Computer-Simulation Analysis of Foraging by Heteromyid Rodents in Relation to Seed Distributions - Implications for Coexistence

A number of hypotheses have been proposed to explain the mechanisms that promote coexistence among sympatric rodents in North American deserts. In an effort to determine how the distribution of seeds influences foraging patterns and coexistence in a three-species community of heteromyid rodents, we developed a computer simulation model that determines the efficiency of foraging for animals of different sizes. Specifically, the simulation determines how long it would take a forager to gather sufficient energy for 24 h if the animal stopped at seed patches of certain densities. The analyses were conducted for naturally occurring seed distributions and densities, for simulated normal and uniform distributions at natural densities, and for natural distributions at seed densities one-third those known to occur naturally. The results indicate that, under natural distributions and densities, each of the three species possessed unique optima for utilising seed patches of different density. However, when either the seed distribution or density differed from actual values, all three species had identical optima. The implications of these results for promoting coexistence are discussed.