1. The Effect of Resource Distribution and the Presence of a Predator on Habitat Selection by Danio rerio Leslie Jaynes, Advisor: Dr. K. Lustofin 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 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 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 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 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. METHODOLOGY 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). HYPOTHESIS 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. INTRODUCTION Figure 1: Apparatus Predator Absent Predator Side A Predator Side B RESULTS & DISCUSSION IDEAL FREE DISTRIBUTION OBSERVED? 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 X 2 = 85.96, X 0 = 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. 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 (X 2 = 96.09, X 0 = 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. BIAS IN DATA? 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: X 2 (232. 32 ) > X 0 (9.68); α = 0.05; df = 11 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. RESULTS & DISCUSSION 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 ACKNOWLEDGEMENTS Dupuch A, Dill LM, Magnan P. 2009. Testing the effects of resource distribution 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. 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