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Colonization of lilypads by Sida crystallina (O.F. Mèuller) in Marion Lake, British Columbia Starr, Paul Joseph 1973

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c ! COLONIZATION OF LILYPADS BY SIDA CRYSTALLINA (O.F. MULLER) IN MARION LAKE, BRITISH COLUMBIA by PAUL JOSEPH STARR B.A., Yale University, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s thesis as conforming to the required standard. THE UNIVERSTIY OF BRITISH A p r i l , 1973 COLUMBIA In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission fo r extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Zoology The University of B r i t i s h Columbia Vancouver 8, Canada Date May 11. 1973 i ABSTRACT Sida c r y s t a l l i n a , a cladoceran, i s found i n densities up to 45 per square centimeter underneath l i l y p a d s (Nuphar poly-sepalum) i n Marion Lake, B r i t i s h Columbia. Floats, boats, and other a r t i f i c i a l substrates are rapidly colonized by Sida to densities comparable to those underneath l i l y p a d s . Sida only p e r s i s t s underneath h o r i z o n t a l - l y i n g substrates. On sub-strates receiving d i r e c t sunlight, filamentous algae grow and displace Sida. The high densities of Sida under li l y p a d s a t t r a c t several predators, both vertebrate and invertebrate; however, the over-a l l Sida populationsappears to be unaffected by predation. At the end of the summer, the population declines r a p i d l y , possibly due to predation as well as to natural mortality. Rapid f l u s h -ing occurs i n Marion Lake a f t e r a rainstorm, and li l y p a d s appear to serve as a refuge from the current. I t i s also l i k e l y that l i l y p a d s serve as feeding locations i n areas of r e l a t i v e l y high phytoplankton concentrations (compared with the open water of the lake). The observed colonization behaviour would then be s e l e c t i v e l y advantageous i f feeding s i t e s are i n short supply and i n t r a - s p e c i f i c competition i s high. The dynamics of colonization were monitored four times over the summer, and population growth parameters were obtained con-currently. From a comparision of these, i t seems that most of the observed growth on the a r t i f i c i a l substrates i s due to im-migration and not to reproduction. A l l population drops are due to emigration. From an experiment te s t i n g the rate of colonization i i as a function of the distance to the nearest Nuphar bed, i t appears that the colonization i s by clumps of Sida at the mercy of the lake currents. During periods of persistent wind, colon-i z a t i o n i s most rapid i n areas where these clumps tend to be concentrated by the wind. Otherwise, the a r t i f i c i a l substrates nearest to the Nuphar beds are colonized f i r s t . The population s t a t i s t i c s obtained over the summer show that a f t e r an i n i t i a l period of rapid growth, the population growth rate becomes very slow (probably not much more than one b i r t h per i n d i v i d u a l ) . I t i s l i k e l y that Sida i s e x p l o i t i n g i t s environment to a maximum by maintaining i t s population as near as possible to i t s carrying capacity. i i i TABLE OF CONTENTS PAGE ABSTRACT i LIST OF TABLES . . . i v LIST OF FIGURES V ACKNOWLEDGEMENTS v i INTRODUCTION . . . . . . . . 1 MATERIALS AND METHODS 11 RESULTS. 25 DISCUSSION . . . 47 CONCLUSIONS. . 60 LITERATURE CITED .61 APPENDIX I. Data for the densities of Sida on natural l i l y p a d s during the summer of 1969. . . . .63 APPENDIX I I . Data for the colonization rate by Sida on a r t i f i c i a l substrates (summer, 19701 T . . . 64 APPENDIX I I I . Data for the colo n i z a t i o n rate by Sida at various distances from a l i l y p a d b e d . . . . . 66 APPENDIX IV. Data for temperature s p e c i f i c growth rates of Sida 67 APPENDIX V. Growth rate increments for post-abdominal abductors before and a f t e r moulting (early June, 1970 - IV inst a r s before maturity) . .68 APPENDIX VI. Growth rate increments for post-abdominal abductors before and a f t e r moulting (summer, 1970 - V inst a r s before maturity) i v LIST OF TABLES PAGE TABLE I. Population growth rate data for Sida c r y s t a l l i n a (abstracted from Voskresensky and Lebedeva, 1964). 4 TABLE I I . Marion Lake open-water plankton samples containing Sida c r y s t a l l i n a , 1963 and 1966. (G. Sandercock, unpub. data.) 7 TABLE III.Sida population s t a t i s t i c s f or summer, 1970 . . . 35 TABLE IV. Growth rate data for Daphnia galeata (from H a l l , 1964) . 50 TABLE V. Growth rates for Sida extrapolated from Figure 8. 52 V LIST OF FIGURES PAGE FIGURE 1. Grid system of Marion Lake. 13 FIGURE 2. Approximate extent of Nuphar beds (and other . macrophytes) i n Marion Lake (Neish, 1970) . . . . 15 FIGURE 3. Lilypad sampler 17 FIGURE 4. Sida c r y s t a l l i n a 23 2 FIGURE 5. Average number of Sida per cm on natural l i l y p a d s taken randomly from Marion Lake (May - July, 1969). . . 27 FIGURE 6. Rate of col o n i z a t i o n by Sida on a r t i f i c i a l substrates at d i f f e r e n t times of the summer, 1970.30 FIGURE 7. Rate of colonization by Sida on a r t i f i c i a l substrates at various distances from a l i l y -pad bed, August and September, 1970 33 FIGURE 8. Temperature s p e c i f i c growth rate for Sida i n s i t u at Marion Lake 37 FIGURE 9. Summary of measurements of post-abdominal abduc-tors from two enti r e natural l i l y p a d populations taken June 3 and 17, 1969 40 FIGURE 10. Summary of post-abdomen growth increments mea-sured i n a l l growth rate experiments .42 FIGURE 11. Sida population growth modelled for each colo-n i z a t i o n experiment, using the regression equa-t i o n from Figure 8. . . . 45 v i ACKNOWLEDGEMENTS This work was supported by the International B i o l o g i c a l Programme grant to Dr. I.E. Ef f o r d and by innumerable teaching assistantships i n Biology 101. I would l i k e to thank Dr. Eff o r d for supporting and advising me and t h i s work i n sp i t e of adversity and mountain climbing. I would also l i k e to thank Kanji Tsumura and G a i l Burnison for preparing the i l l u s t r a t i o n s . I appreciated very much the c r i t i -c a l reviews of t h i s manuscript by Dr. Eff o r d , Dr. T.G. Northcote, and Dr. A.G. Lewis. I f e e l that the time I have spent i n the I n s t i t u t e has been made e s p e c i a l l y worthwhile because of a l l the friends I have come to know and who have gently (I hope) chided me along over the years. F i n a l l y , I wish to thank my wife Marilyn for her care and support, and for her patience as the wife of a graduate student. 1 INTRODUCTION Sid a c r y s t a l l i n a i s a p r i m i t i v e , u n s p e c i a l i z e d c l a d o c e r a n (Branchiapoda, C r u s t a c e a - Brooks, 1959). I t i s t y p i c a l l y a l i t t o r a l , weed-dwelling s p e c i e s and i s r a r e l y found i n the p l a n k t o n . In Marion Lake, B r i t i s h Columbia, S^ c r y s t a l l i n a i s found v e r y abundantly under the l i l y p a d , Nuphar polysepalum. In a d d i t i o n , any f l o a t , boat, or s i m i l a r a r t i f i c i a l s u b s t r a t e i n the l a k e i s c o l o n i z e d w i t h l a r g e numbers o f these animals i n a matter of days. T h i s r a p i d c o l o n i z a t i o n seems t o p o i n t t o a p o o l of organisms which i s always ready t o migrate because i t seems u n l i k e l y t h a t r a p i d r e p r o d u c t i o n c o u l d account f o r a l l •the observed p o p u l a t i o n growth. Although some of the p r e d a t o r s of the l a k e feed on S i d a , none appear t o be a f f e c t i n g substan-t i a l l y the huge numbers which are p r e s e n t . A v a i l a b l e space, however, may be an important l i m i t i n g f a c t o r . I f t h i s i s so, r a p i d c o l o n i z a t i o n o f a l l new s u b s t r a t e s as soon as they appear would be c o m p e t i t i v e l y advantageous. I f the r a t e of c o l o n i z a t i o n and the accompanying r e l e v a n t p o p u l a t i o n growth d a t a were known, growth and immigration c o u l d be p a r t i t i o n e d . T h i s i n t u r n might g i v e some i n f o r m a t i o n on what f a c t o r s l i m i t t h i s p a r t i c u l a r p o p u l a t i o n . The o b s e r v a t i o n t h a t these animals r e g u l a r l y i n f e s t p l a s t i c s u b s t r a t e s was used t o study the c o l o n i z a t i o n p r o c e s s . Standard s u b s t r a t e s were d i s t r i b u t e d i n a l o c a l i z e d a r e a o f the l a k e and sampled a t i n t e r v a l s i n o r d e r t o measure the r a t e of c o l o n -i z a t i o n as a f u n c t i o n of time. In c o n j u n c t i o n w i t h t h i s , b i r t h r a t e and growth r a t e data were o b t a i n e d a t the same temperature 2 regimes as the above experiments. These experiments were r e -peated s e v e r a l times over the summer t o t e s t f o r s e a s o n a l d i f -f e r e n c e s . F i n a l l y , i n o r d e r to t r y and understand the mech-anism o f c o l o n i z a t i o n , the above experiments were repeated s i m u l t a n e o u s l y a t v a r y i n g d i s t a n c e s from a source of i n f e s -t a t i o n (such as a l i l y p a d bed). C o l o n i z a t i o n C o l o n i z a t i o n as a b i o l o g i c a l p rocess has been p r i m a r i l y known i n the l i t e r a t u r e by the i n v a s i o n of i s l a n d s by a l l types of animals and p l a n t s , and by the i n f e s t a t i o n of de novo s u b s t r a t e s by b a c t e r i a , a l g a e , and protozoans. S i m b e r l o f f and W i lson (1969) g i v e the b e s t example of an e x p e r i m e n t a l mani-p u l a t i o n of i s l a n d c o l o n i z a t i o n , and C a i r n s e t a_l (1969) monitored the c o l o n i z a t i o n of g l a s s s l i d e s suspended i n water by protozoans. Both s t u d i e s are concerned w i t h m u l t i - s p e c i e s c o l o n i z a t i o n and the r e l a t i o n s h i p of the c o l o n i z a t i o n r a t e t o the e x t i n c t i o n r a t e . These two r a t e s should become equal as the c o l o n i z e d body reaches a s a t u r a t i o n l e v e l , but the a c t u a l s p e c i e s composition remains i n a c o n s t a n t f l u x as new ones invade and o l d e r ones become e x t i n c t . T h i s i s one of the p r e d i c t i o n s made by MacArthur and Wilson (1967) i n t h e i r com-pre h e n s i v e t h e o r e t i c a l treatment of the s u b j e c t . Of g r e a t e r i n t e r e s t t o t h i s study are MacArthur and Wilson's p r e d i c t i o n s f o r a s u c c e s s f u l s t r a t e g y o f c o l o n i z a t i o n . For a s i n g l e c o l o -n i z i n g p a i r , they p r e d i c t (p. 78) t h a t the p r o b a b i l i t y of l e a v i n g descendants which w i l l reach a maximum p o p u l a t i o n s i z e (K) i s about r / A , where r i s the i n t r i n s i c r a t e of 3 increase. I f t h i s i s so, r can be maximized best by de-( A ) . They predi c t , therefore, that a good colonizing species w i l l have a f a i r l y low b i r t h rate, an even lower death rate, and a very large K. These same c h a r a c t e r i s t i c s should apply to a so-called " f u g i t i v e species" (Hutchinson, 1951), a species which i s incapable of competing e f f i c i e n t l y when i t i s sympatric with i t s a l l i e d species, but i s capable of invad-ing new habitats very quickly. Provided the environment i s i n s u f f i c i e n t f l u x , these species should be able to maintain themselves i n spi t e of t h e i r high p r o b a b i l i t y of ex t i n c t i o n . Population Growth Population growth data for Daphnia sp. i s extremely common i n the l i t e r a t u r e (eg. Slobodkin, 1954; H a l l , 1964). Similar data f o r Sida i s almost non-existent. However, Vosk-resenky and Lebedeva (1964) have observed i n d i v i d u a l Sida  c r y s t a l l i n a i n s i t u and have recorded considerable growth and reproductive data f o r t h i s species. They used glass tub-ing 2 cm. i n diameter and bent at 60° (1/3 of the way along the tube); these tubes were covered at both ends with f i n e s i l k b o l t i n g c l o t h that would not allow any young to escape but would allow f a i r l y free transmission of food p a r t i c l e s . The bend i n the tubing allowed the animals within to remain i n water when the tubing was removed from the lake f o r obser-vation. Their data (Table I ) primarily demonstrates that the population changed some of i t s growth parameters over the summer. Only the time f o r embryo development remained creasing the death rate 4 Table I Population growth rate data for Sida c r y s t a l l i n a (abstracted from Voskresensky and Lebedeva (1964)) June July August Day of reproductive maturation 4 th 4-5th 8-10th Mean length at time of reproductive maturation (mm) 1.99 1.78 1.65 Day of f i r s t c l utch 7-8th 6-7th 12th Intervals between clutches(days) 2 2 2 Mean length a f t e r 15 days (mm) 2.54 2.24 2.14 Mean # of young per clutch 8.4 3.6 3.8 Number of clutches i n the f i r s t 15 days 3 3.7 1.6 Mean number of young i n the f i r s t 15 days 27.8 12.8 6.0 5 the same. They also give data on population age structure. Growth rates of i n d i v i d u a l Sida seem to follow (except f o r some changes over the summer) a normal logarithmic growth curve (steep i n i t i a l growth followed by a l e v e l i n g of the curve). Transferring t h i s information to measurements of natural populations shows that the majority of in d i v i d u a l s on any given day are only 1 - 2 days old. F i f t e e n day old i n -divi d u a l s make up 0 - 6% of the population depending on the time of the summer. They also note that e s p e c i a l l y i n June the number of young per brood fluctuated widely. Unfortunately, there i s no mention of age-specific growth rate, number of in s t a r s to maturity, or any dependency of the growth rate on temperatures or food concentrations. Therefore, i t i s d i f f i -c u l t to decide whether the changes i n population growth para-meters demonstrated between June and August are due to r e a l differences i n the populations or to d i f f e r e n t temperature regimes. I t i s important to note that Sida i s parthenogenic as are many other cladocerans; therefore, during the summer, every i n d i v i d u a l born i s a p o t e n t i a l egg-bearer. Only i n the l a t e summer and early f a l l do males begin to appear. Sida c r y s t a l l i n a i n Marion Lake There also do not seem to by anypublished references to the colonization behavior by Sida. In f a c t , there are very few nontaxonomic references to t h i s animal. C a r l (1940) records Sida c r y s t a l l i n a i n B r i t i s h Columbia as "Common i n a l l regions investigated". He found i t i n a l l the c l i m a t i c 6 b e l t s of the province and i n lakes at every a l t i t u d e i n each b e l t . S c o u r f i e l d and Harding (1958) record Sida c r y s t a l l i n a i n B r i t a i n among weeds, e s p e c i a l l y Potamogeton, along the margins of lakes and ponds. Quade (1969) records great quantities of Sida i n the l i t t o r a l regions of some lakes i n Minnesota. In one lake (Bad Medicine Lake) 85% of a l l the cladoceran population sampled was of t h i s species. Sida  c r y s t a l l i n a was abundant on four species of Potamogeton, but not on Potamogeton natans or Nuphar variegatum. The f i r s t group are broadleaved plants, but the l a t t e r two were choked with f l o a t i n g leaves. The above observations are consistent with those of Marion Lake. 23. c r y s t a l l i n a i s found there primarily under the l i l y p a d , but also on the bottom mud substrate (M. Hoebel, pers. comm.) and i n Potamogeton natans (the numbers are quite scarce r e l a t i v e to l i l y p a d concentrations). I t i s rare-l y found i n the open water plankton samples of Marion Lake (Table I I , G. Sandercock, unpublished data). Observations of Sida colonization indicated that i t only seems to p e r s i s t underneath horizontal substrates. V e r t i c a l a r t i f i c i a l sub-strates are i n i t i a l l y i n fested by Sida, but a f t e r 5 to 10 days they are replaced e n t i r e l y by epiphytic algae (Hyatt, pers. comm.). Only where the a l g a l growth i s i n h i b i t e d due to i n s u f f i c i e n c y of l i g h t , such as underneath a l i l y p a d , do the Sida f l o u r i s h . Predation on Sida i n Marion Lake The number of p o t e n t i a l predators on Sida i n Marion Lake are l i m i t e d to four vertebrate species and perhaps two or 7 Table II Marion Lake open-water plankton samples containing Sida c r y s t a l l i n a i n 1963 (G. Sandercock, unpub. data) Date Depth #/100 l i t r e Percent Sida of t o t a l Cladocera at that depth Percent Sida of t o t a l Cladocera at a l l depths on that date May 28- a l l 0 0 0 August 6 depths sampled Aug. 21 15 cm 40 6.3 1/2 M 20 1.4 2 1/2M 20 1.6 3 1/2M 0 0 4 1/2M 0 0 1.4 Sept. 4 15 cm 20 11. 1 1/2M 40 5.7 3 1/2M 0 0 5 M 0 0 1.3 Sept. 22 0 M 40 3.7 1/2 M 0 0 1 1/2M 0 0 2 1/2M 0 0 3 1/2M 0 0 4 1/2M 0 0 0.7 Oct. 6- a l l 0 0 0 Nov. 23 depths sampled 8 Table II (Cont.) Marion Lake open-water plankton samples containing Sida c r y s t a l l i n a i n 1966 (G. Sandercock, unpub. data) Date Depth #/100 l i t r e s Percent Sida of t o t a l Cladocera at that depth Percent Sida of t o t a l Cladocera at a l l depths on that date May 16-June 5 a l l depths sampled 0 0 0 June 6 0 M 1 M 2 M 3 M 20 0 0 0 25. 0 0 0 2. June 15-July 15 a l l depths 0 0 < 0 July 22 0 M 1 M 2 M 3 M 20 0 0 0 7. 0 0 0 0.9 July 29 a l l depths 0 0 0 Aug. 5 0 M 1 M 3 M 40 0 0 5.9 0 0 1.6 Aug. 12 0 M 1 M 2 M 3 M 20 0 0 0 14.3 0 0 0 0.8 Sept. 1 a l l depths 0 0 0 Sept. 12 0 M 1 M 2 M 3 M 0 0 0 20 0 0 0 5.6 0.9 (dupl.) 0 M 1 M 2 M 3 M 20 0 0 0 2.2 0 0 0 0.9 Sept. 15-Oct.14 a l l depths 0 0 0 9 three invertebrate species. There are two species of f i s h , Salmo gairdneri (rainbow trout) and Qncorhynchus nerka (kokanee salmon), and both can take Sida. However, the larger rainbows (older than 1 year and greater than 15 cm) are primarily bottom feeders and very r a r e l y take Sida (Sandercock, 1970) . E f f o r d and Tsumura (1973) .  have shown that kokanee salmon feed heavily on Cladocera during the l a t e summer (August). At that time, 45% by weight and 75% by numbers of the stomach contents consist of Cladocera. Unfortunately, the sample s i z e f o r these data i s small and may not be t o t a l l y representative. For instance, Sandercock (1970) reporting on the same species at the same time of year does not record s i m i l a r data. Hyatt (pers. comm) has shown that kokanee do not surface feed at temperatures above 18°C, which occur frequently during the month of August. I t would seem l i k e l y that many of the Cladocera eaten by kokanee would be bottom dwellers, rather than Sida which reside j u s t below the surface. Cladocera are a r e l a t i v e l y i n s i g n i f i c a n t source of food at other months of the year. Young rainbow trout are a much more serious p o t e n t i a l predator on Sida. P r i o r to l a t e July, those trout which are less than 15 cm long (less than 1 year old) are known to cue i n on Sida as a food source (Hyatt, pers. comm.). I t i s not known how quickly they cue i n or the proportion of the d i e t which i s composed of Sida. However, the p o t e n t i a l e f f e c t i s quite large. A small f i s h (<6 cm) can eat approximately . 500 Sida every 24 hours at normal lake temperatures (~20°C). 10 Larger f i s h can eat two or three times th i s amount. This assumes stomachs e n t i r e l y f u l l of Sida. There are approximate-l y 1000 to 1500 f i s h i n t h i s s i z e class i n Marion Lake. The young of the year (less than 5 cm) are r e c r u i t e d from the i n l e t beginning i n l a t e July and throughout August (Hyatt, pers. comm.). These f i s h are known to be planktivorous and have been observed grazing the undersides of l i l y p a d s and of logs. A l l rainbow trout can surface feed at normal summer lake temperatures. There are two species of salamanders as we l l : Ambystoma  g r a c i l e and Taricha granulosa. The l a t t e r species i s much less abundant than the f i r s t and does not feed on Sida i n any s i g n i f i c a n t amounts. Ambystoma, however, has a sub-population which l i v e s and feeds i n Nuphar beds (Neish, 1971). During the summer, Sida makes up 63% by volume of the stomach con-tents of these animals. A single Ambystoma occupys a t e r r -2 l t o r y of roughtly 1 M which would contain 2 - 3 Nuphar l e a f s . However, gut contents would only show 200 to 500 Sida at any one time, and digestion turnover time averaged approximately 24 hours at summer lake temperatures. The primary invertebrate predator i s the damselfly larva (Enallagma boreale). Although i t s main source of food during the summer months i s Sida (over 60% by numbers), i t i s s t i l l only capable of eating .7 to 10 per day (Pearlstone, i n press). Another p o t e n t i a l predator i s Hydra sp.; i t seems only to occur during the l a t e summer and early f a l l . Obser-vations i n aquaria indicate that i t i s a voracious feeder on Sida, but no f i e l d data i s a v a i l a b l e . 11 MATERIALS AND METHODS Marion Lake P h y s i c a l C h a r a c t e r i s t i c s The work pres e n t e d i n t h i s study i s p a r t of an i n t e g r a t e d study of a f r e s h w a t e r l a k e community. The p r o j e c t i s p a r t of the Canadian c o n t r i b u t i o n t o . t h e I n t e r n a t i o n a l B i o l o g i c a l Programme and i s p r i m a r i l y concerned w i t h d e f i n i n g the f a c t o r s l i m i t i n g energy t r a n s f e r r a t e s w i t h i n the l a k e ( E f f o r d , 1967/ 1972). Marion Lake ( F i g s . 1 and 2) i s s i t u a t e d i n the C oast Mountains of southwestern B r i t i s h Columbia a t an e l e v a t i o n of 300 meters. The l a k e l i e s i n a narrow, steep s i d e d v a l l e y running i n a g e n e r a l n o r t h - s o u t h d i r e c t i o n . I t i s p a r t of the watershed of the P i t t (and hence, the F r a s e r ) R i v e r . The c l i m a t e i s b e s t d e s c r i b e d as b e i n g m i l d and wet (annual mean temperature i s about 9°C and the average annual r a i n f a l l i s approximately 240 cm) ( E f f o r d , 1967) . The l a k e i t s e l f has an average area of 13.7 h e c t a r e s and i s about 800 meters long and 200 meters wide. The g r e a t e s t depth i s 7 meters and the average depth i s 2.4 meters. Of g r e a t importance to the b i o l o g y of the l a k e i s the f a c t t h a t d u r i n g p e r i o d s of heavy r a i n f a l l , severe f l o o d i n g and f l u s h i n g o c c u r s : the l e v e l of the l a k e can r i s e 1 meter i n 24 hours and a volume of water e q u i v a l e n t to the volume of the l a k e can pass through i n l e s s than one day. Sampler A d e v i c e , w i t h a s l i d i n g trapdoor and powered by s u r g i -c a l t u b i n g ( F i g . 3 ) , was used t o sample an e n t i r e l i l y p a d 12 F i g . 1 Grid system of Marion Lake OUTLET 14 F i g . 2 Approximate extent of Nuphar beds (and other macrophytes) i n Marion Lake (Neish, 1971). ^» Water flow 3+m. E ^ ~ ^ Nuphar Roly.se pq la E I Z J ; Potamogeton natans & Equisetum ipMM& Submerged vegetation ; Dry areas 16 F i g . 3 Lilypad sampler 17 18 and the surrounding water column; i t cut o f f the l i l y p a d leaf plus 15 to 30 cm of the stem. The sampler was as large i n diameter (30 cm) as was p r a c t i c a l . Speed i n engulfing the leaf and i n closing the trapdoor was e s s e n t i a l because the Sida would f a l l o f f the leaf when disturbed and swim away. The water i n the sampler was pumped into a plankton net (112ji) and the animals were preserved. The l i l y p a d and the sampler were rinsed i n lake water as f a r away from the other l i l y p a d s as possible to reduce contamination from free-swimming Sida from disturbed l i l y p a d s . The samples were preserved i n form-aldehyde. This was not t o t a l l y s a t i s f a c t o r y because i t caused the carapaces to f l i p open and the eggs or young would f a l l out. Quick freezing of the samples seemed to have s i m i l a r poor r e s u l t s . Natural l i l y p a d sampling An i n i t i a l program f o r sampling the natural l i l y p a d s of Marion Lake was designed using a g r i d system (Fig. 1). The lake was divided i n h a l f between quadrats 47 and 51 and each half was considered a separate sampling unit. A l l quadrats containing l i l y p a d s - (Fig. 2) were l i s t e d and quadrats from each unit were chosen by means of a random number table. Once a week, four l i l y p a d s , two from each sampling unit (one per quadrat) were sampled and preserved. For the purposes of the sampling program, the sampling units ensured that samples would be taken from a l l over the lake, but a l l l i l y p a d s were assumed to be homogenous and hence r e p l i c a t e d . In addition to the regular sampling program, samples were also taken 19 occasionally i n Potamogeton natans. Sampling was begun i n t h i s fashion A p r i l 29, 1969 and was terminated on November 12, 1969. Relevant data pertaining to water depth at the l i l y p a d , sur-face water temperature, and weather were also recorded on sampling days. A r t i f i c i a l Lilypad Sampling During the summer of 1970, the area i n Quadrat 63 (Fig. 1) was used f o r an intensive study of the colonization of a r t i f i c a l l i l y p a d s . The log marked "D" was used as a p i e r and a f l o a t 10 meters long was constructed p a r a l l e l to and to the north of log "D". This f l o a t was about 5 meters from the log and access to i t was by means of a moveable walkway. In t h i s way, the en t i r e area between the log and the f l o a t could be sampled from the walkway without disturbing the water and the l i l y p a d s . The area was mostly free of l i l y p a d s and the bottom was mainly open mud; the depth varied from IM to 3M. A r t i f i c i a l l i l y p a d s ( p l a s t i c 2 container l i d s ) 22 cm i n diameter (area = 383 cm ) weighted with stones t i e d to strings of appropriate length were d i s t r i b u t e d as randomly as possible i n the enclosed area. Experiments te s t i n g the colonization of a r t i f i c i a l l i l y p a d s were conducted on four occasions i n 1970 by placing about 40 a r t i f i c i a l l i l y p a d s i n t o the experimental area. Approximately every 24 hours, four r e p l i c a t e l i l y p a d s were removed ( a l l l i l y p a d s were assumed to be homogeneous). Following the f i r s t experiment, r e p l i c a t e l i l y p a d s were removed a f t e r the f i r s t 3 hours and 10 hours because colonization was extremely rapid. Experiments t e s t i n g the e f f e c t of proximity to colonization 20 sources ( l i l y p a d beds) were conducted on two occasions i n 1970 by using four p a r a l l e l l i n e s of s i x a r t i f i c a l l i l y p a d s each. The nearest l i n e of a r t i f i c a l pads was only IM from the l i l y p a d bed and 14M from shore (water depth IM) and p a r a l l e l to both. The other l i n e s were 13M (lh - 2%M) 32M (3%M) , and 55M (4%M) from the Nuphar1 bed. This experiment was conducted i n quadrats 68 and 69 and the two most dis t a n t l i n e s were i n the main current at the centre of the lake. In the August experiment, two rep-l i c a t e s from each l i n e ( t o t a l 8 each time) were taken at 3% hours, 11% hours, and 27 hours from the beginning. In the Sep-tember experiment, two r e p l i c a t e s were again taken from each l i n e at 20 hours, 68 hours, and 168 hours from the beginning. In both cases, the weather was sunny during the duration of the experiments (although the water l e v e l was very high at the beginning of the September experiment,it dropped to summer lev e l s by the end). Growth Rate Experiments In order to obtain population s t a t i s t i c s (fecundity, moulting rate, per cent gravid, e t c . . . ) , growth rate experi-ments were conducted on nine occasions i n 1970. A l i v e Sida was pipetted i n t o a small v i a l and covered with coarse netting. One hundred of these v i a l s were f i l l e d as randomly as possible with animals from a single l i l y p a d . In addition, a further twenty-five v i a l s were f i l l e d with singl e gravid females. The v i a l s were then placed i n the lake f o r approximately twenty-four hours. At the end of t h i s period, the v i a l s were examined for moulted carapaces and newly born young. Whenever these were found, the moulted carapace and the Sida (and the young, 21 i f applicable) were mounted on a permanent s l i d e . A l l gravid females were also mounted on s l i d e s . Counting and Sub-sampling: Although several methods f o r subsampling were t r i e d , only one was used f o r a l l counts. The sample was poured in t o a large brass cylinder (Cushing-type sampler) and f i l l e d with water. The sample was then s t i r r e d vigorously. Two methods of s t i r r i n g were t r i e d : 1) as randomly as possible, and 2) c i r c u l a r l y to d e l i b e r a t e l y layer the organisms from the centre to the edge. The l a t t e r worked more s a t i s f a c t o r i l y because the d i v i d e r consisted of s i x wedgeshaped d i v i s i o n s which f i t neatly into the brass cyli n d e r . Since a l l the wedge-shaped d i v i s i o n s were equal and covered an area from the centre to the edge, t h i s method of subsampling should be random i f one assumes that the organisms are d i s t r i b u t e d randomly on a v e r t i c a l plane, but layered according to weight on a horizon-t a l plane. For large samples, one d i v i s i o n (1/6) was sub-sampled again (1/36). At l e a s t two r e p l i c a t e subsamples were done f o r each count; more were done i f the variance exceeded the mean. Measurements of Sida were d i f f i c u l t due to the deforming of the carapace i n the preserving s o l u t i o n ; so the large, horny "foot" (post-abdominal abductor, fig.4) was measured. Several hundred animals were measured from the natural l i l y -pad samples; a l l the preserved s l i d e s (containing a moulted carapace and the next i n s t a r animal) were also measured. In t h i s way, the number of i n s t a r s was obtained and the s i z e at maturity was determined. F i g . 4 Sida c r y s t a l l i n a The post-abdominal abductor i s the lowest part of the exoskeleton, bearing two large spines at i t s end. The length of t h i s animal i s approximately 1 1/2 mm. 23 24 Laboratory Growth Experiments; P e r i o d i c a l l y during the summer and the f a l l of both 1969 and 1970, attempts were made to grow Sida c r y s t a l l i n a i n the laboratory. Various methods were t r i e d . 1) the contents of e n t i r e l i l y p a d s were placed i n a tank of lake water and no extra food was added; 2) same as above, except that plant nut-r i e n t s were added to the water (the tanks were well illuminated); 3 ) i n d i v i d u a l Sida were placed i n p l a s t i c j a r s (containing about 300 cc of lake water) and fed from pure cultures of motile Euglena or Chlamydomonas; 4) large numbers of Sida (10 -50 individuals) were placed i n larger jars (about 1000 cc of lake water) and also fed motile algae cultures every other day. Methods #3 and #4 are standard methods for c u l t u r i n g Daphnia and were performed at controlled temperatures of 15°C and 20°C. No method was successful i n keeping Sida a l i v e f o r more than three weeks and only i n the f i r s t two methods were broods of young Sida seen. Blooms of Hydra i n the f a l l of 1969 quickly (2 - 3 days) cleaned out a l l Sida i n the tank. 25 RESULTS N a t u r a l L i l y p a d sampling S i d a c r y s t a l l i n a f i r s t c o l o n i z e d l i l y p a d s i n mid-May of 1969 ( F i g . 5), about two weeks a f t e r the emergence of s h a l l o w -water Nuphar. Deep-water Nuphar (depths g r e a t e r than 1 M) d i d not appear u n t i l l a t e May. The average d e n s i t y r o s e u n t i l Mid-June. C l o s e l y c o r r e l a t e d w i t h a steep drop i n temperature ( i . e . , heavy r a i n f a l l and consequent f l u s h i n g ) , the average d e n s i t y dropped i n e a r l y J u l y , when sample c o u n t i n g was term-i n a t e d . The samples counted were extremely non-homogenous and d i f f e r e d w i d e l y i n average d e n s i t i e s (as evidenced by the l a r g e c o n f i d e n c e i n t e r v a l s ) . S i d a when found i s always the dominant organism. Mixed i n the samples would be p r e d a t o r s l i k e Polyphemus (Cladocera) and Enallagma (Odonata), but these would be l i m i t e d to one or two i n d i v i d u a l s per l i l y p a d . Copepods would a l s o be found, but i n s m a l l numbers. D e b r i s and e p i p h y t i c algae seemed to exclude S i d a . Shallow water l i l y p a d s ( l e s s than 15 cm deep) were o f t e n choked w i t h e p i p h y t e s and no S i d a would be found. Samples c o n t a i n i n g much d e b r i s g e n e r a l l y would have lower c o n c e n t r a t i o n s of S i d a . Potomageton, which always has c o n s i d -e r a b l e d e b r i s a s s o c i a t e d w i t h i t , was c o l o n i z e d by other l i t -t o r a l C l a d o c e r a r a t h e r than S i d a . On the other hand, deep water Nuphar (greater than 1 M) would always have dense pop-u l a t i o n s of S i d a and fewer a s s o c i a t i o n s of e p i p h y t e s and deb-r i s . E a r l y i n September, e p h i p p i a and males appeared i n the 2 6 F i g . 5 2 Average number of Sida per cm on natural l i l y p a d s taken randomly from Marion Lake (May - July, 1969) (95% confidence l i m i t s indicated next to each point.) LZ 28 population. Sida c r y s t a l l i n a disappeared from Marion Lake i n mid-October, about three weeks before a l l the l i l y p a d s had r o t -ted away. The numbers given i n a l l graphs can be corrected to t o t a l numbers per l i l y p a d by multiplying by the area of the pad. The 2 average s i z e of a n a t u r a l pad i s nearly 400 cm , although the 2 2 range i s from 200 cm to 500 cm . A l l the a r t i f i c i a l pads 2 \ were 383 cm . Colonization Experiments - A r t i f i c i a l Substrates The four experiments performed a l l show the dynamics of colonization by Sida c r y s t a l l i n a at various times of the sum-mer (Fig. 6). The population i n early June shows much slower colonization than the populations i n l a t e June and mid-August, both of which show extremely rapid colonization. Mid-Septem-ber c o l o n i z a t i o n i s slow owing to the low temperatures (and hence low growth rates) and to the low b i r t h rate caused by ephippial production. In a l l four experiments, the densities achieved by Sida on the a r t i f i c i a l substrates are comparable to densities monitored on natural l i l y p a d s f o r that time of year. The two midsummer experiments show sharp population drops that seem to be correlated with temperature drops and the accompanying r a i n storms (June 24 experiment: c o r r e l a t i o n of net density change vs. temperature i s r = 0.74; August 18 experiment: r = 0.45). The early June experiment does not show the rapid r i s e i n density as seen i n the mid-summer ex-periments, even though the i n i t i a l temperatures of a l l three experiments are well above 20°C. However, temperature i s not 29 F i g . 6 Rate of colonization by Sida c r y s t a l l i n a on a r t i f i c i a l substrates at d i f f e r e n t times of the summer of 1970. Population s i z e i s ex-2 pressed as numbers per cm . Associated tem-peratures are given f o r a l l sample dates. (95% confidence l i m i t s f o r these graphs are given i n the Appendix). 30 31 at a l l correlated with net density change i n t h i s experiment (r = 0.09) as i t i s i n the mid-summer experiments. Colonization Transect Experiments ^ The rate of colonization as a function of the distance from the nearest Nuphar bed i s shown i n Figure 7. During August, the colonization of the a r t i f i c i a l substrates was extremely rapid, r i s i n g to even higher densities than the concurrent colonization experiment i n a single day. Coloni-zation was very slow i n the September experiment, even slower than the September colonization experiment which preceeded i t . In the August experiment, samples taken three hours from the beginning showed that the a r t i f i c i a l substrates nearest to the Nuphar bed were colonized the most densely ( F ^ 1 2 ) = ^ " ^ ' p <0.005). A f t e r twelve hours (in the l a t e evening), the substrates nearest to the centre of the lake showed the most dense colonization ( F ^ ^ 2j=20.8, p<0.005), being considerably higher than the densities found on the substrates nearest to the Nuphar bed. F i n a l l y , a f t e r a f u l l day (27 hours), a l l the a r t i f i c i a l substrates were colonized to equal densities * F(3 1 3 ) = 0 * 2 2 ' P ^ 0 - 1 ) -In the September experiment, no d i f f e r e n t i a t i o n could be made between the l i n e s a f t e r a single day of colonization ^ F(3 4 ) = ^ * 4 ^ / P >0.1). A f t e r three days, the l i n e nearest to the Nuphar bed (#1) was colonized s i g n i f i c a n t l y more than the other l i n e s ( F ^ 3 ^=102, p«<0.005), while the l i n e (#4) f a r -thest out into the centre of the lake showed almost no growth at a l l from the beginning of the experiment. A f t e r seven days, 32 F i g . 7 Rate of c o l o n i z a t i o n by S i d a c r y s t a l l i n a on a r t i f i c i a l s u b s t r a t e s a t v a r i o u s d i s t a n c e s from a l i l y p a d bed d u r i n g August and September, 1970. Each l i n e of a r t i f i c i a l s u b s t r a t e s was p a r a l l e l t o the Nuphar bed and was a t the f o l l o w i n g d i s t a n c e s : L i n e #1: 1 M from Nuphar bed (14 M from shore) L i n e #2:13 M " L i n e #3:32 M " " L i n e #4:55 M " (95% c o n f i d e n c e l i m i t s f o r these graphs are g i v e n i n the Appendix). Number of S i d a / c m : o N> CO cn o \ $ * 9 O 0 Se I i - r- r . \ ~° L l ' v 3 3 3 m >^ CD CD 0 CD L I 10 \ • cn o cn 3 4 the three l i n e s c l o s e s t to the Nuphar bed were colonized almost equally (with again a bias towards l i n e #1), while l i n e #4 had almost half the density of the other three ( F ^ '±2) =18.7, p«0.005). Growth Rate Experiments The combined r e s u l t s of a l l the growth rate experiments f i t t e d c l o s e l y a s t r a i g h t l i n e r e l a t i o n s h i p between tempera-ture ( C) and the percentage of animals moulting i n 24 hours (Fig. 8.) Each point represents a singl e experiment and i s plotted against the average temperature encountered during the twenty-four hour period. The average clutch s i z e (based on either number of eggs i n the brood pouch, number of embryos i n the brood pouch, or number of newly released young found i n the v i a l ) per gravid female drops d r a s t i c a l l y a f t e r the beginning of June (Table I I I ) . A s l i g h t r i s e i n clutch s i z e can be seen i n l a t e August and early September. The f r a c t i o n (per cent) of females which were actually gravid as compared with the t o t a l number of p o t e n t i a l l y gravid females varied widely over the summer and no seasonal trend i s apparent Table III) . I t i s important to note that usually less than half of the mature females were act u a l l y gravid. These data are based on measurements of the post-abdomen of moulted animals. Age d i s t r i b u t i o n and i n s t a r data Complete subsamples from natural l i l y p a d s sampled on June 3 and June 17 (1969) were counted, the postabdomens measured, and were subsequently plotted (Fig. 9). On the 35 Table III Sida population s t a t i s t i c s f o r summer 1970 Dates of Average clutch s i z e of percent of t o t a l Experiments a l l females with eggs mature females which ca r r i e d eggs June 5 4.8 40% 9 5.5 50 26 1.5 40 30 1.2 19 July 10 1.1 65 August 10 1.3 33 21 1.7 87 Septemberl3 2.3 20 23 e e 3 6 F i g . 8 Temperature s p e c i f i c growth rate f o r Sida c r y s t a l l i n a i n s i t u at Marion Lake ( a l l age classes are combined). Each point represents an experiment performed on the following dates ( a l l 1970): June 4-5 June 29-30 August 20-21 June 8-9 July 9-10 September 12-13 June 25-26 August 9-10 September 22-23 Regression l i n e equation: y = 2.32 x - 19.5 r = .588 <.901 <.979 (95% confidence l i m i t s ) 37 5 0 H o Temperature (c) 38 basis of 407 measurements, the graph seems to divide best i n t o f i v e i n s t a r s before reaching maturity, and four i n s t a r s a f t e r reaching maturity (before numbers become n e g l i g i b l e ) . I t also seems apparent that the majority of i n d i v i d u a l s are either j u s t about to reach maturity or have j u s t reached ma-t u r i t y (Fig. 9 - - 60% of the population measured). The growth rate experiments seem to substantiate these d i v i s i o n s . Four i n s t a r s are found before maturity i n early June (Appendix V) and f i v e i n s t a r s are found thereafter (Appendix VI). These data are based on growth increment data obtained by measuring the post-abdomen on the moulted c u t i c l e and on the i n t a c t c u t i c l e . A scatter diagram of the same data (Fig. 10) does not reveal any marked differences between June and August populations, although there seems to be a trend i n d i c a t i n g that the June animals are, on the average, s l i g h t l y larger at any given i n s t a r than those at the same i n s t a r i n August (compare Appendix V and VI; F i g . 10 c l e a r l y shows a larger s i z e at maturity i n June over a l l other periods). The number of i n s t a r s i s obscured i n F i g . 10 because of overlapping of s i z e increments. There also seems to be some inconsistency i n the s i z e of the growth increment; i t fluctuates widely i n a l l the experiments, but i t seems to be s l i g h t l y larger i n June (Appendix V). Growth Rate Model In order to be able to p a r t i t i o n immigration from growth, a simple bookkeeping birth-death model was constructed using the data obtained i n the previous experiments. Where assump-tions had to be made, they were made i n favour of maximizing 39 F i g . 9 Summary of measurements of postabdomen abductors from two enti r e natural l i l y p a d populations taken June 3 and 17, 1969. Probable i n s t a r growth i n c r e -ments are indicated. (60 micrometer units =0.1 mm) lnstar-f-* I Per cent "D CO 35 -30 -25-20" ° 15 E z 10 8.6 6.2 m 9.3 IV 22.2 V 17.5 v i 21.9 —•Mature females 8.4 9 It M l IX 3.7 i 2.0 _x_ + 1.7 o r 0 1 1 " T — 1 1 1 1 1 1 i— r r 10 15 20 25 30 35 40 45 50 55 60 65 70 Size of Postabdomen (micrometer un i ts ) o 41 F i g . 10 Summary of postabdomen growth increments mea-sured i n a l l growth rate experiments. Large symbols indicate mature females. (Data are presented i n Appendix V - VI) 42 70 H O) c •4-< o ,.—. <D CO -»—• •«-> *•— • — CO c c CD i _ E CD -4—• o CD T3 E .O o CO ^_ •*-> CO o Po E o 0 N CO 6 0 -5 0 -3 0 -20 oo • o O Q A e ® o & o o o o o o o o o o o o ©OA oo o ^ M • o A • o e A A o o o o A ^ o o o o A • A • • o A • • A A A o A o • J u n e 5 , J u n e 9 o J u n e 2 6 , J u n e 3 0 , J u l y 1 0 A A u g 1 0 , A u g 2 1 , S e p t 1 3 , S e p t 2 3 6 0 m i c r o m e t e r u n i t s = 0 . 1 m m 20 —i— 30 40 50 i— 60 S i z e of Pos tabdomen before Moul t ing (micrometer un i ts ) 4 3 the growth r a t e . Temperature s p e c i f i c growth r a t e s were mod-e l e d using" the r e g r e s s i o n e q u a t i o n o b t a i n e d i n F i g u r e 8. Each c o l o n i z a t i o n experiment was modeled u s i n g the i n i t i a l p opula-t i o n found a f t e r one day of c o l o n i z a t i o n ; t h i s p o p u l a t i o n was d i v i d e d i n t o i n s t a r s u s i n g the percentages found i n F i g u r e 9. Four p r e - a d u l t i n s t a r s and f i v e r e p r o d u c i n g i n s t a r s were allowed f o r i n the June 2 - 9 experiment. A l l t h r e e other experiments assumed . f i v e i n s t a r s b e f o r e m a t u r i t y and f o u r r e p r o d u c i n g i n s t a r s . F o r reasons p r e s e n t e d i n the d i s c u s s i o n , i t was assumed t h a t the i n s t a r s b e f o r e r e p r o d u c t i v e m a t u r i t y moulted a t a r a t e which was t h r e e - q u a r t e r s of the a d u l t moult-i n g r a t e . The c l u t c h s i z e and the- percentage of g r a v i d females was t h a t found f o r the c o n c u r r e n t growth r a t e experiments. High s u r v i v a l r a t e s were assumed (97% s u r v i v a l per day which equals 40% s u r v i v a l i n t h i r t y d a y s ) , but o n l y nine i n s t a r s were allowed f o r , a f t e r which they passed out of the popula-t i o n . F i g u r e 11 models the growth of the p o p u l a t i o n (assum-i n g no more immigration) f o r each c o l o n i z a t i o n experiment u s i n g the temperature regime of t h a t experiment. From F i g u r e 11, i t i s apparent t h a t o n l y the curve f o r e a r l y June comes c l o s e t o modeling the observed d a t a . The o t h e r t h r e e curves bear l i t t l e resemblance t o the a c t u a l experiments. In a l l f o u r curves, t h e r e i s a steep r i s e which r e p r e s e n t s the i n i t i a l i mmigration, which i s f o l l o w e d by a g r a d u a l r i s e of steady growth. The a c t u a l c o l o n i z a t i o n curves show v e r y steep r i s e s and r a p i d f l u c t u a t i o n s t h a t may be c o r r e l a t e d w i t h temperature. F i g . 11 S i d a p o p u l a t i o n growth modeled f o r each c o l o n i z a t i o n experiment (see F i g . 6 ) . P o p u l a t i o n s were assumed t o b e g i n growing a f t e r the f i r s t day of immigration. Im-m i g r a t i o n and e m i g r a t i o n were assumed to be equal a f t e r Day 1. The r e g r e s s i o n e q u a t i o n of F i g . 8 was used to model the growth r a t e , and the r e l e v a n t parameters from T a b l e I I I were used f o r each of the p a r t i c u l a r d a t e s . The temperatures used were the same as i n F i g . 6 46 The model seems to show that drops i n temperature cause growth to slow down, but do not cause sudden decreases i n density. Also, as the density increases, the percentage of the popula-t i o n found i n the youngest ins t a r s increases, which i s to be expected but i s contrary to the observed r e s u l t s on both natural and a r t i f i c i a l l i l y p a d s . DISCUSSION Sida as a colonizing species The behaviour of Sida c r y s t a l l i n a i n Marion Lake i n many ways resembles the pattern of behaviour of a f u g i t i v e species (Hutchinson, 1951). I t shows a remarkable a b i l i t y to colon-iz e new substrates as soon as they appear, and seems to be e a s i l y displaced by competition. This was best observed i n Marion Lake when large v e r t i c a l p l a s t i c experimental enclosures were put out. F i r s t they were colonized by Sida, only to be replaced by epiphytic algae. Unlike a f u g i t i v e species, how-ever, Sida does have a refuge: the underside of l i l y p a d s which are unsuitable f o r a l g a l growth. Sida also seems to f i t MacArthur and Wilson's (1967) model of an i d e a l pioneer colonizing species f o r i s l a n d s . I t c l e a r l y has a large K (carrying capacity): i f one assumes 2 10,000 Sida per natural l i l y p a d (25 per cm on an average sized 2 l i l y p a d of 400 cm ) and a l i l y p a d population i n Marion Lake of 8 10,000 (unpub. data), t h i s gives an estimate of 10 Sida i n Marion Lake! After the i n i t i a l burst of growth i n early June, Sida has a very low b i r t h rate (Table I I I ) , which also f i t s the p r e d i c t i o n of MacArthur and Wilson. F i n a l l y , no data i s available f o r the death rate. One can i n f e r that i t i s prob-ably lower than the b i r t h rate because the population p e r s i s t s i n quite large numbers throughout August, long af t e r the drop i n the b i r t h rate. Voskresensky and Lebedeva (1964) report values of 50 days and 64 days f o r the longevity of Sida, but give no accompanying temperature data. H a l l (1964) states 48 that Daphnia galeata w i l l survive 30 days at 25°C,60-80 days at 20°C, and 150 days at 11°C. He estimates mortality at less than 3% d a i l y (20°C). Although these estimates assume no pre-dation mortality, they are probably reasonable i n the l i g h t of the observed data. Problems with observed Sida growth The only comparable data i n the l i t e r a t u r e pertaining to Sida c r y s t a l l i n a i s that of Voskresensky and Lebedeva (1964) . Unfortunately, t h i s study has many defects: i t makes no men-ti o n of the natural habitat of Sida, nor does i t indicate the densities at which i t i s found. But the greatest lack i s the f a i l u r e to mention the temperatures at which growth occurred over the period of the summer. They do indicate that the per-iod of brood growth remained the same throughout the summer (Table I ) , but t h i s i s su r p r i s i n g because brood growth i s rel a t e d to the length of the i n s t a r period which i s i n turn re l a t e d to temperature. (A new brood i s born every time a mature female moults). But then, growth i n the above study i s only referr e d to i n terms of days, not i n terms of number of days per i n s t a r period. The Russian a r t i c l e does agree with the present study i n several p a r t i c u l a r s . There i s evidence i n both studies that the brood sizes are larger (Table I I I ) , that growth i s f a s t e r (fewer i n s t a r s i n early June - Appendix V), and that s i z e at maturity i s larger (Fig. 9) i n June than i n July and August (see Table I f o r Russian data). Both studies show wide v a r i a -t i o n i n brood sizes observed, and the Russian paper comments 49 on S i d a ' s a b i l i t y t o grow under crowded c o n d i t i o n s . U n l i k e t h i s study, the R u s s i a n study found t h a t the m a j o r i t y of the p o p u l a t i o n was o n l y one o r two days o l d , and t h a t the p o p u l a t i o n as a whole had a s t e e p l y h y p e r b o l i c s u r -v i v o r s h i p curve. T h i s i s c o n t r a r y to the Marion Lake popula-t i o n which seems to be v e r y l o n g - l i v e d and f o r which the modal s i z e c l a s s e s are near s e x u a l m a t u r i t y . T h i s s i t u a t i o n i s v e r y u n n a t u r a l and c o u l d o n l y a r i s e i f one assumes extremely f a s t growth i n the e a r l y i n s t a r s . G e n e r a l l y , one would expect the youngest age c l a s s e s t o be the l a r g e s t i n number f o r an a n i -mal l i k e S i d a . The R u s s i a n study, however, has a much h i g h e r b i r t h r a t e (Table I) which would account f o r the l a r g e r e p -r e s e n t a t i o n i n the younger age c l a s s e s . H a l l (1964), i n h i s f i e l d and laboratory<study of Daphnia g a l e a t a , g i v e s evidence t h a t the growth r a t e of Daphnia i s f a s t e r b e f o r e s e x u a l matur-i t y than afterwards a t a l l the temperatures used (Table I V ) . T h i s may be t r u e , but one might a l s o p o s t u l a t e t h a t the sampling program f a i l e d t o f i n d the young i n s t a r s or t h a t they escaped through the mesh s i z e of the net (young S i d a are about 300-400yAin l e n g t h , however.) Both H a l l (1964) and Voskresensky and Lebedeva (1964) found f a s t e r growth r a t e s than those found i n t h i s study. The R u s s i a n paper s t a t e s t h a t S i d a (Table I) reaches s e x u a l matur-i t y i n 4 days i n June and J u l y and i n 8 days i n August. H a l l found t h a t growth v a r i e d w i t h temperature f o r D^ g a l e a t a and g i v e s a v a l u e of 7% days to r e p r o d u c t i v e m a t u r i t y a t 20°C (Table I V ) . Comparable v a l u e s f o r t h i s study i n d i c a t e a t 50 Table IV Growth rate data for Daphnia galeata (from H a l l (1964)) Instar growth Temp (°C) rate (days) 25 Days to reproductive maturity= 6 d. (IV instars) 1.5/instar 20 Days to reproductive maturity= 7.5 d. (IV instars) 1.9/instar 11 Days to reproductive maturity= 24 d. (IV instars) 6/instar 25 Moulting rate of adult and rate of brood production 2.0/instar 20 Moulting rate of adult and rate of brood production 2.6/instar 11 Moulting rate of adult and rate of brood production 8.0/instar Note: - i l l . = - i l l - = 1^2- = 0.75 ( i . e . , pre-adult i n s t a r * a.u growth rate i s 3/4 of adult growth rate.) 51 l e a s t 15 days to sexual maturity at 20°C (See Table V - assumes IV i n s t a r s ; V i n s t a r s take 18 1/2 days). Even i f one assumes a f a s t e r growth rate before maturity, one s t i l l a r r i v e s at values of 11 days for four i n s t a r s and 14 days for f i v e i n s t a r s . Because the assumptions of the birth-death model a l l tend to maximize the growth rate, i t i s probably reasonable to state that the major component of the steep r i s e s and a l l of the population drops seen i n the colonization experiments are due to immigration and emigration respectively, not to growth. Growth alone, using the parameters found for Sida, seems to produce a gradually r i s i n g curve such as that seen for the early June experiment. During that period, i t may be reason-able to hypothesize that emigration equals immigration and that growth i s b u i l d i n g up the population to i t s carrying cap-a c i t y . Internal evidence seems to substantiate t h i s assump-t i o n : the larger brood s i z e s , the faster growth rate, and the larger size at maturity are a l l c h a r a c t e r i s t i c s of a population i n a rapid growth phase. The population during t h i s period i s not as s e n s i t i v e to temperature fluctuations as i t i s l a t e r i n the summer. This may be due to the high rate of growth at that time. The strategy of coloniz'ation The only evidence that seems to indicate that the pool of c o l o n i z i n g i n d i v i d u a l s i s not of i n f i n i t e s i z e comes from the two experiments run.simultaneously during mid-August. The rate of colonization i n the transect experiment was markedly higher than i n the colonization experiment, even though they 52 Table V Growth rates for Sida extrapolated from Figure 8. . Using equation Using equation i n F i g . 8 X 3/4 Temp(°C) i n F i g . 8 f o r pre-adult instars Days to reproductive 16 23.1 days 17. 0 days maturity (IV instars) 20 14.9 11. 2 24 11.0 8. 3 28 8.8 6. 6 Days to reproductive 16 28.4 days 21. 2 days maturity (V instars) 20 18.6 14. 0 24 13.8 10. 3 28 11.0 8. 3 Moulting rate of 16 5.7 days adult and rate of 20 3.7 brood production 24 2.8 28 2.2 Days to f i r s t brood 16 28.8 days 22. 7 days (IV instars) 20 18.6 S 14. 9 24 13.8 11. 1 28 11.0 8. 8 Equation; % moulting/day = 2.32 X (Temperature) - 19.5 100% moulting = * rr> 7-3— ^ % moulting/day 53 took place at the same time. I f - the pool of colonizing i n d i v -iduals were li m i t e d i n s i z e , one might expect such an observa-2 txon. Forty a r t i f i c i a l l i l y p a d s i n a space of roughly 50 M aremuch denser than twenty-four spread over several hundred square meters. I t would obviously take many more Sida to achieve the same density i n the former experiment than i n the l a t t e r . However, t h i s observation forces one to assume some form of "hunting" mechanism on the part of Sida i n order to be able to f i n d widely scattered suitable substrates. With the above information, and considering the r e s u l t s of the transect experiments, one can speculate on the strategy that Sida might use to colonize substrates. The animals must come from e x i s t i n g refuges (the Nuphar beds): either they spontaneously drop o f f the l i l y p a d or they are disturbed, perhaps by the wind. That some drop off e a s i l y when disturbed was often noted while sampling. Most would probably re-attach to the l i l y p a d , but some would d r i f t or swim away. This may be a behavioural adaptation f o r d i s p e r s a l . Clumps of Sida have been taken i n the open water, usually near the surface (Table I I ) . Those substrates nearest to the colonizing source should be i n f e s t e d f i r s t ; however, the wind c l e a r l y plays a major r o l e i n d i s p e r s a l . In the August transect experiment, a f t e r twelve hours of colonization, the a r t i f i c i a l l i l y p a d s nearest to the centre of the lake were the most heavily colonized. This was probably because a strong wind blew from north to south down the v a l l e y f o r the e n t i r e day. The outermost p a r a l l e l l i n e s 54 were i n the main current of the lake and were probably colon-ized by Sida from many d i f f e r e n t Nuphar beds. Overnight, the wind died down, and i t i s s i g n i f i c a n t that a l l the pads were equally colonized the following day. In the September experi-ment, the outermost p a r a l l e l l i n e was consistently colonized the l e a s t . This may have been because i t was the most exposed to the c e n t r a l current of the lake which would be colder and stronger than i n the summer due to the high runoff which i s c h a r a c t e r i s t i c of the f a l l . The huge numbers of Sida present i n Marion Lake would en-sure that there would be at a l l times clumps of p o t e n t i a l c o l -onizers i n the water column. In f a c t , i t i s quite possible that the population i s i n constant f l u x , some percentage of i t continuously moving from substrate to substrate. By maintain-ing the largest population s i z e possible, Sida would i n f a c t be maximizing i t s a b i l i t y to colonize any new substrates as soon as they became av a i l a b l e . Competive advantages of l i l y p a d s Sida c r y s t a l l i n a has a large gland situated on the back of i t s neck which i t uses to adhere to any smooth substrate. Behavioural observations indicate that i t prefers a p o s i t i o n of adhesion to free swimming. When attached by i t s gland, the legs are free to beat the surrounding water column because they are away from the substrate. On the basis of motion p i c -ture photographs and i n l i g h t of the anatomy of the feeding legs, Cannon (1933) concludes that Sida must be a f i l t e r feed-er. Food i s transferred from comb-like spines by means of a 55 system of spines on the basal segment of each feeding leg. Sida performs th i s feeding i n conjunction with many other 2 individuals(sometimes as concentrated as 50 per cm ). I t would seem to be i n e f f i c i e n t to feed i n such a crowded s i t u a t i o n , competing with thousands of other i n d i v i d u a l s f o r a l i m i t e d amount of phytoplankton. Assuming equivalent phytoplankton concentrations, any decrease i n the r e l a t i v e Sida density would increase the amount of food a v a i l a b l e f o r the remaining i n d i v i d u a l s . I f the emigrating i n d i v i d u a l found a l o c a t i o n which was less crowded, i t too would have benefited. Thus one can see that there may be some r e l a t i o n s h i p between space requirements and food requirements f o r Sida. Conversely, Sida's main competitor i s filamentous algae which occupy the available space, but which would also clog the f i l t e r i n g apparatus. From the point of view of natural s e l e c t i o n , i t would be advantage-ous f o r an i n d i v i d u a l Sida to seek a new substrate when i t s present one becomes unsatisfactory, either from too high a density of other Sida or from i n f e s t a t i o n of algae. I f feeding i n such a crowded s i t u a t i o n seems i n e f f i c i e n t , there must be compensating reasons f o r t h i s observed behaviour. Although i t i s known that the phytoplankton concentration i n Marion Lake i s very low (Efford, 1967), the corresponding con-centrations among the emergent macrophytes i s not known. I t would seem reasonable to assume that the concentration i s higher because of nutrient release, etc. which would make the emergent vegetation a more suitable habitat f o r a f i l t e r feeder i n Marion Lake. I t i s possible that feeding from a r e s t i n g 56 place r e s u l t s i n some energetic savings over swimming while feeding. But t h i s has to be balanced with the increased com-p e t i t i o n f o r the same food supply caused by the crowded s i t u a -t i o n . The l i l y p a d may serve as a predation refuge, but t h i s may be of marginal importance because i f a predator were to cue i n on l i l y p a d s , there would be l i t t l e escape. F i n a l l y , the l i l y p a d may serve as a refuge from the considerable currents of Marion Lake. Although numbers drop d r a s t i c a l l y during periods of r a i n f a l l and high runoff, i t i s probably safe to assume that free-swimming plankton are even more susceptible to such environmental f l u c t u a t i o n s . E f f e c t of predation on Sida Because of the huge numbers of Sida present i n Marion Lake, the only predators capable of seriously eating a s i g n i f i c a n t percentage of the t o t a l number are Ambystoma g r a c i l e and the young (less than 15 cm i n length) of Salmo ga i r d n e r i . Although these two predators do cue i n on Sida (their t o t a l impact i s not known)f the large numbers of Sida seem to p e r s i s t through-out the summer. A l i l y p a d may serve a refuge from predation, but t h i s seems of li m i t e d u t i l i t y when one considers the obser-vations made of young rainbow trout and small Ambystoma graz-ing the undersurface of l i l y p a d s . I t would not take much to f i l l the stomach of ei t h e r animal with Sida. One i s forced, i n the l i g h t of the above information, to assume that there are many more l i l y p a d s and many more Sida than there are p o t e n t i a l predators. By limiting i t s production to a scant three months, Sida can overwhelm i t s p o t e n t i a l pred-57 a t o r s by means of sheer numbers alone. I t would take time f o r those p r e d a t o r s p r e s e n t t o cue i n on the new prey, and by the time they had l e a r n e d , the p o p u l a t i o n would be a l r e a d y on the wane. Any i n c r e a s e i n p r o d u c t i v i t y f o r the p r e d a t o r would be hard t o t r a n s l a t e i n t o i n c r e a s e d egg p r o d u c t i o n because of the i n t e r v e n i n g nine months when a l t e r n a t i v e f o o d sources would have to be e x p l o i t e d . I t i s of some i n t e r e s t t h a t the c l u t c h s i z e r i s e s s l i g h t l y towards the end of August (Table I I I ) . T h i s may be i n d i c a t i v e of the i n c r e a s e d e f f e c t i v e n e s s of the p r e d a t o r s on S i d a . The newly r e c r u i t e d rainbow f r y as w e l l as the kokanee salmon would have d i s c o v e r e d S i d a as a food source. Hydra a l s o begins to appear a t t h i s time. I t i s q u i t e l i k e l y t h a t the r a p i d wane of the p o p u l a t i o n d u r i n g September i s p r o b a b l y due to p r e d a t i o n as much as to n a t u r a l m o r t a l i t y . Evidence f o r f o o d l i m i t a t i o n I t has been shown i n s e v e r a l s t u d i e s (e.g. S l o b o d k i n , 1954, H a l l , 1964, Comita and Anderson, 1959) t h a t food supply a f f e c t s the s i z e of broods. However, food supply does not a f f e c t the m o u l t i n g (growth) r a t e ( H a l l , 1964). Hence, one would expect t h a t s m a l l brood s i z e s (Table I I I ) would i n d i c a t e some degree of s t a r v a t i o n . E f f o r d (1967) has shown t h a t phytoplankton p r o d u c t i v i t y i n Marion Lake i s v e r y low; c o n s i d e r i n g t h a t S i d a i s a f i l t e r - f e e d e r and i s p r o b a b l y the most abundant c l a d o c e r a n i n Marion Lake, s t a r v a t i o n i n the f a c t of a low f o o d supply i s not s u r p r i s i n g . S i d a i s c l e a r l y capable of l a r g e r c l u t c h size; the d a t a from t h i s study show a maximum of nine; Voskresensky and Lebedeva (1964) show an average of 8 d u r i n g June and 3-4 58 during the r e s t of the summer. Slobodkin (1954), working from laboratory populations, indicates that a low per-centage of gravid females (Table III) i s normal i n a population of Daphnia obtusa which i s near i t s carrying capacity. I t usually indicates starvation: most animals only have enough food f o r maintenance; only with the death of an i n d i v i d u a l i s there enough energy available f o r another animal to begin egg production. The r e s u l t of small brood sizes and a low percentage of gravid animals i s slow population growth. Early i n June, the growth rate i s c l e a r l y high due to the higher clutch s i z e . Late i n June, a drop i n clutch s i z e probably indicates that the population i s no longer growing but maintaining i t s s i z e . The many larger i n d i v i d u a l s bear t h i s out (Fig.. 9). F i n a l l y , whenever a s p e l l of good weather occurs (Fig. 5; and 6 show th i s with temperature r i s e ) , the population density of Sida r i s e s quite r a p i d l y . This may be because blooms of algae would occur at thi s time and Sida would respond to t h i s by increasing production, again giving evidence f o r a food li m i t e d population. In addition, a r i s e i n temperature would cause an increase i n the growth rate as predicted i n Figure 8. The r e l a t i o n s h i p of available space and food supply has already been discussed. UncoIonized substrates represent new feeding s i t e s f o r an animal which prefers to be stationary when feeding. If a small brood s i z e and a low percentage of gravid females are d i r e c t l y caused by a scant food supply, one can hypothesize that Sida i s keeping i t s population near the 59 maximum carrying capacity of Marion Lake. Predation must not be cropping a very large percentage of the t o t a l population because one would expect the b i r t h rate to be higher (because of the greater a v a i l a b i l i t y of food). As previously noted, a large carrying capacity, a low b i r t h rate, and an even lower death rate are c h a r a c t e r i s t i c s of a t h e o r e t i c a l l y good c o l o n i z -ing species. Sida i n Marion Lake i s thus an animal which i s per-petually ready to emigrate, and which has maximized i t s a b i l i t y to colonize successfully. 60 CONCLUSIONS ' Sida c r y s t a l l i n a i n Marion Lake exhibits an unusual colonizing behaviour on de novo substrates placed i n the lake. This behaviour i s c h a r a c t e r i s t i c of a f u g i t i v e species, and Sida also shows population c h a r a c t e r i s t i c s that should theoret-i c a l l y maximize i t s success of c o l o n i z a t i o n . Sida, by means of sheer numbers * increases the p r o b a b i l i t y of co l o n i z a t i o n success and seems to temporarily overwhelm i t s pre-f dators and competitors. Lilypads may serve as a refuge from the currents of Marion Lake and as an optimum feeding s i t e . Sida c r y s t a l l i n a shows unusual natural population c h a r a c t e r i s t i c s : a rapid growth phase followed by a long period of s e n i l i t y during which the b i r t h rate, and most l i k e l y the death rate as w e l l , are at a minimum. There i s a curious under-representation of the youngest age classes. These c h a r a c t e r i s t i c s seem to indicate that Sida i s e x p l o i t i n g i t s environment to a maximum, and that any increase i n the food or i n the a v a i l a b l e space supply would r e s u l t i n a corresponding population increase. Predation most l i k e l y a f f e c t s the popula-t i o n only minimally u n t i l mid or l a t e August when the popula-t i o n i s on the wane. 61 LITERATURE CITED Brooks, J.L. 1959. C l a d o c e r a . I n : Edmonson, W.T. (Ed.). Ward and Whipple's F r e s h Water B i o l o g y . J . Wiley and Sons. New York. pp~. 5~87-656. C a i r n s , J.M., M.L. Dahlberg, K.L. Dickson, N. Smith, and W.T. W a l l e r . 1969. The r e l a t i o n s h i p of fresh-water protozoan communities to the MacArthur-Wilson e q u i l i b r i u m model. Amer. Nat. 103:439-454. Cannon, H.G. 1933. On the f e e d i n g mechanism of the Branch-iopoda. P h i l . Trans. Roy. Soc. 222B:267-353. C a r l , G.C. 1940. The d i s t r i b u t i o n o f some C l a d o c e r a and f r e e - l i v i n g Copepoda i n B r i t i s h Columbia. E c o l . Monog. 10:55-110. Comita, G.W. and G.C. Anderson. 1959. The s e a s o n a l develop-ment of a p o p u l a t i o n of Diaptomus a s h l a n d i Marsh, and r e l a t e d phytoplankton c y c l e s i n Lake Washington. Limnol. Oceanogr. 4_:37-52. E f f o r d , I.E. 1967. Temporal and s p a t i a l d i f f e r e n c e s i n phytoplankton p r o d u c t i v i t y i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Bd. Canada. 24 (11) :228 3-2307. E f f o r d , I.E. 1972. An i n t e r i m review of the Marion Lake Pro-j e c t . I n : Kajak and H i l l b r i c h t - I l k o w s k a (Eds.). Pro-ceedings of UNESCO-IBP Symposium on p r o d u c t i v i t y p r o -blems of f r e s h w a t e r s . Warsaw, Poland. May,1970. pp.83-109. E f f o r d , I.E. and K. Tsumura. 1973. A comparision of the food o f salamanders and f i s h . i n Marion Lake, B r i t i s h Columbia. Trans. Amer. F i s h . Soc. 102(1):33-47. H a l l , D.J. 1964. An e x p e r i m e n t a l approach t o the dynamics of a n a t u r a l p o p u l a t i o n of Daphnia g a l e a t a mendotae. Ecology 45_(1) : 94-112. Hutchinson, G.E. 1951. Copepodology f o r the o r n i t h o l o g i s t . Ecology 3_2 (3) :571-577. MacArthur, R. and E.O. W i l s o n . 1967.. The Theory of I s l a n d  Biogeography. P r i n c e t o n Univ. P r e s s . P r i n c e t o n , N.J. 203pp. N e i s h , I . C . 1971. Comparision o f s i z e , s t r u c t u r e , and d i s -t r i b u t i o n a l p a t t e r n s of two salamander p o p u l a t i o n s i n Marion Lake, B r i t i s h Columbia. J . F i s h . Res. Bd. Canada. 28(l):49-58. 62 Pearlstone, P. (in press). Observations of a natural popu-l a t i o n of damselfly larvae. Syesis. Quade, H.W. 1969. Cladoceran fauna associated with aquatic macrophytes i n some lakes i n north-western Minnesota. Ecology 5Q_(2) : 170-179. Sandercock, F.K. 1970. Bioenergetics of the rainbow trout (Salmo gairdneri) and the kokanee (Oncorhynchus nerka) populations of Marion Lake, B r i t i s h Columbia. Unpub-li s h e d Ph.D. t h e s i s , Univ. of B r i t i s h Columbia,Vancouver. Sc o u r f i e l d , D.J. and J.P. Harding. 1958. A key to the B r i t i s h species of fresh-water Cladocera with notes on t h e i r ecology. S c i . Pub. Freshw. B i o l . Assoc. Ambleside 5_:l-55. Simberloff, D.S. and E.O. Wilson. 1969. Experimental zoogeo-graphy of islan d s . The colonization of empty islan d s . Ecology 50_(2) :278-296. Slobodkin, L.B. 1954. Population dynamics of Daphnia obtusa Kurz. E c o l . Monog. 24:69-88. Voskresensky, K.A. and L.J. Lebedeva. 1964. Study of populations of Cladocera with the method.of semi-isolation i n the water body. Zool. Zh. 43:518-524. (In Russian with En-g l i s h summary.) 63 Appendix I Data, plotted, f o r densities of Sida on natural l i l y p a d s during the summer of 1969 (Fig. 5). Date Temp(°C) Quadrat# 2 #Sida/cm Mean Conf. Limits May 15 15 80 0.7 0.3 0.4 100 0.3 42 0.2 33 0.1 May 21 20 91 5.4 3.0 31. 36 0.5 May 28 14 105 1.3 2.9 3.7 117 3.4 51 5.9 3 0.8 June 3 20 13 1.18 3.1 6.0 54 2.2 5 5.8 June 11 24 77 '26.5 13.7 14.1 37 11.7 73 10.1 10 6.4 June 17 26 59 37.9 19.7 41.7 7 16.5 16 4.8 June 2 6 16 77 6.9 8.3 11.9 118 6.0 43 18.8 112 1.4 July 3 15 93 14.9 9.6 68. 74 4.2 64 Appendix II Data p l o t t e d for the colonization rate by Sida on a r t i f i c i a l l i l y p a d s at d i f f e r e n t times of the summer of 1970 (Fig.6). # days 2 elapsed iSida/cm Conf. Limits Day # Temp(°C) June 2 - « 0.75 6.0 1.8 0 22 2.04 8.0 1.1 1 21 2.88 14.7 1.7 2 22 5.88 24.8 4.3 3 23 6.88 25.6 6.2 4 21 5 21 6 19.5 7 18 June 24 - July 3 0.125 5.6 1.4 0 22 1.08 40.4 7.5 1 24 2.08 45.5 2.1 2 23 4.04 36.3 8.3 3 18 5.04 32.0 3.0 4 17 5.92 27.9 1.1 5 16 9.04 22.5 2.2 6 17 — 8 19 9 21 August 18 - 28 0.125 1.9 0.4 0 19 0.42 8.3 2.7 1 20 0.92 9.4 1.0 2 20.5 2.0 28.9 9.4 3 21 2.96 33.4 1.3 4 21.5 4.0 34.5 3.1 5 22.5 5.04 32.7 3.2 6 20.5 5.96 48.4 4.6 7 20 10.04 26.4 5.5 8 20 9 18 10 18 65 Appendix l l (Cont.) Data, plotted f o r the colonization rate by: Sida # days elapsed 2 #Sida/cm Conf. Limits Day # Temp (°C) September 12 - 17 0.15 1.04 0.12 0 14.5 0.58 0.83 0.31 1 13.0 0.96 2.38 1.42 2 13.0 2.9 5.22 1.46 3 13.5 4.92 7.55 1.8 4 13 5 13 66 Appendix III Data pl o t t e d f o r the col o n i z a t i o n rate by Sida at various distances from a l i l y p a d bed (Fig. 7). # days Distance from elapsed Nuphar bed #Sida/cm2 Conf. Limits day # Temp(°C) August 22 - 23 0.15 1 M 12.9 4.2 0 20 (3.5 hrs) 13 M 6.9 1.4 0.15 20.5 32 M 6.8 0.6 0.48 23 55 M 8.5 3.9 1.13 21 0.48 1 M 17.5 6.8 (11.5 hrs) 13 M 20.8 1.6 32 M 28.8 2.5 55 M 27.5 1.0 1.13 1 M 37.8 4.7 13 M 38.0 3.1 32 M 38.4 11.0 55 M 36.4 1.6 September 22 - 29 0.83 1 M 0.32 0.83 0 10.5 13 M 0.36 0.51 1 9.5 32 M 0.49 0 2 9.5 55 M 0.33 0.51 3 9.5 4 10 2.83 1 M 1.39 0.01 5 11 13 M 0.74 0.19 6 13 32 M 0.74 0.12 7 15 55 M 0.46 0.89 7.0 1 M 4.82 0.63 13 M 4.08 0.63 32 M 4.30 0.33 55 M 2.83 0.79 67 Appendix IV Data, plo t t e d for temperature s p e c i f i c growth rates of S. c r y s t a l l i n a (Fig • 8) Dates of experiments Percent Moult/24 hrs Temp(°C) June 5 43.2 22.5 9 29.2 19 26 33.0 23 30 19.4 16.5 July 10 27.9 23.5 August 10 22.1 18.5 -'• 21 22.6 20.5 September 13 9.5 13 23 3.5 10 68 Appendix V Growth rate increments f o r post-abdominal abductors before and a f t e r moulting, arranged i n i n s t a r groups. June 5, 1970 (22°C) (Mean and standard deviation are computed f o r each si z e class.) II III IV V VI VII 21 21 21 x=21 SD=0 28 26 28 x=27.3 SD=1.2 31 39 34 42 32 43 34 41 34 42 31 41 42 53 x=32.7 45 55 SD=1.5 40 49 45 54(G) 44 50 (G) 38 48 52 x=41.8 55 SD=2.2 51 60 micrometer units = 0.1 ram (G) = gravid female mature females x=51.9 SD=2.6 60 61 60 61 x=60.5 SD=0.6 68(G) 69 Appendix V (Cant.) Growth rate increments f o r post-abdominal abductors before and a f t e r moulting, arranged i n i n s t a r groups, June 9, 1970 (19°C) I II II 21 28 22 29 22 28 27 33 x=*21.7 28 33 SD=0.6 28 34 28 34 33 x=28 33 IV V VI VII SD=0.6 x=33.3 SD=0.5 40 40 40 43 40 41 x=40.7 SD=1.2 60 micrometer units = 0.1 mm (G) = gravid female mature females —»• 45 50 48 48 45 51 48 54 x=48.6 SD=3.0 55 58 57 (G) 62(G) x=58 SD=»2.9 70 Appendix VI Growth rate increments f o r post-abdominal abductors before and a f t e r moulting, arranged i n i n s t a r groups. June 26, 1970 (22°C) (Mean and standard deviation are I II III IV 24 30 25 28 28 33 x=24.5 29 33 SD=0.7 30 35 x=28.9 32 38 SD=1.0 31 37 31 36 38 x=31.7 38 SD=1.2 37 V VI VII 36 35 37 35 35 35 x=36.3 SD=1.3 60 micrometer units =0.1 mm (G) = gravid female 44 44 41 44 39 42 44 45 45 39 45 45 43 41 41 44 44 44 45 x=43.1 SD=2.0 mature females 4 7(G) 51 52 4 9 (G) 4 8 (G) 4 6 52 51 53 50 50 50 53 x=50.2 SD=2.2 58 57 59 x=58 SD=1 71 Appendix VI (Cont.) Growth rate increments f o r post-abdominal abductors before and a f t e r moulting. June 30, 1970 (16°C) I I I I I IV V VI V I I 34 34 37 38 37 42 37 41 38 42 38 43 38 42 42 x=37.6 42 SD=0.5 42 42 41 60 micrometer units = 0.1 mm (G) = gravid female x=41.9 SD=0.6 mature females 47 47 47 46 45 49 45 45 45 47 47 47 x=46.4 SD=1.2 52 52 51 51 51 55 (G) 51(G) x=51.8 SD=1.4 72 Appendix VI (Cant.) Growth rate increments for post-abdominal abductors before and a f t e r moulting. July 10, 1970 (24°C) I II III IV V VI VII 28 30 32 36 females —> 38 40 mature 40 43 x=33 .3 44 49(G) SD=4 .2 x=38.7 42 47 SD=2.3 43 47(G) 41 47(G) 43 47 41 47 42 46 (G) 44 47(G) 41 47 43 47(G) 41 45 41 46 (G) 42 47(G) 47 51(G) x=42.2 47 50 SD=1.3 47 50 (G) 46 49(G) 47 51 47 52 47 53 (G) 47 51 x=46.9 x=50.9 SD=0.7 SD=1.2 60 micrometer units = 0 .1 mm (G) = gravid female 73 Appendix. VI (Cont.) Growth r a t e increments f o r post-abdominal abductors before and a f t e r moulting. II III IV V VI VII 37 mature females — 34 35 37 41 35 39 36 40 — 42 45 x=35.7 40 43(G) SD=1.2 40 44 47 51(G) x=40.3 46 50 SD=1.0 46 51(G) 43 47(G) 44 47 46 51 48 51 August 10, 1970 (18°C) 21 26 32 30 32 x=31.3 SD=1.2 (G) = gravid female 60 micrometer units = 0.1 mm August 21, 1970 (21°C) 19 22 22 27 22 25 27 32 x=21 25 30 SD=1.7 33 x=25.6 32 SD=1.3 x=31.8 SD=1.3 37 36 34 x=35.7 SD=1.5 39 41 40 40 40 39 39 41 41 42 x=40.2 SD=1.0 x=45.2 SD=1.7 46 43(G) 45(G) 43(G) 44 44 (G) 45(G) 46 (G) 46(G) 46 43 46 x=44.8 SD=1.3 x=49.8 SD=1.8 51(G) 48(G) 50 (G) x=49.7 SD=1.5 74 Appendix VI (Cont.) Growth rate increments for post-abdominal abductors before and a f t e r moulting. I II III IV V VI VII September 13, 1970 (15°C) 30 35 mature females — * 33 37 37 41 x=31.5 41 45 SD=2.1 x=36. 3 41 44 SD=1. 2 42 45 42 45(G) 45 50 x=41.4 SD=0.6 x=44.8 SD=0.4 September 2 3, 1970 (10°C) 30 35 31 36 32 36 31 36 31 36 35 40 x=31 38 42 SD=0.7 x=35. 7 39 43 (Ephippia) SD=0. 5 42 47 x=39 SD=1 x=42.3 SD=0.6 60 micrometer units = 0.1 mm (G) = gravid female 

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