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 th at promote coexistence among sympatric rodents in North American deser ts. In an effort to determine how the distribution of seeds influences foraging patterns and coexistence in a three-species community of het eromyid rodents, we developed a computer simulation model that determi nes the efficiency of foraging for animals of different sizes. Specifi cally, the simulation determines how long it would take a forager to g ather sufficient energy for 24 h if the animal stopped at seed patches of certain densities. The analyses were conducted for naturally occur ring seed distributions and densities, for simulated normal and unifor m 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 di fferent 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 discus sed.