The Effect of Resource Distribution and the Presence of a Predator on
Habitat Selection by Danio rerio
Leslie Jaynes, Advisor: Dr. K. Lustofin
Danio rerio will disperse proportionally to the ratio of resource available when
predators are absent, thus an ideal free distribution will be observed. However, in
the presence of a predator, D. rerio will experience an anti-predatory response that
will disrupt their “ideal” distribution, ignoring resource availability (Moody et al.,
1996, 139).
METHODOLOGY
D. rerio were divided into 3 test groups consisting of 12 individuals. Test groups
were deprived of food for 24 hours prior to experimental trials.
Satiation (x) was determined via dispersal of 0.01g fish flakes to each test
group. Upon complete consumption of fish flakes, D. rerio were awarded another
0.01g portion until satiation was reached. Satiation values among test groups were
averaged to generate feeding ratios utilized in subsequent experiments.
A 20 gal aquarium, divided equally in two
halves, served as the experimental apparatus
to establish the distribution of D. rerio in
Figure 1: Apparatus
relation to resource distribution in absence
of a predator. The average satiation was used
to generate feeding ratios related to the
location and the amount of food dispersed
per trial. Feeding treatments included
0.50(x) to 0.50(x), 0.67(x) to 0.33(x), and
Predator Absent
0.33(x) to 0.67(x). The repetition of the
0.67(x) to 0.33(x) and 0.33(x) to 0.67(x)
feeding ratios served as a control. A total
of 3 trials were completed for each feeding
Treatment; each trial lasted for a duration
Predator Side A
of 300 seconds.
The effect of predator species Chitala
chitala was determined via replication of
the previous experiment, alternating the
presence of a predator on either side of
the aquaria. A separate aquarium was used
Predator Side B
to house C. chitala to prevent influence of
olfactory and lateral line cues on D. rerio.
Figure 1 depicts the experimental apparatus.
Experimental trials were recorded and used to collect data by counting the
number of fish on each side of the aquaria every 10 seconds. Statistical analysis
included the use of t-test, chi-square, and linear regression.
Percent D. rerio per Side
Figure 2 illustrates the results for experiment I. If IFD were observed, one would
expect the proportion of D. rerio on side A to match the proportion of food dispensed on
side A. Chi-square analysis revealed a significant difference between the observed and
expected distribution (IFD) when X2 = 85.96, X0 = 11.07 α = 0.05 df = 5. Although D. rerio
did not distribute themselves according to IFD, a general trend was observed: as the
proportion of food increased, the proportion of fish also increased.
Figure 2: Percent of D. rerio per feeding ratio (Side A vs. Side B)
100%
80%
65.83
60%
46.02
52.41
Side B
Side A
40%
20%
34.17
53.98
47.59
0%
33% food
50% Food
67% Food
Feeding Treatment in relation to Side A
DOES A PREDATOR ALTER D. rerio DISTRIBUTION?
Figure 3 illustrates the results for the combined data of Experiment II. Chi-square
analysis revealed a significant difference between the observed and expected distribution
of D. rerio, therefore the presence of a predator significantly altered the distribution of D.
rerio observed in Experiment I (X2 = 96.09, X0 = 5.99 α = 0.05 df = 2). Resource availability
was not ignored; only when a majority of food (67%) was dispersed on the side where
predators were present, were a greater proportion of D. rerio willing to risk predation.
Figure 3: Percent of D. rerio per feeding ratio
(Presence vs. Absence of a Predator)
100%
80%
64.86
60%
43.61
63.47
Predators
Absent
Predators
Present
40%
20%
35.14
56.39
36.53
0%
BIAS IN DATA?
33% food
50% Food
67% Food
Feeding Treatment: Predator Present
(Presence vs. Absence of a Predator)
70.09 59.63
29.91 40.37
72.69
27.31
54.26
45.74
50.83
49.17
Feeding Treatment: Predator Present
45
Predators Side B
35
Ideal Free
Distribution
25
30
40
50
60
Percent Food on Side A
70
CONCLUSIONS
Experiment I focused on resource distribution in order to determine if IFD could
be observed. The hypothesis was not supported because IFD was not observed
according to the chi-square analysis, however the data illustrates as the proportion
of food increased, the proportion of D. rerio also increased, therefore resource
availability is not ignored in habitat selection.
Experiment II determined if the presence of a predator altered the distribution of
D. rerio observed in Experiment I. The hypothesis predicted two outcomes: the
presence of a predator would alter the distribution of zebrafish observed in
experiment I and that D. rerio would ignore resource availability in relation to
habitat selection. According to Chi-square analysis, the presence of a predator
significantly altered the distribution of D. rerio thus supports the first portion of the
hypothesis. D. rerio did not ignore resource availability, as indicated by the
increased proportion of D. rerio willing to risk predation when a majority of the
resources were found were predators present.
LITERATURE CITED
Figure 4 illustrates the differences in the distribution of D. rerio when predators were
on side A compared to side B. There is consistently a greater proportion of D. rerio on side
B. A clear bias toward side B was revealed with a t-test comparing replicates of each
feeding treatment.
• 33% Feeding Treatment: t-stat (2.24) > t-crit (1.67) ; p-value = 1.44E-2
• 50% Feeding Treatment: t-stat (5.25) > t-crit (1.67) ; p-value = 1.0E-6
• 67% Feeding Treatment: t-stat (3.85) > t-crit (1.67) ; p-value = 1.5E-4
•Chi-square: X2 (232.32) > X0 (9.68); α = 0.05; df = 11
Figure 4: Percent of D. rerio per feeding ratio
100%
80%
60%
40%
20%
0%
Figure 5 illustrates the data within the context of IFD. When predators were
absent, D. rerio distributed themselves in relation to resource distribution, however,
not to the extent predicted by IFD. A predator’s presence caused a significant shift in
the distribution of D. rerio, favoring the side of the aquaria where predators were
absent. The contrast of D. rerio distribution when predators were on side A vs. side B
suggest bias. Despite the presence of a predator, resource distribution was not
ignored; D. rerio were more willing to risk predation to take advantage of available
resources at high feeding treatment.
Figure 5: Percent of D. rerio vs. Percent Food on Side A
75
Predators Absent
65
Predators Side A
55
Percent D. rerio on Side A
HYPOTHESIS
IDEAL FREE DISTRIBUTION OBSERVED?
Percent D. rerio per Side
The theoretical concept of Ideal Free Distribution (IFD) is often used to describe
and predict habitat selection when resources vary among habitat patches (Fretwell
and Lucas, 1968, 22). Specifically, IFD is the theoretical point where discrete habitat
patches yield equal suitability despite resource abundance or allocation, due to
relative densities of the organisms using those resources (Fretwell and Lucas, 1968,
22). Assumptions of IFD include individuals will maximize access to resources to
promote individual fitness and individuals will have equal access to resources and
thus have equal success probability (Fretwell and Lucas, 1968, 21).
In absence of predators, IFD has been observed in several species including
threespined sticklebacks Gasterosteus aculeatus (Gotceitas and Colgan, 1991, 72),
and cichlid Aequidens curvieeps (Godin and Keenleyside, 1984, 128). Theoretical
models depict predation as a key variable of distribution of foragers (Moody et al.,
1996, 139), yet it has been found that the presence of predators has failed to
disrupt the resource dependent distribution of the northern redbelly dace, Phoxinus
eos (Dupuch et al., 2009, 710). This study seeks to examine the concept of IFD and
determine the effect of a predator’s presence on the distribution of D. rerio when
resources vary among habitat patches.
RESULTS & DISCUSSION
RESULTS & DISCUSSION
Percent D. rerio per Side
INTRODUCTION
36.39
63.61
Predators
Absent
Predators
Present
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and inherent habitat riskiness on simultaneous habitat selection by predators and
prey. Animal Behaviour. 78(3):705-713.
Fretwell SD, Lucas HL Jr. 1968. On territorial behavior and other factors influencing
habitat distribution in birds I. theoretical development. Acta Biotheoretica.
19(1):16-36.
Godin JJ, Keenleyside MH. 1984. Foraging on patchily distributed prey by a cichlid
fish (Teleostei, Cichlidae): a test of the ideal free distribution theory. Animal
Behaviour. 32(1):120-131.
Gotceitas V, Colgan P. 1991. Assessment of patch profitability and ideal free
distribution: the significance of sampling. Behaviour 119(1/2): 65-76.
Moody AL, Houston AI, McNamara JM. 1996. Ideal free distributions under
predation risk. Behavioral Ecology and Sociobiology. 38(2):131-143.
ACKNOWLEDGEMENTS
I would like to thank Dr. Lustofin, Dr. McShaffrey, and Professor Jarrell for their
invaluable help and guidance throughout this process. I would like to thank the
Marietta College Biology Department for funding this project. Last, but certainly not
least, I would like to thank my family, friends, and capstone class which have
continued to support my efforts