UBC Theses and Dissertations

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UBC Theses and Dissertations

Predation interactions between zooplankton and two species of Chaoborus (Diptepa, Chaoboridae) in a small… Fedorenko, Alice Y.R. 1973

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P R E D A T I O N I N T E R A C T I O N S BETWEEN S P E C I E S OF CHAOBORUS  ZOOPLANKTON AND  TWO  ( D I P T E R A , CHAOBORIDAE) I N A  SMALL COASTAL LAKE  by  A L I C E Y. R. B.Sc,  University  FEDORENKO of Toronto,  1970  A THESIS SUBMITTED I N P A R T I A L FULFILLMENT  OF  THE R E Q U I R E M E N T S FOR THE DEGREE OF M A S T E R OF in  SCIENCE  t h e Department of ZOOLOGY  We a c c e p t  this  thesis  required  as conforming  standard  THE U N I V E R S I T Y OF B R I T I S H C O L U M B I A 1973  to the  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r  an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y  a v a i l a b l e f o r r e f e r e n c e and  I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e f o r s c h o l a r l y purposes may by h i s r e p r e s e n t a t i v e s .  study.  c o p y i n g of t h i s  be g r a n t e d by the Head of my  thesis  Department or  I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t written permission.  Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  my  ABSTRACT  Feeding  h a b i t s o f two c o e x i s t i n g  C.trivittatus and of  and C.amerjcanus, were i n v e s t i g a t e d  i n laboratory experiments, larval The  year  crop field  life  species. rates  study  showed  migrates  that C trivittatus  dielly  to  season  and were mostly  and swimming v e l o c i t y  t h e above d a t a  and mig-  Seasonal  on v e r t i c a l  evaluate the a v a i l a b i l i t y  Zooplank-  found  and s i z e  above 6  of  m.  larval  and, together  distribution,  o f zooplankton  abun-  found i n  d u r i n g 1971 and 1972.  head p a r t s were measured i n t h e l a b o r a t o r y , with  has a two  cycle  o f most p l a n k t o n t y p e s  had a low standing crop size  life  a d i s t a n c e o f o n l y 5 m.  Lake were monitored  Zooplankton  survey  d u r i n g t h e summer  C.antericanus has a one year  dance and d i s t r i b u t i o n  ton  and by an e x t e n s i v e  and i s t h e more abundant o f t h e two C h a o b o r u s  a t most o v e r  Eunice  i n lake  contents.  cycle,  d o w n t o 20 m,  species o f Chaoborus,  were  used  as prey f o r  Chaoborus. The of  l a k e and l a b o r a t o r y experiments  larval  f e e d i n g and d i g e s t i o n  temperature. affect Feeding type  of  increase significantly  of the 4th instar  rates increase with larval  and d e n s i t y . diet  that rates with  T e m p e r a t u r e , h o w e v e r , d o e s n o t seem t o  feeding rate  contents,  showed  From a n a l y s i s  d i f f e r e n c e s were  C.trivittatus  age and v a r y w i t h of chaoborid  found  larvae. prey  crop  among a l l i n s t a r s  t h e two s p e c i e s , and t h e s e were r e l a t e d  t o prey  i i i  size, of  abundance,  prey  could  and d i s t r i b u t i o n .  standing crop  potentially  The c a l c u l a t e d  t h a t t h e Chaoborus  remove ranged  from  t o a maximum o f 2 0 % f o r D i a p t o m u s  changes  i n Choaborus  species  composition  single  zooplankton  The o b s e r v e d was  diet  and t h e i r  p r e d a t o r and  kenai.  Seasonal  c o m p o s i t i o n and i n zooplankton i n reduced  p r e d a t i o n on any  group. o f Chaoborus  shown t o be c l o s e l y  Chaoborus of  result  Lake  a m i n i m u m o f 3% f o r  nauplii  instar  i n Eunice  percent  prey  prey.  related  larvae i n Eunice  Lake  t o the morphology o f  and t o t h e r e l a t i v e  distribution  iv  T A B L E OF  CONTENTS  Page T I T L E PAGE  . . . . . . . . .  i  ABSTRACT T A B L E OF  i i CONTENTS  iv  L I S T OF  FIGURES  v i i  L I S T OF  TABLES  L I S T OF  APPENDICES  x i x i i i  ACKNOWLEDGEMENTS I II  III  IV  xiv  INTRODUCTION  .  D E S C R I P T I O N OF 1  Physical  2  Biological  THE  and  STUDY A R E A  Chemical  4  Features  4  Features  G E N E R A L M A T E R I A L S AND  1  4  METHODS  8  1  T e m p e r a t u r e and  2  Plankton Sampling  8  3  Plankton Counting  1°  4  Plankton Weighing  5  S i z e Measurements  6  Swimming V e l o c i t y  7  Chaoborus Growth Experiment  B I O L O G Y OF 1  Oxygen  8  ... - . r.  .  10 11  of  Zooplankton  11 13  ZOOPLANKTON  16  Results  16  a  Body s i z e  and  weight  b  Speed o f  c  Seasonal changes i n s t a n d i n g crop in species composition  swimming and  16 movements  16 and 19  V  Page  3 V  d  Diel  distribution  e  Patchiness  and m i g r a t i o n  i n plankton  . . . . . .  distribution  . . . .  Summary  25 30  B I O L O G Y O F CHAOBORUS L A R V A E  31  1  31  Results a  Head morphology  b  Development  c  Seasonal  d  Seasonal changes  of larval  instars  31  of larvae  changes  31  i n standing  crop  36  i n d i s t r i b u t i o n and  migration e  VI  23  Potential  38  growth o f larvae  38  2  Discussion  41  3  Summary  46  F E E D I N G OF CHAOBORUS  47  1  47  2  Methods a  Digestion  b  Feeding  c  Temperature e f f e c t  d  Long  e  Efficiency  f  Analysis  g  Diel  47  rates  47  rates  term  feeding  on feeding  rates  . . . .  49  experiment  o f copepod  ingestion  50  o f l a r v a l crops  feeding  49  51  activity  52 53  Results a  Digestion  b  Feeding  c  Temperature e f f e c t  53  rates  53  rates on feeding  rates  . . . .  59  vi  Page  VII  d  Long  term  feeding  e  Efficiency  f  Analysis of larval  g  Diel  of prey  feeding  experiment ingestion  59 . . . . . . .  crops  62 64  activity  73  3  Discussion  78  4  Summary  86  E F F E C T OF CHAOBORUS P R E D A T I O N ON ZOOPLANKTON 1  Methods a  2  87 87  Calculation of overall  predation  impact on zooplankton b  . . .  C a l c u l a t i o n o f consumption  87 b y C . t r 4°  larvae89  Results  92  a  Prey-nauplii  92  b  Prey-D.tyrelli  94  c  Prey-D.kenai  94  d  Pr ey-D i a p h a n o soma  96  e  Consumption  9  3  Discussion  4  Summary  BIBLIOGRAPHY APPENDICES  b y C . t r 4° l a r v a e  6  98 107 1°  8  H3  vii  L I S T OF  FIGURES  FIGURE  Page  1.  C o n t o u r map ( i n meters) of Eunice Lake. Sampling s t a t i o n s are c i r c l e d . Positions o f r a f t i n 1971 a n d 1972 a r e i n d i c a t e d by squares  2.  Isotherms  i n Eunice  Lake,  L a t e r a l v i e w ( a ) , a n d v e n t r a l v i e w (b) , o f a l a r v a l head showing the t h r e e head p a r a meters measured. (MAG.=40X).  12  4.  Tubes used  experiment.  15  5.  M e a n s * 1 S.E. o f s w i m m i n g v e l o c i t i e s o f zooplankton at d i f f e r e n t temperatures. . . .  18  Standing crop of zooplankton groups i n 1 9 7 1 ( d o t t e d l i n e ) a n d i n 1972 (solid line). Holopedium were not r e c o r d e d i n 1971.  20  T o t a l s t a n d i n g c r o p by number ( N ) , and by b i o m a s s ( B ) , o f z o o p l a n k t o n i n 1971 ( d o t t e d l i n e ) a n d i n 1972 (solid line). Rotifers and Chaoborus were e x c l u d e d . Holopedium w e r e n o t c o u n t e d i n 1971  22  N o o n a n d m i d n i g h t (MT) v e r t i c a l d i s t r i b u t i o n o f z o o p l a n k t o n t y p e s (on l e f t ) , and o f C h a o b o r u s t y p e s (on r i g h t ) , i n E u n i c e LaKe i n 1972. Letters indicate type of plankton: N - n a u p l i i , K-D.kenai, B-BQsmina, D-Paphnia, DI-Diaphanosoma, H-Holopedium, P-Polyphemus, CL-combined c l a d o c e r a n t y p e s . Roman n u m e r a l s show i n s t a r s o f C . a m e r i c a n u s , am, (on l e f t ) , and o f C . t r i v i t t a t u s , t r , Jon right) .  24  M e a n s t 1 S.D. of head l e n g t h , antenna and s e t a l e n g t h , and mouth d i a m e t e r o f l a r v a l i n s t a r s ( i n Roman n u m e r a l s ) o f C . a m e r i c a n u s (open c i r c l e s ) and C . t r i v i t t a t u s (solid circles). F i r s t i n s t a r s of botn species are combined (hatched c i r c l e s ) . Number o f animals measured i s g i v e n i n p a r e n t h e s i s . .  32  6.  7.  8.  9.  f o r Chaoborus growth  v i i i  FIGURE  10.  11.  12.  13.  14.  15.  16.  Page  S u c c e s s i o n o f l a r v a l i n s t a r s o f C. americanus ( l e f t ) and o f C . t r i v i t t a t u s ( r i g h t ) I n 1971 ( d o t t e d l T h e l and i n 1972 (solid line). Year hatched i s shown f o r 4 t h i n s t a r l a r v a e  33  Seasonal changes i n l a r v a l i n s t a r l e n g t h i n 1971. Means and 95% c o n f i d e n c e l i m i t s a r e s h o w n f o r e a c h i n s t a r (Roman n u m e r a l s ) o f C.americanus ( d o t t e d l i n e s ) and C . t r i v i t tatus (solid l i n e s ) . (from Fedorenko and S w i f t d972)  34  S e a s o n a l c h a n g e s i n l a r v a l w e i g h t i n 1971 and 1972. Means, 95% c o n f i d e n c e l i m i t s , and t h e y e a r h a t c h e d a r e shown f o r e a c h species. ( f r o m S w i f t 1973)  35  C u m u l a t i v e s t a n d i n g c r o p by number ( N ) , a n d b y b i o m a s s ( B ) , o f C . a m e r i c a n u s a n d C. t r i v i t t a t u s i n 1971 ( d o t t e d l i n e ) and 1972 (solid line). A l l i n s t a r 1 l a r v a e were included with C.trivittatus  •  37  D i e l v e r t i c a l m i g r a t i o n of C.americanus and C . t r i v i t t a t u s l a r v a e on 16-17 September, 1971. I n s t a r s o f l a r v a e and d e n s i t y p e r 100 l i t e r s a r e a s s h o w n . (from Fedorenko and S w i f t 1972)  39  Mean w e i g h t s and u p p e r 95% c o n f i d e n c e l i m i t s of t h r e e t y p e s o f Chaoborus l a r v a e from the tube experiment: dotted bars are i n i t i a l w e i g h t s i n l a k e and t u b e s ; c o a r s e l y h a t c h e d bars are f i n a l weights i n lake; grey bars are f i n a l weights i n tubes A v e r a g e t i m e r e q u i r e d t o a c h i e v e 50% 80% o f c o m p l e t e d i g e s t i o n o f D . k e n a i C.trivittatus 4 larvae at different temperatures  4 0  and by  Y  17.  M e a n s t 1 S.D. o f C h a o b o r u s f e e d i n g r a t e s on D . t y r e l l i a t d i f f e r e n t t e m p e r a t u r e s . ( c u r v e s w e r e f i t t e d by eye)  55  57  ix FIGURE 18.  19.  20.  Page Means + I S . D . o f C h a o b o r u s f e e d i n g r a t e s on D.kenai (a-d)., on D i a p h a n o s o m a ( e ) , and on n a u p l i i ( f ) . Solid lines indicate feeding rates; dotted l i n e s give the t o t a l o f e a t e n and k i l l e d p r e y . (curves were f i t t e d by e y e ) . . . . .  5 8  P r e y consumed by a Chaoborus l a r v a a t d i f f e r e n t temperatures: ( a ,b ,c) o n s e c o n d day o f e x p e r i m e n t , ( d , e , f ) on f o u r successive days. Day n u m b e r i s g i v e n o n extreme r i g h t . Prey are P.kenai f o r 4th i n s t a r l a r v a e , and" D . t y r e l T i f o r 3 r d instar larvae. G i v e n a r e t h e means - 1 S.E. ( c u r v e s w e r e f i t t e d by eye)  60  Daily food r a t i o n of 9 t y p i c a l larvae of C.am 4 (A), C.tr 4 ( B ) , a n d C . t r 4° ( C ) . Hatched bars are f u l l y d i g e s t e d D.kenai; c l e a r bars are p a r t i a l l y digested" D.kenai.  . .  61  S e a s o n a l d i e t o f C . a m e r i c a n u s l a r v a e by i n s t a r and t h e c o m p o s i t i o n o f l a k e p l a n k t o n i n 1972. N (clear bars), i s p e r c e n t c o m p o s i t i o n by number; B ( h a t c h e d b a r s ) , i s p e r c e n t c o m p o s i t i o n by b i o m a s s . Letters refer to prey types: R-rotifers, B-Bosmina, P-Polyphemus, D-Daphnia, H-Holopedium, C-miscellaneous c l a d o c e r a n s , K - D . k e n a i , T - D . t y r e l l i , O - C h a o b o r u s , XunTdentifiable m a t e r i a l  •  68  Y  21.  22.  23.  24.  S e a s o n a l d i e t o f C . t r i v i t t a t u s l a r v a e by i n s t a r i n 1972. " F o r e x p l a n a t i o n see F i g . 21  69  D i e l f e e d i n g p a t t e r n on D.kenai o f C . t r 4° l a r v a e i n 1 9 7 2 . Arrows i n d i c a t e peaks of feeding a c t i v i t y . Sample s i z e f o r each d a t a p o i n t r a n g e d from about 100-300 larvae  74  D i e l f e e d i n g a c t i v i t y on Bosmina ( s o l i d l i n e ) , and on a l l p r e y t y p e s combined (dotted line)., of d i f f e r e n t instars of C.americanus and C . t r i v i t t a t u s l a r v a e i n T972~: Sample s i z e f o r each d a t a p o i n t r a n g e d f r o m a b o u t 50-100 C . a m e r i c a n u s l a r v a e a n d f r o m a b o u t 10 0 - 2 u u c . t r i v i t tatus larvae ~ ~ • ~ • • • •  75  X  FIGURE  25.  26.  27.  Page  The e f f e c t o f Chaoborus p r e d a t i o n on n a u p l i i ( l e f t ) , and on D . t y r e l l i ( r i g h t ) , (ayd) - p e r c e n t o f p r e y s t a n d i n g c r o p removed by Chaoborus i n 1971 ( d o t t e d l i n e ) and i n 1972 ( s o l i d l i n e ) ; (b,e) a n d ( c , f ) - percent of t o t a l predation attributed t o d i f f e r e n t l a r v a l i n s t a r s i n 1971 and 1972 respectively  93  The e f f e c t o f Chaoborus p r e d a t i o n on D . k e n a i ( l e f t ) , and on Diaphanosoma ( r i g h t ) . For e x p l a n a t i o n see F i g . 25.  95  The mechanisms f o r p r e d a t o r a v o i d a n c e f r o m May t o N o v e m b e r o f 1972 b y f o u r p r e y t y p e s . S-seasonal segregation, V - v e r t i c a l segr e g a t i o n , D-low p r e y d e n s i t y , H - s i z e i n compatibility. Solid lines represent o p t i m a l p e r i o d s f o r p r e d a t i o n s i n c e no known p r o t e c t i v e mechanism i s o p e r a t i n g ; dashed l i n e s i n d i c a t e t h a t t h e mechanism i s o n l y p a r t i a l l y e f f e c t i v e a n d some p r e d a tion can occur; dotted l i n e s represent l e a s t optimal periods f o r predation because of t h e above mechanisms o p e r a t i n g . P e r i o d s f r e e o f l i n e s i n d i c a t e t h a t no p r e d a t i o n i s o c c u r r i n g because o f absence or scarcity of predators. Roman n u m e r a l s indicate larval instars  99  xi LIST  OF  TABLES  TABLE  I  Page  Mean l e n g t h and zooplankton  II  III  1  dry weight  of  EuniceLake  .  17  Comparison of 4 h o r i z o n t a l Clarke-Bumpus t o w s t a k e n a t n o o n b e t w e e n s t a t i o n s 1 a n d 2. V a l u e s a r e g i v e n i n n u m b e r s p e r 100 liters. S a m p l i n g d e p t h s and d a t e s a r e i n d i c a t e d i n parenthesis  27  C o m p a r i s o n o f t h e t o t a l number o f C h a o b o r u s larvae per standard v e r t i c a l net haul taken at each of the 5 s t a t i o n s i n Eunice Lake d u r i n g 1972. V a l u e s a r e g i v e n i n numbers p e r 0.62 m '.  28  Comparison o f z o o p l a n k t o n and o f C h a o b o r u s biomass between s t a t i o n 5 and s t a t i o n 1 i n 1972. V a l u e s a r e g i v e n i n mg p e r m^ . . . .  29  Digestion different  54  2  IV  V VI VII VIII  IX  X  r a t e s of Chaoborus p r e y t y p e s T '. ". T~  feeding  I n g e s t i o n success of Chaoborus copepods '. ". '. ". L a r v a l mouth s i z e  and  prey  oh  feeding  on  size  63 65  L a r v a l food overlap i n d i c e s f o r J u l y , August, September, and October c a l c u l a t e d from n u m e r i c a l d i e t p e r c e n t a g e s A, a n d f r o m b i o m a s s d i e t percentages B 70 A chi-square a n a l y s i s of the numerical d i e t c o m p o s i t i o n o f a l l l a r v a l i n s t a r s c a u g h t on some d a t e ( a ) , o f two i n s t a r s o f s i m i l a r a g e s c a u g h t o n same d a t e ( b ) , o f t h e same l a r v a l i n s t a r s caught on d i f f e r e n t d a t e s ( c ) , and o f t h e s e a s o n a l l a k e p l a n k t o n compos i t i o n (d) A chi-square analysis of the d i e l feeding p a t t e r n o f Chaoborus l a r v a e based on D.kenai a l o n e ( a ) , on Bosmina a l o n e ( b ) , and on a l l p l a n k t o n types combined ( c ) .  72  x i i  TABLE  XI  XII  XIII  Page  A sample c a l c u l a t i o n t i o n on D . t y r e l l i  of  Chaoborus  preda88  S a m p l e c a l c u l a t i o n s o f mean d a i l y consumpt i o n b y C . t r . 4° u s i n g (1) f e e d i n g r a t e s a n d p r e y a b u n d a n c e d a t a , a n d (2) t h e e n e r g y budget equation C a l c u l a t e d d a i l y food consumption of l a r v a e i n 1971 a n d 1972  C.tr_  4°  gg  9 7  x i i i  L I S T OF A P P E N D I C E S  APPENDIX  Page  I  Predation  on n a u p l i i ,  1971  H  II  Predation  on n a u p l i i ,  1972  115  III  Predation  on D . t y r e l l i ,  1971  116  IV  Predation  on D . t y r e l l i ,  1972  117  V  Predation  on D.kenai, 1971  118  VI  Predation  on D.kenai,  119  VII VIII  IX  X  1972  P r e d a t i o n o n Diaphanosoma, 1971  . . . . .^  C a l c u l a t i o n o f t h e mean d a i l y c o n s u m p t i o n (C) o f c o p e p o d p r e y b y C . t r 4 ° i n 1 9 7 1 and 1 9 7 2 , u s i n g f e e d i n g r a t e s a n d p r e y abundance data  2  4  Q  ^21  C a l c u l a t i o n s o f t h e mean d a i l y consumpt i o n b y C . t r 4° i n 1 9 7 1 a n d 1972 u s i n g t h e energy""Fudget e q u a t i o n C a l c u l a t i o n o f t h e mean d a i l y t i o n b y C . t r 4° i n 1972 u s i n g analysis data  consumpthe crop 123  xiv  ACKNOWLEDGEMENTS  I would  like  t o thank  the staff  search F o r e s t and i n p a r t i c u l a r , their  help and i n t e r e s t Numerous f r i e n d s  pleasant tion,  particularly  with the  work.  Regina  their  Clarotto  Waterman and R e g i n a  i n the laboratory. t h e computer work.  interest  and t h e W a l l i n  Clarotto  assisted  Judy  Dayton k i n d l y  C. W a l t e r s a n d A. L e w i s  helped  made v a l u a b l e s u g g e s t i o n s d u r i n g t h e c o u r s e  and  counselling.  good Dr.  T.G. N o r t h c o t e , my  supervisor,  much e n c o u r a g e m e n t t h r o u g h o u t grateful.  during I with  i n field helpful with  read the manuscript  Thanks a r e due t o D r . I . E f f o r d  very  family.  D o l o r e s L a u r i e n t e was v e r y  study.  and  and p a r t i c i p a -  typing. Drs.  and  Mr. Jack W a l t e r s , f o r  h a v e made t h e w o r k a m e m o r a b l e a n d  experience through  Kim and  i n this  o f t h e U.B.C. R e -  am e s p e c i a l l y  executed  skillful  grateful ingenuity,  m a n y o f my r o u g h e r  provided  t h e study  guidance  f o r which  and support were  I am  invaluable  t o M i c h a e l C. S w i f t , a n d a know-how t h a t  c h o r e s , a n d w h o w a s my  who I lacked, chief  i n formulating the thesis.  Finally Council  f o rh i s i n t e r e s t  the preparation of the manuscript.  zeal,  editor  His criticism  of the  I would  like  t o thank  o f Canada f o r t h e i r  me t o b e i n t h i s  the National  financial  Research  support that  enabled  p a r t o f C a n a d a a n d m e e t s o many f i n e  people.  1  I  INTRODUCTION  Chaoborus are larvae  dipterans, with predaceous, planktonic  t h a t emerge as  common i n l a k e s a n d quently and  an  non-biting flies.  ponds a l l over  important  food  item of  h a v e b e e n shown t o be  tain  they  are  larvae are easy  Sprules  1973), cer-  1970).  animals  survive well  are  fre-  components of  (Welch 1968;  and  are  (Sikorowa  good e x p e r i m e n t a l  to handle  larvae  world,  fish  important  aquatic communities  Chaoborus  the  The  because  under l a b o r a t o r y  conditions. Chaoborus t r a n s p a r e n t and a  by  strikes the  prey  are  The  remains of  gitated  (G.  through  19 6 6 ) .  prey,  larval  larvae Parma  mouth.  on  (1971) l i s t s and  as  some a l g a e —  in fact  size  for swallowing.  The  regur-  morphology  Montshadsky  and  of  (1945).  Chaoborus  limited food,  several benthic  few  are  functional  larval  anything  prey.  d i g e s t i v e mechanism.  qualitative  potential  produced  specialized  crop,  feeding ecology  rotifers,  even  The  larval  "make  ingesting their  i s g i v e n by  the  have been m o s t l y  crustaceans  Chaoborus have  semi-  communication).  vibrations  digested i n the  (1965) d e s c r i b e s t h e Observations  personal  t r i g g e r e d by  Chaoborus mouth-parts  Pucat  1972,  f o r c a p t u r i n g and the  that rest  i n t h e w a t e r column and  Sprules  probably  (Horridge  head appendages  ambush p r e d a t o r s  motionless  stab at anything"  The  of  larvae are  in  a l l planktonic  species,  that i s of  investigators  scope.  a  and  reasonable  that  have  2  looked  a t the food  (Deonier exist 2nd  of the individual  1943; Main  i s mainly  rotifers  and n a u p l i i ,  consists  mainly  The  diets  Sikorowa  ious  the crop  instars. contents  approach  compared prey  practical  of  quantitatively  times  however, has  collected  from  of the year.  indirectly Kajak  Roth s 1  laboratory  and a f t e r  i n situ  three prey  4th  instar The  types  incubations  relies  on  there I n both  d i d not differentiate  Swuste e t a l ^ ( i n press) s e t up w i t h  t o study  (1970)  method i s n o t always  as i t s accuracy  instars.  experimental  and  radio-  and a r e t h e r e f o r e  and Ranke-Rybicka  However, t h e i r  or realistic  larval  var-  Few  an u n n a t u r a l l y h i g h d e n s i t y o f organisms.  between  by  d i f f e r e n c e s i n food  t h e above examples, t h e authors  lake  larvae  o f C . f l a v i c a n s and  Sikorowa,  numbers b e f o r e  Chaoborus.  as  (1971) was awkward a n d t i m e - c o n s u m i n g .  somewhat q u e s t i o n a b l e .  being  instars  o f animals  r e s u l t s were o b t a i n e d  with  of the older  q u a n t i t a t i v e s t u d i e s have been done.  isotope  such  copepods and cladocerans.  who a l s o f o u n d  locations at different  other  His  and t h e food  have been analyzed  (1973),  o f 1 s t and  the small zooplankters  of the larger  among t h e l a r v a l pooled  o f l a r v a e ; t h e food  of a l l four larval  C.crystallinus  instars  1953) r e p o r t t h a t d i f f e r e n c e s do  among t h e i n s t a r s  instars  larval  7-day s t a r v e d  selective  used  larvae  p r e d a t i o n by t h e  larvae of C.flavicans.  p r e s e n t w o r k was c o n d u c t e d  on t h e western  coast  of British  a  i n a small Columbia.  mountain This  3  lake an  i s conveniently  easy  object life  (2)  transport of of  the  of  i n Eunice  by  prey  type,  species  evaluate  and  the  populations pattern  of  The and  was  the  the and  prey  two and  related to  by  instar  density  (1)  the  the  the  to prey i n four ecology  feeding,  impact of  larval  feeding  and on  of  relate  larval  of  temperature, and  the  the  (3)  to  zooplankton  nature  and  availability. sections. of  Eunice  Sections Lake  Section  zoothree  section four describes  the  prey  feeding;  feeding; on  the  their  the  effect  Chaoborus r e s p e c t i v e l y .  larval  The  and  larval  predation to  for  to determine  species  larval  Lake,and  discusses  lake.  on  larval  predation  deal with  and  allowing  laboratory.  Chaoborus  i s presented  of  the  natural composition  i n Eunice this  to  institute  threefold:  two  impact of  work  plankton  animals  L a k e as  to determine  diet  one  study  histories  found  c l o s e to the  prey  populations  in  the the  4  II  D E S C R I P T I O N OF THE STUDY A R E A  I  The  P h y s i c a l and Chemical  field  study  was c o n d u c t e d  small  oligotrophic lake  Haney  (Fig. 1).  and  i n Eunice  Lake,  a  i n t h e U.B.C. R e s e a r c h F o r e s t  I t h a s a n e l e v a t i o n o f 4 8 0 m,  near  mean  maximum d e p t h s o f 15.8 a n d 42.0 m r e s p e c t i v e l y , a n d a  surface  area  imately  318 h a .  o f 18.2 h a .  I t s drainage  l a k e w a s a b o u t 2 2 , 2 0 0 m^  370  days.  The l a k e  December t o A p r i l mocline  was  Secchi  therOxygen  50% s a t u r a t i o n  d u r i n g 1972.  Features  zooplankters  - Diaptomus  cladocerans  of  from mid-  (Fig. 2).  d o w n t o 25 m w h e r e o v e r  Biological  dominant  species  into  The w a t e r had a brown humic c o l o u r and a  2  pod  i s u s u a l l y i c ecovered  d e p t h o f 5-6 m r e c o r d e d  The  discharge  o r May a n d h a s a w e 1 1 - d e v e l o p e d  were h i g h  recorded.  i s approx-  g i v i n g a r e t e n t i o n time  i n t h e s u m m e r a t a b o u t 4-6 m  readings  area  I n 1 9 7 1 t h e mean d a i l y  the  of  Features  i n t h e summer w e r e t w o c o p e -  tyrelli  and D.kenai,  - Bosmina l o n g i r o s t r i s ,  five  Daphnia  species  rosea,  Diaphanosoma brachyurum, Polyphemus p e d i c u l u s , and Holopedium gibberurn, and  and two s p e c i e s  C.trivittatus.  Conochiloides  were p r e s e n t  There were no f i s h except that  Rotifers  o f Chaoborus —  C. airier i c a n u s  such as K e r a t e l l a and  but their  i n the lake.  abundance n o t recorded.  In the winter, a l l plankton  Chaoborus became d r a s t i c a l l y  reduced.  f o l l o w s , C.americanus and C . t r i v i t t a t u s  In the text are referred  Fig.l  Contour map ( i n meters) o f E u n i c e Lake. Sampling s t a t i o n s a r e c i r c l e d . P o s i t i o n s o f r a f t i n 1971 and 1972 a r e i n d i c a t e d by squares.  6  Fig.2  Isotherms  i n E u n i c e Lake.  7 to  a s C.  am 1 - 4 ,  developmental being  a n d C.  t r 1-4,  stage or i n s t a r  the oldest.  Fourth  t h e numbers  of the larva,  instar  indicating 4th  the  instar  C.trivittatus  will  be  y called life the  C.  cycle  t r 4  i f they  are i n the 1st year  ("young" l a r v a e )  2nd y e a r  of their  life  a n d C. cycle  of  their  t r 4° i f t h e y  ("old"  larvae).  are i n  8  III  G E N E R A L M A T E R I A L S AND I  Temperature and  T e m p e r a t u r e was of  1971  and  1972,  usually  1 m  intervals  The  accuracy of the  were taken and  July  1969  (T.G.  1971  and  Hach k i t w i t h an  follow  vertical and  1972.  and  2  25 a  m  vertical (Fig.  1)  and  October  Plankton  I n 1971,  1  and  August  in  1972  from  l a r v a e by May  Assoc-  gradually  x 0.  A  20 mm)  30  was  a t each  Nets  w i t h 69  or  89  cm  mesh and  a No.  mm  mesh) b u c k e t  the  sampling.  to determine  square used.  of the  depth.  sampler  m,  cm  0-20  Clarke-Bumpus  a  weekly  depending  diameter,  w i t h a No.  s e a s o n a l changes  5  on  0.5  1  to  net  with  In  1972,  stations  station mm  square  were used  20  1971  stations  l o w e r i n g t h e n e t down  moving boat.  (0.08  using  instar,  h a u l s w e r e made b e t w e e n  (0.65  in  t o November i n  or  used  profiles  ppm.  m,  was  thermistor.  Sampling  h a u l s were t a k e n , one  20  at  Oxygen  of  0-15  A  m  Biological  from  1972  November  N o r t h c o t e , u n p u b l i s h e d d a t a ) , and  samples were taken  r e c t a n g u l a r mesh  1967  w i t h a Freshwater  the development of  a slowly  +1°C.  September of  accuracy of +  ( F i g . 1 ) , by from  through  o n c e a w e e k , d o w n t o 20  i n August  2 To  f r o m May  r e a d i n g s was  i n J u n e and  Probe  of  Oxygen  using a Yellow Springs Instruments  September o f  iation  recorded  METHODS  nylon  during  net  i n abundance,  9  density,  and  Chaoborus  vertical  i n Eunice  between s t a t i o n s (surface  and  distribution  Lake.  1 and  every  2  ( F i g . 1) meter  from  at biweekly  through  In  midnight  samples were taken  was  On  29-30 A u g u s t and  done e v e r y  plankton.  three hours  In each  filtering  0.5-1  factor  4.2  of  Institute  tow  16-17  1971  to study  liters  replicability  1972.  minutes,  calibration  (determined used  to  by  samples were p r e s e r v e d  in  o f C l a r k e - B u m p u s s a m p l e s was  on  July  20  of  19 72  f o r Chaoborus.  in  the  abundance o f  of  the  lake,  station  1,  representing the  the  l a k e and  station  5,  r e p r e s e n t i n g the narrow  the  lake  The  Clarke-Bumpus  1971  f o r zooplankton To  zooplankton  sampler  the other  The  depth  similar  and  determine  ( F i g . 1 ) , were sampled  occasions;  4%  borax.  f o u r tows i n c l o s e s u c c e s s i o n a t s e v e r a l of  the  calculate  taking  b u t was  sampling  migration of  by  hauls.  fourth  1971,  A  o f O c e a n o g r a p h y , U.B.C.) was  Formalin buffered with  and  o p e n f o r 1.5-3  revolution  The  a t noon  the d i e l  t h e n e t was  per  1-3  and  September  depths  for  only every  cubic meters of water.  the volume sampled.  The  1 t o 2 1 m)  November o f  of  taken  intervals  f r o m May  week.  tows,  and  at set sampling  midnight 1971,  zooplankton  Horizontal  second  minutes,were repeated  of  was  on  two  i n 1972  used  on  f o r both  stations  on  on  0-7  any  ends  "open" p a r t "arm"  of of  8 occasions.  four of  from  24  differences  extreme  samples were c o l l e c t e d  sampled v a r i e d  depths  September  general  at the  tested  these  with t o 0-20  one  day.  vertical m  10  3 Plankton  Counting  Chaoborus l a r v a e were removed  from t h e samples and  c o u n t e d by s p e c i e s  and i n s t a r .  were counted  a d i s s e c t i n g microscope.  with  high  divided  using  densities of a particular  i n t o 6 o r 36 p a r t s  This  was r e p e a t e d  that  species.  < 1.75 mm  ful  species  sub-  and one s u c h p a r t was to obtain  nauplii,  D.tyrelli  i n length;  mm.  counted.  t h e mean v a l u e f o r  Diaptomus  categories  tyrelli,  These  included P.kenai  the small  Diaptomus  included  s i z e c l a s s e s were  copepodids  the large found  from  individuals  1971 were s e p a r a t e d o n t h e same  4  into small  Plankton  Freshly  from other  c o l l e c t e d zooplankton  of  t o prevent  contained  plankton.  immediately feeding.  w e r e d r i e d a t 100° o r on a Cahn Gram  5 r e p l i c a t e s o f each sample were  replicates  large  Weighing  zooplankton  60°C f o r 2 d a y s a n d w e i g h e d Usually  and  species.  basis.  Chaoborus c o l l e c t e d f o r weighing were separated  copepodids  t o be meaning-  f o r d i s t i n g u i s h i n g between t h e two copepod  Paphnia  size  were  Bosmina, Polyphemus, P a p h n i a , Diaphanosoma, and  Holopedium.  ^1.75  3 times  plankton Samples  The f o l l o w i n g e i g h t p l a n k t o n  were e s t a b l i s h e d : kenai,  The r e m a i n i n g  electrobalance.  weighed;  50 o r m o r e a n i m a l s d e p e n d i n g o n t h e  11  5  All  Size  m e a s u r e m e n t s w e r e made u s i n g a c a l i b r a t e d  micrometer  i n a dissecting  magnification. each prey of  Measurements  microscope,  sizes  type were determined,  excluding the t a i l  antenna and l o n g e s t s e t a l e n g t h s , and  (except 1st instar)  as  3.  of a l l larval  The m a x i m a l gape o f t h e l a r v a l  from  a ventral  region of larva meaningful  view.  Swimming  Swimming  Velocity  velocities  m e a s u r e d d u r i n g 1972  to a  behind  prey  taken  the eyes,  of  i n the lake.  showed t h i s  t o be  Zooplankton were from  o f Diaptomus k e n a i ,  the f i r s t  hours  tray  few days a f t e r  collection.  room  Plankton  lighting.  with a gridded  for Five  placed with a pipette  X 4 5 c m X 2cm)  en-  tested  t o the experimental temperatures  under incandescent  ( 3 0 cm  The  t h e p l a n k t e r s commonly  A l lzooplankton were  as  o f t h e mouth  f o r s i x types of zooplankton  t e n i n d i v i d u a l s were then flat  C.  mouth was  a t various temperatures  used were those  were a c c l i m a t i z e d several  of  Bosmina, Diaphanosoma, and Polyphemus.  temperatures countered  instars  examination  Lake - a d u l t s and j u v e n i l e s  D.tyrelli,  within  large  mouth  measurement.  6  Eunice  just  Close  swallowing  Head  were m e a s u r e d a s shown i n  t h e w i d t h o f t h e head c a p s u l e  seen  X  spine  setae of copepods.  americanus and o f C . t r i v i 1 1 a t u s , Fig.  a t 20 X o r 30  Maximum l e n g t h , w i d t h , a n d t h i c k n e s s o f  c l a d o c e r a n s and t h e c a u d a l  lengths,  ocular  into  floor  a  12  MOUTH  Fig.3  MOUTH DIAMETER  L a t e r a l view (a), and v e n t r a l view (b) , o f a l a r v a l head showing t h e t h r e e head parameters measured. (MAG.=40X).  13  (l/2cm  x  l/2cm) c o n t a i n i n g w a t e r  perature, cover A  a  1 cm  few  single  minutes  deep.  The  and  the  was  their  recorded.  Animals which  the  tray during  the  10-15  To  a  determine  speed of  filming,  the  probe.  To  distances  32  The of  the  into  covered  by  a  shallow  of  swim  included  of  D.kenai,  the  petri  d i s h and  filmed  During  the  mean v e l o c i t y  each leap  in a  90  seconds  escape w i t h of  each  of a  leap,  sequence of  frames  averaged.  experimental  design  were r e s t r i c t e d  in particular,  shallow  vessels than not  time  the w a l l s  Each experiment  frames/sec.  D.kenai  h e r e may  re-  1-3  p e r i o d or d i d not  leaping velocity  c a l c u l a t e the  plankton  for  in that  with  D.kenai were s t i m u l a t e d t o  w e r e added and  to  animals.  copepods were p l a c e d at  collided  tem-  measured.  continuously  observation  measured.  different  was  squares crossed  was  f r e e l y were not  experimental  velocity  observed  number o f  the  p l a n k t e r s were a l l o w e d  minutes before  individual  at  was  such  movements  to a h o r i z o n t a l plane.  were observed  i n deep ones.  t h e r e f o r e be  that the  to cruise faster The  values  representative of  the  in  obtained natural  situation. 7  In of  Chaoborus Growth  testing  the  effect  Chaoborus l a r v a e , three  tubes,  1 m  i n diameter,  and  of  Experiment  excess  clear, 30  m  food  10 m i l  on  the  growth  polyethylene  l o n g , were  fixed  to  a  14  raft  i n t h e deep p a r t o f t h e  measured  j u s t b e f o r e t h e end  near  f u l l saturation  with  70%  saturation  left  the  experiment which Three  larvae,  The  weekly,  groups  about  2.  litres  i n the  tubes filled  to the s t a r t  o f am  density  Initial  were measured  20  was  (2 A u g u s t - 1 1  density  ten times the natural  t h r e e Chaoborus  and  month p r i o r  times the natural  and  Oxygen,  e n c l o s u r e s were  r a n seven weeks  were added on August  Twice  i n the lake  u n d i s t u r b e d f o r one  1972).  ton  both  (Fig. 4).  of the experiment,  a t 20 m.  and  4°  lake  October,  3,  of  of  t r 3,  and  zooplank-  dry weights of a l l at that  time.  of concentrated Eunice  Lake  2 zooplankton,  collected  with  were added t o each  tube.  excluded  mixture.  from t h i s  a net of Chaoborus Growth  0.5  mm  mesh  and  Holopediurn were  o f l a r v a e was  as t h e d i f f e r e n c e  between i n i t i a l and  Weights  from the t h r e e tubes were pooled  no  of larvae  significant  tubes.  differences  were  final  f o u n d among  P i g m e n t a t i o n o f t h e head  and  length  dibular  appendages were the c h a r a c t e r i s t i c s  entiate  between t£  Old  l a r v a e had  broken  4  V  and  strongly  t r 4°  pigmented  p r e m a n d i b u l a r appendages;  pigmented appendages.  and  had  larvae  longer,  young  unbroken  defined  dry weights. since  individual of the used  from the  heads and  size,  to  premandiffer-  tubes.  usually  l a r v a e were  premandibular  less  16  IV  B I O L O G Y OF 1  a  A wide available  Results  Body s i z e  size  range  t o Chaoborus  Prey  individuals  than  6 ug  of  i n weight  ZOOPLANKTON  and  of potential larvae  1 mm  included  next  size  dium,  Daphnia,  adults.  Diaptomus  large  envelope  up  t o 4 mm  Speed o f swimming and  (Fig. 5).  double those of  rature  caused  Polyphemus, types. speed  b u t had  Diaptomus  >15°C.  the  The  included  Holope-  and  latter  D.kenai  some 2.3  virtually tyrelli  and  becoming  no  which  the magnitude  increase  of the plankton tested.  faster,  tyrelli.  D.kenai mm  and  have  a  movements  size  and  of  swimming  species  of adult  i t s juveniles.  a striking  Bosmina,  i n diameter.  Swimming speeds  nearly  more  ug, were the l a r g e s t z o o p l a n k t e r s  o f p l a n k t o n were f o u n d t o be  specific  not  a mean l e n g t h o f  Response t o t e m p e r a t u r e and speeds  and  except f o r a d u l t Holopedium  gelatinous  b  mm)  was  (Table 1).  nauplii,  kenai juveniles  A d u l t D.kenai, with  Eunice Lake,  less  Diaptomus  ( a p p r o x . 1-2  a mean d r y w e i g h t o f 42.7 in  or  rotifers,  Diaphanosoma, and class  zooplankton prey  i n Eunice Lake  i n length  Polyphemus, larger  weight  D.kenai  were  I n c r e a s e i n tempe-  i n t h e swimming speed effect  on  other plankton  Diaphanosoma had Bosmina and  very active  were the f a s t e s t  at  of  the slowest  Polyphemus  swam  temperatures  of the zooplankton at  TABLE I  Mean l e n g t h and d r y w e i g h t o f E u n i c e Lake z o o p l a n k t o n .  Length K e r a t e l l a sp.  0.10  (mm)  Dry w e i g h t 0.005*  Calanoid n a u p l i i  0.35  0.01*  Bosmina l o n g i r o s t r i s  0.29  1.90**  Polyphemus p e d i c u l u s  0.59  3.07  Diaphanosoma brachyurum  0.64  5.0*  Holopedium  gibberum  (small)  0.64  Diaptomus t y r e l l i Holopedium  gibberum  (ug)  1.08  5.9  (large)  (without g e l a t i n o u s envelope)  1.28  (with g e l a t i n o u s e n v e l o p e )  3.98  Paphnia r o s e a (small)  1.29  12.5  f  Paphnia rosea (large)  1.93  23.0  f  6.8  30.6  C a l a n o i d copepodids  (small)  1.38  C a l o n o i d copepodids  (large)  2.0  28.0  2.33  42.7  Diaptomus k e n a i  f t  *  Hall et al.  **  from mean volume e s t i m a t e s o f f o u r models m u l t i p l i e d by s p e c i f i c g r a v i t y o f 1.025 ( H a l l e t a l . 1970).  T tt  Baudouin  (1970).  and Ravera  (1972).  from f o r m u l a W = 0.055 h' { Edmonds on and Winberg 73  1971).  a  18  Fig.5  Means t 1 S.E. o f swimming v e l o c i t i e s o f z o o p l a n k t o n a t d i f f e r e n t temperatures.  19  all  temperatures  except  f o r Polyphemus a t h i g h  tempera-  tures . Swimming b e h a v i o r o f species with for  short jerky  Bosmina and leaps.  aggregating into  which By  specific.  may  and  lengthy  intervals.  Unlike disturbance  3-10  from  away f r o m  cm  smoothly  w i t h each  unit  of  a probe,  (V. K o r i n e k  1972,  as  Zooplankton and  aggre-  horizontal column f o r  tortuous  than  a l l o w e d D.kenai  to  time. d i d not  leaps.  the  November  crop of  covered  147  cm/sec.  jump a d i s t a n c e o f  3-6  communication).  z o o p l a n k t o n was  the average  o f noon and  were most abundant i n the (Fig. 6).  Diaphanosoma, and  The  expressed,  where  midnight values. l a k e between  standing crops of  P . k e n a i , w e r e much l o w e r  to  diaptomids  D.kenai of  react  Seasonal changes i n s t a n d i n g crop and i n s p e c i e s c o m p o s i t i o n  Standing possible,  were l e s s  l e a p a t a mean v e l o c i t y  personal  1971),  their predators.  Diaphanosoma and  i t with rapid  be  about"  Butorina  i n a near  Polyphemus which  D i a p h a n o s o m a , i f d i s t u r b e d , may  c  confuse  Polyphemus; t h i s  to  noted  the copepods d i d not  Their paths  Bosmina and  found  "scurried  remaining motionless i n the water  a greater area per  darted  also  Diaphanosoma and  t h o s e o f Bosmina and cover  Polyphemus  (Dumont 1967;  but  and  also  s p e c i e s have been  clusters  moved s l o w l y  position,  Both  tend to a t t r a c t  contrast,  gate  z o o p l a n k t o n was  May  Paphnia,  i n 1972  .  cm  20  D. T Y R E L L I  O X  DC LU D.  0C LU CO  1  J r-j i A i s i oi*~i5^-i o 30  20r  20  HOLOPEDIUM  k  10  10  J I 10  DIAPHANOSOMA  AIS1O  BOSMINA  1 N~l  0  10  POLYPHEMUS  NI 0 Fig.6  S t a n d i n g c r o p o f zooplankton groups i n 1971 (dotted l i n e ) and i n 1972 ( s o l i d l i n e ) . Holopedium were n o t r e c o r d e d i n 1971.  21  than was  i n 19.71.  abundant i nt h a t y e a r .  which 48  occurred on J u l y  o u t much o f t h e  have caused July ing  the  o f that year crops  i n 1972  the  and  after  the J u l y  scarce  andmodified the  "flood"  overall  3-4.  and probably T h i s may  s e a s o n a l change Paphnia the  entirely  i n 1972.  were  from  the  personal  lake  communication). b y number  two years by a f a c t o r o f 2  mg/m  2  i n 1971  but  were r e c o r d e d  only  30,000 i n d i v i d u a l s / m  i n1972.(Fig.  7).  l i t e r , during both Lake,  (Fig. 8).  when c o m p a r e d t o o t h e r  a lowzooplankton In  the  lakes  standing  On t h i s (Allan  seasonal comparison  Rotifers,  the grouping nauplii,  one time,  o f prey  less  basis,  1972;  than 10/ Eunice  Podson  1972),  o f species composition,  f o r the  seven c a t e g o r i e s t o study o f l a r v a l  and Chaoborus were not  2-4 z o o p l a n k t o n  and  crop.  l a k e p l a n k t o n were s u b d i v i d e d i n t o  parallel  any  years  2  2  P e n s i t y o f cope-  pods a n d c l a d o c e r a n s o f a l l s t a g e s was u s u a l l y  the  data)  P e a k v a l u e s o f 9 0 , 0 0 0 i n d i v i d u a l s / m a n d 9 0 0 mg/m  were recorded  has  recorded  relatively  o f zooplankton  i nthe  i n stand-  summer s e a s o n o f  They were  1973,  standing crop  by biomass d i f f e r e d  cm o f r a i n i n  Northcote, unpublished  disappeared  i n 1 9 7 3 (C. W a l t e r s  The and  but  rainfall  o f Holopedium and o f Paphnia i n  a n d 1 9 7 0 (T.G.  i n 1971,  heavy  epilimnetic water.  o f the other cladocerans.  1969,  i n 1971 b u t  (14.7  lake level  c o n s i d e r a b l e numbers t h r o u g h o u t  1967,  200  decline  counted  An extremely  11-12  hours), sharply raised  flushed  in  Holopedlurn was not  included.  food. At  species contributed over  T o t a l s t a n d i n g c r o p by number (N), and by biomass ( B ) , o f z o o p l a n k t o n i n 1971 (dotted l i n e ) and i n 1972 ( s o l i d l i n e ) . R o t i f e r s and Chaoborus were e x c l u d e d . Holopedium were n o t counted i n 1971.  23  80%  of  the  ber  and  by  cally and  t o t a l standing crop biomass  ( F i g . 21).  August, Bosmina were the i n the  D . k e n a i and plankton  The t o n was cussed  fall  Diel  very  i n the  i n 1971  i n 1972  two  and  was  found  n i g h t t o any down t o 5 m  vertical  numeri-  great  15  (1971  m,  the  data).  1972,  Lake  day,  from midnight late  to  and  will  Monthly  migrate  be  dis-  distribution  Throughout  thermocline  During  6 A.M.,  and  the  at  midday  (0-6  m).  vertically;  the  day  up-  upward  they  moved t o t h e  concentrated  became d i f f u s e l y  morning.  the  zooplank-  were upper-  slight  D.kenai a strong reverse  the  by  and  Eunice  at night they  0-7  layers  of  a d u l t Daphnia migrated  D.kenai u s u a l l y  during  numerous,  (70%-90%) o f  Polyphemus showed a  m i g r a t i o n and  species.  H o l o p e d i u m moved s l i g h t l y  extent.  but  July  migration  above the  migration. m  and  years.  D . t y r e l l i d i d not  Only  num-  In  highest concentration of organisms  ward a t n i g h t .  found  the bulk  i s s h o w n i n F i g . 8.  Bosmina, Diaphanosoma, and  m  by  lake.  distribution  similar  midnight  Nauplii  20  were  w h e n H o i o p e d i u m became v e r y  j o i n t l y f o r the  plankton  most  both  second most abundant  vertical distribution  summer t h e  at  D.tyreHi  D . t y r e l l i comprised  biomass  d  and  plankton  the most abundant s p e c i e s a t a l l t i m e s .  Except  of  of  reverse  vertical  at a depth  of  s t r a t i f i e d down  returned  to the  to  surface  24  ZOOPLANKTON NOON  MT NUMBER  Fig.8  CHAOBORUS  OF PLANKTON  NOON PER 100  MT  LITERS  Noon and midnight (MT) v e r t i c a l d i s t r i b u t i o n o f z o o p l a n k t o n types (on l e f t ) , and o f Chaoborus types (on r i g h t ) , i n E u n i c e Lake i n 1972. L e t t e r s i n d i c a t e type o f p l a n k t o n : N - n a u p l i i , K-D.kenai, B-Bosmina, D-Daphnia, DI-Diaphanosoma, H-Holopedium, P-Polyphemus, CL-combined c l a d o c e r a n t y p e s . Roman numerals show i n s t a r s o f C.americanus,' am,(on l e f t ) , and o f C . t r i v i t tatus, tr,(on right).  25  e  Patchiness i n plankton  A chi-square analysis  to test  Clarke-Bumpus samples taken that  randomly;  non-randomly While  this  sampling  Chaoborus  ing of other The  ness  no tal  showed  Chaoborus  t h e 10 s e r i e s  sampled  (Table I I . ) replicable  f o r accurate  to test  monitor-  f o rhorizontal  less  than  o f random  1% o n a l l s a m p l i n g (Table I I I ) .  each  distribdates and  Such h o r i z o n -  l a r v a e has a l s o  been noted  by  and N o r t h c o t e , 1966. o b s e r v a t i o n s d u r i n g 1971 and 1972 showed  abundant i n t h e s h a l l o w e r , narrow i t s deeper,  "open" p o r t i o n .  two areas  unit  patchi-  throughout  zooplankton, b u t n o t Chaoborus, were c o n s i s t e n t l y  per  hauls  made o n  hauls collected  showed t h a t t h e p r o b a b i l i t y  p a t c h i n e s s i n Chaoborus  these  towing  replicated  A chi-square analysis  s e a s o n a l t r e n d was e v i d e n t  Field  in  results  size with a  series of five  of vertical  o f l a r v a e was  Teraguchi  sample  were  zooplankton populations.  i n 1972 were u s e d  summer  level  may b e n e c e s s a r y  i n the larvae.  ution  a larger  of  for P.tyrelli,  t h a t these were  technique produced  larvae,  weekly  collected  indicated  a t 0.99 p r o b a b i l i t y  time > 2 minutes,  the  a t t h e same d e p t h ,  chi-square values  D.kenai,and Paphnia  of  forreplicability  samples o f Chaoborus l a r v a e and o f Polyphemus  obtained  for  distribution  area  showed t h a t t h e biomass o f  a t t h e s h a l l o w end  more  "arm" o f t h e l a k e , Simultaneous  (station  that  than  sampling  of  zooplankton 5) e x c e e d e d t h e  26  biomass  a t t h e deep  c a s e s b u t one Chaoborus  end  (station  (Table I V ) .  larvae  a t t h e two  1) b y  up  In contrast, s t a t i o n s was  to 7 fold biomass similar.  of  in a l l  TABLE I I Comparison o f 4 h o r i z o n t a l Clarke-Bumpus tows t a k e n a t noon between s t a t i o n s 1 a n d 2. V a l u e s a r e g i v e n i n numbers p e r 100 l i t e r s . Sampling d e p t h s and d a t e s a r e i n d i c a t e d i n p a r e n t h e s i s .  CHAOBORUS  ZOOPLANKTON Tow No.  i.  tyrelli  7  3 m  )  l_. k e n a i  f 3m  \  Paphnia  ( 3 m )  \20-7-71j  \20-7-71j  1 2 3 4 •  186.9 ' 203.0 217.1 154.6  Polyphemus / 3 m \  (10 + 11 m) ^24-9-72 /  1 _ C. t tr r 44" C. t r 4" (10 ++ 11 11 ml /14 + 15 \24-9-72 •9-72 / I 24 -9-72  212.5 293.2 259.1 154.6  2.8 2.9 2.9 3.3  2.3 2.0 3.1 2.2  3.3 4.2 2.7 3.1  5.1 5.0 4.6 3.7  3.9 2.6 4.9 3.1  9.6 2.4 23.7  13.2 3.3 44.7  18.4 4.6 85.5  14.5 3.6 55.8  761.6 190.4 147,182.3  922.7 230.7 215,836.2  919.4 229.8 222,143.1  11.9 3.0 35.3  x2  11.4  12.9  47.2  0.1  0.01-0.001  0.01-0.001  <0.001  * good r e p l i c a b i l i t y  \24-9-72/  C. t r 4  240.9 222.9 192.1 267.0  X  P  C. am 4 ( 2 + 3 m]  >0.99*  0.28 0.99-0.95*  0.37 0.95-0.05*  0.27 0.99-0.95*  0.85 0.95-0.05  o f tows  No  TABLE I I I  S t a t i o n No.  2  July 5 111 86 , 85 ' 27 68  1 2 3 4 5  £x  X  x p  Comparison o f t h e t o t a l number o f Chaoborus l a r v a e p e r s t a n d a r d v e r t i c a l n e t h a u l t a k e n a t each o f t h e 5 s t a t i o n s i n E u n i c e Lake d u r i n g 1972. V a l u e s a r e g i v e n i n numbers p e r 0.62 m.  2  J u l y 19 108 63 151 124 .316  762. 377. 152. 4 75.4 32,295. 153 ,666. 51.32 <.001  246. 31 001  Aug. 2  Aug. 6  94 53 74 78 255 554.0 110.8 88 ,230. 242.30 -c .001  Sept. 6  63 81 110 139 174  81 72 58 37 70  318. 567.0 63. 6 113.4 72,227. 21 ,378. 69.92 < .001  18. 13 01  S e p t . 21 122 7 98 73 134 434. 86. 8 47,822. 116. 94 001  Oct. 4  O c t . 22  74 71 86 127 50 408. 81.6 36 ,542. 39.82 < .001  60 94 83 90 301  Nov. 4  Nov. 18  83 157 66 62 79  87 39 126 437 191  628. 880. 447. 125. 6 89.7 176. 0 90 ,601. 45 ,979. 252 ,416. 93. 35 001  67.31 < .001  554. 18 001  CO  TABLE IV  Date 7 June * 22 Aug.t 22 Aug.t 12 Nov.* 18 Nov.* 18 Nov.t 18 Nov t 26 Nov.*  Comparison of zooplankton and of Chaoborus biomass between s t a t i o n 5 and s t a t i o n 1 i n 1972. Values are given i n mg per m. ;  Time  Station 5  Noon Noon Midnight Noon Noon Noon Midnight Noon  53.0 130.5 126.8 42.8 29.0 57.6' 79.2 24.3  ZOOPLANKTON Station 1 Station 1 {Station 5 53.5 108.5 84.8 7.8 4.3 21.3 20.2 9.0  1  1:1 1:1.2 1:1.5 1:5.3 1:6.7 1:2.7 1:3.9 1:2.7  CHAOBORUS Station 5 19.7 86.3 184.9 155.1 254.9 156.4 346.6 174.0  Station 1 65.4 97.2 392.0 , 132.5 115.8 51.8 199.6 254.3  Station 1 :Station 5 3.3:1 1.1:1 2.1:1 .1:1.2 1:2.2 1:3 1:1.7 1.5:1  1  *  samples c o l l e c t e d with v e r t i c a l hauls  t  samples c o l l e c t e d with a Clarke-Bumpus sampler  to  30  3 1  Eunice of  2  Lake  Summary  i s o l i g o t r o p h i c w i t h a low standing  zooplankton.  Most o f t h e p l a n k t o n were found 6 m a t a l l times. and  each  6  differed  o f study.  and n o t n e c e s s a r i l y  coincident with  other.  size,  swimming speed,  A l l o f t h e above  factors  s p e c i e s were  found i n  a n d t y p e o f movement.  may  affect  feeding  by d e t e r m i n i n g t h e p h y s i c a l  of prey  and t h e n a t u r e o f s i z e  tive  con-  o f Chaoborus and o f i t s  D i f f e r e n c e s among z o o p l a n k t o n body  varied  and p l a n k t o n abundance  distribution  p r e y was p a t c h y  depth  respectively.  between t h e two y e a r s  The h o r i z o n t a l  of  Daphnia  below t h a t  The s p e c i e s c o m p o s i t i o n o f z o o p l a n k t o n  significantly  5  stayed well  t h e day and n i g h t  s i d e r a b l y w i t h season,  4  above a depth  E x c e p t i o n s were a d u l t  a d u l t D.kenai which  during  3  crop  p r e d a t i o n by t h e l a r v a e .  Chaoborus availability  and s p e c i e s  selec-  31  V  B I O L O G Y OF CHAOBORUS L A R V A E 1  a  Head m o r p h o l o g y o f l a r v a l  The  three  species  length,  specific,  (Fig. 9).  and mouth d i a m e t e r ) ,  larvae  Size  tween s p e c i e s similar  cribed  species:  Development o f  larval  smaller  instars of C.triv-  eg. C a m t o C.am  be-  3 were more  2 a n d C.am  4.  larvae  development p a t t e r n  (Fedorenko and S w i f t  pro-  among t h e i n s t a r s .  t o C . t r 2 and C . t r 3 than  The  instar  b e t w e e n a n y t w o i n s t a r s was g r e a t e r  than w i t h i n  b  were  A l l 3 i n s t a r s o f C.americanus had  T h e r e was no o v e r l a p  similarity  length,  t h a n among t h e y o u n g e r  head dimensions than t h e corresponding ittatus .  (head  a n d t h e s i z e v a r i a t i o n was more  n o u n c e d among t h e o l d e r ones  instars  Chaoborus head measurements  antenna and seta and  Results  has already  1972).  been  des-  Instar succession i s  shown f o r 1971 a n d 1972 i n F i g . 10.  The l a r v a e o f b o t h  species  i n late  had a short  egg-laying  period  early  summer, m o l t e d  stars  from June t o August, and grew t o near a d u l t  during time, spring  this  to laytheir  larvae  eggs.  their  therefore,  four  in-  length generation  emerging t h e f o l l o w i n g  C.trivittatus  t i m e o f two y e a r s  one t i m e ,  through  C.americanus had a one y e a r  the overwintering  generation any  time.  synchronously  s p r i n g and  larvae with  emerged a y e a r  later.  E u n i c e L a k e was i n h a b i t e d  a At  by  32  2.2  2.0  1.8  1.6  I  1.4  -  1.2  n |  1.0  LU  .4  HEAD  ANTENNA AND  Fig.9  MOUTH  SETA  Means t 1 S.D. o f h e a d l e n g t h , a n t e n n a a n d s e t a l e n g t h , a n d m o u t h d i a m e t e r o f l a r v a l i n s t a r s ( i n Roman n u m e r a l s ) o f C . a m e r i c a n u s (open c i r c l e s ) a n d C . t r i v i t t a t u s (solid c i r c l e s ) . F i r s t i n s t a r s o f both s p e c i e s a r e combined ( h a t c h e d c i r c l e s ) . Number o f a n i m a l s m e a s u r e d i s g i v e n i n parenthesis.  o\° O F  vQ  LARVAE  P 05  MOW  -J  o MO o  a  • (D rt in H cn H<O 3 rt rt  g  m rt  c  cn  CD  vQ  3"  D> rt o  3  3 cn ft p)  in 3" CD vo O Cu -J rh M H- | 0 cn  rt CD  l  rh O H 3 CD ft 3" Cu 3 &  trt-  e-r H CD rh ft  ee  18  2-  I MAY  Fig.11  | JUNE  I JULY  I AUG  I  SEPT I OCT  I NOV  T  Seasonal changes i n l a r v a l i n s t a r l e n g t h i n 1971. Means and 95% c o n f i d e n c e l i m i t s a r e shown f o r each i n s t a r (Roman numerals) o f C.americanus (dotted l i n e s ) and C . t r i v i t t a t u s ( s o l i d l i n e s ) . Tfrom Fedorenko and S w i f t 1972).  co  1971  Fig.12  1972  S e a s o n a l changes i n l a r v a l weight i n 1971 and 1972. Means, 95% c o n f i d e n c e l i m i t s , and t h e y e a r h a t c h e d a r e shown f o r each s p e c i e s , (from S w i f t 1973).• • \  1973  36  C . a m e r i c a n us and year The  and one  1971  by  C.trivittatus  C.trivittatus  week d i f f e r e n c e  and  1972  may  be  larvae in their  i n instar  attributed  spring  i n 1972  when p u p a t i o n  curred  earlier  than  was  similar  gained  most o f  ittatus their  second  about  1,200  biomass of  loss  the  1,000  ( F i g . 11). C.americanus  the winter. the  final  C.  triv-  weight  in  crop  Chaoborus i n Eunice 2  i n 1971  and  t h e m a x i m u m b i o m a s s e s w e r e 700 ( F i g . 13).  i n the  T h i s was  i n Eunice  standing crop  the  emerging  and  the  recruitment of  summer.  Other  4th  instar  Chaoborus p o p u l a t i o n ;  only  1972  and  Lake. to  some 1 5 %  were p r o b a b l y 1971  and  of  the  total  C.trivittatus  was  the  species during the  study.  the  some  larvae i n the  In  500  Seasonal  the newly hatched  fluctuations  Lake  about h a l f  reflected  in larval distribution.  C . a m e r i c a n u s made up  Chaoborus  species  of  of  patchiness  increase i n length  larvae/m  a l l the plankton  fluctuations  in  2/3  oc-  Rate of  changes i n s t a n d i n g  and  respectively  spring,  over  warmer  egg-laying probably  before  maximum a b u n d a n c e o f  respectively;  the  weight  between  year.  Seasonal  The  mg/m  their  year.  relatively  i s shown i n F i g . 12.  larvae gained  c  was  Chaoborus  i n that  second  succession  to the  and  i n 1971.  f o r both  Growth i n weight  l a r v a e hatched  extent  late larvae due 1972  dominant  to  Fig.13  Cumulative standing crop by number (N), and by biomass (B), of C.americanus and C . t r i v i t t a t u s i n 1971 (dotted line) and 1972 Fsolid l i n e ) . A l l instar 1 larvae were included with C. t r i v i t t a t u s .  38 d  Seasonal  changes  i n distribution  Seasonal d i s t r i b u t i o n Chaoborus l a r v a e  and d i e l  previously  distribution  (Fig. than as  8).  C.trivittatus  t h e C.amerIcanus  they matured.  1  agreed w e l l  four  instars  ( F i g . 1 4 ) a n d f o r 19 72  larvae  inhabited  mocline  a t a l l times o f t h e day. larvae  at night.  overlap  among  instars  of both  Older stayed  As a r e s u l t ,  l a r v a e was l i m i t e d species  and 4 t h i n s t a r i n the lake.  overlapped  instars  with  the other  p a t t e r n became d i s r u p t e d  effect (Fig.  species  A l l  3rd instar  below the  incubation  only  i n the late  growth o f  a t high  spatial  C.americanus 0«tr  food  when-  4°  larvae  at night.  This  fall  and  moved d e e p e r , o v e r l a p p i n g  Potential  and  thermocline,  continuous  winter  extensively.  larvae  levels  on t h e growth o f each o f t h e three 15).  marked  t o 1 s t , 2nd, and 3 r d  e v e r any o f them o c c u r r e d  situ  deeper  l a r v a e were found above t h e t h e r -  C.trivittatus  m o v i n g up o n l y  In  layers  o f C.americanus and 1 s t , 2nd, and young 3 r d  of C.trivittatus  e  deeper  than d i d C . t r i v i t t a t u s .  instars  when b o t h  1972).  i n the years  C.americanus underwent a l e s s  v e r t i c a l migration  instar  1969 a n d 1971  l a r v a e , and a l l l a r v a e moved  diel  4th  of  (Fedorenko and S w i f t  of larvae  s a m p l e d a s i s shown f o r 1971  migration  migration  i n Eunice Lake during  have been presented Vertical  and  had a marked  larval  G r o w t h i n t h e l a k e was f a s t e s t  types  f o r C.americanus  1200  10  TIME - HOURS 1800 Pion P 4 0 p 030Q  0 6 n  n 0900 o T"C I  C. a m e r i c a n u s IV  iSr  2*  10 15  CO DC UJ 20[-  C. trivittatus III  LU  10 LU  15  C. trivittatus I V  y  20>  10 15  201 C. trivittatatus IV° 14  D i e l v e r t i c a l m i g r a t i o n o f C.americanus and C . t r i v i t t a t u s l a r v a e on 16-17 September, 1971. I n s t a r s o f l a r v a e and d e n s i t y p e r 100 l i t e r s a r e as shown, (from Fedorenko and S w i f t 1972).  40  2.0  r  1.8  1.6  < >  1.4  _i  1.2  DC <  GC 111  D_ 1.0  O  .8  .6  X  o LU >CC Q  0  in-ivy  Fig.15  tr ni-iyy  tr iv°  Mean w e i g h t s a n d u p p e r 9 5 % c o n f i d e n c e l i m i t s o f t h r e e types o f Chaoborus l a r v a e from t h e tube experiment: d o t t e d bars a r e i n i t i a l weights i n l a k e and t u b e s ; c o a r s e l y hatched bars a r e f i n a l weights i n l a k e ; grey bars a r e f i n a l weights i n tubes.  41  and  slowest  gain and  i n t h e t u b e s was g r e a t e s t smallest  weight gain for  f o r young C . t r i v i t t a t u s  larvae.  f o r t h e young  f o rthe o l d C.trivittatus, o f tube  larvae  Weight C.trivittatus  The r a t i o s o f  t o weight gain  of lake  larvae  am y , t r y , a n d t r o , w e r e 2 . 6 , 6.2 a n d 1.9  tively.  Due t o t h e d i f f e r e n c e s  the  weights o f a l l t h e "tube l a r v a e " were  final  2  The  instar  Parma  o f growth, similar.  Discussion  and species  heads and o f antennae w i t h have been used  i n the rate  respec-  forlarval  specific setae,  lengths  of  as reported  identification  larval  here,  b y , among  (1971) w o r k i n g o n C f l a v i c a n s , a n d S i k o r o w a  others, (1973)  working on C . p a l l i d u s , C.obscuripes, and C . c r y s t a l l i n u s . Stahl  (1966a) has s u g g e s t e d  that  this  may b e r e l a t e d t o t h e f o o d s  that  the different  types in  ingest,  turn  and t h a t  explain  the regular  Chaoborus species. discussed The  the possible  This  i n the latter 2-year l i f e  diet  coexistence  proposition  part  cycle  due  i n part  Chaoborus  t o the lower  C.trivittatus photoperiod  experience  food  larval  differences  may  among t h e  will  of C.trivittatus  larvae.  specificity  be  briefly  of the study.  when c o m p a r e d t o t h e 1 - y e a r o r s h o r t e r most o t h e r  size  This  life  i s unusual cycles of  d i f f e r e n c e may  be  and temperature that t h e  i n Eunice  o f these deep d w e l l i n g  Lake.  The  l a r v a e may  shorter further  42 act  t o s l o w down t h e i r  personal  maturation  (S. Parma  1971),  communication).  The  standing  crop  o f Chaoborus  i n Eunice  Lake,  about  2 1,000  individuals/m  studied. in  Juday  , was l o w c o m p a r e d t o most o t h e r  (1922) r e c o r d e d  Lake Mendota; Eggleton  larvae/m  i n Third  (1931) r e p o r t e d  Sister  here no doubt r e f l e c t  18,000-30,000  Lake.  larvae/m  a high  o f 71,000  The l o w numbers  the o l i g o t r o p h i c nature  lakes 2  of  reported Eunice  Lake. The others  strong  dominance o f one Chaoborus s p e c i e s  (here,C.trivittatus  common o b s e r v a t i o n of  the minor  generalized, Chaoborus, area be  i n North  nation  the date and  found  rare  may  s i n c e Chaoborus a r e u s u a l l y  f o r the planktonic nature A  Chaoborus  at night.  of larvae  species  i n o n e l a k e may b e p a r t i a l l y  Lake, one i s b a s i c a l l y  other  i n an  p l a n k t o n i c , as i n Eunice  that  i s entirely  benthic  a non-migratory  i s a strong migrator.  f o rvertical  migration  Theories  include both  exogenous r h y t h m i c i t i e s where food,  oxygen, and p o p u l a t i o n  i n t e r a c t i o n s , may  Expla-  i s f a r from  i s a l s o n o t c l e a r why, o f t h e two Chaoborus  Eunice  with  some s p e c i e s  i n t h e day and p l a n k t o n i c only  limnetic  (1966b)  represented.  satisfactory.  It  of lakes  c o e x i s t , even though  are relatively  benthic  survey  exclusion  Stahl  America a l l species  Larvae that are e n t i r e l y Lake,  i s a  gradual  through competition.  from h i s extensive  that  C.americanus)  and need n o t imply  species  can probably  poorly  over  over  i n  another.  species i n form  presented  while to  endogenous light,  temperature,  a c t as t h e r e g u l a t i n g  43  or  inducing factors  Northcote  i n weight  was v e r y  Chaoborus s p e c i e s , b u t both  summer a n d e a r l y  fall  was a t i t s maximum. duction  This  and  by Jonasson  d i f f e r e n t water  levels  than  found  migration  o f prey  o f these  indicate  r a t e o f food  low, they prey  a t t h e warm  consumption rates.  o f which  tem-  T r 4° o u t g r e w t r 4  V  In the  high growth o f  l a r v a e o r an e x t r a t h i c k both  abundance  Assuming t h a t t h e main-  may h a v e b e e n a r e s t r i c t e d  i n the tubes,  types  due t o a g e - s p e c i f i c  f o r the unexpectedly  a f o o d - r i c h zone.  growth  levels  i n the epilimnion.  grow t o t w i c e t h e i r may  patterns.  turnover  young C . t r i v i t t a t u s  in  different  because o f higher  t h e cause  obser-  (1970),  t r 4^ o r t r 4 ° b e c a u s e o f h i g h  and a high  probably  layer  has a l s o been  c o s t o f C . a m e r i c a n u s was r e l a t i v e l y  peratures  tubes,  coincidence i n pro-  each o f t h e l a r v a l  temperatures  distribution  grew f a s t e r  crop  (1972).  the lake experienced  tenance  i nthe  standing  and Ranke-Rybicka  the growth experiment,  vertical  f o r the  grew most r a p i d l y  temporal  f o r C . f l a v i c a n s by Kajak  and  1970).  different  o f Chaoborus and o f i t s prey  In  (Teraguchi and  when t h e z o o p l a n k t o n  ved  in  migration  1 9 6 6 ; LaRow 1 9 6 8 , 1 9 7 0 ; R u d j a k o v  Rate o f gain two  f o rvertical  would  keep  downward  plankton C.trivittatus  The c a p a c i t y o f C.americanus t o normally  t h a t , when f o o d  observed  prepupal  i s abundant,  weight  excessive  i s p o s s i b l e i n the absence o f a p p r o p r i a t e  stimuli  44  for  pupation such  1970). the  T h i s may a l s o  tubes In  they  i n t r 4  experiment  independent  the lack  studies  of pupation i n  less weight  gain because o f food  h y p o t h e s i s came f r o m  than  those  further from  sities  i n t h e l a k e were w e l l  for  maximum l a r v a l  30%  o f t h e 19,000 l a r v a e  this  feeding rates.  with  food usually  c o n t a i n e d o n l y one prey collected  lake  consume s e v e r a l  average  i s retained  population  and S c o t t i n Eunice  t h e mean d a i l y  l a r v a e were  prey.  i n a crop  Lake t h a t  f o r 8 hours  = 90%  4  of the  that the (this i s  (1945), and of  feeds d a i l y  o f prey  = 30% / |  during  Yet  each  Assuming  % population with food  time  about  incubated  an hour  (1971), t h e percentage  mean d i g e s t i o n  required  only  item.  t o t h e value r e p o r t e d by Montshadsky  Goldspink  den-  ( F i g . 2 4 ) , and those  a dense m i x t u r e o f prey, w i t h i n  l a r v a e would  close  prey  examined a t v a r i o u s times crops  tubes  hypothesis.  Secondly,  i n their  prey  feed-  other  below t h e d e n s i t i e s  had any food  with  Three  feeding experiments,  1972  freshly  shortage.  i n plankton enriched  support  as determined  than  an i n s i t u  i n the lake.  First,  whenever  (Bradshaw  larvae.  where Chaoborus  grew much f a s t e r  photoperiod  Chaoborus gained  could potentially forthis  explain  a n d t r 4°  V  Eunice Lake,  Evidence ing  as a s p e c i f i c  larval  i s g i v e n by:  i n crop  i n days  45  Therefore,  the  average chaoborid  c a t c h more t h a n laboratory sities  one  prey  any  feeding experiments  showed a n - i n c r e a s e  densities  on  (Swift  1973).  larva given  i n the day.  at a variety  in larval  lake  cannot  Thirdly, of  prey  growth at high  denprey  46  3  1  Significant  Summary  differences  among a l l i n s t a r s  americanus and C . t r i v i t t a t u s various  head parameters,  suggest corresponding 2  Larvae of both their had  instars  pattern  3  i n c l u d i n g t h e mouth  size,  molted  generation  of weight  compared  1972  than  to other  migratory older  synchronously  through  a t t h e same r a t e b u t time and a  different  lakes  i n E u n i c e L a k e was studied.  were p r e s e n t  species  very  I n 19 7 1 a n d  a t much h i g h e r  i n E u n i c e Lake were  C.americanus were b a s i c a l l y  and i n h a b i t e d  C.trivittatus  Growth o f t h e l a r v a e sities  diets.  den-  C.americanus.  Both Chaoborus planktonic.  i n their  gain.  C.trivittatus  sities  5  their  Standing crop o f Chaoborus low  4  of  and elongated  a different  i n the sizes  differences  species  o f C.  i n the lake.  entirely  non-  the top layer of water;  were strong was l i m i t e d  vertical  migrators.  by l o w p r e y  den-  47 VI  F E E D I N G OF" CHAOBORUS 1 a  Digestion  Methods  Digestion  rates  rates  o f 3 r d and 4 t h i n s t a r  C.americanus and C . t r i v i t t a t u s types  i n the laboratory  and  their  for  D.kenai;  arated  prey  several  hours.  of a particular  f e d , i t was  containing water  time  intervals  after  24 h o u r s ) , 5-10  (5-25°C  Larvae,  sepwere  to the experimental temperature f o r g i v e n a l a r g e number o f  type and observed  vial  the predators  s t a r v e d f o r a few days,  They were t h e n  soon as a l a r v a  continuously.  transferred  As  a  labelled  o f t h e same t e m p e r a t u r e .  At set  the ingestion  into  of prey  l a r v a e were removed from  (1,3,5,10, up t o  the v i a l s ,  anaesthe-  w i t h t h e c h l o r o f o r m : e t h a n o l m i x t u r e , and k i l l e d  Formalin.  T h e i r crops were then d i s s e c t e d  examined.  P r e y were c o n s i d e r e d t o be  clearly  r e c o g n i z a b l e ; d i g e s t i o n was  when r e g u r g i t a t i o n gradation degree  system  of digestion  In lake  occurred.  from  b  the  that  17-20°C f o r o t h e r p l a n k t o n ) .  to acclimatize  tized  at the temperatures  by t y p e and p r e v i o u s l y  of  w e r e m e a s u r e d o n s i x prey-  normally experience i n the lake  allowed  prey  larvae  o f D.kenai  Feeding  1971, i n c u b a t i o n t o determine  "fresh"  assumed  In the case  0%-100% was  and crop  i n larval  contents  i f still  t o be  complete  of D.kenai,  established  with  based  a  on t h e  crops.  rates  experiments  the effect  were c a r r i e d  of prey  density  out i n on t h e  48  feeding  rates  C. a m e r i c a n u s diaptomid Freshly pairs  o f 2nd, 3 r d , and 4 t h i n s t a r and C . t r i v i t t a t u s .  nauplii,  caught  into  D.tyrelli,  D.kenai,  and Diaphanosoma were used  Chaoborus  as p r e y .  l a r v a e were i n t r o d u c e d  a t r a n s p a r e n t bag h o l d i n g  lake water  (0.37-30 l i t e r s ) ,  of  There  prey.  larvae of  a known  s i xreplicates.  number  The  bags  were i n c u b a t e d from a r a f t  f o r 24 h o u r s  the  A t t h e end o f t h e i n c u b a t i o n  desired  period, into and  large white trays, the remaining prey trial  D.tyrelli  large  t h e bag water  at similar  copepodids  larvae  rates.  and D.kenai.  tyrelli  appropriate  test  three  copepodid  included with cases,  groups.  term  several sizes,  trial  rate  on l a r v a l  to  To d e t e r m i n e t h e t h e e x p e r i m e n t , and  prey o n l y were  the effects  absent, usually  In nearly a l l  of different  f o r incubation, feeding  agreed  sized  and o f  intensity,  experiments were r u n u s i n g v a r i o u s  5 m a n d 20 m d e p t h s  data f o r  counts of the controls  o f changing depths starvation  true f o r  a l s o be a p p l i e d  t h e e x p e r i m e n t a l bags.  To d e t e r m i n e  containers,  measured,  copepodids  also  when p r e d a t o r s w e r e  bags w i t h  t h e b e f o r e and a f t e r  closely.  short  control  ate small  The f e e d i n g  can therefore  f o r prey mortality  or four  temperature  T h i s was  a c c u r a c y o f counts b e f o r e and a f t e r to  emptied  counted.  r u n s , Chaoborus  D. k e n a i a n d D. the  a t the depth of  t h e c o n t e n t s o f each bag were c a r e f u l l y  In and  temperature.  or i n  a s t a n d a r d volume o f  and c o n t a i n i n g  were u s u a l l y  singly  f o r incubation,  and  bag  freshly  49  c a u g h t o r one density  Temperature  Freshly species  larvae.  days.  on  feeding  of a s p e c i f i c  were placed  singly  or i n pairs  Only and  the  copepod  p r e y and  3 r d and  4th instar  C . t r i v i t t a t u s were used  instar  Temperature  and  end  the replicates  o f each day,  4 , V  and  (September kept  i n 300  term feeding  18,  containers as food.  under  natural  light conditions.  restored  dead  copepods  5,  At  the exam-  at a l l  to  times.  a m o n t h i n May,  Individual  Incubations  was  to the o r i g i n a l  of C.tr  f o r 25 c o n s e c u t i v e  were p r o v i d e d  D.kenai  and  larvae  s i x ) , were  larvae  1971).  adult  live  instar  July,  experiment  seven  4, w e r e i n c u b a t e d  24-October ml  C.ameri-  1972.  groups, each w i t h am  4  t h e number o f p r e y r e s t o r e d  experiments were performed once  tr  of  Prey were abundant  November o f  of  for 3 to  third  (usually  The  Three  larvae  mis  o f t h e w a t e r was  original density.  Long  300  i n the experiments.  the  d  into  and  t h e l i g h t r e g i m e , 16D/8L.  f o r consumed p r e y and  and  instar  incubated  l a r v a e were f e d D.kenai;  .10, 1 5 , o r 2 0 ° C ,  August,  rates  larvae  10-20  and  constant.  effect  were f e d D . t y r e l l i .  ined  Temperature  caught  water with  Fourth  starved  of prey were kept  c  canus  day  r e c o r d e d and density.  daily  day,  days  larvae  were h e l d  Each  4°,  with  20  outdoors  t h e number  their  number  of  50  e  Efficiency  Ingestion a larva  o f copepod  e f f i c i e n c y was  t o swallow  ingestion  d e f i n e d as the a b i l i t y  a captured prey.  used  t o measure t h i s  sure  the success o f copepod i n g e s t i o n  larval of  instars  prey  eaten  predator. of  of both from  each  five  o f 15-17 °C  o f 24 h o u r s .  served  as a c o n t r o l .  was  the control attributed  larva  (12 °C A dish  determined  by  d i s h e s was  t o mea-  different fraction  and e a t e n by t h e  and a s a t u r a t i o n  density  were  placed  i n S e p t e m b e r , 1971) of prey without  for a  predators  and t h e number e a t e n  subtraction.  negligible  the  and  Prey m o r t a l i t y i n  and a l l deaths  were  to the predators.  second  m e t h o d was  t o compare t h e mouth gape o f  to the cross-sectional was  larva.  assumed  not  was  A t t h e end o f t h e e x p e r i m e n t ,  when t h e l a t t e r  smaller  killed  larvae  r e m a i n i n g prey were counted  a  by t h e  ( 2 0 D. k e n a i do" o r D. t y r e l l i )  period  The  first  were  o f s i x , 350 m l c o n t a i n e r s a n d i n c u b a t e d a t t e m -  peratures  killed  The  approaches  s p e c i e s by d e t e r m i n i n g t h e  the t o t a l  Usually  copepod prey,  into  efficiency.  Two  of  I t was  "best" oriented  than the prey,  impossible.  area of a potential  that  prey  f o r s w a l l o w i n g by  i f t h e gape o f a l a r v a  a  was  i n g e s t i o n w o u l d be d i f f i c u l t i f  Methods f o r measuring  were d i s c u s s e d i n e a r l i e r  sections.  these  parameters  51 f  Analysis  S e v e r a l hundred hauls  f o r 24  from June omitted  Chaoborus  hours, a t 3 hour  t o October  of  from the study.  following  of larval  and  were c o l l e c t e d intervals,  1972.  First  and  tents  a p a r t under identified  lOOx) w i t h Prey  counted  rotifers,  and  as  enumerated  category  group  The  adult  (Conochiloides) because tents of  of rapid  filtering  and  crops  and  were  their  h i g h power  con-  (40X  or  Daphnia,  and  near  adult  The  nauplii  could  and  n o t be  Holopedium,  kenai,  small  and  and  was  appendages and  based  on  The  identification  depended on  claw.  Other  used  i n prey  the  "kenai"  the copepods,  rotifers crops of crop  the  con-  presence  the postabdominal  species  un-  included  and  non-loricate  Identification  miscella-  soft-bodied  detected i n the  digestion.  features  categories:  " c l a d o c e r a n s " group  as c l a d o c e r a n i n o r i g i n  the  "full"  contained a l lthe other smaller  such as copepod  analysis  D . t y r e l l i , Chaoborus,  most o f which were t y r e l l i . prey  The  were  ("full")  nonrecognizable cladocerans.  included  "tyrelli"  larvae  (in press).  non-empty  under  Polyphemus,  material.  Diaphanosoma and  month  c r o p s w e r e a s s i g n e d t o 10  neous c l a d o c e r a n s , D.kenai, identifiable  verical  microscope.  larval  Bosmina,  instar  a dissecting microscope  a compound from  once a  Fedorenko  empty; t h e l a t t e r were r e j e c t e d . teased  in  Crops were prepared f o r  t h e method o f S w i f t  Crops were s o r t e d  crops  claw;  postabdominal  identification  were  52  the  long rod-like  the  carapace  on  copepod  of  Polyphemus, r o t i f e r the  Diel  crop  f o r use  Chaoborus;  feeding  analysis data,  i n determining the  percent  of  crops  containing food  of  larvae containing a certain  f e e d i n g had  carapace  and  for  relatively the  because of  types  relatively  rapid  prey  setae  of  of  either  periods.  the  The  was  only  then  study  of  easily  being  ingested.  suitable  easily  percent  percentage  f o r the  for  this  identifiable  5 hours.  so o n l y  D.kenai  those  copepods  considered  D . k e n a i d i g e s t i o n was the  extent of  were abundant but loss  and  o f d i g e s t i o n were  on  activity  abundant and  and  cal-  containing  category  used  much l o n g e r  degree of  occurred  short  crops  seemed t o be  stages  P.tyrelli their  feeding  3 hours a f t e r  e v a l u a t i o n based  tegration.  plankton  The  diel  larval  prey  a durable  crops  early  index.  arbitrary  and  i n d i c e s were  a l l types.  a d i g e s t i o n time  i n the  the  relatively  D.kenai  Bosmina had  in  The  t o be  study.  persisted  of  for at least  Bosmina and  three  containing D.kenai,  against time.  recognizable Both  percent  of  the  diel  numerous s p i n e s  activity  Bosmina,  plotted  loricas,  appendages.  From the  °f  of  B o s m i n a , and  g  culated  tail  their  an  disin-  unsuitable  identity.  Other  i n very  numbers o r  low  zoofor  53  2 a  Digestion of  Digestion  of  rates  were pooled Chaoborus  so  f a s t as  of  to  until  final  which  left  effect  on  (Fig.  16).  and At  hours;  Although not  at  25  5 °C,  l a r v a e was  Feeding  rates  concentrations  temperatures tr  undigested  3 instar  temperature.  about  twice diff-  l e a s t a day  remains  adult  due  than to  did  their a direct  D . k e n a i by  nearly was  time  Cladocerans,  T e m p e r a t u r e had  d i g e s t i o n was  of  i n g e s t i o n but  digested  d i g e s t i o n of  at  of  degree  water  variable.  shown, v a r i a b i l i t y  b  prey  °C  groups  rates  size,  and  hours of  less easily  80%  at  M o s t p r e y became  thicker exoskeleton. 50%  larvae  progressed  were d i g e s t e d  r e g u r g i t a t i o n was more c o n s p i c u o u s  apparently  prey  exoskeleton,  w i t h i n 4-5  be  instar  Digestion  l a r g e r D.kenai.  c o p e p o d s , may  different  V).  D.tyrelli,  recognize  4th  from d i f f e r e n t l a r v a l  (Table  prey  prey, the  icult  four  and  l a r v a e w e r e a f f e c t e d by  smaller  the  3rd  C.trivittatus  that data  together  keratinization The  rates  c o p e p o d s by  b o t h C . a m e r i c a n u s and  similar  as  Results  complete  tr  4  V  after  required.  i n d i g e s t i o n among  the  considerable.  Feeding on  rates  D.tyrelli  and,  ( F i g . 17).  except The  l a r v a e were 2 prey  increased  with  f o r t r 4°,  maximum r a t e s and  6-7  prey  with of per  increasing increasing tr 2  and  larva  TABLE V  Prey  D i g e s t i o n r a t e s o f Chaoborus f e e d i n g on d i f f e r e n t p r e y  type  Temperature °C  D. t y r e l l i p.  kenai  J). k e n a i  (juvenile)  Time t o end o f " f r e s h " appearance  types.  Time t o regurgitation  S p e c i e s and i n s t a r of larva tested*  17-20  1 hr  8 hr  am 3, am 4, t r  "  3 hr  8 hr  am 4, t r  4°  4 hr  12+ h r  am 4, t r  3, t r  (adult)  4°  Number o f p r e y analyzed . 140 51  4 , tr 4  122  Bosmina  "  5 hr  5 hr  am 4  Polyphemus  "  4 hr.  5 hr  tr  4°  36  Paphnia  "  9 hr  12 h r  tr  4°  30  d a t a from d i f f e r e n t l a r v a l groups were p o o l e d s i n c e no d i f f e r e n c e s among them were  130  observed  55  Fig.16  Average time r e q u i r e d t o a c h i e v e 50% and 80% o f complete d i g e s t i o n o f D.kenai by C . t r i v i t t a t u s 4Y l a r v a e a t d i f f e r e n t temperatures.  56  per  day r e s p e c t i v e l y , a t a c o n c e n t r a t i o n  of 5  D.tyrelli  per  liter  that  t h e young  ( F i g . 17 a , b ) .  C. a m e r i c a n u s h a d s i m i l a r  I t i s likely  feeding  larvae o f both  rates.  of  4th instar  20  p r e y p e r l a r v a p e r d a y b u t a t much h i g h e r  of  60-80 D . t y r e l l i  per l i t e r  Chaoborus l a r v a e D. k e n a i other the  prey  types  (Fig. 18).  of the predators,  ( F i g . 18 c ) .  maximum c o n s u m p t i o n r a t e s a t higher  (Fig. was  only  larvae  similar  ( F i g . 18 a ) .  tively  i n unsuccessful  an o v e r a l l  approximately  f o r the  obtaining  V  a t prey  on  were  their densities  a n d am 4 l a r v a e h a d  t o t h o s e o f t r 4° 5 prey per  larvae  liter  of t r 3  larvae  of the  H o w e v e r , b o t h am 4 a n d t r 3 20% and 50% o f D.kenai  capture  attempts.  This  respec-  resulted  r e m o v a l b y am 4 a n d t r _ 3 o f u p t o 3 D . k e n a i  l a r v a per day. Rates o f feeding  similar instar about of  rates  1.5 D . k e n a i p e r d a y o r a b o u t h a l f t h a t  killed  per  concentrations  T r 4° l a r v a e  Maximum c o n s u m p t i o n r a t e  larvae  in  Tr 4  d e n s i t i e s o f about  18 b , d ) .  older  up t o about  maximum f e e d i n g  r a t i o n o f 2.5-4.0 k e n a i  1-2 p e r l i t e r  rates  ( F i g . 17 c , d ) .  achieved  studied  most e f f i c i e n t  but  increased  a t d e n s i t i e s w e l l below those required  maximum d a i l y of  species  Feeding  on Diaphanosoma by t r 3 l a r v a e  t o the feeding larvae  30 p r e y  rates  ( F i g . 18 e ) .  on D . t y r e l l i  by t h e 4 t h  T h e maximum d a i l y  p e r l a r v a p e r d a y was r e a c h e d  ration of  at a  density  80 D i a p h a n o s o m a p e r l i t e r . Nauplii  were eaten  least efficiently  were  o f the prey  Fig.17  Means ± 1 S.D. o f C h a o b o r u s f e e d i n g r a t e s o n D . t y r e l l i t e m p e r a t u r e s , ( c u r v e s were f i t t e d by e y e ) .  at  different  4CH  NUMBER  Fig.18  OF  PREY  /LITER  Means i 1 S.D. o f C h a o b o r u s f e e d i n g r a t e s o n D . k e n a i ( a - d ) , o n Diaphanosoma ( e ) , and on n a u p l i i ( f ) . S o l i d l i n e s i n d i c a t e f e e d i n g r a t e s ; d o t t e d l i n e s g i v e t h e t o t a l o f e a t e n and k i l l e d p r e y , ( c u r v e s were f i t t e d by e y e ) .  59  studied.  Feeding rates  20  per  nauplii  per  liter c  l a r v a p e r day  Temperature  tization,  (Fig.  to standardize  data from  from  the  a l l four  19).  increase  2nd  and  3rd i n s t a r  i n the  ( F i g . 19  collected  i n 4 t h and  tested  i n May  larvae  to  prey  ( F i g . 19  f r o m day d  Daily  t o day  Long term  food  intake  V  and  Cam  acclima-  are also  directly  given  with C.  July respectively, tested  larvae  the  showed  of both  o r no  in  larvae  throughout  i n J u l y when t h e y of  used  rates;  r a t e s o f C . t r 4°  to  Maximum c o n s u m p t i o n  at  on  four  for C.tr  d)  4°  a  species  response  successive  but v a r i e d  ( F i g . 19  con-  e).  experiment  individual  i n both Chaoborus species C.tr 4  feeding  ( F i g . 19  feeding  by  and  similar  larvae  and  3rd i n s t a r s of  little  a,b,c).  t e m p e r a t u r e s was  siderably  rates  of temperature  Feeding rates  f o r C.americanus  this,  160  of C . t r i v i t t a t u s  Feeding  i n November showed  different  of  up  of experiments were  increased  c , e , f ) , except  °C.  temperature  irregular  day  days  a,b,d).  ( F i g . 19  p e a k a t 15  days  of  level  consecutive  were l a r g e l y independent season  hunger  on  i n temperature larvae  feeding  temperature  Feeding rates  americanus  July  increased  at a density  e f f e c t on  show t h e e f f e c t o f  results  2 larvae  ( F i g . 18 f ) .  In order  to  o f am  l a r v a e was ( F i g . 20).  4 consumed, on  the  quite In  spite  average,  NUMBER OF D. KENAI O  _i  rp  co  J>  EATEN / PREDATOR / DAY cn  p  -t  ro  co  j>  oi  -J.  ro  Co  ' 3 * • -O—.  p; IO  IO  O  IP DJ  3  PJ *». PJ >tf H rt D) PJ hj fD 3 ^ - (D tn t r ^ 3" 3 OO fD W O — O rt Cu 3 3 p) O tn n> H 3 C B) 3 3 3 C tn ro cn PJ 3 (D Cu  i+<  ID 1  cn Oi  •  PJ H-  c_  0) c c/>  c -b—  c_  . 0-, ,--*>-.  p)  P>  ro o  p) o  P>  o'  o tr  I-•  CD  >J-4^«.  -JO.-.-..  3* PJ  < 0O H P• CD Hitr o o 3 rr ro:-( n O X c < K 3 ti roro ro to r-J ro i-i (-• X H- pj s: H- rt 3 H ro H ro <P>! Hi ro 3 3 rt- PJ ro0 ro h Hi rt OJ hj ^ rt h( h" PJ PJ rt PJIQ <• H(D 3*roHi PJ H- rt N HI 3 • HI ro tr w ro ^< rt n p) ro 3rt (D rj >< Hi rt •< M roPH phj oC ro 3 PJ ro ro|D w K • • c pi X o rt  m  D  o  to  j*-  o  Co  NUMBER OF D. TYRELLI  'o  °  ro  A  oi  co  EATEN / PREDATOR / DAY  m  > H C  o  -»  ro  co  J>  co  m  o  O  o ro o c H 3 ro ^1 < pi tn ro 1  ro H- m w 3  H-»  Hi < o ro H  03  09  A  -* fO  5  4  1  2-  2-f 0  TIME — Fig.20  DAYS  D a i l y f o o d r a t i o n of 9 t y p i c a l l a r v a e o f C a m 4 (A), C . t r 4 (B) , and C . t r 4o (c). Hatched b a r s are f u l l y dTgested D . k e n a i ; c l e a r b a r s are p a r t i a l l y d i g e s t e d D.kenai. V  62  similar  daily  C.tr  consumed  4°  instar 4°  food  larvae -  frequently  observation hour  plankton This  3X 4.5  left  high  larvae,  Efficiency  according  tr  and tr  20%  about to  9 0%  field  of am  on  tr 4  the  of  the  2nd  day  t r  for  another  1971).  food  levels.  instar (Table  are  larvae VI).  were n e a r l y  a b o u t 10X  eaten  (August  by  am  23,  as  2,  killing  D . k e n a i c o p e p o d s was The  100% large  am  3,  September  than d i d the  Wasteful  of Older  11),  younger  2), p o s s i b l y because  90%  24  incomplete  (Butorina  observations,  4 larvae respectively.  and  the  an  less efficient  high  s e e n t o be  over  C.tr  ingestion  t r 3 larvae  captured  D.kenai w i t h V  Such  also noted  successful  August  4th  However,  field.  prey  more D.kenai p e r 21,  young  larvae during  result  D . t y r e l l i by  older  (July  the  p a r t i a l l y digested,  f o r any  i n the  mouth appendages.  3 and  rates for  6X  3 larvae  stronger  only  Mature D.kenai which  The  about  prey  of  individual;  individual.  at continuously  D ' t y r e l l i were never t r 2.  per  the  e  successful.  ate  be  prey  was  per  intake of  d e n s i t i e s was  of  species  kenai  Polyphemus p e d i c u l u s  p h e n o m e n o n may  both  or  their  predator,  Ingestion of  s  kenai  prey  1,6  daily  experiments  at  digestion  a  the  never recorded  feeding  digestion  rations -  of  of about  observed  highest  i n g e s t i o n success  50% for  feeding were  noted  4°.  Measurements of  l a r v a l mouth  size  and  of  prey  size  TABLE V I  Ingestion success  Date  o f Chaoborus f e e d i n g on copepods.  Predator-prey combinationf -  Number prey eaten/larva/24  hr  Number p r e y k i l l e d but not eaten/larva/24  hr  % successful ingestion  July  21/72  am 2 - D. t y r e l l i  1.4  0.2  87  July  5/72  tr  2 - D_. t y r e l l i  2.5  0.1  96  Aug.  2/72  am 3 - R' k e n a i 0*  0.01  0.37  3  July  21/72  tr  3 - D. k e n a i c?  0.03  0.20  13  Aug.  2/72  tr  3 - D. k e n a i c?  0.03  0.23  12  Aug.  23/72  tr  3 - D_. k e n a i c?  0.28  1.44  16  S e p t . 11/71  tr  3 - p_. k e n a i c f  1.0  0.34  75  Aug.  am 4 - D. k e n a i <S  0.9  0.38  70  S e p t . 11/71  am 4 - D. k e n a i o"  2.7  0.30  90  S e p t . 11/71  tr  4  3.7  0.29  93  Aug.  tr  4° •- p ., k e n a i d"  3.7*  0.20  95  tr  4° •- p_., k e n a i <f  3.8  0.25  94  23/72  23/72  S e p t . 11/71  Y  •- p . k e n a i d"  +  u s u a l l y 30 l a r v a e t e s t e d  *  value underestimated  because o f p r e y  shortage  64  indicated was  that larval instars  not studied)  most prey and  should  types;  larvae  be c a p a b l e  of freely  however, l a r g e Paphnia,  adult P.kenai,  instar  2, 3, a n d 4 ( 1 s t i n s t a r swallowing  large  Holopedium  c o u l d be s w a l l o w e d o n l y by t h e 4 t h  (Table V I I ) .  f  Analysis of larval  From t h e a n a l y s i s food  o f crop  that  a given  category  diet  was g i v e n b y t h e f o r m u l a :  crops  contents, the proportion  contributed to the species'  n i=l  where  "Pj_j"  contributed  i s the proportion t h a t a food to the diet  number o f " j " of  type  a l l the food  items  that  Composition multiplying the  found  "i"  "n" i s t h e t o t a l  a n d " a " i s t h e sum  i n sample  "n".  p e r l a r v a l c r o p was  should r e f l e c t d i r e c t l y  containing  " j " ;  larvae analyzed,  u s u a l number o f p r e y "P^/'  of instar  category  Since the  1 o r 2,  numerical  the proportion of larvae  prey. of diet  the numerical  b y b i o m a s s was  determined  p r o p o r t i o n o f a food  dry weight of that food  item,  by  item  summing up a l l t h e  by  TABLE V I I  L a r v a l mouth s i z e and p r e y  Mouth gape o f Chaoborus l a r v a ( d i a m e t e r i n mm)  size.  C r o s s - s e c t i o n a l area of prey i n the best orientation f o r being ingested ( w i d t h and h e i g h t i n mm)  0.30  Keratella  0.08 x 0.03  0.43  nauplius  0.12  am 4  0.71  Bosmina  0.21 x 0.16  tr 2  0.36  Diaphanosoma .  0.23 x 0.23  tr  3  0.51  Polyphemus  0.26  (diameter)  tr  4*  0.85  D.  0.28  (diameter)  tr  40..  0.89  Daphnia  am 2 am 3 1  tyrelli (medium)  (diameter)  0.74 x 0.53  D. k e n a i  0.62  Holopedium ( l a r g e , w i t h o u t g e l a t i n o u s envelope)  1.01 x  Holopedium ( l a r g e , w i t h g e l a t i n o u s envelope)  3.17  (diameter) 0.68  (diameter)  66  c a t e g o r i e s by weight, from the  t h e sum.  and d e t e r m i n i n g  The w e i g h t  importance  the  percentage  proportion served  of the larger  prey  to stress  items.  A  An  overlap index,  and  m o d i f i e d by Horn  the  food  The  formula  (1966),  similarities for  , developed  by M o r i s i t a  (1959),  has been used t o summarize  between p a i r s  of coexisting  larvae.  i s :  s  Y~ —  2  c = A  _  i=l  where  X.Y. i l  z  "S" i s t h e t o t a l  i = l  n u m b e r o f f o o d c a t e g o r i e s and"x.T  and"Y'^ a r e t h e p r o p o r t i o n s o f t o t a l of  i n s t a r " Y " r e s p e c t i v e l y taken  food  "i".  gories with The  distinct  a given category v a r i e s from  c a l c u l a t i o n s w e r e made f r o m  available  values >  for  0.80 i n d i c a t e  category  percent  cate-  identical  composition.  composition  of the  S i n c e no s i g n i f i c a n c e  , an assumption  of  0, w h e n t h e  ( c o n t a i n i n g no food  respect t o p r o p o r t i o n a l food  larval  o f i n s t a r "x" a n d  i n common), t o 1 when t h e s a m p l e s a r e  d i e t by number and by b i o m a s s . is  from  The o v e r l a p c o e f f i c i e n t  samples a r e completely  diet  test  was made t h a t  strong overlap i n the diet  t y p e s , a n d 0 . 6 0 ^ <2^< 0.80 i n d i c a t e  o f t h e two  a weak o v e r l a p .  67  The  diets  of  a pair  assumed t o be than  of  coexisting  larval instars  significantly different  i f  were  was  less  0.40. The  diets  numerical  (Figs.  larval  21,  instars  and  22),  the and  biomass p r o p o r t i o n s the  food  f o r each month  overlap  of  larval  index  (Table V I I I ) ,  are  among presented  together. In  June, only  study.  diet In  dominant prey; by  weight  July,  a  major prey  of  were Bosmina contributed 50-60%  both  diet  of  The C.tr  Bosmina.  s p e c i e s were  diversity,  number and Together  numerical  t h e i r biomass d i e t .  on  C.tr  t r 3 by  the  o v e r l a p was  b e t w e e n t r 2 and  D.tyrelli.  70-80% t o  exclusively of  t r 2 and  to  4°  and  The  l a t t e r made u p  their to  diets  by  the  67%  of  the  2.  The  biomass  two  prey  types  diet  of  C.am  2 larvae fed  of  the  t r 2 and  2nd  c h a r a c t e r i z e d by  e m p h a s i s on  observed  am  significantly different  w h i c h was an  were  (32%).  t r 3 and  and  D.tyrelli,  for  D.kenai c o n t r i b u t e d most  s i g n i f i c a n t food  between t r 2 and  and  l a r v a e were a v a i l a b l e  Bosmina,, P o l y p h e m u s , and  numerically their  the' t r 4°  D a p h n i a and  tr  instar  from  a much  diet  almost larvae  the greater  D . k e n a i as  biomass i n the  prey.  of  4°. In  August,  numerical of which  food ate  food  o v e r l a p was  proportions  observed  only  b e t w e e n t r 3 and  D . t y r e l l i most f r e q u e n t l y .  in  t r 4°,  Diets of  3  the both tr  4°  JUNE  JULY  AUG  SEPT  OCT  : B 50-  Cam II  o :  I  N  I  50-  r  n  RBPDHCKTOX  50-  Q  C.arnlll § o. .  50  o  RBPDHCKTOX  CO j-  O O  n  5~  Cam IV  ; B  o  N > .  0J  BPDHCKT  — -  BPDHCKT  BPDHCKT  FOOD Fig.21  1 _ n n rfl r L n n  RBPDHCKTOX  BPDHCKT  RBPDHCKTOX  BPDHCKT  CATEGORIES  Seasonal d i e t o f C.americanus l a r v a e by i n s t a r and t h e c o m p o s i t i o n o f laJce p l a n k t o n i n 1972. N ( c l e a r bars), i s p e r c e n t c o m p o s i t i o n by number; B(hatched bars), i s p e r c e n t c o m p o s i t i o n by biomass. L e t t e r s r e f e r t o p r e y t y p e s : Rr o t i f e r s , B-Bosmina, P-Polyphemus, D-Daphnia, H-Holopedium, C - m i s c e l l a n e o u s c l a d o c e r a n s , K-D.kenaT, T - D . t y r e l l i , ; 0-Chaoborus , X - u n i d e n t i f i a b l e material".  JUNE  JULY  AUG  SEPT  OCT  B 50H  C.tr II  0 50H  JL  RBPDHCKTOX  ]  B  !  o o  Ctr  LL  ]  1 J  I  N  I  LL '  o  _TL-,—  n RBPDHCKTOX  r-TL _  n  RBPDHCKTOX  n_  RBPDHCKTOX  cn O ] B a. 50-  C.trlV  O o  v  :  N  RBPDHCKTOX  Ul  RBPDHCKTOX  5CH  C t r IV  0  0  50-  1  N  RBPDHCKTOX  RBPDHCKTOX  FOOD  Fig.22  . J  r-TU  RBPDHCKTOX  r-f-T - I T RBPDHCKTOX  n RBPDHCKTOX  CATEGORIES  Seasonal d i e t o f C . t r i v i t t a t u s For e x p l a n a t i o n see F i g . 2 1 .  l a r v a e by i n s t a r  i n 1972.  L a r v a l f o o d o v e r l a p i n d i c e s f o r J u l y , A u g u s t , September and O c t o b e r , c a l c u l a t e d f r o m n u m e r i c a l d i e t p e r c e n t a g e s A, and from biomass d i e t p e r c e n t a g e s B.  TABLE V I I I  am 2  -  am 2 am 3 tr 2 tr 3 t r 4°  am 3  -  -  .42 .17  am 2  am 3  -  tr 2  JULY tr 2 tr 3 .80  SEPTEMBER  A  t r 4°  .53  .19  .90  .39  -  .44  am 4  am 2 am 3  am 4 tr 3  tr 2 tr 3  tr 4  Y  t r 4°  t r 4°  .86 tr 3  •  -  9  tr  .68  1  tr 3  am 2  -  am 3  -  tr 2 tr 3  -  .51  • -  t r 4°  -•  .11  -  am 2  am 3  AUGUST  tr 2  tr 2  B  am 4  tr 3  t r 4°  .64  .32  am 2 am 3  am 4  -  .07 -  .86  .11  tr 2  tr 4  tr 3  t r 4°  -  .25  t r 4°  .46 tr 3  t r 4°  t r 4° .37  am 4  .55  tr 3 tr 4 t r 4°  .85 .97 tr  4  Y  JULY am 3  Y  Y  t r 4°  OCTOBER  AUGUST  am 2  4  .80  .71 .75 am 4  t r 4°  tr 3  SEPTEMBER tr 4 t r 4°  tr 3  Y  .51 -  tr 3 Y  .95 .95 am 4  - ' tr 3  .83  .57  .66  .28 .69  .96 tr  4  Y  am 4 tr 3 tr 4 t r 4° Y  t r 4°  OCTOBER  o  71  and  am  3 were s i g n i f i c a n t l y  C. t r 4 °  fed mainly  on  diet  number).  C.am  by  Bosmina  (84% o f  probably very  D. kenai and  by  4^,  on  number).  source  of  time.  (87% o f  rotifers Rotifers  energy  the  and were  because of  their  size.  September, food  o v e r l a p among a l l t h e  became more i n t e n s e , p a r t i c u l a r l y tr  at that  D.tyrelli  3 fed mainly  diet  a negligible  small By  the  different  a l l of which  ate mainly  a m o n g am  rotifers,  4,  larvae t r 3,  Bosmina  and  and  D. t y r e l l i .  However, Bosmina were encountered  about  3X  D.tyrelli  the  was  more t h a n  true for C.tr  numerical  diet  i n the  am  3 larvae.  of  am  4 and  4 larvae,  The t r 4°  a b s e n c e o f c a n n i b a l i s m i n am  low may  4 and  be  number) , as  cannibalism  and  absence of r o t i f e r s  The  D.tyrelli  (36%)  Chaoborus  larvae, mostly  The  absence of  produced By instar. all  the  compared  most f r e q u e n t l y eaten but  their  these  low  October,  two  major t r 3, prey  attributed  to their  (5.1% b y  larvae.  types  high  to the i n the  prey  source (38%)  both  food of were  of biomass  were  D.kenai  i n the  diet  were b e i n g  eaten,  dium, D.kenai,  and  D.tyrelli.  The  60-70% t o t h e  food  biomass of  rotifers  the  considerable tr  (33%). of C.tr t r  particularly  4th and  Holope-  copepods c o n t r i b u t e d  a l l three  larval  were n u m e r i c a l l y important  types. in  3  4°.  s p e c i e s were i n the  prey  Bosmina and  to  the  consumption  Food o v e r l a p i n d i c e s were g e n e r a l l y h i g h  potential  in  t r 4°  and  of  o v e r l a p i n d e x between them and larvae of  reverse  overlap index  of r o t i f e r s  the  and  the  4°  \  TABLE I X  A c h i - s q u a r e a n a l y s i s o f t h e n u m e r i c a l d i e t c o m p o s i t i o n o f a l l l a r v a l i n s t a r s c a u g h t on same d a t e ( a ) , o f two i n s t a r s o f s i m i l a r ages c a u g h t on same d a t e (b) , o f t h e same l a r v a l i n s t a r s c a u g h t on d i f f e r e n t d a t e s ( c ) , and o f t h e s e a s o n a l l a k e p l a n k t o n c o m p o s i t i o n ( d ) . 2  Compared d a t e s July (a)  Aug. Sept. Oct.  (b)  July  am 4, t r 3, t r 4 , t r 4° am 4, t r 4 , t r 4°  24 12  Y  Y  t r 2, t r 3 am 2, t r 2 t r 3, t r 4°  9  X 1268.5 1015.2 716.3  P < .001 < .001 < .001  261.6  < .001  6  26.7  < .001  5  135.0  6  232.3  am 4, t r - 3 t r 4 , t r 4°  6  54.9  .001  8  174.9  7  143.3  Oct.  t r 3, t r 4 t r 4 , t r 4°  6  36.6  < .001 < .001 < .001  J u l y , Aug., S e p t .  tr 3  16  802.1  < .001  Sept. , Oct.  tr 4  Aug. Sept. Sept. Sept.  Y  Y  Y  7  188.3  36  2744.3  < .001 < .001  am 4  6  89.1  < .001  J u n e , J u l y , Aug., S e p t . , Oct. l a k e  24  40,634.0  < .001  Y  J u n e , J u l y , Aug., S e p t . , Oct. t r 4° Sept. , Oct. (d)  d. f . 27 12  < .001 •c.001  July  (c)  Compared i n s t a r s am 2, t r 2, t r 3, t r 4° am 3, t r 3, t r 4°  to  73  diet tr  4  a n d t r 4° l a r v a e  Y  A chi-square differences coexisting the most by d i e t instar  (p <  (Table  species  highly  pairs  together  diet  (Table  of coexisting between  significant  found  IX d ) .  instars  by age and  seasons w i t h i n any  The most  abundant  i n t h e l a k e a t any one time  f r e q u e n t l y eaten  ofa l l  IX a ) , between  IX c ) , and i n t h e composition  (Table  the most  taken  I X b)„  prey  abundance  eaten  zooplankton were u s u a l l y  i n a l l larval  types.  i n spite  Diel  Chaoborid observed  feeding  f o r t r 4° o n a l l s a m p l i n g a n i g h t peak o c c u r r e d  o v e r l a p w h i c h was most  dates,  D.kenai passed  this  p a t t e r n was r e v e r s e d . between  the ascending  ( F i g .2 3).  i n those  spatial  l a r v a e a n d a t dawn when  The c o n s i d e r a b l e d a y t i m e  D.kenai and Chaoborus i n J u l y  ( F i g . 8) may  except i n  i n t e n s e a t d u s k when t h e d e s c e n -  ding  observed  their  activity  These peaks c o i n c i d e d w i t h t h e p r e d a t o r - p r e y  August  of  f e e d i n g p e a k s o n D . k e n a i a t d u s k a n d dawn  O c t o b e r when o n l y  overlap  were  i n the lake. g  were  by a l l Chaoborus  larval  of the lake  e x c e p t i o n was i n S e p t e m b e r when Holopediurn  infrequently  of the  (10%).  a n a l y s i s showed  instars  (Table  but not i n the diets  .001) i n t h e n u m e r i c a l  similar  plankton  An  C47%)  o f am 4 l a r v a e  explain the afternoon  months.  and  feeding  peaks  74  16-17 JULY  7-8 AUGUST  I  £  6-7  5"  SEPTEMBER  V) DL  O DC 0 O 10-i  ~I  I  1  I  I  1  I  DC <  I  I  6-7 OCTOBER  1000  1 — i  1300  1600  1  1 — i  1  1 — i  2200 0400 1000 1900 0100 0700  TIME - HOURS  Fig.23  D i e l f e e d i n g p a t t e r n on D.kenai o f C . t r 4° l a r v a e i n 1972. Arrows i n d i c a t e peaks o f f e e d i n g a c t i v i t y . Sample s i z e f o r each d a t a p o i n t ranged from about 100-300 l a r v a e .  AUGUST  JULY  (a) C a m II  (r4> C. am IV  (c) C. am IV  (b) Q. am III  1 I  OCTOBER  SEPTEMBER  I  I  Q  o o  (f) C tr III  (e) C tr II to-  u.  la  o(i) C tr IV  (rft C trll  (j) C t r IV*  Y  40' 20-  f  0-  1300  1600  1900  2200 0400 1000 0100 0700  40  40  20<"  20-  1000  1300  1600  2200 0400 1000 1900 0100 0700  TIME  Fig.24.  f  — i — i — i — i — i  W C.tr IV>  (I) C tr IV°  1000  1  —  1000  1300  1600  1900  2200 0400 1000 0100 0700  (ro C t r i v o  1000  1600 2200 0400 1000 1300 1900 0100 0700  HOURS  D i e l f e e d i n g a c t i v i t y on Bosmina ( s o l i d line),, and on a l l prey t y p e s combined (dotted l i n e ) , o f d i f f e r e n t , i n s t a r s c f C.americanus and C . t r i v i t t a t u s l a r v a e i n 1972. Sample s i z e f o r each d a t a p o i n t ranged from about 50-100 C.americanus l a r v a e and from about 100-200 C. : t r i v i t t a t u s larvae. —  76 A  chi-square  hypothesis  that the  randomly. the of  a n a l y s i s was  The  null  September data  hypothesis  (p<.025,  combined.  few  was  dawn and  the  season.  slow d i g e s t i o n of  sampling tively  intervals.  wide  feeding  times  The feeding but  on  As  their  was  diel  with  Since  and  somewhat  predation  a tendency  zones a t  a l l times  pattern  of  prey  expected.  the  older C.trivittatus  Bosmina-rich A  hour p e r i o d  C.tr  feeding  allowed  them o n l y surface  chi-square  the a  ( F i g . 24  larval  few  layer  on  Bosmina  actual  larvae  sampled  feeding  2 f e d on e).  Bosmina  The  night  f-i,k),  migratory  a-d).  depth  diel  hours at night  was  behaviour in  the  (Fig. 8).  t o have non-random d i s t r i b u t i o n  little  rela-  ( F i g . 24  ( F i g . 24  a n a l y s i s showed each  (p < . 0 0 1 , T a b l e X b )  successive  the  identical  observed  24  that  in  the  peaks were  each date  occupied  ( F i g . 8), the  f o r by  trend  throughout  C.americanus  on  the  accounted  to  reduced.  throughout  easily  peaks  f o r a peak a t midnight  f l u c t u a t i o n s were not  by  obvious  for indicating  different  l a r v a e and  contained  s e r i e s had  D . k e n a i by  the  for  number  e f f e c t s between  a result,  accuracy  B o s m i n a was  these  feeding  overlapping  The  diel  i s an  appearance of  produced  only  October which  there  dusk  null  series varied  Table X a).  the  chaoborids  the  disproved  f o r a n a l y s i s and  Nevertheless,  The  test  f o r each d i e l  l a r v a e c o l l e c t e d i n A u g u s t and  D.kenai, were too be  points  used to  except  i n October  the  series of  for a l l larval tr 4  ( F i g . 24  y  which j ) , and  points types  preyed the  tr  4°  TABLE X  Date  A chi-square analysis of the d i e l feeding pattern of Chaoborus l a r v a e based on D. k e n a i a l o n e ( a ) , on Bosmina a l o n e ( b ) , and on a l l p l a n k t o n t y p e s combined ( c ) .  Instar  d. f .  X  P  (a) J u l y  t r 4°  8  13.0  .25>p>.l.  Aug.  t r 4°  2  3.7  .25>p>. 1  Sept. Oct.  t r 4°  8  18.8  t r 4°  3  3.7  am 2 tr 2  6 8  37.2 61.3  p<.001*  July July  tr 3  8  124.5  p^.OOl*  July  t r 4°  6  87.1  p<.001*  Aug.  am 3  8  56.1  p<.001*  Aug.  tr 3  8  43.3  p<.001*  4  31.1  p<.001*  (b) J u l y  Sept.  am 4  Sept.  tr 3  Sept.  tr 4  Oct.  am 4  Oct.  tr 4  Oct.  *  „5>p>.25 p<.001*  4  34.8  p<.001*  Y  4  p<.001*  8  25.0 44.4  Y  4  11.6  t r 4°  7  10.0  p>.05  am 2  7  30.8  p<.001*  tr 2  8  30.0  p<.001*  July July  tr 3 t r 4°  8  78.8  p<.001*  8  25.1  p<.001*  Aug. Aug.  am 3  8  41.1  p<.001*  tr 3  8  31.9  p<.001*  Aug.  t r 4°  8  7.2  Sept.  am 4  5  46.8  p<.001*  Sept.  8  56.3  p<.001*  Sept.  tr 3 tr 4  8  66.4  p<.001*  Sept.  t r 4°  8  54.2  p<.001*  Oct. Oct.  am 4  8 8  67.1 30.7  p<.001* p<.001*  Oct.  t r 4°  8  30.5  p<.001*  (c) J u l y July  -  . ,025>p>.01*  tr 4  Y  Y  d i e l s e r i e s v a r y non-randomly a t 95% l e v e l  p<.001* .05>p>.01*  p>.05  78.  which  essentially  d i d not prey  Bosmina  October  ( F i g . 24  rapidly  d i g e s t e d Bosmina p r o b a b l y gave an  indication  l,m,n).  on  of their  Feeding  from August  peaks based  on  to  the  accurate  most i n t e n s e c r o p p i n g times  by  Chaoborus. Variation all  i n each  diel  series  p l a n k t o n t y p e s c o m b i n e d was  Table  X c)  for a l l larvae  D.kenai not  and  Bosmina alone  give the actual  spatial  (P  <.001,  t h e t r 4°  in  August.  ( F i g . 24  effect  distributions  3  a-n),  rates  density  for a l l larvae  with  increased w i t h both  feeding experiments  of  the  tested  of  z o o p l a n k t o n i n 1971  in  Eunice  rates  D.kenai,  and  except  1972.  the  since  not  of the prey  Diaphanosoma, and  c o u l d be  D.tyrelli  any  rates  types.  2nd  of  larvae  the  and  prey  t r 4° w h i c h  Prey  and  lake  densities  feed at their tested,  nauplii. 3rd i n s t a r  A  that  full  ie. D.tyrelli,  possible  larvae  used  rates  I t i s probable  types  did  densities  t o a c h i e v e maximum f e e d i n g  L a k e C h a o b o r u s do on  digestion  temperature.  l a r v a e were h i g h compared t o the  potential  larvae  temperature  to temperature.  in  tion  of the  of the various prey  to increase directly  seem t o r e s p o n d  probably d i d  Discussion  Feeding  not  and  of different  In the present study, d i g e s t i o n were found  from  the ones o b t a i n e d f o r  feeding activity  because of the masking and  non-random  except  These curves were smoother than  of points obtained  excep-  feeding  there i s considerable spatial  on  overlap  79  between predator  and prey.  Also,  below the s a t u r a t i o n d e n s i t y probably  a valuable  because o f t h e i r  prey  large  for larval  of  on f e e d i n g  both  rates  species,  regime that  may  be due t o d i f f e r e n c e s The  experiments where  larvae  were p l a c e d  into a  t e m p e r a t u r e e n v i r o n m e n t were p r o b a b l y more C . t r 4° t h a n t o t h e o t h e r  forms.  This  the  of temperature c o n t r o l over,  of  lack  t r 4° l a r v a e  explain  the daily  i n the 3-4  is  species  day  feeding  "upsetting"  to  v a r i a t i o n i n , and the feeding  rates  larvae.  The feeding  c o l l e c t e d i n November  unknown. The  during in  of both  thermal  non-migratory  as compared t o t h e other  of the larvae  larvae  uniform  cause o f l a c k o f temperature r e g u l a t i o n on t h e rates  tempera-  o f C . t r 4°, and on t h e o t h e r  experience.  may  are  larvae  i n the effect of  larvae  migratory  well  size.  these  the  although  feeding,  f o r the 4th i n s t a r  The o b s e r v e d d i f f e r e n c e s ture  D.kenai,  l a c k o f any f e e d i n g  the long  term  view of constant  fluctuations, variability the  small  feeding prey  d o e s seem,  experimental  of prey  marked d i f f e r e n c e s at high  surprising  normal  daylight  water temperature.  containers  effect  intake  availability,  h o w e v e r , t o be r e a l  f r o m one a n o t h e r . density  i n individual larvae  e x p e r i m e n t was  and n e a r - n a t u r a l  larvae  food  pattern  Since  on l a r v a l  i n spite of  and t h e i s o l a t i o n  of  t h e e x p e r i m e n t s on t h e feeding  also  among i n d i v i d u a l s i n t h e i r and low p r e y  This  showed daily  d e n s i t i e s , t h e random  80  nature for  of predator-prey  this  food  variability.  supply  probably  i n Eunice  Lake  do n o t f e e d w h e n e v e r t h e y  Anderson  on  state  ment and v e l o c i t y  density  study.  (1972)  ability  a d u l t D.kenai  t o Chaoborus  of D.kenai  types  actions  between each o f these  size  The s w a l l o w i n g time  than  were c a p a b l e  of pre-  played  between  prey  t o b e much more rates,  and Diaphanosoma.  than  The  a d i s t a n c e o f up t o absence o f  such  l e d t o very different prey  a  F o r example,  and ChaObOrus.  o f D . k e n a i made t h e m i n a c c e s s i b l e  interThe  to instars  o f " s t r e a m l i n e d " copepods r e q u i r e d  swallowing  Daphnia o f s i m i l a r  tured  partly  probably  appeared  t o leap through  i n BOsmina, p r o b a b l y  less  depends  i n terms o f encounter  agility  1-3.  that the  f o r Chaoborus  cm w h e n d i s t u r b e d , a n d t h e c o m p l e t e  large  found  the relationship  were t h e slow-moving D . t y r e l l i  10  of the larvae.  and t h e f e e d i n g r a t e s o f l a r v a e .  accessible  prey.  The d i f f e r e n c e s i n move-  of zooplankton  i n determining  very mobile  a  larvae  i n capturing the  T h i s was a l s o f o u n d  i n the present  major r o l e  although  and b e h a v i o r a l c h a r a c t e r i s t i c s  and prey.  larvae  that,  account  Chaoborus  of aquatic invertebrate predators  dator  alone  encounter  of difficulty  (1970) a n d Monakov  the physical  the  i s limited,  or of the physiological  diet  cannot  I t i s suspected  T h i s may b e t h e r e s u l t prey  encounters  bulk  of dragging  of thick-cuticled,  (Swift their  disc-shaped  1973).  Large  predator  a b o u t when  and were e v e n t u a l l y r e l e a s e d .  This  Daphnia  apparent  cap-  81  "selectivity" was  noted  by  Chaoborus of  a l s o by  Deonier  copepods over  (194 3 ) , R o t h  There i s disagreement i n the feeding  pattern  studied  were t y p i c a l l y  night.  Gut  of^ C h a o b o r u s  examination of  (1937) f r o m b e n t h i c clusive Roth  results.  (1973),  But who  larvae  feed  possible  that both of  was  present and  but  daytime  study,  the  C•trivittatus  diel has  each predator-prey intensely eaten at but  by  at night  of  the  by  the  day  mud  night  Sikorowa  of  fed the  However, i t i s  surface  at  and  of  situa-  actually where  zones.  activity  In  the  C.americanus  specific  for  by  a t dawn; B o s m i n a the  younger  diel  l a r v a e , and  feeding at  most  were  instars  C.trivittatus  above, have looked  preserved  and  D.kenai were eaten  older the  incon-  mainly  have looked  a l l depth  d u s k and  the  by  Berg  l a r v a e were not  feeding  i n v e s t i g a t o r s of  Chaoborus, c i t e d caught or  at  species  daytime, believe that  combination: 4°  are  b e e n f o u n d t o be  a l l times of  mainly The  C.tr  diel  the  (1970)  proportions  the  abundant at  the  zones, gave  a l l times.  near  others.  planktonic  (1971) and  these authors  planktonic  equally  Scott  i n the  equally w e l l at  t i o n s where d u r i n g benthic  and  on  c o l l e c t e d by  larvae  similar  and  and  Ranke-Rybicka  that their  have found  day  larvae  and  Goldspink  Chaoborus a t n i g h t  by  and  Most of  from p e l a g i c  Kajak  (1971) b e l i e v e  feeders.  food  and  (1971),  literature  larvae.  benthic  cladocerans  larvae.  pattern  crops of  i n most cases  of  freshly have  82  scored  these  actual  contents.  value  The l a t t e r  the considerable  spatial  tendency  times  important  o f t h e prey  A l l o f these  t o work w i t h  individual  mentioned  some e v i d e n c e  effects  a l l t h e prey  few.  darkness  would  types  t h e day  of diel  Since  combine  I t i s therefore encountered  that daytime  deepest p o i n t ) ,  cyclic  on  feeding of  Chaoborus capture  can feed  (Parma 1 9 7 1 ) ,  e x p l a n a t i o n may  while  feeding  buried  continuous  i s unlikely  sediments where prey be v a l i d  f o r h i s lake  a n d f o r some o t h e r  are scarce. (10 m a t t h e  l a k e s where  Chaoborus  (Northcote  Rakusa-Suszczewski  (1971)  i fthe larvae  for  i s limited  i n the  However, Roth  f o u n d a t d e p t h s o f 10 m o r m o r e w h e r e f o o d  1972).  prey  feeding  are  Swift  respect  (Duhr 1 9 5 5 ) , and s i n c e t h e r e i s  that they  i n t h e deep water  This  species with  t h e c l o c k may b e e x p e c t e d .  suggested are  and t h e d i f f e r e n t  above f o r each one.  i n total  around  workers  b a s i s , a n d t o know t h e c h a r a c t e r i s t i c s  Chaoborus a r e very  during  remedied  by most  feeding pattern.  Hypotheses on t h e nature  mud  t o r e g u r g i t a t e when  i n d i g e s t i o n r a t e s and  o f t h e various prey  distributions  questionable  ( S w i f t and Fedorenko, i n  variability  the predators.  well  however, a r e o f  their  problem has been l a r g e l y  t o mask t h e a c t u a l d i e l  an  analyzing  Another problem not considered  retention  to  These d a t a ,  t h e use o f an a n a e s t h e t i c  press). is  o r empty w i t h o u t  because o f the l a r v a l  preserved. by  as f u l l  Chaoborus suitable  1964; Fedorenko and  (1969) a n d P e a r r e  (1973)  83  have observed  that the feeding  activity  of  chaetog-  n a t h s was m o s t i n t e n s i v e a t n i g h t a n d was r e l a t e d their the of  migration.  Eunice  i n s t a n c e s , as i n t h e case o f  Lake Chaoborus, an i n c r e a s e  predator-prey  explain  I n those  encounters  the observed  during  occurrence  hypothesis  from t h e crop  abundance and s p a t i a l to  the predator.  distinct from  pieces  the crop  diets  f o r Bosmina.  f a c t o r s o f Chaoborus  analysis data, distribution  This  that greater  appear  o f prey  relationship  o f evidence.  data  First,  ferent  than  i n the diets  with  A reversed  was s u p p o r t e d  similarities  o f t h e same i n s t a r  of the sizes  exist  instars  o f two  o f C.americanus;  D.tyrelli  the larval  Secondly,  rela-  based on t h e appen-  Bosmina  was  was t h e m a j o r p r e y  of C.trivittatus.  c o u l d n o t t h e r e f o r e be o f prime  determining  dif-  i n terms o f b i o m a s s , o f t h e 2nd and 3 r d  2nd and 3 r d i n s t a r s  predator  i nthe  of their  of grasping  dages and mouth gape o f Chaoborus l a r v a e . major prey,  by two  the observation  e f f e c t was e x p e c t e d  c o m p a r i s o n among i n s t a r s  prey  respect  s p e c i e s , was c o n t r a d i c t o r y t o t h e e x p e c t e d  tionship.  the  diet,  t o be  of larvae within a species, irrespective  instar,  the  scarcity i n  above.  major determining  obtained  may  o f t h e feeding peaks a t  i n t e g r a t e s t h e idea o f prey  deep w a t e r s mentioned The  i n the likelihood  night migration  d u s k a n d dawn f o r D . k e n a i a n d a t n i g h t This  to  of  Size of the importance i n  diet.  i t was p o s s i b l e t o e x p l a i n l a r v a l  diets  84  quite  s a t i s f a c t o r i l y using  distribution large  prey  example, larvae, nearly in  abundance,  relative t o the predator,  c a n n o t be h a n d l e d  t h e most d i v e r s e particularly  a l l the prey  their  the prey  extensive,  apparent preference  was t h a t  sizes, daily  identical  The  inhabited  apparent  s e l e c t i v i t y o f C.tr_  by t h e h i g h  feeding  low D.kenai  densities.  by  t h e younger  larvae  diet  changes Larvae  overlap  index  i n spatial overlap that  inhabited  higher  could  D.tyrelli. be larvae  n o t be  consumed  incompatibility.  reflected  vertical  food-rich  T h i s was t r u e  than  of these  the seasonal  among t h e l a r v a l  had n e a r - i d e n t i c a l  diets.  efficiency  D.kenai  clearly  types.  4 ° f o r D . k e n a i may  because o f s i z e  when i n t h e e p i l i m n e t i c , similar  and Bosmina  by t h e young C . t r i v i t t a t u s and  at  am  f o r by t h e d i f f e -  depths which were c o n s i s t e n t l y  explained  The  o f C.americanus  of C.trivittatus  be a c c o u n t e d  and August, C.americanus  types  The  i n v e r t i c a l d i s t r i b u t i o n of these plankton  July  those  easily  handle  a l l prey  o f 2nd and 3 r d i n s t a r s  D . t y r e l l i could  In  could  v e r t i c a l migrations.  for  For  of the 4th instar  and encountered  Bosmina and o f 2nd a n d 3 r d i n s t a r s  that  larvae.  t h e t r 4° b e c a u s e t h e y  for  rences  and t h e f a c t  by t h e younger  diet  their  instars.  distributions  zone a l s o  had very  o f am 2 a n d t r 2 i n J u l y ,  4, t r 3, a n d t r 4^ i n S e p t e m b e r , a n d a l l t h e 4 t h  instar  larvae  distinctly overlap  i n October.  different  indices  with  Conversely,  larvae  vertical distributions other  instars  with  had low d i e t  a s d i d t r 4°  throughout  85  most of of  the  summer.  Chaoborus  determined  instars  largely  between predator This food  and  cularly  on  by  and  prey  to the i n the  the  time  of  seems t o be  1971),  fish  1969).  overlap  a  involved, Stahl's  size  food  d i f f e r e n c e s does not  the  size  appear  populations.  in  parti-  such  as  the  larvae  chaetognaths nature  except  (1966a)  differences in coexisting  predator's  a common o n e  and  Since  larval  that  Lake Chaoborus  was  distribution  chironomid  ( G e r a l d 1966)  independent of were  of  o p p o r t u n i s t i c feeders  (Izvekova  prey  activity  D.kenai  nature  a b u n d a n c e , and  larvae described here,  large  feeding  o f maximum s p a t i a l  Chaoborus  f o o d was  on  between the  predator  (Rakusa-Suszczewski  diel  prey.  size,  case  the  Bosmina and  relationship the  relation  Finally,  where  larval extremely  suggestion  l a r v a e may  to apply  of  to  also the  imply  Eunice  86  4  1  Digestion and  2  rates  varied  inversely with  Feeding  rates  density,  prey  increased  except  apparently 3  Summary  food  temperature  size.  with  temperature and prey  f o r t r 4° where  h a d no  Maximum d a i l y  directly with  temperature  effect. ration  increased  directly  Maximum c o n s u m p t i o n r a t e s  generally  could  with  l a r v a l age.  4  realized 5  Daily  i n the lake  ration  despite  due t o l o w p r e y  of individual  the steady  larvae  environmental  n o t be  density.  was v e r y  variable  conditions  i nthe  laboratory. 6  Composition of l a r v a l diet with  7  8  with  instar  and  species.  Diversity the  differed  of diet  individual  Large prey leading  size  increased  with  age  (instar)  of  larvae. was a d e f i n i t e  to "size-selective"  restrictive  predation  force  i n t h e younger  instars. 9  Diel in  migrations  determining  of larvae larval diet  play  an important  and t h e time o f  role feeding.  87 VII  E F F E C T OF CHAOBORUS 1 a  P R E D A T I O N ON  Methods  Calculation of overall predation impact on zooplankton  Predation  effect  on n a u p l i i ,  D i a p h a n o s o m a , was c a l c u l a t e d in  1971 and 1972.  a particular was  ZOOPLANKTON  prey  calculated  f o reach  The f r a c t i o n type  from  D. t y r e l l i , - D . k e n a i , o f the dates  and  sampled  of the standing crop of  removed by a l l Chaoborus  instars  the equation:  n  .-} = !• M  i=  p  . ri o  where  "M^"  of prey (No/m  i s the total  type  the  The  and prey  crops  number o f C h a o b o r u s i s the daily  " j "  on prey  This rate and lake  included  type " i " types  feeding  " i " taken  i s corrected  to the  both k i l l e d  (uneaten) f o reach  t y p e was t h e mean o f n o o n a n d m i d n i g h t Second and t h i r d  differentiated  l a r v a e were t r e a t e d  to species.  from  temperature.  The s t a n d i n g c r o p v a l u e used  where p o s s i b l e . not  instar  density  feeding rate  eaten prey. tor  Chaoborus  prey  and o f prey  " i " , and " f ^ j "  feeding experiments.  appropriate  " j "  "n" i s the t o t a l  feed on prey o f each  (No/m )'  n  ) o f Chaoborus type  which  predation mortality  " i " , "Ch." and P r / ' a r e t h e s t a n d i n g  respectively,  rate  daily  instar  larvae  A l l fourth  and predasamples  were  instar  s e p a r a t e l y by s p e c i e s and by  instar  TABLE X I  A sample c a l c u l a t i o n o f Chaoborus p r e d a t i o n on D. t y r e l l i .  (2) T°C  (1) Date  V  26-7-72  15-19  (3) Potential predators 3 t r 4°  Col. 1 2 3 4 5 6 7 8 9 10  = = = = =  = = = = =  Equation:  M. =  (4) Pr.  (5) Ch . 2 (No/m )  (6) Prey d e n s i t y (No/1)  343  2.2  105  1.2  3  (No/m ) 2  6,517  (7)  (8) M. . 2 (No/m )  (9) i (No/m )  (10) % Pr  1.5  515  568  8.7  0.5  53  f  H  1 3  M  ±  2  date o f sampling w a t e r t e m p e r a t u r e i n t h e zone where p r e d a t i o n c a n o c c u r p o t e n t i a l l a r v a l p r e d a t o r s p r e s e n t i n t h e l a k e on t h a t d a t e s t a n d i n g crop o f prey standing crop o f predator types mean prey d e n s i t y e n c o u n t e r e d d a i l y by l a r v a l t y p e j d a i l y consumption o f p r e y by a l a r v a o f each t y p e u s i n g d a t a f r o m c o l s . 2 and 6 ( c o l . 5 x c o l . 7) = d a i l y m o r t a l i t y o f p r e y p e r l a r v a l t y p e sum o f e n t r i e s i n c o l . 8 = t o t a l d a i l y p r e d a t i o n m o r t a l i t y on p r e y by a l l l a r v a l t y p e s ( c o l . 9 / c o l . 4 x 100%) = p e r c e n t a g e o f p r e y s t a n d i n g c r o p removed by a l l p r e d a t o r t y p e s on t h a t day  89  and,  i n t h e case  density as  used  of C.trivitattus,  to interpolate  Because D.kenai  from o l d e r due  a t noon and mid-  and predator  overlapped  were s p a t i a l l y  separated  opposite migration patterns,  t h e mean  d e n s i t y was s e t a t one q u a r t e r o f t h e i r  density.  A sample c a l c u l a t i o n  D.tyrelli lations  taken  C . t r 3 and from C.tr_ 4 f o rmost o f t h e day  to their  prey  densities  i n t h e r e g i o n where prey  spatially.  The p r e y  t h e f e e d i n g r a t e s was  t h e mean o f maximum p r e y  night  by age.  i s given i n Table  f o r each  prey  type  daily  maximum  noon  o f Chaoborus p r e d a t i o n on  XI.  The i n d i v i d u a l  and year  a r e found  calcu-  i n Appendices  I-VII. In Eunice densities measured purpose  required  densities  o f these c a l c u l a t i o n s ,  predation  o f one prey rate  i n the field.  caloric  feeding rates  b y C . t r 4°  intake  larvae  p e r C . t r 4°  30 w a s c a l c u l a t e d  ways:  (1)  energy  b u d g e t e q u a t i o n , a n d (3)  estimates  Forthe  p o p u l a t i o n does n o t a f f e c t t h e  1 and September  crop contents.  as  i t i s assumed t h a t t h e  o f consumption  mean d a i l y  between June  below t h e  on o t h e r p r e y p o p u l a t i o n s .  Calculation The  were w e l l  f o r maximum f e e d i n g b y l a r v a e  i n feeding experiments  presence  b  Lake prey  and prey  i n three  abundance d a t a ,  an a n a l y s i s  Sample c a l c u l a t i o n s  a r e shown i n T a b l e X I I .  larva  of  (2)  larval  f o rthe f i r s t  two  an  90  TABLE X I I  Sample c a l c u l a t i o n s o f mean d a i l y c o n s u m p t i o n ^ by C. t r 4° u s i n g (1) f e e d i n g r a t e s and p r e y abundance d a t a , and (2) t h e e n e r g y budget e q u a t i o n . i  =r n  (1)  tyrelli  C  (kenai) D.  Date  f. eg. 1-6-71  8  f  i = .1  tyrelli f  5.  i  f c  i  f c  D. f.  i  40.  i  kenai t .  2.5  t  i  20.  8 170.1 = rr—— i^o  C/day = tyrelli 8  V' 1  = 1.42  D_.  tyrelli/larva/day  = 1.84  D_. k e n a i / l a r v a / d a y  8 1 C/day = kenai 8 . t .  1  221.1  1  120  r  C a l o r i c i n t a k e o f copepod /larva/day =  '  '  •*  r /  , tyrelli <Y * 5^2  [5.4 x 10  = 470 x 1 0 (2) A x C = P + R = [7.8 u g / l a r v a / d a y ) ( 5 . 4 7  cal/ug]  cal/larva/day  - 3  x 10~  kenai ug) + (1.84-xT2.7 ug) ]  J  cal/ug)  3  (0.6 u l 02/mg/hr)(24 h r ) ( 4 . 8 3 x 1 0 " = 112.2 x 1 0 ~ c a l / l a r v a / d a y  3  +  cal/mi 0 ) J  3  C =  P+R A  =  112.2  x .68  10~  3  = 165 x 1 0 ~  3  in  cal/larva/day 1971  2  91  The w o r k i n g  equation f o r the f i r s t  e s t i m a t e was:  n C  =  Y.  f  ii fc  i=l  n  II  where C i s t h e t o t a l consumed p e r l a r v a September during  30, " f ^ " i s t h e consumption  number o f d a y s  as  d u r i n g t h e 120 d a y s  the interval  holds,  number o f D . t y r e l l i  "i"  i n each  consumption  o f each  rate  VIII),  interval  (Schindler  D.kenai  June  1 to  p e r t r 4°.  "t^"  i s the  " i " f o r which " f ^ "  number o f t h e s e  intervals  dates.  Daily  c o p e p o d s p e c i e s was c o n v e r t e d data  i n Table  t h e v a l u e o f 5400 c a l o r i e s  The s e c o n d u  from  b y t h e number o f s a m p l i n g  biomass u s i n g weight  pod  time  and "n" i s t h e t o t a l  determined  using  (Appendix  or of  1 and then  into  into  p e r gm d r y w e i g h t  calories of  cope-  e t a l 1971). e s t i m a t e was b a s e d  on t h e energy  budget  eqution:  A x C = P + R  where"A" i s a s s i m i l a t i o n "p"is  P  (1973):  (June  1971  a n d 5.7  and'Vis  A l l values except A=68% f o r b o t h  1 - September  1968)  efficiency,"c  production (growth),  respiration. Swift  (Ricker  i s food consumed,  metabolic loss  C ,were a v a i l a b l e  from  copepods and c l a d o c e r a n s ,  30)=7.8 ug p e r l a r v a  ug p e r l a r v a  through  p e r day i n  p e r d a y i n 1 9 7 2 , a n d R=0.6 u l  92  0^ p e r mg  p e r hour.  tion  this  that  R was m e a s u r e d  i s also  t h e mean t e m p e r a t u r e  o f C . t r 4° seems t o be r e a s o n a b l e continuously  migrate  using the respective  calories  p e r gm d r y w e i g h t  on  p e r m l O2  third  larval  (Hargrave  data  from  p o p u l a t i o n was f o u n d  larva  D.kenai.  The c a l o r i c  i n the first  be  found  i n Appendices 2  The  a).  (Swift  consumption  1973) and  was  t o consume one p r e y by a t t r i b u t i n g prey  based  per day.  t h e 0.9  prey  available i e .  The above c a l c u l a t i o n s  VIII,  may  I X , a n d X.  Results Prey-nauplii  mean p e r c e n t a g e  of the standing crop of  nauplii  1971 a n d 1972 ( F i g .  Most o f t h e p r e d a t i o n o c c u r r e d i n J u l y and o f b o t h y e a r s when d i a p t o m i d n a u p l i i  larval  instars  80%  o f 5469  90% o f t h e  August  time  into  1971).  r e m o v e d b y C h a o b o r u s w a s 3% i n b o t h 25  and t h e  c o n v e r s i o n f a c t o r w a s t h e same  estimate.  a  larvae  deep w a t e r s  1971 where  p e r day t o t h e l a r g e s t  as  these  o f Chaoborus  T h i s e s t i m a t e was m a x i m i z e d per  of the habitat  conversion factors  estimate of larval  the crop analysis  The assump-  "p"and"R" w e r e c o n v e r t e d  calories  The  since  between t h e c o l d ,  warm, s u r f a c e w a t e r s .  4.83 c a l o r i e s  a t 1 0 C.  1-3 w e r e m o s t a b u n d a n t .  2nd and 3 r d i n s t a r of the total  Predation  rates  During  this  l a r v a e were r e s p o n s i b l e f o r over  p r e d a t i o n on n a u p l i i rarely  and Chaoborus  exceeded  ( F i g . 25 b , c ) .  one n a u p l i u s p e r day f o r  D.TYRELLI  NAUPLI  1971  1971  1972  1972  2  100  MONTHS Fig.25  The e f f e c t of Chaoborus p r e d a t i o n on n a u p l i i ( l e f t ) , and on D . t y r e l l i ( r i g h t ) . (a,d) - p e r c e n t o f prey s t a n d i n g c r o p removed by Chaoborus i n 1971 (dotted l i n e ) and i n 1972 ( s o l i d l i n e ) ; (b,e) and ( c , f ) p e r c e n t o f t o t a l 'predation a t t r i b u t e d t o d i f f e r e n t l a r v a l i n s t a r s i n 1971 and 1972 r e s p e c t i v e l y .  94;  the  2nd  and  the  4th instar  An was  3rd i n s t a r  average  removed  of  Prey  of  14%  -  were even lower  the  6%  especially  I, I I ) .  standing crop of  i n 1972  heavy  ( F i g . 25  i n August  p o p u l a t i o n was  eaten.  y e a r , c r o p p i n g was  u n i f o r m l y low  one  of  Second and  consumed t h e population  that  i n 1971.  l a r g e s t p r o p o r t i o n of the  eaten  i n 1971;  i n 1972,  daily  exceeding with  intake of D . t y r e l l i 6 prey per  a maximum o f  2.5  c The  1972  26 was  Prey  and  a ) , but  the  o n l y about  (Appendices C.tr  prey  V,  VI).  1972  per  this  period,  numbers a c c o u n t e d d a t i o n on  D.kenai.  - only  i t was  low  (Appendices  of the D.kenai were  14%  third  and  of  instar  sometimes in  1972  I I I , IV).  standing crop  25%  respectively  than  In late  removed  t h a t removed  to July  4 larvae,  for less  larvae  D.kenai  F r o m May  C.am  about  D.tyrelli  4th  a b s o l u t e number o f p r e y one  the  h i g h i n 1971,  day;  over  ( F i g . 25 e , f ) .  of both  4° w e r e t h e m o s t i m p o r t a n t p r e d a t o r s  During  In  total  3 r d and  p e r day  -  mean p e r c e n t a g e s  removed i n 1971 (Fig.  larva  was  when  3rd i n s t a r  l a r v a e were the most important p r e d a t o r s The  D.tyrelli  d).  1971  following third  for  D.tyrelli  of  and  the D . t y r e l l i  and  (Appendices  b  i n 1971  P r e d a t i o n was 30%  larvae  larvae  30%  in  1971  years,  ( F i g . 26  b,c).  because of t h e i r of the o v e r a l l  summer a n d  i n the  in  low pre-  fall,  t r 3  1971  1972  1971  lOCh  1972  CO  50-  PREDATION NEGLIGIBLE  M  MONTHS Fig.26  The e f f e c t of Chaoborus p r e d a t i o n on D.kenai ( r i g h t ) . F o r e x p l a n a t i o n see F i g . 2 5 .  ( l e f t ) , and on Diaphanosoma  96  larvae  and a l l t h e 4 t h i n s t a r  predators 1971  on' P . k e n a i .  w a s 1.8 D . k e n a i  P.kenai  The a v e r a g e per larva,  (Appendix V ) . p e r day  d  Prey -  1971 an average  with  over a  80% o f t h e t o t a l  rate  o f about e  The ranged The  larvae  ( F i g . 26 d ) .  prey  from  first  indicated  these  I n 1972 t h e  the presence  P i a p h a n o soma e a t e n  removed  ( F i g . 26 e ) , a t  p e r day (Appendix V I I ) .  b y C . t r 4°  larvae  t h e three consumption  148-470 c a l o r i e s  o f 2nd  These l a r v a e  per larva  estimates  p e r day  e s t i m a t e u s i n g t h e p l a n k t o n abundance  (Table  XIII).  data  t h a t o v e r o n e t o t h r e e c o p e p o d p r e y may h a v e b y a C . t r 4° l a r v a  (Appendix V I I I ) .  was h i g h when c o m p a r e d t o t h e d a i l y  larval  when  T h e peak, p o p u l a t i o n o f  i n the lake.  Consumption  consumed d a i l y  fraction  consumption  s p e c i e s was v e r y l o w a n d  3 prey per larva  v a l u e s from  a m a x i m u m o f 3.0  and August  Diaphanosoma i n 1971 c o i n c i d e d w i t h 3rd instar  i n  o f 19% o f t h e s t a n d i n g crop o f  p r e d a t i o n was n e g l i g i b l e .  and  consumption  Diaphanosoma  prey were most abundant crop of t h i s  important  (Appendix V I ) .  D i a p h a n o soma was r e m o v e d i n J u l y  standing  daily  I n 1972 t h e mean  w a s 0.6 P . k e n a i  In  l a r v a e were  o f prey per larva  crop contents  consumption  been  This  of only a  estimated from t h e a n a l y s i s o f  (Appendix X ) .  9 7  TABLE X I I I  C a l c u l a t e d d a i l y food consumption of C i n 1971 and 1972.  Method  tr 4  C a l o r i e s consumed (10~  3  cal/larva/day)  1971  1972  F e e d i n g and p l a n k t o n abundance d a t a  470  223  E n e r g y budget equation  165  148  Crop a n a l y s i s d a t a  207  larvae  98  3  Predation be  reduced  (S)  - prey  water (V)  on Eunice  by four  Lake  places  zooplankton  "mechanisms":  and p r e d a t o r  and predator  appears t o  seasonal  segregation  a r e i n t h e same p l a c e  column b u t a t d i f f e r e n t  - prey  are  Discussion  times;  vertical  i n t h e water column;  low prey  density  (D) -  below the t h r e s h o l d c o n c e n t r a t i o n a t which f e e d i n g by l a r v a e c a n o c c u r ;  and s i z e  bility  (H) - t h e p r e d a t o r  t o handle  Predator prey  d e n s i t y was c o n s i d e r e d  a t t h a t d e n s i t y was < The  only  C.tr  years  t h e 1972 d a t a  Nauplii except  f o rboth  C.tr4  during  0.1 p r e y  Of  from these  from  by t h e i r prey  3rd instar  liters;  predation together  by a l l l a r v a l  Feeding  seasonal  instars  by t h e  by o t h e r  and v e r t i c a l  because o f t h e i r  Major predators Chaoborus  instar segre-  density.  s t u d i e d , D . t y r e l l i were  larvae of both  (Fig.27).  ( F i g . 27 a ) .  feeding on n a u p l i i  and by low prey  g r e a t e s t numbers m a i n l y t h e season.  escaped  some p a r t o f t h e summer  the zooplankton  throughout  2/100  per day.  and a r e d i s c u s s e d  absence o r low d e n s i t y o f prey.  gation  prey.  are illustrated graphically  4^ w e r e p r e v e n t e d  l a r v a e was r e d u c e d  incompati-  low i f the feeding r a t e per  c o u l d have been eaten V  prey  signi-  l o w i f i t was <  ways i n w h i c h p l a n k t o n i c p r e y  were s i m i l a r but  i s unable  d e n s i t y was c o n s i d e r e d  larva  and  segregation  are concurrently i n different  ficant  in  i nthe  consumed  abundance  were t h e 2nd s p e c i e s and C a m  4,  (a) NAUPLII M  J  i  J  i  i  A i  V  (b)  S  O  i  V  N  .  D. TYRELLI  M  i  t  J 1  J  A S  1  1  " O N  1  1  1—  D  AM IV  S  D  s  -  TJR IVY  S  V  D  J_R D  (c) M  IV° s"  S  D. KENAI J  J  A  ,  S  ,  O  (d) DIAPHANOSOMA ,  N  M  r-  II  H+V  D  ~v~"  b"  J  A  S  O  N  S  1 , 1  v  J  S  D+V  AM iv  *"s"  D  S  V+D  S  TR ""b+v".IVY V+D  Fig.27  D  TR IV  0  V+D  S  The mechanisms f o r p r e d a t o r avoidance from May t o November of 1972 by f o u r prey t y p e s . S - s e a s o n a l s e g r e g a t i o n , V - v e r t i c a l s e g r e g a t i o n , D-low prey d e n s i t y , H - s i z e i n c o m p a t i b i l i t y . S o l i d l i n e s r e p r e s e n t o p t i m a l p e r i o d s f o r p r e d a t i o n s i n c e no known p r o t e c t i v e mechanism i s o p e r a t i n g ; dashed l i n e s i n d i c a t e t h a t the mechanism i s o n l y p a r t i a l l y e f f e c t i v e and some p r e d a t i o n can o c c u r ; d o t t e d l i n e s r e p r e s e n t l e a s t o p t i m a l p e r i o d s f o r p r e d a t i o n because of the above mechanisms o p e r a t i n g . P e r i o d s f r e e of l i n e s i n d i c a t e t h a t no p r e d a t i o n i s o c c u r r i n g because of absence or s c a r c i t y of p r e d a t o r s . Roman numerals i n d i c a t e larval instars.  100  all of  o f which overlapped high  could  prey  density  not handle  with  D.tyrelli  ( F i g . 27 b ) .  this  copepod.  Instar 1 larvae  Predation  and  C . t r 4° was r e d u c e d  by v e r t i c a l  the  day.  D.tyrelli  low  f o rpredation  In the f a l l ,  Unlike  to  these  2nd and young  segregated  hour p e r i o d  during  d e n s i t i e s were t o o  D.kenai were never  or size  refuge  3rd instar  l a r g e copepods.  spatially  segregation  fully  Fourth  larvae could instar  from D.kenai  due t o t h e i r  ( F i g . 27 c ) .  opposite  not handle  larvae  were  f o r m u c h o f t h e 24 migration  patterns.  H o w e v e r , i n t h e s p r i n g a n d e a r l y summer, m i g r a t i o n C.tr  4° l a r v a e was s t i l l  spatial rable  overlap  with  undeveloped  the D.kenai  and t h e i r  of the  marked  resulted i n conside-  predation. The  brief  combined w i t h  occurrence their  the  l a r v a e , made  few  weeks  o f Diaphanosoma i n t h e l a k e ,  partial  ( F i g . 27 d ) .  Perhaps reducing  predation  This  segregation  pressure  feeding  to  f o ronly  a  occur.  factor responsible f o r  on a l l prey  turnover  probably  from  I n 1972, Diaphanosoma d e n s i t i e s  t h e most important  and synchronous  instars.  vertical  them a v a i l a b l e t o p r e d a t o r s  were t o o low f o r a p p r e c i a b l e  rapid  Y  f o r t h e e n t i r e 24 h o u r p e r i o d b u t  a l w a y s h a d some s p a t i a l First,  by C . t r 4  occur.  the D.tyrelli,  exposed t o predation  i n the region  types  was t h e  of the different  r e s u l t e d i n a continuous  larval shift  1 0 1  of  emphasis  least Any  f r o m one  partial  one  of  prey  recovery  the  of  above f o u r  type  to another  prey  populations  f o r dampening o r  even stopping  Where low  prey  vertical  partially  but  d e n s i t y and  simultaneously,  spatial  distribution and  the  predator,  may  be  avoid  predation.  p r e d a t i o n was  operated  also  Cyclops  viewed  predation.  was on  the  prey  of  the  seasonal  p l a n k t o n i c prey  relative  handling as  of  prey  by  (1969) r e p o r t e d  predator.  to  the  by  prey  similar  community  More emphasis to predators  and  the  p o s s i b l e ways e v o l v e d  i n h i s zooplankton  responses  histories,  ability  McQueen  mechanisms o p e r a t i n g  life  fully  segregation  above mechanisms i n v o l v i n g  predator,  placed  place.  absent.  The  to  at  to take  "mechanisms" c o u l d be  effective  usually  allowing  where  should  be  i n terms of  spatial-temporal distribution,  prey  and  prey  behavior. It  i s evident  particularly on  weakened  i f the  his  1971;  a  zooplankton  tively  study  accounted  Sprules  1972).  f o r 37%  (1970) r e p o r t e d on  the  larger  of  This  have a h i g h Welch  that  that  "the  Chaoborus,  exert considerable  community.  zooplankton  Allan  energetics  chain  literature  i f a b u n d a n t , may  pressure  (Roth  from the  predation  pressure  turnover  rate  (1968) c o n c l u d e d  from  crustacean-Chaoborus  a l l herbivore  food  growth".  t h a t C h a o b o r u s , by. f e e d i n g  diaptomid  is  s p e c i e s , may  keep  selec-  this  102  form In  rare or extinct  two  i n ponds t h a t the  lakes i n Poland,  p o p u l a t i o n was Ranke-Rybicka  1970).  f o r 10%  buted  to the  B a s e d on  zooplankton statement (19 71)  of  the  total  Cyclops  Mesocyclops  on Of  the  the n a u p l i i mortality  crops  four prey  cropping  contri1972).  that small  large  part of for  (1969) and  by  Confer  found  significant  the  this  species of Cyclops  exerted a  types  of Eunice  and that  depressive  least  during the  two  summer s e a s o n s  and  D.kenai  unpublished  two  (10% and  larval  no  which  sporadically  by w a t e r  severe  of  copepod  on  recorded their  (A.Y. total  during the not  (19% of  Feeding  probably  Fedorenko, copepod Diaphanosoma  years  so much by  temperature.  i n 1971  two  for  standing  species  doubt c o n s i d e r a b l y higher.  seems t o h a v e b e e n c o n t r o l l e d as  was  20%  effect  Chaoborus,  Considerable  generations a year  p r o d u c t i o n was appeared  damage.  Since these  d a t a ) , the  zooplankton  t o p r e d a t i o n by  the  more t h a n  predation  Lake  suffered  respectively).  s o m a was  larval  (Dodson  These authors  f o r l o s s e s due  D.tyrelli  h a v e no  McQueen  and  the prey p o p u l a t i o n s .  investigated  both  remove a  a predatory  respectively.  force  (Kajak  Further evidence  Mesocyclops and  zooplankton  Chaoborus  Dodson c o n c l u d e d  p r o v i d e d by on  the  daphniid mortality  production.  working  by  of  inhabit.  D a p h n i a p o p u l a t i o n and  p r e d a t o r s may  was  13%  In Leechmeere, d a i l y  his finding,  invertebrate  and  removed d a i l y  accounted 9 3%  7%  larvae  of  study,  Chaoborus on  Diaphano-  p o p u l a t i o n removed  daily  103  in  July  prey has  and A u g u s t ) ,  densities. appeared  exceeded  but negligible  Yet, i n both  when t e m p e r a t u r e  years, this  20° C a n d d i s a p p e a r e d  were p r o b a b l y preyed  summer s e a s o n .  cladoceran  of the surface rapidly  B o s m i n a , commonly e n c o u n t e r e d 1972,  i n 1972 due t o l o w  as t h e l a k e c o o l e d .  i n larval  upon h e a v i l y  D a p h n l a may h a v e b e e n c r o p p e d  i n 1 9 7 1 when t h e y w e r e a r e l a t i v e l y  species  and t h e o n l y prey  c r o p s may  indicate  The  very  similarity  of d a i l y  poor  indication valid.  the  prey  This  from  estimates good  i-  n  i n t h e tube  t o t h e much  prey  growth  experiments  i n 1971 than i n  by growth  1972 g a i n e d  g a i n o f C . t r 4° i n 1 9 7 1 .  abundance on l a r v a l  intake  i n two o f t h e e s t i m a t e s ,  a n d may b e a t t r i b u t e d  4  calories  However, t h e h i g h c a l o r i c  t o 1972, found  £•'*•£ °  were  t h e 1971 p r e d a t i o n d a t a ,  suggestion i s supported  two y e a r s .  strated  year.  h i g h v a l u e o f 470 x 10~3  standing crop o f zooplankton  the weight  probably  b y C . t r 4° l a r v a e was a  p e r day o b t a i n e d  seems t o be r e a l  1972.  i n their  t h a t t h e data used,and t h e c a l c u l a t i o n s  1971 r e l a t i v e  higher  water  I n 1972, t h e low  o f the three independent  may b e a n o v e r e s t i m a t e . in  the deeper  l o w numbers i n t h a t  The r e l a t i v e l y  larva  the  abundant  f e e d i n g on these prey  food consumption  from  consi-  o f l a r v a e w i t h Daphnia o r Polyphemus  because o f t h e i r  per  that shared  C . t r 4° l a r v a e i n t h e d a y t i m e .  proportion  crops  throughout  derably  with  water  data f o r  o n l y 7/10 o f  The e f f e c t o f  has a l s o been  demon-  where an excess  o f food  104  resulted  i n faster  C.tr duration high  weight  4° l a r v a e , b e c a u s e o f t h e i r time,  high  i n Eunice  Lake.  consumption, determined larva,  larvae  values  culated the rate the  sources  data:  curves,  f o rthe f i r s t  variation  variation  lack of plasticity  the  dynamic nature This  of daily  last  point  was  based on two sampling each  maximum p r e y  spectrum due t o l a c k o f d a t a ,  predator-prey  times  only  d e n s i t i e s were used and prey.  express  spatial  i s o f most concern  14 - d a y i n t e r v a l ,  values.  i n the feeding  occasions,  daily  inter-  because  by a  - noon and  larva midnight  and i n a l l cases, i n the region of This  treatment  may w e l l h a v e r e s u l t e d i n a n o v e r e s t i m a t i o n consumption  using  density estimates i n  density encountered  between p r e d a t o r  i n the cal-  i n the calculations to  average prey  during  2.8%  (1970)  estimate  about t h e p o i n t s  i n t h e prey  the  lap  and Ranke-Rybicka  o f e r r o r were i n h e r e n t  and  -  consumed d a i l y  lakes.  o f part o f the prey  actions.  calories per  d r y w e i g h t o f 1.2 mg p e r  l a k e due t o l o w number o f s a m p l i n g  neglect  daily  o f 3.6% a n d 1 2 . 5 % f o r t h e C . f l a v i c a n s  consumption rates  field  plankton  h e r e a s 185 x 1 0 "  Kajak  i n two P o l i s h  Several  long  relatively  t h e mean  ( F i g . 1 2 ) , a C . t r 4° l a r v a  i t s body weight.  reported  t h e major  Given  a n d t h e mean l a r v a l  individual  16 m o n t h  consumption r a t e s , and  abundance, were probably  predators  of  gain.  over-  of data  of the final  105  The  energy  inaccuracies  budget equation  i n the  estimates  application  of  a respiration  temperature  of  10°  have produced The analysis time  was  or  hours time  crop after  was  observed time  contents prey  the  too  considerably those  prey  low  higher  that C t r  4°  regurgitation  crops (1971)  agrees  indicate Scott  actually full  used  well  temperature  cases,  here.  the  for C f lavicans.  that 4 - 5  digestion  However,  the  derived times  I f anything, this  value  b e c a u s e i t was (17°  - 20°  obtained C)  is at  than  experience.  largely  the value  with  large  of digestion  temperatures  and  (1945)  f o r one the  crops  (1971) r e p o r t e d  In both  types.  normally  digestion  to the midgut w i t h i n  one  f o r C . t r 4°  crop  Montshadsky  estimates  Improved methodology of  was  i s m o r e r e a l i s t i c b e c a u s e i t was  different  probably  and  the  larvae with  3 - 5 hours  ingestion.  s e v e r a l independent  using  of  passed  8 hours,  may  cost.  i f t h e mean  30%.  d i d not  Goldspink  shorter than  8 hour value from  the  H o w e v e r , he  the water.  larval  proportion of  a digestion  Daphnia. of  i f the  t o be  constant  migrating larva,  d e r i v e d from low  The  at a  of metabolic  have been too  contained  i t s parameters.  C to a v e r t i c a l l y  assumed here  than  doubt a l s o  v a l u e measured  underestimate  d a t a may  higher  reported  of  consumption estimate  of prey,  shorter,  an  no  of  removed the 30%  t h a t g i v e n by I f a l l the  of  problem  larvae with  Goldspink  and  full  Scott  above d i s c r e p a n c i e s  106  tended this  to underestimate  may h a v e b e e n o f f s e t  D.kenai as prey prey  the final  consumed In  thus  t o some e x t e n t  maximizing  fairly  little  t h e r e was a v a i l a b l e  dation  rates reported  actual  values.  on  vary  with  well  from  the only  estimates  here a r e probably  season and w i t h  previously,  considerable  standing  crop.  composition  predation  This  seems t o be t r a n s i t o r y instar  the pre-  close to the  as has been noted  Lake do e x e r t  group  what  from t h e l i t e r a t u r e ,  on t h e zooplankton prey  predation  among t h e m s e l v e s a n d w i t h  Therefore,  i n Eunice  any s i n g l e  by t h e use o f  the biomass  since the three  agreed  pressure  value,  daily.  general,  Chaoborus  consumption  effect  and t o  of predators.  .107  4  1  Summary  P r e d a t i o n by Chaoborus on Eunice seems t o b e r e d u c e d segregation, bility  2  zooplankton  and v e r t i c a l  d e n s i t y , and s i z e  incompati-  with the predator.  D.tyrelli 1972.  3  low prey  Chaoborus removed  to  by seasonal  Lake  10% and 20% o f s t a n d i n g crop o f  and" D . k e n a i  respectively  Predation pressure  increase with their  £«^£ ^° l  on c l a d o c e r a n s  seemed  abundance.  consumed d u r i n g  a r v a e  i n 1971 and  t h e summer  season  _ •)  about 2.8% 4  1 8 5 x 10 of their  Close  body  of daily  estimate  per larva  p e r day o r  weight.  a g r e e m e n t was f o u n d  estimate the  calories  food  between t h e e n e r g e t i c s  consumption by l a r v a e and  from t h e f i e l d  data.  108  BIBLIOGRAPHY  A l l a n , D . J . MS 1 9 7 2 . Competition a b u n d a n c e o f two c l a d o c e r a n s , Univ. of Michigan. 110 p.  and t h e Ph.D.  relative thesis.  A n d e r s o n , S.R. 1970. P r e d a t o r - p r e y r e l a t i o n s h i p s and p r e d a t i o n r a t e s f o r crustacean zooplankters from some l a k e s i n w e s t e r n C a n a d a . Can. J . Z o o l . 48: 1229-1240. 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S p r u l e s , G. MS 1 9 7 0 . The e f f e c t s o f s i z e - s e l e c t i v e p r e d a t i o n and food c o m p e t i t i o n on crustacean zooplankton communities o f h i g h a l t i t u d e ponds. P h . D. t h e s i s . P r i n c e t o n U n i v . 47p. S t a h l , J . B . 1966a. Lake, Indiana.  The e c o l o g y o f Chaoborus i n Myers L i m n o l . OceanogrT T H T77-183.  . 1966b. Coexistence i n Chaoborus and i t s ecological significance. Invest. Indiana Lakes a n d S t r e a m s 7: 99-113. S w i f t , M.C. a n d A . Y . F e d o r e n k o . 1 9 7 3 . A r a p i d method for t h e a n a l y s i s o f t h e crop contents o f Chaoborus larvae. Limnol. Oceanogr. In press. S w i f t , M.C. MS 1 9 7 3 . Energetics of vertical migration i n Chaoborus l a r v a e . P h . D. t h e s i s . U n i v . o f B r i t i s h Columbia. In preparation.  112  S w i i s t e , H . F . J . , R. C r e m e r , a n d S. P a r m a . 1973. S e l e c t i v e p r e d a t i o n by l a r v a e o f C h a o b o r u s flavicans (Diptera, Chaoboridae). I n t . Ver. T h e o r . Angew. L i m n o l . V e r h . 18: In press. T e r a g u c h i , M. a n d T.G. N o r t h c o t e , 1966. Vertical d i s t r i b u t i o n and m i g r a t i o n o f C h a o b o r u s f l a v i c a n s i n Corbett Lake, B r i t i s h Columbia. ETmnol. Oceanogr. 11: 164-176. W e l c h , H.E. MS 1 9 6 8 . Energy flow through the major m a c r o s c o p i c components o f an a q u a t i c e c o s y s t e m . P h . D. t h e s i s . Univ. of Georgia. 97p.  113  APPENDICES  APPENDIX I .  PREDATION ON N A U P L I I , 1 9 7 1 .  (Dates on which  DATE  T^C  POTENTIAL PREDATORS  PREY STANDING CROP (No/m 2 ) Pr  5-13  20 May  am 4  .  14,109  t r 4° 5  9-14  July  1  5,170  t r 4° 20  11-25  July  2  11,959  t r 4° 3 Aug.  .  9-23  2  14,742  3 t r 4° 17 A u g .  19-21  3 am 4  2,642  predation could  CHAOBORUS STANDING CROP (No/m 2 )  not occur a r e omitted.)  PREY DENSITY (No/-*)  CONSUMPTION /LARVA /DAY  PREY REMOVED PER PREDATOR TYPE (No/m 2 )  TOTAL PREY REMOVED (No/m 2 )  M. .  M.  Ch. J  IJ  54  67  5.5  0.8  189  5.5  0.8  151 204  408  3.0  0.5  51  2.7  0.5  26 521  434  9.0  1.2  148  1.0  0. 1  15  64  9.0  1.2  77  71 1  9.0  \ .2  853  193  4.0  0.6  1 16  862  1.0  0. 1  86  116  1.0  0.1  12  mean M. = 3 0 2 i ( 2 0 May - 17 A u g . )  I  i PREY STANDING CROP REMOVED % Pr.  i  205 •  1.5  230  4.4  536  4.5  1,046  7.1  98  3.7  3.0?  APPENDIX I I .  PREDATION ON N A U P L I I ,  1972..  ( D a t e s on w h i c h p r e d a t i o n c o u l d n o t o c c u r are omittedJ  DATE  T°C  POTENTIAL PREDATORS  PREY STANDING CROP (No/m 2 ) Pr,  3 May  17 May  14 J u n e  4  5-13  am 4 tr  <P  tr  4°  am 4 tr  4y  tr  4°  5-19  1  12,008  5,606  3,677  am 4  June  7-13  17  July  9-19  tr  (NoV)  PREY DENSITY Wo/l)  CONSUMPTION /LARVA /DAY f. .  Ch. J  PREY REMOVED PER PREDATOR TYPE M. ij  (No/m2>  1 10  1.4  0.2  22  215  1.4  0.2  43  126  1.4  0.2  '25  66  1.2  0.2  13  51 1  1.3  0.2  102  26  1.3  0.2  5  1. 1  0.2  104  I.I  0.2  8 94  521 40  t r > 28  CHAOBORUS STANDING CROP  TOTAL PREY REMOVED (No/m 2 )  M;  •  t PREY STANDING CROP REMOVED * P  rl  90  0.7  120  2.1  206  5.6  470  I.I  0.2  4°  6,197  258  0.9  . 0.1  26  26  0.4  2  9,284  395  6.3  0.8  316  538  5.8  167  4.0  0.6  100  2.2  3 t r 4°  306  2.8  0.4  122  July  16-19  3  5,660  343  2.1  0.4  124  124  8 August  13-20  3  3,394  352  I.I  0.2  70  70  2.1  22 A u g u s t  13-19  3  3,025  334  . I.I  0.2  67  74  2.4  1.0  0. 1  26  am 4  72  mean M. = 139 ( 3 May - 22 A u g u s t )  7  APPENDIX I I I .  PREDATION ON D. T Y R E L L I . 1 9 7 1 .  ( D a t e s on w h i c h p r e d a t i o n c o u l d DATE  POTENTIAL PREDATORS  T°C  PREY STANDING CROP (No/m 2 ) Pr. i  20 May  7-11  am 4 tr  1 J une  7-15  CHAOBORUS STANDING CROP (No/m 2 ) Ch. J  8,433  67  4°  am 4  189 20,861  ^ 4 ° 14 J u n e  5-11  am 4  29,218  t r > 5  July  5-14  20  July  5-25  3 Aug.  5-23  -  tr  tr  1  J  TOTAL PREY , REMOVED  IJ  I  2.3  0.2  13  2.3 .  0.6  113  1 10  9.8  5.0  550  296  9.8  5.0  1,480  65  11 .3  3.0  195  209  7.0  2.0  418  9.7  613  2.1  87  0.6  1 .7 2.3  998  148  5.0  1 .8  266  1,264  7.0  64  5.1  2.2  141  4,600  32.2  71 1  5.1  6.0  4,266  193  3.0  liO  662  7.0  6,289  34.3  1 16  1,167  1 1 .3  1,001  ' 1 1 .0  4° 14,293  18,359  193  4.0  464  222  3.5  i :o  222  543  2.0  1.5  815  am 4  168  1.5  1.0  168  t r 4*  221  1.5  0.5  1 1 1  t r 4 °  146  1.5  0.5  383  2.3  1 .5  575  128  3.3  1.5  192 167  3  3  10,371  9,095  am 4 4Y  .  tr 4° 3 am 4  5,538  .  87  7.0 .  1 1  2,030  7.5  5,603  tr  1 .5  4.3  6.5  16 S e p t .  126  % Pr.  51  3  12-17  M.  % PREY STANDING CROP REMOVED  434  tr 4°  3 Oct.  f. .  PREY REMOVED PER PREDATOR TYPE (No/m 2 ) M. .  18,177  am 4  Sept.  CONSUMPTION /LARVA /DAY  13,670  3  3  (No/V)  4°  2.  5-21  PREY DENSITY  2  t r 4° 17 A u g .  n o t o c c u r a r e omitted.)  73  557  1.3  0.3  223  1.3  0.3  67  176  3.4  3.5  616  89  6.0  1.8  160  tr  4Y  562  3.0  1.0  562  tr  4°  156  3.0  1.0  156  Mean M. = i (20 May - 3 O c t . )  '  1,494  27.0  1,867  I3.7S&  APPENDIX I V .  PREDATION ON D. T Y R E L L I . 1 9 7 2 .  ( D a t e s on w h i c h p r e d a t i o n c o u l d DATE  T°C  POTENTIAL PREDATORS  PREY STANDING CROP (No/m2) P r  17 May  7-12  '  am 4  i  8,945  t r 4Y t r 4° 31 May  .7-14  am 4  12,603  t r 4° 7-12  14 J u n e  am 4  10,680  t r 4° 28  7-12  June  2  3,769  tr 4° 17  July  17-19  2  5,909  3  15-19  8 Aug.  9-20  1  3  22 A u g .  11-21  3  11-16  24  Sept.  7 Oct.  1 1  530  5.0  511  2.4  1 .0  5.0  2.5  200  469  3.6  1 .5  704  40  3.1  1.5  ' 60  470  2.6  1 .0  470  565  0.9  0. 1  57  258  1.0  0.5  129  395  2.2  0.4  158  167  2. 1  1.5  251  105  1 .2  0.5  352  1 .7  1.0 0.8  1.2  1.0  1 .0  0.5  144  2.5  425  .  4.0 '  2.5  183  3.1  1.5  275  353  3.1  1.5  530  75  2.2  1 .0 0.7  142 155  203 ,  tr 4°  309  1.1  0.5  1 13  3.0  1.0  113  262  1.6  0.8  210  223  1 .6  0.8  178  1.3  0.2  16  9,699 Y  am 4  6,761  82  '  75  1.7  am 4  4.9  56?  9.5  568  8.7  358  5.2  483  8.3  72  228  91  10,759  267  1.3  3.1  % Pr.  53  72  170  . 186  358  334  288  1  26  26 80  6,951  t r 4° . 8  7.2  66  1.0  t r 4V  tr 4  21 O c t .  904  1.0  2.4  153  tr 4° 1 1-13  6.7  2,4  515  18,063  am 4  • 603  66 511  1.5  t r 4* -  % PREY STANDING CROP REMOVED  0.5  am 4  •  TOTAL PREY REMOVED (No/m2) K.  1.0  5,793  3  f .1 . J  PREY REMOVED PER PREDATOR TYPE (No/m2) M.1 . J  2.2  tr 4° Sept.  CONSUMPTION /LARVA /DAY  306  am 4  6  PREY DENSITY <No/£)  343  tr.4° 3  CHAOBORUS STANDING CROP (No/m ) Ch. J  6,517  tr 4° July  26  not occur a r e omitted)  1,458 '  8. 1  372  3.5  501  5.2  16  0.2  .  mean Mj  =  545  (17 May - 21 O c t . )  6.0* \~>  APPENDIX V.  PREDATION ON D. K E N A I , 1971.  (Dates on which POTENTIAL PREDATORS  DATE  PREY STANDING CROP (No/m2) Pr,  20  May  9-11  t r 4 ° 1 June  am 4  7-15  tr 14  June,  3,732  am 4  5-11  10,816  4°  am 4 tr  -  12,689  4°  p r e d a t i o n c o u l d n o t o c c u r a r e omitted.)  CHAOBORUS STANDING CROP (No/m 2 ) Ch. J  PREY DENSITY (no/*)  CONSUMPTION /LARVA '/DAY  PREY REMOVED PER PREDATOR TYPE (No/m 2 ) M. .  J  2.0  2.3  i 154  189  1 .0  2.4  454  67  •  TOTAL PREY REMOVED (No/m 2 ) M.  110  3.5  3.0  330  296  3.6  2.5  740  65  3.6  3.0  195  .209  3.7  2.5  '523  $ Pr,  608  16.3  1,070  9.9  718  5.7  t r 4°  11,399  51  1.3  2.5  128  128  1 . 1  July  5-25  t r 4°  8,424  148  1 • 1  2.5  370  370  4.4  3 Aug.  5-24  3  7,723  613  I.I  1 .7  1,042  1,621  21.0  193  1 .4  3.0  579  799  2.2  2.2  1,758  2,558  25.3  116  2.1  2.3  267  222  I.I  2.4  533  543  0.7  1 .2  652  1,049  17.9  168  1.1  1.7  286  221  0.6  0.5 ,  1 1 1  383  0.5  1 .0  383  947  20.8  128  1.1'  1 .7  218 279  425.  23.0  5 July . 20  5-15  .  tr 4° 17 A u g .  5-21  3  10,106  am 4  IT 4 ° 3  Sept.  5-17  3  5,865  am 4 tr 16 S e p t .  5-15  4y 3  4,550  am 4  3 Oct.  tr  4Y  557  0.7  0.5  tr  4°  223  0.6  0.3  67  176  0.3  0.9  158  89  0.6  I.I  98  562  0.3  0.3  I6S  67  0.2  0.2  13  398  0.1  0.1  40  3  1 1  1,824  am 4 tr 17 O c t .  9  -  4Y  am 4 tr  4Y  1,162  •  PREY STANDING CROP REMOVED  53  mean M.  =  868  ( 2 0 May - 17 O c t . )  4.6  13.6?.  APPENDIX V I .  PREDATION ON D. K E N A I , 1 9 7 2 .  (Dates on which DATE  T°C  POTENTIAL PREDATORS  PREY STANDING CROP (No/m?) • Pr.  i  3 May  5  t r 4*  323  tr 4° 17 May  31 May  6-9  7-14  am  4  tr  4Y  831  ti  4°  am  4  1,061  tr 4° 14 J u n e  am 4  5-13  June  5-13  17  July  5-23  2,285  26  July  5-23  tr 3  5-23  5-18  7 Oct.  63  66  • 0.2  0.3  20  511  0.2  1.0  51 1 26  26  0.2  1.0  80  0.2  0.3  0.2  1.0  24  0.25  1.4  361  167  0.4  1.0  167 459  193  306  0.25  1.5  139  0.2  0.5  70  105  0.1  0.5  53  260  0 . 15  0.5  130  192  0.2  1.0  192  0 . 17  0.5  167  0.15  0.2  334 72  1,103  t r 4°  % Pr.  171  53.0  557  67.0  493  46.5 -  870  361  38.1  12.0  626  20.9  123  10.0  322  23.6  325  23.7  123  1 1 .2  14  288  0.08  0.5  144  170  0.1  0.2  34  0 . 17  0.2  18 71  91  % PREY STANDING CROP REMOVED  I  469  258  f  40  TOTAL PREY REMOVED (No/m 2 ) M.  353  0.08  0.2  5-10  am 4  761  75  0.13  0.2  15  15  2.0  5-10  am 4  735  1 13  0 . 14  0.2  23  75  10.0  262  52 20  5.8  tr 21 O c t .  108  0.5  2,996  1,371  3  " Sept.  0.5  0.1  2,935  am 4  24  0.1  126  24  tr 4° Sept.  215  846  am 4  6  IJ  1.8  1,365  3  5-19  'J  0.6  IX 4 ° 22 A u g .  f. .  J  PREY REMOVED PER PREDATOR TYPE (No/m 2 ) M. .  0.4  l  tr 3  CONSUMPTION /LARVA /DAY  0.45  t r 4° 8 Aug.  PREY DENSITY (No#)  470  tr 4° tr 3  CHAOBORUS STANDING CROP (No/m 2 ) Ch .  • 469  t r 4° 28  predation d i d not occur a r e omlttedJ  5-9  4  am 4  y  345  0.1  0.2  82  0.07  0.1  8  117  0.03  0.1  12 mean M.  =  ( 3 May - 21 O c t . )  314  24.9?  APPENDIX V I I .  PREDATION ON DIAPHANOSOMA. 1971.  ( D a t e s on w h I c h p r e d a t i o n d i d n o t o c c u r a r e o m i t t e d . )  DATE  20  July  T°C  POTENTIAL PREDATORS  17 A u g u s t  3 September  CONSUMPTION /LARVA /DAY  PREY REMOVED PER PREDATOR TYPE (No/m 2 )  7,194  435  5.0  3.0  1,305  148  2.5  1.5  222  64  9.0  5.0  320  3  711  9.0  5.0.  t r 4°  193  5.5  3.0  579  862  6.0  3.0  2,586  am 4  1 16  6.0  3.0  348  tr  4°  222  3.0  1.5  333  3  543  1.0  1.0  543  am 4  168  2.0  1.0  168  1.0  220  2  20  4° 2  14  16  PREY DENSITY (No/4)  Ch.  17  -  CHAOBORUS STANDING CROP (No/m2)  Pr, 1  tr 3 August  PREY STANDING CROP (No/m2)  3  t r 4V  33,503  17,927  f  J  220  2.0  U  TOTAL PREY REMOVED (No/m2)  M. .  M.  % PREY STANDING CROP REMOVED SPr.  I  I J  1,527  21.2  4,454  13.3  3,267  18.2  931  22.1  <: 3,555  mean M  = 2,545  18.7?  (20 J u l y - 3 S e p t . )  I—1 O  APPENDIX V I I I .  C a l c u l a t i o n o f t h e mean d a i l y c o n s u m p t i o n , ( C ) , o f copepod p r e y by C. t r _ . 4 ° i n 1971 and 1 9 7 2 , u s i n g f e e d i n g r a t e s and p r e y a b u n d a n c e d a t a .  IV i C /day tyrelII (kenai)  120 d a y s 1972  1971  t. i  D. f. i  8  5.0  "  16  5 July  18  "  3 Aug.  Date 1 June 14  20  17  "  3 Sept. 16  "  Vl  D. k e n a i f. I  Vi  D. kena i f .t. f. I i  Date  t. i  f. I  f .t. i i  31 May  8  1.5  12  1.0  14  i  8.  40.  2.5  20.  2.0  32.  2.5  40.  14 J u n e  14 •  1.0  1 .8  25.2  1.7  30.6  2.5  45.  28  15  0.5  7.5  1 .4  21 .  15  1 -8  27.  2.5  37.5  17 J u l y  14  0.5  7.  1.5  21.  13  1 .0  13.  3.0  39.  26  "  12  0.5  6.  0.5  14  1.0  14.  2.4  33.6  8 Aug.  12  0  0  1 .0  16  0.5  8.  0  0  6.5  0.5  20  0.3  6.  0.3  6.  \  r> tA  221 • I C /day = - f ^ g kena i = 1.42 D . t y r e l I i / l a r v a / d a y = 1.84 D . k e n a j / l a r v a / d a y  C / d a y = 170.I tyrelIi 120  Copepod b i o m a s s  consumed/Iarva/day  = ( 1 . 4 2 x 5 . 9 u g ) + ( l . 8 4 x 42.7ug) tyrelIi kenai  22 6 24 C /day tyrelIi  "  " Sept. "  13  0.5  16  1.5  15  0.5  84.5 120 =0.70  24. 7.5 C /day kena i  D.tyrelIi/larva/day  Copepod biomass  6. 12. 7.5  0.2  3.2  0  0  103.9 120 0.87  D.kenai/larva/day  consumed/Iarva/day  = ( 0 . 7 0 x 5 . 9 u g ) + ( 0 . 8 7 x 42.7ug) tyrelIi kenai  = 87.1 u g / l a r v a / d a y  =41.3  Caloric intake/larva/day  Caloric intake/larva/day  ug/larva/day  = 8 7 . l u g x 5.4 x I O - 3 c a l  = 4 1 . 3 y g x 5.4 x I O - 3 c a l  = 470 x I 0 ~ 3 c a l / l a r v a / d a y  = 223 x I 0 ~ 3 c a l / l a r v a / d a y  1\J  APPENDIX I X .  C a l c u l a t i o n o f t h e mean d a i l y c o n s u m p t i o n by C . t r . 4 1972 u s i n g t h e e n e r g y b u d g e t e q u a t i o n .  i n 1971 and  A = 68? R = 0.6 p i 0°C  02/mg/hr  1971  , = ( 0 . 6 1 ( 4 . 8 3 x I0"- 5 c a l / u g = 69.5 x I P "  3  0 2 > x 24 h r .  A x C  =  1972  = (42.7 + 69.5) X I 0 "  cal/larva/day  A x C  P t R  P/day 1971  = 0.94 mg  "  940)jg 120 d a y s  =  1 9 7 2  "  x I 0 ~ J cal/ug)  42.7 x I P " 3 c a l / l a r v a / d a y  AP <I J u n e - 30 S e p t . )  - ffjtvs  .'.  7.8 u g / l a r v a / d a y = (7.8X5.47  %7?  cal/larva/day  June - 30 S e p t . ) = 1.80 mg - 0.86 mg  1 9 7 1  5  =  1.15 mg - 0.47 mg  =  0.68 mg  ' 7 «/'.n«/d.y  = (5.7X5.47  x 10  J  cal/ug)  = 31.2 x I 0 ~ 3 c a l / l a r v a / d a y  P t R  = (31.2 + 69.5) x I 0 " 3  cal/larva/day AP(I  =  3  C = 165 x I P " 3 c a l / l a r v a / d a y  .'.  C = 148 x I 0 ~ 3 c a l / l a r v a / d a y  APPENDIX X.  Calculation of the mean dally consumption by C.tr 4° In 1972 using the crop analysis data.  90? of larval population feeds dally Assume that a £.tr_ 4° larva eats 0.9 p_. kenai/day Caloric Intake/C.tr 4°/day = (0.9 D. kenai)(42.7ug/D. kenal)(5.4 x I0~ cal/ug dry wt. copepod) 3  = 207' x IP" cal/larva/day 3  

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