UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Analysis of geographic variation in the antipredator adaptations of the guppy : Poecilia reticulata Seghers, Benoni Hendrik 1973

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A1 S43.pdf [ 13.94MB ]
Metadata
JSON: 831-1.0100947.json
JSON-LD: 831-1.0100947-ld.json
RDF/XML (Pretty): 831-1.0100947-rdf.xml
RDF/JSON: 831-1.0100947-rdf.json
Turtle: 831-1.0100947-turtle.txt
N-Triples: 831-1.0100947-rdf-ntriples.txt
Original Record: 831-1.0100947-source.json
Full Text
831-1.0100947-fulltext.txt
Citation
831-1.0100947.ris

Full Text

AN ANALYSIS OF GEOGRAPHIC VARIATION IN THE ANTIPREDATOR ADAPTATIONS OF THE GUPPY, P O E C I L I A RETICULATA  by BENONI HENDRIK B.Sc,  University  SEGHERS  of B r i t i s h  Columbia,  1967  A THESIS. SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in  t h e Department of ZOOLOGY  We a c c e p t t h i s to  thesis  the required  THE  as c o n f o r m i n g  standard  UNIVERSITY OF BRITISH January,  197 3  COLUMBIA  In  presenting  this  thesis  in  at  the  University  make  it  an a d v a n c e d d e g r e e the t  Library  further  for  agree  freely  this  written  representatives. thesis  for  financial  gain  of  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a  of  Columbia,  British  by  Columbia  for  the  is understood  permission.  Department  of  extensive  be g r a n t e d  It  fulfilment  available  that permission for  s c h o l a r l y p u r p o s e s may  by h i s of  shall  partial  shall  requirements  reference copying of  Head o f  that  not  the  I  agree  and  be a l l o w e d  that  study,  this  thesis  my D e p a r t m e n t  copying or  for  or  publication  without  my  ABSTRACT The explain  main o b j e c t i v e o f  this  study  was  to describe  s e v e r a l features of geographic v a r i a t i o n  isolated  and  semi-isolated populations  o f the  aspects  o f g e o g r a p h i c v a r i a t i o n were c o n s i d e r e d : ( i i ) body  size,  and  reticulata.  (iii)  (i) . Extreme d e v i a t i o n s t h e o r e t i c a l Mendelian  sex  Rivulus  that  v a r i a t i o n was  this  hartii.  the  sex  determination  not  c o r r e l a t e d with Predation  Rivulus  of a small  genetic  (ii) 1969  Populations  Rivulus attacked  o f o v e r 41%  the  revealed  differences in ratios  were  demonstrated but  were  Size-selective predation  t o be  the  sampled  i n body l e n g t h ii  less by  liability  demonstrated  of guppies  that  disadvantage.  showed a s t a b l e p a t t e r n o f v a r i a t i o n  differences  a  dimorphism i n c o l o u r .  Whether c o n s p i c u o u s c o l o r a t i o n i n c r e a s e s yet  behavior.  I n a d d i t i o n , sex  selectively  has  sex  cyprinodontid  a l s o p l a c e d males a t a s e l e c t i v e  males t o p r e d a t i o n  (i)  experiments  c a u s e d by  system.  capture.  main  ( f a v o u r i n g females) from  experiments with  male g u p p i e s were n o t adept at a v o i d i n g  antipredator  Laboratory  not  sexual  Three  r a t i o were c o r r e l a t e d w i t h  p r e s e n c e of dense p o p u l a t i o n s predator,  among  ( T r i n i d a d , West  Indies)  ratio,  guppy, P o e c i l i a  and  and  of  unequivocally. i n 1967  i n body 200%  and  size;  i n weight  iii were d i s c o v e r e d .  In compliance w i t h  was  a significant  negative  and  stream temperature.  size  variation  Bergmann's  correlation  b e t w e e n body  c a n be e x p l a i n e d  as a d i r e c t  to environmental  evidence  f o r microevolutionary differences. a multitude  there size  Though a s u b s t a n t i a l p o r t i o n o f t h e  response  Of  Rule  phenotypic  d i f f e r e n c e s , there  of potential  i s a l s o good  selective  factors that  m i g h t be r e s p o n s i b l e f o r t h i s  genetic diversity,  s i z e - s e l e c t i v e p r e d a t i o n , was  investigated.  Field  and  laboratory  the hypothesis  that  large  evidence  guppies enjoy but  supported  an a d v a n t a g e w i t h  a r e more v u l n e r a b l e  predators  respect to Rivulus  t o l a r g e c h a r a c i d and  s u c h as H o p l i a s m a l a b a r i c u s  c a u s e d by d i f f e r e n c e s i n t h e h a n d l i n g  other  however, i n n a t u r e  f a c t o r s must be (iii)  characid  Field  and c i c h l i d  absent) guppies, shore,  cichlid  efficiency  the i n t e r a c t i o n  of the  of several  considered. observations predators  r e v e a l e d t h a t where  were p r e s e n t  (a) were more r e s t r i c t e d  a potential  predator  lower alarm  threshold.  predation  alta.  a p p e a r e d t o be  (and R i v u l u s  t o the stream  (b) showed a g r e a t e r t e n d e n c y t o s c h o o l ,  evolutionary  predation  and C r e n i c i c h l a  In t h e l a b o r a t o r y , s i z e - s e l e c t i v e p r e d a t i o n  predators,  o n l y one,  a t a g r e a t e r d i s t a n c e , and To a s s e s s  significance  (d) h a d a  t h e f u n c t i o n a l and  of this behavioral  e x p e r i m e n t s were c o n d u c t e d w i t h  c a u g h t and p r e d a t o r - n a i v e  (c) a v o i d e d  variation,  s a m p l e s o f wild-r  (laboratory-bred)  guppies  iv  originating strated ions  from 5 n a t u r a l p o p u l a t i o n s .  that f i s h  either  taken,  exposed to c h a r a c i d s  less vulnerable To  than  those  d e t e r m i n e why  and  or descended, from c i c h l i d s were  exposed t o  the  and  preferences,  predator-naive  d i f f e r e n c e s were f o u n d ally,  these  may  tion  hypothesized  concluded  more  the  observations. populations  geographic  i s c a u s e d by  to d i f f e r e n t i a l  pressures.  In some c a s e s ,  these  differences  are  maintained  apparently  gener-  rapidly.  attributable  flow.  field  that certain  differences  t o gene  reaction distance,  t h a t much o f t h e  i n antipredator behavior  barrier  their  f o r s e v e r a l o f the measures;  l e a r n to avoid predators I t was  g u p p i e s were  Significant interpopulation  were c o n s i s t e n t w i t h  In a d d i t i o n , i t was  relatively  made o f  schooling behavior,  escape motor p a t t e r n s .  populat-  Rivulus.  s e l e c t e d n o n - r a n d o m l y , a c o m p a r i s o n wa,s habitat  T h e s e t e s t s demon^-  genetic  predation  microevolutionary without  a major  varia^  ACKNOWLEDGEMENTS This extend  t h e s i s was s u p e r v i s e d by D r . N. R. L i l e y .  s i n c e r e thanks  t o h i m f o r i n t r o d u c i n g me t o t h e  problem c o n s i d e r e d i n t h i s the manuscript.  study  f o r guidance  Ainscough,  t o my r e s e a r c h  C. S. H o l l i n g ,  i n the Zoology  Sciences, University  St. Augustine,  reading  a n d J . D.  and comments on t h e t h e s i s .  For h o s p i t a l i t y of B i o l o g i c a l  and f o r c r i t i c a l l y  I am a l s o g r a t e f u l  c o m m i t t e e , D r s . A. B. A c t o n , McPhail  I  Trinidad,  S e c t i o n , Department  o f t h e West I n d i e s ,  I am i n d e b t e d t o D r . B. D.  P r o f . F . G. Cope, D r . J . S. Kenny,  and Mr. R. L .  Loregnard. Senator collect  fish  Fisheries maintain  Jeffrey  p e r m i t t e d me t o  on h i s e s t a t e and Mr. Hugh Wood, C h i e f  Officer, fish  Stollmeyer kindly  Ministry  of Agriculture,  a t the Freshwater  Fisheries  a l l o w e d me t o  Research  Station,  Bamboo G r o v e . Miss freely  S h i r e e n Imam and Mr. R o b e r t  of their  time  I profitted  t o help with greatly  from  W. D e F o r e s t  the f i e l d  gave  work.  t h e a d v i c e a n d good  humour o f my f e l l o w s t u d e n t s , e s p e c i a l l y Mr, P e t e r J . Ballin,  Mr. Kim D. H y a t t , Finally,  and Dr. Donald  I t h a n k my p a r e n t s v  L . Kramer.  for their  patience,  and  c h e e r f u l encouragement This  i n v e s t i g a t i o n was  Research C o u n c i l Dr.  throughout t h i s  N. R. L i l e y  o f Canada  financed  study.  by t h e  through operating  and p o s t g r a d u a t e  scholarships  National  grants  to  to myself.  TABLE OF  CONTENTS Page  Abstract  . ,  . . . . . . . . .  Acknowledgements List  of Tables  List  of Figures  i i  ,  v  ,  x i i x  i  v  Chapter 1.  Introduction.  .  1  Main o b j e c t i v e s o f the study. The b i o l o g y relevant 2.  Materials  of Poecilia literature  and Methods  Introduction.  . . . . . . .  reticulata:  . . . . . . . . . . .  . ,  , . ,  . . . . . . . . . . . . . . .  Collection  techniques  Laboratory  populations  . . . . . . . . . . . a t Vancouver  . . . .  Maintenance of f i s h Observation  E c o l o g i c a l measurements  3.  7 10 10 10 12 13  and r e c o r d i n g  Measurements  3  methods  . . . . .  14  . . . . . . . . . .  15  on g u p p i e s  17  The E n v i r o n m e n t  19  Introduction  19  Classification  o f streams  Geographic d i s t r i b u t i o n vii  of f i s h  20 species  . .  20  viii Chapter  Page Predators  o f t h e guppy.  Distribution of  and n a t u r a l h i s t o r y  t h e main p r e d a t o r s  Migration  and d i s p e r s a l 3  Summary o f C h a p t e r 4.  Geographic  Variation  .  .  . . . . . . . . . .  31  o f guppies.  35  .  .  .  .  .  . . . .  .  .  .  .  .  39  i n t h e Sex R a t i o , . . . .  41  •  41  . . . . .  42  Introduction. Sex  ratios  of natural populations  Sex  ratios  of laboratory stocks  Relationship in  Size hypothesis  . . . . . . . . . . . .  49  . . . . . . . . . . . . . .  57  Behavior  hypothesis  Relative  survival  o f the sexes i n  experiments  fish,  . .  60  laboratory stocks  , .  64  . .  64  with wild-caught  B.  Experiments  with  f o r standard of survival  Tests of the behavior  59  . . . . . . . . . .  Experiments  Discussion  58  . . . . . .  A.  Procedure  46  . . . . . .  of predation to variation  the sex r a t i o .  predation  23  . . . . . . . . . .  survival  test.  . . .  71  . . . . .  75  experiments,  hypothesis.  D i s c u s s i o n o f sex d i f f e r e n c e s i n behavior.  82  C o n c l u s i o n and g e n e r a l d i s c u s s i o n o f geographic  variation  Summary o f C h a p t e r  4  .  i n t h e sex r a t i o .  .  .  .  .  .  .  .  .  , . .  ,  83 89  ix  Chapter 5.  Page G e o g r a p h i c V a r i a t i o n i n Body S i z e Introduction.  . . . . . .  92  . . . . . . . . . . . . . . .  92  Body s i z e v a r i a t i o n  i n natural  populations  . . . . . . . . . .  R e l a t i o n s h i p o f body s i z e  and t e m p e r a t u r e  R e l a t i o n s h i p o f body s i z e  and p r e d a t i o n  Evidence  from t h e f i e l d  .  97  . .  103  f o r size  selection  . . . . . .  Experimental  analysis of size  Mechanisms o f p r e d a t o r  and g e n e r a l  geographic  variation  selection  . .  . . . . . . . .  112  i n body s i z e  . . . . .  Geographic V a r i a t i o n i n Behavior. Introduction. Field  Distribution  of behavior  o f guppies  stream environment. Schooling Reaction  123 129 131  , . .  observations  107  discussion of  Summary o f C h a p t e r 5 . . . . . . . . . . . 6.  104  selection for  s i z e d i f f e r e n c e s i n prey. Conclusion  95  f  .  131 132  i n the  . . . . . . . . . .  behavior  133 137  distance to potential  predators  . . . . . . . . . . . . . . .  Motor p a t t e r n s behavior  141  used i n a n t i p r e d a t o r 143  X Chapter  Page Population  d i f f e r e n c e s i n escape  motor p a t t e r n s  148  Summary o f t h e f i e l d of  behavior  Survival value  . . . . . . . . . . . . . .  fish  151  for survival  with wild-caught Relative  survival  , . »  of laboratory stocks.  . ,  (b) R e a c t i o n  161  166  i n the antipredator  of laboratory stocks  (a) M i c r o h a b i t a t  159  of survival  . . . . . . . . . . . . . . .  Geographic v a r i a t i o n behavior  experiments  guppies  Discussion of results experiments  150  of behavioral differences  in wild-caught Conclusion  observations  . . . . . .  169  selection.  170  distance t o predators.  . . .  182  (c) E s c a p e motor p a t t e r n s o f individual (d)  Schooling  Conclusion  fish  behavior.  and g e n e r a l  geographic  188  variation  208  discussion of i n behavior.  . . . .  Summary o f C h a p t e r 6 . . . . . . . . . . . 7.  General The  D i s c u s s i o n and C o n c l u s i o n s .  .  226  . . . . .  231  environment  Coloration Body s i z e  and t h e sex r a t i o ,  217  231 . . . . . . .  232 234  xi  Chapter  Page Antipredator Suggestions  Literature Appendix  cited  ,  behavior  ,  for future research  235 239 244 261  L I S T OF  TABLES  Table 1.  2. 3.  Page C l a s s i f i c a t i o n and p h y s i c a l f e a t u r e s o f s t r e a m s i n t h e N o r t h e r n Range (March-June, 1 9 6 9 ) . , . . . , . , . , . , Natural history predators The  5A. 5B.  fish  predators  a t t h e main s t u d y  areas.  . . . . .  S i t e attachment of guppies i n the P e t i t e C u r u c a y e R. . . . . . . . . . . . . The The  sex r a t i o s o f n a t u r a l p o p u l a t i o n s (1967) sex  ratios  36 .  38  , .  43  of n a t u r a l populations  (1969)  44  6.  The  sex  7.  The  relationship  8.  the presence of f i s h p r e d a t o r s . . . . . . . R i v u l u s abundance i n two s t r e a m s i n 1967 and 1969  9. 10.  ratios  12.  13.  of l a b o r a t o r y populations of the  Sex r a t i o o f g u p p i e s i n 1967 and 1969 P r e d a t i o n by guppies  11.  21  32  principal fish  occurring 4.  o f t h e main  .  ratio  at Blue  R i v u l u s on  i n a 40  sex  liter  . , .  48  to 50 53  Basin ,  male and  female  aquarium  . . . . . . .  54  61  The o r i g i n , s e x , and s i z e o f i n d i v i d u a l C r e n i c i c h l a used i n experiments a t Vancouver  67  Reaction distance of naive a dead C r e n i c i c h l a  81  Predators  and  prey  used  guppies  to  i n E x p e r i m e n t 5.1. xii  . .  109  xiii Table 14. 15.  Page D i r e c t i o n o f change o f mean body i n 18 s i z e s e l e c t i o n t e s t s The  relationship  o f body s i z e  size , .  and  r e a c t i o n distance to a predator. 16.  Predation on  17.  l a r g e and  19.  20.  and  22.  24.  25.  26.  small guppies  117  on  . . . . . . . . . .  The  development of  122  schooling behavior  of guppies  138  in  . . . . . . „ . , .  Relative m o r t a l i t y of wild-caught guppies exposed to p r e d a t o r s R e l a t i v e m o r t a l i t y of naive  119  on  The d i s t r i b u t i o n o f 5 p o p u l a t i o n s o f guppies i n r e l a t i o n to water v e l o c i t y , d e p t h , and d i s t a n c e f r o m t h e s h o r e . . . . .  141 156  laboratory  of guppies exposed t o C r e n i c i c h l a  . .  165  A comparison of the frequency of occurrence of 5 stocks of guppies i n r e l a t i o n to water depth. ,  174  Escape motor p a t t e r n s o f 5 l a b o r a t o r y s t o c k s o f guppies exposed t o a dead Crenicichla  190  C o m p a r i s o n o f p r e d a t o r y s u c c e s s and prey escape behavior f o r 5 l a b o r a t o r y stocks of guppies. . . . . . . . . . . . . .  196  Responses of n a i v e  Guayamare and  guppies to a simulated 27.  . . . . . . . . .  Predation e f f i c i e n c y of Rivulus l a r g e and s m a l l g u p p i e s  stocks 23.  115  Crenicichla  small guppies.  5 populations 21.  of  . . . . . .  P r e d a t i o n . e f f i c i e n c y of Astyanax large  18.  efficiency  112  aerial  Paria predator  Concordance o f b e h a v i o r a l measures on 5 s t o c k s o f g u p p i e s  , . ,  206  taken 220  L I S T OF  FIGURES  Figure 1.  2. 3.  4. 5.  6. 7.  8.  9.  10.  11.  Page Map o f t h e n o r t h e r n h a l f o f t h e i s l a n d o f T r i n i d a d , West I n d i e s , s h o w i n g the major r i v e r systems, . . . . . . . . . .  11  The d i s t r i b u t i o n o f f i s h s p e c i e s i n t h e N o r t h e r n Range r e g i o n  22  A schematic r e p r e s e n t a t i o n of the d i s t r i b u t i o n of the major f i s h s p e c i e s i n the northwest c o r n e r of T r i n i d a d  24  Photograph o f the major f i s h p r e d a t o r s o f t h e guppy . . . . . . . . . . . . . . . .  27  A c o m p a r i s o n o f t h e sex r a t i o o f 13 p o p u l a t i o n s o f g u p p i e s sampled i n 1967 and r e s a m p l e d i n 1969  45  The r e l a t i o n s h i p o f t h e s e x r a t i o t o the r e l a t i v e d e n s i t y o f R i v u l u s .  52  R e l a t i v e s u r v i v a l o f m a l e and f e m a l e guppies i n the experimental s e c t i o n of the P e t i t e Curucaye R i v e r , , ,  63  R e l a t i v e s u r v i v a l o f male and f e m a l e Caparo stock guppies exposed t o Crenicichla.  69  R e l a t i v e s u r v i v a l o f m a l e and f e m a l e g u p p i e s o f two s t o c k s e x p o s e d t o Rivulus  71  P r e d a t o r y b e h a v i o r o f R i v u l u s exposed t o male and f e m a l e g u p p i e s o f t h e Paramaribo stock . . . . . . . . . . . . . .  78  The r a t i o o f p r e d a t i o n a t t e m p t s t o successful captures f o r Rivulus f e e d i n g on male and f e m a l e g u p p i e s  79  xiv  . . . . .  xy Figure 12. 13.  14. 15.  16. 17. 18.  19.  20.  21.  22.  23.  24.  Page The body s i z e o f a d u l t male g u p p i e s c o l l e c t e d a t 20 s i t e s i n 1969, . . . . . . .  96  A c o m p a r i s o n o f t h e body s i z e o f a d u l t male g u p p i e s f r o m 13 p o p u l a t i o n s sampled i n 1967 and r e s a m p l e d i n 1969  98  The r e l a t i o n s h i p o f mean body s i z e of a d u l t males t o stream temperature  . . . .  The r e l a t i o n s h i p o f R i v u l u s body s i z e t o t h e s i z e o f g u p p i e s t a k e n as prey Size selection experimental  105  by p r e d a t o r s on 18 populations o f guppies  The d i s t r i b u t i o n o f a d u l t g u p p i e s across a s e c t i o n of the P a r i a River,  101  I l l . . . .  136  Relative s u r v i v a l of wild-caught f e m a l e g u p p i e s o f two p o p u l a t i o n s exposed t o e i t h e r a s i n g l e C r e n i c i c h l a o r two Hop 11 as , .• ,  158  D e p t h p r o f i l e o f s p o n t a n e o u s swimming behavior of 5 laboratory stocks of guppies,  173  Habitat selection of 5 laboratory stocks of guppies placed i n a depth g r a d i e n t . . . . . . . . . . . . . . .  179  Reaction distance of 5 laboratory s t o c k s o f g u p p i e s t o a dead Crenicichla  , . , .  186  R e l a t i o n s h i p o f escape motor p a t t e r n s t o s u r v i v a l t i m e i n two l a b o r a t o r y stocks o f guppies exposed t o R i v u l u s  . . . .  199  T e s t apparatus used f o r measuring t h e responsiveness of laboratory stocks o f Guayamare and P a r i a g u p p i e s t o a simulated a e r i a l predator.  202  Mean i n d e x o f c o h e s i o n f o r f i v e l a b o r a t o r y stocks o f guppies  211  xvi  Figure 25.  Page P r e d a t o r y b e h a v i o r o f R i v u l u s exposed t o e q u a l numbers o f P a r i a and Lower A r i p o guppies ( l a b o r a t o r y stock)  216  CHAPTER 1 INTRODUCTION An natural  animal  f a c e s many c h a l l e n g e s  environment.  influence  Numerous b i o t i c  the l i k e l i h o o d  offspring.  Most animals  survival—predation. populations risk  In t h i s  functional,  predator-prey  systems a t  or evolutionary  level.  a t t e m p t t o measure t h e i m p a c t o f p r e d a t o r s  the  number o f p r e d a t o r s  (e.g. R i c k e r ,  and how i n t u r n p r e y that a given  1954; H u f f a k e r  level,  factors controlling  of the predator  density  area  e t a l , 1963).  a r e emphasized, p a r t i c u l a r l y  behavior  a,re a d a p t e d t o t h e  e c o l o g i s t s work p r i m a r i l y a t t h e n u m e r i c a l  numbers o f p r e y  prey  fish  u s u a l l y study  the  functional  produce v i a b l e  <  the numerical,  level—they  factors  t h e s i s I examine how n a t u r a l  of a small t r o p i c a l  Biologists  Population  will  i ni t s  a common c h a l l e n g e t o  of predation.  either  and a b i o t i c  t h a t an a n i m a l share  to survival  (e.g.  on  governs  can support At the  t h e consumption o f  t h e p h y s i o l o g y and  I v l e v , 1961; H o l l i n g , 1966;  Beukema, 196 8 ) . The  third  level  a t w h i c h we c a n v i e w a  s y s t e m i s t h e more g e n e r a l  evolutionary level;  made t o measure t h e c o n t r i b u t i o n o f p r e d a t i o n 1  predator-prey an a t t e m p t i s to natural  2 selection  i n the prey  (e.g. C a i n  Kettlewell,  1961;  This  approach adopted  i s the The  lations is  not  Curio,  1969,  populations  Occasionally  are  o f the  isolated  relatively  by  are  of the  few  o r how  popu-  Often i t effectively exchange.  i s d i s c o v e r e d where s e v e r a l isolated  short distances  the  prey  i n t e r m s o f gene  same s p e c i e s a r e  to assess  on  directly.  important  isolated  predation pressures.  opportunity  1969).  here.  a natural situation  populations  1954;  1970a; M c P h a i l ,  d i f f i c u l t to assess  known what p r e d a t o r s  different  Sheppard,  e v o l u t i o n a r y impact of p r e d a t o r s  i s normally  the prey  one  1965,  and  and  or  are  This presents  semiexposed  to  an e x c e l l e n t  impact of p r e d a t i o n because i t i s  ecological  f a c t o r s t h a t v a r i e s among  the  populations. A situation H a s k i n s and Poecilia native  co-workers  reticulata  t o the  Caribbean  of t h i s  rivers  islands.  frequency  and  colour patterns in  fish  species.  of north-east On  the  island  an  selection,  freshwater  genes  (expressed  t h a t two  (cross-selection),  some Indies,  controlling only  predaceous  opposing  i n the d i r e c t i o n  guppy,  between  phenotypically  one,  P.  fish  o f T r i n i d a d , West  the presence or absence o f  driving  of the  apparent c o r r e l a t i o n  They s u g g e s t e d  C.  S o u t h A m e r i c a and  linkage of c e r t a i n  f o r c e s were a t p l a y sexual  r e p o r t e d by  Peters, a t r o p i c a l  of guppies  t h e male) and  was  (1961) f o r p o p u l a t i o n s  Haskins e t a l d i s c o v e r e d the  type  selective  possibly o f more  3 conspicuous selecting  body m a r k i n g s and  the o t h e r , p r e d a t i o n ,  f o r a more c r y p t i c male p h e n o t y p e .  This predator-prey interaction inviting of t h i s in  f o r a comparative  r e s e a r c h I intended to study  relation  to geographic  i n mind t h a t  discovered.  of microgeographic  i n both w i l d Because  variation  fish  I felt  and  this  behavior thesis  time  (Chapter  bearing  behavioral variathat  i n b e h a v i o r does  of behavior,  Nevertheless  4)  (Chapter  5).  as w e l l  term  of  Main o b j e c t i v e  of the  a  exist  into  devoted  include i n  w i t h the  as an  and  this  "Haskins  analysis of  variation  c a n be  in  the  i n body that  size  these  c o n s i d e r e d under  "antipredator adaptations".  study  main o b j e c t i v e significance  t i o n s o f t h e guppy and  I  a b l e to demonstrate  three aspects are i n t e r r e l a t e d the c o l l e c t i v e  I do  of geographic  I hope t o be  v a r i a t i o n m i g h t be  predators  study of p o p u l a t i o n d i f f e r e n c e s  6).  significance  evolutionary  by  d i s c o v e r y m i g h t g i v e some i n s i g h t  adaptive  The  selection  laboratory-reared offspring.  t h e o r i g i n a l work c o n c e r n e d  hypothesis"  At the o u t s e t  in coloration,  variation  their  to the  (Chapter  very  I t soon became o b v i o u s  t h e mechanisms o f t h e e v o l u t i o n most o f my  study.  a d d i t i o n a l m o r p h o l o g i c a l and  t i o n m i g h t be wealth  ethological  appeared  of t h i s  of natural  to determine  related  s t u d y was  to assess  variation  i n popula-  t o what e x t e n t  t o the d i s t r i b u t i o n  the  and  this abundance  4 of aquatic predators.  Three aspects  o f t h i s p r o b l e m were  considered: 1.  Sex r a t i o Though p o p u l a t i o n  fish not  are normally present  variation  n o t g e n e t i c a l l y d e t e r m i n e d and h e n c e do  an e v o l u t i o n a r y p r o b l e m p e r s e , I s t u d i e d  i n some d e t a i l  c o u l d be v a l u a b l e  clues  s e l e c t i o n by p r e d a t o r s  Body  or other  of differential  f a c t o r s on c o l o u r  size t h a t a n i m a l body  growth r a t e s a r e i n f l u e n c e d by b o t h g e n e t i c mental f a c t o r s . environmental  3.  s i z e and  and e n v i r o n -  I wished t o determine i f p r e d a t i o n  f a c t o r s m i g h t be r e s p o n s i b l e  variation  i n the size  of adult  or other  f o r microgeo-  fish.  Behavior The  of guppies. populations of  patterns  basis).  There i s abundant evidence  graphic  this  because sex r a t i o d i f f e r e n c e s t o the nature  (which do have a g e n e t i c 2.  d i f f e r e n c e s i n the sex r a t i o s o f  third  aspect  concerns the a n t i p r e d a t o r  I wanted t o d e s c r i b e i n nature  some o f t h e s e  wished t o t e s t  the v a r i a t i o n  natural populations.  the s u r v i v a l  value  My o v e r a l l  in  the behavior  of natural populations  More i m p o r t a n t l y ,  In p a r t i c u l a r  o f the behavior  adaptive?).  the d i s t r i b u t i o n  among  and among l a b o r a t o r y - r e a r e d o f f s p r i n g  it  with  behavior  hypothesis  (how i s  was t h a t d i f f e r e n c e s w o u l d be c o r r e l a t e d  and abundance o f t h e m a j o r  I p r e d i c t e d these  I  predators.  d i f f e r e n c e s w o u l d be  5 heritable. To  falsify  demonstrate t h a t persist  behavioral  It indeed of  i s fair  t o ask a t t h i s  sensitive to detect  point  i f such a study i s  of comparative  variation i n antipredator  a l l animal  important  such a study  relative  stocks are  s a m p l e s and t h a t  There i s a p a u c i t y  (and many p l a n t )  adaptations.  devices  g r o u p s and a r e There-  could  f o r the  have i m p l i c a t i o n s n o t o n l y  b i o l o g i s t who i s a t t e m p t i n g  of local  populations  (e.g.  the impact o f p r e d a t o r  subsequent behavior and  t o assess  morphological  such c o n d i t i o n s ?  concerned  What'behavioral  w o u l d be s e l e c t e d f o r u n d e r  How r a p i d l y c o u l d p r e y  counteradaptations.  evolve? These q u e s t i o n s  with  i n t r o d u c t i o n s on t h e  of the prey population.  characters  i n the  E h r l i c h and  Raven, 1 9 6 9 ) , b u t a l s o t h e a p p l i e d b i o l o g i s t predicting  occur i n  i m p o r t a n c e o f s e l e c t i o n and gene f l o w  differentiation  data  to the s u r v i v a l of the species.  "pure" e v o l u t i o n a r y the  of f i e l d  i s . s u r p r i s i n g because a n t i p r e d a t o r  vitally fore  conditions, i n the  i f present.  necessary.  virtually  i n n a t u r e does n o t  laboratory  t e s t s are s u f f i c i e n t l y  intraspecific  This  assumes t h a t  representative  differences,  i t w o u l d be n e c e s s a r y t o  r a i s e d under c o n s t a n t  This  genetically  hypothesis  the v a r i a t i o n observed  i n fish  laboratory.  this  a r e a l s o r e l e v a n t when man, i n  6 harvesting predator  a natural population,  (Miller,  of population important  1957).  acts  More s p e c i f i c a l l y ,  v a r i a t i o n i n defensive  in fish  (1971) r e f e r r i n g  as a s e l e c t i v e  s t o c k i n g programs.  behavior  behavior  c o u l d be  Raleigh  to trout f r y migrations  t o match t h e i n n a t e  an a p p r e c i a t i o n  and Chapman  stated,  "failure  o f t h e donor p o p u l a t i o n  to the  r e q u i r e m e n t s o f t h e r e c i p i e n t environment has l e d t o f a i l u r e o f many  fish  Calaprice  transplant efforts  i n the past  (1969) h a s warned, t h e c o n t i n u o u s  ill-adapted  fish  mean p o p u l a t i o n  to a natural population fitness  (p. 3 9 ) . " As stocking of  can decrease the  and p o s s i b l y c u l m i n a t e i n l o c a l  extinctions. My s t u d y i s a l s o r e l e v a n t genetics, behavioral and this  a field  Bruell  of behavioral  l a r g e l y t o t h e measurement o f  d i f f e r e n c e s among i n b r e d  Drosophila. field  devoted  to the science  s t r a i n s o f mice,  (1967) h a s c r i t i c i z e d  and made some u s e f u l s u g g e s t i o n s  past  rats,  work i n  f o r future  research: The w i l d b a s e p o p u l a t i o n s f r o m w h i c h t h e a n c e s t o r s o f o u r l a b o r a t o r y s t r a i n s were drawn a r e s h r o u d e d by t h e m i s t o f i n c o m p l e t e r e c o r d s and t h u s , i n most c a s e s , we do n o t know a n y t h i n g a b o u t t h e n a t u r a l e n v i r o n m e n t a l c o n d i t i o n s under which the founders o f o u r s t r a i n s evolved. Work w i l l have t o s t a r t w i t h p r o p e r samples o f i n d i v i d u a l s drawn f r o m l o c a l w i l d p o p u l a t i o n s w h i c h e v o l v e d u n d e r d i s t i n c t and w e l l - k n o w n e n v i r o n m e n t a l conditions. . I n v e s t i g a t i o n o f forms o f b e h a v i o r c h o s e n on t h e b a s i s o f e v o l u t i o n a r y c r i t e r i a i s p r o b a b l y t h e most c r i t i c a l requirement o f future behavior-genetic analyses.  7 To go b e y o n d i n t u i t i o n and t o u n d e r s t a n d t h e adaptive s i g n i f i c a n c e o f a b e h a v i o r , we must know t h e e n v i r o n m e n t a l c o n d i t i o n s u n d e r w h i c h i t o c c u r s and how i t v a r i e s as e n v i r o n m e n t a l c o n d i t i o n s v a r y . (pp. In t h i s  research  Bruell's  I shall  m o r p h o l o g y and  the  problem of n a t u r a l v a r i a t i o n i n  behavior of  encompassing a g r e a t evolutionary natural  and  to assess  My  is ironical  main aim  that  time  (about  culture,  b e e n u s e d as  tissue these  ranging  studies The  cal  guppy has  studies.  g a t e d by  domestic  Noble  the  guppy  and  and  the  guppy  guppy i s s m a l l ,  adapts r e a d i l y to  and  been the sexual  the  subject  to  In most  guppy were of  several  Haskins  of  used. ethologi-  s e l e c t i o n have b e e n  (1938), H a s k i n s and  in  organism  gerontology  mutation research.  has  aquarium  a convenient bioassay  s t r a i n s of  Aspects of  on  ecologist.  3 months), i s always  from t o x i c o l o g y  transplantation  some o f  f a m i l i a r to a l l  unknown t o t h e  Because the  supply,  i t has  of  and  significance.  exists for studies  good c o m m e r c i a l  studies  i s to i d e n t i f y  a species  is virtually  conditions.  generation  complex,  reticulata;  meagre l i t e r a t u r e  under n a t u r a l  the  of ecology, ethology,  i t s evolutionary  amateur a q u a r i s t s  in  i s very  v a r i a t i o n i n Trinidad populations  The b i o l o g y o f P o e c i l i a relevant literature It  animal species  portion  biology.  the  a short  some o f  recommendations. Clearly  A very  endeavour to implement  284-286)  investi-  (1949, 1 9 5 0 ) ,  and  8 (1961).  Haskins e t a l  Liley  (1966) has  e x a m i n e d how  guppy i s e t h o l o g i c a l l y i s o l a t e d f r o m t h r e e , o t h e r poeciliid  fish.  male guppy has (Brederand  The  conspicuous courtship  a t t r a c t e d the  Coates,  1935;  B a e r e n d s e t a l , 1955; The 1922b, 1927)  and  e x t e n d e d by primarily in  Clark  sex-linked  Ditlevsen  the  s u b s e q u e n t l y been c o n f i r m e d and  Haskins  1951;  o f Winge  (1922a,  (1948)(recently  have e s t a b l i s h e d  guppy.  pattern  the  inheritance  Winge's f i n d i n g s  for natural populations  (1951, 1954)  Laboratory populations  and of  the  Haskins e t a l  1944;  regulation  Rose, 1959;  Kosobutskii,  ( B r e d e r and  S i l l i m a n and  However, no  dynamics of n a t u r a l  populations.  A d d i t i o n a l work o f studies  of  feeding  (Svardson,  1943,  G i b s o n and  H i r s t , 1 9 5 5 ) , and  Useful Waldman  d a t a on  ( 1 9 6 9 ) , and The  has  and  Davis,  1959;  Shoemaker, Geodakyan  ever  studied  1968),  Bertalanffy,  i n Lang  (1965,  includes  1938; 1961).  1967),  (1970). zoogeography o f  the  and  the  growth  l o n g e v i t y . (Comfort,  given  Protasov  systematics  1964;  i n Aim,  v i s i o n are  one  used  of  ecological significance  (Hester,  cited  1932;  G u t s e l l , 1958;  1972).  by  guppy have b e e n  Coates,  have  (1961).  as m o d e l s y s t e m s f o r i n v e s t i g a t i n g s e v e r a l a s p e c t s population  the  1961).  studies  nature of colour  s t r a i n s of  behavior of  Aronson,  Tucker,  H a s k i n s e t a l , 1970)  laboratory  Haskins  and  genetical  Winge and  sympatric  a t t e n t i o n o f numerous w o r k e r s  Rosen and  pioneering  the  family  Poeciliidae  have b e e n r e v i e w e d by Rosen and B a i l e y  Avoidance behavior laboratory  studies  h a s b e e n i n v e s t i g a t e d i n two  (Werboff and L l o y d ,  1967b).  Williams  behavior  and S c h u t z  (1963).  (1964) has b r i e f l y  196 3; R u s s e l l , 1967a  considered  (1956) t o u c h e d upon t h e  schooling  relationship  between pheromones and t h e " f r i g h t r e a c t i o n " . Finally geographic  there  variation  three populations companion t o my  i s the study  by B a l l i n  (1973) o f  i n c o u r t s h i p and a g g r e s s i v e  of T r i n i d a d guppies.  This  r e s e a r c h because the study  on s i m i l a r  genetic m a t e r i a l but explored  behavioral  parameters.  behavior  o  i s a valuable  was  carried  a different  out  set of  CHAPTER 2 MATERIALS  AND  METHODS  Introduction This tory  research  study.  The f i e l d  made i n t h e r i v e r s the  island  observations  o f T r i n i d a d , West I n d i e s  conditions  and c o l l e c t i o n s were  ( F i g . 1) and t h e b u l k  work was c o n d u c t e d u n d e r c o n t r o l l e d  work i n T r i n i d a d was b a s e d on two f i e l d  The f i r s t  introduction  of these  (June-August,  observations,  and c o n d u c t  These c o l l e c t i o n  periods  include parts  an  me t o 1967  wild  o f t h e wet  fish.  (June-  seasons.  techniques  G u p p i e s were c o l l e c t e d w i t h  nets,  e x t e n d my  some e x p e r i m e n t s w i t h  O c t o b e r ) a n d d r y (November-May)  to c o l l e c t  1967) p r o v i d e d  ( M a r c h - J u n e , 1969) a l l o w e d  make more d e t a i l e d c o l l e c t i o n s o f f i s h ,  a fine  expedi-  t o the problem of v a r i a t i o n i n T r i n i d a d  g u p p i e s and t h e s e c o n d  or  labora-  i n the l a b o r a t o r y .  The  Collection  and  o f t h e N o r t h e r n Range M o u n t a i n r e g i o n o f  of the experimental  tions.  i s a combination of f i e l d  "one-man  seine".  the predators  castnet,  a fine  circular  dipnet  A v a r i e t y o f methods were  including dipnets,  and h o o k - a n d - l i n e . 10  seines,  The c a s t n e t  used  gill-  proved  t o be  11a  FIGURE 1.  Map  o f the northern  half  of the i s l a n d  of Trinidad,  West I n d i e s , s h o w i n g t h e m a j o r r i v e r s y s t e m s . Collection  no.  1 2 3 4 5 6 7 8 9 10 11 12 . 13 14 15 16 17 18 ' 19 20 20a 21 22 23  a r e i n d i c a t e d by numbers c o r r e s -  p o n d i n g t o t h e key b e l o w .  I n s e t map  the p o s i t i o n  j u s t o f f the n o r t h -  east coast  Map  sites  o f the i s l a n d  indicates  of Venezuela.  Name o f s t r e a m S i e r r a Leone Road Blue Basin Maracas V i l l a g e Upper Curumpalo Lower Curumpalo Grande C u r u c a y e P e t i t e Curucaye Santa Cruz Caroni Guayamare Caparo Lower T a c a r i g u a Upper T a c a r i g u a Upper A r o u c a Yarra Marianne Lower P a r i a Upper P a r i a Upper Guanapo Upper A r i p o ( N a r a n j o ) Upper A r i p o ( C r o s s i n g ) Lower A r i p o Oropuche Tompire T r i b u t a r y  Standard abbreviation SLR BB MV UCur LCur GCur PCur SC Car Guay Cap LTac UTac UArouc Yar Mar LPar Par UGuan UA(N) UA(X) LA Oro TT  12 the  b e s t way t o c a p t u r e Collections  poses. of  the larger f i s h  o f g u p p i e s were made f o r s e v e r a l  An i n s t a n t "dead" c o l l e c t i o n was made a t e a c h  i n t e r e s t by p l a c i n g t h e f i s h  directly  solution.  This  characters  and d e t e r m i n e t h e s e x r a t i o .  was  pursite  i n t o a 10% f o r m a l i n  c o l l e c t i o n was u s e d t o measure m o r p h o m e t r i c  made a t c e r t a i n s i t e s  ments i n T r i n i d a d , at  predators.  to obtain:  (2) f o u n d e r s  A "live"  collection  (1) f i s h  f o r experi-  f o rlaboratory  populations  V a n c o u v e r , Canada a n d (3) m a l e s f o r t h e a s s e s s m e n t o f  variation  i n colour  patterns  (Liley  and Seghers,  unpublished  data). E v e r y e f f o r t was made t o c o l l e c t sentative  sample f o r e a c h s t r e a m .  fluctuated at  a random,  Because d e n s i t i e s  f r o m s t r e a m t o s t r e a m , more t i m e was  some s i t e s  to collect  repre-  sufficient  numbers  required  for statistical  comparisons.  Laboratory  populations  Live 1967  fish  and 1969.  a t Vancouver  were s h i p p e d  by a i r t o V a n c o u v e r i n b o t h  These shipments i n c l u d e d  predators  a n d samples o f g u p p i e s t a k e n  streams.  Samples f r o m d i f f e r e n t  As  many f i s h  that  as p r a c t i c a l l y  the laboratory  "stocks") natural  from  representative  s t r e a m s were k e p t  f e a s i b l e were s h i p p e d  populations  isolated. to insure  ( r e f e r r e d t o h e r e a f t e r as  w o u l d be r e p r e s e n t a t i v e counterparts.  several species of  of their  respective  13 In and  a l l c a s e s no f e w e r  than  25 m a t u r e m a l e s were u s e d  tures.  50 l a r g e g r a v i d  to start  the laboratory  I n 1969 t h e m a j o r i t y o f t h e s t o c k s s t a r t e d  were r e p l e n i s h e d o r r e p l a c e d w i t h f r e s h was  as  i n 1967 This  i n laboratory  i . e . t o m a i n t a i n as much o f t h e n a t u r a l  variability  possible. A total  and  cul-  collections.  done t o a v o i d i n b r e e d i n g and s e l e c t i o n  stock,  females  fish  o f 2 3 s i t e s were s a m p l e d  d e r i v e d from  behavioral  studies  by o t h e r w o r k e r s unpubl.;  Liley,  comparative others,  a t Vancouver.  unpubl.).  Ballin,  I selected  1973;  of  glass  found  (24-28°C).  were k e p t  numerous a q u a r i a . mixed t o reduce  Morrell,  several  Surinam  experiments.  fish  40 and 60 l i t e r i n nature  used  5 stocks f o r the  Kreek), f o r various other  f r e s h w a t e r f i s h were u s e d .  The  unpubl.;  one s t o c k f r o m P a r a m a r i b o ,  Standard procedures  locality  S e v e r a l s t o c k s were  s t u d y o f a n t i p r e d a t o r b e h a v i o r and u s e d  (Sommeldijske  ( F i g . 1)  10 o f t h e s e were s e l e c t e d f o r  (Henderson,  including  Maintenance  i n Trinidad  f o r the c u l t u r e Guppies  W i t h i n each  at  from each  s e p a r a t e and b r e d  tropical  were h o u s e d m o s t l y i n  aquaria maintained Fish  of  temperatures geographic  i n mass c u l t u r e i n  s t o c k f i s h were  i n b r e e d i n g and p r e v e n t g e n e t i c  periodically drift.  p r e d a t o r s were h o u s e d i n g l a s s o r w o o d - a n d - g l a s s  t a n k s o f 40 t o 400 l i t e r s ;  i n Trinidad  the l a r g e r  14 i n d i v i d u a l s were k e p t of  700 t o 1600 All  side,  ( i n d o o r and  outdoor)  liters.  a q u a r i a were f i t t e d  or inside  approximately used  i n concrete pools  filters.  with  The t a n k  4 cm o f l i g h t - b r o w n  f o r experiments  either  sub-gravel,  f l o o r s were c o v e r e d fine  sand.  outwith  Aquaria not  contained water p l a n t s ( C e r a t o p t e r i s  sp.,-Lemna s p . , S a g i t t a r i a  sp.).  I l l u m i n a t i o n was p r o v i d e d by c o o l w h i t e f l u o r e s c e n t tubes  mounted 20-30 cm above t h e w a t e r s u r f a c e .  was c o n t r o l l e d connected light—12  by I n t e r - m a t i c a u t o m a t i c  t o the l i g h t s ;  fish  switches  t h e s t a n d a r d p h o t o r e g i m e was 12  dark.  ;  G u p p i e s were f e d d a i l y w i t h dry  time  Photoperiod  food supplemented  chopped, l i v e  finely-ground Clark's  s e v e r a l times  T u b i f e x worms.  per- week  with  The p r e d a t o r s were f e d on  whole o r chopped T u b i f e x supplemented i r r e g u l a r l y w i t h guppies. and  Special  will  f e e d i n g regimes were.used'for  be d e s c r i b e d i n t h e a p p r o p r i a t e  live  experiments  experimental  sections.  Observation  and r e c o r d i n g methods  Trinidad. are e a s i l y  observed  the p r e d a t o r from  from  t h e edge o f a s t r e a m .  s p e c i e s may be o b s e r v e d  a bridge over  the p r e d a t o r s  Under most c o n d i t i o n s i n n a t u r e ,  a stream.  (and g u p p i e s  Several of  i n t h i s way a l s o , o r  U s u a l l y upon i n i t i a l  at certain  guppies  sites) w i l l  approach, f l e e and  15 move t o d e e p e r w a t e r o r h i d e or  leaf detritus.  minutes the f i s h  under b o u l d e r s ,  I found t h a t i f I s a t q u i e t l y resumed' t h e i r  normal a c t i v i t y .  observations  underwater u s i n g  observations  were made a t n i g h t w i t h  Behavioral field The with  Angus  I a l s o made  patterns  recorded  into a  tape-recorder.  was' m e a s u r e d i n t h e f i e l d  a stopwatch.. Vancouver.  able  f o r a few  a headlamp.  i n f o r m a t i o n was d i r e c t l y  of behavior  logs,  a s n o r k e l and f a c e mask; a few  notebook o r d i c t a t e d i n t o a p o r t a b l e  duration  submerged  More s o p h i s t i c a t e d e q u i p m e n t was  at Vancouver—both  Rustrak  avail-  (4-channel) and E s t e r l i n e -  ( 2 0 - c h a n n e l ) e v e n t r e c o r d e r s were u s e d t o r e c o r d t h e  frequency  and d u r a t i o n  a key c o r r e s p o n d i n g  of behavior  patterns.  t o a b e h a v i o r a l event  These w i l l  other  moving  methods were u s e d t o s t u d y  be i n c o r p o r a t e d  depressing  (1 k e y p e r c h a n n e l )  a p e r m a n e n t r e c o r d was made on a c o n t i n u o u s l y Several  By  i n t o the s p e c i f i c  chart.  behavior.  experimental  sections. Ecological  measurements  A d e t a i l e d . l i m n o l o g i c a l survey this  study  important  was n o t w a r r a n t e d f o r  b u t I d i d want q u a n t i t a t i v e m e a s u r e s o f t h e most v a r i a b l e s t h a t might a f f e c t  fish.  the behavior  of the  • (a)  observation  Stream dimensions. site  A t e a c h c o l l e c t i o n and'  I measured t h e average d e p t h and w i d t h o f  16 the  stream  and r e c o r d e d  changes caused  (b) Water v e l o c i t y . surface  float  A s e p a r a t e measurement was made . f o r t h e  p o r t i o n o f t h e stream  i n h a b i t e d by g u p p i e s  (microhabitat).  t h e mode o f 5 t o 10 r u n s was u s e d . .  (c) Volume o f f l o w using  was m e a s u r e d w i t h a  placed i n the centre o f a representative  s e c t i o n o f stream.  In e a c h c a s e  Velocity  by r a i n f a l l .  the standard  formula  (discharge).  T h i s was c a l c u l a t e d  g i v e n by Needham a n d Needham  (1962: 1 0 4 ) . (d) T e m p e r a t u r e . nearest  0.1°C w i t h  T e m p e r a t u r e was m e a s u r e d t o t h e  a mercury thermometer p l a c e d i n t h e  m a i n s t r e a m and t h e m i c r o h a b i t a t s .  relative  (e) p_H.  Fresh Hydrion  pH p a p e r .was . u s e d  acidity  or'alkalinity  o f t h e water.-  v a l u e o f s e v e r a l d e t e r m i n a t i o n s was (f) DH.  a Rila  H a r d n e s s T e s t K i t and a l l d e t e r m i n a t i o n s were  turbid,  an i m p r o v i s e d  attenuation  of  ranging  stream  S e c c h i d i s c was u s e d  (degree  c o v e r was e s t i m a t e d from  no shade  (i)  Substrate.  Water  replicated.  I n t h e few s t r e a m s t h a t were •  of l i g h t with  (h) Shade  The modal  used.  H a r d n e s s was m e a s u r e d w i t h  (g) T u r b i d i t y .  t o measure  t o measure t h e .  depth. o f overhead  cover).  The amount  on a s e m i - q u a n t i t a t i v e 5 - p o i n t (0) t o c o m p l e t e  scale  shading (4).  C o l o u r p h o t o g r a p h s were t a k e n  of the  bottoms. (j) Other  fish  species.  An a t t e m p t  was made t o  collect  a l lfish  s p e c i e s t h a t were  lations  o f t h e guppy.  Stomach  c o n t e n t s were  (k) P o p u l a t i o n e s t i m a t e s . n o t made f o r most  streams  comparison  gave a r o u g h  of guppies  and o t h e r f i s h  was  removed;  analysed.  An a c c u r a t e c e n s u s  although a  species.  i n another  was  "catch-per-unit-effort"  estimate of the r e l a t i v e  C u r u c a y e ) a 35 m e t r e s e c t i o n was were  s y m p a t r i c w i t h t h e popu-  I n one  abundance  stream  (Petite  s c r e e n e d o f f and a l l f i s h  (Paria) a v i s u a l  count of guppies  made.  Measurements  on  guppies  (a) Sex r a t i o .  The guppy  mature males a r e i d e n t i f i e d (modified Immature fully  immature m a l e s i s u n c e r t a i n thesis  m a l e s p e r one  sex o f f i s h  or  s m a l l e r than  and t h e y a r e c l a s s e d  as  immature.  as t h e number o f  Two  measurements  o f l e n g t h were  ( t i p o f snout t o p o s t e r i o r  and t o t a l  length  t h e n e a r e s t 0.1 mm. t h e n e a r e s t 0.5 fish  made,  end o f c a u d a l  (tip* o f snout t o t i p o f  Some s a m p l e s were m e a s u r e d w i t h s l i d i n g  Live  markings.  female.  length  peduncle)  The  I e x p r e s s t h e sex r a t i o  (b) L e n g t h . standard  developed colour  gonopodium  l a c k c o l o r a t i o n b u t show a p a r t i a l l y  d e v e l o p e d gonopodium.  In t h i s  dimorphic—  by t h e p r e s e n c e o f a  a n a l f i n ) and f u l l y m a l e s may  i s sexually  vernier  tail).  calipers  to  O t h e r s were m e a s u r e d w i t h a r u l e r t o  mm. used  i n experiments  were m e a s u r e d t o t h e  18 nearest  0.5 mm  total  length.  The f i s h were p l a c e d  from t h e water i n t o a d r y p e t r i moving  This  be t h e most e f f i c i e n t fish  method t o measure t h e t h o u s a n d s o f  i n this  thesis are t o t a l  (c) W e i g h t . nearest  .001 g.  length  e x c e p t where  fluid  patterns.  variation  method was d e v e l o p e d  f i s h were p l a c e d prior  fish  ice-water.  To r e c o r d  on a p a p e r  i n d i v i d u a l and  i n the c o l o r a t i o n o f males, a s c o r i n g (Liley  and Seghers, unpubl.) f o r  Colour  patterns  t h a t had been f r e s h l y  were a s s e s s e d killed  individuals.  b l u e and on w i l d -  by i m m e r s i o n i n  In a d d i t i o n c o l o u r photographic  made o f t h e same  another  t o weighing.  r e d - o r a n g e - y e l l o w , and i r i d e s c e n t (mainly  green) markings.  fish  designated.  The p r e s e r v e d  (d) C o l o u r  caught  study.  A few samples were w e i g h e d t o t h e  t o w e l t o remove s u r f a c e  population  this  l e n g t h measurements o f g u p p i e s and o t h e r  measurement i s s p e c i f i c a l l y  black,  stopped  c a u s e d no m o r t a l i t y a n d p r o v e d t o  t h a t were u s e d d u r i n g  All given  When t h e f i s h  (few s e c ) , a r u l e r was p a s s e d u n d e r t h e d i s h t o  measure t h e l e n g t h .  live  dish.  directly  slides  were  CHAPTER 3 THE  ENVIRONMENT  Introduction Beebe  (1952) h a s g i v e n a g e n e r a l a c c o u n t  geography, c l i m a t i c  conditions,  and p l a n t  assemblages o f T r i n i d a d w i t h s p e c i a l Valley.  This valley  Mountains  near  r e f e r e n c e t o the Arima  i n the Northern  Range  Beebe d i d n o t  f a u n a n o r was any a t t e n t i o n  given to the  ecosystem. A  Joseph  and a n i m a l  t h e c e n t r e o f my s t u d y a r e a .  deal with the f i s h stream  i s located  of the  s t u d y o f t h e M a r a c a s R.  (tributary  R., s e e F i g . 1) by T h o r n h i l l  of the St.  e t a l (1966)  indicated  t h e m a i n f o o d webs i n t h e s t r e a m  and d e s c r i b e d t h e m i c r o -  habitat  species.  distribution  treatment with  o f t h e e c o l o g y o f streams  special  included  of the f i s h  i n Haskins  (1960, 1964) h a s c o m p i l e d  r e v i e w s most o f t h e e a r l y  tional  Range  e t a l (1961).  species of freshwater f i s h  fish  i n the Northern  r e f e r e n c e t o t h e guppy a n d i t s p r e d a t o r s was  Boeseman  Trinidad  A more g e n e r a l  but lacks  of Trinidad. collections  ecological  data. 19  a key t o the  T h i s monograph  and taxonomy o f  and d e t a i l e d  distribu-  20 In has  g e n e r a l the ecology o f stream  been l i t t l e  applies  to Trinidad  Classification Using possible  studied  (Gery, 1969;. A l l e n ,  t h e methods o u t l i n e d  to erect  a classification and r i v e r s  T h i s was an a b i o t i c  sites  detailed.breakdown  are  greatly  1969)  stream  based  Range on t h e  i n the region  ( T a b l e 1) .  A more  o f t h e s e measurements can. be f o u n d i n .  (Table 1).  make m e a s u r e m e n t s • i n  of a representative  classification  surrounding,the c o l l e c t i o n  (June, J u l y ,  and t h i s  2, i t was  i n Chapter  of the Northern  o f each  Appendix  1969)  o f streams'  w i d t h , d e p t h , and v e l o c i t y  the  i n the tropics  as w e l l .  sample o f t h e s t r e a m s region.  fish  Wherever p o s s i b l e  d r y (March, A p r i l , seasons  because  I attempted t o .  1969)  several  a n d wet  o f t h e streams  a f f e c t e d by t h e change i n r a i n f a l l  (increase i n  volume o f f l o w a n d t u r b i d i t y ) .  Geographic As tion  distribution  noted above, t h e r e i s l i t t l e  regarding the d i s t r i b u t i o n  2 summarizes t h e r e s u l t s For  of f i s h species  specific It  main f a c t o r streams ished  o f t h e 1967  names", c o n s u l t  i s clear  that  limiting.the  of fish  published informai n Trinidad.  a n d 1969  the Appendix  collections.  ( T a b l e 2) .  t h e s i z e o f t h e streams i s t h e diversity  of.the fish  fauna  i s o l a t e d by p h y s i c a l b a r r i e r s may have an  fish  Figure  f a u n a a n d many s p e c i e s w h i c h  might  though  impover-  o t h e r w i s e be  TABLE 1 .  Stream  C l a s s i f i c a t i o n and p h y s i c a l f e a t u r e s of streams i n the Northern Range (March - June, 1 9 6 9 ) .  type  Width PCur GCur UCur TT  Springwater  UA(N) UTac UArouc UGuan BB Yar Par  Headstream  (m)  0 . 5 0 - 1 . 0  Depth  Velocity (in)  0 . 0 5 - 0 .15  (m/sec) (mVsec) 0.11-  0 . 0 6 - 0 .15  Temp. (°C)  Shade  2 4 . 3 26.2  3-4  0  0 . 0 2 8 0.267  24.627.4  2-3  0 - 1  0.67  1  0 . 3 2 -  Midstream  LA LTac SC Mar Oro  3 . 0 - 8 . 0  0 . 1 3 - 0 . 2 0  0 . 4 2 1.18  0 . 1 5 0 1.129  2 4 . 3 30.0  2  Lowland R.  Guay Cap Car  2 . 0 - 2 5 . 0  1 . 5 - 3 . 0  0.33-  0 . 5 6 3 22.50  2 6 . 9 -  0-1  l  0 1 2 3 4  -  Turbidity  0.00850.0128  0.29  1 . 2 0 - 5 . 0  Volume of Flow  0.40  29.1  no- shade s m a l l amount of shade r e s t r i c t e d mainly to streambank medium shade ( 5 0 % cover) medium to dense ( 7 5 % cover with few exposed p a r t s ) very dense cover w i t h v i r t u a l l y complete shading  0 - always c l e a r 1 - t u r b i d only a f t e r heavy r a i n s 2 T t u r b i d throughout year  22a  FIGURE 2.  The d i s t r i b u t i o n Range r e g i o n . refer the  For a l i s t  t o F i g . 1.  principal  of f i s h  species of  i n the Northern  abbreviations,  S t r e a m s o u t l i n e d by a box a r e  ones t h a t were i n v e s t i g a t e d .  14 cn 13UJ 12o 11 LU 10CL 9 CO 8 o 7rr 65 DD 4 3 -  POECILIA  CHARACIDAE Q  RIVULUS  OTHERS  CICHL/DAE  2 1 Z3  o  Z3  O  a: —I  ZD Q_ W  >  i —  2  h  SPRINGS  3 o O  < 3  «CD k. id id QQ CL >  o •3 O  c  < —\  3  u  «-  ZD  HEADSTREAMS  J 2  J  «  O  < —1  a .  id  i_  rd  >  id  O o CD  M I D S T R E A M S LOWLAND to to a*  23 expected  to occur The  are not  Northern  present.  Range has  served  (no i n t e r c o n n e c t i n g f r e s h w a t e r cichlid  dispersal  from the  flowing  south the  Basin  Upper A r i p o  and  The  access  I shall the  this  Since river,  distance. contained  at the A r i p o  guppies are  are u b i q u i t o u s  Predators  of  t h a t the  p r e d a t i o n by  the  Blue  the  As of  continuously populations over  a very has  guppy  short never popula-  species.  i n f o r m a t i o n on form  passage  are predators  hence the  from these  the  inter-  Upper A r i p o R.  fish,  i n schematic  in this  the  distribution  (Fig. 3).  Guppies  region.  guppy  I t w o u l d be s u c h as  to  upper r e g i o n s .  predation pressures  "protected"  the  streams  blocks  distributed  characid or c i c h l i d  the major s p e c i e s  north-  i s extremely  i t i s p o s s i b l e to study  I have summarized  fish  R.  5 metre w a t e r f a l l  I t i s probable  t i o n s have b e e n  In  cichlids  l a r g e r s p e c i e s t o the  exposed t o d i f f e r e n t  of  and  d e m o n s t r a t e b e l o w , some o f t h e s e  guppy.  along  system t o the  and  Rivers.  situation  s e v e r a l of the  barrier  Range, w a t e r f a l l s have  of characids  e s t i n g because a s i n g l e of  R.  Yarra Rivers.  o f f the Northern  prevented  the major  streams) t o c h a r a c i d  Caroni  f l o w i n g P a r i a , M a r i a n n e and  as  expected  a priori  guppy w o u l d be  large fish  and  that a small  subject to  abundant  considerable  possibly fish-eating  birds,  24a  FIGURE 3.  A schematic r e p r e s e n t a t i o n o f the d i s t r i b u t i o n of the major f i s h of T r i n i d a d . are  shown.  occur  i n the northwest  Major b a r r i e r s Small  populations  i n the v i c i n i t y  characids pools  species  and c i c h l i d s  or ditches.  to f i s h  dispersal  of Rivulus  o f streams  corner  do  containing  but are confined  to small  CARIBBEAN  SEA WATERFALL BARRIER  GULF  NORTHERN  RANGE  MOUNTAIN  BARRIER  UJ  of PARIA  (£>•  CD  I-  Z) t- CC Ul 3 0- O —  I WATERFALL BARRIER  0_  I |2 -  C  'o  A  R  O  N  I  : • . *. •.: .*.'•  GUAYAMARE  CAPARO  RIVER  RIVER  R  i....  11.. J  I  V  E  R  MCHARACIDS4 UCICHLIDS  l  RIVULUS  l-o *« a 4  25 mammals, a n d i n s e c t s .  Direct  o b t a i n e d by o b s e r v i n g  evidence  of this  attacks i n nature  guppy r e m a i n s i n t h e d i g e s t i v e t r a c t  c a n be  o r by r e c o v e r i n g  of the suspected  predator. It evidence 1969) . in  i s often d i f f i c u l t to obtain extensive  o f p r e d a t i o n on a s p e c i f i c Many, v e r t e b r a t e p r e d a t o r s  their habits.  the r e l a t i v e  prey.  (e.g.  McPhail,  are not s p e c i a l i s t  species w i l l  abundance and a v a i l a b i l i t y  Even i n t h e s o - c a l l e d  seasonal d i e t  item  are notoriously secretive  In a d d i t i o n , i f they  f e e d e r s , p r e d a t i o n on a g i v e n p r e y with  prey  direct  "stable"  fluctuate  of alternate  tropical  environment,  changes a r e well-known f o r f r e s h w a t e r  ( L o w e - M c C o n n e l l , 1964, 1969b; Z a r e t and Rand,  fish  1971).  A n o t h e r p r o b l e m i s t h a t p i s c i v o r o u s f i s h may go f o r long periods without  f e e d i n g , and when t h e y  d i g e s t i o n may be r a p i d .  Therefore  do f e e d ,  a high proportion of the  s t o m a c h s a r e empty o r t h e f o o d may be d i g e s t e d b e y o n d recognition. Finally,  predators  occupying  a high trophic  a r e n u m e r i c a l l y n o t a b u n d a n t ; sample s i z e s  level  a r e bound t o be  small. I encountered assess  the r e l a t i v e  t h e guppy  a l l these  impact  problems i n attempting  o f each suspected  predator  to on  populations.  (a) M a j o r p r e d a t o r s . 5 species of f i s h  predators  Haskins o f guppies  e_t a l  (1961) l i s t e d  i n the Northern  26 Range s t r e a m s  ( F i g u r e 4)  Astyanax bimaculatus, Crenicichla and  including  Aeguidens l a t i f r o n s  saxatilis  ( p r o b a b l y C.  Hoplias malabaricus.  hartii,  "less  fifth  d a t a were g i v e n f o r t h e b a s i s o f t h i s  a d a p t a t i o n s , and  p r e d a t o r s were u s e d  feeding tendencies  good f i r s t  approximation  A e g u i d e n s was  of t h i s  Rivulus  species  sampled had  Before  (see T a b l e  guppy  the present  shows t h a t  Aeguidens.  I n c o n t r a s t 10%  study,  of these  s h o w i n g H o p l i a s and  1970  a  and  no or  f o r the of a l l  stomachs;  attacks  i n nature. little  was  known a b o u t  (cited  the  5 potential predators ( a l l H o p l i a s and  Thornhill  Crenicichla  Astyanax  e t 'al_ (1966) drew as p r e d a t o r s  T r i n i d a d ) o f H e m i b r y c o n , A s t y a n a x and  (no o t h e r d a t a g i v e n ) .  Knoppel,  evidence  3 i n Appendix  South American mainland;  t h e M a r a c a s R.,  together  stomachs o f j u v e n i l e s  have a v e r y w i d e d i s t r i b u t i o n ) . a f o o d web  field  guppy r e m a i n s i n t h e i r  f e e d i n g h a b i t s o f any the  the.  T h i s w o u l d be  to a t t a c k guppies the  of  t h e main c r i t e r i a ,  guppy p r e d a t o r t h a n  from  classifi-  abundance,  laboratory.  o f stomach c o n t e n t s ) .  were a l s o o b s e r v e d  o c c u r on  as  t h o u g h my  never.observed  were r e c o v e r e d  relative  wide d i s t r i b u t i o n  i n the  i s a more s e v e r e  analysis  Rivulus  Few  suspected  guppies  predator,  1960)  severe".  P r e s u m a b l y t h e body s i z e ,  Rivulus  Boeseman,  termed  morphological  adults  The  alta,  (= A. p u l c h e r ) ,  was  cation.  with  4 termed " s e r i o u s " :  Lowe-McConnell  i n Roberts,  1972)  found  (1969a) fish  (in  the and  remains  27a  FIGURE 4.  Photograph o f the major the  guppy.  fish  predators  ASTYANAX  HEMIBRYCON  AEQUIDENS  RIVULUS  0  5  10  15  cm  28  in  the  stomachs o f  tively.  Sterba  typical  predatory  the  manner o f  r u s h and  Hoplias  f r o m Guyana and  (1962) s t a t e d  the  that  European P i k e ,  a  is  successful—and (p.  predator  Poecilia  r e t i c u l a t a , Rosen and  have f i s h  stomachs, several strict also  remains  I also  individuals, piscivore  recovered  Guyana- ( s h r i m p s  380)."  (as  706)."  quite  Bailey, of  Haskins et  al_ i m p l i e d ) .  a n t s and  Crenicichla  is a specialized  o f my  p r e d a t o r under i d e a l c o n d i t i o n s — 6 3 e a t e n by Hoplias  a sub-adult C r e n i c i c h l a i s also (b)  fish  capable of  considering b u t i o n , or  either low  f e e d on  the  adult  i s not  stomachs  from  There are  a  (1925) in  C.  thesis  that example  potential  of  this  male g u p p i e s were period.  feat. a number o f  guppies o c c a s i o n a l l y  t h e i r s m a l l body s i z e ,  numbers,  their from  Beebe  o v e r a 48-hour  a similar  Minor predators.  s p e c i e s w h i c h may  fish the  in  species  guppy p r e d a t o r , an  experiments u n d e r l i n e s  =  sample  larvae  invertebrates.from Crenicichla  Though t h e s e d a t a v i t i a t e  f r o m one  i n my  insect this  lugubris).  which  specialized  species)  that  alta;  al  1963).  suggesting  f r o m C.  a  reticulatus  other  s n a i l s and  lightning  carnivore  Crenicichla  ( g u p p i e s and  "are  after  Haskins et  possibly  (Lebistes  majority  recovered  i t with  is a pike-like  Lebistes  A l t h o u g h the  seize  (p.  "Crenicichla  did  species, prey  swallow i t h e a d - f i r s t  extremely  Crenicichla  respec-  f i s h e s which l i e i n w a i t ' f o r  (1961) c l a i m e d , an  Brazil  limited  I have assumed t h e y have  other but  distria  negligible  effect  populations  on  i n the  the  present-day  N o r t h e r n Range r e g i o n .  R o b o i d e s d a y i , Corynopoma r i i s e i , I found a l l o f . t h e s e only  would e a t  Synbranchus c o u l d Terrestrial  attack  of  only  episodic  two  hrs)  h e r o n s and  observation,  of L i t t l e on  an  and  J u n e 29,  the  fauna of  (1936) r e p o r t e d (tunnel), o f  the  finding  this  of P a r i a  on  on  (1600  R.  hrs)  P a r i a R.  species  area);  scales of  species.  guppies.  guppies  the  basis  They a l s o  1969  americana) collection  sitting site.  in  the  (1952) l i s t e d i t .  fish  and  Smooker  in a  found a nest  (C. amazona) on  years  J u n e 22,  Belcher  small  of  predation  a t P a r i a and  Beebe  but  I observed a p a i r  (Chloroceryle  this  aquaria  the  nest of  the  Madamas R.  (east  R.). The  Junge and  Pygmy K i n g f i s h e r  Mees  M a r a c a s Bay  Valley  feed  source of  Arima V a l l e y .  Great Green K i n g f i s h e r  at  this  guppy  include  k i n g f i s h e r s o v e r 13  o v e r h a n g i n g b r a n c h a t the  Gaura V a l l e y . (Tacarigua  adult  N e v e r t h e l e s s on  1969  (1961) r e p o r t e d  These  i n small  ingest  also  no  that  Green K i n g f i s h e r s  Herklots  with  and  of the  Synbranchus marmoratus.  (1961) i n f e r r e d ,  pressure.was unimportant. (1300  and  guppies  a n i m a l s may  although Haskins et a l sighting  structure  and  the  (1961) n e a r t h e and  Herklots  Aripo  been s i g h t i n g s o f winter migrant  (C. aenae) has  the  road  a river  (1961) r e p o r t e d (Aripo  Belted  from the  mouth o f  R.)  area.  Kingfisher  north,  i n the  been seen (Burro  R.?)  i t . f o r the  Caura  T h e r e have  also  (Ceryle  region  by  of  aIcyon), the  a  30 Northern  Range. No  for  any  details  of  of these reports  populations  Trinidad.  the  Most o b s e r v a t i o n s  were f e e d i n g  of  toes  a n d ' c l a w s t o s c o o p up  Bloedel in  Panama.  t o 40  He  small  experimental  and  Mollienisia  pool  the  capture  Suthers its  ripples reveal  guppies  fish  suggests that  bat  could  poeciliids  hind the  and  given.  leporinus  capture  30  Gambusia night times  from  an  the  g a f f i n g appeared  below the  i n nature  water  bat fish  sections  Bloedel's  water  the  However surface  caught i f they surface.  s t r e a m and. i n  fish) create  not' use  because  echolocate  m i g h t be  of  could  surface  could  d i s t u r b i n g the  i n smooth-flowing probably  that N o c t i l i o  impedance m a t c h i s p o o r .  t h e i r p r e s e n c e by  (and  elongated  methods o f N..  Random d i p p i n g  demonstration t h a t the  Certainly  (1967:  skim over  sphenops) per  (1965) c o n c l u d e d  air-to-water.acoustic 1  they  where  technique.  sonar to l o c a t e  Suthers  Worth  their  maintained a t about four  n a t u r a l prey density. t o be  hunting  ( i n c l u d i n g the  behavior  f u r t h e r d e t a i l s were  d e m o n s t r a t e d t h a t one  fish  nicaraguensis  the  no  in  northwest coast  use  g u p p i e s as  Unfortunately  (1955) s t u d i e d  feeding  small marine f i s h .  stated that Trinidad N o c t i l i o  guppy  leporinus occurs  i t s natural  224)  water s u r f a c e .  given,  remains c o n j e c t u r a l .  i s l a n d s of the on  o r d i e t were  p o t e n t i a l i m p a c t on  fish-eating, bat N o c t i l i o  have been made o f f t h e bats  so  behavior  of k i n g f i s h e r predation  The  the  feeding  surface  pools,  31 disturbances  in localized  areas  t h a t might a i d the  U n d o u b t e d l y T S i o c t i l i o does e a t g u p p i e s b u t tative  a number o f o t h e r  guppy i n t h e N o r t h e r n  on.their and  due  to hunting impact  presumably  steadily  I now  and  ( i f any)  of  f o r the  a q u a r i u m and  attack  some a s p e c t s  of t h e i r  is  and  distribution  history  the  important  i s b a s e d on  f e a t u r e s of  i n Table  field  i s probably  t h o u g h I f e e l my  i t from the p r e d a t o r  n o c t u r n a l h a b i t s and  2..  low  observations  density  the data  fish  I have  least  A l l the  Hoplias. in  strong  altogether.  ( i n c l e a r water) of  of i t s feeding behavior  an  already  important  are not  category  the  observations  s t r a t e g y o f A e q u i d e n s and  outdoor pool r e s p e c t i v e l y .  5 predators  make f i e l d  the  guppy p o p u l a t i o n s  were made on w i l d - c a u g h t  that Aequidens  exclude  e x t i n c t i o n on  habitat destruction.  t h e main p r e d a t o r s  information  These o b s e r v a t i o n s  to  larger reptiles  history.  natural history  the  the  information  wish to r e t u r n to the major p r e d a t o r s  I have summarized  stated  on  and  of  decreasing.  D i s t r i b u t i o n and n a t u r a l of the main p r e d a t o r s  behavioral  I have no  Many o f t h e  pressure  i n more d e t a i l ,  natural  except  quanti-  p o t e n t i a l predators  unfortunately nearing  Thus t h e i r  consider  Range b u t  f i s h - f e e d i n g habits."  mammals a r e  island  no  data a r e ' a v a i l a b l e . There are  the  bat.  of enough The Hoplias  difficult.  TABLE 2.  Natural  Crenicichla Maximum l e n g t h Principal  (mm)'  food  200  h i s t o r y of the main f i s h  CICHLIDAE Aequidens  (350)  148  (170)  predators.  CHARACIDAE Hoplias Astyanax 392  116  (500)  (150)  CYPRINODONTIDAE Rivulus 105  (100)  fish  benthic  Principal habitat  headstreams midstreams  headstreams midstreams  l a r g e t u r b i d headstreams rivers midstreams  Microhabitat  under l o g s , rocks; digs p i t s to hide  around l o g s , rocks, leaf d e t r i t u s , shore vegetation  open bottom at night; under l e a f detritus, i n day  open midwater i n pools; i n riffles  ubiquitous pools  Social organization  s o l i t a r y or s m a l l groups of 2 to 5 individuals  loose aggreg a t i o n s or dispersed breeding p a i r s  solitary  tight  dispersed out p o o l  through-  Activity  mainly d i u r n a l  diurnal  mainly nocturnal  diurnal  nocturnal diurnal  and  ambush o r s t a l k ; occas i o n a l continuous pursuit  continuous pursuit  s t a l k or continuous pursuit  increase i n d i r e c t i o n and v e l o c i t y of normal swimming  continuous  period  Attack strategy on g u p p i e s  b  L e n g t h s i n b r a c k e t s a r e the maxima g i v e n Trinidad collections. a  present  invert.  D i u r n a l i n c l u d e s p e r i o d s o f dim  fish  f o r the  l i g h t before  aquatic i n s e c t larvae  s p e c i e s by  s u n r i s e and  Sterba  after  schools  terrestrial springwater  (1962); o t h e r s  sunset.  insects  are  in  from  pursuit  the  Hoplias rivers; Caroni  i s primarily a fish  most o f t h e i n d i v i d u a l s and Guayamare R i v e r s .  o f the l a r g e r t u r b i d  I c a u g h t came f r o m t h e  Hoplias  a l s o occurs  i n lower  numbers i n a l l m i d s t r e a m s and h e a d s t r e a m s n o t b l o c k e d major w a t e r f a l l s . off  the north  face.of the Northern  Crenicichla Hoplias but i s less rivers.  shares  abundant than  distribution of  Hoplias  i n lowland  for lowland'rivers.  50 o f t h e s e  predators  3 km o f t h e Lower A r i p o  o f - C r e n i c i c h l a : H o p l j a s was  As a v e r y  rough estimate o f  i n a t y p i c a l midstream, I  on a h a l f - d a y e x c u r s i o n  r a n g e as t h e p r e v i o u s  prominent  midstreams b u t tends t o decrease  similar  i n lowland  r i v e r s and  i n numbers i n t h e h e a d -  c h a r a c i d o f t h e genus H e m i b r y c o n appears t o r e p l a c e Astyanax.  than  A s t y a n a x b u t has s i m i l a r  Appendix, Table recovered  3 fordiet);  (probably  Hemibrycon i s '  f e e d i n g b e h a v i o r (see  f r o m t h e stomach o f a H e m i b r y c o n .  smaller  cousin.  H.  one j u v e n i l e guppy was  when I r e f e r t o A s t y a n a x i n t h i s its  t h e same  In the s m a l l e r mountain streams a m o r p h o l o g i c a l l y  taeniurus) smaller  over  two s p e c i e s b u t some d i f f e r e n c e s do  Astyanax i s very  streams.  along  R.  A s t y a n a x and A e g u i d e n s a r e d i s t r i b u t e d  occur.  turbid  10:1 f o r h e a d s t r e a m s and m i d s t r e a m s b u t t h e  t h e numbers o f a d u l t C r e n i c i c h l a counted  flowing  Range.  the o v e r a l l  I n my s a m p l e s , t h e r a t i o  approximately reverse  I t i s absent, f r o m a l l s t r e a m s  by  thesis,  Generally,  I am a l s o i n c l u d i n g  34 Aeguidens has a s i m i l a r though I d i d n o t c o l l e c t  distribution  to Crenicichla  i t i n t h e C a r o n l o r Guayamare  Rivers. I have s t a t e d b e f o r e springwaters cichlids.  that Rivulus  o r i n l a r g e r streams d e v o i d  in  escape behavior  of Rivulus  Crenicichla.  Small  populations  but are confined  may i n f a c t be a s m a l l e r Kenny, p e r s . The  the of  ineffective  approaches o f Hoplias o r  o f R i v u l u s do o c c u r  t o small pools  "lowland  or ditches.  r a c e " o f R. h a r t i i  important  point arising  of predators  i t s range i n n o r t h e r n  i s that a l l populations of  predation or Rivulus  i n the c h a r a c i d - c i c h l i d  situation  intensities insufficient  O v e r most  there  predation.  are predators  that can handle the s m a l l e s t or l a r g e s t  I have t e r m e d t h e p r e d a t i o n p r e s s u r e severe.  ( J . S.  T r i n i d a d , t h e guppy i s e x p o s e d t o  c h a r a c i d and c i c h l i d  of a l l sizes  This  out of t h i s discussion  guppy a r e n o t e x p o s e d t o t h e same p r e d a t o r s .  Since  i n the  comm.; s e e a l s o Boeseman, I960.: 1 2 0 ) .  the d i s t r i b u t i o n  either  as  In the laboratory  o f t h e s t r e a m s c o n t a i n i n g c h a r a c i d and c i c h l i d  predators  of  i s l i m i t e d by  is, p a r t i c u l a r l y  t h e f a c e o f t h e slow, s t a l k i n g  vicinity  o f c h a r a c i d s and  I t appears t h a t i t s d i s t r i b u t i o n  the presence o f the l a r g e r p r e d a t o r s . the  i s found i n  Undoubtedly there  t o warrant  environments  are differences i n predation  between some o f t h e s e data  i n these  guppy,  l o c a t i o n s b u t I have  splitting  this  category.  R i v u l u s on t h e o t h e r hand i s a s m a l l p r e d a t o r — i t s  major impact  falls  tion  case  in this  distribution in  equal  than  been a b l e that  small guppies.  must depend on  of the predator  supply).  assessed  on  The  the  s e v e r i t y of  abundance and  B e c a u s e R i v u l u s d e n s i t y i s more  the d e n s i t y o f c h a r a c i d s  and  s u f f e r i n g o n l y m o d e r a t e o r weak p r e d a t i o n . Rivulus density i s very Populations  c o n d i t i o n s must e n j o y For (Chapter  the  6)  t o compare  occurring  detailed  (Table  very  and  large  of guppies under  these  of a n t i p r e d a t o r  isolated  Range a r e a .  or  case  were  range of p r e d a t i o n  f o r my  For  predators.  behavior of  guppies  chosen pressures  In a d d i t i o n they  semi-isolated--gene  s m a l l among them.  these  hypothesis  are  exchange  reasons,  they  are  as o u t l i n e d i n .  1.  M i g r a t i o n and  dispersal  I have u s e d t h e in- t h i s  In some s t r e a m s few  These p o p u l a t i o n s  i n the Northern  excellent test  Chapter  3).  I have  those  freedom from a q u a t i c  study  encompass t h e  geographically must be  virtual  low  be  guppies  and  I have s e l e c t e d 5 main p o p u l a t i o n s  because they  an  of  to  easily  cichlids,  are exposed to i n t e n s e R i v u l u s p r e d a t i o n  i n d i v i d u a l s occur.  size  (assuming a l t e r n a t e prey  t o d i s t i n g u i s h between p o p u l a t i o n s  (e.g. P a r i a )  preda-  thesis—it  of  guppies  term  should  ideally  d i s p e r s a l o r gene m i g r a t i o n . points out,  a definition  "population" r e l a t i v e l y  As  be  d e f i n e d by  Dobzhansky  of geographic  rates  (1970:  isolation  loosely of  240)  must-  36  TABLE 3.  River  The p r i n c i p a l f i s h p r e d a t o r s a t t h e main s t u d y a r e a s .  Crenicichla  Aequidens Hoplias  Guayamare  +  -  Lower A r i p o  +  P.  Curucaye  '  occurring  Astyanax  Rivulus  +'  +•  +  +  +  -  -  -  -  -  +.  Upper -Aripo  -  -  -  Paria  -  -  -  Guayamare d o e s have t h e Cichlasoma bimaculatum.  -  morphologically  +  similar  R i v u l u s i s not absent from t h i s geographic a r e a does n o t o c c u r i n t h e r i v e r i t s e l f , h e n c e g u p p i e s a r e exposed to i t . b  but not  +  37 i n c o r p o r a t e both  absolute  d i s t a n c e and  the  vagility  of  the  organism. Although collection sites  site,  i n Table  discrete  I associate a there  3)  units.  remained  i s good e v i d e n c e  suggesting  site  s t r e t c h o f t h e A r i m a R.  abruptly.  the  permanently  m a r k e r gene up  t o 10  These o b s e r v a t i o n s r i v e r may  e x c h a n g e must be  (at l e a s t km  from the  Petite was 50  4)  i n the  placed  i n Pool  noted  distribution  2.  uniform colour change  were a b l e  to a  point of i n t r o d u c t i o n . within  a  t h a t some gene  i n an  screened-off  c l e a r e d o f a l l g u p p i e s and  On  to Pool  of c e r t a i n  experiment s e c t i o n of  ( r e f e r t o F i g . 1, A p p e n d i x ) .  "vacant"). their  a  t o about.36 g e n e r a t i o n s )  observed  f e m a l e g u p p i e s were c o l l e c t e d and  of  occurring.  C u r u c a y e R.  section  guppies  subpopulations  t h a t over  they  q u i t e i s o l a t e d : but  conducted  initially  of c e r t a i n  that subpopulations  S i t e a t t a c h m e n t was (Chapter  that  5  quite  controlled) could  same r i v e r  suggest  be  f o r the  d e a l i n g with  frequencies  genetically  However i n t h e  establish  single  integrity  They a l s o d i s c o v e r e d  (known t o be  specific  attachment; even d u r i n g p e r i o d s  f l o o d i n g the  intact.  patterns  t h a t I am  a  (at l e a s t  H a s k i n s e t a l (1961) f o u n d  show c o n s i d e r a b l e sudden f l a s h  "population" with  2  then  f r o m above and  (Pools  1,  3,  subsequent days I r e c o u n t e d  Although  i n the  I had  50  and  section  male  and  below  the  4 were  a l l the  s e c t i o n , and  expected  The  now  fish,  returned  considerable  the  them  migration  38 t o P o o l s . 3 and. 4,  t h i s was  TABLE 4.  not  observed  S i t e attachment C u r u c a y e R.  No. i n Pool 2  ( T a b l e 4)..  of guppies  No. o u t s i d e Pool 2  i n the  Section total  Petite  Percent migration  June 14/69  84  2  86  2.3  16/69  80  5  85  5.9  18/69  79  2  81  2.5  20/69  76  3  79  3.8  22/69  79  0  79  0  26/69  70  5  75  6.7  1/69  71  2  73  2.7  July  Mean  These d a t a be  a relatively  suggest  isolated  approximately  50  pools  sampling  site  from the  1.6  km),  gene f l o w  the  c o n t r i b u t i o n of  that.the f i s h  breeding  separate Santa  the  i n each p o o l  (deme).  Petite  C r u z R.  i s probably juvenile  unit  3.4  Because .  Curucaye  (total  distance  s m a l l between them.  fish  to the  may  total  of However,  gene f l o w i s  unknown. T h i s c o n d i t i o n i s r e m i n i s c e n t of. t h e "stepping  s t o n e " model e n v i s a g e d  Even i n t h e  by  unidimensional  K i m u r a and  absence o f major b a r r i e r s  Weiss  t o gene f l o w ,  (1964). isolation  39 by  distance alone  might f a c i l i t a t e  the d i f f e r e n t i a t i o n of  l o c a l populations  by g e n e t i c d r i f t  ( R o h l f and S c h n e l l , 1971)  or d i f f e r e n t i a l  selection  (Ehrlich  In a d d i t i o n t o i s o l a t i o n tions  ( P a r i a and Upper A r i p o )  physical barriers the C a r o n i  River  (refer  system i s probably  isolated  live  In recent T r i n i d a d h i s t o r y fish  fish  (the p h e n o t y p e —  i n pools  predators  o r t o r n a d o e s may a c c i d e n t a l l y d r o p  to carry small  with  immediately  between Upper A r i p o and  t o these  must be f o r t u i t o u s — t e r r e s t r i a l  was o b s e r v e d  falls  r e g i o n may be a n a r r o w h y b r i d  Dispersal of fish  barrier.  Gene exchange  r a r e t h o u g h some  the Aripo  i s intermediate  Lower A r i p o ; . t h i s  popula-  a r e a l s o i s o l a t e d by m a j o r  and c o l o u r - - o f m a l e s c o l l e c t e d  below t h e f a l l s  1969).  by d i s t a n c e , two  to Fig. 3).  u n d o u b t e d l y ' g e t swept o v e r size  and Raven,  zone).  populations  (bats, k i n g f i s h e r s )  fish  at least  above a one  tornado  f o r a considerable  distance.  Summary o f C h a p t e r 3 1.  The l i m n o l o g y  o f T r i n i d a d streams i s r e l a t i v e l y  2.  In the Northern  unknown.  classified  into  species  t h e s t r e a m s may be  four i n t e r g r a d i n g types  number o f a b i o t i c 3.  Range a r e a  and b i o t i c  To a c e r t a i n  in a  parameters.  extent  i s c o r r e l a t e d with  differing  this  the d i s t r i b u t i o n  of f i s h  classification.  Diversity  is  g r e a t e s t i n the lowland  rivers  and l e a s t  i n the spring-  waters . 4.  The d i s t r i b u t i o n  e n c e d by t h e t o p o g r a p h y . certain rivers  of f i s h i s also greatly  The N o r t h e r n  species i n the Caroni flowing northward  into  predators alta,  I t i s concluded  the Caribbean  have b e e n f o u n d 6.  7. rivers  important Crenicichla  and R i v u l u s h a r t i i .  Guppies  i n t h e stomachs o f t h e l a s t t h r e e occur  species.  i n the  i m p a c t on guppy  i s unknown. The guppy i s u b i q u i t o u s of northern  i n i t s distribution i n  T r i n i d a d but there  i n the d i s t r i b u t i o n  guppies a r e preyed  are important  of predators.  upon by R i v u l u s ; o t h e r s  suffer  Some characid  c i c h l i d predation. 8.  G u p p i e s show c o n s i d e r a b l e  small portions of t h e i r tion  t h a t t h e most  Fish-eating a e r i a l predators  discontinuities  and  I n some  t h e upward p a s s a g e o f f i s h .  under c o n s i d e r a t i o n b u t t h e i r  populations  the  Sea.  o f t h e guppy a r e H o p l i a s m a l a b a r i c u s ,  Astyanax bimaculatus,  regions  Range has p r e v e n t e d  R. s y s t e m f r o m c o l o n i z i n g t h e  s t r e a m s w a t e r f a l l s have b l o c k e d 5.  influ-  home s t r e a m .  s i t e attachment t o Together with  by d i s t a n c e a n d p h y s i c a l b a r r i e r s ,  probably  isola-  t h i s ..behavior  r e d u c e s gene f l o w between p o p u l a t i o n s a n d  facilitates  the d i f f e r e n t i a t i o n  of local  populations.  CHAPTER- 4  GEOGRAPHIC VARIATION IN THE SEX RATIO Introduction In t h i s differences these  chapter  I shall  i n the sex r a t i o  describe population  and a t t e m p t  relationship  l o s s o f male, g u p p i e s  between p r e d a t i o n and t h e s e l e c t i v e  from n a t u r a l p o p u l a t i o n s h a s . r e c e i v e d a  g r e a t d e a l o f a t t e n t i o n from Haskins workers used t h e sex r a t i o hypothesis flicting  guppies  of different  populations  important  repeating  the behavior o f  this  earlier  differences  with  the predator-prey  study,  firstly  respect to predation, should  e t al_, b u t  behavioral  that i f conspicuous  i n t h e sex r a t i o  predation pressure  i t was  i n T r i n i d a d and s e c o n d l y , by  I reasoned  a liability  by t h e con-'  grey-brown c o l o u r ) ,  assess  examining i n m o r e - d e t a i l  indeed  f o r the  and p r e d a t i o n .  some o f t h e e x p e r i m e n t s o f H a s k i n s  interactions.  These  ( i . e . male c o l o u r s — f e m a l e s o f  are a cryptic  extensive c o l l e c t i n g  selection  s e t out t o study  colours  to c r i t i c a l l y  evidence  i s determined  demands imposed by s e x u a l I originally  e t a l (1961).  as i n d i r e c t  t h a t male c o l o r a t i o n  Since  by  o u t why  d i f f e r e n c e s occur. The  all  to find  coloration i s geographic  be c o r r e l a t e d  ( i . e . a greater loss  o f males  with relative  42 to  f e m a l e s where p r e d a t i o n i s s e v e r e ) . During  this  study o f the sex r a t i o ,  geographic v a r i a t i o n the  following  Sex  ratios  1967  ratio  discovered; this  of natural populations  and  5 lists  1969.  t h e sex r a t i o s  The  o f m a l e s t o one To d e t e r m i n e  sex r a t i o  The  collections  mately  6 generations  adults  1967  sampled  collections  1 year, Haskins in  sampled  had  (longevity  analysis The  1969  The  (n = 14245) and (X  1  d  correlation  f  in  than  between y e a r s  s i t e s are not  t o o n l y one  year,  dropped  from  elsewhere.  f o r a l l 1967  c o l l e c t i o n s , i s 0.77;  pooled r a t i o  f o r both years i s  When t h e s e x r a t i o s  the  simply  collection  B l u e B a s i n was  =305.47, p <  the  suggesting that  i s significantly different  2  were r e s a m p l e d  I assume t h a t none o f  ( F i g . 5)  among s t r e a m  f o r reasons given  i t i s 0.73.  1:1.ratio  The  Note t h a t  sex r a t i o  i n 1967  i n the  i n nature i s probably less  random d e v i a t i o n s p e r t a i n i n g  the  the  been b o r n a t the time o f  is significant  s e a s o n , o r sample.  e x p r e s s e d as  of the d i f f e r e n c e s  (18-26 m o n t h s ) .  i n 1969  sex r a t i o d i f f e r e n c e s  made  were s e p a r a t e d i n t i m e by a p p r o x i -  e t a l , 1961).  t h e sex r a t i o  i s always  the s t a b i l i t y  1969.  of the c o l l e c t i o n s  female.  sex r a t i o , 13 o f t h e s i t e s  the  i s described i n  two c h a p t e r s .  Table in  was  additional  from.an  for  0.74  expected  .001).  f o r a l l streams  are pooled  (and  43  TABLE 5A.  The s e x r a t i o s (1967).  Collection date  Source  of natural  Males  Females  populations  Immat.  N  Sex  Ratio  Springwater Upper C u r u m p a l o (1) U p p e r C u r u m p a l o (2) total  5/7/67 16/8/67  24 53 77  69 118 187  31 16 47  124 187 311  0 .35 0 .45 0,.41  Sierra Sierra  17/7/67 16/8/67  115 210 325  243 335 578  19 446 4.65  377 991 1368  0,.47 0,.63 0,.56  M a r a c a s V i l l a g e (1) M a r a c a s V i l l a g e (2) total  25/7/67 25/7/67  179 44 223  219 98 317  37 22 59  435 164 599  0 .82 , 0,.45 0,,70  Tompire T r i b u t a r y  22/7/67  L e o n e Rd. (1) L e o n e Rd. (2) total  50  114  10  174  0,.44  675  1196  581  2452  0..56  6/7/67 6/7/67  70 83 153  115 127 242  79 122 201  264 332 596  0..61 0..65 0..63  19/8/67  95  213  12  320  0,.45  Upper P a r i a (1) Upper P a r i a (2) total  10/7/67 24/8/67  122 85 217  162 150 312  53 150 203  337 385 722  0,.75 0..57 0.,66  Yarra  10/7/67  65  57  3  125  1..14  U p p e r T a c a r i g u a (1) U p p e r T a c a r i g u a (2) total  1/7/67 17/8/67  106 261 367  81 161 242  88 234 322  275 656 931  1..31 1.62 1.,52  887  1066  741  2694  0.,83  T o t a l Springs Mean s e x r a t i o  ( n = 4 ) : 0.53  Headstream Upper A r i p o Upper A r i p o  Upper B l u e  (1) (2) total Basin  T o t a l Headstream Mean s e x r a t i o ( n = 5 ) :  0.88  Midstream Lower P a r i a  27/7/67  59  111  42  212  0.,53  Marianne  24/7/67  97  67  6  170  1,.45  5/7/67  112  102  203  417  1.,10  Lower T a c a r i g u a (1) Lower T a c a r i g u a (2) total  24/7/67 7/8/67  150 268 418  150 276 426  199 849 1048  499 1393 1892  1..00 0.,97 0..98  Lower A r i p o Lower A r i p o  12/7/67 21/7/67  81 65 146  118 77 195  116 115 231  315 257 572  0..69 0,.84 0.,75  Santa Cruz  (1) (2) total  Q u e b r a d a d.II. T o t a l Midstream Mean s e x r a t i o ( n - 6 ) :  Lowland  3/7/67  73  71  80  224  1,.03  905  972  1610  3487  0.,93  0.97  Rivers  Guayamare  19/7/67  105  122  70  297  0,.86  Caroni  12/7/67  92  112  351  555  0,.82  197  234  421  852  0.,84  2664  3468  3353  9485  0.77  T o t a l Lowland R i v e r s Mean s e x r a t i o ( n - 2 ) :  1967 T o t a l  0.84  44  TABLE 5B.  The s e x r a t i o s (1969).  Collection date  Source  of natural  Males  Females  populations  Immat.  Sex  ratio  Sprlnqwater U p p e r C u r u m p a l o (1) U p p e r C u r u m p a l o (2) total  13/3/69 13/3/69  30 40 70  73 70 143  19 8 27  122 118 240  0.41 0.,57 0.,49 -  Petite Petite  13/6/69 26/6/69  84 43 127  251 134 385  129 • 85 214  464 262 726  0..34 0.,32 0.,33  Grande C u r u c a y e  22/4/69  263  432  381  1076  0.,61  Torapire T r i b u t a r y  25/4/69  C u r u c a y e (1) C u r u c a y e (2) total  Total Springs Mean s e x r a t i o  26  94  85  205  0. 2 8  486  1054  707  2247  0..46  ( n - 4 ) : 0.43  Headstream (1) (2) (3) total  29/3/69 13/5/69 13/5/69  55 86 111 252  89 164 275 528  365 87 113 565  509 337 499 1345  0.,62 0. 52 0.,40 0,,48  B a s i n (1) B a s i n (2) total  6/5/69 29/5/69  224 194 418  261 164 425  417 305 722  902 663 1565  0.,86 1.,18 0. 98  18/4/69  292  256  212  760  1,,14  19/3/69  53  58  55  166  0.,91  Upper A r i p o Upper A r i p o Upper A r i p o  Upper B l u e Upper B l u e  Upper  Paria  Yarra  15/4/69  286  293  347  926  0. 98  U p p e r Guanapo  2/5/69  331  449  585  1365  0. 74  Upper A r o u c a  2/5/69  158  184  164  506  0. 86  1790  2193  2650  6633  0. 82  Upper  Tacarigua  T o t a l Headstreams Mean s e x r a t i o (n=7) : 0.87  Midstream Marianne  19/3/69  68  85  81  234  0. 80  Santa Cruz  14/4/69  219  241  898  1358  0. 91  Lower  Tacarigua  5/4/69  317  350  528  1195  0. 91  Lower  Aripo  2/4/69  153  216  525  894  0. 71  25/4/69  138  275  324  737  0. 50  895  1167  2356  4418  0.,77  16/3/69  110  120  85  315  0. 92  Caroni  7/4/69  84  114  58  256  0.,74  Caparo  17/6/69  50  50  48  148  1.,00  244  284  191  719  0. 86  3415  4698  5904  14017  0. 73  6079  8166  9257  23502  0. 74  Oropuche  T o t a l Midstreams Mean s e x r a t i o (n=5) -. 0.77  Lowland  Rivers  Guayamare  T o t a l Lowland R i v e r a Mean s e x r a t i o (n-3) : 0.89  1969  Total  Total 1967 i. 1969  45a  FIGURE 5.  A comparison of  guppies  1969.  o f t h e sex r a t i o o f 13 p o p u l a t i o n s  sampled  i n 1967  F o r sample s i z e s  and  refer  stream a b b r e v i a t i o n s r e f e r  resampled  in  t o T a b l e 5; f o r  t o F i g . 1.  45b  r t df p s  15 -  LU  <  tt -  UJ Lu  15 -  CC  12 -  UJ CL  CO UJ _l  <  = • 052 =192 =10 <.05  •UTac Mar  (Yar >SC  1.1 10 -  > LTac  09»Car LA  0.8CD  0.7-  as-  LU  0.4-  Par  UA  c n 0JB-  x  •Guay  TT  UCur  BB  CO 0 3 -  02-- — i — i 1 1 1 — i 1—i 1 02 03 OA 05 0.6 0.7 08 09 10 1.1  SEX RATIO 1969  1  12  (MALES PER FEMALE)  46 hence g e o g r a p h i c the  f i n d i n g s of Haskins  (sex r a t i o guppies It  d i f f e r e n c e s obscured) these  = 0.61,  (F. F.  i s clear  excess  n =  et al  3994) and  of females  the  some  geographic  The  the p o s s i b i l i t y ratio  few  are produced  weeks o f l i f e  possibility  Sex  ratios To  of  females  be  i n my  females  inside  balanced.  l o s s of males, e t . aJL sex  the  the  a  ratio  raises  secondary  abnormal m e i o s i s  and  the  (1961).  b e c a u s e more  sex  female  or  partial  birth  embryos spend t h e  the mother).  I considered  first this  laboratory stocks. •  of l a b o r a t o r y determine  stocks  i f my  s t o c k s w o u l d p r o d u c e an  (for genetic or other  number o f g u p p i e s  well  Table and  a good c l u e t o  Haskins  7825).  significant  o r more m a l e s d i e b e f o r e  are o v o v i v i p a r o u s  n =  e q u a l l y unbalanced  selective  (through  American  However as  are remarkably  by  guppies  = 0.61,  is a  t h a t i n some p o p u l a t i o n s  sperm i n v i a b i l i t y )  (guppies  ratio  of d i f f e r e n c e s i n the  i s biased i n favor of  zygotes "Y"  overlooked  presence  are not  v a r i a t i o n may  mechanisms i n v o l v e d i n t h e point apparently  sex  i n natural populations.  ( e . g . Lower T a c a r i g u a )  Therefore  mainland South  average there  5 reveals, a l l populations  corroborate  (1961) f o r T r i n i d a d  Bond c o l l e c t i o n ,  t h a t on  data  reasons),  to sexual maturity  predator-free conditions.  under  I raised  both  a large  controlled  I used s t o c k s d e r i v e d  natural populations exhibiting  excess  balanced  from  (e.g.  Guayamare) and The  unbalanced  data were.obtained  (e.g. P e t i t e  by  Curucaye)  (a) s e x i n g t h e a d u l t s  t h a t had been s t a r t e d w i t h immature  fish  not recorded)  and  t o check  for variation  i n t h e sex r a t i o .  immature  of l e s s  fish  (b) r u n n i n g t e s t s  t h a n 12 mm,  p o i n t where s e c o n d a r y The  ratio  excess of females that  t h e r e i s no  produce  though  (sex r a t i o  t h e r e was = 0.90,  i n h e r e n t tendency  (1961).  in  rivers  working  at b i r t h  these experiments  domestic  guppies  i n d e e d 1:1  resulted  and  t o be  concluded that  consequently died  H a s k i n s e t a l (1961) w o r k i n g  slight I conclude  applies  to the  of Haskins when 3359  and C o a t e s  et al  guppies to maturity  (1932)  from a Jamaican p o p u l a t i o n  w i t h an  i n very unbalanced  expected  of the stocks to  0.5.  Shoemaker  "Illinois" the r a t i o  Comfort  with domestic  of  at b i r t h  a t a younger  sex r a t i o s .  (1944)  strain  b u t t h a t m a l e s were more s u s c e p t i b l e  temperatures  the  well.  However B r e d e r  repeated  and  only  an o v e r a l l  i n T r i n i d a d were r a i s e d  with a stock derived  f o u n d t h e sex r a t i o  from the  f o r any  support the f i n d i n g s  the l a b o r a t o r y .  specifically  n = 1049).  They o b t a i n e d a r a t i o o f 0.94  from u n s p e c i f i e d  length  experiments  I assume t h i s  r e s p e c t i v e n a t u r a l p o p u l a t i o n s as results  (number and  a s i z e w e l l below  significantly  an uneven sex r a t i o .  My  i n stocks  (b) I r a i s e d  obtained i n these  ( T a b l e 6) d i d n o t d i f f e r 1:1  ratios.  s e x u a l c h a r a c t e r s become e v i d e n t .  sex r a t i o s  theoretical  In  sex  was  to high age;  this  (1961)  and w i l d  and  stocks  48  TABLE 6.  Stock  The s e x r a t i o s o f l a b o r a t o r y  Replic.  Lower A r i p o  1 2 3 4  5 Total  X Upper A r i p o  2  Total  Guayamare  2  Total  Petite  Curucaye  2  Total  Paria  2  Total  Grand T o t a l :  2  0 3 4 13 39  0.45 1.04 1.39 0.90 1.21  200  232  59  0.86  41 25 24  45 37 15  17 28 22  0.91 0.68 1.60  90  97  67  0.93  400 400 40  unknown  40 120  unknown  40 200 200  unknown  40 400  unknown unknown  250 135 210 75  165  unknown  p > 0.50  18 24  17 26  2 17  1.06 0.92  42  43  19  0.98  39 43 33  43 45 47  37 4 13  0.91 0.96 0.70  115  135  54  0.85  25 24  20 26  33 19  1.25 0.92  49  46  52  1.07  f e m a l e s : 553  170 -  125 160  sex  r a t i o = 0.90  N = 1049  (adults)  0 2  unknown  = 0.04; p > 0.80  males: 496 x  200 200 200 400 400  = 1.44; p > 0.20  1 2  x  77 24 36 81 14  = 0.00; p > .99  1 2 3  x  35 25 50 73 17  = 0.19;  1 2  X  Sex Tank v o l . Orig.No. Males Females Immat . r a t i o ( l i t e r s ) of f r y  (males:females) = 2.22 ; p > 0.10  1 2 3  X  populations.  2.99;  p > 0.05  respectively, t h e r e was  no  concluded  ( i n an  "the.sex r a t i o  ratio  of the  this  play  a  Kosobutskii  predation  parent  generation  sexes.  (1972) have shown e x p e r i stock  of natality.depends  feedback.is  guppies)  i n t u r n on  (p. 1 2 4 ) . "  accomplished but  of  the  I t i s not  vision  sex  known  appears  to  role. It  unstable account tories  i s p o s s i b l e t h a t the  and  that r a c i a l  (Winge, 1934;  Why  of the  strain  the  evidence  system i s q u i t e  ratio?  c o n t r o l o f sex  is  d i f f e r e n c e s might  reports  from v a r i o u s Kallman,  labora-  1965).  f o r a s t a b l e XX-XY  For sex  convincing.  then i s there-such  sex  genetic  Shoemaker, 1944;  populations  determination  the  or  for the-conflicting  Trinidad  in  absence of  unspecified laboratory  that,  how  i n the  d i f f e r e n c e i n l o n g e v i t y between t h e  Geodakyan and mentally  that  striking  Selective predation  geographic  variation  on m a l e s may  be  part-  answer.  R e l a t i o n s h i p of p r e d a t i o n to v a r i a t i o n i n t h e sex r a t i o When t h e related  sex  ratios  to the presence of  clear-cut  correlation  of  the  fish  ranged  is discernible.  Rivulus  and  cichlids.  f r o m 0.28 0.50  to  1.00  to  1.14  collections  predators  f o r w h i c h t h e most c o m p l e t e d a t a ratio  field  are  (Table  I n 1969  7)  (the  a v a i l a b l e ) the  f o r streams  are no year sex  containing  f o r s t r e a m s wit,h c h a r a c i d s  and  50  TABLE 7.  The r e l a t i o n s h i p o f t h e s e x r a t i o t o t h e presence of f i s h predators. Sex r a t i o s a r e b a s e d on t h e 1969 c o l l e c t i o n s .  RIVULUS Sex r a t i o  River  AND CICHLIDS Sex r a t i o  Trib.  0 .28  Oropuche  0.50  Curucaye  0 .33  Lower  0.71  Tompire Petite  CHARACIDS River  Aripo  Upper  Aripo  0 .48  Upper Guanapo  0.74  Upper  Curumpalo  0 .49  Caroni  0.74  Grande C u r u c a y e  0 .61  Upper A r o u c a  0.86  Marianne  0 .80  Santa Cruz  0.91  Yarra  0 .91  Lower  0.91  0 .98  Guayamare  0.92  Upper  0.98  Blue Paria  Basin  • 1 .14  Caparo  Tacarigua  Tacarigua  1.00  51 It with  i s important  Rivulus  to r e c a l l  are smaller,  that  i n general,  streams  c o o l e r , and more h e a v i l y  shaded,  t h o u g h where p h y s i c a l b a r r i e r s p r e v e n t characids  and c i c h l i d s ,  Rivulus  mental c o n d i t i o n s resembling cichlid with  habitats.  Rivulus)  Tacarigua  does o c c u r  under  some o f t h e n o r m a l  Thus Upper A r i p o ,  of  environcharacid-  P a r i a , and Y a r r a ( a l l  are p h y s i c a l l y similar  a n d Upper A r o u c a  the immigration  s t r e a m s t o Upper  (both w i t h  c h a r a c i d s and  cichlids). The  r e l a t i o n s h i p between p r e d a t i o n  becomes more e v i d e n t the or  when p r e d a t i o n  abundance,of p r e d a t o r s (Fig. 6).  absence  Rivulus and  This  characids  and c i c h l i d s  a slight  For balanced high  t e n d e d . t o be f a i r l y  temperature, or s i z e  exposed t o balanced  F o r these  Rivulus  streams  and t h e  t h e sex r a t i o  was  d e n s i t y was low b u t u n b a l a n c e d when (low d e n s i t y = l e s s t h a n  i n 1 t o 2 hours; high  a d u l t s caught with  with  o f the stream.  streams c o n t a i n i n g R i v u l u s ,  caught  f o r characids  With t h e e x c e p t i o n o f  of a l l populations  d e n s i t i e s were o b s e r v e d  adults  presence  a n a l y s i s c o u l d be made o n l y f o r  preponderance o f females.  when R i v u l u s  i n terms o f  their  r e l a t i o n s h i p was f o u n d between t h e s e x r a t i o  turbidity,  50  r a t h e r than only  were i n a d e q u a t e .  Oropuche, t h e sex r a t i o s  no  i s assessed  h a b i t a t s because the d e n s i t y estimates  cichlids  only  and t h e s e x r a t i o  same  density  density = greater  10 than  effort).  i s a l s o c o r r e l a t e d t o some  extent  52a  FIGURE 6.  The  relationship  relative the  1969  density  of  the  sex  of Rivulus.  collections.  ratio  to  the  Data are  for  52b  LU  LU  tr  LU Q_ CO LU  1.2 H  < 1.1 H cn 1.0  UJ  a . 0.9 a. 0.8 O  o  < tr x LU  cn  0.7 0.6 0.50.40.3Q2-  I  NONE  1  1  1  LOW MEDIUM HIGH  RELATIVE DENSITY of RIVULUS  53  with  t h e amount o f c o v e r and  s i z e of the stream.  e x t r e m e sex r a t i o s were o b s e r v e d and  Petite  Curucaye  R.;  i n the Tompire  these streams  volume o f w a t e r f l o w and  the  largest  also  had  The  most  Tributary the s m a l l e s t  individuals,  and  densest populations of Rivulus. There relating  i s some a d d i t i o n a l  (>  Although in  1969  evidence  R i v u l u s abundance t o sex r a t i o s o f g u p p i e s .  Blue Basin i n 1 9 6 9 , large  comparative  50 mm)  t h e r e was  a conspicuous  R i v u l u s compared t o t h e  t w i c e t h e e f f o r t was ( c o l l e c t i n g g e a r was  8).  stream  (Tompire  suggesting  The  < 50  levels.  i d e n t i c a l and  both  collections  R i v u l u s were c a u g h t  same b e t w e e n - y e a r s c o m p a r i s o n  or  with  T r i b u t a r y ) r e v e a l e d no p a r a l l e l  t h e d e c r e a s e was  TABLE 8 .  1967  of  spent s e a r c h i n g f o r R i v u l u s  were i n t h e a f t e r n o o n ) v e r y few (Table  absence  At  seen  another  differences  s p e c i f i c t o Blue Basin.  R i v u l u s abundance i n two s t r e a m s i n 1 9 6 7 and 1 9 6 9 . Twice the e f f o r t . w a s spent, c o l l e c t i n g specimens a t Blue B a s i n i n 1969 compared.to 1 9 6 7 . The e f f o r t b o t h y e a r s a t T o m p i r e T r i b u t a r y was a b o u t t h e same.  BLUE BASIN > 50 mm mm  Total  TOMPIRE TRIBUTARY < 50 mm > 50 mm T o t a l  1967  21  40  61  36  18  54  1969  16  6  22  41  15  56  Total  37  46  83  X .-. 1 df 2  8.11,  p <  .005  . . x x  . 77. . .  .  , 33 .  .0.29,  2  i df ;  p >.  110 .50  54  As w e l l of  as a s i g n i f i c a n t  decrease  l a r g e R i v u l u s a t B l u e B a s i n i n 1969,  striking  Sex r a t i o o f g u p p i e s 1967 and 1969.  (Rivulus  high)  1969  (Rivulus  low)  Total  X  The  main  t o be  s m a l l mountain stream  1967  t h e r e was  little  Total  95  213  308  418  425  843  513  638  1151  31.32, p  1 df  through  <  i n 1969  o f women w a s h i n g c l o t h e s  years t h e use  i n the  I observed  i n the  stream.  Pools a  had  of  foam and  A few  empty d e t e r g e n t b o t t l e s .  guppies  and  I observed  f o u n d no d e a d R i v u l u s , I p u t decrease  s e v e r a l dozen  a d e a d S y n b r a n c h u s marmpratus . forth  i n R i v u l u s numbers i n 1969  meters dead  Although  caused  few  accumulations  I  the h y p o t h e s i s t h a t was  In  several  meters below the main l a u n d r y s i t e  below the l a u n d r y s i t e  of  headwater  hundred soap  .001  f o r the l a u n d r y of c l o t h e s .  human a c t i v i t y  regions of Blue Basin, but groups  Females  of p o l l u t i o n  this  a  (Table 9).  e c o l o g i c a l d i f f e r e n c e between  the l e v e l  also  a t Blue Basin i n  Males  1967  abundance  t h e r e was  change i n t h e s e x " r a t i o s o f g u p p i e s  TABLE 9.  appeared  i n the  directly  the or  55 indirectly  by  still  high  that  very  pollution. (perhaps  t h e y were n o t  immediate v i c i n i t y r e d u c t i o n of the restoration  and  1969  differing reason tion  above 1967  affected  by  13  stream  ( F i g . 5)  in  Therefore  B a s i n was  dropped.from the  the  the  1969.  t h a t were compared  noticeably i n i t s predator  i t was  i n the  c o u l d have f a c i l i t a t e d  sites  Blue  source).  ratio  was  i t is possible  the p o l l u t a n t s (except  Rivulus stock sex  number o f g u p p i e s  levels),  o f the p o l l u t i o n  of a balanced  (Of t h e 1967  Because the  the o n l y  one  population;.  calculation  between  of the  For  this  correla-  coefficient.) On  the b a s i s of the  above, the h y p o t h e s i s guppies  is certainly  that Rivulus compelling;  c i r c u m s t a n t i a l evidence. determined  Sex  field  data  selectively  presented  feeds  however i t s t i l l  on  field  evidence  on  be'  that also influence  are c o r r e l a t e d with) R i v u l u s d e n s i t i e s .  to get d i r e c t  male  relies  r a t i o s might a c t u a l l y  by more s u b t l e c a u s a l f a c t o r s  (or a t l e a s t attempted  comparative  by  examining  I stomach  contents. Unfortunately sex  i n predator  I found  stomachs.  Of  few 58  R i v u l u s t h e r e were-10 a d u l t s o r female-, and fish  3 uncertain) .  guppies guppies  vertebrae)  a p p e a r e d t o be  stomachs  of l a r g e r  (mostly  1  from Astyanax  b u t most o f  fish,  from  (6 m a l e s ,  recovered  H e m i b r y c o n were j u v e n i l e s (< 13 mm)  recognizable  recovered  sub-adults  A l l guppies  remains i n C r e n i c i c h l a  of  scales  probably  the. and adult  56 guppies  (sex unknown) and  Therefore except versus  1 female  demonstrating  for limited recovered)  an e x p e r i m e n t a l  tions  approach.  direct  (6 m a l e s field  I had the  "Haskins  specialized  fish  ("probably  predators of a d u l t L e b i s t e s " ) are  found.  ratio  i n 1967 If  sex r a t i o s  s e l e c t i o n by colour,  1969  observations  =  reflect  (a) and  expected.  Curucaye,  where c o n s p i c u o u s n e s s probably  least  Upper.Aripo are  however t h e  the i n t e n s i t y  (b) a r e  sex.  differential,  that  i n small, clear  (based on e i t h e r  hue  their  the o p p o s i t e of  I found  Tompire T r i b u t a r y ) ,  to v i s u a l  of  the b a s i s of  just  Furthermore,  important  females  0.48).  a r e n o r m a l l y most u n b a l a n c e d  (e.g. P e t i t e  severe  l a r g e b l a c k markings t h a t  p r e d a t o r s a g a i n s t m a l e s on  what w o u l d be ratios  (e.g.  i r i d e s c e n t pigments;  = 0.63;  less  outnumbered by  conspicuously coloured  often ocellated with  the  (few m a l e s ) where . o f the  m a l e s a r e c h a r a c t e r i z e d by  hypothesis'':  predators" (characids  one  (b) m a l e s a r e o f t e n g r e a t l y  observa-  b a l a n c e d where  are unbalanced  good•numbers o f R i v u l u s  adopted  because,  made s e v e r a l  are r e l a t i v e l y  occur but  yet are s t i l l  evidence  to natural predation.  T h i s seemed m a n d a t o r y  t h a t were a t v a r i a n c e w i t h  cichlids)  fish  I have no  p r e l i m i n a r y stage  "more d a n g e r o u s and  Rivulus  Astyanax.  support of the h y p o t h e s i s , I  (a) sex r a t i o s  and  d a t a on  m a l e s a r e more l i a b l e  For a d d i t i o n a l  even a t t h i s  j u v e n i l e Aequidens or  (c)  sex  streams  an e n v i r o n m e n t ' or contrast) i s  predators.  57 These aimed  conflicting  at testing  o b s e r v a t i o n s prompted  a l t e r n a t e hypotheses  the observed v a r i a t i o n  in.the  sex  experiments  t h a t might  account f o r  ratio.  Size hypothesis It about  i s w e l l known t h a t male g u p p i e s c e a s e ' g r o w i n g  the time o f s e x u a l m a t u r i t y whereas females c o n t i n u e  t o grow u n t i l  death.  Consequently  t h e same s i z e d i s t r i b u t i o n . example, 73% the  F i g . 2).  sex, d i f f e r e n c e  feeding  This  t h e s e x e s do n o t  In the P e t i t e Curucaye  of the females exceed  l a r g e s t male..  Appendix,  the s i z e  i s shown v e r y ' c l e a r l y  i n .wet body w e i g h t was  share R. f o r  (in length) of'  In the r e g i o n o f o v e r l a p  i n the. i n length,.no  found.  S i n c e many p r e d a t o r s a r e s i z e - s e l e c t i v e  i n their  ( I v l e v , '19.61; J a c k s o n , 1961;  Dodson,  1965;  Mason, 1965;  1969;  P a r k e r , 1971),  Galbraith,  equally vulnerable p r e d a t i o n might  a l l size  1967;  play  Curucaye  t h e mean s i z e  population, o f males  unbalanced  selection  sex r a t i o s  high densities  of  LeBrasseur, not  this  (22,9 mm  alone might  i n the observed  F o r example" I f o u n d  upper  limit  ± 1.41  SD)  (30.1 mm  For  coincides but f a l l s  ± 5.63  SD).  a c c o u n t f o r the.  observed i n p o p u l a t i o n s exposed  Rivulus.  be  Size-selective  i n t h e stomachs o f R i v u l u s .  w e l l b e l o w t h e mean s i z e o f f e m a l e s Therefore.size  1968;  o f p r e y may  an i m p o r t a n t r o l e  mm  and  Brooks,  to a given predator.  no g u p p i e s above 23.0 the P e t i t e  Brooks  classes  g e o g r a p h i c t r e n d s i n t h e sex r a t i o .  with  at  to  .  58 Conversely, predators, actually prefer  the  be  larger relative  a disadvantage  to devour'victims  (Ivlev,  1961:  half-grown the  (a) t h e  85).  m a l e s by  of the  and  small predators  f e m a l e s may  Where " e s c a p e by smaller  sex  sex  Range.  s e l e c t i o n by  be.balanced  (b)  very  by  colour  selection  of  small  a l t o g e t h e r , or predation with  should  be  least sex  hypothesis  see  ratio  Chapter  observations  A  stemming sizes.  predators)  This  variation  demonstration  model in of  the size  5.)  .. . ' of guppies  q u i c k l y r e v e a l t h a t the  identically.  (no l a r g e  abundant.  (For e x p e r i m e n t a l  either  a wide spectrum o f  growth" i s p o s s i b l e  predators,  Casual  spent  selective  r a t i o might t h e r e f o r e r e f l e c t  appears to f i t the observed  laboratory  the  even  or H o p l i a s ) .  f r o m a community o f p r e d a t o r s  Behavior  pools,  o f m a l e s b a s e d on and  might  size"  overwhelm  However i n n a t u r e ,  ( A s t y a n a x and  absence of p r e d a t i o n  Northern  easily  large  "Predators  l a r g e outdoor  H a s k i n s e t a l , 1961)  A balanced  the  and  greater conspicuousness  Crenicichla  of a d u l t females  largest possible  Hoplias  l a r g e . p i s c i v o r e s on  by  t o a t t a c k , by  i f i t i s true that,  f e m a l e guppy.  (as s u g g e s t e d  liable  size  In a q u a r i a  Crenicichla  largest  impact of  the  i n populations  i n the  field  sexes.do not  or  behave  l a r g e p r o p o r t i o n of the m a l e s a c t i v i t y  i n courtship while  !  the  f e m a l e shows l i t t l e  sexual  is  59 behavior  and It  sex  a p p e a r s t o be  has  r a t h e r wary.  been p o s t u l a t e d  differences i n behavior  m o r t a l i t y o f one 1955,  cited  Estes  and  that  o f t e n . t h e male  G o d d a r d , 1967; the  female  confirmation  vertebrates  might c o n t r i b u t e t o . a  i n Maher, 1970;  occasionally field  sex,  for other  Aim,  (Lack,  1959;  Holcomb and (Olson,  1965).  (c) a r e more a c t i v e , territories,  (d) a r e  Although  e i t h e r d e t e c t i n g the prey  to  within attacking distance. by-products  or  I shall  per  ences i n behavior  facilitating  later  aggressive,  defend,  t h a t sex  some o f in this  vital  predator  a close  These disadvantages  se m i g h t be  consider  because  courtship displays.  of otherwise  There remains the p o s s i b i l i t y escape behavior  suspected,  are presumed t o a i d the  in  extent  (e)  and direct  (b) a r e . m o r e  "timid",  ( f ) have c o n s p i c u o u s  T h e s e male t r a i t s  certain  less  1965;  1970)  i s generally lacking, i t i s  (a) have l a r g e r home r a n g e s ,  Thompson,  Selander,  i n some s p e c i e s m a l e s a r e more v u l n e r a b l e  they:  greater  1954;  Twiest,  that  approach  are t o  a  male f u n c t i o n s .  differences in  present. t h e p o s s i b l e sex  differ-  chapter.  R e l a t i v e s u r v i v a l of the sexes i n p r e d a t i o n experiments As alter  the  a f i r s t - step sex  ratio,  I conducted  ments w i t h w i l d - c a u g h t eliminate  the  i n understanding  and  how  predators  several predation  experi-  l a b o r a t o r y - r e a r e d guppies.  "size hypothesis"  as  a possible  might  To  explanation  60 for  any s u r v i v a l d i f f e r e n c e s , I c o n t r o l l e d - s i z e  as p o s s i b l e by m a t c h i n g male and f e m a l e  A.  Experiments with  E x p e r i m e n t 4.1  wild-caught  Predation  as  strictly  sizes.  fish  by R i v u l u s  i n the laboratory.  Methods A  l a r g e sample o f g u p p i e s and R i v u l u s  f r o m above and b e l o w t h e e x p e r i m e n t a l  was c o l l e c t e d  section of Petite  C u r u c a y e R., b r o u g h t t o t h e l a b o r a t o r y ' and m e a s u r e d f o r size.'  The f o l l o w i n g day 2 f e m a l e R i v u l u s  were s e l e c t e d and p l a c e d natural decaying  P e t i t e Curucaye s u b s t r a t e citrus  leaves).  natural photoperiod Ten lation,  i n a 40 l i t e r  with.natural  sunrise  and  o f new f i s h  (from  density  those eaten. (prey  popu-  f o r the addition  as t h e i n i t i a l  20  To a v o i d l a r g e ' f l u c t u a t i o n s r i s k ) these additions  i n t e r v a l s during  added were m a t c h e d f o r s i z e  prey  with the  called  t h e same c o l l e c t i o n  and s e x r a t i o  made a t f r e q u e n t  design  sunset.  (initial  s e x e s same s i z e ) were t h e n p l a c e d  to replace  containing  (deep brown d e t r i t u s and  male and 10 f e m a l e g u p p i e s  The e x p e r i m e n t a l  in  aquarium  mm)  The t a n k was m a i n t a i n e d u n d e r a  predators.  fish)  (80 and 82  t h e day.  The.fish  (x f o r m a l e s = ,22.6 mm,  20-26; x f o r f e m a l e s = 22.9, r a n g e  were  range  21-25).  Results A total predators)  o f 61 g u p p i e s were a d d e d  o v e r a 12-day p e r i o d  (Table  ( i . e . e a t e n by t h e  10).  This  was  composed o f 44 m a l e s a n d 17 f e m a l e s  showing  clearly  that  2 m a l e s were t a k e n s i g n i f i c a n t l y more o f t e n  (X ^  d  f  = 11.08,  p < .001). TABLE 10.  P r e d a t i o n by R i v u l u s o n male and f e m a l e g u p p i e s i n ' a 40 l i t e r a q u a r i u m . Predator and p r e y were w i l d - c a u g h t .  Day.  Males  1 2 3 4 5 6 7 8 9 10 11 12  NUMBER ADDED Females  6 3 1 5 4 2 9 2 0 2 7 .3 Total  2 1 4 3 1 1 2 2 0 0 0 1.  44  E x p e r i m e n t 4.2'  17  P r e d a t i o n by R i v u l u s i n t h e  61  field.  Methods T h i s e x p e r i m e n t was c o n d u c t e d section in  of the P e t i t e  t h e Appendix  Curucaye  for details  R.  i n the cleared  ( r e f e r t o map and f i g u r e s  on t h i s  site  and. the. a b s o l u t e  number o f p r e d a t o r s and p r e y p r e s e n t p r i o r Following of  the Rivulus,  t h e removal  I collected  to clearing).  o f a l l guppies  fish  and o v e r 90%  f r o m above a n d b e l o w t h e  62 screened-off  section.  Eight  Rivulus  63-89) were added t o t h e s e c t i o n others of s i m i l a r  size  original  The  census.  matched f o r s i z e f e m a l e s = 21.7, placed  t h a t had guppies  i n this  i n the s e c t i o n  mm,  1600  6  i n the  experiment  range  were  19-25; x f o r  Then 50 o f e a c h  (released,at  range  about  n o t been caught  used  19-25) .  mm;'  t o supplement  (x f o r m a l e s = 21.5 range  (x = 73.6  s e x were  hr i n Pool 2).  Thus a " s y n t h e t i c " p o p u l a t i o n o f p r e y w i t h a 1:1 r a t i o was  created.  intervals  f o r 22 d a y s .  this  stream  more  quickly.  I monitored  i s 0.33,  t h e sex r a t i o  Because the n a t u r a l  I predicted  sex  at frequent  sex r a t i o  of  t h a t males would d i s a p p e a r  ResultsBy stabilised  Day  22  t h e sex r a t i o  a t 6.74  (Fig. 7).  of the s e c t i o n  The  had  number o f f i s h ' d i s 2  appearing fails  (8 f e m a l e s  to reach the Since  and  .05  i t was  19 m a l e s ,  level  of  X ^ ^  not f e a s i b l e  guppies  f o r a l l the l o s s e s .  collected  at Petite  just  probability. to run a c o n t r o l  without p r e d a t o r s , i t i s not c e r t a i n accounted  = 3.70)  that  section  Rivulus predation  However a l a r g e g r o u p  Curucaye  at about'the  of  same  time  a s . t h e e x p e r i m e n t a l sample and p l a c e d i n l a r g e , p r e d a t o r f r e e o u t d o o r p o o l s showed no m o r t a l i t y .  (Handling m o r t a l i t y  caused b y capture, t r a n s p o r t ,  and measurement i s n o r m a l l y  about  evidence that  1%.)  c o u l d escape  A l s o t h e r e was  no  from the s e c t i o n  the  guppies  under' o r t h r o u g h t h e  fine  63a  FIGURE 7.  Relative in  s u r v i v a l o f male and  female  the e x p e r i m e n t a l s e c t i o n of the  Curucaye  River.  guppies  Petite  tt  7D  1  0  0  -  H 0  1  1  1  2  4  6  r—i 1 1 1 1 1 1 r 8 10 12 14 16 18 20 22 24  DAYS  64 screen.  As I i n d i c a t e d  guppies remained  i n Chapter  i n Pool 2 during  3, a b o u t  95% o f t h e  the course of the.exerpi-  ment. S i n c e g u p p i e s had b e e n f o u n d p r e v i o u s l y stomachs o f R i v u l u s and I by  occasional  conclude that selective  laboratory B.  from t h i s  section  the greater m o r t a l i t y  results  This  (Exp.  field  I exposed  addition  the experiment,  o f m a l e s was  test  laboratory  then confirms the  stocks  stocks  The methods u s e d i n t h e s e i n considerable d e t a i l  same p r o c e d u r e was u s e d  i n experiments  refer  fish,  ( i . e . predator-naive) to  ments s h a l l be o u t l i n e d  I shall  caused  t o these 2 experiments with w i l d  Crenicichla or Rivulus.  chapters.  approaches  4.1).  Experiments w i t h l a b o r a t o r y In  and numerous  a t t a c k s were o b s e r v e d d u r i n g  predation.  i n the  experi-  because the  i n subsequent  t o i t as t h e " s t a n d a r d ' s u r v i v a l  test".  Procedure In stainless L  f o r standard s u r v i v a l a l l tests steel  of this  frame  test  t y p e a 200 l i t e r  aquarium  was u s e d  = 92 cm, W = 48 cm, D = 46.5-cm).  (dimensions:-  Four  identical  a q u a r i a were s e t up i n t h e same room so t h a t tests  c o u l d be c o n d u c t e d  c o v e r e d on t h e b a c k  g l a s s and  simultaneously.  several  These  t a n k s were  and s i d e s w i t h b l a c k p l a s t i c ;  pane was c o v e r e d w i t h a m o v e a b l e b l a c k c u r t a i n .  the front The depth.  was k e p t guppies  a t 30 cm t o a l l o w s p a c e  beneath  t o " s u r f a c e jump" when a t t a c k e d .  was p l a c e d i n one s i d e o f t h e t a n k the p r e d a t o r ( s ) .  i n diameter.  A large  flower pot-  t o s e r v e as a r e f u g e f o r  The s u b s t r a t e c o n s i s t e d  sand m i x e d w i t h f i n e p e b b l e s  no  the cover glass f o r  of light  and some l a r g e r  brown  s t o n e s t o 10 cm  The t a n k was d e v o i d o f a q u a t i c p l a n t s  since  submerged v a s c u l a r p l a n t s o c c u r i n most N o r t h e r n  Range  streams  (sedges  periodically  and g r a s s e s n e a r  t h e s h o r e do g e t c o v e r e d  i n t h e wet s e a s o n ) .  Normally were s e l e c t e d b = females).  50 g u p p i e s  o f type  a t random f r o m  " a " and 50 o f t y p e "b"  stock aquaria  T h e s e were m e a s u r e d  (e.g.  24 t o 48 h o u r s  a =  before the  s t a r t o f the experiment.  The p r e d a t o r was u s u a l l y t h e  resident  and t h e g u p p i e s  it  i n the t e s t  (after  normally  a 1 hour  tank  period  i n the l a t e  S u r v i v a l was m e a s u r e d  floating  afternoon.  i n a screen basket),. 1  s i m p l y by r e m o v i n g  They were i m m e d i a t e l y  This procedure  d i d n o t appear  were p l a c e d w i t h  T h i s was termed. "Day 0' .  l a r g e n e t and c o u n t i n g t h e s e x e s , question.  males,  sizes,  the guppies with a stocks, e t c .  returned to the test  to disturb  in tank.  either predator or  prey. When a p p r o x i m a t e l y eaten, a l l remaining possible 16).  size  selectivity  When d e n s i t i e s  to count  fish  f i s h without  50% o f t h e p o p u l a t i o n h a d b e e n were m e a s u r e d a g a i n t o t e s t f o r by t h e p r e d a t o r  reached  less  removing  than  them.  ( C h a p t e r 5, F i g .  15, i t ' was p o s s i b l e The t e s t was  66  t e r m i n a t e d when numbers e i t h e r  reached o r approached  When t h e p r e d a t o r was C r e n i c i c h l a , i n d i v i d u a l was u s e d  f o r 3 reasons':  very aggressive species to  injury  tions and  revealed  that  in  and d o m i n a n c e by one f i s h  adult Crenicichla  (c) C r e n i c i c h l a o f even  sume- a l a r g e number  rate  o f water,  o f about  juvenile  of adult  s u r v i v a l w i t h an i n i t i a l  liters  density  overall mortality  so t h a t  size  s h o u l d not exceed  a mean  u s u a l l y more t h a n one  Also,  social  t o be p a r t o f t h e . n a t u r a l b e h a v i o r a l .  of this  species;  at Petite  Curucaye  several  a single.guppy.  a l l e x p e r i m e n t s p r e d a t o r s were f e d an e x c e s s o f o f the experiment;  the i n i t i a l  hunger l e v e l  this  on Day 1 as w e l l  (motivational  D u r i n g t h e e x p e r i m e n t p r e y were f e d f i n e d r i e d the  differences  o f 100 g u p p i e s p e r 135  to prevent a predator " o v e r k i l l "  control  observa-  are able t o con-  Crenicichla.  T u b i f e x t h e day b e f o r e t h e s t a r t was  lead  are s o l i t a r y predators,  Rivulus,  p r e d a t o r s were o b s e r v e d t o p u r s u e In  could  t h e p r e d a t i o n r a t e s w o u l d be  to that of a single  appears  repertoire  is a  10 p e r d a y .  i n d i v i d u a l was u s e d  feeding  (b) f i e l d  guppies; to detect  When t h e p r e d a t o r was  comparable  o n l y one  (a) C r e n i c i c h l a  o r death o f subdominant f i s h ,  zero.  as t o  state). food.which  predators d i d not eat. Four out of the 5 C r e n i c i c h l a  Vancouver variety  used  were w i l d - c a u g h t as j u v e n i l e s  o f foods  (see C h a p t e r  2).  i n experiments a t  a n d ' r a i s e d on. a  R i v u l u s were a l l  67 aquarium  bred.  experience  Both  species  had had c o n s i d e r a b l e  f e e d i n g on male a n d f e m a l e guppies..  was u n s u c c e s s f u l  i n breeding Crenicichla,  same i n d i v i d u a l s  i n many o f t h e e x p e r i m e n t s .  caution  against bias resulting  identity  (Table  11).  differences  likely  to bias results  standard action  survival  tests,  of 6 predators.  the r e s u l t s Also  As a p r e -  several  differences,  i n presenting  experimental r e s u l t s are less  With  Because I  I had t o use t h e  from i n d i v i d u a l  I have r e t a i n e d t h e i r i n d i v i d u a l  prior  Rivulus  individual  because  in a l l  are the c o l l e c t i v e "6-man teams" were .  used.  TABLE  11.  The o r i g i n , s e x , a n d s i z e o f i n d i v i d u a l C r e n i c i c h l a used i n experiments a t Vancouver.  Code no. Sex  Source  Home t a n k no.  T o t a l l e n g t h (mm) when c a u g h t max. r e a c h e d  Lower  Aripo  C-l  m  T51  75-100  205  Lower  Aripo  C-2  f  T52  75-100  185  Lower  Aripo  C-3  f  T53  75-100  173  Lower  Aripo  C-4  m  T52  75-100  187  C-5  m  15A  Vancouver supplier  250  68 Experiment  4.3  P r e d a t i o n by  Crenicichla  on C a p a r o  stocky  test,. I exposed  Caparo  Methods Using the standard s u r v i v a l s t o c k m a l e s and  females  cates per p r e d a t o r ) . the s i z e for  of the  to C r e n i c i c h l a  F o r one  s e x e s was  C - l and  r e p l i c a t e w i t h each  matched as c l o s e l y  t h e o t h e r a random sample o f a d u l t s was  sample w i t h g r e a t e r ' v a r i a n c e , f e m a l e s males). below  The  mean s i z e s  and  C-2  size  (2  repli-  predator  as p o s s i b l e taken  (i.e. a  generally larger  ranges  used  are  and  than  given  (refer also to F i g . 8). Test  Sex,  a  m f  b  Mean l e n g t h ,  (mm)  Range  19.8 21.8  16.0-25.0 17.0' - 32.0  m f  20.3 20.1  16.5-24.0 17.0 - 24-.0'  c  m f  20.2 20.1  18.0 16.0  -  23.5 24.5  d  m f  19.5 24.2  15.5 18.5  -  24.0 32.5  Results It  i s clear  ( F i g . 8)  that  a d v a n t a g e o v e r m a l e s u n d e r my is 4.2  i n sharp  with wild-caught  those  R i v u l u s and  outdoor  Haskins  Petite  p o o l s they  et al  had  little  i f any  conditions.  o b t a i n e d i n Exp.  i s the d i f f e r e n c e  p u b l i s h e d by  a q u a r i a and  experimental  c o n t r a s t t o the r e s u l t s  Even more s u r p r i s i n g and  females  Curucaye  4.1  results  In t e s t s  showed a d r a m a t i c  and  guppies.  between t h e s e  (1961).  This  sex  in  69a  FIGURE 8.  Relative  survival  o f male and  stock guppies exposed  to  female  Crenicichla.  Caparo  MALES © FEMALES •  0  i i i i i i i i 2 4 6 8  10 12  PREDATOR  2  4  6  8  10  DAYS  0  2  4  6  8  10 12 14  25  C-1  12  DAYS  * cr  70 difference  i n survival  m a l e s were o v e r Unfortunately used,  rate—in  5 t i m e s more v u l n e r a b l e t h a n  Crenicichla females.  t o o few d e t a i l s were g i v e n a s . t o t h e . m e t h o d s  t h e r e f o r e I am u n a b l e  for the d i f f e r e n c e  Experiment  2 tests with  4.4  t o f o r m u l a t e a. p l a u s i b l e  reason  i n our-results.  P r e d a t i o n by R i v u l u s on C a p a r o a n d ' P e t i t e Curucaye  stock.  Methods . The methods u s e d were t h e same a s i n E x p . 4.3 t h a t body s i z e was r i g i d l y Two  controlled  r e p l i c a t e s were p e r f o r m e d  Petite  Curucaye  same 6 R i v u l u s aquarium.  stock.  in all.4  except  replicates.  w i t h C a p a r o s t o c k s and 2 w i t h  A l l 4 t e s t s were c o n d u c t e d  (75, 75, 85, 73, 73, 85 mm)  with the  i n t h e same  S i z e s o f p r e y a r e g i v e n below.  Test  Sex  Mean l e n g t h  (mm)  Range  a  m f  19.9 19.9  17.0-23.0 16.0-23.5  b  m f  19.2 19.8  15.0-22.5 16.5-23.0  c  m f  20.4 20.4  18.5 - 23.5 17.5 - 23.5  d  m f  20.1 ,20.5  17.5-23.0 17.5 - 23.5  Results, Again taken  i t i s obvious  t h a t m a l e s and f e m a l e s  a p p r o x i m a t e l y e q u a l l y by t h e p r e d a t o r s  were  (Fig. 9).  In  71a  FIGURE 9.  Relative o f two  survival  stocks  o f male and  exposed  to  female  Rivulus.  guppies  NUMBER  of  SURVIVORS  72  one  of  the  r e p l i c a t e s w i t h P e t i t e Curucaye stock,  showed b e t t e r  s u r v i v a l but  chance d e v i a t i o n  (no.  t h i s could  e a t e n by  have been'due t o  4 -  Day  the' f e m a l e s  2 1 females,  a  3 4 males;  2 e x p e c t e d no. 2.62,  by  > p  .25  Discussion  non-selective  >  i l l u s t r a t e  the  predators.  male sex  the  r e s u l t s of  d  =  f  i s not  circumstances.males are  1. caused by.a  be  The  suggested difference  difference  (a) d i f f e r e n c e environment, (b)  the  4  previous  t h a t when body s i z e i s a c o n t r o l l e d a l w a y s more v u l n e r a b l e  However'Exp. 4 * 1 and  reasons could  4.2  show t h a t  under  t a k e n more o f t e n .  for.these could  cer-  Several  conflicting  have b e e n an  to  results:  artifact  i n e x p e r i m e n t a l methods. i n apparatus,  light  regime,  micro-  etc. difference  vulnerability—Exp. Exp.  2 7 . 5 , X ^  of - s u r v i v a l ' experiments  experiments  tain  =  .10).  Taken t o g e t h e r ,  variable,  predation  4 . 3 and. 4 . 4 by  i n measurement o f r e l a t i v e  4 . 1 by the  the  " r e p l a c e m e n t method"  "standard  and  survival test".  (c) d i f f e r e n c e . i n body s i z e o f . p r e y - - f i s h u s e d Exp.  4 . 1 were (d)  4.1  and  larger.  difference  in experience—fish  4 . 2 were w i l d - c a u g h t ;  were l a b o r a t o r y - r e a r e d . 2.  Possibly  there  those  i n Exp.  used  in  4 . 3 and  • i s a stock  Exp. 4.4 .  difference  in  the  in  73 degree bf to  their  sexual  (colour or behavior).  r e s p e c t i v e females,  vulnerable  C a p a r o m a l e s may  Subtle  s e x . d i f f e r e n c e s m i g h t be  a l a r g e p i s c i v o r e s u c h as  Several of  these  Light  was  12  important My  t h a t the  occurred  a l s o observed  only  own  ( u n p u b l . ) - has  further elaboration.  observations  i n Exp.  or dark  4.1:  600  light  of the and  hrs;  18 00  sunset,  Since  sudden t r a n s i t i o n  from dark t o l i g h t  nature  (Exp.  exhibiting that the  or  atypical  i n nature  the  Exp.  the  4.1,  hr  Under t h e s e  would p r o b a b l y  attack  I have no  the  1800  evidence  Hyatt  remarkable  t h e r e . w a s a more (and  vice-versa)  R i v u l u s may  u n d e r dim  than  have b e e n  I t i s .possible between  illumination; in .  female i s s t i l l  capture  added,  hrs).  has  conditions a visual  and  This  (sunrise in.  d i f f e r e n c e i n conspicuoushess  l i g h t while  feeding  guppies  i r i d e s c e n t p i g m e n t s o f t h e male may  reflecting  invisible..  4.4  feeding pattern.  s e x e s i s most a c c e n t u a t e d  twilight be  an  4.2)  i n Exp.  in  conditions.  61  also observed that Rivulus  scotopic vision.,  in  of Rivulus  greatest proportion of  u n d e r dim  approximately  4.3).  e c o l o g i c a l f a c t o r i n most  were added between 900  Trinidad  less  inconsequential  C r e n i c i c h l a (Exp.  require  systems.  revealed  activity  points  i s an  predator-prey nature  be  Relative  t h a n P e t i t e C u r u c a y e males.-  3. to  dimorphism  already  relatively predator  more m a l e s .  t h a t the  " r e p l a c e m e n t method"  74 u s e d i n Exp. females. of  the  4.1  c o u l d have b i a s e d  the  From s l i g h t . d i f f e r e n c e s i n . t h e  fish,  I was  able  to r u l e out  the  n e w l y - a d d e d f i s h were more v u l n e r a b l e residents of  food  (as B e y e r l e  selectivity The  4.1  upper h a n d l i n g  i n escape behavior becomes r e a l l y difficulty this  and  This  4.2. had  own  roughly  the  considerably  does e x i s t ,  not  aquarists  as  the  study  be  relevant  prey.  As  to  question  of  same s i z e ,  (b)  implies that  guppies. easier  female guppies  there  i s no  evidence  has  f o r the  are  differ  inexperienced other).  female guppies  advantage through a f o r t u i t o u s form of B a t e s i a n  Certainly  to  from j u v e n i l e s of  colour,-but  species  Exp.  or.(b). Rivulus  locomotory behavior;  o f t e n m i s t a k e one  used i n  i f , (a) m a l e s a r e  s h a p e , and  above,  prior-experience.  t o a t t a c k male  and  greater  large Crenicichla.  Rivulus  size,  it.only  encounters  I suggested  be.applicable i s the  c l o s e r to  I f a sex d i f f e r e n c e  predator  (immature R i v u l u s  Alternative  the  in a  i t i s possible that  been c o n d i t i o n e d  in their  that  original  o f g u p p i e s was  d i s t i n g u i s h i n g female guppies  species  morphology  possibility  than the  for Rivulus.  than females of a s i m i l a r  difficulty  an  limit  c o n d i t i o n i n g might occur  capture  and  s i z e d i f f e r e n c e s . may  t h e mean s i z e  there  size  pike).  important  c o n d i t i o n may  i n favour, o f  (1968) f o u n d  i s p o s s i b l e t h a t the w i l d - c a u g h t  4.1  its  by  Williams  i n subduing the  Finally It  and  problem of prey  b e c a u s e i n Exp. the  test  of cannibalism  enjoy mimicry.  in natural  75 populations  o f R i v u l u s — I examined o v e r  s p e c i e s and  found  Attacks but  on  no.trace  c o n s p e c i f i c s have b e e n o b s e r v e d  tion  be  fails  inhibited  by  the  In 2 p i l o t  added 15  50 m a l e s and survival  relative  female guppies  females).  the presence of  The that  results  under c e r t a i n  vulnerable  of  impossible  less  of  population  tests  the  virtually  identical  decrease  the  P o s s i b l y I used  ( c f . Brower,  of the p r e v i o u s circumstances  able  observations to decide  (size  too  1960).  hypothesis  to Rivulus predation..  males are direct  females.  I  reinforcement  ( i n i t i a l prey  "models" d i d n o t  R i v u l u s hunts non-randomly o r but  mimicry  37 mm  negative  f e m a l e s was  experiments  of the b e h a v i o r  this  to  However i n b o t h  r a t e o f p r e d a t i o n on  "models" i n t h e s e  Tests  to t e s t  j u v e n i l e R i v u l u s o f .16  r a t e o f m a l e s and  suggesting  few  50  recogni-  of guppies to a d u l t Rivulus,  f e m a l e g u p p i e s ) t o a c t as p o t e n t i a l a g a i n s t a t t a c k s on  ( i f species  preda-  experiments concerned p r i m a r i l y with  avoidance'.conditioning  purposely  laboratory  level).  I"made a p r e l i m i n a r y a t t e m p t hypothesis.  in. the  unharmed, s u g g e s t i n g  a taste factor  a t the v i s u a l  this  o f p r e d a t i o n on c o n s p e c i f i c s .  o f t e n t h e . f i s h were e g e s t e d  t i o n may  300. s t o m a c h s o f  e x p e r i m e n t s have shown  m a l e g u p p i e s a r e more This  suggests  (b) R i v u l u s h u n t s  t o a v o i d capture.. of predatory  that  randomly  In the  behavior,  (a)  absence  i t is  w h i c h mechanism i s o p e r a t i v e .  I  shall  76  now t e s t et  the assumption  (implicit  i n the study  of  Haskins  a l , 1961) t h a t t h e r e a r e no s e x u a l d i f f e r e n c e s  i n escape  behavior.  Experiment  4.5  Predator behavior  o f R i v u l u s and e s c a p e  b e h a v i o r o f male and f e m a l e  guppies.  Methods Six  Rivulus  (60 t o 70 mm)  f e e d i n g on male and f e m a l e aquarium.  After  (approximately  starving  the time  meal o f 3 g u p p i e s ) , added t o t h i s basket all  stock. and  guppies  r e q u i r e d -to c o m p l e t e l y  They, were f i r s t  and s e c o n d  released.  They had n e v e r  guppies  f o r size  before  ( r a n g e - — 2 1 t o 24  mm),  soon as t h e f i s h ' w e r e r e l e a s e d , t h e p r e d a t o r y  60 m i n .  discarded.  were  o f the Paramaribo  b e h a v i o r o f R i v u l u s was r e c o r d e d on a R u s t r a k for  were  placed i n a screen  been' e x p o s e d t o p r e d a t o r s  w e r e ' a l l matched c l o s e l y As  digest a  These guppies  generation f i s h  liter  f o r 24 h o u r s  10 male and 10 f e m a l e  aquarium.  experience i n  were p l a c e d i n a 4 0  the predators  f o r 20 min and t h e n  first  with p r i o r  After this  recorder  t h e s u r v i v o r s were removed and  This procedure  same 6 R i v u l u s .  event  was r e p l i c a t e d  The f o l l o w i n g b e h a v i o r  10 t i m e s  with the  p a t t e r n s were  recorded: (a) A p p r o a c h — t h e movement o f a p r e d a t o r guppy.  T h i s may v a r y  rapid dart.  i n speed  No a t t e m p t  from  towards a  a s l o w movement t o a  was made t o s e p a r a t e  these.  The  pursuit of  of  a guppy by  acceleration  received  and  a single (b)  "approach"  w i t h the  swallowed  be  separated  into  renewed  phases  acceleration  score.  successful  approach..  The  predator  prey.  (c) C a p t u r e — a normally  can  deceleration—each  Attack—a  makes c o n t a c t  Rivulus  successful  immediately  attack.  The  prey  ( i . e . capture =  is  kill).  Results The  results  ( F i g . 10)  reveal  m a l e s were a c t u a l l y a p p r o a c h e d and (Wilcoxon t e s t ; approach: T = 4,  n =  8,  two-tailed  p  <  test  .05).  (no  T =4, The  that  f e m a l e s and  a t t a c k e d more n =  10,  p  <  often  .02;  m a l e s t h a n f e m a l e s were k i l l e d to  T =  .01  >  > p  0,  n = 9,  per  overlap (Fig. and  <  predatory  single k i l l  between t h e  11). weight,  avoiding  p  .01;  a  (kills  total  kill:  that  took  more  less  f o r matched X  =  2 1  d  f  7.51,  .005).  When t h e ratio  indicating.it  c a p t u r e males s u c c e s s f u l l y  pairs:  for  made).  The. most i n t e r e s t i n g r e s u l t however, was  effort  attack:  p r o b a b i l i t y l e v e l s are  prediction  not  attempts  (predatory  s e x e s f o r any  Because the  t h e y were- a b l e  expressed  "effort"), of  the  p r e y were a l l o f  i t i s clear that  capture.  are  however, were u s u a l l y  a  is  no  replicates  similar'length  f e m a l e s were, more' a d e p t  E v e n when c o n t a c t e d by  to dart  10  there  as  away t o captured  safety i n 3 or  the  at  predator  more o f t e n . less attacks  Males under'  78a  FIGURE 10.  Predatory behavior of Rivulus male and stock.  female guppies o f the  exposed  to  Paramaribo  KILL (no.)  PER CENT ATTACK  PER CENT APPROACH  TOTAL KILL (no.) K>  o  o  C D C D  o  BBB  o  o  j^n^^  >  i ii iiii  m  79a  FIGURE 11.  The  ratio  captures  of predation f o r Rivulus  female guppies.  attempts  feeding  to successful  on m a l e . a n d  — J 160  MALES o FEMALES •  140 a} 120 LJJ 80 X O 60 < O 40  cr  CL 20 CL < 0  "l—I—I—i—i—i—I—i—i—r 1 2 3 4 5 6 7 8 9 10  20 18 1  _J  16 14 12 -  a> Q_ 10 CO  TA  o  <  »—  8 dm  6 4 2 i—i—i—i—i—i—i—i—i—T 1 2 3 4 5 6 7 8 9 10  TEST  80  these experimental conditions. The  g r e a t e r number o f a p p r o a c h e s  f e m a l e s s h o u l d n o t be preferred results approach  females.  f r o m my  and a p p r o a c h e s  t a k e n t o mean t h a t  To  some e x t e n t t h i s  inability  starting  within  a  towards  the p r e d a t o r s greater  score  t o d i s t i n g u i s h between an  a bout of chasing  In c o n c l u s i o n  initial  ( i . e . a choice of  prey)  bout.  this  t h e r e a r e sex d i f f e r e n c e s Paramaribo  directed  experiment  demonstrates  that  i n escape b e h a v i o r , a t l e a s t f o r  stock guppies.  E v i d e n c e f r o m o t h e r e x p e r i m e n t s f o r sex differences i n antipredator behavior A l t h o u g h Exp.  4.5  a r e more a d e p t a t a v o i d i n g this  sex d i f f e r e n c e was  level.  demonstrates  clearly  Rivulus predation,  o b s e r v e d on o n l y  Because o f the f l u r r y  a  of a c t i v i t y  that  females  the nature of  qualitative d u r i n g the  experi-  ment, I c o n c e n t r a t e d on t h e b e h a v i o r o f t h e p r e d a t o r s ; i t was  not  feasible  t o s i m u l t a n e o u s l y measure t h e  escape  behavior of the guppies. However, i n e x p e r i m e n t s d e s i g n e d t o measure behavioral differences u s e d m a l e s and separately.  (Chapter 6 ) ,  f e m a l e s and q u a n t i f i e d  Without  sex d i f f e r e n c e  among s t o c k s  going into d e t a i l  i n (a) t h e f o r m and  t h e i r behavior here, I found  frequency of  motor p a t t e r n s ,  (b) t h e t e n d e n c y  depth or remain  i n a s h o r e r e f u g e , and  I often  t o swim a t a (c)  no  escape.  particular  schooling  81 behavior. potential  I did find  a difference i n reaction distance to a  predator.  The  details  o f t h e methods u s e d i n m e a s u r i n g  reaction distances are given m e a s u r e d was avoidance  i n Chapter  Briefly,  the d i s t a n c e a t which i n d i v i d u a l  behavior  dead C r e n i c i c h l a .  to a potential predator, For a l l 5 stocks tested  mean r e a c t i o n d i s t a n c e o f t h e f e m a l e s males a l t h o u g h of the stocks. sexes f a i l e d  6.  these  d i f f e r e n c e s were v e r y  Though t h e o v e r a l l  to reach  t r e n d d o e s seem t o be  TABLE 12.  was  statistical  guppies  i n this  showed  case  g r e a t e r than the slight  f o r some  d i f f e r e n c e between t h e significance  (p > . 0 5 ) , a  apparent.  Reaction distance of naive dead C r e n i c i c h l a .  guppies  to a  n  Lower A r i p o  14.0 •± 0.64  15.6 + 0.98  25 p e r  Guayamare  11.7  +  1.29  11.9 ± 1.11  25  Upper A r i p o  12.3  +  0.72  13.0 ± 1.12  25  6.8  ±  1.09  10.2 ± 1.09  25  7.8  +  0.94  10.4 ± 1.12  25  + 0.49  12.20+ 0.51  Petite  Curucaye  Paria Total  a  ( T a b l e 12) t h e  Mean r e a c t i o n d i s t a n c e (cm) ± standard e r r o r Males Females  Stock  what I  10.53  125 p e r  sex  sex  82 Discussion  of  It  sex  differences in  i s noteworthy t h a t the  reaction distance i s in Petite derived ratio  behavior g r e a t e s t sex d i f f e r e n c e i n  Curucaye stock,  from a n a t u r a l p o p u l a t i o n w i t h  i n favour  of  females.  comparable d a t a  on  the  but  reason  there  i s no  different  Unfortunately  Earlier  stock  unbalanced  I do  not  to suspect  that these  (Table  12),  guppies  w o u l d be  i . e . no  sex  stock d i f f e r e n c e s i n the degree of  sexual  dimorphism  hinted  a role  i n the  experiments  ( P e t i t e C u r u c a y e and  These data observed  in  the  suggest  i n populations  p r e d a t i o n may  apparently  i n p a r t be  more d i m o r p h i c  For increased  of the  of the  and  lost  each  v i z . predation,  from the  sexual  mechanism t h a t p l a c e s t h a t would otherwise  escape behavior  sexes.  the  sexes  a  greater  able to  sexual  a liability be  similarity  However, i n are  "afford"  this  dimorphism.  i s usually inferred  may  ratios  generation.  a premium on be  used).  some s u r v i v a l b e n e f i t s  r e t e n t i o n of  selection  sex  greater  consequently  i n d i v i d u a l m a l e s t o be  risk,  must a c c r u e  suggest  a result  and  characid-cichlid  exposed t o R i v u l u s p r e d a t i o n ,  p e r c e n t a g e o f males are  Strong  exposed to severe  one  of  survival  C a p a r o s t o c k s were  t h a t the b a l a n c e d  antipredator behavior  populations  very  I drew a t t e n t i o n t o t h e p o s s i b i l i t y  t h a t t h i s m i g h t have p l a y e d  sex  have  r e a c t i o n d i s t a n c e s o f Caparo  f r o m Guayamare s t o c k  difference.  a very  a  t o be  c e r t a i n male (Selander, "concession"  the  traits 1965). made t o  I  83 sexual  selection  predation this.  A  i s absent. series  P a r i a and  of experiments  operative.  aspects  4.5  m i g h t be the  confirm but  with  profitable.  "size  hypo-  m o r t a l i t y may C u r u c a y e R.  be a male  become a t a r g e t o f R i v u l u s b e c a u s e i t i s s m a l l , the p r e d a t o r  of geographic  c o n s i s t e n t with both Although  applicable  t o approach too c l o s e l y .  variation these  i n the  sex  ratio  The  is  ideas.  the d i s c o v e r y o f a b e h a v i o r a l d i f f e r e n c e  the escape a b i l i t y  underline  i n the P e t i t e  cichlid  done t o  t o Exp.  females  of d i f f e r e n t i a l  F o r example,  or i t allows  in  similar  s u g g e s t i o n does n o t v i t i a t e  thesis"—both  guppy may  More work n e e d s t o . b e  Upper A r i p o m a l e s and  This  pattern  i n p o p u l a t i o n s where c h a r a c i d , and  o f the  sexes  (Exp.  to a l l populations of guppies,  4.5)  may  not  i t certainly  the need f o r a c a u t i o u s i n t e r p r e t a t i o n o f  results  of simple  1961).  Colour  determines  survival  i s but  one  i t s relative  experiments  be  ( c f . Haskins  o f many a t t r i b u t e s  does  the 'et a l ,  of a prey  that  vulnerability.  C o n c l u s i o n and g e n e r a l d i s c u s s i o n o f g e o g r a p h i c v a r i a t i o n i n the sex r a t i o In t h i s geographic  chapter  variation  comparative  and  differences  occur.  I have d e s c r i b e d t h e p a t t e r n o f  i n the  experimental The  sex r a t i o  and  have u s e d  a p p r o a c h t o d i s c o v e r why  main c o n c l u s i o n t h a t c a n be  •from t h i s work i s t h a t p o p u l a t i o n d i f f e r e n c e s ratio  are r e l a t e d  a  to d i f f e r e n c e s  i n predation.  i n the  these  drawn sex  However,  84 this  relationship  i s not simply  dimorphism i n c o l o u r . other  I have d e m o n s t r a t e d t h a t s e v e r a l  sex d i f f e r e n c e s a r e r e l e v a n t t o d i f f e r e n t i a l  especially  i n environments i n f e s t e d with  Few c o m p a r a b l e on  the r e l a t i o n s h i p  Nevertheless theoretical ratio. is  ratio  between t h e s e x r a t i o  of population variation  "anti-selectionist",  (Nikolskii,  1969: 1 3 0 ) . "  studies, Nikolskii  From a r e v i e w  c o n d i t i o n s are conducive  o f males.  These  "adaptive"  and h o r m o n a l  The Fisher's Natural  theory  Williams from d a t a  t o an e x c e s s  alterations  ( F i s h e r , 1958: 1 6 2 ) :  produc-  i n sex r a t i o v i aunspecified  tend  "the a c t i o n o f  to equalize the parental  devoted to the production  on s e x r a t i o s In a broad  (1961) f o u n d  while  s c h o o l a d h e r e s more c l o s e l y t o  (1966: 152) c o n c l u d e d  adaptation."  females  routes.  Selection will  expenditure  Anderson  opposing  of f i s h  i s abundant  a r e n o t s e e n as h e r e d i t a r y c h a n g e s b u t o c c u r metabolic  of the  i n t h e sex  (1969) a s s e r t s t h a t  p r e d o m i n a t e when d e n s i t y i s low a n d f o o d  tion  i n the sex  a r e t h e main c a u s e s o f a l t e r a t i o n s  opposite  conducted  and p r e d a t i o n .  "Changes i n t h e q u a n t i t y and t h e q u a l i t y  population  the  Rivulus.  t h e r e has been c o n s i d e r a b l e debate about t h e aspects  supply  predation,  s t u d i e s a p p e a r t o have b e e n  One v i e w , w h i c h m i g h t be t e r m e d  that,  food  a function of sexual  that,  to support review  o f t h e two s e x e s ''there i s no  the concept  (mostly  no good e v i d e n c e  . . ,"  evidence  of b i o t i c  of insects), f o r a feedback  from  the  sex  ratio  to population density.  I n two  more  s t u d i e s o f i n s e c t s however, e x t r e m e c r o w d i n g and shortage was  did result  caused  1966)  and  genetic these than  i n the  other  examples the  (1969)  supply  these  had  and  populations  the  sex  and  Tacarigua balanced  respectively). support  By t h e  differences  Petite  (1969) sex  dense  Curucaye R i v e r s ,  (1.14)  and  same t o k e n  a t Santa  Petite  very  low  C r u z and  0 . 8 0 , and  I n summary, my r e s u l t s  i n the  sex  correlation of  a t C a p a r o , Guayamare, and  (1.00, 0 . 9 2 ,  Nikolskii's  severe  o fpopulations o f  R i v e r s ; however a l l p o p u l a t i o n s ratio  for  I n 1969 v e r y  ratio  very high d e n s i t i e s  sex  f a r more  q u a n t i t a t i v e d a t a on  densities  ratio.  sex  (0.33).  d e n s i t i e s were o b s e r v e d Rivers,  little  a t P a r i a and  a balanced  Curucaye d i d not  In both  populations.  relative  occurred  y e t P a r i a had  "evolved".  a p p e a r s t o be no o b v i o u s  factors with  1966), a  Pimentel,  ratio  case i t  (Dingle,  i m p l i e d was n e c e s s a r y  I have v e r y  t h e guppy, t h e r e  sex  food  i n one  c o m p e t i t i o n was p r o b a b l y  changes i n f i s h  food  ratios;  ( F e i n b e r g and  change i n t h e p r i m a r y  Although the  sex  by an i n c r e a s e d m o r t a l i t y o f females  Nikolskii  ratio  in altered  recent  hypothesis  ratio  Marianne Lower  showed a 0.91,  do n o t  a.91  appear t o  that population  are governed by food  supply  or d e n s i t y . I concur of  females  i n any  with  Haskins  e t ajL (1961)  t h a t an e x c e s s  given population i s probably  caused  by a  86 greater my  vulnerability  i n t e r p r e t a t i o n as  effect.  t o how  In a s e a r c h  discovered  t h o u g h t h i s may  s e l e c t i o n was  less not  predators  be  true  unknown.  I t seems i n t u i t i v e l y  the  Not  camouflage but predator  hypothesis" the  the  possibility  the  proficient predators  the  I t should  to predators  the  m a l e s may  be  only  from  his  be  allow  a  possible  of d i s p l a y i n g  "conspicuousness  can  however,  become c o n d i t i o n e d sex  is  Where l a r g e c h a r a c i d and  e n e r g y r e t u r n t o be  suggests  a minor f a c t o r i n  There remains,  abound, t h i s d i s a d v a n t a g e may  greater  to s t i m u l i  f e m a l e may  the males because t h i s  at escaping.  o f males i s  c i r c u m s t a n t i a l evidence  that predators  attack  Whether  nature.  sense of camouflage.  selectively  be  obtained  to  less cichlid  counterbalanced from  the  females. I t w o u l d be  to other  on  unable to t e s t  c o l o u r ' o f the  strict  larger  I was  predation,  his display jeopardize  males i n  directly,  the  the  i s attending  reaction distance  non-displaying  Rivulus  o b v i o u s t h a t when a male i s  his concentration  Although  by  o n l y may  I  a l s o males  vulnerability  t o a p p r o a c h more c l o s e l y .  t o measure t h e  that  the  c o u r t s h i p d i s p l a y , he  female.  and  increases  in  selective  for a l l populations.  activity  full  I differ  this  important;  adept at escaping  courtship  in  exert  but  f o r a l t e r n a t e mechanisms t o c o l o u r  that size  were f o u n d t o be  of males to p r e d a t o r s ,  species  of  of  interest  t o see  i f my  s e x u a l l y dimorphic  fish.  findings  apply-  Unfortunately  87 I could find ratios  and  s t u d i e s where b o t h  t h a t sex  ratios  t o be more b a l a n c e d  s u p p o r t my  findings  gaunt" or  "emaciated"  tions.  m a l e s had  size the  and  I observed  m a l e s and  (1963)  Gambusia manni  thought  rates.  patruelis,  senile  "thin  under such  t o be  than males but  higher death  I n G.  no  females  severe,  and  condiKrumholz  i t i s not  known  (Sexual dimorphism i n  colour i s considerably less  guppy.)  sex  i n the absence o f p r e d a t i o n  although  more f e m a l e s  Krumholz's  i n the p o e c i l i i d  Where p r e d a t i o n was  always found why  e x t e n s i v e d a t a on  p r e d a t o r s were a v a i l a b l e .  observation tended  few  George  i n G.  manni t h a n  (1960.) f o u n d  in  that  females  were more r e s p o n s i v e t o p r e d a t o r m o d e l s t h a n  males  (cf.  Table  the  my  12).  Gambusia t o a r e a l the  s u r v i v o r s was In  noted 2:1  U n f o r t u n a t e l y , when he p r e s e n t e d predator not  the average  (n = 2 1 2 7 ) .  Although  ratio  occurred,  species  i n h a b i t s weedy a r e a s larger  dimorphism i s seasonal. can  fish  (cf. Rivulus) .  the  penetrate  Hastings  Yerger  they d i d not  sex  that  the  sex  than  females  of  i t i s noteworthy t h a t i n very the  and  F e m a l e s w o u l d be  the  colour  Possibly a small f i s h  shallow water s e l e c t i v e l y  this  this  shallow water,  female,  (1971)  about  s p e c u l a t e why  predator  f e e d s on  small  moire a b u n d a n t i n t h i s  of the p o p u l a t i o n , o p p o s i t e to the  guppy.  and  males outnumbered  unusual  male i s s l i g h t l y  americanus),  recorded.  t h e Diamond K i l l i f i s h ,  t h a t on  fraction  (Esox  situation  in  88 Liley  (1966) f o u n d  that  at several  G e o r g e t o w n , Guyana, t h e s e x r a t i o (including  t h e guppy) a p p e a r e d  of the water.  Collections  sites  of 3 species of  t o be  related  from green  and  Liley  poeciliids  to the  cloudy  showed a r o u g h l y b a l a n c e d r a t i o w h i l e t h o s e water c o n t a i n e d fewer males.  in  from  suggested  clarity  water clear  that  in clear  w a t e r t h e m a l e s a r e more v u l n e r a b l e t o v i s u a l p r e d a t o r s . However i t i s i n t e r e s t i n g r a t i o was less  found  f o r P.  c o l o u r e d t h a n P.  species are nearly other than  to note  picta,  that  t h e most  even though  r e t i c u l a t a males  identical).  P.  extreme  p i c t a males  (females of  Perhaps  sex  are  both  differences  c o l o u r p l a y a more i m p o r t a n t r o l e  i n determining  vulnerability. With t i o n s o f P.  r e s p e c t to water c l a r i t y reticulata,  The  clear  characid  Although  this  not t h i n k the r a t i o  I am  unable  other the  i t has  to explain  similar  "Haskins  that  turbid  (Caparo,  T a c a r i g u a , Upper A r o u c a )  and  generalization cichlid  f o r most o f t h e y e a r , y e t t h e  (n = 4 1 3 ) . do  (Upper  i n either  outstanding exception to this  O r o p u c h e R.;  popula-  t o the major p r e d a t o r s , i t tends  sex r a t i o  Guayamare) o r c l e a r  Trinidad  I have a l r e a d y p o i n t e d o u t  where t h e guppy i s e x p o s e d t o have a b a l a n c e d  and  resulted this  environments.  sampling  f r o m my  Perhaps  hypothesis" i s v a l i d ,  is  0.50  sampled o n l y o n c e ,  from  ratio  i s the  p r e d a t o r s and i s  sex r a t i o  r i v e r was  water.  this  error.  I Thus  experience with i s one  c a s e where  i . e . s e v e r e p r e d a t i o n by  89 Crenicichla, sex r a t i o  Hoplias, etc. resulting  i n favour of  Summary o f C h a p t e r 1. yielded  8166  f e m a l e s , and  is  Mendelian  ratio  2. the  (p <  3.  Sex  predator-free  4. tions  ratios  .05)  Sex  6079 a r e  sex r a t i o f r o m ah  interpopulation found  with those  ratios  are  observed  in  i s 0.74  and  expected  stocks of guppies  o r low  densities  ratios  i n favour of females  1969.  started  i s caused  from  and  of Rivulus h a r t i i .  that  by g e n e t i c  system.  are r e l a t i v e l y characid  positively  a g a i n s t the h y p o t h e s i s  sex d e t e r m i n a t i o n  ratios  in  u n i t y were f o u n d i n  i n the sex r a t i o  exposed t o e i t h e r  balanced  i n popula-  c i c h l i d predators, Very  unbalanced  sex  o c c u r where R i v u l u s d e n s i t y i s  high. 5. between 1967 significant ratio.  I n one  stream  ( h i g h ) and (p <  and  males,  differences  i n 1967  approaching  This i s evidence  i n the  The  (p < .001)  are large  variation  differences  of these  i n 1967  1.00.  laboratory  fish.  geographic  of  from T r i n i d a d  o f 23502 f i s h ;  different  The  correlated  of guppies  9257 immature.  There  sex r a t i o .  immature  4  a total  significantly  unbalanced  females.  Collections  1969  i n a very  .001)  a change i n R i v u l u s d e n s i t y  1969  (low) was  restoration  correlated with  of balance  i n the  a  sex  90 6.  Sex  ratios  geographic v a r i a t i o n 7. the  in  i n male  the s i z e - s e l e c t i v e  appears  Rivulus  body s i z e was  single  distribution  i n the f i e l d  a controlled  laboratory  and  laboratory  variable.  demonstrated  However i n e x p e r i m e n t s  s t o c k s o f g u p p i e s as t h e p r e y and  i n s u r v i v a l was  apparent. results  I sought  f o r these c o n f l i c t i n g  differences  i n e x p e r i m e n t a l d e s i g n and p r i o r  either  a  no  an  i n terms o f experience of  predators. 9.  In a s e p a r a t e experiment  on a l a b o r a t o r y  capture.  of Rivulus  s t o c k o f g u p p i e s , m a l e s were n o t  a t t a c k e d b u t were l e s s  (p  and  t o p r e d a t o r s e v e n when  explanation  the  variation  C r e n i c i c h l a o r s i x R i v u l u s as t h e p r e d a t o r ( s ) ,  sex d i f f e r e n c e  of  feeding behavior of the  Experiments with wild-caught guppies  conducted  with  streams.  t h a t m a l e s were more v u l n e r a b l e  using  the s i z e  t o f i t t h e o b s e r v e d sex r a t i o  t h e N o r t h e r n Range 8.  t o be c o r r e l a t e d  coloration.  A model i n c o r p o r a t i n g  s e x e s and  predators  do n o t a p p e a r  adept than females a t  C o n s e q u e n t l y more m a l e s were k i l l e d  predation selectively  avoiding than  females  < .005) . 10.  potential  The  r e a c t i o n d i s t a n c e o f female guppies t o a  predator i s larger  there appears  t o be  sexual d i s s i m i l a r i t y 11.  than t h a t  of males,  geographic v a r i a t i o n in this  In c o n c l u s i o n ,  however  i n the degree  of  trait.  the geographic v a r i a t i o n  i n the  91 sex r a t i o Trinidad males. only  of guppies appears  i n t h e N o r t h e r n Range r e g i o n  t o be  Other b i o t i c  c a u s e d by d i f f e r e n t i a l  and  to the e x t e n t that  abundance o f p r e d a t o r s . male s e x hunting in  abiotic  factors  they govern The  of  p r e d a t i o n on  seem t o be  the d i s t r i b u t i o n  relative  vulnerability  involved and of  the  i s d e p e n d e n t upon t h e i n t e r a c t i o n o f t h e s i z e s tactics  the s i z e  o f t h e p r e d a t o r s , and  and b e h a v i o r o f t h e p r e y .  reasonable that  conspicuous c o l o r a t i o n  the sex  differences  Although  i t seems  is a liability,  has y e t t o be d e m o n s t r a t e d u n e q u i v o c a l l y .  and  this  CHAPTER 5 GEOGRAPHIC VARIATION  IN BODY S I Z E  Introduction P o p u l a t i o n d i f f e r e n c e s i n body aspect  of geographic  chapter  I explore  variation  size  are a  conspicuous  i n T r i n i d a d guppies.  some o f t h e e n v i r o n m e n t a l  In t h i s  f a c t o r s and  s e l e c t i o n mechanisms t h a t m i g h t be r e s p o n s i b l e f o r t h e observed  size  hypothesis  trends.  to size-selective  In s p i t e problems o f f i s h review) there  This  i s very  that  variation  response  i s reasonable  are very  to  ( s e e Aim, 1959 f o r  i n natural populations.  to a given  size  temperature  flexible  In  i n terms o f a and f o o d  b e c a u s e u n l i k e most o t h e r  sensitive  devoted  known a b o u t t h e g e n e t i c  m o d e l s v i e w body  have e x t r e m e l y  (Weatherley,  supply.  animals,  g r o w t h and m a t u r i t y  to environmental  fish rates  conditions  1966).  Although size  little  extent  predation.  g r o w t h a n d body s i z e  fisheries  generally  a r e t o some  o f the voluminous l i t e r a t u r e  component o f s i z e  phenotypic  I wish t o evaluate the  t h a t d i f f e r e n c e s i n body s i z e  adaptations  general,  In p a r t i c u l a r  i t i s w e l l - k n o w n t h a t d i f f e r e n c e s i n body  are h e r i t a b l e  ( C a l a p r i c e , 1969) and t h a t  m o r t a l i t y may be s i z e - s e l e c t i v e  (Nikolskii,  fishing  1969; R i c k e r ,  93 1969) , t h e fishing or  r e s u l t a n t g r o w t h and  are  competition  literature of  usually  and  i n t e r p r e t e d as  (p.  Miller  concluded,  " T h e r e i s no  (1957) r e v i e w e d  managed f i s h  best  paucity  the  clear-cut  early  evidence  h e r i t a b l e changes  o f d a t a on  populations,  in  i t i s not  selective mortality surprising that  l e s s i s known a b o u t n a t u r a l  p a r t i c u l a r the  The  structure  803)."  With t h i s  siderably  a change i n age  f o r food.  e x p l o i t a t i o n h a v i n g c a u s e d any  fishes  in  s i z e responses to s e l e c t i v e  examples  invertebrate  in  con-  selective mortality,  response to s i z e - s e l e c t i v e predation. f o r t h i s phenomenon a r e  prey organisms  studies  (Mason, 1965;  Brooks,  on 1968,  1971). Two piscivores rates  and  history the  the  as  the  cm)  adults  C o o l a R.,  (1972: 134)  (but  and  on  fish  by  Congo R.  selected  see  Fryer,  be  that small  species  1965  critique).  for  speculated  opposite  that  "evolved  a  that  in"the strategy"  (coho  salmon  d i r e c t i o n , Roberts  commented t h a t m i n u t e f i s h  s y s t e m s may  argued  for fish  s i z e - s e l e c t i v e predator i n the  evolutionary  H y d r o c y n u s v i t t a t u s on  (1971) has  evolution has  has  i n the  (1961, 1965)  chum s a l m o n f r y have  to outgrow a s m a l l , For  Jackson  tiger-fish,  More r e c e n t l y P a r k e r  parr).  have o c c u r r e d  species.  ( l e s s t h a n 20  Bella  s i z e - s e l e c t i v e predation  body s i z e may  of  large  of  have s u g g e s t e d t h a t h e r i t a b l e c h a n g e s i n g r o w t h  impact of  fish are  studies  less vulnerable  i n the to  Amazon  predaceous  94 fish  because  t h e y a r e , "below  W h i l e p r e d a t i o n may  the s i z e  be  mechanism i n some c a s e s , body  threshold for  an i m p o r t a n t s e l e c t i o n s i z e must i n e v i t a b l y  compromise between numerous c o m p l e m e n t a r y selective  forces.  Hamilton  tive  f o r c e s which might  size  trends  otherms  i n birds;  (1961)  interact  has  of  Dodson, 1965; abiotic  Estes  stresses  for:  1968);  interactions  and G o d d a r d ,  Hartman,  1967);  (Struhsaker,  S o u l e , 1966); (Hanson  and  important  to this  to note t h a t  last  Henderson  no c l e a r - c u t  size.  related  resisting (Hubbs, 1968;  1940;  Berry  and  interspecific (4)  securing 1967;  This  implies  intensity,  i tis  (i.e.  aggres-  c o u r t ) more  (1973)  could  c o r r e l a t i o n o f a g g r e s s i v e b e h a v i o r and  to s i z e per se.  courtship  force,  (unpubl.) found t h a t  females than d o c i l e males, y e t B a l l i n  body  ( B r o o k s and  Smith,  selective  s i v e m a l e g u p p i e s were a b l e t o " o r i e n t "  detect  favour  1969). With r e s p e c t  to  (2)  (3) a v o i d i n g n o n - p r e d a t o r y  some f o r m o f m a t i n g a d v a n t a g e  t o home-  s e l e c t i o n may  s u c h as h i g h w a t e r v e l o c i t y  ( H a m i l t o n , 1961;  selec-  intraspecific  (1) f o o d - g e t t i n g  Hartman, 1 9 6 9 ) , o r wave a c t i o n Crothers,  7  flight.  F o r numerous a n i m a l s n a t u r a l size  tabulated  to cause  a  conflicting  most o f t h e s e a r e p e c u l i a r  or concern problems  an o p t i m a l body  and  be  and  that mating  s u c c e s s may  Presumably male s i z e ,  not  be  colour,  aggressive behavior a l l interact  in  sexual  selection.  With adaptive  this brief  significance  i n t r o d u c t i o n to the problem of the  of intraspecific  s h a l l now document t h e s i z e and  search  Body s i z e  forecological  variation  Figure about  12 g i v e s  a n a l y s i s because  coloration  o f mature males  and complete  a f u n c t i o n o f age.  once  albeit  trends  variance  positive  r  g  size  full i s not  i s smaller  are easier to discern. i s indeterminate,  c o r r e l a t i o n between m a l e  (9 p o p u l a t i o n s  Spearman r a n k c o r r e l a t i o n ,  (rank  com-  t h e male h a s a t t a i n e d  t h a t f e m a l e body s i z e  length  i n 1969  are used i n t h i s  Hence t h e sample  i s a significant  female t o t a l  sampled  gohopodium d e v e l o p m e n t ,  the o v e r a l l population  Nevertheless,  and  and t h e v a r i a t i o n  t h e mean f o r t h e 20 p o p u l a t i o n s  parative  variation.  populations  t h e mean s i z e  The s i z e s  there  o f T r i n i d a d guppies  correlates of this  i n natural  order).  and  variation  size differences, I  =•+  were  compared:  0.72, t = 2.74, d f = 7,  p < .05) . Figure variation  12 r e v e a l s t h a t t h e r e  among p o p u l a t i o n s  t o 17.9 mm.  ranging  T h i s may n o t a p p e a r  in  absolute  it  represents  i n mean s i z e  f r o m 25.3  t o be a l a r g e d i f f e r e n c e  terms, b u t f o r a s m a l l  (150 mg v e r s u s  i s considerable  fish  s u c h as t h e guppy  a t h r e e - f o l d d i f f e r e n c e i n wet body  weight  50 mg).  By a r r a n g i n g  the s i z e s  i n rank o r d e r ,  the s i z e  96a  FIGURE 12.  The at the  body 20  size  sites  o f a d u l t male g u p p i e s  i n 1969.  mean, h o r i z o n t a l  black  rectangle  The  sample s i z e  the  total  range.  Vertical line  line  the t o t a l  collected indicates range,  i 2 SE, open r e c t a n g l e i s shown a t t h e u p p e r  i 1 end  SD. of  16 GRANDE  18  20  22  24  26  30  28  CURUCAYE  •100  UPPER ARIPO (N)  -48  UPPER CURUMPALO BLUE  BASIN  UPPER  ARIPO  (X)  YARRA SANTA  CRUZ  PETITE  •100  CURUCAYE  PARIA UPPER  AROUCA  MARIANNE UPPER LOWER UPPER TOMPIRE LOWER  GUANAPO TACARIGUA TACARIGUA TRIBUTARY ARIPO  GUAYAMARE OROPUCHE CARONI CAPARO  ~i—i—i— —r 1  16  18  20  T—i—i—i—i—i—'—i— —r  TOTAL  1  22  24  LENGTH  26  (mm)  28  30  97 trends  a p p e a r t o f o l l o w a smooth, g r a d u a l  indicating  a phenotypic  r a t h e r than a g e n e t i c selective  factor.  cline  perhaps  r e s p o n s e t o an e n v i r o n m e n t a l  response t o a g e o g r a p h i c a l l y v a r i a b l e  B u t when t h e s e  size  trends  are viewed i n  terms o f a c t u a l g e o g r a p h i c d i s t a n c e s , t h e c l i n e s very For  steep  suggesting  selective  (X) t o Lower A r i p o ,  a size  a distance  To  those  (Figure  determine i f these  size  13).  Though o n l y  the c o r r e l a t i o n  remarkable, e s p e c i a l l y  seasonal  supply  Relationship  o f body s i z e  Temperature  i s highly  1962;  differ-  before  i n 1967  a r e comparable significant  This consistency i s  f o r the lowland  r i v e r s and  environments with  respect  for fish. and t e m p e r a t u r e  i s known t o have a c o n s i d e r a b l e  t h e g r o w t h , a d u l t body s i z e ,  populations  reveals  c h a n g e s i n t e m p e r a t u r e , volume o f f l o w , a n d  perhaps food  on  5 km,  differences are a stable  13 p o p u l a t i o n s  midstreams, which a r e unstable to  of only  6 generations  = + 0.90, t = 6.69, p < . 0 0 1 ) .  indeed  f r o m Upper  I compared t h e 1969 measurements  taken approximately  between y e a r s , g  important.  populations.  feature of the populations, with  are often  d i f f e r e n c e o f n e a r l y h a l f t h e maximum mean  ence f o r a l l t h e T r i n i d a d  (r  f a c t o r s may be  e x a m p l e , t h e change i n mean body l e n g t h  Aripo  gradient  (reviews:  effect  and m e r i s t i c s o f f i s h  Brown, 1957; B a r l o w , 1961; S h o n t z ,  P a l o h e i m o and D i c k i e , 1 9 6 6 ) .  The r e l a t i o n s h i p between  98a  FIGURE 13.  A comparison guppies and  o f t h e body s i z e  f r o m 13 p o p u l a t i o n s  resampled  tions  refer  i n 1969.  to Figure  o f a d u l t male  sampled.in  For stream 1.  1967  abbrevia-  e E25-  ^242 _23022 Z ^21 -  < " o«« P19 2 0  18 H 18  ' .UCur'UA .UTac X •» SC  r a r  • Mar .TT • LA »Car  • LTac  r =*a90 t = 6£9 df = 11 s  «6uay 1  1  1  1  19 20  21  22  .001  1  P < 1  23 24  25  26  1  1—  TOTAL LENGTH 1969 (mm)  99 temperature food  a n d body s i z e  supply i s also a v a r i a b l e  majority of fish and  i s n o t a simple one, e s p e c i a l l y i f ( B r e t t e t a l , 1969).  s t u d i e d , warm t e m p e r a t u r e s  hasten  growth  s e x u a l m a t u r i t y ; s i n c e growth d e c r e a s e s o r s t o p s a t  m a t u r i t y , p o p u l a t i o n s i n warm w a t e r u s u a l l y smaller  individuals  strated  experimentally f o r the t r o p i c a l  (Gunter,  dontid, Cynolebias a d l o f f i raised kept  1950).  consist of  T h i s h a s b e e n demonfreshwater cyprino-  ( L i u and W a l f o r d ,  1966):  a t 22 C; i n a d d i t i o n  t h e l i f e - s p a n was d o u b l e d  those  a t the  temperature. I n a .study o f p r e - a d u l t g r o w t h o f d o m e s t i c  Gibson  males  a t 16 C were 19% l o n g e r a n d 76.3% h e a v i e r t h a n  cooler  and H i r s t  (1955) n o t e d  that  temperatures. temperatures  Also,  larger  a t h i g h e r o r lower  f e m a l e s were f o u n d  Bertalanffy  t h e growth r a t e  domestic  a t the cooler  (20, 23, 25 C ) .  Even under c o n s t a n t temperature regime,  guppies,  f a s t e r g r o w t h and  m a t u r i t y o c c u r r e d a t 2 3 a n d 25 C t h a n  in  In the  guppies.  (1938) n o t e d  (24 C) a n d f o o d  considerable differences  and a s y m p t o t i c w e i g h t  o f 3 "breeds" o f  He c o n c l u d e d t h e s e d i f f e r e n c e s  were  genetic. Liley evidence that in  several  that  (unpubl. data)  also provided experimental  genetic differences  stocks of Trinidad  temperature  grew t o a l a r g e r  i n body  guppies.  had a s i g n i f i c a n t size  than those  s i z e were p r e s e n t  His results  effect  showed  ( f i s h a t 23 C  a t 28 C; c f . L i u and  100 Waiford,  1966)  the  descended  fish  large-sized  b u t more i m p o r t a n t l y , a t e i t h e r  at  least  p o p u l a t i o n s w h i c h had  individuals  small-sized wild My  from  own  grew l a r g e r  data  ( F i g u r e 14)  indirectly  temperature  variation,  a d u l t males taken  from  were s i g n i f i c a n t l y  with  (-)  (e.g.  0.64,  a c a u s a l one food  daily  populations l i v i n g than  those  t = 3.48, (Ray,  p <  1960).  and  could possibly  and  In t h e Upper A r i p o R.  .01),  2.0 23.1  mm  n = 85).  e a c h o t h e r and virtually and  had  (UA(N) = 25.1  Since these  the e c o l o g i c a l  identical  This relationship  be  affect  need  factors  correlated  body  evidence  size. however, factors.  subpopulations  at f i r s t .  mm,  n = 4 8;  subpopulations conditions  of  this  size  UA(X)  difference  of  =  were  guppies  seemed  However I s o o n d i s c o v e r e d t h a t  a much more v a r i a b l e  by  are c l o s e to  ( i n 1969)  (roughly equal d e n s i t i e s  R i v u l u s were f o u n d ) ,  puzzling  compliance  d i s c o v e r e d t h a t the males o f each d i f f e r e d  i n mean l e n g t h  mm,  f r o m warmer . in  may  of  water  p r e d a t i o n are important  I s a m p l e d two  is  trends  Samples  because o t h e r environmental  temperature  and  size  i n cool  taken  T h e r e i s some c o n v i n c i n g f i e l d  guppies  from  1, A p p e n d i x f o r  changes, e t c . ) .  supply, predator pressure)  temperature  that both  derived  the observed  (refer to Table  larger  Bergmann's R u l e  n o t be  with  =  g  those  r e v e a l t h a t temperature  involved with  i n F i g u r e 12  (r  than  typically  founders.  illustrated  water  temperature,  (and g e n e r a l l y warmer)  UA(X)  temperature  101a  FIGURE 14.  The r e l a t i o n s h i p males t o stream  o f mean body temperature.  size  of  adult  TOTAL co  ro  LENGTH ro CO  (mm) ro cn  ro  ro  m  ro cn  ~o ro m cn  >  ro  m O  ^3  o ro co ro co co  o -|  <IT0T  -a PA II  ~ II  n  o co co p co cn ^  102  t h a n UA(N). water  The  reason f o r t h i s  o f t h e s t r e a m b e l o w UA(N)  series  of ditches  used  the temperature  a r e a was  up  t o 4.0  T h i s warmer w a t e r was  diverted  The stream,  a  c r e s s beds.  than the water  These  sunny  e n t e r i n g the c r e s s  beds  leaving i t .  s u b s e q u e n t l y f l o w e d t o t h e UA(X)  lower  (cf. Liley's  t h e mean l e n g t h d r o p p e d 5 km  s i t e was  unlikely  that  temperature. sites  downstream.  site  and  the s i z e The  mm  dispersal  from below  The  upper  as a b a r r i e r  a direct  (details  location  to characid i n Chapter  are ipso  i t i s not p o s s i b l e  p r e d a t o r s but c o o l water  guppies  and  samples at  and  3).  this  i t is effect  i s above  f a c t o exposed to f i n d  of  these a  cichlid Because  the  i s of i n t e r e s t the water  a r e n o t as  ( i . e . < 26  to  "natural large  C).  t o n o t e t h a t where R i v u l u s d e n s i t y  i s cool  large  to Rivulus  o t h e r good  e x p e r i m e n t s " where g u p p i e s h a v e b e e n e x p o s e d  low  same  o f p r e d a t o r s i s such t h a t p o p u l a t i o n s o f  i n c o o l water  It  in  Since the temperature  d e c r e a s e c o u l d be  i s predation.  distribution  another.3.3  in this  most c o n s p i c u o u s d i f f e r e n c e between  serving  predation,  experiments).  a p p r o x i m a t e l y t h e same as a t U A ( X ) ,  waterfall  guppies  laboratory  i m p o r t a n t p o i n t , however, i s t h a t  taken about  is  the  through  (no c o v e r ) h e n c e on a  o f the water C cooler  that  probably instrumental i n producing .phehotypically  smaller f i s h  two  was  t o i r r i g a t e water  c r e s s b e d s were v e r y e x p o s e d day  d i f f e r e n c e was  (Paria, Yarra, Marianne),  as a t s i t e s  having s i m i l a r  the  temperatures  103 but  good numbers o f R i v u l u s  (N)).  But another  a c c o r d i n g . t o Hynes that  trout  (Grande C u r u c a y e , Upper A r i p o  confounding  v a r i a b l e may be i n v o l v e d :  (1970: 340) t h e r e  grow f a s t e r  i n harder  1, A p p e n d i x ) ,  water.  limited  (see T a b l e  a lower  density of Rivulus, Paria,  R i v e r s a l s o have s o f t e r  Relationship If body s i z e constant  but i n a d d i t i o n t o having Y a r r a , and Marianne  water.  o f body s i z e  of fish  and p r e d a t i o n  then  directional,  under a  and f o o d r e g i m e r e p r e s e n t s  natural selection  stabilizing,  environment there  genetic  f o r body s i z e  or disruptive.  c o u l d be a s h i f t  c o u l d be  I n an u n s t a b l e  f r o m one mode o f s e l e c -  t o another. When t h e s e  are viewed with of predators immediately space,  simple  of different very  models o f q u a n t i t a t i v e g e n e t i c s  regard t o the s e l e c t i v e  complex.  a s i n g l e prey  of d i f f e r e n t  sizes,  (1) s p e c i e s ,  the h o s t  o f a number  the s i t u a t i o n i s  A t any g i v e n p o i n t i n t i m e a n d  (2) s i z e s ,  (e.g. hunger).  A l l o f these t h a t a prey  be a t t a c k e d a n d c a p t u r e d ,  of size-specific  predators  (3) age c l a s s e s , a n d  a r e known t o i n f l u e n c e t h e p r o b a b i l i t y size w i l l  impact  may be e x p o s e d t o p o t e n t i a l  (4) m o t i v a t i o n a l s t a t e s  given  variation i n  (same age a n d s e x ) m a i n t a i n e d  temperature  t o show  My d a t a o n t h i s a r e  i t i s assumed t h a t t h e p h e n o t y p i c  variation,  tion  a r e some d a t a  factors  of a  n o t t o mention  antipredator adaptations  the prey  104  m i g h t have acuity,  (swimming s p e e d , p r o x i m i t y t o c o v e r ,  etc.).  For  a diverse predator  Aripo  and  these  f a c t o r s w o u l d be  these  size-specific  project  in itself  tion  the  enormous.  and  I d i d not that  ( e . g . Lower  capture  small predator)  attempt  efficiency and  a  this  here. to determine  consequence t o the  cichlids  if  i n n a t u r a l popu-  of average-sized Rivulus  c h a r a c i d s and  of  separate  f o l l o w s , I wish  a r e o f any  of  s t u d y o n l y a few  o f the magnitude observed  (see F i g u r e 12)  and  To  i n t e r a c t i o n s w o u l d be  analysis  differences  lations  community  Guayamare R i v e r s ) t h e number o f c o m b i n a t i o n s  In size  visual  detec(a  (small to  very  large predators). Evidence  from  the  Except evidence  predator  size  guppies.  Rivulus d i d not  Chapter  are i n f a c t The  a positive  size-selective of the  curvilinear size  stomach  capture  f o r sex  guppies  (Figure 15).  ratio  i s 23.0  mm.  v a r i a t i o n was  direct  in  their  analyses  relationship In  p o i n t beyond which even v e r y The  of  my  large signifi-  outlined  in  4. For Astyanax the  a 13.0  results  t o maximum p r e y  the c u t - o f f  cance o f t h i s  selection  f o r R i v u l u s and A s t y a n a x I have l i t t l e  Rivulus reveal'  samples  for size  that predators  p r e d a t i o n on for  field  mm  estimate  juvenile. of the  size  largest  I should  o f 18  stress  capabilities  guppies  that this  recovered i s not  was  a good  bf the Astyanax p o p u l a t i o n  105a  FIGURE 15.  The  relationship  s i z e of guppies taken  from  o f R i v u l u s body s i z e taken  several  as p r e y .  The  to  the  data  are  natural populations.  23-  E E 21 -  > CL CL 3 O *o  19 17 15 13 -  I— o  11 -  UJ —J  9  -  7  -  5  -  £ o  •  30  40  •  •  • •  •  60  -r~  70  TOTAL LENGTH of  80  RIVULUS  90  (mm)  loo  106 as a w h o l e — m y individuals  s a m p l i n g was v e r y b i a s e d t o w a r d s s m a l l  because  t h e methods were i n a d e q u a t e  many o f t h e v e r y s w i f t only  3 individuals  many i n d i v i d u a l s roving  be  larger  than  g r e a t e r than  these  fish  required  (fork  length)  100 mm were s e e n  field  i n large,  probably  o r p o i s o n i n g would  site  either  200  no g u p p i e s were f o u n d  25 mm.  (> 30 mm)  female  i nthe  were o f f i s h  a t t h e O r o p u c h e R.  an u n s u c c e s s f u l  guppy by a C r e n i c i c h l a  mm. a l o n e , H o p l i a s w o u l d be e x p e c t e d  s e l e c t o u t even l a r g e r p r e y that  t h e remains  In a d d i t i o n ,  On t h e b a s i s o f s i z e  possible  than C r e n i c i c h l a .  adult Hoplias prey mainly  t h a n t h e guppy.  It i s  on s p e c i e s  A t Lower A r i p o , one j u v e n i l e  this  idea.  The c h a r a c t e r i s t i c  marks o f H o p l i a s were a l s o (> 90 mm  fork  tooth  f o u n d on a m o r i b u n d  larger  Crenicichla  65 mm was r e c o v e r e d f r o m t h e s t o m a c h o f a 205 mm  supporting  less  were t o o d i g e s t e d t o g e t s i z e  ( a t 1500 h r ) I o b s e r v e d  a t t a c k on a l a r g e about  this.  I n one C r e n i c i c h l a  l a r g e r than  collection  each.  d a t a f o r t h e o t h e r p r e d a t o r s a r e even  because  measurements.  though  by e l e c t r o f i s h i n g  stomachs o r t h e remains  of  100 mm  included  a d u l t guppies o f  to confirm  satisfactory  to  The s a m p l e s  can normally handle  s i z e s but sampling  The  of  fish.  s c h o o l s o f a p p r o x i m a t e l y 20 t o 100 f i s h  Presumably all  larger  to capture  Hoplias  puncture Astyanax  l e n g t h ) a t t h e O r o p u c h e R. a n d on s e v e r a l  o c c a s i o n s a t C a r o n i and Guayamare R i v e r s I o b s e r v e d  small  107 characids  o f unknown s p e c i e s  jump o u t  response to p u r s u i t from a v e r y  of the water i n  large predator  (probably  Hoplias). In Rivulus on  summary, t h e  and  small  small guppies  distribution); Hoplias on  (i.e. fish  scanty  what a r e  predators  the  t o r s would predators  on  o f the  size  a d u l t C r e n i c i c h l a and  probably  prey  more h e a v i l y  mechanisms?  out  w o u l d do should  My  the be  some o f  in size  due  I shall  demonstrated  in this  p r e d i c t i o n was i n body s i z e ,  large fish  first  s t r e s s e d t h a t the  the  i n s i z e but  fish will  be  to h e r e d i t y but  argue t h a t i f s i z e  prey  evolutionary  a s s u m i n g body s i z e  "average-sized"  in a  large the  can  i f so,  preda-  small  predators  o f f e r e d i n sub-  a l s o i n age;  of the  this  by  same age  and  i s impossible  s e l e c t i o n can  i n a synthetic experimental  m i g h t a l s o have an  and  that  the  while  section:  reverse.  sequent experiments d i f f e r coincidence  were a s k e d  demonstrated experimentally,  select  It  force.  lower t a i l  selectively  size selection  sample o f g u p p i e s d i f f e r i n g  tions,  the  data  basic questions  s e l e c t i o n be  assess.  on  field  a n a l y s i s of  Two  differ  indicate that  guppies.  Experimental  size  observations  to medium-sized Astyanax prey  suggest these  large  field  i m p a c t on  to  be  population, i t natural  t o be  a heritable trait  exert  the  greatest  populaand  selective  that  108 To of  answer t h e f i r s t  guppies  proceeded  differing I noted  s u r v i v i n g prey. tion these  i n body s i z e  i fa s h i f t Because t h i s  of behavior, tests  question,  I exposed l a r g e groups  to predators.  occurred  As p r e d a t i o n  i n t h e mean s i z e o f  d i dnot require close  observa-  I used t h e l a r g e s t p o s s i b l e arena f o r  so t h a t p r e d a t o r  and prey  were n o t u n d u l y  crowded. For  the detailed  I had t o s a c r i f i c e ment.  observations  reality  to obtain precision  behavior  i n measure-  T h u s s m a l l e r a q u a r i a were u s e d a n d f e w e r p r e y , a n d  the p r e d a t o r s  were s t a r v e d s u f f i c i e n t l y  would a t t a c k d u r i n g t h e o b s e r v a t i o n Experiment  5.1  testing  size  dealing with  sessions.  a summary o f 18  Some o f t h e s e were d e s i g n e d selectivity;  antipredator behavior  o f guppies  presented  separate  especially for  o t h e r s were m a i n l y (Chapter  e x p e r i m e n t s h a d one common f e a t u r e : the sizes  they  sizes.  This experiment i s a c t u a l l y experiments.  to insure that  P r e d a t i o n by s e v e r a l s p e c i e s on g u p p i e s o f different  in  of predatory  f o r tests 6).  t h e r e was  A l l the  variability  to the predators.  Methods Table these  tests.  start.of mortality  13 l i s t s  the s t o c k s , p r e d a t o r s , e t c . used i n  The g u p p i e s  each t e s t point.  were m e a s u r e d t h e d a y b e f o r e t h e  a n d r e - m e a s u r e d a t a b o u t t h e 50% The p r e d a t o r s were n o t f e d any o t h e r  food  109 TABLE 13.  Test  Duration (days)  Predators  and p r e y  Stock(s)  Sex  Predators  used  i n E x p . 5.1.  Mean s i z e o f prey(mm) b e f o r e a f t e r change  a  4  PCur  m+f  Rivulus  20.43  20.92  +0.49  b  3  PCur  m+f  Rivulus^  20.30  20.81  +0.51  c  2  Cap  m+f  Rivulus  19,89  20,50  +0.61  d  3  Cap  m+f  19.52  20.05  +0.53  e  4  Cap  m+f  Rivulus^ • c Rivulus  18.42  19.90  +1.48  f  3  SC  f  Hoplias^  27.8  26.4  -1.4  .g  4  LA+PCur  f  C-l  21.81  22.60  + 0.79  h  2  LA+Par  f  C-l  21.88  21.86  -0.02  i  4  LA+UA  f  C-l  22.31  22.24  -0.07  j  3  LA+Guay  m  C-l  20.75  20.65  -0.10  k  3  LA+Par  m  C-l  20.70  20.62  -0.08  1  2  LA+UA  m  C-2  21.35  21.17  -0.18  m  3  LA+Par  f  C-4  21.44  20.89  -0.55  n  2  LA+Guay  m  C-4  18.93  18.99  +0.06  o  3  Cap  m+f  C-l  20.18  20.13  -0.05  P  3  Cap  m+f  C-2  20.18  20. 30  +0.12  q  4  Cap  m+f  C-l  .20.81  20.68  -0.13  r  2  Cap  m+f  C-2  21.83  21.78  -0.05  I n i t i a l number f o r e a c h 50 LA + 50 P C u r ) . 85  stock or sex e q u a l  (e.g.  T h r e e m a l e s and 3 f e m a l e s  (75, 75, 73, 73, 85,  T h r e e 'males *arid?3.,-females  (75, -75 , >82 ,'- 85.',. 88 ,  Two w i l d - c a u g h t  specimens  (175 and 2 05  C  (refer to Table 11).  mm). c  90  e  mm).  e  = Crenicichla  "^For sample  sizes,  refer  t o F i g . 16.  mm).  110 during  the t e s t s .  ducted  i n 200 l i t e r  (standard 1600  A l l tests  survival  liter  tanks  e x c e p t E x p . 5.1  ( f ) were con^-  s e t up a s d e s c r i b e d  test).  E x p . 5.1  before  ( f ) was c o n d u c t e d  in a  o u t d o o r c o n c r e t e p o o l w i t h a d e p t h o f 50 cm; t h e  H o p l i a s and guppies  used  i n t h i s t e s t were w i l d - c a u g h t and  had b e e n i n c a p t i v i t y f o r o n l y a few weeks. Results I have p r e s e n t e d t h e r e s u l t s of  the i n i t i a l . s i z e s  (Figure in  16).  T a b l e 13.  To r u l e  the r e s u l t s  days  are given.  simply  size  out size  o f experiments  most o f t h e t e s t s  c a n n o t be a c c o u n t e d  i n less  Although the s i z e  with Crenicichla direction;  were s m a l l ,  than 5  as size changes 9 out of  o v e r a l l the r e s u l t s  f o r by c h a n c e .  This  must have b e e n o c c u r r i n g  since  predators could handle  offered.  growth,  o f t h e change i n t h e mean body  12 were i n t h e p r e d i c t e d  the  completed  are given  changes a r e a n a l y s e d s t a t i s t i c a l l y  the d i r e c t i o n  selection  50% m o r t a l i t y  c h a n g e s c a u s e d by  f o l l o w i n g p r e d a t i o n (Table 14). for  a t about  histograms  The mean " b e f o r e " a n d " a f t e r " , s i z e s  only  The  and t h e s i z e s  as f r e q u e n c y  a l l the sizes  indicates  some  i t was known t h a t of prey that  were  111a  FIGURE 16.  Size  selection  by p r e d a t o r s on 18  populations of guppies. selection,  lower  are i n d i c a t e d size  to Table  13.  Upper h i s t o g r a m  histogram  after.  and t h e d i r e c t i o n  change f o l l o w i n g  experimental  predation.  before  Sample  sizes  o f mean body Refer  also  111b  16 22  28  34  '5 18  21  24  15  TOTAL  18 21  24  15  18 21  LENGTH  24  16  (mm)  22 28  34  16  22 28  34  112 TABLE 14.  D i r e c t i o n o f change o f mean body 18 s i z e  size i n  selection tests  D i r e c t i o n o f change i n mean body s i z e + total  Predator  Crenicichla  3  10  13  Rivulus  5  0  5  Total  8  10  18  p =  & Hoplias  .01 ( F i s h e r E x a c t  P r o b a b i l i t y Test,  one-tailed)  Mechanisms o f p r e d a t o r s e l e c t i o n f o r s i z e d i f f e r e n c e s i n prey The p r e v i o u s small predators  e x p e r i m e n t s have shown t h a t  exert directional  d i r e c t i o n s ) when p r e y i n g  upon  s e l e c t i o n (in opposite  laboratory populations of  g u p p i e s w h i c h e x h i b i t a r a n g e o f body those  of natural populations.  evident  i n tests with  Rivulus  l a r g e and  This  s i z e s comparable t o  s e l e c t i o n was much more  and H o p l i a s  than t e s t s  with  Crenicichla. S e v e r a l mechanisms  m i g h t have b e e n o p e r a t i v e  i n these  experiments: (a) R e l a t i v e c o n s p i c u o u s n e s s o f p r e y . predators than  small prey;  larger fish  u s u a l l y can d e t e c t  visual  species  at a given  angle  l a r g e prey distance,  on t h e p r e d a t o r ' s  t h a t have b e e n s t u d i e d  Visual  at greater  distances  the former subtend a retina,  I n t h e few  ( c o d , Brawn, 1969;  113 mackerel  and m u l l e t , P r o t a s o v , 1970;  r e a c t i o n d i s t a n c e t o moving p r e y as a l i n e a r  or c u r v i l i n e a r  (b) A c c e s s i b i l i t y are  often  guppies deeper  found  of prey  of prey.  are n o r m a l l y found  the  (or o t h e r o b j e c t s ) i n c r e a s e s  function  in different  t r o u t , Ware, 1 9 7 1 ) ,  size.  Prey o f d i f f e r e n t  m i c r o h a b i t a t s , e.g.  further  from  shore  sizes  large  and  over  w a t e r ; c o n s e q u e n t l y t h e y a r e more a c c e s s i b l e  to  large predators. (c) speed  Escape  behavior of prey.  is positively  1960) , a l a r g e  fish  fish  may  b e c a u s e i t has  i s less  the  angle of  guppies  guppies  acuity  used  of the  acuity. t o my  a  Also a  Protasov's  stocks, i t i s evident 5.1  had  almost  s m a l l e s t (measured as t h e  twice  minimal  resolution).  capturing  apparatus  over a l i m i t e d range  size  of predator.  range  and  of prey.  prey-  P r e y above o r b e l o w  ( i . e . grasped prey escape  place limits  a p r e d a t o r may  and  swallowed) w i t h  i s more p r o b a b l e .  (e) C o n d i t i o n i n g o f p r e d a t o r . constraints w i l l  The  o f most p r e d a t o r s f u n c t i o n s o p t i m a l l y  are handled  greater d i f f i c u l t y  handled,  o v e r t a k e n by  I f I apply  i n Exp.  (d) H a n d l i n g e f f i c i e n c y  this  t o be  o f t h e same s p e c i e s .  better visual  largest  the v i s u a l  likely  detect a predator at a greater distance  (1970: 81-82) d a t a on that  swimming  c o r r e l a t e d w i t h body l e n g t h ( B a i n b r i d g e ,  predator than a small f i s h large  Because  Although  on what s i z e  actually  anatomical  o f prey can  be  s e l e c t p r e y o v e r a much  114 narrower range, presumably determined schedule  of reinforcement  spectrum of prey. (40-50 mm)  shifts can  F o r example,  i f juvenile  swallowed with  (f) Hunger l e v e l of a predator  rises,  the  towards the  However, t h e s e  great d i f f i c u l t y  of predator. size  limits  As  the hunger  range of a c c e p t a b l e of handling  ability  (5 mm);  female guppies  Though a l l o f t h e s e to determine the  a certain be  5.1; small  (b) and  factors  ( f ) c a n be  f i s h was  provided  (> 30 mm)  factors  relative  s i z e , mechanisms  t h e most l i k e l y  starved  too  (and  Hoplias  large to  probably  the p r e d a t o r s  swallow.  in  o f a guppy  of  (e) seem t o  selection  o u t b e c a u s e no  will  Rivulus  interact  vulnerability  that affected  level  prey  (and n a i v e )  ( a ) , ( c ) , ( d ) , and  ruled and  and  prey  all).  guppies.  a t t a c k newborn g u p p i e s attack  ( i f at  resumes f e e d i n g on  Starved C r e n i c i c h l a  nature  and  larger  predator  o c c a s i o n a l l y beyond).  will  Aequidens  w i t h Aequidens, the  t o i g n o r e them and  increases  size  aquarium c o n t a i n i n g guppies  h i s attack to Aequidens.  s e v e r a l encounters  learns  favorable  ( C r e n i c i c h l a or H o p l i a s ) , the predator q u i c k l y  o n l y be  After  t h e most  a t t a i n a b l e from a g i v e n  a r e a d d e d t o an  a predator  by  in  refuge  Exp.  for  could feed  ad  libitum. I a l s o have some e v i d e n c e ences i n v i s i o n In C h a p t e r  (mechanism  that size-related  (c) ) may  have b e e n  differ-  unimportant.  6 I measured the r e a c t i o n d i s t a n c e o f 5  stocks  115 of  guppies  t o a d e a d 190 mm  " p r e d a t o r " was Though  motionless  significant  Chapter  and i n t h e o t h e r  s t o c k d i f f e r e n c e s were  6) , a n o n - p a r a m e t r i c  i n d e p e n d e n c e o f body revealed  these  size  2 v a r i a b l e s were  likely  t o show a v o i d a n c e  guppy,  and v i c e - v e r s a .  Body  test  15.  i n one t e s t t h e i t was found  ''animated".  (details i n  of the a s s o c i a t i o n or  and r e a c t i o n d i s t a n c e  (5 s t o c k s x 2 t r e a t m e n t s ) .  TABLE  Crenicichla;  (Table  i n d e p e n d e n t i n a l l 10  Thus a l a r g e guppy  15) tests  i s just  as  a t a l a r g e d i s t a n c e as a s m a l l  The r e l a t i o n s h i p o f body s i z e and reaction distance to a predator. For e a c h s t o c k and t r e a t m e n t / the sample was d i c h o t o m i z e d a t t h e m e d i a n body l e n g t h and r e a c t i o n d i s t a n c e ; s c o r e s f a i l i n g above (+) o r b e l o w (*-) t h e m e d i a n s were p o o l e d i n a 2 x 2 contingency table. I n d e p e n d e n c e was t e s t e d by c h i s q u a r e . (n = 125 f e m a l e s ; s c o r e s f a l l i n g on a m e d i a n were o m i t t e d )  P r e d a t o r n o t moving Reaction distance  P r e d a t o r moving Reaction distance  ~ F 1  ~ F 1  (+1  FT"  (-)  28  25  30  25  (+)  29  29  25  31  length  X  visual  2  = 0.089,  .80  > p > .70  However,  I do n o t know i f e x p e r i e n c e  cues emanating from, a l i v e  X  2  = 1.09,  .30  with,  > p >  .20  or  C r e n i c i c h l a might  affect  116  large  and s m a l l g u p p i e s d i f f e r e n t l y .  visual the  a c u i t y o f l a r g e g u p p i e s o n l y becomes s i g n i f i c a n t  fish  greater  have b e e n c o n d i t i o n e d distance  reaction  standard  this  to l i v e  examine mechanism  I conducted  recorded  directly  and s m a l l  when  from a  With e x p e r i e n c e , the. increases  a l m o s t 50%; f o r during  tests).  closely,  Experiment  Rivulus  a predator  i s o v e r 100% ( c a s u a l o b s e r v a t i o n s  survival To  to avoid  ( i . e . > 40 cm).  distance  Crenicichla  large  Perhaps the g r e a t e r  (d)—handling  3 short p i l o t  the behavior  efficiency—more  e x p e r i m e n t s where I  of predators  exposed t o  guppies.  5.2  Handling  efficiency  of Crenicichla.  Methods Five mm, in had  large  (24-27 mm,  x = 19.4) f e m a l e g u p p i e s o f t h e same s t o c k were a 400 l i t e r  aquarium w i t h  placed predator  n o t b e e n f e d f o r 24 h r ( i . e . i t was m o d e r a t e l y  hungry).  and c a p t u r e  Rustrak event recorder  C r e n i c i c h l a C-5.  (18-20.5  The  Approach, a t t a c k ,  the  x = 26.1) and 5 s m a l l  scores  were r e c o r d e d  f o r 60 m i n a f t e r  on a  the introduction of  prey. Though I a l r e a d y  knew t h a t t h i s p r e d a t o r  handle guppies  l a r g e r and s m a l l e r  object of this  e x p e r i m e n t was t o s e e i f a mean  difference  o f 6.7 mm  might a f f e c t  (typical  the handling  than those  of adult f i s h  efficiency  could  o f f e r e d , the size  i n nature)  of a large  predator.  117 Results Although that  this  t e s t was n o t r e p l i c a t e d ,  i t t o o k many more a p p r o a c h e s  contact)  to capture  (pursuits without  a s m a l l guppy t h a n  l a r g e one ( T a b l e 1 6 ) .  t h e y c o u l d sometimes e s c a p e  attempted  grasp.  A t t a c k s on l a r g e  under these e x p e r i m e n t a l  prey  i t d i d to capture a  E v e n when t h e s m a l l f i s h  attacked,  c l e a r water, b r i g h t  i ti s clear  were  the predator's  fish  were 100% s u c c e s s f u l  c o n d i t i o n s (no p r e y  refuge, very  illumination). t  TABLE 16.  P r e d a t i o n e f f i c i e n c y o f C r e n i c i c h l a on l a r g e and s m a l l g u p p i e s .  Small  Frequency/hr  Large  guppies  13  28  Approach Attack  5  4  Capture  2  4  2.5:1  Attack:Capture  Although  this  aquarium, the s i z e detection to  experiment  differences  o f the prey  from  1:1  was c o n d u c t e d  i n a large  d i d n o t appear t o a f f e c t t h e  a distance  e v e n t h e s m a l l e s t guppy f r o m  distance—1.2  3.25:1  14 :1  Approach:Capture  guppies  (the p r e d a t o r r e a c t e d  t h e maximum  m), b u t i t i s p o s s i b l e  that  available  the smaller  118  g u p p i e s were l e s s seconds p r i o r resulted  easily  tracked  during  the c r u c i a l  t o t h e o p e n i n g o f t h e jaw.  i n an e r r o r i n t h e d i r e c t i o n  speed cinematography  b a s s most p r e y - c a p t u r e  E x p e r i m e n t 5.3  of attack.  With  high-  s m a l l g u p p i e s an edge o v e r  i n dealing with  o p e n e d t o o soon  T h i s might have  i t m i g h t be p o s s i b l e t o a s c e r t a i n t h e  p r e c i s e mechanism t h a t g i v e s large guppies  milli-  a Crenicichla.  failures  (Nyberg,  occur  In largemouth  when t h e mouth i s  1971).  Handling  efficiency  o f Astyanax.  Methods The was  same i n f o r m a t i o n  as i n t h e p r e v i o u s  d e s i r e d , however a s m a l l e r p r e d a t o r  were u s e d . liter  Two A s t y a n a x o f 65 mm  a q u a r i u m , were p l a c e d w i t h  classes  (5 p e r c l a s s ) d i f f e r i n g  for  each  was  starved  f o r 24 h r .  and s m a l l e r  aquarium  ( f o r k l e n g t h ) , one p e r 40 female guppies o f 2  size  by a mean l e n g t h o f 7.3  (x l a r g e = 24.8; x s m a l l = 1 7 . 5 ) . predator  experiment  Before  mm  each t e s t the  The t e s t was  repeated  once  predator. Results Overall  the r e s u l t s  a p p r o a c h e d and a t t a c k e d total  capture  success  small is  fish  but spent  interesting  were  more o f t e n t h a n s m a l l o n e s , b u t t h e  was  means t h a t t h e p r e d a t o r s  r e v e a l t h a t l a r g e guppies  a b o u t t h e same  (Table  were more e f f i c i e n t  more t i m e p u r s u i n g  17).  This  i n handling  the large prey.  t h a t t h e r e were i n d i v i d u a l  It  d i f f e r e n c e s i n the  119  TABLE 17.  Frequency/hr  Astyanax  Predation e f f i c i e n c y and s m a l l g u p p i e s .  Test  Small guppies 1 Test 2 Total  of Astyanax  Test  on  large  Large Guppies 1 Test 2 Total  1  Approach  10  9  19  29  22  51  Attack  .3  1  4  16  10  26  1  0  1  2  4  13  27  40  37  63  100  Attack  2  6  8  4  9  13  Capture  1  5  0  0  0  Capture  Astyanax  2  2  Approach  4  Pooled Approach  59  151  Attack  12  39  6  4  Capture  120 ability  to handle  on  4 o f 26  13  attacks.  large guppies.  Astyanax  a t t a c k s while Astyanax The  reason(s)  2 was  for this  1 was  u n s u c c e s s f u l on a l l  difference  t h e p r e d a t o r s were t h e  same s i z e ,  feeding history  l a b o r a t o r y , and were  i n the  had  successful  had  an  i s unknown;  identical probably  siblings. The that  results  of t h i s  experiment  a small predator selects  e f f i c i e n c y may large guppies. indicates  that  be  one  The  out  small prey;  escape  field  evidence  i n nature, the  behavior  r o l e under n a t u r a l conditioned  (stomach  selection  it  i s possible  hungrier than  the Astyanax  their wild  time)  Presumably  normally  easier  important  might a l s o as  to handle.  i n the experiment  caught  i s even  accessibility  because,  c o u n t e r p a r t s and  more l a r g e g u p p i e s ; A s t y a n a x  of  samples)  Wild Astyanax  are r e l a t i v e l y  that  handling  (swimming speed) p l a y a more conditions.  they  hypothesis  of Astyanax  to a t t a c k only s m a l l guppies  demonstrated,  the  mechanism f a v o r i n g t h e e s c a p e  more b i a s e d t o w a r d s s m a l l g u p p i e s . and  support  I have Finally,  were  hence a t t a c k e d  i n nature  have o v e r o n e - h a l f o f t h e i r  be  ( i n the  day-  stomachs f u l l  of  food.  Experiment  5.4  The evidence on  has  field  Handling  efficiency  ( F i g u r e 15)  already indicated  small guppies;  and  laboratory (Figure  that  the upper l i m i t  of Rivulus. 16)  Rivulus preys mostly  f o r the  field  is  about  .  121 23.0  mm  and  f o r the l a b o r a t o r y  i t i s about  Rivulus c o u l d not take the m a j o r i t y "large"  c a t e g o r y i n Exp.  interest  to quantify  attacking size  5.2  t o know how  that  limit  much e f f e c t  even  Thus  i n the  Rivulus  because  this  a few m i l l i m e t r e s  larger  i s the  It i s  on t h e c a p t u r e  slightly  mm.  However i t i s s t i l l  o f male g u p p i e s .  i n m a t u r e m a l e s has  I predicted difficult  5.3.  guppies near the upper  difference  of guppies  the p r e d a t o r y behavior of  range o f the m a j o r i t y  important  and  26.0  length  efficiency.  f i s h would  be  more  to capture.  Methods For t h i s size  classes  experiment  i t was  of males d i f f e r i n g  important to obtain  by o n l y a few mm,  a small  s i z e v a r i a n c e , and o f t h e same s t o c k .  fortune  I was  had b e e n r a i s e d  temperature  by N.  "cool" 24.0)  R.  Liley  of temperature  at either  (x = 18.1,  By  good  on body  t h e ones f r o m t h e range  a low o r h i g h  i n h i s experiments size.  t r e a t m e n t were a l l l a r g e and  each w i t h  a b l e t o use m a t u r e m a l e s o f t h e Guayamare  stock which  effects  2  The  (x = 22.8  on  fish mm,  the  from range  the 22.0-  "warm" t r e a t m e n t were a l l s m a l l  16.5-19.5).  My  t e s t s were c a r r i e d o u t a t  a constant intermediate temperature. Four R i v u l u s  (2 o f e a c h  were u s e d as t h e p r e d a t o r s . in  a 40  liter  the 2 s i z e  aquarium.  The  sex)  o f g r e a t e r t h a n 70  e x p e r i m e n t was  For each t e s t ,  g r o u p s were p l a c e d  performed  2 male g u p p i e s  i n the aquarium  mm  with the  of  of  121 a predator  (after  t h e g u p p i e s had  had  p e r i o d b e h i n d an opaque p a r t i t i o n  a 15 min  i n one  " c a l m i n g down"  corner of  the  tank). The previous  same b e h a v i o r a l m e a s u r e s were t a k e n as f o r t h e  tests with Crenicichla  were f e w e r  prey  in this  b e f o r e a t e s t was  experiment,  terminated.  c o n s e c u t i v e days.  and A s t y a n a x .  a l l p r e y were consumed  A t e s t was  I n most t e s t s  conducted  of each  new  on  10  each o f the p r e d a t o r s con-  sumed 1 p r e y ; t h u s t h e y were a l l a t c o m p a r a b l e at the s t a r t  Since, t h e r e  hunger  levels  test.  Results S m a l l g u p p i e s were c a u g h t w i t h g r e a t e r e a s e l a r g e ones are  (Table 18).  significantly  Both  the approach  d i f f e r e n t between t h e s i z e  ( W i l c o x o n S i g n e d Ranks T e s t , a p p r o a c h : p < .01;  attack:  T=4,  n = 10,  tailed) .  T h e r e was  no  attracted  to either  size  p<  evidence that class  large prey. experience  (approaches  I t w o u l d be  over the 1 0 - t r i a l overall  groups  T = 5, n =  .01;  slight  t h e p r e d a t o r s were was  had b e e n i n i t i a t e d , i t  expected that with  d i s c r i m i n a t i o n was  increasing  attacks,  not  experiment.  improvement i n t h e a b i l i t y and  one-  and a t t a c k s ) t o c a p t u r e t h e  period of this  (compare a p p r o a c h e s  10,  both t e s t s  the p r e d a t o r s would p r e f e r e n t i a l l y  small guppies but t h i s  attack scores  (the o r d e r o f c a p t u r e s  r a n d o m ) , b u t o n c e an a t t a c k s e q u e n c e t o o k more e f f o r t  and  than  tests  1-5  a t t a c k the observed T h e r e was  to handle  an  guppies  v s . 6-10),  but  TABLE 18.  Test  Predation  Total length of small  efficiency  p r e y (mm) large  of Rivulus  Survival t i m e (sec)  on l a r g e and s m a l l  Approach small large  guppies.  Attack small large  Capture sequence  1  18.0  19.0  23.5  22.0  235  27  22  11  10  LLSS  2  19.0  17.0  23.0  22.5  155  14  32  5  17  SLSL  3  16.5  18.5  23.0  23.5  115  13  27  7  13  SLSL  4  18.0  17.0  22.0  22.0  65  16  24  4  9  SLLS  5  18.5  19.0  22.0  24.0  65  15  19  6  5  SSLL  6  18.5  18.5  22.0  24.0  55  17  16  6  7  LLSS  7  19.0  19.5  24.0  22.0  90  15  26  4  8  SSLL  8  17.0  18.5  22.5  23.0  100  16  34  4  12  LSSL  9  16.5  18.0  22.0  22.0  60  9  18  2  10  SSLL  10  17.0  19.0  23.0  23.0  35  10  14  2  4  SLSL  97.5  15.2  23.2  5.1  9.5  Mean  18. 1  22. 8  123 t h i s was  not  size-dependent.  consume a l l 4 p r e y ) experiment, guppies  due  and  to  The  survival  time  (time t o  a l s o decreased over the course of (a) t h e i n c r e a s e d p r o f i c i e n c y  (b) a d e c r e a s e  the r e l e a s e o f the prey  i n the l a t e n t p e r i o d  from b e h i n d  C o n c l u s i o n and g e n e r a l d i s c u s s i o n g e o g r a p h i c v a r i a t i o n i n body s i z e  the  the  i n handling following  partition.  of "  In g e n e r a l , the p a t t e r n o f g e o g r a p h i c v a r i a t i o n body  size  (Figure  14)  t o p o i k i l o t h e r m s by lations  living  the apparent  unknown.  Ray  The  appear  temperature upper  and  i s not the primary  upon t h e o v e r a l l  v a r i a t i o n which cannot  genetic or phenotypic fish  t o be  responses  maturity feel and  this  readily  be  result  ( c f . Svardson, i s important Both  here.  e x p l a i n e d by  to temperature,  i . e . the  particular  that differences  i n r e t a r d e d or  near  the  1943,  cited  i n food  accelerated  thereby determining the s i z e  Santa Cruz.  residing  i n F i g u r e 12) .  Though i t i s p o s s i b l e  growth r a t e s ,  popu-  are  concern  (e.g. the p o p u l a t i o n s f a l l i n g  lower- e x t r e m e s  might  those  applied  temperature-size trend  too l a r g e or s m a l l f o r a  regime  availability  than  from  a d a p t a t i o n s to temperature  However, t h i s  geographic  taken  as  p h y s i o l o g i c a l mechanisms r e s p o n s i b l e  size  Superimposed is  (1960), v i z . f i s h  i n c o o l water are l a r g e r  i n warmer w a t e r . for  c o n f o r m s t o Bergmann's R u l e  in  o f males a t  i n Aim, .1959: 9 7 ) ,  i n o n l y 2 streams,  I  Lower T a c a r i g u a  o f t h e s e have b e e n e n r i c h e d  through  124  human a c t i v i t y .  The r e s u l t a n t i n c r e a s e  i n primary  produc-  tivity  a p p e a r s t o have f a v o r e d  t h e growth o f guppies t o a  larger  size  " n a t u r a l " streams.  than i n comparable  Nevertheless, and  Upper A r i p o  evidence  Liley's  stocks  that genetic  (nutrition  The has  question  favored  affect  that  o v e r 16 b i o t i c  genetic  populations.  i n some e n v i r o n m e n t s and  Temperature  (via the Baldwin  of selection factors  body s i z e .  I have m e n t i o n e d  f a c t o r s i n -the i n t r o d u c t i o n ; Ray and a b i o t i c  i n v o l v e d b u t many o f t h e s e For  among o t h e r  i s b u t one o f a m u l t i t u d e  t h a t might c o n c e i v a b l y  lists  are present.  work, i t i s p r o b a b l e  animals  ones i n o t h e r s .  some o f t h e o t h e r  provided  now a r i s e s a s t o why n a t u r a l s e l e c t i o n  large-bodied  small-bodied effect?)  be c o n f i r m e d  Guayaniare  c o n t r o l l e d ) have  d i f f e r e n c e s i n body s i z e  With a d d i t i o n a l experimental differences w i l l  experiments with  (1960)  f a c t o r s t h a t m i g h t be  a r e n o t a p p l i c a b l e t o t h e guppy.  some o f t h e more p l a u s i b l e mechanisms, - i n f o r m a t i o n i s  either  unavailable  competition) 1973).  (feeding s p e c i a l i z a t i o n ,  or inconclusive  (sexual  interspecific  selection,  C l e a r l y t h e p r o b l e m w a r r a n t s an i n t e n s i v e  study.  In t h i s  attempt  chapter  I have made a p r e l i m i n a r y  t o t e s t one o f t h e many a l t e r n a t e e x p l a n a t i o n s trends--the reflect  hypothesis  an a d a p t a t i o n  idea arose Aripo  see B a l l i n ,  that variation  f o r the size  i n body s i z e  may  t o s i z e - s e l e c t i v e predation..  out of the observation  R. a r e much s m a l l e r  This  t h a t g u p p i e s i n t h e Lower  t h a n i n t h e Upper A r i p o  R.,  though  125  apart  from p r e d a t i o n ,  the e c o l o g i c a l conditions  temperature) a r e very For able  l a r g e s i z e , t o be an a d v a n t a g e , a f i s h  to  be a d a p t i v e  to  a predator  and  i t should  i n the Aripo  R.,  predation,  f o r small  large prey  of a  i n i t s diet.  be size  fish  Cer-  the r e q u i s i t e . p r e d a t o r s are present  field  and l a b o r a t o r y e v i d e n c e ' t o  l a r g e g u p p i e s do e n j o y  Rivulus  and c o n v e r s e l y ,  should  reduce the v u l n e r a b i l i t y  that requires  I have a s s e m b l e d  that  or  similar.  t o "outgrow" a p r e d a t o r ,  tainly  (including  an a d v a n t a g e w i t h  b u t a r e more, v u l n e r a b l e  show  respect to  to Crenicichla  Hoplias. Predation  m i g h t a l s o a c t on body s i z e  Where t h e l a r g e p r e d a t o r s very  shallow  restricted tion  w a t e r a t t h e s t r e a m edge  t o new s e l e c t i o n p r e s s u r e s  initial  small  are found i n  (see Chapter 6 ) .  surroundings.  Thus an  producing  and (b) l e s s  able  cichlid  r e s u l t e d i n the e v o l u t i o n o f large offspring w i l l  b e c a u s e t h e i r p r o g e n y a r e (a) more a t t r a c t i v e  water.  feeding,  r e s p o n s e t o e s c a p e c h a r a c i d and  Parents  This  popula-  favoring efficient  confined  may have i n d i r e c t l y  fish.  predators  t o cope w i t h  life  be  less  to large  i n shallow  B o t h d i s a d v a n t a g e s may r e d u c e t h e r e p r o d u c t i v e  potential size  e t c . i n very  behavioral  predation  guppies  environment presumably exposes the f i s h  reproduction,  fit  are.present,  indirectly.  o f t h e o f f s p r i n g ; h e n c e genes f a v o r i n g l a r g e body  should  be g r a d u a l l y e l i m i n a t e d  from the p o p u l a t i o n .  126  trends, size  If predation  i s partly  there  be o t h e r  should  correlation.  responsible  f o r the size  examples o f a p r e d a t o r - b o d y ,  O v e r a l l , o f t h e 10 p o p u l a t i o n s  above t h e  m e d i a n mean s i z e o f m a l e s ,  8 a r e e x p o s e d to" R i v u l u s  to characids  and c i c h l i d s ;  f o r t h e 10 p o p u l a t i o n s  median, o n l y  2 a r e e x p o s e d to' R i v u l u s  and  cichlids.  .Thus t h e r e  characids  Rivulus.  However, I have a l r e a d y  F i s h e r Exact  and c i c h l i d s ,  distribution  cases  mechanism i s o p e r a t i v e .  cautioned  2-tailed),  as t h e A r i p o  that  and t e m p e r a t u r e  with  temperature  (p < .01,  so i t i s i m p o s s i b l e ,  R., t o d e t e r m i n e  Perhaps c a r e f u l  N o r t h e r n Range m i g h t u n c o v e r o t h e r where p r e d a t i o n  body  and l a r g e body s i z e  are also associated  P r o b a b i l i t y Test,  except i n i s o l a t e d  and 8 t o c h a r a c i d s  2-tailed) of small  size with  predator  below t h e  i s a good a s s o c i a t i o n (p = .05,  Fisher Exact-Probability Test,  and  and 2  searching  "natural  i n the  experiments"  are not confounded.  Though t h e a s s o c i a t i o n of. l a r g e body s i z e w i t h selective there  predation  by R i v u l u s  are s e v e r a l anomalies  (Figure..1-2) satisfactory  that militate explanation  does e x e r t d i r e c t i o n a l guppies  should  populations  i s an a t t r a c t i v e  i n the.field  against  this  f o r the s i z e  This  c a s e s i n c e t h e mean body s i z e  size-  hypothesis,  collections  simple" idea, as a trends.  s e l e c t i o n on body s i z e ,  be i n p o p u l a t i o n s  of Rivulus.  which  If R i v u l u s the l a r g e s t  exposed t o t h e densest  clearly  i s n o t always t h e  o f males a t Tompire T r i b u t a r y  127 and  Petite  Curucaye  (both w i t h dense R i v u l u s p o p u l a t i o n s ) i s  w e l l b e l o w t h e maximum o f 25.3 mm For  Tompire  attributable  Tributary,  (Grande  Curucaye).  t h e s m a l l . s i z e may be p a r t l y  t o warm t e m p e r a t u r e  (26.2 C ) , s a m p l i n g  (n = 2 1 ) , a n d a d i f f e r e n t  genetic history  from t h e C a r o n i system).  B u t t h i s does n o t a c c o u n t  s m a l l males a t P e t i t e tributary  Curucaye.  o f Grande Curucaye  temperature, populations historically gene f l o w  pH, h a r d n e s s ,  Petite  Curucaye  f o r the  isa  substrate, e t c . ; both are undoubtedly  and a r e p r o b a b l y c o n n e c t e d  fish  closely  related  a t p r e s e n t by some  colour patterns are very s i m i l a r ) .  there are 2 conspicuous d i f f e r e n c e s Curucaye  ( i t i s isolated  and i s i d e n t i c a l t o i t i n  i n t h e s e streams  (male  error  between them:  However, P.  R. i s s m a l l e r a n d h a s a g r e a t e r abundance o f  Rivulus. Thus i t w o u l d a p p e a r velocity) factor. The  tions  o f t h e stream might There  first  that  are at least  the size  be an i m p o r t a n t  2 ways t h i s  i s t h e mechanism I a l l u d e d  o f guppies  ment—small  "forced"  to live  s i z e may have d e f i n i t e  generally  second  select  factor  i s water  microenvironments  could  effect  operate. f o r popula-  i n ,a v e r y s m a l l e n v i r o n advantages,  partly  to Rivulus.  velocity.  Though  where w a t e r  w e l l b e l o w t h e s t r e a m maximum, l a r g e body s i z e concomitant  selective  to earlier  counteracting the greater v u l n e r a b i l i t y The  (and h e n c e t h e  on swimming speed) m i g h t  guppies  velocity i s (with i t s  allow a  fish  128 to  maneuver more e a s i l y  stream. and  up and down o r a c r o s s  T h i s may have a d v a n t a g e s  i n intraspecific  es.cape f r o m R i v u l u s and t e r r e s t r i a l  m i g h t e x p l a i n t h e l a r g e body s i z e I suggest literally  f o r the f i s h  behavior  predators.  This  o f Grande C u r u c a y e  that i n the P e t i t e  no p l a c e  a fast-flowing  males.  C u r u c a y e R. t h e r e i s  t o go.  This  presents  u n i q u e s u r v i v a l p r o b l e m s w h i c h c a n n o t be s o l v e d by l a r g e body s i z e predator in  a n d swimming s p e e d a l o n e . behavioral adaptations  of Petite  the a n t i -  Curucaye  guppies  the' f o l l o w i n g c h a p t e r . Possibly  s i z e - s e l e c t i v e p r e d a t i o n p e r se h a s no  b e a r i n g w h a t s o e v e r on g e o g r a p h i c If  I explore  this  variation  i n body  size.  i s t r u e , t h e d i s c o v e r y t h a t t h e body s i z e o f t h e  majority  o f adult,  above t h i s  males exposed t o R i v u l u s  predator's  upper h a n d l i n g  limit  falls  near o r  must be  coincidental. As  with  c h a r a c i d and c i c h l i d  must be i n t e r p r e t e d n o t o n l y handling e f f i c i e n c y on  the other  i n i t s direct  and p r e f e r e n c e  selective  p r e d a t i o n , body  factors  effects  of'the predator  that predator  size  on t h e but also  avoidance  m i g h t impose upon t h e p r e y . Finally, populations distance. to  i n the Caroni  populations  t h a t many o f t h e  s y s t e m a r e i s o l a t e d o n l y by  G e o g r a p h i c t r e n d s may s i m p l y  which l o c a l  features  i t s h o u l d be r e c a l l e d  reflect  are able to preserve  i n t h e f a c e o f gene f l o w  from o t h e r  the degree adaptive  populations.  129 Summary o f C h a p t e r 1.  5  Populations of guppies  show c o n s i s t e n t d i f f e r e n c e s of  over  41%  sampled  i n a d u l t body s i z e .  in- body l e n g t h and  200%  i n weight  measurements on a d u l t m a l e s ) have b e e n 2.  In compliance  negative correlation  temperature  and  response account  observations indicate  appears  3. of  fish  (p < .01)  that  to environmental temperature  variation  t o have a g e n e t i c  p r e d a t o r s and  of  these  exists  to  distribution  are  Small  large predators  selective to assess  impact because  confounded. demonstrate selection  that  large  (in opposite  when p r e y i n g upon l a b o r a t o r y p o p u l a t i o n s o f  guppies which  exhibit  a range  o f body s i z e s  comparable  those of n a t u r a l p o p u l a t i o n s . 5.  and  infested with a small  and p r e d a t i o n i s d i f f i c u l t  small predators exert d i r e c t i o n a l  directions)  phenotypic  geographic  of guppies.  the p o t e n t i a l  Laboratory experiments  stream  and  i s inadequate  between t h e  i n streams  2 environmental variables 4.  and  I n most s t r e a m s  temperature  Field  a strictly  g u p p i e s o c c u r where t h e r e a r e p r i m a r i l y  predator.  (mean  basis.  t h e body s i z e  l a r g e guppies predominate  Differences  between  t r e n d s , i . e . much o f t h e  A relationship  1969  found.  t h e body s i z e o f g u p p i e s .  f o r the s i z e  and  w i t h Bergmann's R u l e t h e r e i s a  significant  laboratory  i n 1967  One  aspect of s i z e - s e l e c t i v e p r e d a t i o n , the  handling e f f i c i e n c y  o f t h e p r e d a t o r , i s shown t o be  an  to  important factor determining the r e l a t i v e v u l n e r a b i l i t y of guppies of d i f f e r e n t body sizes. 6.  In conclusion, s i z e - s e l e c t i v e predation i s a  plausible mechanism f o r the evolution differences explain  i n guppies.  of body size  However, i t does not adequately  a l l the geographic v a r i a t i o n — o t h e r  selective  factors must be involved, including water v e l o c i t y , the size of stream, and the i n d i r e c t effects of antipredator behavior. The adaptive significance of geographic variation in body size can only be understood i n terms of the action and counteraction of numerous selective factors, coupled with an appreciation of the magnitude of gene flow.  CHAPTER 6  GEOGRAPHIC VARIATION  IN  BEHAVIOR  Introduction In t h i s c h a p t e r behavior of  I shall  describe  tion  i n the  this  v a r i a t i o n with  of  the  habitat.  I am  interested in ascertaining  the  s i g n i f i c a n c e of  differences.  Are  g u p p i e s and  geographic v a r i a -  features  these d i f f e r e n c e s  make f u n c t i o n a l s e n s e i n t e r m s o f  endeavor to  correlate  In p a r t i c u l a r ,  heritable?  the  major  Do  the they  challenges.to  survival? The  emphasis  i s on  predator b e h a v i o r — t h e animal  t o s h a r e an  already  attempted  grounds  (see  insight  t o be  evolution  of  The discovery in nature. to c o n t r o l studied  population  behavioral  Chapter gained  justify  i t s predators.  t h i s research  1 ) ; most i m p o r t a n t i n t o the  in  anti-  components e n a b l i n g  environment with to  differences  on  i s the  an  I have  several potential  mechanisms a f f e c t i n g  the  behavior. w o r k i n g h y p o t h e s i s was  of b e h a v i o r a l To  differences  erected  following  in several  situations  examine t h e s e d i f f e r e n c e s more c l o s e l y  f o r the  behavior  e f f e c t s of  i n the  the  and  environmental d i f f e r e n c e s ,  laboratory, 131  using  mostly  the  I  132 offspring  of  samples t a k e n  from 5 r e p r e s e n t a t i v e  (Lower A r i p o , Guayamare, U p p e r A r i p o , P e t i t e Paria).  These r i v e r  sent  range o f e c o l o g i c a l  the  commonly f o u n d 3).  (at l e a s t  in this  Therefore,  f o r Northern  apparent i n a comparative  predation  Field  range of p r e d a t i o n  region of T r i n i d a d  degree) a m i c r o e v o l u t i o n a r y  observations  variation  of  3).  ( t o some become  populations,  exposed to e i t h e r  a r e b a s e d on  streams sampled  extreme  town, Guyana  and  of  The  of guppies i n sex  ratio  In a d d i t i o n , in a  stream  d i t c h e s i n George-  (both are m a i n l a n d ' S o u t h American  populations).  q u a n t i t a t i v e comparison  the b e h a v i o r a l d i f f e r e n c e s i n nature.  Distribution  and  populations  i n pools  I d i d n o t make a d e t a i l e d  mostly  study  to Chapter 2).  were made on  a t P a r a m a r i b o , S u r i n a m , and  the  f o r body s i z e  ( f o r methods, r e f e r  casual observations  is  5  Table  behavior  observations  most'of the  then  3,  does r e p r e s e n t  of these  Chapter  pressure.  My  of  (Chapter  are  pressure  phenomenon, i t s h o u l d  study  the p o p u l a t i o n s  T r i n i d a d , see  and  repre-  c o n d i t i o n s where g u p p i e s  i f behavioral variation  especially  Curucaye,  s i t e s were c h o s e n b e c a u s e t h e y  They a l s o encompass t h e  occurring  populations  This  section i s  descriptive. of guppies  i n the  distribution  s e l d o m random.  In the  of  stream  fish  environment  across  and  along  a  stream  streams I examined, d i f f e r e n c e s i n  133 depth occurrence able.  and p r o x i m i t y  I n some p o p u l a t i o n s  each s i d e o f the stream quite  uniformly across Several  differences.  Obviously  distribution. larly  reasons  fish  while  than  water v e l o c i t y ,  guppies  abiotic  bunched  t h e y were  near  spread  f o r these  factors.can influence  are small f i s h  and n o t p a r t i c u -  do n o t o c c u p y w a t e r  flowing  In s e c t i o n s o f streams w i t h a r e found  e x t r e m e edge o f t h e s t r e a m water v e l o c i t y  i n others  c o u l d be s u g g e s t e d  Since guppies  0.3 m/sec.  were t i g h t l y  the stream.  s t r o n g swimmers, t h e y  faster  t o t h e s h o r e l i n e were n o t i c e -  i n back-eddys o r a t the  "clinging"  u s u a l l y approaches  a high  t o the s h o r e l i n e ; the  z e r o m/sec i n t h e s e  regions. Even a l o n g regions with lower  velocity.  restricting out  i n these  tions, playing threat  pools  f a s t - f l o w i n g s t r e a m s however, t h e r e a r e and w i d e r ,  smooth-flowing s e c t i o n s o f  I f water v e l o c i t y  i s the only  t h e movement o f g u p p i e s , sections.  suggesting a role,  the f i s h  This i s not observed  t h a t i n some c a s e s  other  possibly the d i s t r i b u t i o n  factor should  spread  i n a l l popula-  factors are of food or the  from l a r g e p r e d a t o r s . (a)  The e f f e c t  of predators  T h e r e i s good f i e l d e v i d e n c e have an e f f e c t  on t h e d i s t r i b u t i o n  mentioned b e f o r e ,  tha,t p r e d a t o r s  of guppies.  t h e A r i p o R. i s d i v i d e d i n t o  may  As an " u p p e r "  134 and  " l o w e r " r e g i o n by  a series  One  of these w a t e r f a l l s  of f a l l s  i s 5 m high, completely blocking  upward p a s s a g e  of characids  depth o f water  above and b e l o w t h e f a l l s  the d i s t r i b u t i o n  was  samples  only  falls,  are comparable  but  markedly.  evidence that  avoiding To  characid test  this  different—both  the s h o r e l i n e o f f e r s  idea,  the  the males  This i s  some p r o t e c t i o n  I t o o k some g u p p i e s  deeper water.  immediately  them 1-2  from a  discontinued  shore  m from shore over  I observed  several  p u r s u i n g t h e g u p p i e s as t h e y d a r t e d b a c k  Astyanax  the  and c i c h l i d p r e d a t o r s .  and p l a c e d  Astyanax  Above  a c r o s s the stream.  r e f u g e a t Lower A r i p o Almost  females).  strikingly  f e m a l e s were d i s t r i b u t e d  indirect  The  and  from below the f a l l s , i t  (mostly l a r g e  t h e s i t u a t i o n was  the  velocity  a s m a l l number o f f i s h were s e e n n e a r  c e n t r e o f the stream  in  of f i s h  The  n e c e s s a r y t o sample t h e v e r y edge o f t h e s t r e a m and  side-pools;  and  and c i c h l i d s .  of guppies d i f f e r s  To c o l l e c t  (limestone ledges).  t h e i r p u r s u i t once  the  to shore. guppies  reached the s h a l l o w e r water. The variable. t h e few  depth a t which Where c h a r a c i d  fish  g u p p i e s o c c u r r e d was and c i c h l i d  p r e d a t o r s were p r e s e n t ,  t h a t d i d v e n t u r e f r o m s h o r e swam v e r y c l o s e  the s u r f a c e o f the water.  I n a few  streams  to  Where t h e s e p r e d a t o r s were  a b s e n t , t h e g u p p i e s were d i s t r i b u t e d column.  also  throughout the  water  ( P a r i a , Y a r r a , Upper A r i p o ) I had  t h e i m p r e s s i o n t h a t most o f t h e f i s h were i n t h e  bottom  135 one-third  of  (b) To  The  effect  of water v e l o c i t y an  effect  on  of guppies i n a stream v i r t u a l l y  devoid  of  predators,  transect  column.  d e t e r m i n e i f w a t e r v e l o c i t y has  distribution aquatic  the water  across  I made a c e n s u s o f  the  P a r i a R.  fish  (Figure 17).  along This  a  the  4-meter  transect  was  2 divided  i n t o four  representing 2 and  3 as  the  the  1.0  m  sections with  regions  two  on  inner  the  full  other  2 sections with  the  protected  center  of  the  effect  o f v e l o c i t y on f o r the To  proceeded rapidly 16  was  the  fish  fish  i n each s e c t i o n .  out  variability  However t h e that  One  other  of  near  the  of guppies  the  from  the  i n each s e c t i o n , I counted  T h i s was  very  replicated  a 4-min i n t e r v a l between c e n s u s p e r i o d s .  considerable  clearly  through  p o s s i b l e to separate  distribution  number o f  moved r a p i d l y i n and  time.  velocity.  f r o m s e c t i o n 1 t o 4 i n s e q u e n c e and  a l l the  from  immediately  shore, the  Thus i t was the  difference  the water passed  increased  a t the  and  shoreline.  estimate  times with  fish  stream.  important  large boulders  an  s e c t i o n s was  4  them were p r o t e c t e d  T h i s meant t h a t most o f  the  affinity  The  that 2 of  s t r e a m v e l o c i t y by  upstream.  1 and  e i t h e r s i d e o f the- s t r e a m  sections.  among t h e s e s e c t i o n s was  sections  data  fewer f i s h  of  these sections  i n the  i n Figure occurred  17  so  The  there  numbers s e e n a t any demonstrate  i n the  one  quite  sections with  a  high  136a  FIGURE 17.  The  d i s t r i b u t i o n of  section  of  the  Paria  adult  guppies across  River.  the  d i r e c t i o n of water flow.  for  census methods.  Arrows  a  indicate  Refer to  text  CrtOSS SECTION SECTION No. MAX. WATER DEPTH = 30 cm  PARIA RIVER  (JUNE 29.1969)  rtr  1  137 water v e l o c i t y , This  suggests  regardless of the proximity  themselves  s p e n d i n any p a r t i c u l a r  can l i m i t  is  severe.  factor  limiting  water v e l o c i t y  site  in this  on t h i s  a small  dam  stream).  distributed  Since  behavior  to predator  for  stressed of  that this  stream having  Obviously  too shallow  too  fast  both  on  under study. i s only  value  of this  distribution  I t should  for a typical  a d e p t h and v e l o c i t y  section  gradient.  be s e c t i o n s o f e v e n t h e P a r i a R.  that  the f i s h  t o be s p r e a d  across  the stream.  behavior  across  be  f o r g u p p i e s t o be f a r f r o m t h e s u r f a c e , o r  to allow  Besides fish  information  there w i l l  are  Schooling  populations  large  avoidance.  19 summarizes t h e o b s e r v a t i o n s  the 5 p r i n c i p a l  the  around the p e r i p h e r y .  lake, the s u r v i v a l  Table  km  zero, the  H o p l i a s were c a u g h t i n t h i s linked  "lake" i s  Although  m a j o r i t y were w i t h i n 1 m o f t h e s h o r e .  i s probably  predation  ( l o c a t e d 0.5  l a k e was e s s e n t i a l l y  g u p p i e s were n e v e r t h e l e s s The  of the year  t h e Guayamare i r r i g a t i o n  below t h e c o l l e c t i o n  that velocity i s  t h e d i s t r i b u t i o n where  A t c e r t a i n , times  formed b e h i n d  the time  area.  T h e r e i s some a d d i t i o n a l e v i d e n c e the only  fish,  throughout the a v a i l a b l e  e n v i r o n m e n t ; however, w a t e r v e l o c i t y  not  shore.  t h a t i n t h e a b s e n c e o f p r e d a t i o n by l a r g e  guppies d i s t r i b u t e  fish  to the  d i f f e r e n c e s i n the gross  a stream,  I found  d i s t r i b u t i o n of  differences i n schooling  TABLE 19.  The d i s t r i b u t i o n o f 5 p o p u l a t i o n s o f g u p p i e s i n r e l a t i o n t o w a t e r v e l o c i t y , d e p t h , and d i s t a n c e f r o m t h e s h o r e .  Water v e l o c i t y (m/sec) Microhabitat Mainstream of guppies  Stream  D i s t r i b u t i o n of guppies Position across Position in stream water column  0.61  0 -  Guayamare  0.40  approx.  P.  0.29  0 -  0.20  ubiquitous  no p r e f e r e n c e  0.55  0 -  0.20  near  bottom  no p r e f e r e n c e  0.16  0 -  0.16  near  bottom  no p r e f e r e n c e  L.  Aripo  Curucaye  Upper Paria  Aripo  0.20  near  surface  near  shore  0  near  surface  . near  shore  to CO  139  behavior.  I use  aggregation  can  are  together  not  because of  Keenleyside's be  considered  because they similar  a school, provided  are  (p.  of guppies  may  water the  stream  edge so  i t is difficult  effect  of the  groups of  5 t o 50  moving t o g e t h e r to the and  shore.  width  Aripo  fish  are  to  already confined to  to separate  both  o r down t h e . s t r e a m ,  school  "linear"  the  a  the  aggregating  social  i s very  m a l e s and  force of  parallel  small—the  and  fish  fashion.  see  females,  s c h o o l s because  in "single.vfile"  commonly  and  have s e v e r a l c o n f i g u r a t i o n s .  including  These a r e  f o l l o w each other  fish  r e g i o n s , however, i t i s . common t o  fish,  up  of the  s c h o o l was  each i n d i v i d u a l  e x t e r n a l environment.from the  In such  the  fish  183)."  In f a s t - m o v i n g  schooling.  "any  r e a c t i n g to each o t h e r ,  r e a c t i o n s by  common e x t e r n a l s t i m u l u s Schools  (1955) d e f i n i t i o n :  close the.depth  appear  to  T h i s type  of  s e e n i n some p o r t i o n s o f t h e  Lower  R. I f water v e l o c i t y  larger  s c h o o l s may  be  or nearly s p h e r i c a l sections  of the  schools ranged schools  observed.  Lower T a c a r i g u a f r o m 75  of  to over the  t o movement,  Several large  elliptical  R. 200  in  Counts  smooth-flowing  f o r these  adult fish.  l a r g e s t diameter  large  Elliptical parallel  to  flow.  When l a r g e s c h o o l s a r e o r human), t h e y  restrictive  s c h o o l s were o b s e r v e d  are o r i e n t e d with  the d i r e c t i o n  i s less  may  b r e a k up  d i s t u r b e d by  into  a predator  sub-schools  and  (fish  reform  140 into  a single unit after  varies with gradual  a few s e c o n d s .  the i n t e n s i t y  approach w i l l  f o l l o w e d by i m m e d i a t e  a cleaving of the school  (e.g. l a r g e Aequidens)  (especially  by a p o t e n t i a l p r e d a -  or i n the shore vegetation)  a rapid fan-like  s c a t t e r o f the f i s h ,  m o v i n g i n h i s own p a r t i c u l a r source.  A t Lower T a c a r i g u a  majority  o f such d i s p e r s e d  to  direction  will  each  individual  away f r o m t h e s t i m u l u s  R. I was a b l e  to follow the  i n d i v i d u a l s and they  a l l appeared  re-unite. Schooling  streams.  engaged  i s noticeably poorly  developed  F i s h i n t h e P a r i a R. b e h a v e v e r y  individuals;  t h e most common s o c i a l  i n courtship a c t i v i t y  female).  groups i n v o l v e  A number o f s t r e a m s have f i s h  cohesion large,  f o r more t h a n a few females.  populations  exhibiting  development o f the s c h o o l i n g response.  may be q u i t e  i . e . the f i s h  manner.  fish  (e.g. 3 males f o l l o w i n g a  T h e s e g r o u p s do n o t p e r s i s t  intermediate  i n some  much a s  s e c o n d s as t h e m a l e s move o f f t o c o u r t o t h e r  an  a slow,  reformation.  h i d i n g under r o c k s  elicit  only  object  Sudden a p p r o a c h e s tor  splitting  of the disturbance:  elicit  around t h e t h r e a t e n i n g  This  I f these  loose  and d i s t a n c e s  do move t o g e t h e r  fish  are threatened,  between  fish  but i n a less they  The  organized  o f t e n escape i n  g r o u p s b u t q u i c k l y d i s s o c i a t e o n c e t h e emergency h a s p a s s e d . This  i s f o l l o w e d by a r a p i d r e s u m p t i o n o f f e e d i n g and  courtship  behavior.  141 When t h e t e n d e n c y t o s c h o o l tors  i n the surrounding  characid  and c i c h l i d  more p r e v a l e n t schooling abundant  i s related  to the preda-  environment, the trend  i s t h a t where  predators  (Table  20).  occur,  Also,  schooling behavior i s  i n streams with  i s b e t t e r d e v e l o p e d where t h i s ( e . g . P.  TABLE 20.  predator  Rivulus, i s very  Curucaye).  The d e v e l o p m e n t o f s c h o o l i n g b e h a v i o r 5 populations o f guppies  in  Stream  Predator(s)  Guayamare  c h a r a c i d s and cichlids  well-developed  L.  Aripo  c h a r a c i d s and cichlids  well-developed  P.  Curucaye  Rivulus  intermediate  D.  Aripo  Rivulus  poorly-developed  Rivulus  absent  Paria  Reaction  distance to p o t e n t i a l Reaction  the  distance  the  (= r e a c t i v e ) d i s t a n c e  an o v e r t  direction,  velocity,  term i s thus roughly (Walther,  i s d e f i n e d h e r e as a t which a  change i n b e h a v i o r .  antipredator behavior,  this  behavior  predators  f r o m an e x t e r n a l s t i m u l u s  responds with of  Schooling  fish  In the context  usually entails  a change i n  o r f o r m o f swimming b e h a v i o r .  equivalent  to "flight  1969, f o r Thomson's g a z e l l e ) ,  The  distance"  "approach  distance"  142 ( H e a t w o l e , 1968, a n d J o h n s o n , "Feindabstand"  distance tor  i s made between t h e d i s t a n c e  approach a predator a t which a prey  (flight It  situ.  from t h e approach o f a preda-  distance). i s regretable  on a more g r o s s  approached  that  I d i d n o t have t h e f o r e s i g h t  important behavioral  qualitative scale.  streams c o n t a i n i n g  g u p p i e s were o b v i o u s l y at  a considerable  at  any g i v e n  They u s u a l l y  very  distance;  reactive. although  t i m e , t h e s e were v e r y spread  with  is  a dipnet.  a t my  This  probably  predators  They a v o i d e d I could  the net  s e e many  d i f f i c u l t to  fish  capture.  T h i s was e s p e c i a l l y t r u e a t C a p a r o , and O r o p u c h e  Rivers.  some s t r e a m s i t was much e a s i e r t o a p p r o a c h t h e  where the. f i s h also pick  When I  o u t a t r a p i d s p e e d , moved t o d e e p e r  Guayamare, Lower A r i p o , In  moved.  parameter  the larger predators, the  water, o r f u r t h e r from shore.  fish  and t h e  However, I d i d n o t e d i f f e r e n c e s i n r e a c t i o n  distance  Caroni,  Some-  a t which a  (avoiding distance)  flees  t o a c c u r a t e l y measure t h i s in  and  ( C u r i o , 1969, f o r D a r w i n ' s f i n c h e s ) .  times a d i s t i n c t i o n prey w i l l  1970, f o r l i z a r d s ) ,  The e x t r e m e s i t u a t i o n was a t P a r i a  c o u l d be c a u g h t by hand.  These f i s h  l e g s e v e n when t h e s e l a r g e  short'reaction distance r e l a t e d to the v i r t u a l  from the P a r i a  R.  would  " o b j e c t s " were  to a potential  predator  absence o f a l l a q u a t i c  14 3 Motor p a t t e r n s  used i n a n t i p r e d a t o r  behavior  A number o f d i s t i n c t m o t o r p a t t e r n s patterns)  were o b s e r v e d d u r i n g  and  predators  their  here but they  i n nature.  e n c o u n t e r s between These w i l l  studied i n greater d e t a i l  have b e e n q u a n t i f i e d f o r t h e  patterns  that are  distinct  from group responses  elicited  in a later laboratory  u s e d by  individual s u c h as  i n a number o f a n i m a l s  the  case f o r a 1 p r e d a t o r — 1  1.  Weak, " a v o i d a n c e  the  perceiving  the  prey  pattern  predator  guppy's v i s u a l  s e c t i o n where stocks.  These  s c h o o l i n g but  simultaneously,  are may  also  should  Here I s h a l l  consider  system.  or  i s s e e n most commonly when a  strange  o b j e c t has  range a t a c o n s i d e r a b l e  predator,  the  guppy may  appeared  distance.  e i t h e r stop  in On  swimming  m o m e n t a r i l y , o r a c t u a l l y move c l o s e r t o t h e p r e d a t o r . certain to the turns all  critical predator  a r o u n d and  times the  d i s t a n c e , the and  guppy t u r n s  moves some d i s t a n c e  repeats  eyes are  i t i n the  k e p t on  fixation,  head h e l d  surveying  i t from d i f f e r e n t  roughly  a  drift  This behavior fish  guppies  introduced  guppies.  group suddenly encounter a p r e d a t o r .  potential  be  action  t o d i s t i n g u i s h 6 main e s c a p e motor  I have b e e n a b l e  be  (= f i x e d  slightly  e q u i d i s t a n t from the  the  i t s body  one  opposite predator  downwards), as angles. predator  The  way,  and  (with i f the  a  lateral then  direction.  fish  during  At  At  binocular fish  was  remains this  "inspection".  144 T h e r e a p p e a r s t o be a c o n f l i c t drawal motivation  involved i n this  may a l t e r n a t e l y move c l o s e r predator.  Should  direction  of  approach-with-  behavior  t o , and then  because t h e f i s h  away f r o m t h e  t h e p r e d a t o r move, e s p e c i a l l y  o f t h e guppy, t h e b e h a v i o r  i n the  r e v e r t s t o one o f t h e  o t h e r motor p a t t e r n s d e s c r i b e d below. I n some r e s p e c t s , t h e body c o n f i g u r a t i o n i n weak avoidance  drift  and avoidance  o f t h e weak s i g m o i d ship. be  held 2.  rather  (below) i s r e m i n i s c e n t  d i s p l a y o f t h e male guppy d u r i n g  I use the term  s c u l l i n g mainly  drift  "drift"  with  because t h e f i s h  i t s pectoral fins  and t h e body i s  drift  T h i s p a t t e r n i s a more s t e r e o t y p e d  sigmoid  one.  The body  position  turns  and h e l d r i g i d l y .  3.  around  i n direction  a rapid  There i s l e s s than  fins move-  i n the previous  a r e smooth and r a p i d .  T h i s p a t t e r n i s simply swimming a c t i v i t y  and a d e f i n i t e  The d o r s a l and c a u d a l  ment t o w a r d s o r away f r o m t h e p r e d a t o r pattern;  form o f the  i s h e l d more r i g i d l y  i s assumed.  are u s u a l l y spread  Turn  appears t o  rigidly.  Avoidance  previous  court-  a sudden c e s s a t i o n o f  towards a p o t e n t i a l p r e d a t o r  coupled  with  "about t u r n " , f o l l o w e d by swimming i n t h e o p p o s i t e  direction.  145  4.  Rapid  dart  T h i s motor p a t t e r n has  o c c u r s most o f t e n when a  a c t u a l l y moved t o w a r d s a guppy, o r has  at a close  range  of t h i s pattern  (e.g.  ambush).  would r e q u i r e  a n a l y s i s because the  pattern  second.  time the  as  During  20-30 cm.  position fins  thrust  i n a short  the  is  possible  had  before  burst,  predator  f o r the the  the  the  i s uninterrupted  fish  the  usually  of  the  a much  rigid caudal upwards  water.  It  same p o s i t i o n i t  i . e . i t seems t o  binocular  but  in a  p e c t o r a l and  guppy t o m a i n t a i n t h e  the  cinematographic  a f r a c t i o n of  o c c a s i o n a l l y out  t h i s way,  a l l the d e t a i l s  body i s h e l d  initiated,  suddenly  have moved as  p r o p e l l i n g the  d a r t was  In  only  f i s h may  i s a p p l i e d by  w a t e r c o l u m n and  backwards.  lasts  appeared  describe  slow-motion  I t appears t h a t  and  in  this  To  predator  fixation  guppy i s a t a  on  swim the  safer  distance. A be  r a p i d d a r t may  followed  (zigzags,  a bout of r a p i d  etc.)  describe. class  by  that  are  very  jerky  with a turn  of b e h a v i o r termed  i r r e g u l a r and  sufficiently  in  detail  the  Driver,  p.  actions  286)."  of  and  difficult  to  fall  a  into  i . e . , "behavior  unsystematic to prevent a reactor  p o s i t i o n or  1970,  "protean",  around  swimming movements  These- l a t t e r movements a p p e a r t o  is  and  intergrade  the  actor  which  predicting  (Humphries  146 5.  Surface A  is  skim  surface  i n progress  skim i s e l i c i t e d  o r has j u s t  when an a t t a c k  ended u n s u c c e s s f u l l y .  swims r a p i d l y away f r o m t h e p r e d a t o r , water f i l m commonly  o f t e n making a r i p p l e  s u d d e n l y by a p r e d a t o r more s u r f a c e  6.  Surface  and i s o f t e n  fish  This i s  i s approached  a c c o m p a n i e d by one o r  jumps.  jump  In t h i s b e h a v i o r  pattern,  the f i s h  t h e w a t e r o n c e o r maybe a d o z e n t i m e s occurs  The  j u s t below t h e s u r f a c e  on t h e s u r f a c e .  s e e n i n n a t u r e when a s c h o o l  sequence  normally  only  when a p r e d a t o r  actually  leaves  i n succession. has s t r u c k  o r i s about  to  strike.  an  a q u a r i u m c o n t a i n i n g wary g u p p i e s t h a t have r e c e n t l y b e e n  attacked feature water  However, i t c a n a l s o be e l i c i t e d  It  by a p r e d a t o r . of schools  appears t h a t  reverses  last  o f g u p p i e s , numerous f i s h  leaving the  behavior  i n c e r t a i n cases  i t s p o s i t i o n i n mid-air  In m u l t i p l e  the f i s h  surface  o f t h e sub-  because o f i t s s h o r t  duration.  ( s i n g l e jumps) t h e guppy and r e t u r n s  t o the water  i t s head f a c i n g towards t h e p o i n t o f e x i t  water. and  jumps a r e a c o n s p i c u o u s  i s a l s o d i f f i c u l t t o see t h e d e t a i l s  components o f t h i s  with  on  simultaneously. It  It  Surface  by t a p p i n g  from t h e  jumps t h e o r i e n t a t i o n i s f o r w a r d  l i t e r a l l y skips along  f o r m was s e e n when a l a r g e  the water  surface.  The  f e m a l e guppy was p u r s u e d by  147  a Crenicichla  (Oropuche R . ) ; a b o u t a d o z e n s e p a r a t e  were c o u n t e d  before  very  response  similar  described  with pickerel  The  entities,  Gambusia p a t r u e l i s  (George,  show weak a v o i d a n c e  a rapid  an  attack occurs,  be  elicited.  on  a scale of reactivity  d a r t i f the predator  drift  attack-escape o f a guppy,  at first  but s h i f t  s u r f a c e s k i m s and e v e n s u r f a c e jumps  Thus t h e m o t o r p a t t e r n s a p p e a r t o be ranging  behavior  ( r a p i d d a r t , s u r f a c e skim Presumably  drift,  from  (avoidance  If may  arranged  "precautionary"  t u r n a r o u n d ) t o "emergency" and jump).  the sensory-motor c o o r d i n a t i o n centres  on a s y s t e m o f r i s i n g  thresholds with  f o r each motor p a t t e r n .  be f i x e d .  here  approaches t o o c l o s e l y .  behavior  to  during  1960).  may be p a r t o f a s i n g l e  to  priate  A  has been  As a p r e d a t o r moves i n t h e v i c i n i t y  t h e guppy may  operate  safety.  6 p a t t e r n s d e s c r i b e d above, though viewed  separate  sequence.  reached  ("surface breaking")  f o r the p o e c i l i i d  encounters  as  t h e guppy f i n a l l y  jumps  These  T h i s c a n be r e a d i l y  a model o f a p r e d a t o r  levels  levels  appro-  do n o t a p p e a r  d e m o n s t r a t e d by m o v i n g  at a constant v e l o c i t y  towards a  g r o u p o f p r e d a t o r - n a i v e and a g r o u p o f e x p e r i e n c e d  guppies.  The  first  while  the  second  group w i l l will  show a v o i d a n c e  respond  with  rapid  drift  behavior  dart or possibly  surface  jump, i . e . t h e t h r e s h o l d f o r t h e r e l e a s e o f emergency patterns is  i s lowered  not only s p e c i f i c  with  experience.  to visual  stimuli  T h i s t h r e s h o l d change since the  148 responsiveness is  also  to mechanical  disturbances  i n f l u e n c e d by e x p e r i e n c e w i t h  predators.  Though t h e a c o u s t i c o - l a t e r a l i s may f u n c t i o n i n p r e d a t o r a v o i d a n c e , modality  appears  c a n be e l i c i t e d isolated  when a p r e d a t o r  " a t t a c k s " a group o f guppies  i n a clear  glass jar.  1956; P f e i f f e r ,  responses  I d i d not study  chemical  o r between g u p p i e s  1962).  and p r e d a -  Disturbances  Similarly,  predators  O b j e c t s moved o v e r  d a r t " response.  a stream  conditions.  aquaria  elicit  responses a "down-  t o a deeper  s t r e a m s i t may  on t h e s u b s t r a t e . i n escape motor p a t t e r n s  a l l t h e p a t t e r n s d e s c r i b e d above c a n be  i n a l l the p o p u l a t i o n s o f guppies  that quantitative  no  from w i t h i n t h e  The f i s h moves v e r y q u i c k l y  Population differences Although  from  a l s o evoke  p o r t i o n o f t h e water column; i n s h a l l o w e v e n come t o r e s t  I observed  1972).  do n o t a l w a y s a r i s e  a q u a t i c medium; t e r r e s t r i a l  elicited  to "Schreckstoff"  ( c f . Goz, 1941; G e o r g e , 1960; Reed,  R u p p e l l and G o s s w e i n ,  guppies.  attributed  t o samples o f w a t e r t a k e n  containing predators  from  sensory  b u t o b s e r v a t i o n s d u r i n g a c t u a l p r e d a t i o n r e v e a l e d no  (Schutz,  1969;  the primary  systems  A l l t h e e s c a p e motor p a t t e r n s  b e h a v i o r a l changes o f t h e type  overt  and o l f a c t o r y  t o be v i s i o n .  c o m m u n i c a t i o n between g u p p i e s , tors,  (water v i b r a t i o n s )  i t was e v i d e n t  d i f f e r e n c e s were p r e s e n t u n d e r n a t u r a l  I saw v i r t u a l l y  a l l t h e s u r f a c e s k i m and  149  surface  jump b e h a v i o r  cichlid  predators,  the  dipnet  to e l i c i t  pole.  i n streams c o n t a i n i n g  e v e n when t h e Using  the  these responses  "predator"  to characids  and  there  geographic v a r i a t i o n i n the  may  be  t i o n necessary The variable.  to e l i c i t  also  passed with  G u a y a m a r e ' R i v e r s t h a t had water p a i l s . "panic"  g u p p i e s on wards  The  Guayamare f i s h  r e a c t i o n but  the  other  this  time a l l the  to a p o p u l a t i o n  r e s p o n s e and qualitative could in  Yarra.  the  rate of  the  only  a  bottom of  had  fully  surface  recovery,  and opaque  The  Paria  directly  down-  the  pail.  form of  population  the  Often  sec;  recovered  again.  there  "Paria response"  other  and  d i f f e r e n c e i n the  d i f f e r e n c e i n the  never e l i c i t  fact  near the  velocity  b o t t o m f o r o v e r 10  Guayamare f i s h  were swimming n o r m a l l y addition  the  demon-  in,adjacent  quickly re-surfaced.  on  stimula-  s c a t t e r e d r a p i d l y downwards  (no v i o l e n t s c a t t e r ) t o t h e remained m o t i o n l e s s  that  geographically  a. u n i f o r m  hand moved s l o w l y  they  exposed  patterns.  from P a r i a  been p l a c e d  of  difficult  degree.of  T h i s q u a n t i t a t i v e . d i f f e r e n c e c o u l d be o b j e c t was  and end  were n o t  c e r t a i n escape motor  over a group of•newly-caught guppies  a  the  I t appears, t h e r e f o r e ,  d o w n - d a r t r e s p o n s e was  s t r a t e d when an  in  was  same s t i m u l u s , - i t was  f r o m g u p p i e s who  cichlids.  characid  by  and  Thus i n  i n t e n s i t y of  the  a l s o seems t o be behavior.  f r o m Guayamare  showing t h i s  a  I guppies,  response  was  150  Summary o f  the  The review of and  field  previous  antipredator  d i s t r i b u t i o n of  w a t e r column and  proximity  abiotic factors  water v e l o c i t y .  of  differences  an  fish to  microdistribution  i n the the  fish  f o r t h the  i s also  littoral  antipredator  behavior.  shore i s a f f e c t e d  in  hypothesis  part and  that  a sensitive indicator  predation.  restriction  Where  of  large  g u p p i e s may  in  mechanism. were o b s e r v e d  Schooling  i n the  of  schooling  of  guppy b e h a v i o r i n s t r e a m s w i t h c h a r a c i d  p r e d a t o r s b u t , t e n d s t o be  development  i s a conspicuous and  feature  cichlid  l e s s prominent i n streams  with  Rivulus. Gross estimates of  the  the  streambed morphology  q u a l i t y of  •Large d i f f e r e n c e s  only  with  i n terms of depth i n  the  However, I p u t  predators occur, be  i n the  guppies i n streams  i n c l u d i n g the  m i c r o d i s t r i b u t i o n of  itself  been m a i n l y a q u a l i t a t i v e  differences  behavior of  behavior  predators.  The  the  of  s e c t i o n has  some.of t h e  different  by  observations  field  and  tion  and  cant  aquatic  reaction  t h e s e were a l s o  threatening  stimulus  streams w i t h c h a r a c i d The  guppy may  (Paria)  was  very  were made i n  c o r r e l a t e d w i t h the  abundance o f p r e d a t o r s . predation  distances  the  In  cichlid  use  at  absence of  reaction  small,  and  the  distribu-  distance  whereas i t was  signifito  a  large  in  predators.  least six fairly  distinct  motor  151  patterns  i n response to p o t e n t i a l predators.  a p p e a r t o be pattern  appearing  animal s  i n a ranked  scale with  under c o n d i t i o n s o f a m i l d  i m m e d i a t e e n v i r o n m e n t and  1  attack  organized  conditions.  patterns  No  the  qualitative  but  lowest  under  exposed to  by  t h r e a t i n streams w i t h  severe  levels  than streams with  these  different  exposed to d i f f e r e n t  of escape p a t t e r n s  only  predators  It  are  c h a r a c i d and  Rivulus.  elicited cichlid  Therefore,  have d i f f e r e n t  the  direct  q u a n t i t a t i v e d i f f e r e n c e s were f o u n d . higher  predators  patterns  change i n  highest  appears t h a t the a less  the  differences in  were s e e n among p o p u l a t i o n s  predators,  These  alarm  fish  thres-  holds. The surface it  r e s p o n s e t o an  i s a stereotyped  downward  aquatic  r e l a t e d to the predators  Survival value in wild-caught I f my tion  i n each  taken  with  the  hypothesis  importance of a e r i a l  observed  i s c o r r e c t t h a t much o f t h e i n nature  and  from  "low  predation"  natural predators.  and  be  possible to  "high p r e d a t i o n "  I t w o u l d be  predicted  w h i c h showed  to p o t e n t i a l predators,  varia-  i s r e l a t e d to d i f f e r e n c e s  i t should  guppies taken from p o p u l a t i o n s distances  This  stream.  impact of p r e d a t o r s ,  fish  while  of b e h a v i o r a l d i f f e r e n c e s fish  i n behavior  the  relative  water  "freeze" at Paria  i s a more sudden random s c a t t e r a t Guayamare.  m i g h t be  in  o b j e c t passed over the  (2)  (1)  test regions  that  long, r e a c t i o n  well-developed  152 schooling behavior, patterns surface  (3) e a s i l y - e l i c i t e d  and (4) w e l l - d e v e l o p e d h a b i t a t and s h o r e ) w o u l d have b e t t e r  escape  motor  selection  (close t o  s u r v i v a l when p l a c e d  experimentally with the natural predators. T h i s p r e d i c t i o n makes no a s s u m p t i o n s causation of the phenotypic d i f f e r e n c e s c o u l d be t h e r e s u l t  experiential  have s u r v i v a l and g e n e t i c  My o r i g i n a l populations predator  stream  Samples  from  Here I am  factors w i l l  (showing  for survival  i n a predator-infested  and c i c h l i d  are usually  the s u r v i v a l  stream.  identically  The main p r o b l e m s "guppy-proof"  a  response might i n  viewed  by  Rivulus. ethologists  value of behavior.  I h a d t o abandon my  and p e r f o r m t h e e x p e r i m e n t s  "pollute"  differences)  i n a stream i n f e s t e d with  F o r numerous r e a s o n s  maintaining  f r o m a low  A l s o I wanted t o see i f perhaps  Such t r a n s p l a n t e x p e r i m e n t s as t h e b e s t way t o t e s t  later.  the d i f f e r e n t  s t r e a m w o u l d be h a n d l e d  anti-characid  f a c t be d i s a d v a n t a g e o u s  pools.  be d e a l t w i t h  concomitant b e h a v i o r a l  s e r v e as a c o n t r o l .  tests  The s e p a r a t i o n o f  e x p e r i m e n t s " where f i s h  the l a t t e r  well-developed  value.  p l a n had been t o t e s t  in "field  w o u l d be t e s t e d  to  of both e f f e c t s .  selection  concerned w i t h d e m o n s t r a t i n g whether o r n o t t h e  differences  and  i n behavior—they  of experience with, or natural  by p r e d a t o r s , o r an i n t e r a c t i o n only  regarding the  field  i n a q u a r i a and o u t d o o r  with the f i e l d  tests  c e n t e r e d on  s c r e e n e n c l o s u r e s (I d i d n o t want  a s t r e a m by t h e a c c i d e n t a l  release of foreign  153  genotypes). water  During the r a i n y  level  material  and  and  difficult.  secondary  6.1  variable  macrophytic  i n t h e w a t e r made t h i s work v e r y problem  ference with materials l e f t  Experiment  the h i g h l y  t h e abundance o f s u s p e n d e d  detritus A  season  Relative  resulted  at f i e l d  survival  f r o m human  inter-  sites.  of wild-caught  guppies.  Methods An  " i n d o o r " and  were d e s i g n e d of  guppies  to t e s t  taken  from  done u s i n g e i t h e r  "outdoor"  for survival  The  i n d o o r a q u a r i a o f 80  a t ambient  liters  of  experiments  differences  4 populations.  i n d o o r c o n c r e t e p o o l o f 700 were m a i n t a i n e d  series  first  samples  series  l i t e r capacity  ( d e p t h 50  temperature  among  and  cm).  was or  an  These  natural  photo-  period. The  second  s e r i e s was  c o n c r e t e p o o l s o f 1600  liters  the i n d o o r experiments  was  in  the outdoor  plankton  experiments  (Secchi d i s c In  ( d e p t h 50  cm).  The  d u r i n g t h e day  method).  The  was  very t u r b i d with  water  phyto-  p r e y were added a t f r e q u e n t  to r e p l a c e those eaten  (replacement  number o f 2 o r more p r e y t y p e s  o v e r a p e r i o d o f 5 o r more d a y s o f p r e d a t i o n was  In  water i n  d i s a p p e a r e d a t 35 cm) .  intervals  the index o f  outdoor  completely c l e a r while the  the indoor t e s t s ,  relative  done i n 2 a d j a c e n t  used  added as  vulnerability.  the outdoor  tests,  relative  s u r v i v a l was  simply  154  m e a s u r e d as t h e number o f f i s h individuals  o f each  made w i t h a  "one-man  In in  from  population; periodical  an  censuses  t h e p r e d a t o r s and  for only a short period  selectivity  by  B e c a u s e my  of time.  Prey  these t e s t s .  learn of  control  minimal,  I usually  population of o r i g i n ;  f o r the p o s s i b i l i t y  ease  (though-,  as  for  is still  I have p o i n t e d o u t  on  w i t h a #30  among t h e  colour patterns  conspicuousness  female  4,  se  evidence  Blue  types, those of  (vital  t h a t had stain)  were n o t p l a c e d w i t h p r e d a t o r s f o r a t l e a s t marking.  The  mortality  than  The  mark f a d e d n o t i c e a b l y  Where p r e y  good  per  the lower o r upper  hypodermic needle  a c o n c e n t r a t e d Trypan  visible  might  In a d d i t i o n i t  i n Chapter  p o p u l a t i o n were marked on e i t h e r  remained  con-  lacking).  To d i s t i n g u i s h  1%.  guppies  a  that predators  of capture.  would r u l e out s e l e c t i o n based  in  female  t h i s was  the p o p u l a t i o n - s p e c i f i c  the males w i t h t h e i r  peduncle  used  learning  Females are a l l m o r p h o l o g i c a l l y s i m i l a r ,  to associate  this  sizes  for potential  knowledge o f t h e d i s c r i m i n a t i o n  regardless of t h e i r venient  been  the p r e d a t o r s .  o f • t h e p r e d a t o r s was for  50  were  p r e y had  were matched between p o p u l a t i o n s as a c o n t r o l size  initial  seine".  a l l experiments  captivity  remaining  on  survived  during this  close  been  caudal dipped  solution. 24 h r  one  Fish  after  r e c o v e r y p e r i o d was  less  after  but  inspection  l o n g e r than t h i s ,  the f i r s t  for at least t h e y were  day  a week.  re-marked  155  as  s o o n as In  the  mark became a l m o s t  a control  unmarked f e m a l e s o f Crenicichla.  The  experiment, the  imperceptible. I placed  same p o p u l a t i o n w i t h  survival  rate  of  marking procedure d i d  ability  fish  the  to  marked and a  not  50  juvenile  e a c h g r o u p was  s u g g e s t i n g the of  50  affect  identical the  vulner-  predators.  Results Table  21  shows t h e  results  ( r e p l a c e m e n t method) g i v i n g  the  of  the  indoor  experiments  r e l a t i v e number o f  fish 2  a d d e d e a c h day  over the  were c a l c u l a t e d difference of  fish  test  between t h e  the  the  n u l l hypothesis that  explained  (for 1 df  s i m p l y by  Yates's c o r r e c t i o n  X  values  the  expected  number  sampling for  continuity  applied). It  rejected  is clear  that  the  n u l l hypothesis could  i n most e x p e r i m e n t s . ( T a b l e 21  of  predation" populations  the  Petite  "low  A,  B,  and  In  Crenicichla  tests  C)  The  (Lower  i n the The  juvenile  (Paria, "high  Upper  fish  Aripo,  predation"  Aripo).  results  with a juvenile  with a  be  s i g n i f i c a n t l y more  C u r u c a y e ) were t a k e n t h a n t h e  population  but  experiment.  t o t a l o b s e r v e d and  e a t e n c o u l d be  fluctuations was  to  course of  for a replicate  Hoplias  ( T a b l e 21  of  D)  one  of  were l e s s  these  tests  significant  same d i r e c t i o n . results with  males from 3 p o p u l a t i o n s  an  adult  indicated  Crenicichla that  Paria  preying was  most  on  TABLE 21.  Day  TEST A Lower Aripo Paria  R e l a t i v e m o r t a l i t y of wild-caught guppies exposed t o p r e d a t o r s . T e s t s A, B,C-—95 mm C r e n i c i c h l a , 80 l i t e r a q u a r i u m ; T e s t D— 95 mm H o p l i a s , 80 l i t e r a q u a r i u m ; T e s t E — 2 0 0 mm C r e n i c i c h l a , 700 l i t e r i n d o o r p o o l .  TEST B Lower Upper Aripo Aripo  TEST' C Petite Lower A r i p o Curucaye  TEST D Lower Upper Aripo Aripo  1 2 3 4 5 6 7 8 9 10 11 12 13 14  0 0 1 2 3 1  0 0 7 9 9 6  2 3 5 6 5 2  2 10 15 7 4 8  0 5 7 0 2  0 8 11 3 9  0 . 9 4 5 2 7 13 2 6 3 7 7 10 4  Total  7  31  23  46  14  31  79  X X  P  13  2  (1 d f )  1  J  #  92  < . 001  7. 01  5. 69  01  02  TEST E Lower Upper Aripo Aripo Paria 0  1 11 10 12 2 4 11 7 15 4 8 9 7 5 106  3. 65 .10 > p• > .05  x X  0  0  -3 12  -6 -12  -9 20  15  18  29  2  (2 d f ) .10 > p >  5.25 .05  157  vulnerable  (Table  On  the  21  average i t would appear t h a t about t w i c e  many g u p p i e s t a k e n those  E).  from R i v u l u s  from c h a r a c i d - c i c h l i d  time these  h a b i t a t s were e a t e n  habitats.  e x p e r i m e n t s were done I was  enough Guayamare a d u l t s t o compare t h e i r Aripo for in  fish.  the  "predation hypothesis" features  shade, t u r b i d i t y ,  separated cichlid  by  over  30  predators.  the  collect  s u r v i v a l with  km;  because these  (temperature,  however, b o t h  Lower  water  Their survival  differ  velocity, and  are  have c h a r a c i d  rates probably  than  Lower A r i p o v s .  this  test  laboratory stocks  I do  streams  substrate composition)  b e e n more s i m i l a r chapter  at  T h i s w o u l d have b e e n a n i c e c o n t r o l e x p e r i m e n t  several abiotic  depth,  than  Unfortunately unable to  as  Paria etc. of  and  would  have  (later  in  Guayamare  a g a i n s t Lower A r i p o ) . Besides  survival  exposed t o d i f f e r e n t interest  predator  species.  for  purpose, P e t i t e  Upper A r i p o  The  H o p l i a s were The  similar:  21),  d e n s i t i e s of the  2 o u t d o o r e x p e r i m e n t s were Curucaye  (high R i v u l u s  (medium R i v u l u s d e n s i t y ) .  a l a r g e C r e n i c i c h l a was large  (Table  populations i t i s of  a r e d i f f e r e n c e s between  exposed t o d i f f e r e n t  predator  versus  species  to determine i f there  populations  this  e x p e r i m e n t s between  the p r e d a t o r ,  and  same designed  density)  In one  test  i n the o t h e r  2  used.  results  a parallel  ( F i g u r e 18) decrease  of  the  f o r the  2 t e s t s were q u i t e first  4 to 5 days  158a  FIGURE 18.  Relative s u r v i v a l of wild-caught guppies a single  o f two p o p u l a t i o n s Crenicichla  exposed t o e i t h e r  o r two H o p l i a s .  were c a r r i e d o u t i n a d j a c e n t outdoor  pools.  female  1600  Tests  liter  158b  PETITE CURUCAYE  DAYS  O I  159 f o l l o w e d by guppies.  a reduction  The  t e s t was  i n m o r t a l i t y of P e t i t e  Curucaye  more d e c i s i v e when C r e n i c i c h l a  was  used. It  should  guppies occur Petite  be  recalled,  above a m a j o r b a r r i e r  Curucaye f i s h  superior  survival  of  isolated  the  l a t t e r might thus  are abundant.  described  i n Chapter  selection  i s intense.  have t h u s  f a r presented  anything  t o do  with  t o gene f l o w  are  i n f l u x o f genes f r o m t h e cichlids  however, t h a t Upper  o n l y by  S a n t a C r u z R. On  the  3 might  other  Aripo  whereas  distance. reflect  The the  where c h a r a c i d s  hand, t h e p h i l o p a t r y  favor l o c a l  adaptation i f  But  this  i s prejudging  no  data  t o show t h a t g e n e t i c s  these  and  differences in  the  issue—I has  survival.  Conclusion f o r s u r v i v a l experiments with wild-caught guppies The  overall  used a v a r i e t y different the  results  of predators,  of these  d i f f e r e n t methods,  s i z e s of experimental  conclusion that  apparently  fish  taken  from p o p u l a t i o n s  heavy p r e d a t i o n p r e s s u r e  a priori cichlid  enjoy  type  of p r e d a t i o n — t h e r e  The  question  exposed  i s no  reason  to  (or a assume  from c h a r a c i d -  arises  to  from popu-  i n a q u a n t i t a t i v e manner).  t h a t immediately  to  survival  light predation  that Rivulus predation d i f f e r s predation only  and  better  samples taken  exposed t o o n l y moderate or  different  which  environments, a l l p o i n t  when t e s t e d c o m p e t i t i v e l y a g a i n s t lations  experiments,  from  these  160  results  i s why  especially  s u r v i v a l should d i f f e r  i n experiments that  differences  among p o p u l a t i o n s  among  control  f a c t o r a p p e a r s t o be b e h a v i o r .  earlier  that  different behavior  predators that  antipredator  f o r morphological  ( s i z e and c o l o u r ) .  obvious  under n a t u r a l  populations,  conditions  show s e v e r a l  I have  The  stressed  guppies exposed t o  conspicuous d i f f e r e n c e s i n  a p p e a r t o make f u n c t i o n a l s e n s e i f v i e w e d a s devices.  I t seems r e a s o n a b l e t h a t  some o f  t h e s e d i f f e r e n c e s may have b e e n o p e r a t i v e  i n the aquarium  and  the environment  pool  s u r v i v a l experiments a l b e i t  was more homogeneous t h a n i n n a t u r e gradient, finite that  little  some o f t h e b e h a v i o r a l  The  the d i f f e r e n c e s  question  avoidance control  occurring  then  i n natural  even i n a " s i m p l i f i e d "  I asked a t t h i s p o i n t  i n survival a function  (avoidance c o n d i t i o n i n g ) ,  of -m^groevolutionary  behavior.  differences  was:  of phenotypic  i n b e h a v i o r r e s u l t i n g from d i f f e r e n t i a l  to predators tion  current,  encounter s i t u a t i o n .  crucial  differences  depth  I t may be c o n c l u d e d  do have s u r v i v a l v a l u e ,  predator-prey  (no s h o r e l i n e  v a r i a t i o n , no w a t e r  volume f o r e s c a p e , e t c . ) .  populations  Are  substrate  that  I have a l r e a d y thresholds;  o r are they a  ( i . e . genetic)  exposure reflec-  differences i n  r e m a r k e d upon t h e'.l a b i l i t y o f  f o r t h i s reason  for experiential factors.  i t was n e c e s s a r y t o  161 E x p e r i m e n t 6.2  Relative survival of laboratory  stocks.  Introduction The the  study o f b e h a v i o r a l  majority  genetics  of h e r i t a b l e behavior  has r e v e a l e d  patterns  (or d i f f e r e n c e s  between s i m i l a r p a t t e r n s )  a r e c o n t r o l l e d by complex  systems  O n l y r a r e l y have a d a p t i v e  (Caspari,  potentially (one  1967).  adaptive  patterns  o r two f a c t o r ) g e n e t i c  Rothenbuhler, 1964). evidence  f o r a polygenic  j u s t more d i f f i c u l t for  This  In t h e p r e s e n t with  obtaining  behavioral  wild  study,  conditions If  genetic  e t a l , 1971,  I was n o t d i r e c t l y  heritability  estimate  1967; Van O o r t m e r s s e n , i f phenotypic  (and r e f l e c t e d  f i s h ) would p e r s i s t  simple  methodology).  (DeFries,  in, nature  or  B a s t o c k , 1956;  1969; s e e L i n d z e y  my c h i e f a i m was t o d e t e r m i n e observed  polygenic  s y s t e m c a n n o t be o b t a i n e d — i t i s  an a c c u r a t e  trait  (e.g.  d o e s n o t mean t h a t d i r e c t  (Franck,  a review o f research  b e e n f o u n d t o be u n d e r  control  that  concerned o f some 1970);  differences  i n the s u r v i v a l t e s t s  i n animals r a i s e d under  with  identical  i n the laboratory. such d i f f e r e n c e s s t i l l  several generations  of laboratory  t o assume t h a t g e n e t i c t e r m e d an i n n a t e  persist  breeding) then  d i f f e r e n c e s are present.  d i f f e r e n c e by t h e m a j o r i t y  ethologists  (e.g.  above, t h i s  term i s a l s o acceptable  psychologists  (especially after  Tinbergen,  (Lehrman,  i t i s safe This i s  o f European  1959; H i n d e , 1 9 5 9 ) ; d e f i n e d a s  1970).  t o American  experimental  162  When g e n e t i c d i f f e r e n c e s a r e f o u n d lations,  they  to s e l e c t i v e  are normally pressures  at the molecular possibility  level  i n n a t u r a l popu-  assumed t o have a r i s e n  i n response  (adaptive genetic d i f f e r e n c e ) , there  though  i s much d e b a t e a b o u t t h e  o f n e u t r a l genes and " n o n - D a r w i n i a n " e v o l u t i o n .  Methods The tory the  procedures  f o r the establishment  o f the l a b o r a -  s t o c k s have a l r e a d y been o u t l i n e d (Chapter 5 stocks  I studied i n d e t a i l ,  c u l t u r e s were m a i n t a i n e d . e x p e r i m e n t s where s t r i c t experience, raise  The survival  procedure  predation  of the f i s h ,  one must  animals.  and f i f t h  4.  ( C - l , C-2, C-3, C-4) were u s e d i n as d e s c r i b e d b e f o r e  The g u p p i e s  laboratory stock  under i d e n t i c a l naive  origin  as o u t l i n e d i n C h a p t e r  aquaria f i t t e d  dark photoregime).  fourth  to replicate  i s p l a c e d on t h e s i z e , s e x ,  thousands o f a d u l t  Individual Crenicichla  generation  control  large  e x p e r i m e n t s were p e r f o r m e d u s i n g t h e " s t a n d a r d  test"  3 adjacent  In o r d e r  and g e o g r a p h i c  literally  especially  2). For  generation  were a t l e a s t  (12 l i g h t - 1 2 second  and t h e m a j o r i t y were fish.  A l l had been  l a b o r a t o r y c o n d i t i o n s and were  (excluding attempted  probably  maintained predator-  c a n n i b a l i s m w h i c h was  rarely  observed). Two p a r a l l e l only  females,  petitive  s e t s o f e x p e r i m e n t s were r u n .  the other males.  type with  Lower A r i p o  One u s e d  A l l t e s t s were o f t h e comas t h e r e f e r e n c e  stock  163  a g a i n s t which the  other  order  possible bias resulting  to r u l e out  tive predation, closely  refer  each p a i r  as p r a c t i c a l l y  r a n g e , and  variance  4 x 2  4).  the  light  starved  experimentally)  predation occurred insure  t h a t the prey  statistics,  dim,  by  peduncle. was  also  Preliminary  repeated  observations  libitum tests  were a b l e t o  This provided  as  mean,  were r e c o g n i z e d  or dark l i g h t .  mounted a 7-watt i n c a n d e s c e n t surface.  matched  (predator  r e v e a l e d t h a t the m a j o r i t y  i n dim  In  size-selec-  r e s p e c t to the  ( s t o c k s x sex)  i n ad  from  (for relevant  regime.  Crenicichla predation  at a time.  t e s t e d was  Stocks  caudal  design  under a d i f f e r e n t  stocks  o f body s i z e s  marks on  This  of  f e a s i b l e with  to Appendix, Table  Trypan Blue  on  4 were t e s t e d , one  see  bulb  of  Therefore,  the p r e d a t o r ,  65  cm  over  the  even i l l u m i n a t i o n  not  to I  water  during  the  p e r i o d when t h e m a i n l i g h t s were o f f . In e a c h e x p e r i m e n t t h e 100,  50  of each s t o c k .  24-hour i n t e r v a l s density fish  S u r v i v a l was then  i n the  entire  zero.  d e n s i t y was  followed  always  initially  intervals  until  The  number  e x p e r i m e n t was  total  1600,  at  the  i . e . 800  of per  regime. To  facilitate  statistical  the  relative  the  census p e r i o d c l o s e s t  fish  at longer  approached or reached  used  light  and  initial  remain).  comparisons,  numbers o f e a c h s t o c k  The  t o 50%  observed  t h a t had  survival  m o r t a l i t y and  I compared  been e a t e n  (50 o u t that  of  at 100  expected  164  under t h e n u l l  hypothesis  (random p r e d a t i o n )  were t e s t e d f o r  2 significance  using  the X  statistic  (corrected f o r  continuity). Results In t h e e x p e r i m e n t s w i t h  a 12 l i g h t - 1 2 d a r k  regime, m o r t a l i t y d i d not d i f f e r levels  except  for Petite  significantly  Curucaye females  Surprisingly,  P e t i t e Curucaye guppies  survival  Lower A r i p o  than  (the t r e n d  m a l e s was i n t h e same d i r e c t i o n  photo-  from  (Table  chance  22 A ) .  showed b e t t e r for Petite  Curucaye  as t h e f e m a l e s b u t n o t  significant). I n t h e 12 l i g h t - 1 2 d i m p h o t o r e g i m e , t h e r e several notable Lower A r i p o Aripo,  d e v i a t i o n s f r o m random p r e d a t i o n  fish  showed l e s s m o r t a l i t y t h a n  confirming  the r e s u l t s with  21 A and 21 B r e s p e c t i v e l y ) . Aripo  was s t i l l  i n favour  for  of the P e t i t e  fish  difference light-12  laboratory  X  d  f  fish  (Table  laboratory stock  2 ( 1  Curucaye  table with  i s highly significant  dark:  )  (Table  Curucaye  case,  the trend  stock.  o f t h e Lower A r i p o v s . P e t i t e  i n a 2 x 2 contingency  t h e same t e s t w i t h  22 B ) .  The d i f f e r e n c e s b e t w e e n Lower  Curucaye t e s t s with wild-caught pared  wild-caught  though i n the l a t t e r  When t h e r e s u l t s  (Table  P a r i a o r Upper  v s . Guayamare, and Lower A r i p o v s . P e t i t e  were n o t s i g n i f i c a n t ,  were  21 C) a r e com-  the r e s u l t s (sexes  obtained  pooled), the  ( w i l d v s . l a b o r a t o r y 12  = 12.61, p < .001; w i l d v s .  12 l i g h t - 1 2 d i m :  X  2  , . = 7.88, p < . 0 1 ) ; when f  165 TABLE 22.  A. T e s t  Relative m o r t a l i t y of naive laboratory stocks o f guppies exposed t o C r e n i c i c h l a . A = 12 l i g h t — 1 2 d a r k p h o t o r e g i m e ; B = 12 l i g h t — 1 2 dim l i g h t photoregime; C = males and f e m a l e s p o o l e d (NS = n o t s i g n i f i c a n t ; S = s i g n i f i c a n t a t 5% l e v e l o r l e s s ) .  Predator  Number e a t e n a t approx. 50% m o r t a l i t y  Total  X  p  (females) 1 2 3 4  C-3 C-l C-l C-l  Lower Lower Lower Lower  Guayamare P. Curucaye Paria Upper A r i p o  26 31 26 28  Aripo Aripo Aripo Aripo  111  Total  17 14 17 29  43 45 43 57  77  188  25 17 21 22  43 44 44 48  85  179  20 26 32 34  50 57 48 50  112  205  37 24 33 31  63 60 48 49  125  220  1,.49 5 .69 , 1,.49 0..00  > .20 < .02 > .20  0.,84 1..84 0.,023 0..188  > > > >  . 30 .10 .80 .50  1,.62 0..281 4. .69 5..78  >  .20 .50 .05 .02  1..59 2. .02 6 .02 , 2. .94  >  -  (males) 1 2 3 4  C-l C-2 C-l C-2  Lower Lower Lower Lower  18 27 23 26  Aripo Aripo Aripo Aripo  Guayamare P. Curucaye Paria Upper A r i p o  94  Total  B.  (females) 1 2 3 4  C-l C-4 C-4 C-l  Lower Lower Lower Lower  Aripo Aripo Aripo Aripo  30 31 16 16  Guayamare P. Curucaye Paria Upper A r i p o  93  Total  >  < <  (males) 1 2 3 4  C-4 C-l C-2 C-4  Lower Lower Lower Lower  Aripo Aripo Aripo Aripo  Guayamare P. Curucaye Paria Upper A r i p o  26 36 15 18 95  Total  12 l i g h t - 1 2  dark X  Lower A r i p o  X  l i g h t --12 dim  light  Lower A r i p o  X  2  p  Guayamare  0 .012  > 0..90  (NS)  Petite  7 .59  < 0..01  (S)  Upper A r i p o  0 .038  > 0..80  (NS)  Paria  1 .15  > 0..20  (NS)  Guayamare  0 .00  > 0..90  (NS)  2 .19  > 0,.10  (NS)  9 .09  < 0..005  (S)  11 .34  < 0..001  (S)  Petite  Curucaye  Curucaye  Upper A r i p o Paria  > < <  .20 .10 .02 .10  166 only  the  light  treatments  f o r laboratory stock  are  compared  2 there p >  i s no  significant  d i f f e r e n c e (X  ^  of  survival  experiments  Some c a s u a l n i g h t o b s e r v a t i o n s feeding behavior the  d u r i n g Exp.  d i f f e r e n c e i n the  supplementary  light  were n o t  of  the  t h a t had  been p r o v i d e d .  adjacent  aquaria,  realized  that this  from the  prey. When t h e  the p r e d a t o r s and  the  I t was  tank.  front  dug  pits  the b e s t  obvious  first  at guppies  t h a t the  consisted  flower in  but  moving i n t o  visual  This  a d v a n t a g e u n d e r low  light  of  g u p p i e s were more  predator  suggests  the  i n a l l regions  o f t e n taken prey.  I soon  o f f at night,  a c t i o n was  the  of  concealment  under c o n d i t i o n s o f n o c t u r n a l p r e d a t i o n ;  engulfed  the  underside  "helpless"  when t h e  pot  in exactly  the  automatically turned  striking  without  From  isolated  g l a s s and  bear  Crenicichla  i n a p i t under the  location provided  then  B).  seemed p u z z l i n g a t f i r s t  lights  and  Daytime a c t i v i t y  w o u l d become a c t i v e ,  flower pot  with  t h a t the  a l l 4 Crenicichla  This  brought to  22  Though v i s u a l l y  same l o c a t i o n between t h e flower pot.  22 A v s .  clear  Crenicichla  be  obtained  day.  "resting"  of  should  results  i t was  feeding during  almost e n t i r e l y  6.2  ( i . e . Table  numerous o b s e r v a t i o n s  the  1.01,  .30) .  Discussion of r e s u l t s  on  =  had  evasive  almost  t h a t C r e n i c i c h l a has intensity.  Since  a  under  my  167 experimental stock  c o n d i t i o n s t h e g u p p i e s h a d no r e f u g e ,  d i f f e r e n c e s i n escape behavior  (except  the i n t e r -  Petite  C u r u c a y e ) may have b e e n i n c o n s e q u e n t i a l when t h e l i g h t levels  a t n i g h t were v e r y l o w . When l i g h t was added t h o u g h , d i f f e r e n c e s d i d a p p e a r  in  the predicted d i r e c t i o n with  provided  at night  probably  w o u l d n o t have a f f e c t e d t h e r e s u l t s used  fish.  resembled  obtained  Crenicichla  wild-caught  and c l o s e l y  Although  no d i m l i g h t  i n tests with wild-caught  i n these  t h e y were q u i e s c e n t .  the r e s u l t s  guppies,  i n nature  this  because the  t e s t s were d a y - a c t i v e ;  Since  was  at night  I have s e e n  Crenicichla  a t t a c k g u p p i e s a t midday, i t i s p o s s i b l e t h a t t h e n o c t u r n a l h a b i t s observed reasonable  i n E x p . 6.2 were u n n a t u r a l .  explanation  i s that the C r e n i c i c h l a  g u p p i e s a r e much e a s i e r t o c a p t u r e Night streams w i t h in  observations characids  a narrow r i b b o n  The most  i n nature  have r e v e a l e d t h a t i n guppies are d i s t r i b u t e d  t h e s t r e a m edge  (shallow  T h i s might f u n c t i o n t o reduce the a c c e s s i b i l i t y to nocturnal predators  (e.g. H o p l i a s ) .  s e l e c t i o n may be e f f e c t i v e s t a l k o r ambush unwary f i s h typically  during  swim f u r t h e r f r o m s h o r e .  shifted  The  water).  o f guppies  This habitat  enough t o f o r c e C r e n i c i c h l a t o  "work" was n o t r e q u i r e d i n E x p . 6.2 predators  that  i n darkness.  and c i c h l i d s ,  along  learned  to nocturnal  t h e d a y when Apparently  guppies this  (dark n i g h t s )  extra  so t h e  predation.  a d d i t i o n o f a dim l i g h t  at night,  however,  168 allowed  the  (increase obtained  g u p p i e s t o use  i n reaction distance) are probably  predation.  The  apparently that  had  i n the  accessible  at  not  been i n c a p t i v i t y  raises  the q u e s t i o n  6.1  l o n g enough t o l e a r n  refuge,  guppies are  more  o f why  laboratory stocks vulnerable  of nocturnal predation.  First  i t i s important  than  conditions;  i n nature,  unless  laboratory. no  refuge  ineffectual strategies are, the  the  founders  feeds  required.  evidence  f r o m Exp.  6.2  a t n i g h t and not  suggests  Petite  s e v e r a l f a c t o r s i n c l u d i n g an  l e n s d i a m e t e r o r number o f r o d c e l l s .  s t r e a m s u c h as i n other a l s o be  acuity  better  the  developed.  This  is  survival  i n a very  n o t be  these  c o u l d be  increase i n  (cone v i s i o n ) b u t  fish,  shore  Curucaye  T h i s m i g h t be  P e t i t e C u r u c a y e , t h i s may  nocturnal  same  the  other  dark  c e r t a i n what  function  expense o f v i s u a l  or  i t does t h e  have s u p e r i o r s c o t o p i c v i s i o n .  of  to  Thus h a b i t a t s e l e c t i o n  Though I am  con-  suffer  light  i t i s a small predator,  f o r guppies.  under  of  Petite  u n d e r dim  conditioned otherwise, Since  stock  A l s o , i n the  for avoiding Rivulus are  of t h i s  g u p p i e s may  may  (day-active)  least  Rivulus normally  As  results  night.  C u r u c a y e R.,  offers  experimental  C r e n i c i c h l a u s e d i n Exp.  Rivulus predation.  the  the  effectively  more r e p r e s e n t a t i v e o f n a t u r a l  from severe  in  more  C u r u c a y e g u p p i e s were t h e  ditions recall  vision and  absence of a shallow  This Petite  their  too  acoustico-lateralis  a  the at  the  small critical. system  169 The confined  hypothesis  e n v i r o n m e n t has  evolution  and  i n the  experimental  experiments with  Since  these  t h a t had  Lower A r i p o  to C r e n i c i c h l a  a t the  results  than  i s not  photobehavioral  of the be  survival  concluded  impaired  very  Guayamare s t o c k s a r e  less  Upper A r i p o and  are almost  low  Paria stocks.  i n predator-naive  f o r several generations  c o n d i t i o n s , they  pursue  by  differences persisted  been b r e d  laboratory  and  adaptations  I plan to  l a b o r a t o r y s t o c k s , i t may of guppies  micro-  population.  to the,overall  t h a t when t h e v i s i o n levels,  sensory  testing.  features of t h i s  Returning  vulnerable  b e h a v i o r a l and  future, looking i n d e t a i l  anatomical  light  been r e s p o n s i b l e f o r the  of s p e c i a l i z e d  demands a d d i t i o n a l this  that intense Rivulus predation i n a  under  certainly  stocks  identical genetically  determined. Geographic v a r i a t i o n i n the a n t i p r e d a t o r behavior of l a b o r a t o r y stocks The by  overall  4 previous 1.  occur  question  to predators  from n a t u r a l p o p u l a t i o n s  Differences in vulnerability  The  of  (2) and  (Exp.  (3) a r e  (Exp.  occur  6.1).  to predators  from l a b o r a t o r y s t o c k s  results  behavior  (observational evidence).  Differences in vulnerability  among s a m p l e s t a k e n 4.  prompted  Behavioral differences i n antipredator  among s a m p l e s t a k e n 3.  s e c t i o n was  findings:  i n natural populations 2.  in this  6.2).  positively  occur  170 correlated  (except  for Petite  These r e s u l t s differences is  occur  To  among l a b o r a t o r y s t o c k s ?  founders  of the laboratory  answer t h i s  i n nature:  distance  question  fish,  (a)  (d) s c h o o l i n g  from the  stocks. measurements  selection,  varia-  (b) r e a c t i o n  behavior.  selection  f i e l d observations  have shown t h a t  populations  g u p p i e s t h a t a r e e x p o s e d t o h e a v y p r e d a t i o n by c h a r a c i d cichlid  fish  a r e more r e s t r i c t e d  s e c t i o n s o f stream with velocity,  the f i s h  to the shoreline.  In  deep w a t e r and low t o m o d e r a t e  who do l e a v e  the s h o r e l i n e occur  near  surface. I wished t o t e s t  the  5 laboratory stocks  the  shore,  a shore it  this  (c) e s c a p e m o t o r p a t t e r n s o f  Microhabitat  The  the  In e f f e c t ,  I made d e t a i l e d  (a) m i c r o h a b i t a t  to predators,  individual  and  What b e h a v i o r a l  t h e b e h a v i o r a l p a r a m e t e r s t h a t showed g e o g r a p h i c  tion  of  the question:  a s k i n g what d i f f e r e n c e s have b e e n i n h e r i t e d  wild-caught  of  raise  Curucaye).  i f there i n their  a r e a l s o d i f f e r e n c e s among tendency t o remain c l o s e t o  o r near the s u r f a c e , or both.  gradient  was n e c e s s a r y  i s a l s o movement t o w a r d s t h e w a t e r to separate  e x p e r i m e n t s , one w i t h  these  surface,  2 f a c t o r s i n separate  and one w i t h o u t  a shore  B a s e d on t h e f i e l d o b s e r v a t i o n s expected  S i n c e movement up  (Table  depth  gradient.  19), I  t h a t P a r i a , Upper A r i p o , and P e t i t e C u r u c a y e w o u l d  171 spend  less  t i m e n e a r t h e s h o r e edge and more t i m e  water  than e i t h e r  Upper A r i p o  Lower A r i p o o r Guayamare.  and P e t i t e C u r u c a y e  s p r e a d i n g a c r o s s t h e s t r e a m and stratum,  I predicted  between P a r i a  Experiment  and  6•3  Depth  distinct  adhesion to the  t h e s e s t o c k s would  Lower  Since i n nature,  showed l e s s less  i n deeper  sub-  f a l l intermediate  Aripo/Guayamare.  preference of 5 laboratory  stocks of  guppies. Methods In taneous  this  experiment  swimming and e x p l o r a t o r y b e h a v i o r .  aquarium  the  The  s t r a t a o f 7 cm  tank.  water  t o p a r a l l a x was  The  per  stock  at  a time.  (5 m a l e s and  filled into  a c r o s s from the middle  then r e l e a s e d  (prior  an a d d i t i o n a l  5  of the stratum  to the 5 s t r a t a .  the p o s i t i o n  G r o u p s o f 10  5 f e m a l e s o f u n i f o r m s i z e ) were  to s e l e c t i o n of free  o f e a c h a n i m a l was  of  fish used  a t random f r o m s t o c k a q u a r i a ,  basket i n the t e s t  5 min  to  small).  They were s e l e c t e d  in a plastic  position  liter  on t h e f r o n t pane o f  procedure consisted of recording  f i s h with reference  After  divided  spon-  O b s e r v a t i o n s were made f r o m 1 m i n f r o n t  ( e r r o r due  placed  c o l u m n was  e a c h by a g r i d  tank w i t h the v i e w i n g l e v e l  each  A 200  ( b a r e e x c e p t f o r a s a n d s u b s t r a t e ) was  a d e p t h o f 35 cm. depth  I measured the depth o f  t a n k f o r 10 min  and  a l l s u b j e c t s were f e d ) . swimming i n t h e t a n k ,  r e c o r d e d a t 1-minute  the  intervals  172  for  a total  was  randomized.  fish  of  30 min.  The  order  f o r each  F i v e r e p l i c a t e s were c o m p l e t e d .  (5 s t o c k s x 5 r e p l i c a t e s  cate)  of t e s t i n g  were u s e d i n t h i s  per  s t o c k x 10  experiment with  30  stock  Thus  fish  per  250 repli-  observations  per  fish. Results The surface  results  stratum  are  shown as a d e p t h p r o f i l e  t o the bottom  casual analysis i t i s clear spend e q u a l  time  statistically fish  a t the  by  in either  was  compared w i t h  the  results  23).  are  the  The  the  other  not  d a t a were t r e a t e d of occurrence Each  4 u s i n g t h e Mann-Whitney U  a matrix  of p r o b a b i l i t i e s  o f s t o c k s were n o t p r e d i c t e d t o  two-tailed probabilities  the  with  5 stocks d i d  frequency  (Lower A r i p o v s . Guayamare; P e t i t e Aripo),  Even  top or bottom depth stratum.  shown as  Where p a i r s  t h a t the  same d e p t h .  comparing  the  (Figure 19).  from  Curucaye vs.  are given;  of stock Test;  (Table differ  Upper  a l l other  tests  are o n e - t a i l e d . The  results  r e v e a l t h a t P a r i a had  ence f o r t h e bottom different  from the o t h e r  significantly but  (deep w a t e r ) ;  more t i m e  t h i s was  4 stocks. near the  a definite prefersignificantly  Lower A r i p o  s u r f a c e than  no  d i f f e r e n c e was  observed  Petite  Curucaye spent  s i g n i f i c a n t l y more t i m e  bottom than  either  f o r the bottom  Lower o r Upper A r i p o .  spent  Upper  Aripo  stratum. near  A l l other  sons showed d i f f e r e n c e s t h a t c o u l d have o c c u r r e d by  the comparichance.  173a  FIGURE 19.  Depth of  profile  o f spontaneous  5 laboratory  Table  swimming  stocks of guppies.  23 f o r s t a t i s t i c a l  analysis.  behavior  Refer to  173  0  20  40  60  80  100 120  140  160 180  0  20  40  60  80  100 120 140  160 180  MEAN  F R E Q U E N C Y / 3 0 min.  b  174  TABLE 23.  A.  A comparison o f the frequency o f occurrence o f 5 stocks o f guppies i n r e l a t i o n t o water depth. Values i n the m a t r i x a r e p r o b a b i l i t i e s f o r each p a i r o f c o m p a r i s o n s (Mann-Whitney U Test).  Top d e p t h s t r a t u m  H :LA/Guay >PCur/UA>Par 1  Mean frequency  LA  Guay  Lower A r i p o  81.4  -  Guayamare  63.6  . 42  P.  46.2  .075  .345  41.8  .048  .421  10.8  .004  .004  Curucaye  Upper  Aripo  Paria  B.  Bottom  depth stratum  Aripo  77.8  UA  1.00 .004  .048  LA  Guay  UA  PCur  123.2  .15  -  P.  133.2  .048  .345  -  96.2  .500  .210  .008  -  183.2  .004  .016  .016  .004  Upper Paria  Aripo  -  Par  -  Guayamare Curucaye  Par  H,:LA/Guay<PCur/UA<Par  Mean frequency Lower  PCur  -  175 When b o t h  t h e u p p e r and  lower  stratum  comparisons  are viewed t o g e t h e r ,  i t i s clear  the  Paria i s distinct  the o t h e r  Lower A r i p o  and  Guayamare do  freely  4 stocks.  i n a l l depth s t r a t a but  near the  surface.  category. and  The  other  These r e s u l t s  suggest  support  t h a t even i n the  observed  i n nature  persist  fall  into  of the  differences. substrate. are  fish  i n laboratory stocks.  when f i s h  identically, i n t h e new  differential  was  habitat  the  the the  are  in a  test  tank.  between t h e  the stock  the  explored.  as was  was  of the sexes  the tanks  S i n c e a l l 5 s t o c k s were i n the  experimenter,  P r e s u m a b l y o n c e no  waned and  observed 250  fish.  i n depth  the  preferences  familiar holding  d i f f e r e n c e s observed  c h o i c e became t h e r e g i o n o f  f o r any  depth  "wary s t a t e " ,  from t h e i r  a p p l i e d by  responses  feeding behavior test  t a n k showed no  but  a r e a l d i f f e r e n c e i n the p o r t i o n of  t h a t was  found,  hr a f t e r  first  e n v i r o n m e n t c o u l d n o t have b e e n due  stress  have r e f l e c t e d habitat  test  I t appears t h e r e f o r e , t h a t the  introduced into  30 min  gradient,  Most f i s h were n e a r t h e b o t t o m f e e d i n g on  important  handled  intermediate  some o f t h e d i f f e r e n c e s  to the  c a s e when t h e y were t a k e n and  time  the p r e d i c t i o n s r a t h e r w e l l  A s i m i l a r d e p t h measurement made 24 introduction  an  absence of a shore  water c u r r e n t , o r p r e d a t o r s ,  move  spend a c o n s i d e r a b l e  stocks  from  real  to must  the "danger"  t h e main d e t e r m i n a n t food  d u r i n g the  abundance. first  A l s o t h e r e was  preference.  of  No  30-minute no d i f f e r e n c e  176  E x p e r i m e n t 6.4  Shore p r e f e r e n c e  of  5 l a b o r a t o r y stocks  of  guppies. In t h i s were any  e x p e r i m e n t I wanted t o d e t e r m i n e i f t h e r e  stock d i f f e r e n c e s i n the  choice of h a b i t a t , given  a g r a d i e n t f r o m deep w a t e r t o d r y placed new  land.  i n a wary c o n d i t i o n when t h e y  Because f i s h  are t r a n s f e r r e d to  (and p o s s i b l y d a n g e r o u s ) e n v i r o n m e n t , i t m i g h t  expected found  t h a t s t o c k s d e r i v e d from p o p u l a t i o n s  restricted  to the  stream  show a h a b i t a t p r e f e r e n c e with predators. quickly  learn  exposed to  edge  are  19)  may  absence of  had  experience  shown t h a t  t o r e m a i n i n s a f e r e g i o n s o f an  a  be  that  (see T a b l e  even i n the  (Preliminary tests  are  guppies  a q u a r i u m when  predators.)  Methods I t e s t e d the of a stream One  and  i n a simulated cross-section  (tank d i m e n s i o n s :  s i d e of the  gravel,  5 stocks  t a n k had  sand.  L = 240,  a stream  T h i s bank was  d e p t h g r a d i e n t f r o m 2 0 t o 0 cm. divided clear  from the  rest  glass partition.  "shore"  of the  "bank" made o f  partition On  An  a q u a r i u m by  Tests with  opaque c o v e r  to v i s u a l l y the prey  was  isolate  cm).  rocks, a  smooth  This gradient section a  guppies  were done on  the p r e d a t o r s  s i d e of the p a r t i t i o n ,  the  a  4 A e q u i d e n s , and  placed over  was  tight-fitting  t h e deep s i d e had  complement o f 2 C r e n i c i c h l a ,  Astyanax.  D = 30  formed to p r o v i d e  s i d e of the p a r t i t i o n w h i l e  predator  W = 58,  3  the c l e a r  glass  from the  prey.  a reference  grid  177 was  marked on t h e f r o n t pane; f o u r 20 cm s e c t i o n s were  delineated with partition  section  (and a l s o  transitional  1 a s t h e deep zone n e x t  t h e p r e d a t o r s ) , s e c t i o n s 2 and 3 as t h e  z o n e s f r o m deep t o s h a l l o w w a t e r , and s e c t i o n 4  as t h e s h a l l o w e s t s e c t i o n F o r each a t random f r o m of  the f i s h  were f i r s t released  test,  i n each  into  1 (deep  After  t o keep t h e s i z e s  f o r 10 m i n a n d t h e n  portion).  this  The f i s h  the tank;  t h e opaque p a r t i t i o n  then another  following  "settling  30-minute r e c o r d i n g was made  communication.  down" p e r i o d a n d (Test C ) .  30-minute o b s e r v a t i o n was made 24 h r a f t e r  the cover  1 h o u r o f d a t a was c o l l e c t e d  o f the guppies  glass partition  i n isolation  only  threat  from  to the p a r t i -  Thus s e c t i o n s 1 and 2 were  t o t h e p r e d a t o r s and g u p p i e s a visual  on t h e  s e p a r a t i n g p r e d a t o r and prey. A l l  o n c e t h e c o v e r was removed.  encountered  the removal  and 1 hour w i t h  s p e c i e s o f p r e d a t o r s made numerous a p p r o a c h e s  closest  A  (Test D).  Therefore,  tion  were  was removed s o  were i n v i s u a l  f i s h were a l l o w e d a 5-minute  a clear  The f i s h  30-minute r e c o r d i n g was made 6 h r l a t e r  t h e p r e d a t o r s and g u p p i e s  positions  selected  p o s i t i o n was r e c o r d e d e v e r y m i n u t e f o r 30 m i n  (Test B ) .  final  were  as p o s s i b l e .  basket  5 m i n t o move a b o u t  Another  of  I attempted  group as s i m i l a r  section  (Test A ) .  The  5 males and 5 females  placed i n a floating  their  that  terminating a t the shoreline.  stock tanks.  allowed another this  to the  i n these s e c t i o n s  the predators.  178 All replicates  5 s t o c k s were t e s t e d i n t h e per  stock  (total  o f 100  same manner w i t h  fish  2  used).  Results The  results  distribution each of  the  along 4 tests  was  insufficient  the  5 stocks,  Test A  (initial  a l l their  other  clear-cut By the  new  overall  depth g r a d i e n t  to permit  B the  shift  fish  groups  In  remained mainly fish  spent  zone  in  virtu-  (4).  The  less  spent  l e s s wary.  shore  by  6 hr  exploring  T h e r e was  a l l stocks.  an  This  was  f o r Lower A r i p o . C and  D i n c o r p o r a t e d a s e c o n d component of guppies:  the  groups of  water fish  w a t e r when t h e  (1 Lower A r i p o  and  before,  they  (2 p e r  opaque c o v e r 1 Petite  of  never  a l l showed a m a j o r  ( i . e . away f r o m t h e tested  into  v i s u a l presence  Though a l l g u p p i e s t h a t were u s e d had  to shallower  shallower  among  Aripo  responses with  already  were now  been exposed t o p r e d a t o r s  10  had  away f r o m t h e  the h a b i t a t s e l e c t i o n  the  Lower  extreme s h a l l o w  showed i n t e r m e d i a t e  Test  Tests  Of  comparison  preference.  most e v i d e n t  shift  Paria fish  during  replication  were e v i d e n t .  (1) w h e r e a s Lower A r i p o  e n v i r o n m e n t and  predators.  f o r each stock  a statistical  responses:  frequency  Although t h e  (Figure 20).  time i n the  3 stocks  t h e mean  h a b i t a t c h o i c e ) , P a r i a and  deep s e c t i o n  ally  the  as  some n o t e w o r t h y t r e n d s  showed o p p o s i t e the  are presented  predators).  s t o c k ) , 8 moved was  removed.  C u r u c a y e ) moved  Two to  to  179a  FIGURE 20.  Habitat  selection  guppies placed to text f o r  of  5 laboratory stocks  i n a depth g r a d i e n t .  details.  of  Refer  179  b  180 slightly to  deeper water b u t these  sections  i.e.  they  were a l r e a d y  It fish  3 and 4 b e f o r e  nevertheless  the  Test  10 g r o u p s  Aripo  Upper A r i p o  D  shifted  replicates,  since  and P a r i a  considerable per f i s h i n  = 12.9; P a r i a = 1 2 . 4 ) . 3 stocks  This  (Lower A r i p o =  =0.9).  t o deeper water again.  however, moved t o s h a l l o w e r  Both  8 out of Upper  water.  by d i f f e r e n c e s i n p r e d a t o r  This  activity  I a l s o had a complete r e c o r d o f t h e p o s i t i o n o f each  predator  relative  sec a f t e r  predator  difference  to the p a r t i t i o n  recording  records  area within  negative  the guppies'  30 cm o f t h e p a r t i t i o n .  Since  The  t h e Upper  24 h r e x p o s u r e t o p r e d a t o r s (except.occasional  C r e n i c i c h l a which terminated glass p a r t i t i o n ) ,  they  positions).  every  to the Aripo  between T e s t C and D was s m a l l , i t i s s a f e t o  reinforcement  predators  ( t h e s e were made  i n d i c a t e a n o r m a l number o f v i s i t s  conclude that a f t e r  ever,  visible,  (24 h r o f e x p o s u r e t o p r e d a t o r s ) ,  c a n n o t be e x p l a i n e d  30  spent  Guayamare = 1.8; P e t i t e C u r u c a y e By  Upper A r i p o  (mean o b s e r v a t i o n s  i n sharp c o n t r a s t t o the other  1.2;  were made  towards t h e shore once t h e p r e d a -  time i n s e c t i o n s 1 and 2 1 and 2:  restricted  zone.  i s noteworthy t h a t although  t o r s were e x p o s e d , t h e y  is  the predators  i n a "safe"  d i dexhibit a shift  sections  f i s h were a l r e a d y  a t t a c k s by  when t h e p r e d a t o r  t h e g u p p i e s became h a b i t u a t e d  a n d were l e s s  restricted  without  struck the to the  to the shoreline.  How-  d i d remain c l o s e r t o the shore than before the  181 predators  were v i s i b l e  (Test B ) .  p r e s e n c e o f l a r g e moving o b j e c t s response that  i s not contingent  observed a f t e r  slightly  the d i s t r i b u t i o n The  ences.  made up t o 1 week  that the habitat  observed a t Test from t h i s  these  differences.  response  fish  habitat prefer-  i s very  f a c t o r s may be i m p o r t a n t  i s curious  a r e a l s o found very  Guayamare h a b i t a t d o e s d i f f e r  i n determining  t h e w a t e r i s t u r b i d and i n most p l a c e s  gentle  gradient  drop-off  With the appearance o f p r e d a t o r s behavioral  initial to  predators).  i n 2 main there  (reaction distance  i s sudden.  t o modify the and h a b i t u a t i o n  The r e s p o n s e s o f t h e d i f f e r e n t  the  appearance o f the predators  the  presence of predators  the  behavior  of a l l stocks  gives  i s no  (Tests C and D ) ,  components come i n t o p l a y  habitat choice  The  f r o m Lower A r i p o  ways:  other  habitat  since i n nature  c l o s e t o shore.  t o deep w a t e r — t h e  reminiscent  suggesting  The a b s e n c e o f a w e l l - d e f i n e d  i n Guayamare g u p p i e s  For a l l  experiment i s that  seen under n a t u r a l c o n d i t i o n s ,  that genetic  distribution  B d i d not reappear.  The s h o r e a d h e s i o n o f Lower A r i p o  again  after  Even t h e P a r i a  and P a r i a g u p p i e s have d i f f e r e n t  of the behavior  these  an a v o i d a n c e  c l o s e r to the p a r t i t i o n .  main c o n c l u s i o n  Lower A r i p o  elicits  24 h r o f e x p o s u r e was s t a b l e .  f i s h moved o n l y stocks,  revealed  suggests that the  upon a c t u a l a t t a c k s .  Some c a s u a l o b s e r v a t i o n s exposure t o predators  This  the f i r s t  stocks t o hint  that  does n o t have t h e same i m p a c t on of guppies.  In t h i s  experimental  182 design,  however, t h e r e  were t o o many v a r i a b l e s and  enough r e p l i c a t e s t o be following the  c e r t a i n of t h i s  e x p e r i m e n t was  designed  b e h a v i o r a l responses to a  (b)  Reaction  E x p e r i m e n t 6.5  distance  Reaction  I t has the  been p o i n t e d  reaction distance  with  predation.  these  predators stocks  of  genetic  aim  should  of t h i s  that geographic v a r i a t i o n  in  the w i l d  stimuli  is correlated  than those  e x p e r i m e n t was  i n the  experience  with  appear i n these  to a c e r t a i n extent  founders,  c o u l d be  (null  no  hypothesis). stocks  responsiveness  i . e . reaction distance  c a u g h t by  the  predators,  o f Lower  Guayamare>Petite Curucaye/Upper A r i p o > P a r i a . latter  laboratory  are  laboratory the  intense  to determine i f  field  tests  i n v o l v e d , the  predators  exposed to  retained i n predator-naive  f a c t o r s are  resemble  5 laboratory  F i s h f r o m s t r e a m s w h i c h have few  of d i f f e r e n t i a l  differences  of  predator.  I f d i f f e r e n c e s observed  product  should  to  to threatening  d i f f e r e n c e s are  stocks.  If  The  The  predator.  out  respond at a smaller d i s t a n c e predation.  difference.  t o more a c c u r a t e l y measure  distance  guppies to a  not  of  Aripo/  ( R e c a l l the  hand i n t h e  field.)  conducted  i n a long  Methods The filled Exp.  e x p e r i m e n t was  to a depth of  6.4).  The  I l l u m i n a t i o n was  8.0  cm  b o t t o m was  (tank covered  even over the  dimensions with  light  shallow  same as brown  e n t i r e length of  the  tank  in sand. tank  183 (40-watt c o o l w h i t e  f l u o r e s c e n t tubes  the water).  end  liter  In one  tank  (same i n d i v i d u a l  This  " p r e d a t o r " was  i t hung i n m i d w a t e r .  as  At  the o t h e r  white p l a s t i c system. test  T h i s was  arranged  pulley prey,  end  of the  This p a i l  was  pushed i n t o  i t was  with  directly  the p r e d a t o r .  predator,  the  The  a  bottomless  second p u l l e y held  tank f o r  the  an  distance of r e l e a s e With these  directly  was  2  possible to release  r e a c t i o n d i s t a n c e , and  a l l from a p o s i t i o n  fish  sec).  s a n d and the  so  a pulley  tank,  of the p r e d a t o r .  s y s t e m s , t h e r e f o r e , i t was measure t h e  on  to a separate  released into  i n front  4).  up-and-down move-  long outer  connected  before  mm  suspend the  1 c y c l e per  was  fish  cm  = 2 cm,  pail  "encounter" 200  (amplitude  190  21  s u s p e n d e d by m o n o f i l a m e n t  i n m i d w a t e r , o r t o g i v e i t an  ment m a n u a l l y  above  i n photograph, F i g u r e  s y s t e m w h i c h made i t p o s s i b l e t o e i t h e r motionless  cm  I placed a small  g l a s s aquarium c o n t a i n i n g a preserved  Crenicichla  that  of the  mounted 50  the  "animate"  the  i n front of  the  predator. It  s h o u l d be  in  f o r m a l i n but  of  a live  fish.  noted  Tests with  a live  For  this  tor  because i t s "behavior"  predator  colour  proved  high degree of v a r i a b i l i t y  of the p r e d a t o r  reason  preserved  r e t a i n e d most o f t h e m a r k i n g s and  u n f e a s i b l e because of the the b e h a v i o r  t h a t t h e p r e d a t o r was  and  I r e s o r t e d to the and  in  i t s d i s t a n c e from the use  of a preserved  d i s t a n c e to the prey  prey.  predacould  be  184 rigidly  controlled. To  insure that a l l fish  experience,  the  mine w h i c h o f t h e  selected  a test,  5 females) o f t h i s  test,  300  the  pulled  observation area the p a i l  thereby the  fish  releasing  and the  immediately  (exploration period,  up  ml  the  fish  out o f the water w i t h  cm).  the  fish  and  (one  distance  from the p r e d a t o r  and  s i n c e r e l e a s e were r e c o r d e d  and  returned  the  same manner.  had  fish  (to n e a r e s t  gently  the  next  respond  cases,  exploratory other  I n most  1 cm),  the fish  end  of  cases,  avoidance  for this  been e l i c i t e d ,  d i d not  and  described previously).  t o i t s b e a k e r and  Certain  this  gave an  response  response  6 types  I moved  l a r g e tank  During  located.  the  this  In t h e m a j o r i t y o f  began e x p l o r i n g the  p e r c e i v e d the p r e d a t o r  placed i n  the p u l l e y ,  w o u l d e v e n t u a l l y swim t o t h e  of the  small  beaker.  After  t a n k where t h e p r e d a t o r was  s o o n as  A  i n t u r n was  the  time  individual,  of water.  f o r 5 min.  x 216  (5  subsequently  added t o e a c h  fish.  deter-  fish  i n f r o n t o f the p r e d a t o r  test  a r e a = 56  enforced.  Ten  placed i n  each i n d i v i d u a l  t h e opaque p r e - r e l e a s e p a i l to  tested.  s t o c k were  C e r a t o p t e r i s p l a n t was the  strictly  l o t s were drawn t o  a t random, m e a s u r e d , and  For  was  5 s t o c k s w o u l d be  numbered g l a s s b e a k e r s w i t h floating  identical pre-test  f o l l o w i n g procedure  Twenty-four hours before  m a l e s and  had  The  behavior, response.  fish was  was  As  removed  tested in  t o the p r e d a t o r  but  185 swam r i g h t  up  to the  g l a s s and  front  of the p r e d a t o r ;  A  fish  few  failed  t h e maximum t i m e retested  24  hr  t h i s was  a l l o t m e n t o f 15 min.  on  the  The  the  fish  used).  with  test  (A) was they  Two  in  were  f o r each of  t e s t s were  completed  a s s u r i n g t h a t each f i s h  in  t h e b e a k e r s between t e s t s .  had  the  conducted  the p r e d a t o r m o t i o n l e s s  same o r d e r o f t e s t i n g was  i n A,  this  response".  "set" for that  and  fashion described  f o r 1 s e t of  were r e t e s t e d w i t h  as  was  thus  constituted a  the p r e d a t o r moving i n the  first  The  fish  first  5 stocks before  predator.  "no  These f i s h  o f 5 s e t s were c o m p l e t e d  o f 250  second with  above. of  (total  each f i s h :  the  as  down i n  later.  A total  5 stocks  recorded  and  t o swim c l o s e enough t o t h e p r e d a t o r  E a c h g r o u p o f 10 t e s t day.  moved a l o n g o r up  the  each  moving  followed i n test equal  B  residency  Each i n d i v i d u a l t h e r e f o r e ,  t e s t e d t w i c e , o n c e a t t e s t A and  once a t t e s t  B.  After  t h e y were d i s c a r d e d . Results The  results  of the  experiment i n terms of  r e a c t i o n d i s t a n c e to the p r e d a t o r  are given  Non-overlap of the  limits  ficant  95%  d i f f e r e n c e between any  Eberhardt, In t e s t A  1968  (predator s t i l l )  Curucaye.  2 pairs  i n Figure  indicates a  compared  f o r a u s e f u l d i s c u s s i o n of t h i s  between Lower A r i p o and Petite  confidence  t h e r e was  each o f :  Upper A r i p o  the 21. signi-  (see procedure).  a significant difference  Guayamare, P a r i a ,  showed a s i g n i f i c a n t l y  and larger  186a  FIGURE 21.  Reaction  distance of 5 laboratory stocks of  g u p p i e s t o a dead C r e n i c i c h l a . not.moving; line total  (b) p r e d a t o r m o v i n g .  shows t h e mean, h o r i z o n t a l  (a) p r e d a t o r Vertical l i n e the  r a n g e , b l a c k r e c t a n g l e t h e 95%  confidence  limits.  LOWER  ARIPO  UPPER ARIPO GUAYAMARE PARIA  a.  PETITE CURUCAYE  i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i  0 LOWER  ARIPO  UPPER  ARIPO  2  4  6  8  10 12 14 16 18 20 22 24 26 28 30  GUAYAMARE PARIA  b.  PETITE CURUCAYE I  1  0  5  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90  REACTION DISTANCE TO PREDATOR (cm)  187 reaction  distance  t h a n P e t i t e C u r u c a y e and P a r i a .  When t h e p r e d a t o r was m o v i n g order p e r s i s t e d p =  ( t e s t B) t h e same r a n k  ( p e r f e c t rank c o r r e l a t i o n :  .01, o n e - t a i l e d  test).  The r e a c t i o n  approximately doubled with the a d d i t i o n non-parametric t e s t of r e l i a b i l i t y in  t e s t A and B r e v e a l e d  variability was  i n reaction  that  r  = +1.00,  c  distances  were  o f movement.  (A  f o r e a c h o f t h e 250  fish  i n s p i t e of the i n d i v i d u a l  distance,  t h e method o f measurement  a r e l i a b l e i n d i c a t o r o f an i n d i v i d u a l ' s r e a c t i v i t y  2 (X  ^  d  ^  = 4.07, p < . 0 5 ) , i . e . an i n d i v i d u a l  responded a t a d i s t a n c e respective  greater  In  several  t e s t B, Lower A r i p o from a l l the o t h e r  and  d i d not d i f f e r  Upper A r i p o Petite  likely  stocks.  Upper A r i p o ,  Guayamare,  s i g n i f i c a n t l y from each o t h e r b u t  and Guayamare were s i g n i f i c a n t l y d i f f e r e n t f r o m  Curucaye.  r e s u l t s do n o t f i t t h e p r e d i c t i o n s P e t i t e Curucaye had s h o r t e r  expected It  B.)  f i s h were s i g n i f i c a n t l y  W i t h t h e e x c e p t i o n o f Lower A r i p o  and  (for i t s  to respond s i m i l a r l y  days l a t e r a t t e s t  different Paria  than t h e median  s t o c k ) a t t e s t A, was  when r e t e s t e d  that  and U p p e r A r i p o  i s unlikely  that  too c l o s e l y  reaction  had a g r e a t e r  large  distances  reaction  w i t h p r e d a t o r s enhances the r e a c t i o n  distance  than  distance).  and t h e d i s t a n c e  I t i s more p r o b a b l e t h a t  these  (Guayamare  t h i s was due t o e x p e r i m e n t a l  b e c a u s e t h e sample s i z e was ments were a c c u r a t e .  and P a r i a ,  error measure-  experience o f Guayamare  188 fish  relatively  esting  more t h a n Upper A r i p o .  t o measure t h e  Upper A r i p o  tances  reaction distance  a f t e r prolonged  Relative  o f P e t i t e C u r u c a y e and  and  the  make l o n g  turbidity  the  at  of the  P e t i t e Curucaye  would  i s an One  The  u n w e i g h t e d measure a n i m a l may  results  Crenicichla.  has  a reaction  I t i s probably  antipredator behavior  a p r e d i c t i o n of r e l a t i v e  escape motor p a t t e r n s  stated before certain  of  t h a t the  these  predators.  Lower A r i p o even s u r f a c e mild  stimulus  patterns  of  distance when  in  arriving  fish  a v a r i e t y of  to avoid predators.  I have  strength  elicit  required to with  same s t i m u l u s  the  exposure  conditions,  Guayamare q u i c k l y r e v e r t t o r a p i d d a r t s  jumps whereas P a r i a g u p p i e s may  response.  6.2  s a f e s t to  individual  tends to vary  Thus, under the  and  show m i l d  vulnerability.  Under n a t u r a l c o n d i t i o n s , g u p p i e s use different  respond  o f Exp.  t o Guayamare, Guayamare i s l e s s v u l n e r a b l e  (c) E s c a p e m o t o r p a t t e r n s  to  presumably  superfluous.  Upper A r i p o  s e v e r a l measures o f  dis-  reflect  a t a s h o r t d i s t a n c e w h e r e a s a n o t h e r may  exposed to a r e a l use  size  reaction distance  suggest that although  vs.  shorter reaction  Guayamare R.  avoidance at a large d i s t a n c e .  equal  the  animal's avoidance behavior.  vigorously  o f Guayamare  Guayamare m i g h t  small  reaction distances  Finally, o f an  of  inter-  exposure to a l i v e C r e n i c i c h l a .  t o Lower A r i p o ,  h a b i t a t d i f f e r e n c e s ; the R.  I t w o u l d be  T h i s d i f f e r e n c e was  only  not measured  and  show a accurately  189 in  the f i e l d ;  know i f n a i v e stimulus. it  gives  for this fish  reason  i t i s of great  show d i f f e r e n t  r e s p o n s e s t o t h e same  I f d i f f e r e n c e s do o c c u r credibility  differences  Experiment  6.6  i n the predicted  to the hypothesis  i n behavior  occur  that  among n a t u r a l  Escape motor p a t t e r n s stocks  interest to  direction,  microevolutionary populations.  of 5 laboratory  o f guppies exposed t o a  preserved  Crenicichla. The to  behavioral  a preserved  quantified measured  responses o f the 5 stocks  motionless  o f guppies  and m o v i n g C r e n i c i c h l a were  a t t h e same t i m e as t h e r e a c t i o n d i s t a n c e s  were  ( s e e E x p . 6.5 f o r m e t h o d s ) . Results The  r e s p o n s e s o f t h e 250 f i s h  are  tabulated  i n Table  any  o f t h e 500 t e s t s s u g g e s t i n g  conditions of real For is  (predator  Surface  s k i m was n o t o b s e r v e d i n  that  i ti s elicited  of the patterns,  under  i t i s clear that  v a r i a t i o n w i t h i n each stock.  n o t moving) t h e modal r e s p o n s e  Aripo,  (72%, 48%,  76% r e s p e c t i v e l y ) ; P a r i a and P e t i t e C u r u c a y e most  showed weak a v o i d a n c e d r i f t Pooling  the r e s u l t s  often  (46% and 42% r e s p e c t i v e l y ) .  f o r a l l 5 stocks  (125/250) o f t h e a n i m a l s  there  For test A  f o r Lower  Guayamare, a n d Upper A r i p o was a v o i d a n c e d r i f t and  treatment  pursuit.  the rest  considerable  24.  under each  i n t e s t A, e x a c t l y 50%  showed a v o i d a n c e  drift.  TABLE 24.  E s c a p e motor p a t t e r n s o f 5 l a b o r a t o r y s t o c k s e x p o s e d t o a dead C r e n i c i c h l a . (n = 50 f i s h  Behavior pattern A.  Guayamare  STOCK U. A r i p o  _^ Paria  P.  • Curucaye  Total  P r e d a t o r n o t moving  no r e s p o n s e weak a v o i d a n c e d r i f t avoidance d r i f t t u r n around rapid dart s u r f a c e jump Total B.  L. A r i p o  of guppies per stock)  0 6 36 1 7 0  2 14 24 6 0  2 5 38 2 2 1  50  50  50  50  50  250  0 8 17 20 5 0  0 12 13 17 5 3  0 11 . 18 16 5 0  0 21 18 11 0 0  0 24 15 7 3 1  0 76 81 71 18 4  50  50  .50  50  50  4  0  6 23 13 2 6  10 21 14 1 2 2  20 69 125 10 23 . . . .3  .  P r e d a t o r moving  no r e s p o n s e weak a v o i d a n c e d r i f t avoidance d r i f t t u r n around rapid dart s u r f a c e jump Total  .  .  250  191 It to the  i s noteworthy t h a t  predator at  r e s p o n s e was this  the  20%  and  12%  a l l Lower A r i p o  turn  of  motionless.  the  d i f f e r e n c e was  sample  inter-stock  so  and  infrequently.  i n the  In t e s t B r e s p o n s e and  t e s t A = 10;  a general The  The  rapid dart  and  to  A  turn  "escape"  Lower A r i p o  shift  the  main of  animals  avoidance  drift.  showed  t o a more  fish  turn  around no  not  from the  a  reactive the  showing  (turn  next  around  d i s c e r n i b l e change  jump c a t e g o r i e s ,  and  the  inter-stock  suggesting  movement a l o n e ,  around i n t h i s experiment  and  for  jump b e c a u s e  number s h o w i n g t h e  T h e r e was  surface  actual pursuit,  For  trigger was  predator.  Guayamare f i s h ,  most common r e s p o n s e e l i c i t e d and  the  main e f f e c t o f moving  reaction: 71).  or  number o f  increase  t e s t B.=  these responses.  (40%  and  category of  sufficient  of  P a r i a where  moving), a l l animals  to decrease the  avoidance d r i f t  the  was  behavior pattern.  again that  lack  respectively.  surface  r e l a t i v e proportions  (predator  there  p r e d a t o r was  the  respond  t r e n d s were e v i d e n t  s h o w i n g e i t h e r a weak a v o i d a n c e d r i f t  in  A  guppies responded to  around, r a p i d d a r t ,  t h e y were e l i c i t e d  "higher"  d i d not  predator.  In t e s t A no  type of  fish  most common i n P e t i t e C u r u c a y e and  In c o n t r a s t ,  patterns  of  a l l when i t was  g r o u p made up  motionless  8%  by  the  turn  moving  around predator  34%  respectively)  w h i l e weak a v o i d a n c e  drift  remained the  modal p a t t e r n  for Paria  Curucaye  and  Petite  was  (42%  and 48% r e s p e c t i v e l y ) .  moving t h e p r e d a t o r  Therefore,  on t h e l a s t  the only e f f e c t of  2 s t o c k s was t o d o u b l e t h e  r e a c t i o n d i s t a n c e ; t h e motor p a t t e r n s  remained  virtually  unchanged. E x p e r i m e n t 6.7  Escape motor p a t t e r n s  of 5 laboratory  stocks o f guppies exposed t o R i v u l u s . Introduction Exp. distance  6.5 and 6.6 have s u g g e s t e d  and t h e p r o p o r t i o n o f f i s h  m o t o r p a t t e r n s may be s i g n i f i c a n t s t o c k s , e v e n when t h e f i s h ever,  under these  behavior  that reaction  showing c e r t a i n  measures f o r comparing  are not actively  clearly  Therefore,  are important  as a f i r s t  I made s i m u l t a n e o u s  on t h e a t t a c k b e h a v i o r behavior  of the 5 stocks.  predator  forthis  type  (training are  period)  o f t e s t because  a t t a c k prey  attack.  and t h e a n t i i s an i d e a l  i ti s relatively  and s t a r v a t i o n  repeatedly  until  they  s u c c e s s f u l l y captured. It  an  will  line of  q u a n t i t a t i v e obser-  Rivulus  a period of handling  nature.  under r e a l  of Rivulus  predator  s m a l l and a f t e r  How-  c o n d i t i o n s most o f t h e a n t i p r e d a t o r  defense b u t would n o t be.very e f f e c t i v e  vations  attacked.  i s o f an e x p l o r a t i v e o r m i l d l y a v o i d i n g  These p a t t e r n s  escape  attempt  behavior. predator  should  be e m p h a s i z e d t h a t t h i s  e x p e r i m e n t was  t o make c o m p a r a t i v e measurements o f t h e p r e y ' s Therefore,  I had t o c o n t r o l t h e b e h a v i o r  a s much a s p o s s i b l e ; h e n c e o n l y  a single  o f the  female  193 Rivulus  (75 mm)  was  used  in a l l tests.  Methods All a 60  liter  t e s t s were c o n d u c t e d glass  dimensions:  aquarium  L = 61  light-brown  sand  cm,  between 1500  filled  W = 32,  s u b s t r a t e and  D = a  31).  "hiding"  t h e t a n k was  dark)  p r o v i d e d by a 4 0 - w a t t c o o l w h i t e  mounted  35  cm  over the water  rock  Illumination  1945  o f 20  Except  predator, was  bare.  t o a depth  and  (12  cm  for a  f o r the light-12  fluorescent  13 o f e a c h  s t o c k were  They were a l l p r e d a t o r - n a i v e and  ranged  Since  t h a t p r e y body s i z e  known f r o m Exp.  important v a r i a b l e c a r e was  Curucaye 20.8  5.4  from  19.0  = 20.8  tube  used.  t o 23.5  mm.  i s an  i n the c a p t u r e success o f R i v u l u s , g r e a t  t a k e n t o m a t c h t h e s t o c k s f o r body s i z e  Lower A r i p o = 21.7  (tank  surface.  S i x t y - f i v e male g u p p i e s ,  i t was  hr i n  + 1.07;  ± 1.52;  Guayamare = 21.0  Upper A r i p o = 21.9  (x ±  + 1.36;  SD:  Petite  + 1.13;  Paria  =  ± 1.44). The  procedure  w i t h t h e p r e d a t o r and prey r e l e a s e recorder  and  a single  guppy  r e c o r d i n g a l l the i n t e r a c t i o n s  prey k i l l .  (see C h a p t e r  behavioral  consisted of p l a c i n g  2) was  An  between  Esterline-Angus event  used  to quantify  the  following  measures.  Predator behavior 1. t o t a l t i m e , p r e y r e l e a s e to k i l l 2. p r e d a t o r o r i e n t a t i o n t i m e 3. a p p r o a c h f r e q u e n c y 4. a t t a c k f r e q u e n c y 5. c a p t u r e  Prey  behavior  1. a v o i d a n c e d r i f t frequency 2. r a p i d . d a r t f r e q u e n c y 3. s u r f a c e s k i m f r e q u e n c y 4. s u r f a c e jump f r e q u e n c y 5. h i d i n g d u r a t i o n  194 Except  "predator  orientation  been d e s c r i b e d b e f o r e orientation orienting release  time  pause, e t c . ) . the  a l l these  patterns  or are self-explanatory.  i s the t o t a l time  and c h a s i n g  to k i l l ,  time",  the prey,  spent  Predator  by t h e p r e d a t o r  i ^ e . t o t a l time,  minus p e r i o d s o f p r e d a t o r  I t i s a good i n d e x  have  prey  inactivity  (rest  o f the escape a b i l i t y o f  prey. Before  the prey  an opaque p a r t i t i o n Since  the predator  near the p a r t i t i o n , prior  t o prey  confined  equal  had been c o n d i t i o n e d t o r e c e i v e  guppies  i t was u s u a l l y swimming i n t h i s v i c i n i t y  the predator  time  behind  i n one c o r n e r o f t h e a q u a r i u m f o r 5 m i n .  release.  from the p a r t i t i o n .  was r e l e a s e d , i t was p l a c e d  To " g i v e t h e p r e y  a chance'  to i t s hiding place  I  1  l o c a t e d 50 cm  T h i s i n s u r e d t h a t a l l the guppies  to react to the f i r s t  had  few a p p r o a c h e s b y t h e  predator. The  guppies  were p r e s e n t e d  r a t e o f 1 p e r 24 h r ; no o t h e r  to the predator  f o o d was p r o v i d e d  t h e h u n g e r l e v e l was a l w a y s t h e same p r i o r The of Day  s e q u e n c e o f p r e s e n t a t i o n was a r r a n g e d t h e same s t o c k w o u l d be t e s t e d e v e r y 1:  UA; Day 2:  PCur; Day 6:  UA; e t c . ) .  c u t i v e days o f prey interval a test  P a r ; Day 3:  criterion.  so t h a t  t o each  test.  so t h a t a f i s h  fifth  day (e.g.  Guay; Day 4:  This design  a t the  called  LA; Day 5: f o r 65 c o n s e -  p r e s e n t a t i o n t o meet t h e 2 4 - h o u r Unfortunately  I was u n a b l e  on 6 d a y s i n t e r s p e r s e d t h r o u g h o u t  to  t h e 65-day  conduct  195 schedule. Aripo)  Thus on  t h e p r e d a t o r had  This d i d not In was  the  On and  these  T u b i f e x was  n o t r e c e i v e d a guppy f o r 48  the prey  occasions  the prey  same f o r t h e  2 Lower A r i p o , 1 Upper hr.  results.  (3 Lower A r i p o , 1 Guayamare) t h e  u n a b l e .to c a p t u r e  15 min  (3 P a r i a ,  appear t o b i a s the  4 tests  attempts. at  6 tests  test  e v e n t h o u g h i t made numerous the  discarded. the  f e d t o the  predator  r e c o r d i n g s were  terminated  To keep t h e h u n g e r  f o l l o w i n g day,  level  a s m a l l amount o f  predator.  Results The of  results  o f the experiments  showed t h a t s e v e r a l  t h e b e h a v i o r p a t t e r n s o c c u r r e d so i n f r e q u e n t l y  were n o t surface drift  amenable t o s t a t i s t i c a l skim,  supports  prey the  hiding).  The  analysis low  idea that i t serves mainly  Since the predator d i d not  permit  c l o s e approach o f the p r e y ,  the  observed  i n only  (avoidance  occurrence  function.  3 out of the  65  possible pairs  Mann-Whitney U T e s t was each measure: Aripo>Paria.  used  one-tailed probabilities  to t e s t  among t h e s e  (LA v s . Guay; PCur v s . UA) no p r e d i c t i o n was  made.  used  an e x p l o r a t i v e or  was  fish.  of stocks  while  drift,  avoidance  this behavior  for differences  (Table 25).  the h y p o t h e s i s  Lower A r i p o / G u a y a m a r e > P e t i t e Comparisons  of  they  remain m o t i o n l e s s  F i v e o f t h e m e a s u r e s were a n a l y z e d between a l l 10  that  The that for  Curucaye/Upper  3 groups used  the  comparisons w i t h i n groups the t w o - t a i l e d t e s t  because  196 TABLE 25.  C o m p a r i s o n o f p r e d a t o r y s u c c e s s and p r e y escape behavior f o r 5 l a b o r a t o r y stocks of guppies. Values i n the matrix are the s i g n i f i c a n c e l e v e l s f o r each p a i r o f c o m p a r i s o n s (Mann-Whitney U T e s t ) ; NS = p > .05.  Mean frequency A.  Frequency of  Lower A r i p o Guayamare P. C u r u c a y e Upper A r i p o Paria B.  Frequency of  LA  Guay  _  17.8 10.9 9.7 9.7 8.7  .05 .001 .001 .001  predator attacks  - NS  NS NS NS  NS  .02 .001 .001 .001  C.  orientation  time (sec)  D.  Frequency of r a p i d  Lower A r i p o Guayamare P. C u r u c a y e Upper A r i p o Paria E.  64.6 37.7 27.9 27.1 20.2  Frequency of  Lower A r i p o Guayamare P. C u r u c a y e Upper A r i p o Paria  13.4 8.7 7.9 7.6 5.5  NS .05 .025 .001 darts  - NS  .05 NS .05  NS  .025  05  predator  NS NS .01  s u r f a c e jumps away f r o m 5.1 2.9 2.2 2.6 1.5  NS  - NS  NS NS .01  away f r o m NS .01 .01 .001  NS  a t prey  5.7 3.5 3.1 2.9 2.8  Lower A r i p o Guayamare P. C u r u c a y e Upper A r i p o Paria  UA  p r e d a t o r approaches, t o p r e y  Lower A r i p o Guayamare P.. .Curucaye Upper A r i p o Paria Mean p r e d a t o r  PCur  NS .01  01  predator  _  NS .025 .025 .001  .05 NS .001  - NS .05  01  Par  197 The dropped  4 fish  t h a t were n o t  c a u g h t by  predator  from the  a n a l y s i s of  the  t h i s measure t h e  sample s i z e  f o r Lower A r i p o was  Guayamare, 12. was  For  a l l other  c a l c u l a t e d f o r n^ The  dictions  results  f i t the  deviation  = 13,  of  this  from the  expected  the  all  m e a s u r e s , Lower A r i p o  ( a p p r o a c h and  i s apparent  and  U  statistic  13.  rather closely.  The  r e l a t i o n s h i p among t h e  (64.6  significant  effort  per  vs.  37.7  larger  ability kill"  For  the  significant,  had  other  been  f o u n d between Lower  2 motor p a t t e r n s  used i n escape.  m e a s u r e s — t h e mean s c o r e s sharp c o n t r a s t to the see  statisti-  Fig.  No  hypothesis  predicted  d i f f e r e n c e c o u l d be  Upper A r i p o  were v i r t u a l l y  reaction distance 21).  if a  used.  c o m p a r i s o n s , my  between P e t i t e C u r u c a y e and  a  sec r e s p e c t i v e l y ) .  d i f f e r e n c e was  outcome more c l o s e l y .  Crenicichla,  distinct  d i f f e r e n c e m i g h t have b e e n d e t e c t e d  sample s i z e  By  o r i e n t a t i o n times  Guayamare were n o t  Guayamare f o r t h e  significant  stocks  Lower A r i p o .  showed a s u p e r i o r  i n "predator  premain  f r e q u e n c y ) were s t a t i s t i c a l l y  and  for  for  a n a l y s i s r e v e a l t h a t the  fish  were  thus  10,  d i f f e r e n c e between t h e means s u g g e s t s t h a t a  cally  the  =  the  Though t h e mean p r e d a t o r  between Lower A r i p o  No  and  attack  f r o m Guayamare.  The  2  d i f f e r e n c e between Guayamare and  to escape p r e d a t i o n  Aripo  frequency,  comparisons  observed data  was  trend  n  attack  the  f o r any  of the  identical to the  detected 5  (in  preserved  198 As ability  e x p e c t e d , P a r i a g u p p i e s showed t h e  of the  differed  5 stocks;  significantly  d i f f e r e n c e was darts  and  On  the  average,  The  predator  i t took twice  a p p e a r t o d a r t away as  overall  a f o u r t h endured an  predator I can  of  14  rapid darts  and  o r i e n t a t i o n time  for  these  the  survival  tests  value  and  The  are  decided  by  patterns,  guppies  in  fact  caught  while  captured.  P a r i a ) , I have p l o t t e d  the  jumps a g a i n s t  evidence  time, F i g u r e R i v u l u s was  to the is  the 22). the  If  same  c o n t r a r y ) , then  obvious.  s e l e c t i o n by  also superior i n avoiding  can  The  the  of the  to intense  fish  more f i t i n  suggest that populations  Whether t h i s  Paria  to  d i f f e r e n c e s between  surface  behavior  predation. be  (strikes)  were n o t  i t was  the  of the behavior  t h a t have b e e n s u b j e c t predators  and  (= s u r v i v a l  (I have no  These r e s u l t s  only  predator  attacks before  assume t h a t t h e  cichlid  T h r e e Lower A r i p o  (Lower A r i p o  range.  r a p i d l y once s t r u c k .  a i d to v i s u a l i z i n g  2 extreme s t o c k s frequency  of r a p i d  r e a c t i o n d i s t a n c e , escape motor  endurance.  This  striking  guppy t h a n a P a r i a .  exhausted the  As  frequency  g u p p i e s w o u l d t h u s a p p e a r t o be  s e v e r a l ways:  completely  4 stocks.  as many a t t a c k s  did  and  o r i e n t a t i o n time  to w i t h i n easy  a Lower A r i p o  Lower A r i p o  low  escape  P a r i a f i s h were u s u a l l y  capture not  other  i n the  jumps.  the  predator  from the  reflected  surface  a p p r o a c h e d by  the  poorest  a p p l i e s under n a t u r a l  a t r a n s p l a n t experiment.  of  guppies  characid  and  Rivulus conditions Conceivably  199a  FIGURE 22.  Relationship survival guppies  time  o f escape i n two  exposed  to  motor p a t t e r n s  laboratory  Rivulus.  stocks  to of  199b  LOWER 301  3  LU  <  1  9  % CO  O > <  0 10  LU CD  O  PARIA O  20H  Ql  >  ARIPO  15  2  IT  ~ i — i — i — i — i — i — i — r ^ ^ r 30 40 50 60 70 80 90 100  340  H  1  °-  § 1 0 -  LU O LU IT  *  5  CO OO  10  0»  • COO»  20  30  40  50  SURVIVAL  60  i—r  70  80  90  100  TIME (sec)  340  200  the h y p e r r e a c t i v i t y disadvantage Curucaye).  i n a R i v u l u s - i n f e s t e d stream  immunity  a few  Hoplias,  (e.g.  be  mm  s i m p l y by  i s q u i t e capable  of water  animal  of pouncing  (and e v e n on  o r A s t y a n a x on  pursue guppies  a l l o w i n g an  dry  t h a t have e l u d e d  to reach  on  them and  not  good  not a  a guppy i n  land!).  t h e o t h e r hand, do  a  Petite  i n R i v u l u s - i n f e s t e d streams does  refuge—Rivulus only  actually  I n c o n t r a s t t o t h e Lower A r i p o s i t u a t i o n ,  escape behavior guarantee  o f Lower A r i p o f i s h may  Crenicichla, continue  reached  to  shallow  water.  Experiment  6.8  R e s p o n s e s o f Guayamare and a simulated a e r i a l  P a r i a guppies  to  predator.  Introduction The described  behavior  for wild  disturbance either  p a t t e r n "down-dart" has  guppies.  T h i s response  above t h e w a t e r s u r f a c e and  t h e p a s s a g e o f an  a d a p t i v e v a l u e o f such  behavior  the  risk  non-aquatic  o f p r e d a t i o n from  b a t s , and  is elicited  may  be  evoked  o b j e c t o r i t s shadow o v e r  The  birds,  a l r e a d y been  perhaps t e r r e s t r i a l  i s probably  fish.  such  to as  "fishing"  from  shore. It the  i s often stated  antipredator behavior  hunting  o f an  animal  demonstrated) t h a t i s adapted  s t r a t e g y o f i t s most common p r e d a t o r  Keenleyside, of prey,  (but r a r e l y  1955).  For  any  t h e main t h r e a t may  to  the  (e.g.  given species or population stem f r o m  one  or a  few  a  by  linked  predators  animals  a  by  201 predators  (Larson,  1960;  C u r i o , 1970a, 1970b, 1970c)  more commonly a h o s t  of predators  tegies  Thorpe,  (Crane,  Walther,  1969;  Snyder,  1971). As  1952;  Ghiselin  and  an h y p o t h e s i s  wide v a r i e t y  a selective  predator  response  196 3:69; Ricklefs,  i t w o u l d be  of predators  have had  with  a variety  m i g h t be  oh  stra-  Kruuk, 1964,  1972;  1970;  and  Snyder  predicted that i f a  (with d i s s i m i l a r  impact  of  but  a prey  hunting  methods)  p o p u l a t i o n , the  anti-  q u i t e n o n - s p e c i f i c and a p p l i c a b l e  t o a l l s t r a n g e moving o b j e c t s o f a p p r o p r i a t e  size  ("generalist"). Contrariwise, o n l y one  species of predator,  s i m i l a r hunting The Paria  a response  R.  presents  responsiveness  avoided  to a e r i a l  predators  in this  to t e s t  in their  t o compare t h e Guayamare  response  responses  t o an of  from  the  f o r the  since these  environment.  (with  ("specialist").  are  I have  d e s c r i b e d d i f f e r e n c e s between w i l d P a r i a and guppies  specific i f  absence of a q u a t i c p r e d a t o r s  a unique o p p o r t u n i t y  t h e most i m p o r t a n t  very  or group o f s p e c i e s  methods) must be  virtual  m i g h t be  presumably  already  Guayamare  o v e r h e a d o b j e c t ; I now  wish  laboratory stocks of P a r i a  and  fish.  Methods The illustrated quantify  the  e x p e r i m e n t was  conducted  i n F i g u r e 23.  The  response  of  aim  single,  with  the  apparatus  o f t h e e x p e r i m e n t was  isolated,  naive  fish  to  to a  202a  FIGURE 23.  Test  apparatus used  responsiveness Guayamare aerial  f o r measuring the  of laboratory stocks of  and P a r i a g u p p i e s t o a  predator.  simulated  A l l measurements i n cm.  FRONT VIEW 60 W  LIGHT  A WATER  BULB  B  LINE  T DEPTH GRID O N / ONE-WAY A L U M P A P E R  TEST  TANK  'OUTER  TANK RELEASE  TOP  VIEW  OPAQUE  DIVIDER'  OBSERVATION' POINT  J RELEASE  CABLE  LATCH  203 standard  a e r i a l , escape-evoking stimulus.  " p r e d a t o r " was was  monofilament  l i n e that  significance  a n g l e was  s u f f i c i e n t to allow the predator to s l i d e  tank;:—refer t o  over the inner  the  a shadow  s t i m u l u s was  (velocity  about 0.5  at this  The t e s t  black plexiglas  twice i t s s i z e .  sec f o r each h a l f  p o i n t was t a n k was  with black plexiglas  40  see o u t s i d e  the t e s t  The d u r a t i o n o f of the t e s t  tank  e n c l o s e d on t h e s i d e s and  and was  partition.  tank, i t  cm/sec).  divided The f r o n t  c o v e r e d w i t h one-way Alum p a p e r ; to  tank  figure).  As t h e p r e d a t o r p a s s e d o v e r t h e t e s t produced  (no  i s a t t a c h e d t o t h e shape o f t h e m o d e l ) .  down t h e l i n e w i t h a u n i f o r m v e l o c i t y (test  ran over the  l e n g t h o f t h e o u t e r t a n k a t an a n g l e o f 12°  special This  aerial  a b l a c k c a r d b o a r d , b i r d - s h a p e d model w h i c h  attached.to a clear  entire  The  rear  i n t h e m i d d l e by a o f the tank  was  t h u s t h e f i s h were  t a n k o n l y d i r e c t l y upwards.  able A  d e p t h g r i d was marked o f f on t h e Alum p a p e r  i n f i f t e e n 1 cm  intervals  from z e r o t o  15  corresponding to the depth  strata  cm. All  darkened  tests  room.  were c o n d u c t e d  O n l y a 60 w a t t  over the mid-point of the t e s t Water t e m p e r a t u r e  was  held  randomly  from  incandescent bulb tank p r o v i d e d  c o n s t a n t a t 25.0  Twenty male Guayamare selected  i n the evening i n a  and P a r i a  directly  illumination. C.  guppies  were  s t o c k a q u a r i a and a s s i g n e d t o  204 i n d i v i d u a l beakers  c o n t a i n i n g 300  Sagittaria plant.  A l l f i s h were m e a s u r e d t o a s s u r e  homogeneity  (Guayamare:  x = 18.0  ± 0.72  mm  ml  x = 17.7  o f w a t e r and  mm  ± 0.95  SD;  a  SD).  randomized w i t h  r e s p e c t to the  paired with  individual  (A o r B) nine  was  times,  individual  o f Guayamare.  d e c i d e d by  flipping  Guayamare 11  times.  was  swimming a b o u t t h e compartment.  by  this  soon as b o t h  fish  other)  were above t h e  thirds  of the water column).  time  directly  by  P a r i a was  in A  pairs).  p l a c e d i n i t s r e s p e c t i v e compartment  actively  this  compartment  ( t o t a l o f 20  f o r 15 min;  as  was  F i v e p a i r s were t e s t e d on  (A o r B)  started  was  of P a r i a that The  a coin.  each n i g h t f o r 4 c o n s e c u t i v e n i g h t s Each f i s h  size  Paria:  F i s h were t e s t e d i n a p a i r e d d e s i g n w h i c h  the  small  10  cm  a c a b l e which  i n f r o n t o f , and  time  the guppies  (visually g r i d mark The  were  A trial  isolated  always was  from  ( i . e . i n the  p r e d a t o r was  each  top  two-  released at  I held while viewing  the  i n m i d l i n e o f the g r i d  on  fish the  test  tank. The  moment t h e  "bird  c o r n e r o f compartment B, noted the both  (d^).  fish  was  The  as  right-hand  of both  2  The  difference  (d  fish  was  o f movement o f  s o o n as t h e p r e d a t o r had  (d ).  d i s t a n c e moved i n t h e At the  the p o s i t i o n  the  maximum downward p o s i t i o n  noted  compartments  flew" over  2  passed  - d^)  over  i s the  down-dart.  same t i m e  as t h e d,  d e p t h s were  recorded,  205 2 s t o p w a t c h e s were "freezing" defined  ( i . e . t h e swimming  this  each f i s h  s t a r t e d t o measure t h e d u r a t i o n o f  remained motionless  of the f i s h  I repeated  the t e s t  v a l was a l l o t e d fish,  in i t sd  arising  a t t h e moment 5 times  2  I  position).  from d i f f e r e n c e s i n t h e of stimulus  f o r each p a i r ;  between s u c c e s s i v e  the distance  swimming  o f each f i s h ;  p e r i o d o p e r a t i o n a l l y as t h e l e n g t h o f t i m e  To r e d u c e v a r i a t i o n position  inhibition  tests.  presentation,  a 5-minute  inter-  Thus f o r e a c h  o f t h e d o w n - d a r t and t h e d u r a t i o n o f  inhibition  a r e b a s e d on t h e means o f t h e s e  5 sub-  samples . Results To t e s t a stock 95%  f o r the p o s s i b i l i t y  of bias  limits  means d i f f e r e d  f o r these  by o n l y  0.7 cm  pre-stimulus  (Paria:  8.3 cm) and t h e r e was c o m p l e t e o v e r l a p intervals  suggesting  identical  f o r both  Also,  (p =  depths.  9.0 cm,  Guayamare:  i n t h e 95%  that the pre-stimulus  The  confidence  conditions  were  stocks.  a Sign  T e s t was u s e d t o t e s t  i f there  was an  o f t h e s e l e c t i o n o f t h e compartment on t h e swimming  inhibition closer  from  d e p t h d i f f e r e n c e a t d ^ , I c a l c u l a t e d t h e means a n d  confidence  effect  resulting  time  ( t h e w a t e r s u r f a c e o f compartment A i s  to the predator)  but t h i s  a l s o p r o v e d t o be u n t r u e  .504). The o n l y  detected  significant  d i f f e r e n c e s t h a t c o u l d be  were t h e d i f f e r e n c e s between s t o c k s  (Table 26).  206  TABLE 26.  Pair 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 . 18 19 20 Mean Wilcoxon T  N P  R e s p o n s e s o f n a i v e Guayamare and P a r i a guppies t o a simulated a e r i a l predator. The d a t a f o r e a c h p a i r o f f i s h a r e t h e means f o r 5 s e p a r a t e t r i a l s .  Down-dart d i s t a n c e (cm) Paria Guayamare 3.4 3.8 2.6 3.2 3.4 5.2 2.2 3.4 4.6 5.8 3.0 3.8 4.2 4.2 4.0 3.8 8.-6 4.8 4.6 4.2  1.0 4.2 1.0 3.2 2.8 6.2 2.2 3.8 2.0 5.4 0.8 4.2 3.0 2.0 3.0 5.2 5.8 7.8 4.2 2.2  4.14  3.50 41.5 18 < .05  D u r a t i o n o f swimming i n h i b i t i o n (sec) Paria Guayamare 7.4 3.8 5.0 6.4 9.4 13.4 4.0 3.4 3.6 8.0 2.8 3.0 6.2 4.2 3.6 2.6 8.6 12.0 3.0 0.2  10.6 8.2 9.8 6.8 9.2 7.6 8.0 8.4 8.6 10.4 5.8 14.8 8.0 6.0 3.2 7.4 5.8 9.8 5.4 2.6 7.82  5.53 38.5 20 < .01  207 A Wilcoxon  matched-pairs  the h y p o t h e s i s distance  and  Guayamare  g r e a t e r swimming i n h i b i t i o n  c o u l d n o t be  time:  T = 38.5,  These r e s u l t s  the  field  falsified  (down-dart d i s t a n c e :  inhibition  t e s t was  used  suggest  than  > p >  p <  .05;  swimming  .005).  t h a t i n the absence of  aerial  t h r e a t , move d e e p e r i n t h e w a t e r c o l u m n and longer are  validate  this  test  2 stocks with  have t h e  time The  and  f a v o r e d by  hypothesis  or f a c i l i t i e s  hypothesis  remaining  real  who,  i n response  i t w o u l d be  aerial t o do  decreases  (see d i s c u s s i o n i n C h a p t e r  the European  S a l y e r and indicate  3)  are not unreasonable.  on  L a g l e r , 1949;  shallow water.  predators.  and  of  detec-  From what  fish-eating  kingfishers,  Though t h e  these  fishing  habits  and  Belted  (White,  1936;  H y a t t , p e r s . comm.) k i n g f i s h e r  predators  a r e most e f f i c i e n t  However, Eastman  the European k i n g f i s h e r  to  have n o t b e e n s t u d i e d , o b s e r v a t i o n s  (Eastman, 1969)  that these  To  I d i d not  likelihood  feeding habits of  i s known a b o u t t h e  aerial  the  little  Trinidad kingfishers  remain  assumes t h a t m o v i n g i n t o d e e p e r w a t e r  motionless  of  an  this.  by  assumptions  to  necessary  predators but  t i o n or capture, or both,  bats  signi-  natural selection.  further  This  for either behavioral  a q u a t i c p r e d a t i o n , guppies  the  test  observations).  T = 41.5, .01  duration  ficant  motionless  to  t h a t P a r i a w o u l d have a g r e a t e r d o w n - d a r t  (in conformity with  hypothesis measure  signed-ranks  launches  (1969) has an  in  clear  shown t h a t when  a t t a c k from  a  perch,  208 the  aim  a t the perch  underwater. effective  The  than  Nevertheless, suited  " P a r i a response"  a rapid dart i n countering this the  response  Schooling  Differences  previously suggested  that a correlation  Since  have e v o l v e d  as  1967;  exists  schooling behavior an  suffer type  admirably strategy—the  guppies  to understanding  schooling  behavior.  vital  to  see  determine  from n a t u r a l p o p u l a t i o n s Experiments  o u t p r e v i o u s l y and  adaptive  Schooling behavior  to  properties of  predation pressures.  the  significance  are of  of 5 laboratory stocks  guppies.  Methods The  t e s t s were c o n d u c t e d  I  schooling  (for reviews  cohesive  originating  necessary  in  intensity  i s o f t e n thought  i t was  have n o t b e e n c a r r i e d  of  (Table 20).  between t h e  antipredator strategy  from d i f f e r e n t  E x p e r i m e n t 6.9  manner  the development o f  t h e r e were d i f f e r e n c e s i n t h e  this  strategy.  g r o u p s have b e e n d e s c r i b e d  Shaw, 1 9 7 0 ) , I f e l t  groups of n a i v e  of  less  among t h e w i l d p o p u l a t i o n s o f g u p p i e s  a q u a t i c p r e d a t i o n and  that  be  behavior  i n a general q u a l i t a t i v e  behavior.  if  w o u l d a p p e a r t o be  tendency t o form c o h e s i v e  Breder,  would p r o b a b l y  closed  attack.  (d)  of  eyes are  f o r the k i n g f i s h e r ' s a l t e r n a t e f i s h i n g  hovering  the  i s d e c i s i v e because the  i n a bare,  blue-green  209 wooden t a n k  (48 x 110 cm) f i l l e d  t o a d e p t h o f 3 cm w i t h  aged  t a p w a t e r m a i n t a i n e d a t 25 t 2 C.  held  c o n s t a n t w i t h a 40-watt  cool white f l u o r e s c e n t  mounted 60 cm above t h e w a t e r flattened  I l l u m i n a t i o n was  surface.  tube  The s h a l l o w w a t e r  t h e s c h o o l t o a d e p t h o f one o r two f i s h .  A  2 reference bottom  grid  o f t e n 52 8 cm  o f the tank t o r e c o r d  s q u a r e s was marked on t h e the p o s i t i o n  O b s e r v a t i o n s were made by l o o k i n g  o f each into  fish.  a mirror  (mounted  On t h e r e a r w a l l o f t h e t a n k 35 cm above t h e w a t e r  and h e l d  a t a 45° a n g l e t o t h e w a t e r )  in  a blind  covering  could observe f i s h increases  The  without disturbing  5 o f each sex chosen randomly  size distributions  testing  of a l l test  from stock fish  t o , and d i s c a r d e d  s t o c k was t e s t e d  ( t o t a l o f 500 f i s h  E a c h g r o u p was p l a c e d  at  (disturbance  this  the position  1-minute i n t e r v a l s  repeated  5 hr l a t e r  environment  (test  after  testing.  (845-1745 h r ) .  Ten r e p l i -  f o ra total  used).  i n the test  f o r 30 m i n ( t e s t A ) . the f i s h  F o r each  The  t o t h e day and  t a n k f o r 10 m i n .  o f e a c h o f t h e 10 f i s h  after  B).  aquaria.  were t h e same.  f o r e a c h o f t h e 5 s t o c k s were c o m p l e t e d  50 g r o u p s  After  them  s c h e d u l e was r a n d o m i z e d w i t h r e s p e c t  time o f day each cates  I n t h i s way I  r e c o r d i n g s were made on g r o u p s o f 10 m a t u r e  They were f e d p r i o r  of  the top o f the tank.  cohesion).  All fish,  through a small hole  T h i s was  had e x p l o r e d  30-minute  was r e c o r d e d  test  their  new  I calculated  210 an  " i n d e x o f c o h e s i o n " i n t h e f o l l o w i n g way:  1-minute o b s e r v a t i o n t h e maximum d e n s i t y grid  s q u a r e s was r e c o r d e d .  density  and or  minimum o f 1  a maximum o f 10 less).  behavior (e.g.  Although i s less  tive  (1 f i s h  (entire  purposes  maximum  The i n d e x h a s a  i n each  group  o f t h e 10  squares)  i n the area o f 1 square  t h i s method o f q u a n t i f y i n g s c h o o l i n g  precise  than.those  W i l l i a m s , 1964; C u l l e n  Symons, 1 9 7 1 ) ,  f o r any o f t h e 10  The i n d e x i s t h e mean  f o r 30 o f t h e s e o b s e r v a t i o n s .  theoretical  f o r each  i t appeared desired  u s e d by o t h e r w o r k e r s  e t a l , 1965; H u n t e r ,  t o be a d e q u a t e  1966;  f o r t h e compara-  here.  Results W i t h i n each the i n d e x from less  stock I found  test A to test  ( F i g u r e 2 4 ) ; a l l s t o c k s were  c o h e s i v e once t h e y had e x p l o r e d t h e t a n k .  degree  of dissociation  greater either  for Petite  Upper A r i p o , a n d P a r i a  from  closely  a maximum  were t h e d i f f e r e n c e s  among t h e 5  The t r e n d i n t h e mean  I observed  i n nature  The s t o c k s d e r i v e d f r o m r i v e r s where p r e d a t i o n  i n t e n s e have a s i g n i f i c a n t l y h i g h e r s c o r e t h a n  obtained  index  a t Lower A r i p o t o a minimum a t P a r i a  p a r a l l e l s the variation  (Table 20).  Petite  than  Lower A r i p o o r Guayamare.  stocks a t both t e s t p e r i o d s . score  However, t h e  ( s c h o o l s p r e a d , o r b r e a k - u p ) was  Curucaye,  More n o t e w o r t h y  is  B  a s i g n i f i c a n t decrease i n  f r o m r i v e r s w i t h low p r e d a t i o n .  Curucaye  those  Statistically,  i s i n s e p a r a b l e f r o m Guayamare o r Lower  211a  FIGURE 24.  Mean i n d e x stocks  of cohesion  of guppies.  t h e mean, h o r i z o n t a l black  for five  Vertical line  laboratory  line  shows  the t o t a l  r e c t a n g l e s t h e 95% c o n f i d e n c e  (a) = T e s t A;  (b) = T e s t B  range, limits,  40 I  3.0  LOWER  5.0  6.0  7.0  _ L  ao _L  mo _L_  9.0  ARIPO  GUAYAMARE PETITE  CURUCAYE  UPPER  ARIPO  PARIA  LOWER  a.  ARIPO  GUAYAMARE P CURUCAYE UPPER ARIPO PARIA  b.  ao  n— —r 1  T  40  5.0  INDEX  6.0  of  7.0  6J0  COHESION  9.0  10.0  212 Aripo, Aripo  though i n t e s t and  Paria.  transitory but  quick  out  explored hand a r e  I have no  cohesive  once the  (< 5 h r ) . still  e n v i r o n m e n t has  Guayamare and  evidence  Lower A r i p o  after  5  t h a t t h e method o f stock-specific  been  measuring  bias.  Though a l l  i n s p e c t i o n of i n d i v i d u a l  recordings  revealed  f o r any  test  and  testing  stock  tank than  t o be the  feeding motivation i n the schedule  cohesiveness  was  randomized  i n any  one  the  bias  inten-  affect  entire  for  potential  t h a t t h e methods d i d lesser  stock.  results  of t h i s  t h a t d i f f e r e n c e s i n the  controlled  by  underlying genetic  answer t o t h e  the  the  region  favoring greater or  hypothesis  a partial  and  (controlling  I conclude  a systematic  Overall,  (2 v a r i a b l e s known t o  in no  In a d d i t i o n , l i g h t  guppy) were c o n t r o l l e d  circadian differences). introduce  more a t t r a c t e d t o one  other.  on  hr.  g r i d s than  cohesion  not  new  surroundings  4 corner  tendency  sity  i n strange  Upper  a  d i d s p e n d more t i m e i n t h e  others,  o f the  a p p e a r s t o be  quite cohesive  s c h o o l i n g r e s u l t e d i n any stocks  i s greater overlap with  P e t i t e Curucaye thus  to spread  other  there  schooler, very  thoroughly the  B,  question  experiment confirm  tendency to school  factors. of  the  But  this  adaptive  the  are  i s only  signifi-  cance o f d i f f e r e n c e s i n s c h o o l i n g i n n a t u r a l p o p u l a t i o n s  of  guppies.  a  causal  Although  one,  warned t h a t ,  a t the "we  the  c o r r e l a t i o n with  interspecific  level  p r e d a t i o n may i t has  are making a s e r i o u s e r r o r i n  be  o f t e n been forcing  213 ourselves  to f i n d  (Shaw, 1970:  a s i n g l e adaptive  suggests  occasions  for  schooling  471)."  However, I have some f i e l d that  feature  s c h o o l i n g may  I o b s e r v e d an  and  laboratory  reduce p r e d a t i o n .  elliptical  school  of  evidence  On 20  several  to  50  guppies moving upstream towards a p o t e n t i a l p r e d a t o r  (large  Aequidens) concealed  the  f r o n t of the movements  near the  shore.  school perceived  (rapid darts  were t r a n s m i t t e d  and  t o the  the  The  predator  surface  who  d i d not Also,  (Rivulus) school  see  r e a r of the  i n the  switching  of guppies;  outdoor pools  the  school.  fish  do  an  isolated  It  is particularly  their  attack  fixated  and  predator centre may  of a school.  wait  strike  an  a  fleeing  been seen i n  Hoplias  i n a school  or C r e n i c i c h l a .  school  wander t o o  periphery  inhibited  In t h e  eye  are  effect").  movements  of guppies.  f a r are  attacking  ("confusion  r e v e a l i n g to watch the  a p p e a r s t o be  the  predators  behind  same phenomenon has  t h a n one  i f they  shore)  the  a p p e a r t o have l e s s d i f f i c u l t y  away f r o m t h e  evasive  advantageous to  course  a C r e n i c i c h l a l u r k i n g near a school that dart  Thus  I have o b s e r v e d  c o n t a i n i n g g u p p i e s and  These p r e d a t o r s  their  predator.  field  the  and  s k i m away f r o m t h e  a d v a n c e w a r n i n g o f p o t e n t i a l d a n g e r was fish  guppies at  of  Guppies  quickly  often attacked.  from d a r t i n g i n t o  The  the  l a b o r a t o r y a hungry C r e n i c i c h l a  f o r hours before  an  unwary guppy.  This  o p p o r t u n e moment a r i s e s t o anecdotal  evidence  suggests  214 that  schooling behavior  functions to increase the perceptual  a w a r e n e s s o f a g r o u p o f g u p p i e s and a l s o s e r v e s the d e c i s i o n - m a k i n g E x p e r i m e n t 6.91  t o thwart  apparatus o f the predator.  Predatory  behavior  Lower A r i p o  o f R i v u l u s exposed t o  and P a r i a  guppies.  Introduction If the  risk  a well-developed  of predation,  then  r e l a t i v e m o r t a l i t y than stocks  s c h o o l i n g r e s p o n s e does Paria fish  Lower A r i p o  a r e exposed t o a p r e d a t o r .  a l r e a d y b e e n done f o r w i l d - c a u g h t laboratory behavior  stocks  (Table  was r e c o r d e d  greater mortality. Lower A r i p o  series  f i s h when g r o u p s o f b o t h T h i s experiment has  guppies  22 C) b u t i n b o t h  and P a r i a s t o c k s d i f f e r  ( T a b l e 21 A) and e x p e r i m e n t s no  revealed,  i n many ways o t h e r  than  E v e n when s c h o o l i n g i s i m p o s s i b l e guppies are l e s s v u l n e r a b l e  Thus s c h o o l i n g b e h a v i o r  responsible  greater  s o i t i s n o t known why P a r i a s u f f e r e d  6 . 7 ) , Lower A r i p o  Paria.  suffer  As s u b s e q u e n t e x p e r i m e n t s have  schooling behavior. (Exp.  should  reduce  f o r the s u r v i v a l  than  p e r s e may n o t have b e e n  trends  observed  in.the- o r i g i n a l  of experiments. To  check t h i s  I made d i r e c t  observations  a t t a c k i n g m i x e d g r o u p s o f P a r i a and Lower A r i p o  of Rivulus guppies.  Methods Two R i v u l u s 40  liter  of approximately  70 mm were p l a c e d  a q u a r i u m and s t a r v e d f o r 24 h r .  in a  F i v e P a r i a and  215 5 Lower A r i p o m a l e g u p p i e s o f e q u a l t a n k and t h e f r e q u e n c y were r e c o r d e d T h i s was  o f a p p r o a c h e s , a t t a c k s , and  i n the standard  replicated  5 times,  starvation period. second o r t h i r d  s i z e were added t o t h i s  manner  captures  (test duration  1  e a c h t e s t p r e c e d e d by a 24 h r  A l l g u p p i e s were p r e d a t o r - n a i v e  generation  hour).  laboratory  and  stock.  Results When t h e 2 s t o c k s the in  predators'  tank, they  the centre.  At f i r s t  o f g u p p i e s were f i r s t formed a l o o s e  their  effect"  was  u s u a l l y without  clearly  a p p r o a c h e s f r o m one p r e y  Rivulus  collective  school  t h e h u n g r y R i v u l u s were o b s e r v e d t o  dash w i l d l y i n t o the s c h o o l "confusion  added t o  success.  The  s e e n as t h e p r e d a t o r s t o the next.  shifted  Sometimes a  d i d a p p e a r t o g e t a " f i x " on one guppy and w o u l d  chase i t i n c e s s a n t l y , q u i t e o b l i v i o u s of the o t h e r  guppies  t h a t would appear i n i t s path. Eventually  the Rivulus  school but remained The  fish  ceased d a r t i n g i n t o the  some d i s t a n c e  away n e a r t h e b o t t o m .  t h a t were a p p r o a c h e d and a t t a c k e d  ones t h a t d r o p p e d o u t o f t h e s c h o o l ; were P a r i a g u p p i e s .  This  o f a p p r o a c h e s and a t t a c k s (Figure  25).  of attacks  s u g g e s t s Lower A r i p o the  predators  i n most c a s e s  i s reflected  i s greater  these  i n the greater  d i r e c t e d towards P a r i a  Because t h e stock  (contacts)  were u s u a l l y t h e  number  fish  d i f f e r e n c e i n the percentage than i n approaches, i t  g u p p i e s were a l s o b e t t e r a t e l u d i n g  ( c f . Exp. 6 . 7 ) .  216a  FIGURE 25.  Predatory behavior of Rivulus e q u a l numbers o f P a r i a guppies  (laboratory  exposed t o  and Lower  stock).  each histogram a r e the a c t u a l  Aripo  V a l u e s above scores.  216  PARIA  1 0 Q  _  10090807060-  o  <  5040-  <  302010 0 -  LOWER A R I P o |  b  217  It  i s concluded  vulnerability measure o f  of guppies to f i s h  i t s efficacy  tendency t o s c h o o l also  serve  significance  A precise the  to other behavioral t r a i t s  that  predation.  chapter  adaptive  role  and  The  I have a t t e m p t e d  of natural v a r i a t i o n  certain populations  selection  the  and g e n e r a l d i s c u s s i o n o f v a r i a t i o n i n behavior  In t h i s  the  predators.  reduces  i s d i f f i c u l t to o b t a i n because  i s linked  to reduce  Conclusion geographic  of  that schooling behavior  of  the  i n the  guppy.  to determine escape  the  responses  I have a l s o  evaluated  of population d i f f e r e n c e s i n habitat  schooling  behavior.  f i e l d observations  revealed, a c l o s e  correlation  between t h e d e v e l o p m e n t o f presumed a n t i p r e d a t o r  behavior  and  fish.  the  distribution  Predation that  and  abundance o f p r e d a c e o u s  experiments with wild-caught  samples o f g u p p i e s taken  characid ficant  and  cichlid  survival  populations  (Lower A r i p o )  had  a  a d v a n t a g e when t e s t e d a g a i n s t one  Upper A r i p o , P a r i a ) .  relative  demonstrated,  from a stream i n f e s t e d  predators  exposed to only  conducted with  fish  Rivulus h a r t i i  S i n c e most o f t h e s e  was  certainly  signiof  (Petite  several  Curucaye,  e x p e r i m e n t s were  f e m a l e g u p p i e s o f c o m p a r a b l e body  vulnerability  with  size,  b a s e d upon b e h a v i o r a l  differences. In a d d i t i o n , t e s t s w i t h Aripo  females  suggested  Petite  C u r u c a y e and  that differences i n  relative  Upper  218 vulnerability  e x i s t e v e n between p o p u l a t i o n s  same p r e d a t o r . predators given  seems t o be  related  (and h e n c e presumed p r e d a t i o n  stream.  C u r u c a y e and is  This  probably  exposed to  t o the  abundance  intensity)  g r e a t e r than  (major w a t e r f a l l  ( i s o l a t i o n by  between Upper and  b a r r i e r ) , these  Lower  r e s u l t s may  Tests  a p o p u l a t i o n exposed t o i n t e n s e R i v u l u s  but  completely  cichlids will alone  can  Petite  that  isolated be  Curucaye  been b r e d  and  stocks,  predation  i f Rivulus  and predation  i n t h i s chapter  of  the  B e c a u s e t h e r e was  with wild-caught  and  that selective  f o r the m i c r o e v o l u t i o n  i n predator  avoidance.  naive  good  of behavior  notable  be  demonstrated under c o n d i t i o n s of near t o t a l  survival  closely  provided,  paralleled  is  been supported.  importance  the  l i g h t was  taken  laboratory  of  When dim  had  agreement  p r e d a t i o n has  With the  Curucaye stock,  was  of guppies t h a t  u n d e r i d e n t i c a l c o n d i t i o n s were  predators.  tests  Petite  predation.  characids  These experiments a l s o r e v e a l e d the light  have  behavioral characteristics  laboratory populations  the h y p o t h e s i s  responsible  only)  population.  reared  n o n - r a n d o m l y by between t h e  f o r the  to e s t a b l i s h  most s i g n i f i c a n t f i n d i n g  samples o f  to Rivulus  from streams w i t h  necessary  account  The  l o c a l adaptations  a  Aripo  not  reflected  of  Petite  distance  entirely on  within  B e c a u s e . t h e r a t e o f gene f l o w between Santa Cruz R i v e r s  the  of  exception  selective predation could  h o w e v e r , ( T a b l e 22 the  results  of  not  darkness. B)  relative  experiments  219 conducted under b r i g h t i l l u m i n a t i o n reason(s)  f o r the superior s u r v i v a l  guppies under dark o r dim l i g h t is  tempting  to speculate  light-sensitive is  visual  of Petite  that this  apparatus.  o f an a d e q u a t e  A comparative vision tive  using  study  the technique  Curucaye  p o p u l a t i o n h a s a more I hypothesize  this  i n a confined  refuge.  o f the lower l i m i t s o f Lang  that  of scotopic  (1967) m i g h t be  informa-  (Lang's d o m e s t i c g u p p i e s h a d a l o w e r s c o t o p i c l i m i t o f  7 x 10  —6  together King,  l u x , compared t o m a n ' s . l o w e r l i m i t with  tory  an a n a t o m i c a l  investigation  stocks  experiments establishing  discovery of survival  samples  initiated  a series  ( c f . Werner, 1969;  of detailed  aimed a t q u a l i t a t i v e l y  distinct  from each o f the 5 stocks  stocks  of the behavior probably  and q u a n t i t a t i v e l y  (least  on i n d e p e n d e n t  Lower A r i p o and P a r i a a r e t h e 2 most overlap).  I have a r g u e d t h a t much  o f Lower A r i p o g u p p i e s  many o t h e r s )  vulnerability  O v e r a l l there  (Table 27).  has e v o l v e d  p r e d a t i o n b y c h a r a c i d and c i c h l i d  relative  behavioral  t h e d i f f e r e n c e s among s t o c k s .  Behaviorally,  (Exp.  —7 lux),  d i f f e r e n c e s among l a b o r a -  good c o n c o r d a n c e among m e a s u r e s t a k e n  tive  o f 7 x 10  1970). The  and  The  c o n d i t i o n s i s unknown b u t i t  a c o n s e q u e n c e o f s e l e c t i o n by R i v u l u s  environment devoid  is  (Exp. 6.1 and 6 . 7 ) .  o f Lower A r i p o  6.1, 6.2, 6.7) c l e a r l y  (and a l s o Guayamare i n response t o s e l e c fish. fish  illustrates  The low  to predators  the s u r v i v a l  value  220  TABLE 27.  Behavioral  Concordance o f b e h a v i o r a l measures taken on 5 s t o c k s o f g u p p i e s . F o r each e x p e r i ment t h e mean s c o r e s a r e r a n k e d f r o m greatest to least. The e x p e r i m e n t number i s given i n brackets.  measurement  LA  Guay  Stock PCur.  UA  Par  Depth p r e f e r e n c e  (6.3)  a  1  2  3  4  5  Shore p r e f e r e n c e  (6.4)^  1  4  3  2  5  Reaction  d i s t a n c e (6.5)  1  3  5  2  4  Survival  t i m e (6.7)  1  2  3  4  5  -  2  -  -  1  1  2  3  4  5  5  13  17  16  24  Response t o a e r i a l predator (6.8) c  ci Schooling  behavior  (6.9)  Sum o f r a n k s Mean - 15  K e n d a l l W = 0.76; s = 1 9 0 ; •k = 5; p < .01 a  based  at Test A  on T a b l e  b a s e d on mean number o f o b s e r v a t i o n s (refer to F i g . 20).  °omitted d  2 3A.  based  from c a l c u l a t i o n  i n section 4  o f concordance.  on mean o f T e s t A a n d B  (refer t o F i g . 24).  221 of  the b e h a v i o r a l d i f f e r e n c e s . For  predators  i s virtually  predators, results  the P a r i a population,  this  absent.  t h e t h r e a t from  fish  In a l l t e s t s w i t h  real  s t o c k was t h e most v u l n e r a b l e .  are attributable  i n part to a high  inappropriate microhabitat away f r o m s h o r e ) ,  selection  predation, an  I suggest  dispersed  superior adaptation tors be  most e f f e c t i v e l y  there  f o r these  real  aerial  predators,  The  preda-  hypothesis  predator  t o the "predator  response of P e t i t e Curucaye  o f Exp. 6.9).  water.  preferably i n situ.  l o n g r e a c t i o n d i s t a n c e o f Upper A r i p o  schooling  from  which  that this  showing i n t e r m e d i a t e  are several exceptions  serve  fish to  some s a f e t y  i n shallow  i s speculative; i t i s essential  tested with  does  o f P a r i a guppies t o non-aquatic  In t h e s t o c k s  the  The t e n d e n c y  deep w a t e r ,  unadapted t o f i s h  such as k i n g f i s h e r s and b a t s  presumably operate  threshold,  behavior.  t h a t some o f t h e i r b e h a v i o r  i n deep w a t e r may o f f e r  a e r i a l predators  escape  and t h e a b s e n c e o f s c h o o l i n g  antipredator function.  live  These  ( i n o r over  Though P a r i a g u p p i e s a r e c l e a r l y  fish  hypothesis":  g u p p i e s ,.and t h e  (at l e a s t  I have a l r e a d y d i s c u s s e d  avoidance,  i n test A  the question o f  r e a c t i o n d i s t a n c e e l s e w h e r e and e m p h a s i z e d  that  antipredator  behavior  must a l w a y s be v i e w e d w i t h i n t h e framework o f t h e  physical  environment.  there  In very  small or turbid  i s no avenue f o r s e l e c t i o n  t o operate  at great d i s t a n c e s — a q u a t i c predators  appear  streams  f o r avoidance suddenly  at a  222 close  range.  selection  The  of a p r e d a t o r - f r e e m i c r o h a b i t a t  the e f f e c t i v e surface  b e s t s t r a t e g y f o r e s c a p e must be  skim  use and  s e v e r a l m e a s u r e s as  Clearly,  an e s t i m a t e  antipredator behavior. alone and  i s used,  the  I suggest  share  tors occur  attack.  Olson,  suggests  t h a t both  on  1  for pelagic fish  the  predator  adaptive  guppies  s i m p l y by  reducing  a prey  be  (Croze,  1970).  not  My  and  the  guppies  aware o f  o f s c h o o l i n g more  t h e d e s c r i p t i o n s o f M a n t e i f e l ' and  the  (Brock  A t Lower A r i p o ,  p r e y may  preda-  i t is unlikely  predators, or t e r r e s t r i a l  significance  i n a school  potential  concentrations of and  fish  Because f i s h  searching i s probably  f o r concealed prey  parallel  a s i n g l e prey  metres of stream,  of C r e n i c i c h l a n e a r  o t h e r ' s whereabouts;  counteradaptation  awareness o f  1964).  respectively.  an a n t i p r e d a t o r  as a  of. a p r e d a t o r e n c o u n t e r i n g 1960;  Curucaye  laboratory observations  environment.  presence  hunting  of P e t i t e  Furthermore,  few  distance  underestimated,  operates  s c h o o l i n g p r o t e c t s guppies  Riffenburgh,  as  in  and  of v i s u a l  surrounding  along every  probability  of p o p u l a t i o n d i f f e r e n c e s  strategy of f i x a t i n g an  dart, on  and  Field  or  to r e l y  that schooling i s also  a g r e a t e r sphere  danger i n the  that  over  that this behavior  moments b e f o r e  i t i s important  actual vulnerability  mechanism i n t h e guppy.  to a predator's  (e.g. r a p i d  F o r example, i f r e a c t i o n  Upper A r i p o w o u l d be  indicated  ( i f available)  o f escape motor p a t t e r n s jump).  the  as  each  important  predators observations closely  Radakov  (1961),  223  Eibl-Eibesfeldt  (1962), and Hobson  (1968).  Though numerous w o r k e r s have documented d i f f e r e n c e s in  the antipredator  behavior  of closely related  species  ( C r a n e , 1952; C u l l e n , 1957; H o o g l a n d e t a l , 1957; Hoar, 1958;  H a i l m a n , 1965; B e n z i e ,  1969;  Curio,  graphic  1969; B a k e r , 1 9 7 0 ) , a d e t a i l e d s t u d y o f g e o -  (i.e. intraspecific)  behavior fish). ences  1965; H e a t w o l e , 1968; R o b i n s o n ,  variation i n antipredator  has n o t been c a r r i e d o u t p r e v i o u s l y Furthermore,  i n some r e p o r t s  (e.g. W i l l i a m s o n ,  differences  of geographic  1952) a g e n e t i c  has n o t been e s t a b l i s h e d .  t o e s c a p e may v a r y  within  basis Since  the l i f e t i m e  by p r e d a t o r s ,  c o n d u c t some b r e e d i n g history  have b e e n d e s c r i b e d work on f i s h  the tendency  and d i r e c t  experi-  i t i s usually necessary to  experiments  and c o n t r o l t h e p r i o r  difference distance)  differences i n antipredator f o r several species.  has c e n t e r e d  (Gasterosteidae).  McPhail  of the larvae  stickleback.  carnivorous  fish,  an  innate  (including reaction  (taxonbmic s t a t u s  He r e l a t e d t h i s  presence o r absence o f d i f f e r e n t i a l a small  family  (1969) d i s c o v e r e d  o f 2 forms  adaptations  Much o f t h e r e c e n t  on t h e s t i c k l e b a c k  between t h e e s c a p e r e s p o n s e s  of threespine  by  f o r the  o f the o f f s p r i n g . Population  the  differ-  o f an i n d i v i d u a l as  a consequence o f m a t u r a t i o n , h a b i t u a t i o n , ence o f a t t a c k s  (at l e a s t i n  Novumbra  unclear)  difference to  s e l e c t i o n on f r y hubbsi.  224 Moodie Charlotte trout)  (cf.  Islands,  has  pelagic  (1972a, 1972b) a r g u e d t h a t on selective predation  been r e s p o n s i b l e  race  of  McPhail,  large,  1969;  long-spined  Semler,  In a l a b o r a t o r y cutthroat  f o r the  samples o f  study of  actually of  the  If  this  be  (see  i s confirmed,  polymorphism r a t h e r I have d e s c r i b e d Little the  of  S p a n i s h and  owl  with  latter.  of  the  This  Spanish  subspecies of  and  (unpubl.).""... population less may  lateral  plates  Gilbertson,  example o f  1972).  behavioral  d i f f e r e n c e of  the  type  geographic v a r i a t i o n i n  animals.  of  the  mobbed b o t h t h e  since  Curio  mobbing pied  (1961)  behavior  flycatcher.  redbacked  shrike  Spanish population  difference coincides  these predators  Johnson  an  b e e n done on  ( S t r i x a l u c o ) whereas t h e  the  aculeatus  guppy.  German p o p u l a t i o n s  the  bution  number o f  d i f f e r e n c e s between t h e  German p o p u l a t i o n  "black"  difference i n behavior  than a p o p u l a t i o n  The  only  f r o m one  behavior of other  racial  of a  were c o n s e q u e n t l y  i t w o u l d be  work has  cutthroat  squawfish  Hagen  a l s o Hagen and  f o r the  antipredator  described  s e l e c t i o n by  and  c o r r e l a t e d w i t h the  stickleback  by  Gasterosteus  sticklebacks  However, t h i s  Queen  1971).  remained i n a s h e l t e r longer vulnerable.  (mainly  evolution  t r o u t , M o o d i e , M c P h a i l , and  found t h a t  the  the  shrike  with the i s not  and  mobbed distri-  sympatric  population. (1970) f o u n d t h a t  the  lizard  2 geographically  isolated  S c e l o p o r u s o c c i d e n t a l i s showed  225 differences  i n the d i s t a n c e a t which they  a p p r o a c h o f a human " p r e d a t o r " . shortest reaction coloured.  of anoline l i z a r d s The (including  t h e most  d i f f e r e n c e was f o u n d  by Heatwole  cryptically  between 2 s p e c i e s  (1968).  c o n c l u s i o n t h a t c a n be drawn f r o m the present  diversifying  these  level  a quantitative in behavior.  this  or (less  diversity  i s usually  Behavioral differences  spines, protective  expressed  it  to visible  i s very d i f f i c u l t  as c r y p t i c  armour, e t c .  guppy t o a p r e d a t o r with  females  morphological  to predict  or  I n t h e guppy, are less  of a  (of course  I suspect that there are variation  t h a t have r e m a i n e d u n d i s c o v e r e d  no m o r p h o l o g i c a l  aposematic  differences, i.e.  s i m p l y by i t s c o l o r a t i o n  many o t h e r e x a m p l e s o f g e o g r a p h i c behavior  difference  the responsiveness  i ti s impossible).  as  are often linked to  however, m i c r o e v o l u t i o n a r y c h a n g e s i n b e h a v i o r related  At the  commonly) a q u a l i t a t i v e  o t h e r a n t i p r e d a t o r mechanisms s u c h  easily  studies  one) i s t h a t p r e d a t i o n c a n be a  force i n the evolution of behavior.  intraspecific  coloration,  at the  The s u b s p e c i e s w i t h t h e  d i s t a n c e was a l s o  A similar  fled  i n antipredator  because t h e r e a r e  clues to population d i f f e r e n t i a t i o n .  For  example, h a d t h e guppy b e e n a monomorphic s p e c i e s o v e r i t s entire  geographic  been i n i t i a t e d  range,  the present  i n the f i r s t  study might never  place.  P r e d a t i o n may a l s o have e f f e c t s directly  related  have  t o predator avoidance  on b e h a v i o r n o t (Cullen,  1957; W i l z ,  226 1971;  Ballin,  1973).  This  i s not  s u r p r i s i n g because  t o r a v o i d a n c e o f t e n n e c e s s i t a t e s a m a j o r change i n ecological late  niche  of a population.  preda-  the  I t i s tempting to  t h a t i n t h i s manner p r e d a t i o n  may  result  in  specu-  incipient  speciation. Ballin's regard  b e c a u s e he  females of respond  the  has  discovered  support  to t h e i r  f o r the  females p r e f e r the  m a l e s , he  are  inferred  own  very, i m p o r t a n t  a tendency  P a r i a , Upper A r i p o ,  selectively  f o u n d no that  (1973) r e s u l t s  and  virgin  Because  (Haskins  humanly more  this  Guayamare s t o c k s  males.  hypothesis  for  in  to  Ballin  et a l ,  1961)  conspicuously-colored  a behavioral basis  for this  interstock  discrimination. In a n o t h e r tative  d i f f e r e n c e s i n the  s h i p and  intermale  differences  are  predator-free  frequency  aggressive  probably  relaxed predation  guppies  s e r i e s of t e s t s B a l l i n  an  pressure.  stream  behavior.  indirect  Some o f  result  quanti-  of  1.  of intense in a  ( e . g . P a r i a , Upper A r i p o )  can  aggressive  or  relatively male time  displays.  6  Natural  c h a r a c i d and  populations cichlid  o f guppies exposed t o  preda-  fish:  (a) a r e more r e s t r i c t e d shore.  court-  these  " a f f o r d " t o spend a l a r g e p r o p o r t i o n o f t h e i r  Summary o f C h a p t e r  stream  intensity  Presumably o n l y  e n g a g e d i n c o n s p i c u o u s c o u r t s h i p and  t i o n by  and  uncovered  to shallow  water near  the  (b) a r e more c o h e s i v e  (show a g r e a t e r t e n d e n c y  to  school), (c)  avoid a potential predator at a greater reaction  distance. (d) show e s c a p e  motor p a t t e r n s a t a lower  alarm  threshold. 2. guppy may  To use  elude a p o t e n t i a l one  fish  o r s e v e r a l o f 6 main escape  These p a t t e r n s appear  t o be  increasing  r a n g i n g from  reactivity  "emergency" b e h a v i o r . observed  p r e d a t o r , an  No  a r r a n g e d on  individual  motor p a t t e r n s .  a scale  of  "precautionary" to  qualitative  differences  i n t h e s e motor p a t t e r n s i n f i s h  taken  were  from  different  populations. 3. avoidance  The  guppies  cichlid  Experiments taken  5.  tory  from a p o p u l a t i o n exposed v u l n e r a b l e than  Experiments  stock) d e r i v e d from in relative  among w i l d - c a u g h t  (Petite Curucaye), the s c o t o p i c v i s i o n  demonstrated  to characid fish  taken  and  from  to Rivulus. with C r e n i c i c h l a  (second t o a p p r o x i m a t e l y  differences found  i n predator  with natural predators  p r e d a t o r s were l e s s  p o p u l a t i o n s exposed  guppies  sensory m o d a l i t y used  i s vision.  4. that  primary  fifth  and p r e d a t o r - n a i v e  generation  labora-  5 natural populations revealed vulnerability specimens.  parallel  With  one  to  those  exception  s t o c k d i f f e r e n c e s were o n l y e v i d e n t when o f g u p p i e s was  not g r e a t l y  impaired  by  228 very  low  light  Curucaye  levels.  I t i s hypothesized that  g u p p i e s have e v o l v e d a more l i g h t - s e n s i t i v e  s y s t e m t o c o n t e n d w i t h n o c t u r n a l p r e d a t i o n by 6.  Paria  stock p r e f e r r e d  o f a deep a q u a r i u m Upper A r i p o , tendency  7.  Rivulus.  s i g n i f i c a n t l y more t h a n Lower  Guayamare, and P e t i t e  more t i m e n e a r t h e Lower A r i p o  Curucaye.  bottom  Aripo,  T h e r e was  stocks to  a  spend  surface.  and P a r i a  m i c r o e n v i r o n m e n t s when p l a c e d  visual  t o remain near the  f o r Guayamare and Lower A r i p o  relatively  The  Petite  stocks  selected  i n a simulated  former tended t o remain c l o s e r  different  shore  t o s h o r e and  gradient.  the  latter  away f r o m s h o r e . 8.  The mean r e a c t i o n d i s t a n c e o f t h e 5 s t o c k s  g u p p i e s t o a m o t i o n l e s s , dead order),  Lower A r i p o > U p p e r  Curucaye.  When t h e  C r e n i c i c h l a was  of  ( i n rank  Aripo>Guayamare>Paria>Petite  " p r e d a t o r " was  animated,  the  reaction  d i s t a n c e d o u b l e d f o r a l l 5 s t o c k s , however, t h e same r a n k order  persisted. 9.  When Lower A r i p o ,  s t o c k s were e x p o s e d  t o a m o t i o n l e s s , dead  modal e s c a p e m o t o r p a t t e r n was Curucaye  and P a r i a  Guayamare, and Upper  Crenicichla,  avoidance d r i f t ;  s t o c k s t h e modal p a t t e r n was  weak  The m o t i o n l e s s p r e d a t o r e l i c i t e d  response  of P e t i t e Curucaye  The  a d d i t i o n o f motion  and  12%  t o the p r e d a t o r evoked  r e a c t i v e escape motor p a t t e r n  the  for Petite  avoidance d r i f t . f r o m 20%  Aripo  no  of Paria  fish.  a more  from the m a j o r i t y  o f Lower  229 Aripo,  Guayamare, and  effect  on  P a r i a and  10.  The  males p l a c e d  Upper A r i p o  P e t i t e Curucaye  survival  with  fish  time o f  but  the  time.  5 stocks  individual  a h u n g r y R i v u l u s was  S u r v i v a l t i m e was  frequency  of r a p i d d a r t s  11. sive  t e s t e d , P a r i a was  The  to a simulated 12.  significantly  school  were l e s s this  t h a n Upper A r i p o after  d i s p e r s i o n was  Guayamare  predator  Field  decision-making  effect").  because the  in  the  respon-  Guayamare.  Guayamare, and  Petite  e n v i r o n m e n t i n a more A l l stocks  a 5-hour e x p l o r a t i o n p e r i o d  laboratory observations  functions to increase  but  and  the  differences i n schooling  which a l s o serve  as  I c o n c l u d e , t h a t much o f t h e  antipredator behavior  to  i s c a u s e d by  thwart  ("confusion survival behavior  i s l i n k e d to other  antipredator  that  perceptual  predator  to demonstrate the  tendency to school  suggested  a l s o serves  mechanisms o f t h e  It is difficult  of population  14.  than  more  or P a r i a f i s h .  a w a r e n e s s o f a g r o u p o f g u p p i e s and  traits  shortest  l e s s p r o n o u n c e d i n Lower A r i p o  and  schooling behavior  value  P a r i a males.  fish.  13.  the  greater  jumps.  swam a b o u t a s t r a n g e  cohesive  and  significantly  G r o u p s o f Lower A r i p o ,  Curucaye guppies cohesive  aerial  Aripo  c o r r e l a t e d with  surface  P a r i a s t o c k was  Lower  caught i n the  positively and  a lesser  stock.  t h a n t h a t o f P e t i t e C u r u c a y e , Upper A r i p o , Of  had  behavioral  mechanisms. geographic  genetic  variation  differences  230 t h a t have e v o l v e d pressures. and  i n response  to d i f f e r e n t i a l  I t a p p e a r s t h a t i n some c a s e s  Guayamare v s .  Petite  Curucaye) these  b e h a v i o r a l d i f f e r e n c e s are maintained barrier  t o gene  flow.  predation  ( e . g . Lower  Aripo  microevolutionary  without  a major  CHAPTER 7  GENERAL DISCUSSION AND  CONCLUSIONS  Organic d i v e r s i t y i s impressive, wonderful, f a s c i n a t i n g , o r e x a s p e r a t i n g , a c c o r d i n g t o o n e ' s t a s t e s and tempera-^ ment. Does i t have some b i o l o g i c a l f u n c t i o n and meaning? (Dobzhansky, 1970: 24) The findings  purpose  of this thesis.  where a d d i t i o n a l this  study  unpubl.;  broad  I shall also  i s the f i r s t  variation  guppies,  background  The  the major the areas  r e s e a r c h m i g h t be most p r o d u c t i v e . of a series  ( L i l e y and  i n the behavior  i t was n e c e s s a r y f o r f u t u r e work.  a s p e c t s have b e e n i n v e s t i g a t e d left  indicate  B a l l i n , 1973; L i l e y , u n p u b l . ) c o n c e r n e d  geographic Trinidad  o f t h i s chapter i s t o review  Because  Seghers, with  and m o r p h o l o g y o f  to provide a s u f f i c i e n t l y Consequently  intensively  o n l y a few  and many  questions  unanswered.  Environment In C h a p t e r  environment natural  o f t h e guppy w i t h  history,  special  r e f e r e n c e t o the  d i v e r s i t y , and d i s c o n t i n u o u s d i s t r i b u t i o n  of  potential  to  gene m i g r a t i o n .  Crenicichla  3 I d e s c r i b e d t h e b i o t i c and a b i o t i c  p r e d a t o r s , and t h e m a j o r and m i n o r I concluded  a l t a , Astyanax  that  Hoplias malabaricus,  bimaculatus, 231  barriers  and R i v u l u s  hartii  232 are  t h e most i m p o r t a n t  Because the  present-day  distribution  the  distribution  provided  a unique o p p o r t u n i t y variation  Field a wealth  of t h i s  observations  t h e s i s was  predators.  is likely  Coloration The the is  and  the  primary  tion  and  sexual  t h e s i s was  the  concern  differences  of h a b i t a t s  to t e s t  be  obtained related  for  in part  I feel  that  indicator  of a  micros  pressures  to  re-evaluate  in coloration  imposed by that this  predahypo-  satisfactorily.  to understand  and  was  by  aspect/,  I discovered  significance  of  quantifying variation  in  of populations  (Liley  this  selection  v i z . that variation  i n c o l o r a t i o n by  colour patterns  object  ( i f any)  o f C h a p t e r 4 was  conflicting  difficult  The  ratio  selection.  I attempted  this  ratio,  predation,  "Haskins h y p o t h e s i s " , g o v e r n e d by  t h i s may  t h e most s e n s i t i v e  sex  sex  of guppies.  to d i f f e r e n t i a l  e x p e n d e d on  response to  quickly revealed  i n the  most c o n c l u s i v e e v i d e n c e  greater effort  over^  adaptations.  t o what e x t e n t  Although  does n o t  for potential  collections  behavior  attributable  The  evolutionary  and  to assess  behavioral variation.  behavior  to search  and  guppy.  other predators, i t  of i n t e r p o p u l a t i o n d i v e r s i t y  v a r i a t i o n was  to the  of the  i n antipredator  c o l o r a t i o n , body s i z e ,  of the  of Rivulus normally  lap with  geographic  predators  the  living  in a diverse  S e g h e r s , u n p u b l . ) and  by  the  range  studying  233 t h e mechanisms r e s p o n s i b l e Extreme d e p a r t u r e s  from a t h e o r e t i c a l  r a t i o were c o r r e l a t e d w i t h of Rivulus. ratios  differences sex  Laboratory  ( i n favour  f o r sex r a t i o d i f f e r e n c e s , 1:1 M e n d e l i a n s e x  t h e p r e s e n c e o f dense  experiments revealed  populations  that  unbalanced  o f f e m a l e s ) were n o t c a u s e d by g e n e t i c  i n the sex determination  r a t i o s were n o t c o r r e l a t e d w i t h  system. sexual  In a d d i t i o n ,  dimorphism i n  colour. Predation  experiments with  male g u p p i e s were n o t s e l e c t i v e l y adept than females a t a v o i d i n g predation  by R i v u l u s  disadvantage  probably  as w e l l .  Haskins hypothesis  Rivulus attacked  capture.  question  p l a c e s males a t a  adequately,  (1973) c o u l d  I concluded  find  no e v i d e n c e  of  males, the  that  open.  s e x r a t i o s have  on t h e p r o b l e m o f t h e a d a p t i v e  some i n t e r e s t i n g  little  s i g n i f i c a n c e ( i f any)  t h e work i n C h a p t e r 4 d o e s  questions  regarding  There i s a voluminous l i t e r a t u r e  however, most i n v e s t i g a t o r s have j u s t without  i s not a great  f o r conspicuously-colored  of colour p a t t e r n v a r i a t i o n ,  se.  evidence  o f t h e s i g n i f i c a n c e o f g e o g r a p h i c v a r i a t i o n and  Although  raise  selective  the c i r c u m s t a n t i a l  polymorphism i n c o l o r a t i o n i s s t i l l  bearing  less  Though I was u n a b l e t o t e s t t h e  Because B a l l i n  a female p r e f e r e n c e  b u t were  that  Size-selective  s u g g e s t s t h a t t h e c o l o u r o f male g u p p i e s liability.  demonstrated  sex r a t i o s per  on t h i s t o p i c , tabulated  sex r a t i o s  comment, some have o f f e r e d p l a u s i b l e h y p o t h e s e s f o r  234 sex  ratio  test  these ideas.  predation the  d i f f e r e n c e s , but  sex  within  as  an  guppies, but  question  ratio  the  population  (e.g.  s t u d y has  t h i s was  reference  i s what e f f e c t an  d y n a m i c s and rate  of  mating  evolutionary  cerning  g e o g r a p h i c v a r i a t i o n i n the behavior,  the  guppy-Rivulus  For  e x a m p l e , how  fry  and  was  adult  system, are does R i v u l u s  only  extremely  An  unbalanced  the  guppy  on (and  change, c f . G i e s e l ,  r a i s e d i n Chapter 4 sex  differences  possibility worthy of  discrim.ina.te  in  of mimicry  further  con-  in  exploration.  between i t s  own  fry?  striking  g u p p i e s was  treated  (Liley, was  the  determining  size The  of  questions  and  out  variation).  system of  In a d d i t i o n ,  Body  the  to  P e t i t e C u r u c a y e ) has  1972).  guppy  singled  considered  (colour  Tompire T r i b u t a r y ,  perhaps even the  antipredator  have e v e r a t t e m p t e d  important environmental v a r i a b l e  a n a r r o w frame o f  sex  few  S i m i l a r l y , my  r a t i o s of  interesting  very  only  considered  basis  adult  body s i z e .  tions  suggested  that  for population  genetic  body  This  differences  confirmed  topic  if  field  obserya^ probable  this for  even though a s u b s t a n t i a l p o r t i o n  there  i n mean  d i f f e r e n c e s were v e r y  subsequently  size  experiments  underway t o d e t e r m i n e  Nevertheless, preliminary  experiments  populations)  i n C h a p t e r 5.  c u r s o r i l y because c o n t r o l l e d  u n p u b l . ) were s t i l l  a genetic  (Liley's  geographic v a r i a t i o n i n the  of  the  several size  235 d i f f e r e n c e s was environmental significant stream  undoubtedly  differences,  phenotypic  primarily  negative correlation  response  temperature  m i g h t be  (I f o u n d  between body s i z e  a multitude of p o t e n t i a l  selective  responsible for genetic differences  I investigated  o n l y one,  and  evidence  laboratory enjoy  size-selective supported  i n body  predation.  shown t o be  In t h e  laboratory,  an  important  of guppies  mechanisms p r e s u m a b l y  escape  one  Field large  aspect of  size-  o f the p r e d a t o r /  sizes.  additional  interact  to determine  the p r i o r  Under  relative natural  size'-specific  (e.g. the c o n s p i c u o u s n e s s ,  b e h a v i o r of the prey;  as H o p l i a s  f a c t o r determining the  of d i f f e r e n t  c o n d i t i o n s , however, s e v e r a l  vulnerability  size,  the hypothesis t h a t  p r e d a t i o n , the h a n d l i n g e f f i c i e n c y  vulnerability  that  an a d v a n t a g e w i t h r e s p e c t t o R i v u l u s p r e d a t i o n  Crenicichla.  selective was  a  and  factors  b u t a r e more v u l n e r a b l e t o l a r g e p r e d a t o r s s u c h and  to  temperature). Of  guppies  a direct  relative  accessibility,  e x p e r i e n c e and  and  hunger  of the p r e d a t o r ) . Although explanation it  size-selective predation i s a  f o r the e v o l u t i o n of d i f f e r e n c e s  does n o t a d e q u a t e l y e x p l a i n  work w i l l sexual  be  a l l the s i z e  r e q u i r e d on o t h e r s e l e c t i v e  s e l e c t i o n , water v e l o c i t y ,  Antipredator  and  plausible  i n body trends.  factors  such  size, Detailed as  temperature.  behavior  In Chapter  6 I attempted  to assess the  functional  236  and  evolutionary significance  antipredator behavior.  Field  where c h a r a c i d and c i c h l i d were more r e s t r i c t e d  of geographic observations  predators  a potential  g r e a t e r d i s t a n c e , and h a d a l o w e r formulated served  the hypothesis  reflected  differences. with  behavioral  microevolutionary  To t e s t  this  pressure found  my  hypothesis,  geographic  and p r e d a t o r - n a i v e  experiments  (laboratory-  populations.  and t h e d e g r e e o f g e o g r a p h i c  i n the Northern  populations  isolation  Range.  the r e s u l t s  i . e .fish  of these  either  experiments  taken,  supported  o r descended  e x p o s e d t o c h a r a c i d s and c i c h l i d s were  less vulnerable why  traits  encompassed t h e r a n g e o f p r e d a t i o n  (by f i s h ) ,  Overall,  I  ( i . e . genetic)  bred) guppies t h a t o r i g i n a t e d from 5 n a t u r a l These p o p u l a t i o n s  at a  I conducted p r e d a t i o n  samples o f w i l d - c a u g h t  guppies  threshold".  as a n t i p r e d a t o r mechanisms a n d t h a t t h e  variation  that  showed a g r e a t e r  predator  "alarm  that these  revealed  were p r e s e n t ,  t o the stream shore,  tendency t o s c h o o l , avoided  variation i n  than  those  exposed t o R i v u l u s .  some o f t h e p r e d a t o r - n a i v e  from, relatively  To d e t e r m i n e  s t o c k s were t a k e n  randomly,  I compared t h e i r  behavior,  r e a c t i o n d i s t a n c e , and e s c a p e m o t o r p a t t e r n s .  Significant  habitat preferences,  non-  i n t e r s t o c k d i f f e r e n c e s were f o u n d  of t h e measures; g e n e r a l l y , these field in  observations  "competitive"  schooling  for several  were c o n s i s t e n t w i t h t h e  and a l s o t h e p e r f o r m a n c e o f e a c h  predation experiments.  stock  F o r e x a m p l e , Lower  237 Aripo,  one o f t h e l e a s t  vulnerable  t i o n distance t o a standard schooler, tor with the  and r e s p o n d e d vigorous  other  s t o c k s , had a l o n g  "predator",  (on f i r s t  was a  h a n d , t e n d e d t o be l e s s  It apply  cohesive,  (behavior  had a s h o r t e r  tests  falling  Presumably  hypothesis  populations predator  some o f t h i s  and d i r e c t i o n a l  t h e main p u r p o s e o f C h a p t e r 6 was t o t e s t  that behavioral differences,among  o f g u p p i e s a r e h e r i t a b l e and s e r v e  mechanisms, l i t t l e  learning i n predator  that  divergent  can operate.  Although the  stock  a l s o h a s a g e n e t i c b a s i s and f o r m s  raw m a t e r i a l upon w h i c h s t a b i l i z i n g  selection  to  o f any g i v e n  n e a r t h e mean); i n a l l b e h a v i o r  ( P a r i a v s . Lower A r i p o ) ,  intrastock variability  of  individual  t h e r e was some o v e r l a p b e t w e e n e v e n t h e most  stocks  the  predator.  t o s t r e s s that these g e n e r a l i z a t i o n s  to a "typical" scores  on  were more v u l n e r a b l e .  i s important  only  preda-  P a r i a guppies,  r e a c t i o n d i s t a n c e , and r e s p o n d e d w e a k l y t o a Consequently they  cohesive  exposure) t o a r e a l  escape motor p a t t e r n s ,  reac-  a t t e n t i o n was g i v e n  avoidance.  1941;  Hinde,  1960;  Veselov,  as a n t i to the r o l e  I t i s w e l l - k n o w n , however,  t h e t e n d e n c y t o show a n t i p r e d a t o r b e h a v i o r  some d e g r e e on e x p e r i e n t i a l  natural  factors  i s dependent  ( N i c e and T e r P e l k w y k ,  1954; S c h l e i d t , 1961; M e l z a c k , 1961; G e o r g e , 1964; Popov, 1953, c i t e d  Radakov, 1961; B e n z i e ,  1965; C u r i o ,  i n M a n t e i f e l ' and  1969; P i l l ,  Though l e a r n i n g u n d o u b t e d l y o c c u r r e d  1972).  during the  238 course that  o f my  the  long-term  T h i s may  not  P e t i t e Curucaye f i s h  be  correct.  tended  Lower A r i p o and reactive  a few  were t h e  In Exp.  Also  i n Exp.  for surface  occur  at present,  but  jumps, e t c . )  than  Paria  might r e f l e c t  between p o p u l a t i o n s  i n view of  of  s t u d i e s on,  Wahlsten,  domestic r a t populations  1972),  to a r t i f i c i a l  (c) d i f f e r e n c e s between s p e c i e s o f experience  with  a predator  (Wodinsky e t a l , 1962)  tioning  and  habituation to predators.  gations  of h a b i t u a t i o n  in their  such  i s unknown differ-  rats  (Collins,  (b) r e s p o n s e s  of  f o r high  (Bignami,  1965)  effect  or other  and of  stimuli  r a t e s of avoidance  (Russell,  (Werboff and  Lloyd,  u s i n g domestic guppies but  a realistic  stock  i t seems a t l e a s t p o s s i b l e t h a t guppy  may  out  the  strain  i n the  1965)  populations  conditioning  differ  (Benzie,  fish  in  Whether  selection  r a t e s of avoidance c o n d i t i o n i n g  more  guppies.  fish  (a)  than  Crenicichla,  different  e n c e s i n a v o i d a n c e c o n d i t i o n i n g i n m i c e and B o v e t e t a l , 1969;  of  i t  decrease  genotype) x environment i n t e r a c t i o n s .  low  6.2,  Guayamare g u p p i e s became r e l a t i v e l y  differences  and  schools  hours of exposure to a  These o b s e r v a t i o n s  1964;  same between  6.9  ( i n c r e a s e i n r e a c t i o n d i s t a n c e and  threshold  assumed  t o d i s s o c i a t e more r a p i d l y  Lower A r i p o o r Guayamare.  appeared t h a t a f t e r  (i.e.  I implicitly  r a t e s o f change i n b e h a v i o r  stocks.  either  experiments,  predator-prey  Preliminary  1967a) and 1963)  investi-  avoidance  have b e e n  not w i t h i n the  system.  condi-  carried  framework  Perhaps these  of  techniques  239 c o u l d be m o d i f i e d  f o r a comparative  u s i n g more n a t u r a l " p r e d a t o r " change i n b e h a v i o r One  stimuli  known t o be  and  temporal  heterogeneity  (Appendix, T a b l e s  composition,  way  1 and  known  2).  light  to occur  may  antipredator behavior  specifically,  t h e y may  and  the  p l a y an  tests.  For  tively  expected  pressure  alone.  However, t h e s e  when i t i s known t h a t t h e s e turbid  and  Suggestions  very  notably  substrate of other  important  role  fish  i n the More  anomalous  results  C u r u c a y e s t o c k was on  the b a s i s of  results  are  less  relapredation  surprising  respectively,  small.  completion  I hope t h e  f u r t h e r work on 1.  factors,  presence  streams a r e ,  of t h i s  causation of i n t r a s p e c i f i c  o n l y begun.  nature  for future research  With the the  spatial  example-, t h e mean r e a c t i o n  Petite  I had  I  "simpli-  contributes to s u r v i v a l .  d i s t a n c e o f Guayamare and s h o r t e r than  in  turbidity,  e x p l a i n some o f t h e  in certain  in a  o f much o f t h e  Some o f t h e s e  intensity,  (non-predators),  I obtained  quantifying a  primarily  morphometry, w a t e r v e l o c i t y ,  species  and  o f t h e m a j o r w e a k n e s s e s o f t h i s work i s t h a t  l a b o r a t o r y environment devoid  stream  o f l e a r n i n g by  adaptive.  have s t u d i e d a n t i p r e d a t o r b e h a v i o r fied"  study  For  this  thesis,  variation  the  analysis of  i n guppies  f o l l o w i n g suggestions  may  has  stimulate  topic.  each o f the p r i n c i p a l  populations of  guppies,  240 "predation pressure" p r e d a t i o n on g u p p i e s )  ( i . e . p r e d a t o r biomass x frequency o f s h o u l d be e s t i m a t e d  This w i l l  r e q u i r e an i n t e n s i v e  suspected  a e r i a l predators)  sampling  quantitatively.  program  t o be c a r r i e d  (including  out i n a l l  seasons. 2.  The s u r v i v a l  value of behavior  s t r a t e d by t r a n s p l a n t experiments  i n the f i e l d .  answer some o f t h e q u e s t i o n s c o n c e r n i n g i n predator avoidance antipredator 3. scale  the role  of suggestion  2, s e v e r a l l a r g e c o u l d be  The s t r e a m s f l o w i n g o f f t h e n o r t h e r n  the Northern  Range  (e.g. P a r i a , Marianne, Yarra)  o f c h a r a c i d s and c i c h l i d s  (see F i g u r e 3 ) ,  c o n d i t i o n s f o r such  A s t y a n a x a p p e a r t o be i d e a l . t o stock the P a r i a  t i o n o f males,  A revealing  changes  experiment  and s c h o o l i n g b e h a v i o r ,  meters such  and m o n i t o r t h e  (c) body s i z e ,  (d) a n t i reaction  (e) c o u r t s h i p a n d a g g r e s -  1 9 7 3 ) , and ( f ) p o p u l a t i o n p a r a -  a s age s t r u c t u r e and f e c u n d i t y ,  A parallel-flowing Crenicichla  would  ( i f any) i n (a) t h e c o l o r a -  (b) t h e s e x r a t i o ,  (cf. B a l l i n ,  are devoid  Nevertheless the  predator b e h a v i o r — e s p e c i a l l y habitat selection,  sive behavior  face of  s p e c i e s as C r e n i c i c h l a and  R. w i t h C r e n i c i c h l a  i m m e d i a t e and l o n g - t e r m  distance,  of l i g h t  adaptations.  (and l o n g - t e r m ! ) t r a n s p l a n t e x p e r i m e n t s  ecological  T h i s might  and t h e e x i s t e n c e o f p r e d a t o r - s p e c i f i c  As an e x p a n s i o n  conducted.  be  s h o u l d be demon-  stream  (Yarra) a l s o d e v o i d o f  c o u l d serve as a c o n t r o l .  (The c o l o u r p a t t e r n s  241  [Liley  and S e g h e r s , u n p u b l . ] and a n t i p r e d a t o r  [personal observations] similar  to Paria.)  o f guppies  If, after  i n this  behavior  stream a r e very  the i n t r o d u c t i o n of C r e n i c i c h l a ,  P a r i a g u p p i e s t e n d e d t o c o n v e r g e t o w a r d s a Lower A r i p o type,  t h i s w o u l d be c o n v i n c i n g p r o o f  piscivore  i n natural  of the e f f i c a c y  pheno-  of a  selection.  A n o t h e r r e v e a l i n g e x p e r i m e n t w o u l d be t o s t o c k small  stream devoid  of fish  north  coast of Trinidad) with  a  (there are s e v e r a l along the a founder  population  A r i p o g u p p i e s and m o n i t o r t h e same m o r p h o l o g i c a l  o f Lower  and  b e h a v i o r a l p a r a m e t e r s as above. With a n a t u r a l g e n e r a t i o n suspect  that over  opportunity concealed  s e v e r a l years  (through  variation  t i m e o f 3-4 months, I  t h e r e w o u l d be ample  segregation  and r e c o m b i n a t i o n )  for  t o be r e l e a s e d and e x p o s e d t o new  selection pressures,  v i z . relaxed or intensified  predation.  Mather  (1970) h a s s t a t e d t h a t i t i s n o t uncommon i n a r t i -  ficial  selection  trait  experiments  t o be p u s h e d b e y o n d t h e r a n g e o f t h e o r i g i n a l  tion  i n a b o u t 12 g e n e r a t i o n s .  this  rapidly  to  Whether s e l e c t i o n  popula-  can proceed  i n a well-buffered natural population  remains  be d e m o n s t r a t e d . 4.  The work i n C h a p t e r 6 s h o u l d  more s y s t e m a t i c behavior. on  f o r t h e mean o f a q u a n t i t a t i v e  study  be e x t e n d e d  o f the genetics o f a n t i p r e d a t o r  There i s a c o n s i d e r a b l e p s y c h o l o g i c a l  the behavior  into a  g e n e t i c s o f " f e a r " and " b o l d n e s s '  literature 1  i n mammals  242 (Dawson, 1932; but is  information virtually  p o i n t s out, to  Foster,  the  for fish  "Behavioral  both B r u e l l  the  of  necessary  i  of the  which are  hybrids  s u c h as  I t w o u l d be  the  116)  rightly  primarily  impressive Never-  (1972) s t r e s s  available for  that  the  d i f f e r e n c e s ) are i n the  and  a  science  carried  baekcrosses)  showing s u p e r i o r  i f artificial  or  has  out  ( e . g . Lower A r i p o  of considerable  tightly-linked,  be  to d e l i b e r a t e l y s e l e c t  reaction distance  any  on of  x Paria).  (or l e t a  escape  theoretical  interest,  selection for  effect  on  other,  "coadapted" b e h a v i o r a l habitat preference,  traits  courtship  etc. 5.  on  2  stocks  schooling behavior,  display,  now  (F^, F ,  s e l e c t ) f o r animals  example, t o d e t e r m i n e  possibly  Thiessen  s i g n i f i c a n c e of behavior  A n o t h e r a p p r o a c h w o u l d be  increased  general)  s o p h i s t i c a t i o n , . , ."  (1967) and  some o f t h e more d i v e r g e n t  for  in  been l e f t  propose, t h a t a d e t a i l e d s t u d y  behavior.  1971)  genetics.  behavior  predator  (1972?  p r e r e q u i s i t e f o r future progress  of behavior  the  Thiessen.  i n spite of t h e i r  information  (adaptive  Plutchik,  lower v e r t e b r a t e s  As  lack genetic  thesless,  1970;  e v o l u t i o n has  e t h o l o g i s t s , who,  kinds  Whitney,  (and  non-existent.  accomplishments,  guppy  1959;  The  final  proximate  differences.  Why,  suggestion  i s t h a t work s h o u l d  factors responsible on  its first  R i v u l u s , does a Lower A r i p o  f o r the  meeting with  be  done  behavioral a  guppy r e s p o n d w i t h  hungry a rapid  dart  243  f o l l o w e d by a s e r i e s  o f s u r f a c e jumps, when u n d e r t h e same  circumstances  a Paria  20%  C u r u c a y e and 12% o f P a r i a , g u p p i e s n o t  of Petite  guppy h a r d l y r e s p o n d s  "recognize" the motionless  Crenicichla  T h e s e q u e s t i o n s have a d i r e c t for  the e l u s i v e  lying  c a n be g e n e r a t e d 1969), i t w i l l  from  into  1  analyses  e v e n t u a l l y be n e c e s s a r y  behavioral differences or  b e a r i n g on t h e s e a r c h (IRM) u n d e r -  Though i n t e r e s t i n g  ethological  (e.g. C u r i o ,  to translate  (Manning, 1967) *  c o u l d pose q u i t e a c h a l l e n g e because the n e u r a l  animals  (e.g. Ewert, 1970); f u r t h e r m o r e  sensory  mechanisms  very  This  correlates  b e h a v i o r may be c a u s e d sensitivity  ( M a r l e r and H a m i l t o n ,  s i m p l y by d i f f e r e n c e s  o f the eye.  little is  of intraspecific  I n t h e guppy, some o f t h e g e o g r a p h i c  or  overt  b e h a v i o r have been s t u d i e d i n o n l y a few  known a b o u t t h e g e n e t i c a s p e c t s in  hypotheses  g e n e t i c e f f e c t s on t h e s t r u c t u r e  f u n c t i o n o f the nervous system  of avoidance  Why d i d  i n Exp, 6.6?  " i n n a t e r e l e a s i n g mechanism'  antipredator behavior.  at all?  Nevertheless,  variation  1966). differences i n i n the structure  i t i s very  probable  t h a t o t h e r p e r i p h e r a l c e n t r e s and e v e n t h e CNS a r e d i f f e r entially  responsive to stimuli  associated with  predators.  LITERATURE  Allen,  CITED  K. R. 1969. D i s t i n c t i v e aspects o f the ecology o f stream, f i s h e s : a review. J . F i s h . Res. Bd, Canada 26: 1429-1438.  Aim, G.  1959. C o n n e c t i o n between m a t u r i t y , s i z e , and age in fishes. R e p t . I n s t . F r e s h w . Res. D r o t t n i n g h o l m 40: 5-145.  A n d e r s o n , F. S. 1961. Effect of density ratio. O i k o s 12: 1-16.  on a n i m a l s e x  B a e r e n d s , G. P., R. B r o w e r , and H. T. W a t e r b o l k . 1955. E t h o l o g i c a l s t u d i e s on L e b i s t e s r e t i c u l a t u s P e t e r s . I . A n a l y s i s o f t h e male c o u r t s h i p p a t t e r n . B e h a v i o u r 8: 249-334. B a i n b r i d g e , R. 1960. J . Exp. B i o l .  Speed and s t a m i n a i n t h r e e 37: 129-153.  fish.  B a k e r , R. R. 1970. B i r d p r e d a t i o n as a s e l e c t i v e p r e s s u r e on t h e immature s t a g e s o f t h e c a b b a g e b u t t e r f l i e s , P i e r i s r a p a e and P. b r a s s i c a e . J . Z o o l . , Lond. 162: 43-59. Ballin,  P. J .  1973.  M.  Sc. T h e s i s .  Univ. B r i t i s h  Columbia  B a r l o w , G. W. 1961. C a u s e s and s i g n i f i c a n c e o f m o r p h o l o g i cal variation i n fishes. S y s t . Z o o l . 10: 105-117. B a s t o c k , M. 1956. A gene m u t a t i o n w h i c h c h a n g e s a behavior pattern. E v o l u t i o n 10: 421-439. Beebe, W. 1925. S t u d i e s o f a t r o p i c a l j u n g l e ; one q u a r t e r of a square mile of j u n g l e a t Kartabo, B r i t i s h Guiana. Z o o l o g i c a 6: 5-193. Beebe, W. 1952. Introduction to the ecology V a l l e y , T r i n i d a d , B. W. I . Zoologica  of the Arima 37: 157-183,  Belcher,  C., and G. D. Smooker. 1936, C o l o n y o f T r i n i d a d and T o b a g o .  On t h e b i r d s o f t h e I b i s 6: 792-813.  Benzie,  V. L. 1965. Some a s p e c t s o f t h e a n t i - p r e d a t o r r e s p o n s e s o f two s p e c i e s o f s t i c k l e b a c k . D. P h i l , Thesis. Univ. Oxford. 149 p .  245  Berry,  R. J . , and J . H. C r o t h e r s , 1968. Stabilizing select i o n i n t h e dog-whelk ( N u c e l l a l a p i l l u s ) . J . Zool., L o n d . 155: 5-17.  B e r t a l a n f f y , L. von. 1938. A q u a n t i t a t i v e theory o r g a n i c g r o w t h . Human B i o l . 10; 181-213,  of  Beukema, J . J . 1968. P r e d a t i o n by t h e t h r e e - s p i n e d s t i c k l e b a c k ( G a s t e r o s t e u s a c u l e a t u s L . ) . The i n f l u e n c e o f h u n g e r and e x p e r i e n c e . Behaviour 31: 1-126. B e y e r l e , G. B., and J . E . W i l l i a m s , 1968. Some o b s e r v a t i o n s o f f o o d s e l e c t i v i t y by n o r t h e r n p i k e i n aquaria. T r a n s . Amer. F i s h . S o c . 97: 28-31. B i g n a m i , G. 1965. S e l e c t i o n f o r h i g h r a t e s and low r a t e s o f a v o i d a n c e c o n d i t i o n i n g i n t h e r a t . Anim. Behav. 13: 221-227. Bloedel,  P. 1955. H u n t i n g methods o f f i s h - e a t i n g b a t s , particularly Noctilio leporinus. J . Mammal. 36: 390-399.  Boeseman, M, 1960. The f r e s h - w a t e r f i s h e s o f t h e i s l a n d of T r i n i d a d . Stud. Fauna Curacao C a r i b b . I s l . 10: 72-153. Boeseman, M. 1964. The f r e s h - w a t e r f i s h e s o f t h e i s l a n d o f T r i n i d a d : addenda, e r r a t a , e t c o r r i g e n d a , Stud. F a u n a C u r a c a o C a r i b b . I s l . 20: 52-57. B o v e t , D., F. B o v e t - N i t t i , and A. O l i v e r i o . 1969. Genetic a s p e c t s o f l e a r n i n g and memory i n m i c e . Science 163: 139-149. Brawn, V. M. 1969. F e e d i n g b e h a v i o u r o f c o d (Gadus morhua). J , F i s h . R e s . Bd, C a n a d a 26; 583-596. Breder,  C. M., J r . 1967. On t h e s u r v i v a l v a l u e schools. Z o o l o g i c a 52: 25-40,  of  fish  Breder,  C. M., J r . , and C. W. C o a t e s , 1932, A preliminary s t u d y o f p o p u l a t i o n s t a b i l i t y and s e x r a t i o o f Lebistes. C o p e i a 1932: 147-155.  Breder,  C. M., J r . , and C. W. C o a t e s . 1935. Sex r e c o g n i t i o n i n t h e guppy, L e b i s t e s r e t i c u l a t u s P e t e r s . Z o o l o g i c a 19: 187-20TT  246 Brett,  J . R., J . E. S h e l b o u r n , and C. T. Shoop. 1969. Growth r a t e and body c o m p o s i t i o n o f f i n g e r l i n g sockeye salmon, Oncorhynchus n e r k a , i n r e l a t i o n t o t e m p e r a t u r e and r a t i o n s i z e . J . F i s h . Res. Bd. Canada 26: 2363-2394.  Brock,  V, E . , and R. H. R i f f e n b u r g h . 1960. Fish schooling: a possible factor i n reducing predation. J, Conseil I n t . E x p l o r a t i o n Mer 25: 307-317.  Brooks,  J . L. 1968. The e f f e c t s o f p r e y s i z e s e l e c t i o n l a k e p l a n k t i v o r e s . S y s t . Z o o l , 17: 273-291.  by  Brooks,  J . L. Trans.  Brooks,  J . L. and S. I . Dodsbn. 1965. P r e d a t i o n , body s i z e , and c o m p o s i t i o n o f p l a n k t o n . S c i e n c e 150: 28-35.  1971. The e v o l u t i o n a r y e f f e c t s o f p r e d a t i o n . Amer. M i c r o s . S o c . 90: 105-106,  Brower, J . V. Z. 1960. Experimental s t u d i e s of mimicry. IV. The r e a c t i o n s o f s t a r l i n g s t o d i f f e r e n t p r o p o r t i o n s o f m o d e l s and m i m i c s . Amer, N a t u r , 94: 271-282, Brown, M. E. 400. Vol.  1957. E x p e r i m e n t a l s t u d i e s o f g r o w t h , p. 361In M, E. Brown (ed.) P h y s i o l o g y o f f i s h e s . 1. A c a d e m i c , New Y o r k . '  Bruell,  J . H. 1967. B e h a v i o r a l h e t e r o s i s , p. 270-286. In J . H i r s c h (ed.) B e h a v i o r - g e n e t i c a n a l y s i s . McGrawH i l l , New Y o r k .  C a i n , A.  J . , and P. i n Cepaea.  M. S h e p p a r d . G e n e t i c s 39:  1954. Natural 89-116,  selection  C a l a p r i c e , J . R. 1969. P r o d u c t i o n and g e n e t i c " f a c t o r s i n managed s a l m o n i d p o p u l a t i o n s , p, 377-388. I n T. G, N o r t h c o t e (ed.) Symp. on Salmon and T r o u t i n Streams. I n s t i t u t e of F i s h e r i e s , Univ. B r i t i s h Columbia. Caspari,  E. 1967. Gene a c t i o n as a p p l i e d t o b e h a v i o r , p. 112-134. I n J . H i r s c h (ed.) B e h a v i o r - g e n e t i c analysis. M c G r a w - H i l l , New..York.  C l a r k , E . , and L. R. A r o n s o n . 1951, Sexual behavior t h e guppy, L e b i s t e s r e t i c u l a t u s (Peters), Z o o l o g i c a 3 6 l 49-66. Collins,  in  R. L. 1964. Inheritance of avoidance c o n d i t i o n i n g i n mice: a d i a l l e l study. S c i e n c e 143: 1188-1190.  247 C o m f o r t , A. 1961. The l o n g e v i t y and m o r t a l i t y o f a (Lebistes r e t i c u l a t u s Peters) i n c a p t i v i t y . G e r o n t o l o g i a 5: 209-222.  fish  C r a n e , J . 1952. A comparative study of innate d e f e n s i v e b e h a v i o r i n T r i n i d a d m a n t i d s ( O r t h o p t e r a , Mantoidea:) . Z o o l o g i c a 37: 259-293. Croze,  H. 1970. S e a r c h i n g image i n C a r r i o n c r o w s . T i e r p s y c h o l . , S u p p l . 5: 1-86.  Z.  Cullen,  E. 1957. Adaptations i n the K i t t i w a k e t o nesting. I b i s 99: 275-302.  cliff-  Cullen,  J . M., E . Shaw, and H. A. B a l d w i n . 1965. Methods for measuring the three dimensional s t r u c t u r e o f f i s h schools. Anim. Behav. 13: 534-543.  Curio,  E. 1961. R a s s e n s p e z i f i s c h e s V e r h a l t e n gegen Raubfeind. E x p e r i e n t i a 17: 188-189,  einen  Curio,  E. 1965. Zur Geographischen V a r i a t i o n des Feinderkennens e i n i g e r Darwinfinken (Geospizidae), Z o o l . A n z . , S u p p l . 28: 466-492.  Curio,  E. 1969. Funktjpnweise und Sta,mmesgesehichte d e s Flugfeinderkennens e i n i g e r Darwinfinken (Geospizinae), Z. T i e r p s y c h o l . 26: 394-487.  Curio,  E. 1970a. D i e S e l e k t i o n d r e i e r Raupenformen e i n e s Schwarmers ( L e p i d o p t . , S p h i n g i d a e ) d u r c h e i n e n A n o l i s (Rept., I g u a n i d a e ) . Z. T i e r p s y c h . 27: 899914.  Curio,  E. 1970b. V a l i d i t y of the s e l e c t i v e c o e f f i c i e n t of a b e h a v i o u r t r a i t i n hawkmoth l a r v a e . Nature 228: 382.  Curio,  E. 1970c. D i e Messung d e s S e l e k t i o n s w e r t e s e i n e r Verhaltensweise. V e r h . D t . Z o o l . G e s . 64: 348-352.  D a v i s , C. C. 1968. Q u a n t i t a t i v e f e e d i n g and w e i g h t c h a n g e s in Poecilia reticulata. T r a n s . Amer, F i s h , S o c . 97: 22-27. Dawson, W. M. 1932. Inheritance of wildness i n mice. G e n e t i c s 17: 296-326,  and tameness  De F r i e s , J . C. 1967. Q u a n t i t a t i v e g e n e t i c s and b e h a v i o r : o v e r v i e w and p e r s p e c t i v e , p . 322-339. In J . H i r s c h (ed.) B e h a v i o r - g e n e t i c a n a l y s i s , McGraw-Hill, New York.  248  Dill,  L.  1972.  Ph. D. T h e s i s .  Univ. B r i t i s h  Columbia.  H. 1 9 6 6 . The e f f e c t o f p o p u l a t i o n d e n s i t y on m o r t a l i t y and sex r a t i o i n t h e milkweed bug, O n c o p e l t u s , and t h e c o t t o n s t a i n e r , D y s d e r c u s (Heteroptera). Amer. N a t u r . 100: 4 6 5 - 4 7 0 .  Dingle,  D o b z h a n s k y , T. 1970. G e n e t i c s o f t h e e v o l u t i o n a r y C o l u m b i a U n i v . P r e s s , New Y o r k , 505 p , Eastman, R.  1969.  The k i n g f i s h e r .  Collins,  process.  London,  E b e r h a r d t , L . L . 1968. An a p p r o x i m a t i o n t o a m u l t i p l e comparison t e s t . C o p e i a 1968: 314-319, Ehrlich,  P. R., and P. H. Raven. 1969. Differentiation of populations. S c i e n c e 165: 1228-1232.  E i b l - E i b e s f e l d t , I . 1962. F r e i w a s s e r b e o b a c h t u n g e n z u r Deutung des Schwarmverhaltens v e r s c h i e d e n e r Fische. Z. T i e r p s y c h o l . 19: 165-182. Estes,  R. D., a n d J . G o d d a r d . 1967. P r e y s e l e c t i o n a n d h u n t i n g b e h a v i o r o f the A f r i c a n w i l d dog. J , W i l d l . Mgmt. 31: 52-70.  E w e r t , J . - P . 1970. N e u r a l mechanisms o f p r e y - c a t c h i n g a v o i d a n c e b e h a v i o r i n t h e t o a d (Bufo b u f o L , ) . B r a i n Behav. E v o l . 3: 36-56.  and  F e i n b e r g , E . H., a n d D. P i m e n t e l . 1966. E v o l u t i o n o f i n c r e a s e d "female sex r a t i o " i n t h e b l o w f l y ( P h a e n i c i a s e r i c a t a ) under l a b o r a t o r y competition w i t h t h e h o u s e f l y fMusca d o m e s t i c a ) . Amer. N a t u r . 100: 235-244. Fisher,  R. A. 1958. The g e n e t i c a l t h e o r y o f n a t u r a l selection. 2nd r e v i s e d e d , D o v e r , New Y o r k , 291 p .  Foster,  D. D. 1959. D i f f e r e n c e s i n b e h a v i o r a n d t e m p e r a ment between two r a c e s o f t h e d e e r mouse. J . Mammal. 40: 496-513.  F r a n c k , D. 1969. G e n e t i s c h e G r u n d l a g e n d e r E v o l u t i o n t i e r i s c h e r Verhaltensweisen. Z o o l . A n z , 183: 31-46. Fryer,  G. 1965. P r e d a t i o n and i t s e f f e c t s on m i g r a t i o n and speciation i n African fishes: a comment. Proc, Z o o l . S o c . L o n d . 144: 301-322,  249 G a l b r a i t h , M. G., J r . 1967. S i z e - s e l e c t i v e p r e d a t i o n on D a p h n i a by r a i n b o w t r o u t and y e l l o w p e r c h . Trans. Amer. F i s h . Soc. 96: 1-10. Geodakyan, V. A., and V. I . K o s o b u t s k i i . 1972. Control of t h e s e x r a t i o i n f i s h by t h e f e e d b a c k mechanism, p. 122-130. I n B. I . C h e r f a s (ed.) G e n e t i c s , s e l e c t i o n , and h y b r i d i z a t i o n o f f i s h . Israel Program S c i . T r a n s l . , J e r u s a l e m . G e o r g e , C. J . W. 1960. B e h a v i o r a l i n t e r a c t i o n of the p i c k e r e l (Esox n i g e r Le S u e u r and E s o x a m e r i c a n u s Le Sueur) and t h e m o s q u i t o f i s h (Gambusia p a t r u e l i s [ B a i r d and G i r a r d ] ) . Ph. D. T h e s i s . H a r v a r d U n i v . Gery,  J.  1969. The f r e s h - w a t e r f i s h e s o f S o u t h A m e r i c a , p. 828-848. In E. J . F i t t k a u , J . l i l i e s , H, K l i n g e , G. H. Schwabe, and H, S i o l i (ed.) B i o g e o g r a p h y and e c o l o g y i n South America. V o l . 2. J u n k , The Hague.  G h i s e l i n , J . , and R. E . R i c k l e f s . 1970. Prey p o p u l a t i o n : a p a r s i m o n i o u s model f o r e v o l u t i o n o f response t o predator species d i v e r s i t y . S c i e n c e 170: 649-651, G i b s o n , M. B., and B. H i r s t . 1955. The e f f e c t o f and t e m p e r a t u r e on t h e p r e - a d u l t g r o w t h o f C o p e i a 1955: 241-243.  salinity guppies,  Giesel,  J . T. 1972. Sex r a t i o , r a t e o f e v o l u t i o n , , and e n v i r o n m e n t a l h e t e r o g e n e i t y , Amer. N a t u r . 106: 380-387.  Goz,  H.  1941. U b e r den A r t - und I n d i v i d u a l - g e r u c h b e i Fischen. Z. V e r g l . P h y s i o l . 29: 1-45.  Gunter,  G. 1950. C o r r e l a t i o n between t e m p e r a t u r e o f w a t e r and s i z e o f m a r i n e f i s h e s on t h e A t l a n t i c coast. C o p e i a 1950: 298-304.  Hagen, D. W., and L. G. G i l b e r t s o n , 1972. Geographic v a r i a t i o n and e n v i r o n m e n t a l s e l e c t i o n i n G a s t e r o s t e u s a c u l e a t u s L. i n t h e P a c i f i c N o r t h w e s t , A m e r i c a , E v o l u t i o n 26: 32-51, Hailman,  J . P. 1965. C l i f f - n e s t i n g a d a p t a t i o n s of the Galapagos s w a l l o w - t a i l e d g u l l . Wilson B u l l . 77: 346-362.  H a m i l t o n , T. H. 1961. The a d a p t i v e s i g n i f i c a n c e o f i n t r a s p e c i f i c t r e n d s o f v a r i a t i o n i n w i n g l e n g t h and body s i z e among b i r d s p e c i e s . E v o l u t i o n 15: 180-195.  250 Hanson, A. J . , and H. D. S m i t h . 1967. Mate s e l e c t i o n i n a p o p u l a t i o n o f sockeye salmon (Oncorhynchus nerka) o f mixed age-groups. J . F i s h . Res. Bd. Canada 24: 1955-1977. Hartman, G. F. 1969. Reproductive b i o l o g y o f the G e r r a r d S t o c k r a i n b o w t r o u t , p. 53-67. i n T. G. N o r t h c o t e (ed.) Symp. on Salmon and T r o u t i n S t r e a m s . I n s t i t u t e of F i s h e r i e s , Univ. B r i t i s h Columbia. Haskins,  C. P., and E . F. H a s k i n s . 1949, The r o l e o f s e x u a l s e l e c t i o n as an i s o l a t i n g mechanism i n t h r e e species of p o e c i l i i d f i s h e s . E v o l u t i o n 3: 160-169.  Haskins,  C. P., and E. F. H a s k i n s . 1950. Factors governing s e x u a l s e l e c t i o n as an i s o l a t i n g mechanism i n t h e poeciliid fish Lebistes reticulatus. P r o c . Nat. A c a d . S c i . 36: 464-476.  Haskins,  C. P., and E . F. H a s k i n s . 1951. of c e r t a i n c o l o r p a t t e r n s i n w i l d Lebistes reticulatus in Trinidad. 5: 216-225.  Haskins,  C. P., and E. F. H a s k i n s . 1954. N o t e on a "permanent" e x p e r i m e n t a l a l t e r a t i o n o f g e n e t i c c o n s t i t u t i o n i n a n a t u r a l p o p u l a t i o n . P r o c , Nat. A c a d . S c i . 40: 627-635,  Haskins,  C. P., E. F. H a s k i n s , J . J . A. M c L a u g h l i n , and R. E . H e w i t t . 1961. P o l y m o r p h i s m and p o p u l a t i o n s t r u c t u r e i n L e b i s t e s r e t i c u l a t u s , p. 320-395. In W. F. B l a i r (ed.) V e r t e b r a t e S p e c i a t i o n . U n i v . Texas P r e s s , A u s t i n .  Haskins,  C. P., P. Young, R. E . H e w i t t , and E . F. H a s k i n s . 1970. S t a b i l i s e d h e t e r o z y g o s i s o f supergenes mediating certain Y-linked colour patterns i n populations of , L e b i s t e s r e t i c u l a t u s . Heredity 25: 575-589.  The i n h e r i t a n c e populations of Evolution  :  H a s t i n g s , R. W., and R. W. Y e r g e r . 1971. E c o l o g y and l i f e h i s t o r y o f t h e diamond k i l l i f i s h , A d i n i a x e n i c a ( J o r d a n and G i l b e r t ) . Amer. M i d i . N a t . 86: 276-291, H e a t w o l e , H. 1968. R e l a t i o n s h i p of escape b e h a v i o r camouflage i n a n o l i n e l i z a r d s . C o p e i a 1968;  and 109-113.  H e r k l o t s , G. A. C. 1961. C o l l i n s , London.  Tobago.  The B i r d s o f T r i n i d a d 287 p.  and  251 Hester,  F. J . 1964. E f f e c t s o f f o o d s u p p l y on f e c u n d i t y i n t h e f e m a l e guppy, L e b i s t e s r e t i c u l a t u s (Peters). J . F i s h . Res. Bd. C a n a d a 21; 757-764,  H i n d e , R. A. 1954. F a c t o r s g o v e r n i n g the changes i n s t r e n g t h o f a p a r t i a l l y i n b o r n r e s p o n s e , as shown by t h e mobbing b e h a v i o u r o f t h e c h a f f i n c h (Fringilla coelebs), I I . The w a n i n g o f t h e r e s p o n s e . Proc. Roy. S o c . B, 142: 331-358. H i n d e , R. A. lower Hoar, W.  1959. B e h a v i o u r and s p e c i a t i q n i n b i r d s and v e r t e b r a t e s . B i o l . Rev. 34; 85-128.  S. 1958. The e v o l u t i o n o f m i g r a t o r y b e h a v i o u r among j u v e n i l e s a l m o n o f t h e genus O n c o r h y n c h u s . J . F i s h . Res. Bd. Canada 15: 391-428,  Hobson, E . S. 1968. P r e d a t o r y b e h a v i o r o f some s h o r e f i s h e s i n the Gulf of C a l i f o r n i a . U, S. B u r e a u S p o r t F i s h . W i l d l . Res. Rep. 73: 1-92, Holcomb, L . C , and G. T w i e s t . 1970. Growth r a t e s and sex r a t i o s o f red-winged b l a c k b i r d n e s t l i n g s . W i l s o n B u l l . 82: 294-303, Holling,  C. S. 1966. The f u n c t i o n a l r e s p o n s e b r a t e p r e d a t o r s t o p r e y d e n s i t y . Mem. Can. 48: 1-86.  of inverteE n t , Soc,  H o o g l a n d , R., D. M o r r i s , and N, T i n b e r g e n , 1957. The s p i n e s o f s t i c k l e b a c k s ( G a s t e r o s t e u s and P y g o s t e u s ) as means o f d e f e n c e a g a i n s t p r e d a t o r s ( P e r c a and Esox). B e h a v i o u r 10: 205-236. Hubbs, C. L . 1940. Speciation of fishes. 74: 198-211.  Amer.  Natur.  H u f f a k e r , C. F., K. P. Shea, and S. G. Herman. 1963, E x p e r i m e n t a l s t u d i e s on p r e d a t i o n : Complex d i s p e r s i o n and l e v e l s o f f o o d i n an a c a r i n e p r e d a t o r prey i n t e r a c t i o n . H i l g a r d i a 34: 305-330, H u m p h r i e s , D. A., and P. M. D r i v e r . by p r e y a n i m a l s . Oecologia  1970, Protean defence ( B e r l . ) 5: 285-302,  H u n t e r , J . R. 1966. Procedure f o r a n a l y s i s of s c h o o l i n g behavior. J . F i s h . Res, Bd. C a n a d a 23: 547-562. Hynes, H. B. N. 1970. The e c o l o g y o f r u n n i n g U n i v . T o r o n t o P r e s s , T o r o n t o . 555 p.  waters.  252 I v l e v , V. S. 1961. Experimental ecology o f the f e e d i n g of fishes. Y a l e U n i v . P r e s s , New Haven. 302 p . Jackson,  P. B. N. 1961. The i m p a c t o f p r e d a t i o n , e s p e c i a l l y by t h e t i g e r f i s h ( H y d r o c y o n v i t t a t u s ) on A f r i c a n freshwater f i s h e s . P r o c . Z o o l . S o c . L o n d . 136: 603-622.  Jackson,  P. B. N. Greenwood.  1965.. Proc.  R e p l y t o G, F r y e r and P, H, Z o o l . Soc. Lond. 144: 313-321.  J o h n s o n , C. R. 1970. E s c a p e b e h a v i o r and c a m o u f l a g e i n two subspecies of Sceloporus o c c i d e n t a l i s . Amer. M i d i . . N a t u r . 84: 280-282. J u n g e , G. C. A., and G. F. Mees. 1961. The a v i f a u n a o f T r i n i d a d and T o b a g o . Rijksmuseum van N a t u u r l i . j k e H i s t o r i e , Leiden. 172 p. K a l l m a n , K. D. 1965. G e n e t i c s and g e o g r a p h y o f s e x d e t e r mination i n the p o e c i l i i d f i s h , Xiphophorus maculatus. Z o o l o g i c a 50: 151-190. K e e n l e y s i d e , M. H. A. 1955. Some a s p e c t s o f t h e s c h o o l i n g behaviour of f i s h . B e h a v i o u r 8: 183-248. K e t t l e w e l l , H. B. D. 1961. The phenomenon o f i n d u s t r i a l melanism i n L e p i d o p t e r a . Annu. Rev. E n t o m o l . 6: 245-262. K i m u r a , M., and G. W e i s s . 1964. The s t e p p i n g s t o n e m o d e l o f p o p u l a t i o n s t r u c t u r e and t h e d e c r e a s e o f g e n e t i c c o r r e l a t i o n with distance. G e n e t i c s 49; 561-576. King,  J . A. 1970. E c o l o g i c a l psychology: an a p p r o a c h t o m o t i v a t i o n , p . 1-33. I n W. J . A r n o l d and M. M. Page (ed.) N e b r a s k a symposium on m o t i v a t i o n . Univ. Nebraska Press, L i n c o l n .  K r u m h o l z , L . A. 1963. R e l a t i o n s h i p s between f e r t i l i t y , s e x r a t i o , and e x p o s u r e t o p r e d a t i o n i n p o p u l a t i o n s o f t h e m o s q u i t o f i s h Gambusia manni Hubbs a t B i m i n i , Bahamas. I n t . Rev. Ges. H y d r o b i o l . 48: 201-256. K r u u k , H. 1964. P r e d a t o r s and a n t i - p r e d a t o r b e h a v i o u r the b l a c k - h e a d e d g u l l (Larus r i d i b u n d u s L . ) , B e h a v i o u r , s u p p l . 11: 1-130. K r u u k , H. 1972. Chicago.  The s p o t t e d h y e n a . 335p.  Univ.  Chicago  of  Press,  253  L a c k , D.  1954. The n a t u r a l C l a r e n d o n , Oxford'.  L a n g , H.-J. der  r e g u l a t i o n of  animal  1965. Eine lichtmikroskopische Guppy-Netzhaut. Zeiss-Mitt. 3:  numbers.  Untersuchung 415-438.  L a n g , H.-J. 1967. U b e r das L i c h t r u c k e n v e r h a l t e n des guppy ( L e b i s t e s r e t i c u l a t u s ) i n f a r b i g e n und f a r b l o s e n Lichtern. Z. V e r g l . P h y s i o l . 56: 296-340. Larson,  S. 1960. On t h e i n f l u e n c e o f t h e A r c t i c f o x A l o p e x l a g o p u s on t h e d i s t r i b u t i o n o f A r c t i c b i r d s . O i k o s 11: 276-305.  L e B r a s s e u r , R. J . 1969. Growth o f j u v e n i l e Chum s a l m o n (Oncorhynchus k e t a ) under d i f f e r e n t f e e d i n g r e g i m e s . J . F i s h . Res. Bd. Canada 26: 1 6 3 1 - 1 6 4 5 . Lehrman, D. S. 1970. S e m a n t i c and c o n c e p t u a l i s s u e s i n t h e n a t u r e - n u r t u r e p r o b l e m , p. 17-52. In L. R. A r o n s o n , E. T o b a c h , D. S. Lehrman, and J . S. R o s e n b l a t t (ed.) D e v e l o p m e n t and e v o l u t i o n o f b e h a v i o r . Freeman, San F r a n c i s c o . Liley,  N. R. 1966. E t h o l o g i c a l i s o l a t i n g mechanisms i n four sympatric species of p o e c i l i i d f i s h e s . B e h a v i o u r , S u p p l . 13: 1-197.  Lindzey,  G., J . L o e h l i n , M. M a n o s e v i t z , and D. 1971. Behavioral genetics. Annu. Rev. 22: 39-94.  Liu,  K., and R. L. W a l f o r d . 1966. I n c r e a s e d g r o w t h and l i f e s p a n w i t h lowered ambient temperature i n the annual f i s h Cynolebias a d o l f f i . N a t u r e 212: 12771278.  R.  Thiessen. Psych.  L o w e - M c C o n h e l l , R. H. 1964. The f i s h e s o f t h e R u p u n u n i savanna d i s t r i c t of B r i t i s h Guiana, P a r t I. E c o l o g i c a l g r o u p i n g s o f f i s h s p e c i e s and e f f e c t s o f t h e s e a s o n a l c y c l e on t h e f i s h . Zool. J. Linn. Soc. 45: 103-144. L o w e - M c C o n n e l l , R. H. 1969a. The c i c h l i d f i s h e s o f Guyana, S o u t h A m e r i c a , w i t h n o t e s on t h e i r e c o l o g y and breeding behaviour. Z o o l . J . L i n n . Soc. 48; 255-302, L o w e - M c C o n n e l l , R. H. water f i s h e s .  1969b. Speciation i n tropical B i o l . J . L i n n . Soc, 1: 51-75,  fresh-  254 Maher, W. J , 1970. The p o m a r i n e j a e g e r as a brown lemming predator i n northern Alaska. W i l s o n B u l l . 82: 130157. M a n n i n g , A. 1967. Genes and t h e e v o l u t i o n o f i n s e c t b e h a v i o r , p. 44-60. I n J . H i r s c h (ed.) B e h a v i o r g e n e t i c a n a l y s i s . M c G r a w - H i l l , New Y o r k . M a n t e i f e l ' , B. P., and D. V. Radakov. . 1961. The a d a p t i v e s i g n i f i c a n c e of schooling behavior i n f i s h e s . Russ, Rev. B i o l . 50: 338-345. Marler,  P., and W. J , H a m i l t o n I I I . animal behavior. W i l e y , New  1966. York.  Mechanisms o f 771 p .  Mason, L . G. 1965. P r e y s e l e c t i o n by a n o n - s p e c i f i c predator. E v o l u t i o n 19: 259-260. M a t h e r , K. 1970. The n a t u r e in wild populations. McPhail,  and s i g n i f i c a n c e o f v a r i a t i o n Symp. Z o o l . S o c . L o n d . 2 6 : 27-39.  J . D. 1969. P r e d a t i o n and t h e e v o l u t i o n o f a stickleback (Gasterosteus). J . F i s h . Res. Bd. Canada 26: 3183-3208.  M e l z a c k , R. 1961. On t h e s u r v i v a l o f m a l l a r d d u c k s a f t e r " h a b i t u a t i o n " t o t h e hawk-shaped f i g u r e . Behaviour 17: 9-16. Miller,  R. B. 1957. Have t h e g e n e t i c p a t t e r n s o f f i s h e s b e e n a l t e r e d by i n t r o d u c t i o n o r by s e l e c t i v e f i s h i n g ? J . F i s h . Res. Bd. Canada 14: 797-806.  M o o d i e , G. E . E . 1972a. P r e d a t i o n , n a t u r a l s e l e c t i o n and a d a p t a t i o n i n an u n u s u a l t h r e e s p i n e s t i c k l e b a c k . H e r e d i t y 28: 155-168. M o o d i e , G. E . E . 1972b. M o r p h o l o g y , l i f e - h i s t o r y , and e c o l o g y o f an u n u s u a l s t i c k l e b a c k ( G a s t e r o s t e u s a c u l e a t u s ) i n t h e Queen C h a r l o t t e I s l a n d s , C a n a d a . Can. J . Z o o l . 50: 721-732. Needham, P. R., and J . G. Needham. 1962. A guide study o f fresh-water b i o l o g y . Holden-Day Francisco. 108 p .  f  N i c e , M. M., and J . J . T e r P e l k w y k , 1941. t i o n by t h e song s p a r r o w . Auk 58:  t o the San  Enemy r e c o g n i 195-214.  255  N i k o l s k i i , G. V. 1969. Theory o f f i s h p o p u l a t i o n dynamics as t h e b i o l o g i c a l b a c k g r o u n d f o r r a t i o n a l e x p l o i t a t i o n and management o f f i s h e r y r e s o u r c e s , Oliver and Boyd, E d i n b u r g h . 323 p. N o b l e , G. K. Rev. Nyberg,  1938. Sexual s e l e c t i o n 13: 133-155.  among f i s h e s .  Biol.  D. W. 1971. Prey capture i n the largemouth bass, Amer. M i d i . N a t u r . 86: 128-144.  O l s o n , D. P. 1965. D i f f e r e n t i a l v u l n e r a b i l i t y o f male and f e m a l e c a n v a s b a c k s t o h u n t i n g . T r a n s . N. Amer. W i l d l . C o n f . 30: 121-135. O l s o n , F. C. W. 1964. The s u r v i v a l v a l u e o f f i s h schooling, J . C o n s e i l I n t . E x p l o r a t i o n Mer 29: 115-116. O o r t m e r s s e n , G. A. v a n . 1970. Biological significance, g e n e t i c s and e v o l u t i o n a r y o r i g i n o f v a r i a b i l i t y i n b e h a v i o u r w i t h i n and between i n b r e d s t r a i n s o f m i c e (Mus m u s c u T u s ) . B e h a v i o u r 38: 1-92, P a l o h e i m o , J . E . , and L, M. D i c k i e . 1966, F o o d and g r o w t h of f i s h e s . I I . E f f e c t s o f f o o d and t e m p e r a t u r e on t h e r e l a t i o n between m e t a b o l i s m and body w e i g h t . J . F i s h . Res. Bd. Canada 23: 869-908. P a r k e r , R. R. 1971. S i z e s e l e c t i v e preda,ti©n among j u v e n i l e salmonid f i s h e s i n a B r i t i s h Columbia inlet. J . F i s h . Res. Bd, Canada 28: 1503-1510. P f e i f f e r , W. Rev.  1962. The f r i g h t r e a c t i o n 37: 495-511.  of f i s h ,  Biol.  P l u t c h i k , R. 1971. I n d i v i d u a l and b r e e d d i f f e r e n c e s i n a p p r o a c h and w i t h d r a w a l i n d o g s . B e h a v i o u r 40: 302-311. P r o t a s o v , V. R. 1970. I s r a e l Program  V i s i o n and n e a r o r i e n t a t i o n o f f i s h . S c i . T r a n s l . , Jerusalem, 175 p .  Raleigh,  R. F., and D. W. Chapman, 1971, Genetic control i n lakeward m i g r a t i o n s of c u t t h r o a t t r o u t f r y . T r a n s . Amer. F i s h . S o c . 100: 33-40,  Ray,  1960. The a p p l i c a t i o n o f Bergmann's and A l l e n ' s r u l e s t o the p o i k i l o t h e r m s . J . M o r p h o l . 106: 85-108,  C.  256 Reed, J , R. 1969. A l a r m s u b s t a n c e s and f r i g h t r e a c t i o n i n some f i s h e s f r o m t h e s o u t h e a s t e r n U n i t e d S t a t e s , T r a n s . Amer. F i s h . S o c . 98: 664-668. R i c k e r , W. E . 1954. S t o c k and r e c r u i t m e n t . Bd. Canada 11: 559-623,  J. Fish,  Res,  R i c k e r , W. E . 1969. Effects of size-selective mortality and s a m p l i n g b i a s on e s t i m a t e s o f g r o w t h , m o r t a l i t y , p r o d u c t i o n and y i e l d . J , F i s h . Res, Bd. C a n a d a 26: 479-541. Roberts,  T. R. 1972. Congo b a s i n s .  E c o l o g y o f f i s h e s i n t h e Amazon and B u l l . Mus. Comp. Z o o l . 143: 117-147.  R o b i n s o n , M. H. 1969. Defenses a g a i n s t v i s u a l l y hunting p r e d a t o r s , p . 225-259. I n T. D o b z h a n s k y , M. K, H e c h t , and W. C. S t e e r e ~[¥d.) E v o l u t i o n a r y B i o l o g y . V o l . 3. A p p l e t o n - C e n t u r y - C r o f t s , New Y o r k . Rohlf,  F. J . , and G. D. S c h n e l l . 1971. An o f the i s o l a t i o n - b y - d i s t a n c e model. 105: 295-324.  investigation Amer. N a t u r .  Rose, S. M. 1959. Population c o n t r o l i n guppies, M i d i . N a t u r . 62: 474-481.  Amer.  R o s e n , D. E . , and R. M. B a i l e y . 1963. The p o e c i l i i d fishes (Cyprinodontiformes), t h e i r structure, z o o g e o g r a p h y and s y s t e m a t i e s . B u l l . Amer, Mus, N a t u r . H i s t . 126: 1-176. R o s e n , D. E . , and A. T u c k e r . 1961. E v o l u t i o n of secondary s e x u a l c h a r a c t e r s and s e x u a l b e h a v i o r p a t t e r n s i n a family of viviparous fishes (Cyprinodontiformes: Poeciliidae). C o p e i a 1961: 201-212. R o t h e n b u h l e r , W. C. 1964. Behavior genetics of nest c l e a n i n g - i n honey b e e s . IV. R e s p o n s e o f F and backcross generations t o d i s e a s e - k i l l e d brood. Amer. Z o o l . 4: 111-123. 1  Riippell,  G., and E . G o s s w e i n . 1972. D i e Schwarme y o n Leucaspius delineatus (Cyprinidae, T e l e o s t e i ) b e i G e f a h r im H e l i e n und im D u n k e l n , Z. V e r g l . P h y s i o l , 76: 333-340.  Russell,  E . M. 1967a. Changes i n t h e b e h a v i o u r o f L e b i s t e s r e t i c u l a t u s upon a r e p e a t e d shadow s t i m u l u s . Anim. Behav. 15: 574-585.  257 Russell,  E . M. 1967b. The e f f e c t o f e x p e r i e n c e o f s u r r o u n d i n g s on t h e r e s p o n s e o f L e b i s t e s r e t i c u l a t u s t o a strange object. Anim, Behav. HT: 586-594.  S a l y e r , J . C. I I , and K. F. L a g l e r . 1949, The e a s t e r n b e l t e d k i n g f i s h e r , Megaceryle alcyon alcyon (Linnaeus), i n r e l a t i o n t o f i s h management. T r a n s . Amer. F i s h . S o c . 76: 97-117. S c h l e i d t , W. M. 1961. R e a k t i o n e n von Truthiihnern auf f l i e g e n d e R a u b v o g e l und V e r s u c h e z u r A n a l y s e i h r e r AAM's. Z. T i e r p s y c h o l . 18: 534-560, Schutz,  F. 1956. V e r g l e i c h e n d e U n t e r s u c h u n g e n xiber d i e S c h r e c k r e a k t i o n b e i F i s c h e n und d e r e n V e r b r e i t u n g . Z. V e r g l . P h y s i o l . 38: 84-135.  S e l a n d e r , R. K. 1965. On m a t i n g s y s t e m s and s e x u a l tion. Amer. N a t u r . 99: 129-141,  selec-  S e m l e r , D. E . 1971. Some a s p e c t s o f a d a p t a t i o n i n a p o l y morphism f o r b r e e d i n g c o l o u r s i n t h e t h r e e s p i n e s t i c k l e b a c k (Gasterosteus a c u l e a t u s ) . J, Zool., L o n d . 165: 291-302. Shaw, E .  1970. Schooling i n fishes; c r i t i q u e and r e v i e w , p. 452-480. I n L . R. A r o n s o n , E . T o b a c h , D. S. Lehrman, and J . S. R o s e n b l a t t (ed.) D e v e l o p m e n t and evolution of behavior. Freeman, San F r a n c i s c o ,  Shoemaker, H. H. 1944. A l a b o r a t o r y study o f f i s h popular tions. T r a n s . Amer. F i s h . Soc, 74: 350-359. S h o n t z , C. J . 1962. The e f f e c t s o f a l t i t u d e and l a t i t u d e on t h e morphometry, m e r i s t i c s , g r o w t h and f e c u n d i t y of the e a s t e r n blacknose dace, R h i n i c h t h y s a t r a t u l u s a t r a t u l u s (Hermann). Ph. D. T h e s i s . Univ. . Pittsburgh. 161 p. S n y d e r , N. F. R., and H. A. S n y d e r . 1971, Defenses of the F l o r i d a a p p l e s n a i l Pomacea p a l u d o s a . Behaviour 40: 175.-215. Soulg, Sterba,  M. 1966. Trends i n the i n s u l a r r a d i a t i o n lizard. Amer. N a t u r . 100: 47-64, G. 1962. Freshwater f i s h e s o f the world. Books, London. 878 p .  of a Vista  S t r u h s a k e r , J . W. 1968. S e l e c t i o n mechanisms a s s o c i a t e d with i n t r a s p e c i f i c s h e l l v a r i a t i o n i n L i t t o r i n a p i c t a (Prosobranchia: Mesogastropoda). E v o l u t i o n 22: 459-480.  258 S u t h e r s , R. A. bats.  1965. J . Exp.  Acoustic orientation Z o o l . 158: 319-348.  by  fish-catching  Symons', P. E, K. 1971. E s t i m a t i n g d i s t a n c e s between f i s h s c h o o l i n g i n an a q u a r i u m . J . F i s h . Res. Bd. Canada 28: 1805-1806. T h i e s s e n , D. D. 1972. A move t o w a r d s p e c i e s - s p e c i f i c analyses i n behavior genetics. Behav. G e n e t . 2: 115-126. T h o r n h i l l , E . , L. R a m c h a r i t a r , D. H e r r e r a , R. A a r o n , R. Rudder, C. Thomas, K. James, and R. Moore. 1966. E c o l o g i c a l study o f a p a r t o f the Maracas R i v e r . U n i v . West I n d i e s , S t . A u g u s t i n e , T r i n i d a d . 25 p . Thorpe,  W. H. 1963. L e a r n i n g and Methuen, L o n d o n . 558 p.  instinct  i n animals.  T i n b e r g e n , N. 1959. B e h a v i o u r , s y s t e m a t i c s and selection. I b i s 101: 318-330.  natural  V e s e l o v , E. A. 1964. S i m p l e s t methods f o r s t u d i e s on some r e f l e x e s o f f i s h l a r v a e and f r y , p, 297-311, In E. N. P a v l o v s k i i (ed.) T e c h n i q u e s f o r t h e . i n v e s t i g a t i o n o f f i s h p h y s i o l o g y . I s r a e l Program Sci. T r a n s l . , Jerusalem. W a h l s t e n , D. 1972. Genetic experiments with animal learning: a c r i t i c a l review. Behav. B i o l . 7: 143-182. Waldman, B. 1969. Do g u p p i e s 3: 12-16, 58-61.  see c o l o r s ?  The  Aquarium  Walther,  F. R. 1969. F l i g h t b e h a v i o u r and a v o i d a n c e o f p r e d a t o r s i n Thomson's g a z e l l e ( G a z e l l a t h o m s o n i Guenther 1884). B e h a v i o u r 34: 184-221.  Ware, D.  M. 19 71. The p r e d a t o r y b e h a v i o u r o f r a i n b o w t r o u t (Salmo g a i r d n e r i ) . Ph. D. T h e s i s . U n i v . B r i t i s h Columbia. 158 p.  W e a t h e r l e y , A. H. 1966. 212: 1321-1324. Werboff,  Ecology of f i s h  growth,  J . , and T. L l o y d . 1963. Avoidance i n t h e guppy ( L e b i s t e s r e t i c u l a t u s ) . 12: 615-618.  Nature  conditioning P s y c h o l . Rep.  259 Werner, Y. L . 1969. Eye s i z e i n g e c k o s o f v a r i o u s e c o l o g i c a l types ( R e p t i l i a : G e k k o n i d a e and Sphaerodactylidae). I s r a e l J . Z o o l . 18: 291-316, W h i t e , H. C. 1936. The f o o d o f k i n g f i s h e r s and m e r g a n s e r s on t h e M a r g a r e e r i v e r , Nova S c o t i a . J , B i o l . Bd, Canada 2: 299-309. W h i t n e y , G. 1970. T i m i d i t y and f e a r f u l n e s s o f l a b o r a t o r y mice: an i l l u s t r a t i o n o f p r o b l e m s i n a n i m a l t e m p e r a ment. Behav. G e n e t . 1: 77-85. W i l l i a m s , G. C. 1964. Measurement o f c o n s o c i a t i o n among f i s h e s and comments on t h e e v o l u t i o n o f s c h o o l i n g . Pub. Mus. M i c h . S t a t e U n i v . , B i o l . S e r . 2: 351-383. W i l l i a m s , G. C. 1966. A d a p t a t i o n and n a t u r a l s e l e c t i o n . Princeton Univ. Press. P r i n c e t o n , N. J . 307 p . W i l l i a m s o n , K. 1952. Regional v a r i a t i o n i n the d i s t r a c t i o n d i s p l a y s o f the o y s t e r c a t c h e r , I b i s 9 4 ; 85-97, Wilz,  K. J . 1971. Comparative aspects o f c o u r t s h i p behavior i n the ten-spined s t i c k l e b a c k , Pygosteus p u n g i t i u s ( L . ) . Z. T i e r p s y c h o l . 29: 1-10,  Winge, 0. 1922a. A p e c u l i a r mode o f i n h e r i t a n c e and i t s c y t o l o g i c a l explanation. J . G e n e t . 12: 137-144, Winge, 0. 1922b. O n e - s i d e d m a s c u l i n e and s e x - l i n k e d i n h e r i t a n c e i n L e b i s t e s r e t i c u l a t u s . J . Genet. 12: 145-162. Winge, 0. 1927. The l o c a t i o n o f e i g h t e e n reticulatus. J . G e n e t . 18: 1-42,  genes i n L e b i s t e s  Winge, 0. 1934. The e x p e r i m e n t a l a l t e r a t i o n o f s e x chromosomes i n t o autosomes and v i c e v e r s a , as i l l u s t r a t e d by L e b i s t e s . C. R. L a b , C a r l s b e r g 21: 1-50. Winge, 0., and E . D i t l e v s e n . 1947. Colour inheritance"and sex d e t e r m i n a t i o n i n Lebistes. H e r e d i t y 1: 65-83, W o d i n s k y , J . , E . R. B e h r e n d , and M, E, B i t t e r m a n , 1962. Avoidance-conditioning i n two s p e c i e s o f f i s h , Anim. Behav. 10: 76-78. Worth, B.. 1967. A naturalist i n Trinidad, Philadelphia. 291 p.  Lippincott,  260 T. M., and A. S. Rand. 1971. Competition i n t r o p i c a l stream f i s h e s : support f o r the competitive e x c l u sion principle. E c o l o g y 52: 336-342.  APPENDIX Contents TABLE 1  2  Page P h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s o f s t r e a m s i n t h e N o r t h e r n Range r e g i o n The at  3  families 23  and  sites  Summary o f  i n the  the  predators of  4  Size  species of  statistics  diets the  of  fish  262  collected  N o r t h e r n Range r e g i o n of  the  guppy  main  . . .  268  potential . . . . . .  g u p p i e s u s e d i n Exp.  6.2.  . .  269  270  FIGURE 1 2  3  Map o f t h e e x p e r i m e n t a l s e c t i o n o f t h e P e t i t e Curucaye R , . » , , . , S i z e d i s t r i b u t i o n o f t h e e n t i r e guppy p o p u l a t i o n of the e x p e r i m e n t a l s e c t i o n of P e t i t e Curucaye R i v e r S i z e d i s t r i b u t i o n of the e n t i r e R i v u l u s p o p u l a t i o n of the e x p e r i m e n t a l s e c t i o n of P e t i t e Curucaye R i v e r . . . . . . . . . . .  261  271 272  273  262  TABLE 1.  Key  to  P h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s o f s t r e a m s i n t h e N o r t h e r n Range r e g i o n . The measurements were made i n 1969. For methods r e f e r t o C h a p t e r 2. For stream l o c a t i o n s and a b b r e v i a t i o n s r e f e r t o C h a p t e r 2, F i g u r e 1,  symbols  Weather:  S - f u l l sun; no l a r g e c l o u d s SP - sunny p e r i o d s ; no r a i n b u t i n t e r m i t t e n t cloud cover SPR - sunny p e r i o d s w i t h r a i n (L) - l i g h t r a i n (H) - h e a v y r a i n C - c l o u d y w i t h no sunny p e r i o d s CR - c l o u d y w i t h r a i n (L) o r (H) HR - h e a v y c o n t i n u o u s r a i n  Characteristics  of  stream:  W - mean w i d t h o f s t r e a m i n m e t r e s D - mean d e p t h o f s t r e a m i n m e t r e s a - a c o n s t a n t u s e d i n c a l c u l a t i n g volume of flow 0.9 - smooth s a n d , s i l t , mud 0.8 - r o u g h r o c k s , l a r g e p e b b l e s R - volume o f f l o w ( d i s c h a r g e ) i n m^/sec V - water v e l o c i t y o f main p o r t i o n o f stream i n m/sec T - w a t e r t e m p e r a t u r e i n °C DH - t o t a l d e g r e e s o f w a t e r h a r d n e s s i n ppm C - d e g r e e o f o v e r h e a d c o v e r (shade) 0 - no shade 1 - s m a l l amount o f shade r e s t r i c t e d m a i n l y t o streambank 2 .-- medium: shade' (50% c o v e r ) 3 - medium t o d e n s e (75% c o v e r w i t h few exposed p a r t s ) 4 - v e r y dense c o v e r w i t h v i r t u a l l y complete shading Turb - water t u r b i d i t y 0 - always c l e a r 1 - t u r b i d o n l y a f t e r heavy r a i n s 2 - t u r b i d throughout year  TABLE 1  Stream  (Continued)  Date 20 28 14 27 16 17 19 20 20 22 22 27 7 13 18 1 5  Mar Apr May  Jun Jul  Time  Weather  1100 1100 1400 1530 1645 1400 1630 1030 1630 0915 1445 1545 1400 1100 1315 1500 1730  S SP SPR(H)  —  SP s s SP HR S S SPR(H) C SPR S SP S  Means GCur  22 A p r 20 May  1100 0920  SP C  Means UCur  13 Mar  1330  S  TT  25 Mar  1400  SP  W 0.60 0.40 0.60 0.60  —  D  a  0.05 0.04 0.05 0.05  R 0.9  V 0.0072 0.0052 0.0054 0.0064  —  —  0.266 0.363 0.200 0.235  --  0.70  0.04  0.0048  0.190  0.75  0 .06  0.0202  0.500  —  — — -— —  —•  — — — —  — — —  — —  —  T  p  H  D  H  24.7 24.5 25.0 25.0 25.1 25.1 25.0 25.1 24.8 24.8 25.5 25.1 25.0 25.3 25.2 25.1 25.0  7.5 7.3 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7,2  300 300 280  C  Turb 4  —  260 250 250 240 220 220 220 200 210 230 180 150 170  0.90  0.07  0.0142  0.250  0.50 0.60  0.05 0.04  0.0064 0.0066  0.286 0.308  0.63  0.05  0.0085  0.289  25.0  7.2  230  1.00 --  0.15 --  0.0128 —  0.107 —  25,1 25.1  7.0 7.2  — 200  1.00  0.15  0.0128  0.107  25.1  7,1  200  —  24.8  7.4  305  3  0  26.2  7.2  —  4  0  —  —  —  —  —  --  0.8  ••—  0.8 0.90  0.11  0.9  0  0  3  TABLE 1 Stream UA(N)  (Continued) Date  Time  29 Mar 13 A p r 3Jul  1030 1120 1100  Weather SP S SP  W  D  ..  __  — —  -—  a  0.9  .R _  _  --  V  — —  Means UA(X)  29 Mar 13 May 3 Jun 15 21 3Jul  0930 1330 1500 1300 1200 1200  SP SP SPR(L) CR(H) CR(H) SP  Means UTac  15 A p r 24 May  1630 1520  SP S  Means  ——  T  pH  DH  C  24.5 24.8 24.5  7.5 7.6 7.4  210 190 150  3  0  24.6  7.5  183,3  7.6 7.6 7.6 7.0 7.2 7,6  220 190 130 110 90 150  3  0  2  0  0.0480  0.250  0.22  0.7040  1.000  4.00  0.08  0,1024  0.400  24.0 28.1 28.8 24.1 26.3 26,4  3.67  0,13.  . 0,2848 . 0.550  2.6,3  7.4  148,3  1.30 1.10  0.15 0,09  0.0780 0.0297  0.500 0.375  26.9 27.8  7.0 7.0  100 90  1.20  0.12  0.05 39  0.438  2.7.4  7.0  .9.5.  3.00  0.08  4.00  — —  0.8  0,8  Turb  UArouc  2 May  1500  S  2,00  0,06  0,9  0.0348  0.323  26 .8  7.0  2  0  UGuan  2 May  1200  S  5.00  0.10  0.8  0.2667  0.667  26.5  7.0  2  0  TABLE 1 ( C o n t i n u e d ) Stream BB  Date  Time  Weather  6 May 29 24 J u n  1220 1300 1400  SP SPR(L) SPR(L)  Means Mar  19 Mar 29 J u n  1530 1200  SP SP  Means Oro  8 Mar 25 A p r 10 May  1500 1030 1200  S SP S  16 7 9 12 17 30 12 10 30  Mar Apr  May Jun  Means  D  a  R  V  0.80  0.08  0.8  0.0279  0.545 0.500  0.0279  --  — —  0.80  0.08  4.50 5.00  0.20 0.11  4.75  0.16  6.00 —  1000 1115 1600 1100 1500 0630 1400 1500 1330  SP SP S C S S S S SPR(H)  pH  DH  24.9 24.9 25.2  7.6 7.4 7.6  140 150  0.523  25.0  7.5  145  0.360 0.259  0.500 0.588  23.5 25.1  7.1 7.2  ,140 100  0.309  0.544  24.3  7.2  120  „_  26.0 26.8 27.2  7.8 7.2 7.4  250  26.7  7.5  220  7.1 7.0 7.0 7.0 7.0 7.0 7.0 6.8 7.0  110 120 130 120 130 70 80  7.0  108.6  -••—  0.8  0.8 0.20  —  1.129  --  1.176  —  6.00  Means Guay  w  0.20  1.129  --  ---  2.00  1.50  1.08*  0.400  28.0 29.2 30.9 28.6 30.9 28.5 31.0 27.9 27,0  2.00  1.50  1.08  0.400  29.1  —  —  -—  _  —  --  —  ---  — —  0.9  1.176  T  —  —  —  - —  _  — — —  —  —  -T-.  •  * r o u g h a p p r o x i m a t i o n — t h e volume o f f l o w o f l o w l a n d r i v e r s d e p e n d i n g on s e a s o n and w e a t h e r .  i s very  C  Turb  3  0  2  0  2  0-1  1  2  r-T-  190  variable  TABLE 1 Stream Cap  (Continued  Date  Time  Weather  24 A p r 17 J u n 30  1100 1600 1200  S CR(H) CR(H)  Means Car  7 Apr 30 J u n  1100 1400  19 Mar 29 J u n  1700 1400  18 A p r 11 J u n 22 29 Means  1215 1400 1300 1600  a  R  0.9  V  T  PH  DH  7.0 6.8 7.0  110 110  5.00  1.50  2.25*  0.333  28.0 26.2 26.5  5.00  1.50  2.25  0.333  26.9  6.9  110  ~-  - r -  3.00  22.50*  0.333  30.2 27.2  7.0 7.0  170 90  25.0  3.00  22.50  0.333  28.7  7.0  130  0.0280 0.0289  0.667 0.348  24.0 26.0  7.1 7.0  140 80  0.0285  0.508  25.0  7.1  110  0,0828  0,172  7.1 7.0 7.0 7.0 7.0  SP CR(L)  Means Par  D  _ SP SPR(H) 25.0  Means Yar  W  SPR SP SPR(L) CR(L)  0.9  0.75 0.80  0.07 0.13  0.78  0.10  3.00  0.20  — —  4.00  --0.14  3.50  0.17  0.8  0.8  0.0729  0.163  25.0 26.5 25.0 25.1  0,0779  0.168  25.4  — 0.8  •—  -i-  100 100 90  C  Turb  0  2  0  2  2  0  2  0  96.7  to CTi  TABLE 1  Stream LA  (Continued)  Date  Time  Weather  2 Apr 3 Jun 21 3Jul  1115 1600 1600 1300  SP CR SPR(L) SP  Means LTac  5 Apr 10 3J u l  1000 1330 1530  CR —  SP  Means 13 28 14 16 5  Mar Apr May Jul  Means  1500 1330 1530 1715 1700  S SP SPR(H) SP S  w  D  T  pH  DH  C  Turb  7.5 7.2 7.0 7.2  230 90 90 100  2  0-1  127.5 2  0-1  7.00  0.13  0 . 4 C 4 0 0.555  26.5 25.5 25.6 26.4  6.00  0.13  0.3620  0.611  26.0  7.2  3.00  0.15  0  0  8.0 + 190 8.0+ 190 7.6 100  5.00 — —  0.12  V  R  a 0.8  0.3200  0.667  — —  —  3.00  0.15  0.150  0.417  28.4 33.5 30.0  3.00  0.15  0.075 .  0.209  .30.6  -*-  29.9 28.4 27.4 27.5 27,9  7.2 7.2 7.0 7.2  300 280 250 160  28,2  7,2  247,5  —  —  0.8  —  —  —  0.8  —  —  8.00  -—  8.00  0.20  0.768  —  — -  0,20  0.600 —  T- —  0.768  0.600  • . —  160 - r -  268a  TABLE 2.  The f a m i l i e s  and s p e c i e s  of fish  collected at  23 s i t e s i n t h e N o r t h e r n Range r e g i o n . list  o f stream a b b r e v i a t i o n s ,  refer  For a  t o F i g . 1.  FAMILY AND SPECIES  UCur PCur SLR MV TT GCur UA B3 Par Yar UArouc UGuan UTac LPar Mar LCur SC Oro LTac LA Cap Car Guay  F. P o e c i l i i d a e Poecilia reticulata  +  +  +  ++  +  +  +  + +  +  + +  +  +  +  + +  +  +  +  +  +  +  + +  +  + t  +  +  +  +  + b +  + +  +  +  + ++ +  + + + + +  + +  t +  F. Cyprinodontidae Rivulus h a r t i i  +  +  F. Cichlidae Aeguidens pulcher Cichlasoma biroaculatum Crenicichla alta T i l a p i a mossambica F. Characidae Astyanax bimaculatus Hemibrycon sp. Curiroata argentea Roboides dayi Kopliai~malabc Koplias malabaricus Corynopoina r i ji s e i Corynopoma Hemigrammus~unilineatus P r i s t e l l a r i d d l e i or Aphyocharax axelrodi F. L o r i c a r i i d a e Hypostomus r o b i n i i Ancistrus cirrhosus  +  + +  +  +  +  +  +  +  +  +  a  a  +  a  +  +  +  +  +  +  +  + +  + +  +  +  +  b  +  +  + + + + + ++ + + +  +  +  +  +  +  + +  a  +  F. Pimelodidae Rharr.dia sp.  +  +  +  +  F. Synbranchidae Synbranchus marmoratus  +  +  F. C a l l i c h t h y i d a e Corydoras aeneus  +  +  F. Mugilidae Agonostornus F.onticola (?) F. Gobiidae Sicydium sp. (?) Unidentified goby  + +  +  + •  .  + +  a - species not seen or c o l l e c t e d i n t h i s study but presence determined through personal communication residents. b - species present i n r i v e r according to Boeseman (1960).  M with l o c a l  O  °*  269a  TABLE 3.  Summary o f t h e d i e t s  o f t h e main  p r e d a t o r s o f t h e guppy. expressed occurrence  The d a t a a r e  as the p e r c e n t o f each food  potential  frequency  item.  of  RIVULUS B. B a s i n Tomp. T r i b . P. Curucaye  Source  Number examined Number empty S i z e range (mm)  CRENICICHLA L. A r i p o Maracas  259 5 22-105  14 0 60-195  AEQUIDENS  HEMIBRYCON  ASTYANAX  HOPLIAS L. A r i p o L. T a c a r i g u a Maracas Caroni Guayamare  L. A r i p o L. T a c a r i g u a Maracas  L. A r i p o U. A r o u c a Maracas  L. A r i p o L. T a c a r i g u a  42 5 80-148  64 3 62-90  28 1 45-116  Contents P. r e t i c u l a t a Other f i s h Oligochaeta Crustacea Mollusca Ephemeroptera Trichoptera Diptera Coleoptera Plecoptera Komcptera Hemiptera Arachnida Hymenoptera Odonata Orthoptera Chilopoda Diplopoda Thysanoptera Others^ Algae Vascular plants  .  c  10.2  14.3  42. 9  5.5 3.9 10.6 0.8 0.8 7.1 3.9 42.1 0.8 1.2 0.8 2.8 0.4 3.5 3.1 5.9  14.3 7.1 7.1  C  A11  2.7  4.9 1.6 3.3 8.2  29.6 3.7 11.1 3.7  3.3  64.3  2.7  22.9 1.6  3.7 25.9 7.4  10.8 2.7 2.7  27.9 27.9 3.3  18.5 40.7 25.9  alta.  Formicidae.  Unidentified  18.5 3.7a 3.7 3.7  29.7  F i s h vertebrae, scales. Crenicichla  1.6 a  l a r v a l and a d u l t i n s e c t p a r t s .  7 6 90-392  TABLE 4.  S i z e s t a t i s t i c s o f g u p p i e s u s e d i n Exp. 6.2. t o t a l length, n = 50 f o r e a c h mean.  x  A. 12 l i g h t — 1 2 d a r k SD SE Range  x  A l l sizes  a r e i n mm  B. 12 l i g h t — 1 2 d i m l i g h t SD SE Range  Females 1.  Lower A r i p o Guayamare  20. 34 21. 08  1. 61 1. 56  0. 23 0. 22  17. 0 -- 24 .0 17. 0 -- 25 .0  24.40 25.30  3. 32 4. 31  0 .47 0 .61  18 .5 17 .0 -  30 .0 33 .0  2.  21. 54 Lower A r i p o P e t i t e C u r u c a y e 22. 07  2. 32 2. 16  0. 33 0. 31  18. 0 -- 25 .5 18. 0 -- 25 .5  20.76 20.59  1. 84 2. 19  0 .26 0 .31  16 .0 - 25 .0 17 .0 - 26 .5  3.  Lower Paria  Aripo  22. 32 21. 43  2. 48 3. 67  0. 35 0. 52  17. 5 -- 26 .5 17. 0 -- 28 .5  20.92 21.95  5. 01 4. 13  0 .71 0 .58  16 .0 16 .0 -  34 .0 31 .5  4.  Lower Upper  Aripo Aripo  22. 40 22. 21  2. 99 2. 43  0. 42 0. 34  18. 0 -- 29 .0 18. 0 r- 28 .0  21.66 20.68  2. 26 1. 97  0 .32 0 .28  18 .5 17 .0 -  27 .0 25 .5  1.  Lower A r i p o Guayamare  20. 86 20. 64  1. 84 1. 70  0. 26 0. 24  17. 0 -- 27 .5 18. 0 -- 25 .0  19.31 18.54  1. 92 2. 02  0 .27 0 .29  16 .0 15 ,0 -  23 .5 23 .0  2.  21. 10 Lower A r i p o P e t i t e C u r u c a y e 21. 45  1. 48 1. 67  0. 21 0. 24  19. 0 -- 25 .0 18. 5 -- 25 .0  20.39 20.42  1. 48 1. 67  0 .21 0 .24  18 .0 17 .5 -  23 .5 24 .0  3.  Lower Paria  Aripo  21. 00 20. 39  1. 43 1. 38  0. 20 0. 19  18. 0 -- 24 .0 17. 5 -- 23 .0  20.74 20.64  1. 42 1. 31  0 .20 0 .19  18 .0 r- 23 .5 17 .5 r- 24 • 0  4.  Lower Upper  Aripo Aripo  21. 19 21. 50  1. 18 1. 82  0. 17 0. 26  18. 5 -- 24 .0 17. 5 -- 24 .5  18.79 20.18  2. 62 3. 09  0 .37 0 .44  16 .0 - 25 .0 16 .0 r- 26 .0  Males  271a  FIGURE 1.  Map  of the e x p e r i m e n t a l  P e t i t e Curucaye  R.  section of  the  271b  SCREEN 1 P E T I T E  CURUCAYE  POOL 1 (max. depth 17cm)  R I V E R  EXPERIMENTAL SECTION (July 1,1969 )  5 METRES  POOL 2 (max. depth 28cm)  10  POOL 3 (max. depth 16 cm)  4 (max. depth 8 cm) \  \  \  \  X \  \ \ \  N  \  SCREEN 3  l T  iPOOL 5 v|"OUT (to SANTA CRUZ R.-1.6 km)  272a  FIGURE 2.  Size  d i s t r i b u t i o n of the e n t i r e  p o p u l a t i o n of the experimental of  Petite  Curucaye  River.  guppy section  FREQUENCY  (%)  273a  FIGURE 3.  Size d i s t r i b u t i o n  of the  population  experimental  Petite  of the  Curucaye  River.  entire  Rivulus s e c t i o n of  273b  0  10 20 30 TOTAL  40  50 60 70 LENGTH  80 90 100 (mm)  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0100947/manifest

Comment

Related Items