White-Tailed Deer in a Patchy Environment: A Test of the Ideal-Free-Distribution Theory

Abstract

We investigated distributional patterns of captive white-tailed deer ( Odocoileus virginianus ) during feeding trials relative to foraging rewards in two artificial patches of resources under three reward ratios. At equilibrium density, deer used the poor patch more than predicted from a simple density-dependent model of their spatial distribution (ideal-free distribution). Consequently, deer foraging in the rich patch received higher benefits at equilibrium distribution than did those foraging in the poor patch. We tested four alternative explanations of the observed deviation from the simple, ideal-free-distribution model; 1) difference in competitive abilities of individuals, 2) a perceptual limitation in the capacity to distinguish among quality of patches, 3) the role of interference at high densities, and 4) sampling. Foraging rates did not differ among individuals, suggesting that competitive abilities were similar between individuals and did not appear responsible for the observed deviation from the ideal-free distribution. Similarly, we found no evidence for a perceptual constraint or increasing interference among foraging individuals when the number of competitors increased. We suggest that the deviation from the predictions of the ideal-free distribution were a necessary consequence of information gathering and processing from continued sampling of patches by deer.