is, Station 2, Walker Creek, sh011ing mean and 95% confidence limits. Averages · based upon 10,16 om core. . -·" ... - .. -·~"---~~----···------··~---·-~"~" 50 40 WALKER CREEK-2 tf) 0 E § 30 ~I '+- ·0 Ci , I z 20 10f\ t t \ tt j t I t I j l J F M AM J J A s 0 N D J I F M A M. J J 1971 1972 1 1 1 I II Iiiii I! I ' Ill ' ! I I II' !' IIIII ! 11· !: ·1· 1r:!ll : • ! Figllre.34. Estimates of' the population abundance of Ba.t:l.llar:l!!. zom.lls, Stat1Qh 3, Walker Creek, showing 11\ean and 95% confidence liraits. Ave:~.-ages lased upon 10,16 em core, '"" __ .. ,, ',,__ 50 WALKER CREEKJ3 40 (/) I ~ 30 !t\ 1 0 I I t z0 20 . l l : 10 t- I I I I ____ L__ ___~----'-L----' .J F M A M J J A S 0 N D Jl F M A M J J 1971 1972 1-11 '1: 1··· 1 I H 111111!1 i Ill :11 I I i'. ill', I ' Ill' I 'II' 'II' I • Figure 35~ Population structure of Jjat:!.llarla ~l:!.s, Station 1, Walker Creek. liorl:r.ontal line ropresentes range in shell length. Box represents 95% confidence limits of the mean length. •75- t---'-~~~~~~~-=~~~~~·I!!L.....------~------44-1=71'~~~~' ______. ______5-ll-71 ---...... -11------16-11-71 ------7-111-71 ----"'.,IIL.------'-16-11 1-71 -----.Jl!!iilli!!L-..______9-IV-71 _____a.______.....;_-19-IV-71 ------11·&-iiL------21-V-71 ______~!l!lJ!L ______9-VI-71 ----..m•L------24-VI-71 ____me-~m; 1------· 8- Vll-71 ----~------23-VII-71 ------..llii~"'-'""'w:~"----·- 21-IX-71 0 10 20 30 Shell-length (rnm) Figure :36. Population :stJ:ucture of Bat11lajja M,nal,:l,§_, Station 2, Walker Cl:leel,. Horizontal l!ne represents r-.;.!'~e in shell .length, Box represents 95% confidence limits of the mean length, .=~=~=-=-·=·=-=·-==--=--==-=···~·-=-=-~=-=-~-=····===-=-==--=·····=·---~--~--~-----~..~ ... ~ ... ~·=··====~- • . -14-1~71 ------....&!illiL------5-11..:71 ---.lllim!giiltlil.!llii.------16-H-71 --...... £0~·-·i.....------7-111-71 ----~~------16-11 1-71 ___-., ___ __.___.___;_g ... JV-71 ----.~""'-m-..------19-IV-71 ----•------21-V-71 ------9-VI-71 ------24-VI-71 ----•"------8-VII-71 -----L------23-VIf-71 ..A. 21-IX-71 ------!!------11-X-71 _____._...-...... ______15-XI-71 ______• ...._ ___ ,_7-1-72 ------liill·-·-----8-111-72 ------iililiL...------20-IV-72 -----mem---.----.:16-VI-72 0 10 20 30 Shell-length (mm) .~======~~~~~~~====~======~~~~~~======---~~~~~~====----- Figure 37. Population structure of Ba.tillarla Ev.naJ.!c, Station 3, Walker Creelt. Horizontal line represents range in shell length. Box represents 95% confidence limits of the mean length, ==---·----~~-~=~- . -71------l----~---14-1-71 ------'----i.....------5-11-71 ------L------16-11-71 . ------7_;111-71 ______._L_ ____16-111-71 -- ------9-IV-71 ------lililliiiliiiii------19-IV-71------""""------21-V-71 ------...ll!i•-·L------9-VI-71 ------...... -~---24-VI-71 ______...______8-VII-71 ------~------23-V/1-71 ------....~•-·-·~.-.--______;11-X-71 ------15-XI-71• • 7-1-72 ------A•-·--L-8-111-72 ------'-riliO>iiiL------20-IV-72 . ------16-VI-7: ·o 10 20 30 ~ ~~~ Shell-lenath (mm) ------ FigUre )8, Estimates o£ the population abundance of ~:1;1.~ zonalis, Stations 4 aml. 5t :li'alker Creek, showing means and 95% comid.enee limits, Averages based upon 10,16 em core, -78- 50 WALKER CREEK -5 40 30. 20 ~ -- -- (/) 10 0 l E l I c 0 t '+-- • • 0 c5 ·-·-- ~ z -·- !!!!!! ~ 20 -- -- WALKER CREEK-4 ~ 10 t t S 0 N DJ F MA M J J 1------_:______c______-----:- _ _:______----:-, Figur~ 39. Population structure of' Ba.tilla,7la ~li§., Stations 4 andt"5• Walker Creek. Horizontal line represen-ts :runge in shell length. Box.represents 95% confidence limits of the mean length. -79- WALKER CREEK- 4 ------JIIIIIIIii.------21-IX-71 · ,, -- -~ ______._.______.:11-X-71 ------~.. --·------~1~2 ______..J._.L------.20-IV-72 I ------16-VI-71 ] li i WALKER CREEK-5 - 21-IX-71 ______.... iiii.----11-X-71 ------.-.JIIi------·15-XI-71 ------...IIL----7-1-72 ------lliiiiL------20-IV-72 ------~------16-VI-72 0 10 20 30 Shell-length (mm) ~------~ '}~ Fi@fr.; 40, Estimates of the population a'bur.dance of ~tiUa;tla ZO!§l:\Ji!.t Station 1, Millerton, 1!h01>1ing mean arJ!l 95% cor.fidence limits. Ave:rages lased upon 10,16 em core, · -~ -eo- LL. ..-- zI 0 1- ),..... 0:: !'-... w ()) _] , .... _] ~ - 2 !'!l! 2 -- - <( ~ LL 0 0 0 0 "\!" (Y) N .... S!OW[UO JO "ON Figure .41, Estimates o:f the population abundance o:f Batillarla, zona],ll, Station 2, ¥.1llerton, showing mean and 95% confidence limits, Averages 'tased upon 10,16 em core, -81- ...., i j LL ~ j ...., L. i 0 z 0 ~ C\l -+- I z tJJ ~:-= 2 0::: w -I- <( _J _J -+- 2 --1- J.- ....,..-Q)""' -4- .L...> <( -- 2 LL 1-----~~--...., 0 ·0 C\l ..- SiOWJUO J.O 'ON Figure 42. Estimates of the population abundance of ;fu!.tiU&rla zomlis, Station 3o'~all~rton; show!~~ mean aril 95% confidence limits. Ave~ges based upon 10,16 em core, =·==--=-=·=- -==-·=--=-·-=--=--=-=-=-=-=-=-=--=--=--=---=--=-=····-··-=-=------_- __-_ --_-__- __ -----==-~-- l------~------i-bL....------,-, -~ - 0 -- z (V) I z 0 0 1- - et: w lf) _J _J 2 ..... <( -- J .-- r-.... Q) ----- J.-- !!!!! - = -1-- -- <( 0 0 '-'1 g ~ ..-- SjlJW!UO J.O 'ON Figure 43, Population structure of I\i.t,illarb zonalis.• Station 1 1 Millerton, Honzontal l:l.ne represents range in shell length, Box represents 95% confi• dence limits of the mean length, -83------iii------18-l-'71------"1111.------3-11-71 ---...•------17-11-71 ---...1------5-111-71ida ----111-IIIIL------·18-111-71 ------9-IV-71 -...111111111.------10-VI-71 _....._....______25-VI-71 __..~,!,---9-V 11-71 -..&------22-VII-71 ---'·------19-IX-71 ---•------10-X-71..&. ----IBIL..------·16-XI-71 ---lli!IIIIL------5-1-72 --••m'•------7-111-72 _-...~Jm!II\1L.----:20-IV-72 --~•iiiiil1·-.-----15-VI-72 0 10 20 30 Shell-length (mm) ~==-=--- Figure 44. Population structure of Ba.+.illari?.. !Qna11s, Station 2, Millerton. Hortzont.."l line represents range in shell length, Box represents 95% confidence limits of the mean length, -----·-··~•~~-· -· __.,...;.;.;.;..~. --. ..; .. 18..,1..;71 ____m______._...;_· 3-11;,.71 ______,.~gl,g· ------.;.·17-11-71 = ---.lllilli!l!L---.,...... _5-11- 1-71 -----•a...... --18-111-71 ------ilillii.m-----9-IV-71 ----...-...i!!mL.-----21-IV"-71 ------.!iil·ilillii::III!IL----21-V-71 ------10-VI-71 -----...... £ll"""""---25-VI-71 _ _maa....__ .___ 9-VII-71 ---...... "------22-VII-71 .. AiiiiiM. 10-IX-71 ______,.!iil!'l"'"M,.,. .. ------.10-X-71 ------llll•-~---16-XI-71 • 5-1-72 -----~'---7-111-72 --·l!!l!lil!!··ii------20-IV-72 ----~'----~-~-··15-VI-71 0 10 20 30 Shell-length (rnm) FifiUra 45, Popula.tion struet"Qre of ]3atil1aria zonalis, Station 31 Millerton, Horizontal line represents range in shell length, Box re!lresents limits of the mean length, ------18-1~71 ------3-11-71- ----IL------17-11-71• ----•-----5-111-71 ------~·------·-18-111-71 _ _._ _ ___.J...______9-IV-71 ------21-IV-71 ------'------21-V-71 ------~~~~---10-VI-71J. -----""------25-VJ-71.. ----JII-1¥!1-iill.--.ta 9-V 11-71 ---111Gmim5--22-VII-71 nM 19-IX-71 -----""'------·10-X-71 ------"""'""------16-Xl-71 ------"--·-~----·--5-1-7-- 2 -----..1!111!1-.-----7-111-72 = ------20-IV-72 _____..,.p..,. 1""'----15-VI-72 0 10 20 30 Shell-length (mm) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---= FigUre 46, Esti~~~ates of the population abundance of 2ltillari-a zomlls, Stations 4, 5, arid 6$ J.VJ.lle:rton, snGllling means and 9 5% conf'ider.ce limits, Averages based upon 10.16 em core, -86- =.-- ~ - 20 - --- -- MILLERTON-4 -- 10 l I t-j t t t I t t ! ~ =;= ~ 20 ! U) 0 MILLERTON-5 -- E ·-c 0 10 '+- 0 t I d t I t z f t - -- --- ""= - 20 - MILLERTON-6 t ~~~--~~~~~~-~~~--~ S 0 N D J F MA MJ J 1971 1972 ------ Figure 47, Population structure of BatiUarta ~~. Stations 4, 5. and, 6, Millerton. Horizontal line :represents ;:-ange in shell length, Box :represents 95% confidence limits of the mean length, = -8?- MILLERTON- 4 19-lx-71!------'----- 10-X-71------1---- 16-XI-71------ 5-1-72------ 7-111-7~-----"-L--- 20-IY-72:------ I I 15-VI-72------'------MILLERTON-5 19-IX-71------"•---- 10-X-71------"·--- 16-XI-71------""---- 5-1-7~------~----- 7-111-72 ______....!1 ____:. __ 20-IV-72------'""----- 15-VI-72------"-"""'--- MILLERTON- 6 19-IX-71------'---- j 10-X-71------IIlii!L----- 16-XI-71------ - 5-1-72'-----"'..._-,--__ ~ = 7-111-72,..------"'•"""--- 20-IV-72 P 15-VI-72 .dmc_._ ___ 0 10 20 30 Shell-length (mm) I r, I. l' Fi€;\l.'re 48, Estimates of :pepula.tion a'bur!!lance of !Jatillar:I.Jl zonnl:l.s at Uillerton (pooled data), Averages based upon 10,16 em eore, ~--'~"---~- --~---- ..,~- "·-·-·-···---- i I . I I I 30_ . MILLERTON FJ I ~E 20 I I j § t ~10z t H tL t t l t t t t 1--r--..,----r-~---.----'-. J F M AM J J AS 0 N D J F M A MJ J 1971 1972 ;·I 1 11: I I I'll !i.:" "I·~ ' '~ I ' ' 11""1·I ' I! ' I . I 111111111111 'Ill IIi I' I ' FigUre 49. Estimates of population abundance of llatillarl,!, l'lO!l!ll1!!. at .Walker <.'reer< (pooled data), Averages based upon 10.16 em eore. l 40 WALKER CREEK 30 11) 0 E .c ' 0 20 '+- 0 z0 10 t t t t t t t ll I I f ,- --, 1' ------,------.------. • J F M AM J J AS 0 N D JIF M AM J J 1W1 1972 1 I ll:liillllll Ill li I I il! ··I !ill : II·~ ! i il-- I! lj" "'W ::w F'igu..""e. 50. Population st:ructur.., of llat1.lla.tl.!l.. g;_o~l:l.!i• \Talker Creek (pool.ed data !':!:ell the tidal creel".s 2.r..d marsh J:lOrlds), Horizontal line represents ~ge in shell length. Box represents 95% confidence limits of the mean length. WALKER CREEK PONDS -----JlliL-----·14-1-71 ------~------5-11-71 ------~·---·----16-11-71 _____..______7-111-71 ------,------'16-111-71 _____..______9-IV-71 ------IIL------'19-IV-71 21-V-71 -----111------9-VI-71 --.,..--...IIIIIL.------24-VI-71 ----....liL.-----8-VII-71 -----L------23-VII-71 ------.lliiiiiiL.--'----21-IX-71 ------'-.JI!I-,------11-X771 ------...... liiiL----'15-XI-71 ______...______7-1-72 ------L---8-111-72 ------20-IV-72 ------·16-VI-72 - CREEKS !!! 21-IX-71 - 11-X-71 15-XI-71 7-1-72 .. 20-IV-72 16-VI-72 30 0 10 20 Shell-length (mm) Figure 51, :Population stl':Uctll:t'e of futill.ll.rlf! ZiQ!Ja],!s, Millerton (pooled da.t,a :f'rom .t.he tidal creeks a!'!d 1!!-'U'Sh .ponds), Horizontal line rep:resents nnge in shell length, Box represents 95% confidence limits of the mean length, PONDS 18-1-7i---...1111111L----~-- 3-11-71------ 17-11-71------5-111-71---...... JILIL____ _ 18-111-71----IIL-____ 9~V-71-----L-...... : ___ 21-IV-71----.a..____ _ 21-V-71-..,...,.---..a.____ _ 10-VI-71 25-VI-71----'L..-'----- 9-VII-71-_...J·IIIl----- 22-VII-71-...JM-.______ 19-IX-71-·---l-L-____;, 10-X-71-----'---~---- 16->"1-71-----'111Iilllll-'------ 5-!-72--~---L------ 7-111-72------ 20-IV-72--__.1-L------ 15-VI-72----liiiiL------ CREEKS 19-IX-?'1------.JIIillll----- 10-X-71 _____af1'!!1lmu~B~~IL------ 16-XI-71 ~------'""""''-'----- 5-1-72:------..1.1111.,____ _ 7-111-72:------'11--- 20-IV-72------IIiliD~----- 15-VI-72------ d 10 20 30 Shell-length·(mm) Collparative analysis of the feeding biology of Cerithid~ and Eatillaria was acpieved by empla,ring laborat~ and field techniques, 1.:;::_-_ Both species are the only representatives of the family Potamididae ·~~o i=-- found on the coast of' California. The range of' Cerlthidea• which also was collected fUrl:.her to the north in Tomales Bay 9 at the Millerton salt mars !'I. Batillarl.A and Cerithidea are style-bearing mesogastropcds, Driscoll (1972) has described the structure a.nd function of the alilllen- tazy tract of the species, Both species are depos:l. t f'eed.ez'll. .The sm1ls inges.t a Jllixture of mud and detntus with the radula, They are active only when submerged in water, Creeping slowly over the bottom, they move their short pro boscides across the substrate with a side-to-side sweeping motion,. col- leeting food.. Feeding trails left by the snails are commonly 10-:30 em in length. When exposed, the snails retract into their shells closing their opercula and cease all feeding activities, fJaodonaJ.d (1967) has suggested that Cerithida .is strlctly noeturtlll.l in its feeding habits, but l have notices .that. it feeds during overcast da;rs or in sul:duei .light,. Ba,t:l.lleotliJ., on the other hand, has .been seen feeding at all times of the day, Abe (1934) has concluded that ~ exhibits negative phototrophism but also has stated that the sn~l.was commonly seen feeding during all times of the day. =~=====------ The gut contents of the snails were elG!I.Ilined to detemine diet preferences. Large uounts or yellowish detrital uterial was found surrounding clay and other silt-llk olllT a very sull portion of the material ingested. There were large quantities of diatoms,found .in the guts and feces of bath gastropods, :Batilla.r1a, and Certthidea appear to be exclusively herbivorous since no recognizable animal ma.terlal was found though nema.todes, polycha.etes, and oligochaetes were quite co~t~~~ton in sediment samples analyzed from from Walker Creek and Millerton .salt ma.rshes. Mackintosh (192.5), Yonge (1930) and Gra.hwlt (1939) have .postulated ,that the presence of a style in . gastropods can be correlated with the ingestion of diatOJDS 1 unicellular, and small multicellular algae, Yonge (1932), however, noted that while the style is restricted to herblvorous gastropods 1 not all herbivorous gastropods possess styles, Sine~ benthic diatom species formed the majority of distinguishable material ingested.b,r-.the snails, information was collected to determine if the gastropods lfere selectively. feeding upon the microphytes, Jorgensen (1966) divides feeding selectivity into two major subdivisions! quaUta~ tive and quantitative, Qualitative selectton is selection of food particles with respect to food value while quantitative selection applies to sorting of particles in relation to shape, size, or density, It must be remell!b- ered, hmrever, that these two selectivit:;• d.efinatiollS may overlap, For example, the quality of food selected by an organism may be li~rJ.ted by the particle size that the animal ca.n accept 6!S food, For the purposes of this study, the term "selection" refers to the quantitative defina tion, ~ntitative selectivity of food substances has been demonstrated in copepods (Gauld, 1964}, in Ophistobranch larvae (llilliams, 1971) ald. in P:rosobranch larvae (Paulson and Scheltema, 1968). No published studies have delt with the feeding selectivity of diatoiiiS by adult deposit-feeding gastropods, plished by examining diatom species removed from the gut and feces, Length-frequency distributions of 50 ramomly sampled diatoms obtained from the guts o:f different sized snails are shown in Figures 52 and 53, In compa.risor.s of the length-frequency distributions o:f diatoms taken from sediment sa.mpl.-;s (FiFe 54) with those obtained from the guts, a definite trend is evident, . Both species of snails seem to ingest a relatively small size range o:f the diatoms available in the sedimerJt, Comparisor.s of snail length to average diatom length found in the gut from sl'.ails obtained at Millerton, September 1971, show a highly significant linear correlation for both species of snails (Figure 55), In both oases the larger sr.ails are selecting larger diatoms than the smaller snails, Also. J!>!j;ill;gi.a is ingesting relatively larger partie cles than ~;Qthld{t'i!,. This conclusion is in accord with Dr:l.scoll"s (1972) :fUnctional mo1."Phologica.l study, He concluded that Cerlthidea has a much more complex alimental.'Y tract than~ and felt that ~ prombly ingested smaller particles, The selectivity exper- iment was replicated in l1Ja1'Ch 1972, and similar results were obtained (Figure 56), Application of analysis of covariance to the linear regressior~ showed no significant differences between the sampling dates, Ass1mi.1ation, . Experim~nts were pe:rfcmned to determine if the gastropods were assimilating the ingested diatom species, This was accomplished by looking for the presence or absence of pigm.ent in .diatoms obtained f'rom the gut ar.d facal. pellets, Although this techinque does not . necessarily establish that the diatoms are being assimilated, .it does upon by the snails, Using the Kolmogorov-Smirnov non-parametric statistic, there were no significant differences in the relative abundances of diatom species ·and in diatom size of living and dead species in the guts and fecal pellets of both gastropods, . Nearly all of the diatoms found in the fecal pellets had no pigment, This suggests that the gastropods are probably preying on and possibly assimilating all the diatoms ingested, It was determined that both species probably select cert.~in sized diatoms when they are feeding, ~ric Populations o;t: Batilla.ria and Cerithidea Odlllll (1959) used the term "ecological equivalents" to identifY differ- ent species that occupy equivalent niches in different regions, Macdonald (1969} in analyzing salt marsh molluscan faunas· occurring along the Pacific Coast of North America concluded that jl_aj;j.JJ,aria and Cerittlid~ were Hecologic:al equivalents", In his study, he found that both species occupied sinlilar niches, and that their ranges did not overlap, Qmj;Jll.~ was observed by Macdonald (1967) in Tomales Bay, but the species was not found to coexist with MHJ.aria. Driscoll (1969} found a similar distributional pattern, However, as previously ment1or1ed 0 I found coeldstirJg populations -96- of Jla.tillari.i, and Cerithidea in portions of the Millerton ealt marsh, Froa analysis of the feeding biology of both species, it appears that only the emall atillarla and the large Qerlthidea COmpete for diatOIIIS, Examination of abe-frequency distributions of both epecies in the two · sampling locations (see Figures 2,·57, 58) shows that only larger individ• uals of Ba.tillaria and s~~~&ller individuals of Cerithidea occur together, The size-frequency distributions of Batillarta coexisting with Cerithidea =;-- ~~~~~a~rew.•c'-o~mftpl~e~t"e~l"y~di"f~f'-e~r~e~nt~fr~."-o~m~.~o~thh.e~r~s~am~pl"i~n~g~l~oea~li~t~i~e~s~a~t~e~i~th~e~r~s~a1l+t~~~~~--- marsh (see Figures 14-24). In the coexisting populations, small lla.till.V'ia are absent. Often, closely similar species exhibit greater morphological differen- tiation in regions where they are sympatric than in regions where they do nd: occur together,, . This phenomenon .is called character displacement and has been doelU!lented for diverse groups of organisms including ~mts, Cl.'abs, beetles, :frogs, :fistes and birds (Brown and Wilson, 19561 Mayr, 1963). Character displacement has been attributed to selection against. hybridiza• tion (Ehrlich, 1963), Increase of morphological, behavioral or ecological differences in S)'mpatric populations would be expected to minimize the prooobiUty o:f hybridization, ! In th snails that would compete :for the same sizwJ particulate matter (uhether diatol11S or other particles) do not coexist, Olll.:r .. theso age groups having diff'er~nt particle size preferences are sympatric. This suggests the possibility that a modified form of "char.;.cter displacement" is being manifested involving mini~ization o:f competition between those age groups of the two species of snails that have sirdl;~r dietary requirement~, Competitive intm:act:l.ons between these Gpecies ll!ll.y uccoUI'lt for the. o~e:rved size distribut:l.cms, Recher (1967) notes that similar· species of shore -97- bird.s' utilize identical niche spaces but at difi"erent tillles, thliB el1minat,- 1ng cnpetitive interactions, The liatillarl§•jlerithidea phen011enon uy be a fol'll of competitive exclusion in ·which cOlllpeting age groups of the two species do not feed in the same area, It is likely that such excl11B1on may be associated with age-specific behaviorlal interactions between the two species, Confirmation of the aforementioned hypothesis requires longer term information about the, biology o:f' both snails, It has been found. that in the area of co-occurrence, Cerithidea population abundance remained quite stable throughout the sampling period (September, 1971 to June, 19?2) while the abundance of Batillaria sharply declined {Figure 59). These trends could be due to.competitive interactions between the two species or other . factors, The nature of the Batillaria-Cerlthide!l intera.ction must be better known in order to facilitate interpretation cf the age group's displacement in sympatrlc population.-s reported here in the light of the hypothPsis that has been proposed, Figure 52. Size-freqwllncy distributions of 50 rand'.lmly sampled diat.cms taken from the guts of ~~illari~ zonalis. Data collected September 1972 at the Millerton marsh. L = snail length. 20 . / :· L=0.7 L=1.8 10 I I I I l.IJb. I i I i L=2.0 - _-,__ r- r J 20 r L=1.6 L=2.9 - 10 ~ - r- r-- ,...... - 3.6 36.0+ 3.6 36.0+ Diatom-length ()J) ~~------~ Figure 53. Size-frequency distributions of 50 randomly sampled. diatoms taken from the guts of Cerithidea californic~, Data collected September 1972 at the Millerton marsh, L = sr~il length, ------~--·--··· ------ -99- 20 r-- - f.- ...... L=0.6 L=2.4 10 . . C- - - -f.- f- I ~ I h 20 >. u c r- Q) ::J 1 IT r- - L-1- ·' L=3.0 Q) 10 r- L lL f- r. n r h., 20 ...... L=3.2 101- I- - f- f- ~~~~lh~~~ ~~·~~~~h~~,~ 3.6 36.0+ 3.6 36.0+ Diatom- length ( JJ) Figttfe ;4. Size-frequency distributions of 100 randomly sampled diato111S from a sediment core eolleoted September, 1971 at Walker Creek. -100- + ...... , 0 C\.1 ;;;=- r--. - - - =c - - r - ~ '• l j -- ! ' I ...--.. ' =a. ----£ 0 +-' CD Ol (Y) c . -()) E 0 +' 0 0 I .! • I - ! = : ··- 1 • _I .1. 0 0 (\J Figure 55. Linear regres3ion analysis of shell-length plotted against average diatom length of 50 diatoms obtained :from the guts of' Batillaria and Qroj,th:!da. Snails t,aken from· Millerton, Stations 1o. and B, Sep~t~em"'be""'r.______~, 9 1, 0 "' ll&tillalj,a, Y .. 13,44 + 5,216X, r ., 0,822, p I II ~ I P'igure 56. Linear regression analysis of shell-length plotted again1st averags diatoa length o:r .50 diatoms taken from the guts of !l.iliUJ.llrla and .Qerith:Ld~. Snails taken from Mi.llerton. Stations A and B, April 8, 19'12, 0., Bi!,t:ll1arii!t Y,. 5.53 + 8,57X, r., 0,9,51>, p 0 0 3-20~ .s::.... Ol •• ~ •• - E •• I ....0 0 ~~~~~~~-Q; 10 0 10 20 30 40 30 ~ 20 ~ .c ....en c cv ~ d i:5 10 10 20 30 40 ·Shell-length (mm) ,.,._. = ~~~~~~~~~~~~~~~~~~~~~~~~~~~--~~ Figure 51. Size-frequency distrlbutions c:f ~illaria arid Q~ri th1dea, Station A, Millerton. STATION A Batlllorla Cerlthldea 1-X-71 1-X-71 20 10 ~ - - --'- ---- - --- 20 rO-X'-n r6-X'-n Ill! . -- 0 l~ f~ 6-1-72 6-1-72 ~ 20 ~ 0 u c"' 10 &" .,----c '- '-'-" ~~-- 1-111-72 1-111-72 20 10 18-IV-72 18 -IV-72 20 10 10 30 20 30 Shell-length (mrn) Figure 58. Size-freque!ley distributiotiS o£ B&:tiUan.l!, a.nd ~erlthidelJ:, Station B, Millerton. -103- STATION B Botlllarla Cerlthldea 1-X-71 1-X-71 20 10 • .c.:::_- [ 16-XI-71 20r I' ' 10 1 1 l '.rr{t Ln., .rlf h -, 6-1-72 6-1-72 ...._ 20 ;!! 1-111-72 1-111-72 20 - 10 ' !!'! -~ 18-IV-72 18-IV-72 20 10 30 10 30 Shell-len~th (mm) F1g\Jre :fl, Estimates of abundance of Batillam and Cerithidflll at Stat:l;ons A and B, Millerton, showing means and 95% confidence limits, Averages based upon 10,16 em core, -104- 30 Station A ( + o._ >- 1- 1./) 30 z w Station B 10 20 10 + 0 N D J F M A ------ SPEOJE3 DIVERSITY Species diversity is a mea.stl%'8 of complexity within a COIIIIIIunity. Its precise measurement leads to understanding the processes involved in the development, change, a:ld organization of coiiUiunities. Pianka. (1966) separated hypotheses explaining species diversity into six catagories, the tilae theory, the theory of spatial heterogeneity, the competition hypo· thesis, the producti vit:r_~othesis, the predation hypothesis ,L""a..,nd..._t... h'""e.______theory of climatic stability, concluding that most of them contained components of more than one grouping. An ana.lysis of species diversity in salt marshes within the context of these hypotheses follows, and relationships to the development and organization of marsh commu.nities are discussed. As mentioned, sa.U marshes are species depaup-erate (Teal, 19601 Teal, 1962r ~lacdonald, 1969), This may be caused by the highly vartable environmental conditions and the resultant physiological stresses put upon .the marsh animals and plants. In order to survive, each species must adapt to a wider range or fluctuations than is typical of either totally marine. or totally terrestrial env1roments, Salt marshes are located :i.n extremely high intertidal regions and al:e subjected to tidal action and the resulting alternation of periods of submersion and expo· sure. When submerged, the marsh shares man,y of the physieal a.nd chemical characteristics of water within the adjacent estuary, bay or lagoon. When exposed, the marsh is affected b,;r clima.tic variables, such as air temperature, precipitation, and the local wind regime. Additional environmental variation results from diurnal and seasonal fluctuations of' climatic and oceanographic variables. Over long periods of time, such environmental changes may occur and reflect different stages in the ------ -106- developaent a1' the IIA:t'Sh. This spatial and temporal variability is an iaportant characteristic of salt marsh ecos:rstems and surely impQSes severe restraints upoll the plants and animals inhabiting them. According to the theo:ey of climatic stability. (Kl~pf'er; 1959J Fischer, 1960r Dunlar, 196oJ Connell ard O:rlas, .1964) the contrast between species d1 versity in arctic. a!ld tropical regiOJIS is the result of greatly dif'ferlng el.Uiatic variables. In tropical regioM, evolution of' finer adaptations resources (Klopfer, 1959). In contrast, polar and deaert. regions are exposed to v.l.olent fluct\latioM of cl.iJul.tic. variables and exhibit low species. d1 versity. The salt marsh COIIIJIU!Ii ties occur in transitcn:y zones between terrestrial and marine env.l.ronaents and ase exposed to great oliu.tic variability with. a resultant efieet of lowering species diversity. Tides are ef supreme 1mportanc.e in eontrolling species d1 venity of' the salt marshes. 'l'eal (1962.) has four.d that 45% of· the net production of the C:eorg:l.a salt ma.reh ecosystem is lost to nearby estuarine waters b,y' w&)" of .tidal circulation. As H11tCMnson (19.99) has pointed out, if the total.lliomass in a system is restricted; "then the rarer species in a COJMtunity ma;r be so rare that they do not exist". The limitation o:r productivity of a system plays an important role in reducing species diversity (see Connell and O:das 1 1964 for a comprehensive discussion), = Simpson (1964) suggested that COlllil'lunities tend to diversii)r with time. Older communities, therefore, are 111ore diverse than younger ones, Despite the recent origin of most Pacific coast salt marshes (Haedonald, 1969), the presence Qf older lagoonal sequences, possibly including marsh deposits, has been denwnstrated at Mugu Lagoon (lflmlle, 1966) 0 Mission Bay (Ha.nm, 1926) • San Quintin Bay (Gol.'\Sline and Stewart, 1962) and Black ---·------·------·------ •107- Warrior Lagoon (Phl.eger and Ewing, 1962). The occurrence of certain salt JlaJ."Sh aollUBCS ( eg. Mel.amptm ollyacegus and. tl!l!l'i'l:bidea ¢alifornica) ,-- throughout the California Pleistocene {Grant and. Cale, 1931J Valentine, 1961J Valentine and Mallory, 1965) further suggests that the marshes seen today have been present for at least the last million years. The. lack of eompetition from animals at silllilar trophic levels has perhaps allowed marsh animals to occupy broader :niches and be more abtmda.nt than otherwise possible (Teal, 1962). Do'bzhansky (1950) and Williams (1964) have suggested that when competition fer resources is more rigorous, :niches in the communi ties will be "suller" , resulti:ng in ·greater co111111unity species diversit:r. Do'bzha.nsky (1950) has pointed out that eatastrophic mortality causes selection for increased fecundity auil/or accelerated development anil reproduction, :rather than selection for COlilpetitive ability and interactions with other species. He stated that in tropical regions species will be more highly evolved than in temperate regions due to the lack of indiscriminate catastrophic mortality (ie. great fluctuations in climatic variables), causing more "directed" (den- . sity~~ependent) mortality and increased importance of competitive interaction. Odum and Smalley (19.59) have classified salt marsh animals into - two generalized groupss species that directly f'eed on the living ~ plants and those th&t feed on the decaying plant materials, The marshes have very si~ple food-webs characterized b,r few carnivorous species. In the present study on ~1Jlar1a, I have found no animals directly preying upon the snail. Paine (1966) has experimentally shtmn tr.at the presence cf predators helps to reduce monopolization of a community b,r one species. thWI iooreasing species diversity of the systll!ll, 'rhe distinct lack of· ------ -1os- ea.rlUvores in most aa.rshes JI&Y· help to relluce species diversity. Spatial homogeneity in the marsh ecosystem reduces the varietr of possible niches, The Pacific coast salt aa.rshes form a distinct floristic group .containing relativel;y · f'ewer species and simpler plant· successions than found in other regions of' the world (Chapman, 1960). As a group, salt marshes occurring along this coast exhibit geological characteristics that distinguish them from marshes in other regions of develop~~~ent to small areas :f'ringing sheltered bays, estuaries, and lagoons, ·In trying to explain differences in species diversity, Sanden (1968) i praposed a Stability-Time Hypothesis, At one end o:f' a hypothetical spectrum he placed the "physically-eontrolled" eOIIUllunity in which adapta- l tions of a.r..imals are primaril;y to the physical enviro11111ent, The type of ] ~ COilllllunity is chara.cter:l.zed b.!" low species diversity and is ana.lagous to Mar galef's (1968) immature community (Johnson, 1970), At the other ~nd of the spectrum, Sanders places the ·"biologicaUy accommodated" co!lllllunity that develops under relatively predictable physical conditions, It can be easily ascertained from the aforementioned discussion of species diversity, that salt marsh couunities can be classed as "physically- controlled" in Sand.er•s definition of the term, Salt marshes occur in highly stressed environments, and many severe restraints are placed upon not only the plants and animals but also on the ma.:rsh COW!!unity development, ------ STABILITY n1 NATL'RAL ECOSYSTEMS Stability, the reduction of violent fluctuations of animal popula tions, is an important :feature of a c0111111uni ty. The more violent the oscillation, the greater the chance for partial or total extinction of the animal population, Dunbar (1968) has postulated that simple eco• 8J8tt!IRS 1 ,subjec;t to violent oscillations in the numbers of individual ~----s_p~ee~i_e_s~1 _s_h_o_u_l_d_be_s_u_b~j~e~ct_t_o~hi~gh~ra_t_e_s_o~f~e~xt~in~c~t_i_o_n~·-T~h~e~re~w~i~l~l~,~--~----,c therefore, be selection for greater viability of individual populations and hence greater stability, Whether or not such selection may cause a population to reach an equilibriura is speculative1 al'.d even if it does, stability is not a necessary outcome, The hypothesis of a positive correlation between the stability of a I community and its trophic food-web complexity is an old one, The eeolo- I gieal principle was first recognized qy workers in the early 1900's, i Graham (1915) was one of the first to state that the diversity of I association of species in a community is vital to the stability and "balance" of that community. By studying whitepine weevil population I outbreaks, he found that whitepines growing in a mixed-species community were subject to less. attack from the it~ects when compared to pines growing in a pure stand of trees. Since that t:i.me• ma.ny studies dealing with insect pest outbreaks (see l'itmentel0 1961, for a comprehensive historical review) have shown that increased species diversity may bs correlated with eommunlty stability, 'l'he comprehensive review qy Elton (19.58) dealing )tith invasions of plant and animal populations presents both data ani arguments showing that invasion is much more likely in areas of loo species diversity, In one of the earliest attempts to generate a theory of stability as ===~~~~~--~~~~~~--~~~--~-~--~-~~~------~---~~~- -uo- related to species diversity, MacArthur (1955) reasoned that the nll!llber of links in a food-web determines stability in the system, Specifically, if there are n species of :food that can be eaten by any species in a COIDIIIunity, the probability of eating species i 1 if all other things are equal, is pi • 1/n and a measure of stability would be Shannon's (1949) formula ~~~~~~~~~~~~~~~~~------~------The mathematical properties of the equation are such that S increases with n and reaches a maximum when all the ni 's are equal, In biological terms, this theory states that the faunistically and floristically rich tropical regions show greater community stability be- cause of the multiplicity of inter- and intraspecific connections in the food-web, In the arctic and desert regions, where violent :fluctuations in the depauperate :fauna are common. there is absence of alternative pathways through the trophic food-web pyramids, In summary, MacArthur proposed the following! (a) stability in communities increases as the number of energy pathways increase; (b) if the number of prey species for each species remains constant, an increase in the number of species in the community will increase stability, It should be expected that stability would be higher in a system in which two competing species were both preyed upon b,r one predator than in a system in which the predator is so specialised that it preys on only one species; (c) it follows that by combining (a) and (b), stability can either be achieved by a large number of species with fairly restricted di,ets (ie, in t.ropieal regions) • or a smaller number of species with a broad range of diets (ie, in arctic and desert regions), Since !1acArthur's theoretical suggestions, .many e•~ologists have ------ -111- assumed a positive correlation between trophic community complexity and couunity stability. However, in recent years field and laboratory experiments have shown that this hyPothesis is much more complicated 2 thall it has hitherto appeared, I'; Watt (1964, 1965} studied fluctuations in natural populations of forest insects and failed to find a positive correlation between stability and species diversity in the populations, Watt (1968) explained that these results originated from differences in types of community orgaiz- ation. He concluded that there are two types of community structure! interspecific and trophic, Where generalized feeders are collllllon (ie, northern temperate forests) there are . more connections between a species at one trophic level and others on another trophic level, In inter- specific community organization, there occurs more tr.an one species competing for the same resource at the same level, Watt suggested that in this type of COlllllluni ty, trophic complexity is low since there are fewer actual inter- and intraspecif!.c connections than in a coMunity with many specialized feeders, He felt that the apparent inverse correlation between interspecific and.trophic community complexity might explain the differences of his results when testing MacArthur0 s hypothesis, Patten and Witkamp (1967) in analyzing the dynamics of the flow of cesium in a laboratory system, found no evidence that increasing the complexity of their system.s increased the stability of cesium concentration in the systems• compartments, Hairston ~ !!1. (1968) in laboratory studies with protozoa and l:acteria population interaction$0 suggested that stability on a higher trophic level is increased by diversity ~m a !Oller trophic level, but that stability is not predictable from the consideration only of the number of energy pathways in ------.-..-.-_ --c-=---=-----=--·-· ~~~- -112- the system, . ··· Most recently~ Hurd ~ i!J., (1971) have demonstrated that increased diversity at the plant and herbivore levels in an old field terrestrial ecosystem generates decreased stability at the next higher trophic level, at the highest trophic level, For example, an herbivore community may include several competing herbivore species that are attacked b,y many species of carnivores. These carnivores may "be stenophagous rather than elll."y]:lhagous, (?) Coaplexity of community structure in one trophic level may produce stability at that level but instability at another level. According to Watt (1968), this feature ma.y occur in two ways (a) 1f there is a great amount of competition at the predator level, and one species of the predator. increases, the intensity of competition among the predators is increased, Thus, it tends to hold down the total predator effect of the carnivores; and (b) if one species of herbivore increases rapidly. it may escape predators because there is too much stability at the carniQ vore level to allow an instant increased response by one of the predator species, In this way, stability at ona trophic level might conceivably cause or allow instability in another level. One of the obvious characteristics of }~rthur•s initial theory of stability is that very little o<}nsideration is given to the biology -113- of the different COllllll•.mities: and although general predictions are made, there 1B no discussion of exactly what criteria should be used to deter- mine whether stability or instability exists. This is the difficulty with the whole problem -- how does one measure stability or instability in a COI!llllur.ity? For example, in contrast to MacArthur, Sanders and Slobod Jdn {1969) propose a theory predicting chara1:teristics of populations subject to differential levels of physical and biological disturbance• .In ••unpredictable;; environments, they suggest t~ff'erent l~I!Istory stages will have different sensitivities to environmental changes. Characteristics of "unpredictable" and "predictable" environments need elaboration, but tho hypothesis can be readily tested empirically. All of MacArthur's predictions use stability as the criterion that must be measured to check the validity of his theory. Since the parameters of ,stability are undefined, the theory is difficult to test. li'att (1969) examines different criteria for stability ineiuding "variances in amplitude, wave-hngths, zer.1ths 1 nadirs, or even rates of ascent and descent to and from zeniths" of population change, degrees of synchrony between different species within a zoogeographical unit and other measures. A significant result claimed qy Watt (1969) is that weather or climate affects the stability when an appropriate measure is chosen. although the nature of the effect differs. In a recent a.rticlet Jotdan ~ ii:..l• (1972) = conclude that relative stability of mineral cycling in fot•est ecosystems is a funetiot\ of the length of. time it takes for the mineral-cycling system to recover from a perturbation. The recovery time of the system is a function of' the ratio of recycling of the material through the system to steady-state input of material, Therefore,, systems with low ratios of recycling to steady-state input are more stable than systems with high -114- ratios. Thus, empirical studies in nature .may usie a va:r:iety of criteria which may provide a fa.!rly good :l.dea of stability, This would suggest that a theory of stability and its relation to species diversity may not be possible if it is overly general, A theory may have to elllbody lists of particular types of effects given particular types of initial conditions, In short, I believe that the complexity of a theory of stability may require additional empirical studies as well as theoretical studies, }--~~~~~~~~~~~~~~~~----'~~~~~~~~~~~~~~~~~~---'-~~-~·· ! GENERAL FACTORS LIMITING THE GROWTH OF POPULATIONS There are two major ecological mecha.nisms that regulate the growth aM distribution of popula.tione, Popul.atione may be limited when some requisite resource is in short supply. The populatione in this case are saicl. to be l!mited by either intra• or interspecific competltlon, Populations ny al.l:!o be 111111 ted by some c1.1sturl:ance (either physical or biological) operating incl.ependently of the resources which potentially limit the populations, In this type of mechanil!llll 1 the outside disturbance limits the population before a resource becomes limiting, Both mechanisms msy be equally effective, Prob!.bly an populations share some limiting resource with other populations, As the resource becOJIIes more limiting, the populatione are exposed to increased compe tition, and the probability of competitive exclusion is increased {Hardin, 1960), If there are sufficient irxiependent :reaources, on the oth~ hand, competition can cause adaptive changes in the competing species (Dayton and Hessler t' 1972). The degree of change which pemits coexistence between such species in a competition-based system has been formulated into a eomprehensi ve theoretical model wh:l.ch pred:!.ets that there can be no more species in a system than there a.re independent resources within a given level of environmental stability (MacArthur and I.evir.s 1 1964), On ! the other hand, the immediate effect a dlsturbanee has on a populat:l.on is that resources become less limiting and competition and other inter act5.on~ are reduced. The general ecological significance of predation in dete:rroinir.g the distribution and abundance of inte:rtidal organisl!IS has recently been experl!nentally demom;trated in a nUII!ber of vorks (ConrHlll, 1970; Paine, 19661 D..._yton, 1971). A di!lcussion of these (!{:elog:l.cal plumf1mellll. in relation to e:pooies -116- depauperate salt marsh COllllllunities with emphasis on coaponents of stabil• it;r, fcllONs. Enyiromental P:retUctabiUtx In salt u.rsh cOIIIIIIUltltiesl the prba.:ey stimulus for biological . oscillation is pronounced& that is; physical conditions are highly w.rl.a• ble. Both spatial and temporal physical variability are illlpertant cha.r acter:l.stics of the salt marsh habitat and illlpoae !!Ievere restraints upon the aniMls and plants inhabiting them! Not enly de physical conditioiiS ettect the species living 01!1 the marsh; but they also !lave an affect OJl the development, changei and organization of the coaunity. JohMon (1970) has attributed variation in diversity of infa.una.l benthic CODU!Iun- ities to local variations in the env1ro11!11ent. Among the major factors ·that can influence species diversity in salt ma:J:shes i.neluded are f'luctua.tions in temperature and salinity, precipitation, e:rosi.on a.nd accretion of sedil!lent, homogeneity of the physical environment, and variations in larval recruitment. Wide f'luctuatior.s in these para~~eters are prolably due to local envirol!llllenta.l col'lditions on the marsh and can play an important role in the short-term stability of tho ecosystem. &sides being reBponsible for changes in the size of popula.tior.s (Slcbod ,"'- b kin and Sanders • 1969), . unpredictable oscillations in the physical. environ ment u.-;ually CltlJ.Se more flexible life history strategies (MacArthur and Levins, 1964), The numlx'.rs of i!ldividuals in natural populatior'.s are bound to t'luctuateJ however. mechaniaW!I for resisting 'Violent fluctuations IUI!l enhancing stability may evolve, i:t' they a:l."e eompat.ible with natural selection at the org,anism level (Murdock, 1966), In the present study, for ~ple, seve:r.al possible meehan:lmns for reducing the effects of environmental fluctuaticms in Jlat~l.~ were noted. These inoJ.udea -117- (1) During cold wMther, the snails were found buried 1"'2 em beneath the surface of' the sediment, This u:r be a possible escape reaction to the wide fluctuations in tel!lperature and rainf'all that exist on the marsh. (2) As mentioned previously, the snails a1'e very mobile and can possibly escape :f'roJI undesirable loeal physical anil/or biological conditions existing .on the .marsh. (J) Specilllens were cccasionally fo\md C8lllented 'tv glutinous threads to §il1corpia stems 5-10 em above the ground •.This behavior appeared to be more c011111on in areas of soft anaerobic substrates and possibly represents a mechanism for escape :f'roll unnauall:r low o:eygen tensions d'll'rl.ng tidal sub!4ergence. (4) In laboratory alld field studies, the snails . sh~ed high resistance to· desiccation and fluctuations in salinity. It has lmxg b Lee .ll.tr. Alo (19?0) have estimated that primary production in ca.lt marshes is 20,000 tillles greater than in the open sea. This high marsh \•egetation production has been attributed to a variety of factors (see Keefe, 19?2, for a COlllplete s\l!ll.lllar,y). Some of the major factors are; (1) Marsh plants have adapted well to the hostile marsh environment, High salinities, 40-50 ppt~ (Hoose, 1967), and aM.erobic conditions. of the marsh soil (J..aing. 19110) s.:te tolerated by most marsh plants, The vertical orientation of the lea.ves of most marsh plants help redtlce intense heating (Palmer, 1941), expose the marlmUJI. sur:t'aee to the sunlight • all.d lllinisdze mutual shli!.ding (Jervis, 1964), (2) The high nutrtent content of the marsh soil and water help maintain high productivity. The tides play an important role ey m -us- 1962). For example, P0111eroy .!U. ~· (1969) have found that the sedilllent in well-established S;gartim salt ma:rshes of the easte:m coast of North America. has enough phosphorua for ,500 yea.:rs of growth without replenishment b,r additional input or recycling on the marsh. The large supply of phosphorus in the sediment assures a continuous 130urce f'l1r the Spe.rtina, phytoplankton, and mud-algae of the marsh coiiiJ1lunities. The prima.r,y. producem of salt Jfta+'Shes support two food-webs. The stallding, living ma:rsh vegetation. There are typically fewer consumer species in the web (Teal, 1962) and their abundanees are seasonal (Cameron, 1972) since production of their food reduces in the winter months. The primaxy consume:rs of the second food-web feed on the algae and detritus in the water and on the marsh surlace. The! energy flow of these pop!WL tions is l!lore constant (Teal~ 1962) throttgh the year, since de·tritus is produced continually. Mo'!:e dead plant material :!.s typically present in the colder months, but this is co~tnter-balanced b,y more rapid decomposi tion during the SU111111er months, resulting in a continuous supply of food for the consumers of this web (Odum and Smalley, 19591 de la Cruz, 196:3). The microbial fauna and flora growing on the decaying plant material remove dissolved nitrogen compounds :from the water to produce the increased p:roteir1 levels, 1:.hereey increasing the :protein content of the material ingested by the det:L'itu..~ feede:rs, In direct contrast to arctic and desert environments which also exhibit low species dive:rsity, salt marsh food-resource availability is not only higher but ~-s also relatively constant throughout the year, ======~~~-~~~~~--~-~~~~--~-~-~-~----~- In rela.tively short_ food chains (eg. salt marsh .couunities). any radical change in the numbers at populations at any of the trophic levels in a cOllll!lunity may eause violent repercussions on any of the other levels since there is often fev alternative food choices (Odum, 1959). This JIIS.Y' explain why some groups of arctic organisliiS undergo violent nuctua• tions in nWIIbers, running the gamut f'r0111. superabundance to near extinction. On the other ha!'ldi one of the reasons that salt marsh anima.l populatioi!S the populations. Salt Ma;rsh Animal Feeding Strategies and Commun!:ty Stability By applying some of MacArthur's (1955) conclusions to salt marsh COIII!IIunities, it is possible to relate COllll!lunity stability to animal feeding strategies. MacArthur shOKS that a community may achieve stability by having either many speeies with restricted diets or few species ~lth broad diets. The former alternative will permit greater efficiency. all other things being equal, and will be the one selected (MacArthur, 1955: Teal, 1962). The majority of salt marsh animals, howevert exhibit the latter alternative. The majority of salt marsh species are detritus feeders or filter feeders. There are a few species - of carrdvwes that prey upon the detrital feed When analyzing the feeding biology of ~ and BaHUarJ.a from a "populational" point of view, the animals raay be eoi!Siderad generalists, Looking at the possible size range of the material ingested qy the snails, it ean be concluded that as a whole both species are seleeting a l' -uo- uounts of detrital uterial (eg. bacteria, algal bits, etc,) l(hich illerease the' variety of !!IUbsta.nces that can be ingested by the gutrOpods. This type of feeding stratoegy would be advantageous in a c011111uni ty with a short food-web and low species divoersity, Odlll!l {1959) has stated that. the uount. of choice which energy has in following the paths through the food-web call be a measure of stability in a COIIIIIunit:y. Generalized feeders m3¥ also reduce the monopolization of one or more species of prey. Paine (19~) has experimentall.y .shown that stat fish preying upon a variety of organislll! can increSlle species d1 versity by reducing interspecific e0111petition. The lll!llle hypothesis aay be applied to the genl!iralized feeders of salt marshes, :By increasing species diversity of the prey species through eU7yp~~us predation (assmdng that the probability of b!liJJg eaten is proportionate to the abundance cf the prey), there can be a corresponding increase in the stability of a community in MacArthur's (1955) definition of.the term, Fhen analyzing the feeding biology of the indi.viduals . of JlG:Ullaria al'ld Cgrithitlea1 it has been .shown that both species quantitativel.y select diatOlll species with respect to size. Selectivity may have two advantages in relation to ccmunity and population dyn!UI1es. First of all, food selectivity with 1~spect to predator size can reduce the effects of intraspecific com1letit1on, This type of feedil!g strategy in organis!lls with high densities C'.an be a particular .advantage, This may apply to B!!.tU!~ which had. d.ensities greater than 50,000 snails per square metl:lr, Second of allo selectivity can reduce interspecific competition. Dodson (1970) has shown that C<~lllplelllentary f'eedi~ niches of freshwater :Plal'lktiwres can be sustained by size-selective predation•. Galbr-aith's (1967) study of the effect of p~tion of rain~ trout populatio~s supports Dodson•s -121- c011ploefttal:7 niche hypothesis. The !SUe· conclusions ms.y be .applied when ana~ing the eoaparative feeding select!vi ty of Ba.tillaria and Qerithidea (see Feeding Biology Section). J31 radu.oing bath int.er- and ·- intraspecific competition throUgh feeding selectivity, corresponding population oscillations of species caused l:!r c0111petition can also· be reduced. Reducing these oscillations iMures increased populational and comau.~ty stability. Species d~uperate couuriit1:es, sueh as sall: marshes, ut be 1aeal~ suited for testing hypotheses about aspects of community dynamics. The accessibility and relatively short species list of these habitats corAid erably reduces the task of separating out individual components or inte.r acting groups for study. Salt marsh diatoM alld the snails Ba.t111aria and ~rHbidtm 1 comprise a natural interacting .unit involving competition between an introduced and an endemic funct1ona.l herbivore of the plants, regardless of wh~ther the lllajor food soUl'Ce of the snails &:r:e the diatoms, The h0111ogeneity of the salt ~Mrsh e~viroment can aid in future controlled cxperi!llente.tion with this system, and some oi' S,ts basic biology has 'bllen discovered in this study. SUMMARY 1. Populations of the sa.lt ma.rsh gastropod, lla1;1llar1a zonalis, were sampled at two salt ma.rshes located in Tomales Bay, California, over a period of 17 n1onths, 2, The gastropod was patchil;r distributed at Walker Creek but aggregated only occasionally at Millerton. The patchiness at Walker Creek did not change in response to variations in abundance, :3. Annual rates of grOll'tb of Batillarla were estima.ted from the shifts in the modes of size-frequency distributions and from mark• recapture experiments, The data was described by the Ford-Walford equation as1 Lt+l • 0,7016 + 0,8408 Lt. :Both methods of esti!ll 4, Settlement of juveniles of' the 1971 year-group showed that recruitment was not ra!ldom over both salt marshes, .5o Eat.ill¢a was commonly infected by larval trematodes, Analysis showed 1.7.5% of the gastropods were infected at beth salt marshes, 6, Comparative analysis of the estimates of abundance and population age-structure of the srudl at the different san1pllng stations in both salt m.a:t'llhes showed a. compa:rati ve1y large and relatively stable popula~ tion size, 7. Comparative analysis of the fewing biology of l}atilla:ril!: and P~thi.~ QaUfqmi,cf!, an "eeologioal equivalent" of ~tiDarin, sh011ed the deposit feeders ingested great amounts of benthic diatoms, . 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S<".a.sonal infection of the snail, .Qil;tl!.IU.!i~ alli: m;:p~c~ Halde!!lan, w1 th larval tnmatodes. lni l!.!ssays in the Natural Sciences, Univ. So, Calif, Press, Los Angeles, p, 203-210, -----=~·· 19?2, An annotated kgy to the cercariae that develop in the snail Qi:!&~ ~li:t'w:niSA• Bull, So, Calif, Acad, Sci, 7l1 39-42. Mayr, E. 1963, Ani•l Species and Evolution, Harva1'd Univ, Press, Caabri~e. 797 p, Obrebsk1 1 S, 1968, On the population ecology of two intertidal in-vertebrates and the paleoecologi.eal sigftif'ica.nce of size-trequeney distributions of living and dead shells of the bi'l."'l.lve Tra.nsenellj!: tantilla, Ph.D, Dissertation. Univ. Chicago! 102 p, · OdWll, E. P. 19.59. Fu:ndaaentals of Ecology. W, :B, Saunders Co, Philadelphia, . .546 p, OdWll, E, P, and A, A. de ia CruZ, 1963, DetrituS as a ujor e011ponent of ecosystems. A. I, B, S, Bull, 13a 39-40. j-C-~~~~•O!Wl_,-E.-!t.-a.~-A-.-----E.---S=a-1-lsy-,-l9~-.-Sempa...,-iacn-ct"-pepulat.-ion-anerf!3·-~~~~~. flow or a herbivorous and a deposit-feeding invertebrate in the salt marsh ecosystem, Proe, Nat. Acad, 1 U, s. A, 45a 617•622, Paine, R, T, 1966, FoCd web coaplexity and species diversity, .Mer, Natur, lOOt 65-75, . Palmer, E, L, 1941, Marshes and their en\oirons, Nature Mag, :34a 205-212, Patten, B. C, and M, Witkamp. 1967. Systems analysis of l34eesium kinetics in terrestrial mieroeosllll!, Ecology 11.81 813-824, Paulson, T, C, and R, s. Schelte!l'la, 1968. Seleetlve feeding on algal ~ells by the veliger la:rvae of ~rl~ ~~ (Ga.atro~ 1 Pr.)Sobranchia), lliol, Bull, 134a 481--489, Pbelege-r, F, :e. aild c. C, Ewing, 1~62. Sed.iaentary and oceanography of co.&etal lagoons in :Baja California, Mexico, Geol, Soc, Amer. Bull, 73a 145-182. Phillips, B. F, 1969, The population ecology of the whelk :!)1.::Mtbai!!. !C<;&q.t.!l. iB Western Australia, Au.o;t. J, Mar, Freshwat, Res, 201 225·265. Pianka, E, R, 1966, latitudinal g:radients in species divernityl A review of concepts, ~~er, Natur. lOOt JJ-46, Pomeroy, L, R,, R. E, Johannes, E. :!', OdUll! and B, Roffman, 1969. The phosphorus antl zinc cycles and p:roduetivi ty of the salt »a:r.sh, lnt n. J, Nelson and F, c. Evans (Eda,) Proo, 2nd Natl, Symp, on Radioeeolog. 412-419. Redifeld, A, c. 1965. Ontogeny of a salt mamh estuary, Science 1471 . 50-:-55. Sanders, H, L, 1968, Marino benthic diversitya A comparative study, Amer, Natur, 1021 234-282, Shannon, c. E, 1949. The Matheatieal Theon::r o'f COI!Illlunieation. Univ. Illinois Press, . 12.5 p, · Sillpson, c. G, 1964, Species diversity or North American recent 1112111111als, Syst, Zocl, 131 $7•73. S1obodkin, L, B. and H. L, Sallders, 1969. On the contribution of en·r.lronmental ~redictabi11ty to. species diversity, Ina G, M, llocdwell and H. H,. Sl!lith (FAs,), Diversity and Stability in Ecolog ical Systems, Brookhaven Symp, Natl, Lab, 22t 82-9.5. Southwood, T, R, E, 1966, Ecological Methods, Methuen and Co, Ltd, London, 391 P• 1------.'Teal, J-.---K.-----1962-. -Energrfl~i~thel!llllt-marsh-ec Valentine, J, W. 1961, Paleoecologic molluscan geography of the Californian Pleistocene, Univ, Call:f, Pub, Geol, Sci, )41 309-442. Valentine, J, W, and B. Mallory, 196.5. Recurrent groups of bonded. species in mixed death assemblages, J. Geol, '731 683·701• Varme, J, E, 1966. Paleoecological aspects of the recent ecology of Mugu Lagoon, California, Ph,D, Dissertation. Univ. Calif, • Los Angeles, Waters, ll. E, ar.d 1i. R, Henson, Some Sl!JIIpling attrlbutes o:r the nega tive binomial distribution with special reference to :forest ir..sects, For, Sci, 5: 397-412, Watt, K. E. F, 1964, Comments on fluctuations of a!limal populatlooo slid /lliGasures o:f' coDunity stability; Can, Entomol, 961 1434-1442, ----:--· 1965, Co!lll!lunity stability and the strategy o:f biological control, Can, Entomol, 971 887-89.5. --..,---'' 1968, Ecology and Resource Management, ~lc:Graw·Hill, New York, 4.50 p. WilliSJlm, c. B, 1964, Patterns in Nature, Academic Press, New York. 232 p, Williams, L, G, 1971. Larval development and feeding biology of ll!!:::;;;.i~!Jf,a ~;t;~"l.§...\i1£.~i!i (Eschschcltz) and ,Aeo:U£l!£l. lJ:!!l)j.llosa (L,), !<'.aster's Thesis, Uni vemity of the Pacific. 62 p, Wooowell, G, M, and H, H. Smith (Eas,), 1969, Diversity and Stability in Eeologlcal Systems, Brookhll.ven SYJap, Nat, Lab, No, 22, Yonge, C, M, 1930, The crystalline style of the mollusca and a carnivorous habit eannot nomally coexist, Nature 1251 4114·445, -----,....,..-'' 1932, Notes on feedi!lg and digestion in fte>,~era and VermetuJ!, with a diseussion on t.he occurrence of the eeystalline style in the Gastropoda, Brlt, }Ius, Nat, Hbt, 1(10) 1 259w281, Appendix A Estiutes of the Negative ll:l.nomial l'a:rameter k -131- Applications of the negative binomial distribution are reviewed by Bliss and Fisher (195.3). The distribution 1s cOlllpletely defined by two paraaeters, the arithmetic mean (m) and a positive exponent (k), Values for obtaining the probability of observing various n11111bers of units per sample are obtained by't where p • m/k and q • 1 + p, By expansion of this expression, the prob- ability Px an observational unit x will contein o, 1, 2, ••• individ uals ist where R = pfq = m/(k + m), Bliss and Fisher (195.3) have reviewed the various methods of obtain ing estimates for the exponent k, The easiest r.~ethod of calcul.ating k is from the :fh'St and second momenta ( descri bad in the Dispersion Section), but the efficiency of this method is largel:y dependent upon various com binations of k and. m (Anscombe, 19.50). A fully efficient likelihood determination o:f k is described by Bliss and Fisher (1953). Scores (z1) are co!llputed from trial values of k , selected so that they bracket the 1 . required estiute k o for which zi .. 0 in the equ.'\tiona 1 Estimates of the negative binomial parameter k using the moment method are presented in Tables A-I to A-X, Table A-XI shows a ccmpar~ ison of k values at tuo sampling localities using both the moment and Maximum likelihood estimates (see Dispersion Section for a discussion of these resul.ts). c Table A~I, Estimates of negative binomial parameter k for B&t1llaz1i, c Station 1. Walker Creek. ~ 2 Date N X s k V(k) T t S,E, 1~19-?1 20 6,25 )4,46 1.337 0,460 T e • 119,25 + 17;49,3 2~ 3-'71 20. 8,25 27.77 J,486 3.16fl. T • - 93,61 +• 1.5254.29 2~16-'71 20 6,85 20,02 3.560 3. 7,50 T "' • ,58,38 t 5582,55 3- .5-'71 20 4,JO 11.69 2.,500 2,189 T • - 41,24 t 1435• .52 3~17-'i'l 20 7.55 23.31 J,209 2.743 T • - 88,80 t 12220,64 4- 8-71 19 11.52 54.37 3,100 2,155 T ~ - 382,22 + 133197.59 4-21-?1 20 ?.75 29.36 2.?79 1.939 T • - 7,34 t 21384,76 5-21-71 20 11.05 97.10 1,419 0,437 T .. - )48,8 t 1518184,22 6- 9-71 20 15.75 71.78 4,428 3.944 T •- 382,72 t 229382,63 6•25-71 20 18,00 187,05 1,916 0,684 T "' - 1142,48 t 7984408,25 1- 9-'71 19 12,68 115.34 1,567 OS35 T • 294,88 t 240749,5,86 9-21-71 20 14.90 700,94 o.:324 0,047 T .. - 1675),68 + 4738140683 10- e-n 20 3.00 11,15 1,103 0,4)4 T ~ - 26,24 + 2936,84 . - Where N .. number of samples, -x .. sample mea111, s 2 = sample variance, k ~ negative binomial estimate, V(k) m variance of k, T t S,E, ~ 3rd moment test of fit to negative binomial distribution t standard error of T, ======~~~--_--_--~=:cc____ ~- ~~ ~c~~------~-----_c_:-~- -13:3- Table A-II, Fstimates of negative binomial pa:ra.meter k for :Bat111&1a. Station 2. Walker Creek, :~ Date N -X 82 k V(k) T + S,E, . - 1-19-71 26 10,00 52.84 2.:3:34 1,184 T .. - 170,22 + 146689,85 - . 2- 3-71 20 11.55 47.63 3.698 3,02'Z '1' .. - 124,86 t-'2'4704.04 2-16-71 16 10.94 64,19 2,246 1.:3:24 · T., - 435,16 t 341645,52 3- 5-71 20 n.6o 101,52 1.497 0,476 T • 10,31 t 1646470,52 3-17-71 20 10,60 88.57 1,441 0,49l- T .. 28,8:3 + 1130615,34 ~ - 4- 8-71 20 11.75 50.72 :3.542 2,723 T ., - 280,81 t 93067.43 4-21-71 20 11.75 80.30 2.014 o.a:n T ,. - 444,04 t .594755,16 - 5-21-71 20 21.15 2$1.24 1.953 0,688 T a • 2652,08 + 18833335,99 . - 6- 9-71 19 36.68 830,00 1,696 0,527 T = • 127lf7 +- 8410:37290.3 ~ 6-25-71 20 32.25 778.30 1.394 0,363 T = - 1962810 +- 8140:39788,9 7- 9-71 20 24-.20 4-19.85 1,480 0,414 T = - 6055,36 t 1190518082 9-21-71 20 20,20 504.06 0,8:33 0,168 T a - 6846,46 '!:; 41062463?,1 10- 8-71 20 6,40 54.15 0,858 0,205 T = - 412,28 t 484991,35 - 11-1.5-71 20 7.75 63,88 1,070 o,28i T .. - 666,16 t .599739. 91~ 1- 7-72 20 12.90 27:3.99 0,637 0,115 T • • 5J46,82 t 97193048,72 • "' 3- 8-72 20 6.95 26o.79 0,190 0,024 T ~ - 9722.16 t 61008255:3,1 4-21-?2 20 7.40 219,83 0,258 0,035 T = - 4942,90 +- 2139306?5,8 6-16-72 20 7,00 63.78 0,980 0,023 T "' - 665.23 '!; 63187,48 Where N .. nUIIlber of samples, x- .. sample mean, s 2 ... sample variance, k .. negative binomial estimate, V(k) .. "-arianee of k, T t S,E. ,. 3rd moment test of fit to negat1.ve binomial distribution t standa:L'Ii error ofT. Table A-III, Estimates of negative bin!llll:tal pan!.meter k for Ba.ti]J:irl_a, Station 3, · Walker creek. 2• Date N X- s k V(k) T '!: S,E, 1-19-71 20 34,00 775.68 1.559 0,436 T • - 2681,41 t 712796569.9 2- 3-71 19 30.84 . 434.58 2.356 0,964 T • - 6442,22 t 87672410,20 2-16-?l 20 23.70 116,64 6,043 6.704 T = - 1190,34 + 836o35.34 3- 5:-11 20 26,8.5 148,2/.j. 5.939 6,145 T = - 168641 t 1736255,63 3-17-71 20 24.70 6o,85 16,875 85,465 T = 20,06 t 83455,88 4- 9-71 20 2:3,25 106,09 6.525 8,053 T • 106,21 t 605683,82 4-21-71 20 26.45 74.37 14,6oo 54,866 T.=- 326,02 + 157643,86 5•21-71 20 24.30 148.54 4.753 3.908 T = - 945,69 t 1969978,53 6- 9-?1 20 28.30 297,06 2.979 1,449 T ~ 690.94 '!: 2180)201,64 6-25-71 20 25.80 133.'75 6,167. 6,?84 T = - 1163.70 '!: 1250281,09 7- 9-71 20 20.55 92.05 5.906 6,76o T = - 862,99 t 414227.77 7-23-71 20 23,80 106,38 6,859 8,946 T = - 1119,24 t 596895.51 9-21-71 20 11,20 57.32 2.719 1.562 T = 144,80 '!: 164346,6.5 10- 8-71 20 16.65 299.39 0,980 0.218 T "' - :3.88 + 70323569,28 11-1.5-71 20 20,85 182,77 2,685 1,261 T = - 2796,41 '!: 5492006,91 1- 7-(2 20 15,85 320,24 0,825 0,167 T = - 6687,79 t 108053067.5 3• 8-72 20 10,35 42,76 3.305 2,476 T = ~ 166,69 + 58410,68 4-21-?2 20 12.30 137.91 1,204 0,320 T w - 1609,g1 t 5283001,80 6-16-72 20 23.:38 149,63 3.705 3.112 T "' - :3916,28 t 161~534, 38 Where N ,. nUlllber of samples, x- ., sample mean, s 2 .. sample variance, k = negative binomial estimate• V(k) ., variance of k, T +- S,E, ., 3:rd moment test of fit to negative binomial distribution t standard error of T, ------=--·==·-=-"=-- . ~~~--~---- -13.5- Table A-IV, Estilaates of negative binomial paraMeter k for llatillp.rla, StatiOn 4; · Walker Creek, Date N ::c- 82 k V(k) T +- S,E, 9-21-71 20 5.6o .58.36 0 • .594 0,116 T = - 198,35 t 1022361,89 10- 8-71 20 6,85 33.61 1, '7 _5!1. 0,762 T "' - 69,85 t 49101,88 11-1.5-71 20 13.05 177.52 1.035 0,246 T c - 1380,86 t 1)6o830),83 1- 7-72 20 13.30 195.17 0.97.3 0,221 T = - 2139,85 t 196024_52,11 3- 8-72 20 4,01 16.07 1,103 0,352 T = - 6,27 +- 48,66 4-21-'72 20 3.55 15,02 1.513 1,103 T = - 62,12 +- 128,67 6-16-'12 20 6.32 28,13 1.776 1.543 T = 3,82 t 12,68 2 Where N - mmber of sam:ples 0 i • sample mean, s • sample variance, k = negative binomial estimate, V(k) = variance of k, T ! S,E, = 3rd moment test of fit to negative binomial d.istri bution t st.1.ndard error of T. ~~~------=------137- Ta.ble A~VI. Estimates of negative b1n0lll1al parameter k for llatil]M',.i• Station 1. Millerton, -138- Table A-VII, Estilllates of negative binomial parameter k for ~Ulm•· Station 2. Millert '" Date N -X 82 k V(k) T t S,E, 1-14-71 20 13.95 56.36 4 • .588 4.527 T • - 431,65 + 108267,44 2- 6-71 20 13,15 28,66 . 11,149 46,246 '? - 9575.03 +.. 44,1'1* 2-17-71 20 13,60 34.57 8,821 23.545 T • - 1149,13 t 181,08* 3- 6-71 20 9.85 21.40 8,401 27.l26 T • 10,41 t 8,86* 3•18-71 20 11.90 35.36 6,037 6,001 T ,. ,07 +- 22841~.17 4- 9-71 20 10,15 13 • .50 30,731 1581.490 T • - 1484,50 t 820,43* 4-21-71 20 7.85 13.71 10.510 66,176 T • - 4318,21 t 10)4,42* 5-21-71 20 8,00 6.5:3 43.420 0,226 T • - 142,18 t 78,28* 6-10-71 20 9.00 17,05 10,06o 49.880 T • - 2063,09 t 20,26* 6-24-71 20 5.80 13.22 4.533 7.961 T • 1359.32 :!: 35.2lil 7- 8-71 20 2.50 9.11 0,946 0,)49 T • - 8,62 t 1926,51 7-22-71 20 1.25 5.36 0,381 O,l26 T • • 6,91 t 1494,18 9-18-71 20 1.75 2.72 3.145 10,200 T • • 14,28 t 3.14* 10-10-71 20 5.35 29,08 1,206 0,399 T • • 25,38 :!: 48052,21 11-16-71 20 8.20 84,)8 0,883 0,204 T ~ - 108,86 t 1779?22,89 1- 5-72 20 6.85 27.92 2,227 1,261 T .. - 128,84 '!; 2?.245,38 3- 7-72 20 3.50 3.52 465 • .500 10,250 T M 13.24 t 2,53* 4-20-72 20 3.70 15.38 1,172 0,442 T = - 76,1¥) '!; 7218,87 6-15-72 20 ),80 17,12 1,181 0,562 T • - 69,51 + 711819.62 Where N ,. number of samples, x,. sa.Drp1e mean, i .. sample variance. k '" negative binomial estimate, V(k) "' vnriattee of k0 T t s.E ... )rd. moment test of :f'i.t to negative bi.nomia1 distrt'butlon t standard error of T. *Values !'lOt slgnif:l.cant, r===~====~="=------:=--==---=,~-=-_.c::===-=--=- ---...o=:o'-=:=~=-=------ -139- '!'able A-VIII, Estimates of negative binOlllial pamlleter k for Ba.tUls;ta.. Station 3. Millerton• . .. . 2 Date N -X s k V(k) T t S,E, 1... 1~t-'ll 15 11.33 76.23 1.979 1,085 T • 13,69 t 689497,87 2-.~-71 16 34.31 129.16 12,413 38.592 T • 41,39 t 1082715.11 2~1?-'Zl-. 1~~'31!..9J___'Z.5.9_6_2.!l.,:3!K> 20.100 T • 125.._'ll_t 22,42* 3• 6-71 20 29.80 72.91 20.6o1 127.310 T • 138391.91 t 7145,00* I 3-18-71 20 10,15 84.45 1.386 0,428 T • • 474.94 t 1022682,28 I'.I !i 4- 9-71 19 6,84 8.25 33.210 4101,0.50 T • 195,01 + 14,101* - . 4-21-71 20 8,20 21.95 4,887 7.329 T • - 20,06 + 6o45,;)8 ~'I li - ~ 5·21-71 20 6,80 12.91 7.574 29,021 T .. 983.48 t 13,39* l I 6~10-71 20 8,25 17.04 7.744 25.!;46 T • 2257,51~ t 17.55* 6-24-71 20 7.80 20,80 4,680 6,801 1' .. 80.23 + !)260,18 I~ 7- 8-71 20 ).55 6,26 4.649 14,010 T • - 0,95 t 1)9,03 ?-22-71 20 1.55 1.71 2,348 7.277 T • 4.38 t 0,67* 9•18-71 20 3.90 7.67 4,031 8,385 T = 280,67 t 12,04* 10-10-71 20 10,25 58.20 2,191 1.0~31 T ~ - 379,89 t 20?898.57 11·16-71 20 10,20 28.:38 5.723 9.377 T = - 120,71 +- 84,01* 1- 5-72 20 7.45 27.63 2.751 1.934 T = - 96.27 t 17955.65 3- 7-72 20 9.15 32.23 3.626 3.271 T • - 2),48 t 23276,69 4-20-72 20 6.40 . 9.94 11,581 115,010 T ~ 388,09 t 61,88* 6-15-72 20 5,40 6,18 12.131~ 1.5.103 T • 28,1 t 10,96* Where N "' num·oor of :;;anrples; i .. sample mean, l· .. sample varianee, k .. negative binomial estimate~ V(k) ., variance of k, T t S,E. "' 3rd moment test of fit to negative binomial distribution t standard error ~f T. Vallles not stgnificant, Table A-IX, Estimates of negative binomial pa.ra~~~eter k for Ba.tillaria. ~~~~~~~~~~~~~~~-g~~icn-4.~¥~~~e~cn..-~~~~~~~~~~~~~~ Date N X- 52 k V(k) T! S,E, ~ 11 9-19-71 20 5.85 15,18 3.665 3.513 T a - 39,32 t 2366,43 10-10-11 20 5.35 36,03 0,9:3:3 0,249 T • • 30,37 t 126759,63 I ll-16-?l 20 6,90 65/36 0,814 0,185 T "' - 362,87 t 918048,79 ~ 1- .5-72 20 1.05 34.58 1,806 0,799 T m • 119,56 + 519)9,68 I 3- 7-12 20 5.65 14.24 3.116 3.511 T .. • 36,73 t 1928,67 i 4-20-72 20 5.6o 13.20 41,27 4,002 T = • 30,91 t 2:33:3,33 6-15-72 20 6,10 16.25 3.513 3,089 T ~ - 29,89 t 1883,42 - 2 Where N ~· number of samples, x • sample mean 0 s = sample variance, k .. negative binomial estimate, V(k) = variance of k0 T t S,E, "' 3rd moment test of fit to negative binomial distribution t standard error ofT. ------.o--~---~· -141- Table A-X, Estimates of negative binomial parameter k for Batilla;ia. Station 5. Millerton, Date N -X s2 k V(k) T t S,E, 9-19-71 20 4,90 18.20 1,805 0,948 T a • 37,51 ± 7440,83 10-10-71 20 6.20 49.85 0,881 0,216 T • - 261,08 t 364908.99 11-16-71 20 9.90 268.94 0.378 0,056 T • - 1403,53 ± 205782910,1 1- 5-72 20 7.90 46.52 1.616 0.614 T "' - 236.40 t 11~283 5,18 J- 7-72 20 4.15 18.34 1.213 0,449 T • - 57.33 "!: 11820,53 4-20-?2 20 2 • .50 5.53 2,065 2,601 T • - 390,00 t 174.49* 6-1.5-?2 20 2.75 5.03 3.612 3.814 T • • 414,01 t .490* Where N = n1ll!lber of su:p1es, x .. sample mean, s2 .. suple varianoe, k "' negative bino.mial est1mate0 V(k) .. variance of k. T t S,E ... )rd. moment test of fit to negative binomial dietribution t sta.ndard error ofT, *Values not. significant, -142- Table A-XI, COlllparisons of the ma:dmWIIUkelihood (4) and 111011ent (B) estimate for the negative binomial param.eter !c, Walker Creek--Station 2 Millerton--Station 3 .ua;te ~ Date A l:l 1-19-'?1 2,608 2.:3:34 1,14-71 5.553 4,588 2- 3-71 3.708 :3.698 2. 6-71 9.639 11,149 2-16-71 1.969 2,246 2•17-71 8,563 8,821 3-17-71 1.997 1,441 3- 6·?1 23.594 8,404 4- 8-71 2,155 3.542 3~17-71 1,464 6,037 4-21-71 21,.52! 2o014 4- 8-71 100,000+ 30,731 5-21-71 1.733 1.953 4-21-71 5.231 10.510 6· 9-71 1.387 1,696 5-21•71 10,035 43,420 7- 9-'11 1.493 1,480 6- 9-71 8,;394 10,06o 7-23-71 0,944 G,883 6-24-71 7.0'12 4,5)3 9-21-71 0,232 0,833 7-23-7.L 2,598 0.381 10~ 9-71 0.700 1,070 9-21-71 3.711 3.127 11.,.15-71 0,571 0,637 10- 9-?1 1,589 1,206 1- 7•'72 0,206 0,190 11-15-71 4,869 0,883 3- 8-72 0.1~.51 0,258 1- 7-72 2,548 2.227 4-20-'12 0,255 0,980 3- 8-72 4,25) 465.900 Appendix B Estimates of Mean Crowding and Patchiness I The mean of a set o:f samples can be expressed in the couon fonu Q . • • E x-'Q j-1 . j' where Q is the number of samples, The mean relates the nwaber of indiv iduals per quadrat. Lloyd (1967) proposes that mean crowding (Ill)* is the number of other individuals per individual in each quadrat expressed 1!(1 · * If 11 • ~ xJN ~------~------·~~1~------~------where N is the number of individuals in the quadrat, Therefore, m* is expressed in the form of the mean number of other individuals per quadxat per individual, Since Q .& jo-1 Lloyd then exp!'esses mean crowding in the forms m•* -1 B,y substituting the common form for the mean and variance, the relation· ship becomesr : .. m+ (cl /m - l) In other words, the amount qy whieh the variance to mean l'!ltio exceeds Ullity, e.dded to the mean density, gives the expressian "mean crowding", For example, in a random distribution. the variance-to-mean ratio is one and *m will therefore be equal to m, As indieat®d bo.r Lloyd, the underly1.ng assumption of the llllstimat.es of mMn crowding :!.o that the numb!lrs of organisms !if!Uet be v. rando111 I!!W!ple ------_--:;:::_ __ _ -14.5- :f'rolll a negative binolllial distribution. The :paraaeterl! of' this distri bution are 11 (mean density) and. k (from the negative binOIIIial estimate), The variance is as :f'ollowst 2 2 cr • II + (a • k) Sul:stituting this into the expression frOlll mean crOII'ding givest a* • 111 + (m/k) By substituting the maximUlll likelihood esti!Rate form and k (i and k1) into the above equation~ If the ma:x:iaUlll likelihood estimates of k are not available, Lloyd ShOll'S that the moment estimate may be obtained using the eo:r:rection factor for sampling bias such thatt 2 ~ .. i + (s?i - 1)(1 + s /q;h where q is the nUlllber of sa.m];)ling units, A ata.ndard error for mean crowding calculated in the above way is estimated ast * 2 * ...:_ <-=-> (~) S,E, (x)~ q X X (x + 2 i/X) Lloyd proposes that patchiness (m/m)* is expressed bye *m/m .. 1 + 1/k Thus, the negative b"lnomial parameter k has eeological meal'rl.ng in tha.·t the inverse of the k estimate is that proportion by uhich mean CrOII'ding exceeds mean density. 'the estimate of patchiness, therefore, measures how many times as crowded on the average an individual :l.s M it would be if the popul&t:l.on exhibited a l':'l!.r.dom distribution. The sample est:l.m·l;e o:f' patchiness is expressed as& while the standard error for patchiness esti~~&ted by IIIOIIIeftts is1 s.E. (;rx) ~ a2/i2 V (2~qi) Estilla.te of a.ea.n crowding and patchiness with their staMam errors are presented in the following Tables (B-I ~o B•XI), where k is obtained using the moment estimates method. See the Dispersion Section for the discussion of these results with respect to Lla,rd1 s hypothetical model. •147- '!'able B-I. M011ent estimates cf' mean crowding alii!. patchiness. Station 1, Walker Creek. Mean Crowding Patchiness II, II ii Date *X t S.E. *i/x '!: s.E. E ~ 1-19-71 11.1)6 t ),311 1.782 t o.383 t 2• 3-71 10.665 '!: 1.946 1.293 t 0,147 ] 2-16-71 6.074 t 1.487 1.412 t 0.238 )• 5-71 8.815 + 1.661 1,287 t 0,15) 3-17-71 9o9.55 '!: 1.919 1,319 '!: 0,161 4- 8•71 15.324 '!: 2.859 1,)29 t 0.153 I' I 4-21-71 10.606 t 2.171 1,369 t 0,181 5-21-71 19.147 +- 5.288 1.732 t 0.331 6- 9-71 19.359 '!:: 2,824 1,229 t 0,101 6-25•71 27.663 t 6,219 1.537 t 0,226 7- 9-71 21.083 t 5.589 1.662 t 0,299 9~;n~·;1 68,211 '!: 41,804 4,578 t 2,136 - -148- Table B-II. M0111ent estimates of mean crowding and patcl:rl.ness, Station 2, Walker Creek, Mean Crowding Patchinees Date *X'.!; S,E, .it/x* t S,E, 1•19-71 14,397 t 3,082 1,439 ± 0,201 2- 3-71 14.729 t 2.4.58 1,275 '!: 0,127 2•16-71 15.970 t 3.852 1,460 '.!: 0,229 ,_ 5-71 19.644 t 5.246 1,693 '.!; 0,310 3-17-71 18,245 t 5.014 1, 721 t 0,:327 4- 8-71 15.128 + 2,569 1,287 t 0,132 4-21-71 17.754 + 4,028 1,511! 0,226 5-21:•71 32,2851: 7.018 1.526 t 0,218 6- 9-m 59.012 t 14,133 l.6o9 +- 0,254 6-25-11 56.249 + 14,831 1,71¥+ t 0,313 7- 9~71 41,135 + 10.574 1.699 t 0,296 7•23-71 45.633 :!: 16,410 2,259 t o• .587 9:-21-71 14,354 t 5.447 2,243 + 0,626 10- s~n 15.378 t 5,105 1.98/f t 0,473 11-15'-71 )4,806 t 14,881 2.698 :!: 0,855 1- ?-72 53.332 t 42.992 7.674 t. 4,729 3- 8•72 15,684 t 6,114 2.324 t 0,668 4-21-72 41,869 t 21.175 5.658 t J,019 6-16,..72 18,043 +- .5. 978 1. 705 :t 0,326 ------~====~-~------~------ -149- Table B·III, M0111ent estimates of mean crowding and patchiness, Station ), Walker Creek, Mean Crowding Patchiness Date *X '!: S,E, *x/x t S,E, -19-71 • 6 t 1J.92:3 1,66:3 t 0,274 2- 3-71 44,248 +- 8,?78 1.435 '!: 0,1?7 2-16-?1 2?,663 t 3,282 1,167 +- 0,071 3- 5-71 31,418 '!: 3.70:3 1,170 '!: 0,070 3-17-71 26,1?1 :!:: 2,015 1,059 '!: O,OJ2 ] 4- 8-71 26,8ZI8 t ),0(9 1.155 t 0,06? " 4-21-?1 28,271 t 2,257 1.069 '!: 0,0)5 5-21-?1 29.4?? '!: 3.932 1,213 '!: 0,088 6- 9-?1 3?.9'73 t 6,444 1,342 '!: 0,136 6-25-'11 30,026 :l: J,491 1,164 '!: o.o69 ?- 9-71 24,067 t 2.943 1.1?1 t 0,0?5 7-23-'71 2?,J02 t 3,048 1,148 +- o;o64 9-21-'71 15.413 t J,OOl 1,376 t 0,169 10- 8-71 34 • .5'+9 +- n. 469 2,075 ·t 0,492 11-15-71 28.779 '!: 5.293 1,380 t 0,156 1- 7-'72 )6,278 t 13.316 2,289 + o.6o9 3- 8-72 13.5!14 '!: 2,428 -1,309 + 0.144 ~ 4-21-72 22,978 t 6,895 1,868 '2.: 0,394 6-16-72 J8,862 t ?.049 1.344 + 0,142 -1.50- patchiness, Station 4, Walker Creek, Mean Crowding Patchiness *'' Date *X '!: S.E, x/x 1: S,E, 9•21-71 1.5.898 ! 7.3'12 2,839 '± 0.992 10- 8-71 10,896 t 2,843 1, .591 '!: 0,286 11-1.5•71 26,310 +- 8, .567 2,016 '!: 0,468 1- ?-72 27.129 t 9 0:344 2,085 t 0, .504 ,_ 8•72 ).935 '!: 0,115 1.109 +- 0,129 4-21-72 24.973 '!: 5. 777 2,024 ~· o. 6ol . ' 6·16-'72 23,875 '!: 6,825 2,104· t {), 713 -1.51- patchiness, Station 5, Walker Creek, Mean Crowding Patchiness Date *X 1;S.E, *i:/x '!; S,E, 9-21-?1 7.141 !; 2.124 1,661 :!: 0,353 10- 8-71 14.775 "!: 3.789 1,615 t 0,283 11.. 15-?1 50.973 '!; 9.074 1.381 '!: 0,149 1- 1-1'2. .58.663 t 12.905 1, .549 '!: 0,221 3- 8-72 9.654 '!: 1.a:n 1,305 "!: 0,1,56 4•21~72 49.113 t 9.121 1,395 +- 0,152 6-16-'?'2 27.302 t 4.976 1.,142 + 0,134 ~ ------ 'l'able B•VI. M0111ent estilllates of llleaD eroll'dil'lg and patchiness, Stat10l'l 1. M11lert.Cll. Mean Crowdil'lg Patchiness * . Date *X:!; S.E. i/x t s.E. :t-14-n rs;o4ir006o 1~5 :!: 0,24J 2- 6-71 42.455 t 9.265 1,442 t 0,197 2-17-71 39.989 t 7.165 1,296 t 0.1)4 3- 6-71 :35.209 t 5.923 1,3Jij.'!; O,lJJ J-19-71 3J.869 + 4.491 1,217 t 0,087 . - 4- 9-71 23.921 t 3.1:33 1,196 t 0,084 4-21-71 31.043 +- 8,042 1,671 +- 0.287 5-21-71 35.145 t 14.997 2,693 +- 0,852 6•10-71 45.529 +- 23.895 3.557 t 1.410 6-24-71 20,265 t 7,704 2,016 t 0,478 7- 8-71 20,813 :!; 8,093 2,365 t 0,676 7-22-71 15,406 t 3.691 1.548 +- 0,249 9•19-71 12.357 "!: 2.1+79 1.:3'13 t 0,172 1o-1o~n 25.010 +- z~. 769 1.397 t 0,166 11•16•71 49.423 t 19,613 2 • .509 t o. 729 1- .5-72 ,511-,865 + 24,728 2.918 ± 0,979 " 3- 7-72 25,805 +- 5.024 1,4·14 t 0,1'7J 4-20-72 11.1.5? + 2.849 1, 571 + 0,275 . - 6-15-72 20,265 +- 7.703. 2,109 t 0.469 • Table ll-VII, M0111ent estiutes fit aean crowding and patchiness. Station 2, Millerton, Mean Crowding Patchiness Date *X t S,E, *i/x t s.E, ...J:-- _.I..·-J:.at-t.L l7•u;5-...-Z;489 .r.22~...--tr.lo - . - 2• 6-71 14.:3:39 t 1,490 1,090 +- 0,055 2-17'"71 15,1.56 t 1, 693 1,114 +- 0,062 3- 6-11 11,035 t 1,368 1,120 t 0,074 3-19-71 13,896 + 1,8,56 1.168 + 0,085 - . - 4- 9-71 10~482 t 0,950 1,032 +- 0,042 4-21-71 8,605:!: 1,076 1,096 t 0,074 5-21-71 7.815 +- 0,614 0,97'7 t 0,032 6-10-71 9.904 +- 1,195 1,100 t 0,068 6-24--71 '7 ,105 t 1,276 1,225 t 0.138 7- 8•71 5.335 t 2,213 2,133 t 0,673 7•22-'71 .. 5.09'7 t 3.455 4,0?8 t 2.189 9•19·71 2.:m t o.75l 1.3:32 t 0,325 lOql0-71 10,011 t 3.259 1,8?1 +- o.439 ll-16-?1 18,0'73 t 6,621 2,204 +- o• .589 1- 5-72 10,018 +- 2,327 1,462 t 0,228 3- '7-72 3. 508 + 0,.528 1,002 t 0,091 ~ 4-20-?2 7~034 t 2,462 1.981 '!: {),489 6-15-72 5.091 t 3.455 4,078 +- 2.189 Table B-VIu. Moment estil!lates of mean crowding and pa.teb1ness. Statton ), Millerton, Meaft Crowding Patchiness * .. *• ·. Date X+-- S.E, i/x + s.E. 1-J},.a.-11 ,.J.(~f.J- .., "c?--+--l'..-58"- ..,.. l-.5's--rir.zoa. - . 2- 6-71 37.096 t 3.369 1,081 t 0.040 2•17-71 )1.934 t 2,629 1.049 t 0.032 3- 6-71 31.252 t 2.153 1.049 +- 0,027 3-19-71 17.770 t 5.007 1.751 t 0,343 4- 9-71 7.049 + 0,787 1.030 t 0,058 . - 4-21-71 9.905 + 1.5'71 1,208 t O.llJ - . 5-21-71 7. 710 t 1.113 1.134 t o.o94 6-10•11 9.329 t 1.2,511-. 1.131 t o.o84 6-24-71 9.495 t 1.551 1.217 +- 0,119 7- 8-71 14-.3:32 t 0.919 1.220 t 0.174 7-22-71 1.671 t 0.709 1.4.53 +- 0.491~ 9-19-71 4,892 t 1.044 1,254 t 0,179 10-10-'71 15.05? +- 3.319 1,469 ...- 0.21.2 11·16-71 32,006 t 1.696 1,177 t 0.094 1- 5-72 10.226 t 2.119 1.373 "!: 0.184 3- 7-?2 11. '(22 t 2,058 1,281 t 0,1)8 4-20-'(2 6.959.'!; 0.922 1.087 t 0,079 6~15-72 1,673 + 0.805 1.455 + 0.561 - m -155- patchiness. Station 4. Millerton, Mean arowding Patchiness Date *X~ S,E,.. *i/x t S,E, .. 9-19~71 7,481 t 1,4-50 1.2'79 t 0,1.59 10-10-71 11.445 t 4,2)6 2,139 t 0,582 11•16-11 15.9.54 t 6,182 2,312 '!: 0,66o 1- .5-72 11.090 + 2,839 1.577 t 0,276 J- 7-72 7.204 t 1,1.!{)3 1,27.5 t 0,159 4-20-72 6.986 t 1,312 1.24-7 t 0.149 6-15·72 7,005 '!: 1.523 1,467 :!; 0.397 I------"Ta.:-b-le-B-x.-Memant-as-t-1-lr.ates-of-me:an-._A,:on-ding-arlll~:------~- patchiness, Station 5. Millerton, Mean Crowding Patchiness Date *X 1: S,E, *i/x 't S,E, 9-19-71 7.'117 +- 2,10.5 1.5'75 ± o.:;o1 10-10-71 13.697 ! .5.142 2,209 t 0,609 11-16-'11 39.656 +- 22,613 4,001 ! 1. 737 1- 5-72 12,970 t 3.459 1,642 t 0,302 :;- 1-72 7.752 t 2,618 1,868 t 0,460 4~20-72 3. 764 :!: 1.167 1,,506 t 0,343 6-1.5-72 7.842 t 2,965 1.7!12-- t 0,399 l------'~ble-B--X!-.-Me-l'lt~nt-sst-L-nates-l;,.:'f m.ean-ero-w"ding-and:-----~---- patchiness, Station 6. Millerton, Mean Crowding Patchiness Date *X '!; S,E. *x/x t s.E, 9-19-71 7.487 + 0.729 1.012 t 0.047 ~ i. 10-10-71 6,968 ± 1, 585 1.)79 t 0,211 ! 11-16-71 16.318 ± 4.744 1,783 t O,J6J 1- 5-72 17.518 ± 6,)49 2.176 t o. 57.5 J- '1-'12 5.!'#3 t 0,879 1.119 t 0,107 4-20-72 8,192 t 3,027 2,048 t 0,.559 6-1.5-72 14.437 :!: .5· 967 1.497 t 0,488