Transcript Fowler - York College of Pennsylvania

Predation on guppies (Poecilia reticulata) by oscar cichlids (Astronotus ocellatus):
effects of varying prey color and prey size
Jason Fowler, Department of Biology, York College
Methods
Results
The aquarium was 205 liters, with 2 plastic guppy
containers on opposite ends and a 30 cm line
marked from each end.
Approaches
Introduction
Color is a sexually selected trait in guppies.
Female guppies prefer to mate with brightly
colored males over plain, grey colored ones.
Color seems to be an indicator of the quality of
the male guppy, with colored ones showing
greater boldness toward predators and a superior
ability to escape from them (Godin and Dugatkin
1996). However, color can also make the
guppies more visible and thus attract more
predators.
Limitations in previous research:
1) A small number of predator fish
species have been thoroughly
studied.
2) In the lab, predators have always been
tested individually.
3) Predator preferences for different
characteristics have never been directly
compared.
30 cm
60 cm
SP SP
SC SP
SP BP
BP SC
BC SC
Test
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3
10
4
5
6
8
30 cm
5 cm
Attacks
1
CONCLUSIONS
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1) Predator fish tested in groups display
similar preferences to those previously
tested individually.
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120 cm
2
Figure 1. The set-up of the aquarium (overhead view).
0
12 oscars were split into 2 equal groups.
Placed one guppy into each container and
subjected both groups to 5 tests:
1) Small Plain vs. Small Plain
2) Small Colored vs. Small Plain
3) Small Plain vs. Big Plain
4) Big Plain vs. Small Colored
5) Big Colored vs. Small Colored
3 measurements made during the testing period:
1) Number of approaches to each guppy
2) Number of attacks on each guppy
3) Time spent within each 30 cm line
Oscar acclimation period
1 day
Guppy acclimation period
5 minutes
After both groups were done testing, the groups
were rearranged and tested again. The groups
were then rearranged and tested for a third time.
Therefore, a total of 6 groups were tested.
SP SP
SC SP
(b)
BP SC
BC SC
250
2) Prey color and prey size are both
important factors in the selection of
guppies by oscars.
3) Prey color seems to play a larger role
in attracting oscars to the guppies.
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4) Once the guppy is visible, prey size
seems to be important in the decision
of whether or not to attack.
150
100
50
0
Future Studies
SP SP
SC SP
(c)
(d)
SP BP
Test
SP BP
BP SC
BC SC
Test
0.5
0.4
This study contained a very limited sample size,
so testing a larger number of fish will lead to an
even greater understanding of their preferences.
Also, future studies could examine predator
preferences for additional guppy characteristics,
such as group size.
Literature Cited
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Godin, J.J. and Dugatkin, L.A. 1996. Female mating
preference for bold males in the guppy, Poecilia reticulata.
Proceedings of the National Academy of Sciences of the
United States of America 93:10262-10267.
0.2
0.1
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Testing period
5 minutes
Based on the results of the five tests, the oscars
preferred:
1) Colored over plain
2) Big over small
3) Small colored over big plain
4) Big colored over small colored
These results were consistent across the three
measurements.
12
30 cm
2) To test predators as a group.
3) To determine whether prey color or
prey size is a more preferred
characteristic.
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(a)
OBJECTIVES
1) To study predator preferences in a new
species (Astronotus ocellatus).
Results
15
0
Time within 30 cm line (sec)
Predators seem to prefer:
1) Brightly colored over plain (Godin and
McDonough 2003).
2) Large over small (Johansson et al. 2004).
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5
Attacks per approach
Field and laboratory studies have been performed
to examine predator preferences for guppies
containing various intensities of color. In the field,
researchers have observed the color intensities of
guppies in high and low predation areas. In the
lab, they have exposed predator fish to guppies
and studied their behaviors. Similar experiments
have also been done looking at predator
preferences for different sizes of guppies.
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SP SP
SC SP
SP BP
BP SC
BC SC
Test
Figure 2. Means for the three measurements made during the fiveminute testing period. Six groups of oscars were tested. The four
types of guppy: small plain (SP), small colored (SC), big plain (BP),
and big colored (BC). Error bars represent one standard error of the
mean. (a) Number of approaches to each guppy. (b) Number of
attacks on each guppy. (c) The total amount of time spent within
each 30 cm line. (d) Number of attacks per approach to each guppy.
Godin, J.J. and McDonough, H.E. 2003. Predator
preference for brightly colored males in the guppy: a viability
cost for a sexually selected trait. Behavioral Ecology
14(2):194-200.
Johansson, J., Turesson, H. and Persson, A. 2004. Active
selection for large guppies, Poecilia reticulata, by the pike
cichlid, Crenicichla saxatilis. Oikos 105:595-605.
Acknowledements
I would like to thank Dr. Rehnberg for his guidance throughout this project.