Effects of seed distribution and competitors on seed harvesting efficiency in heteromyid rodents.

The foraging strategies of four naturally co-existing heteromyid rodent species were investigated: Dipodomys deserti (≈100 g), D. merriami (≈38 g), Microdipodops pallidus (≈13 g), and Perognathus longimembris (≈7 g). In 208 over-night laboratory foraging trials animals were provided with millet seed distributed in clumped and scattered patterns. Net removal of seeds from the foraging arena and amounts of seeds in cheek pouches and in caches were determined. When alone in an areana none of these species specialized extensively on either clumped or scattered seeds, although each tended to take more clumped than scattered seeds. When placed together with other individuals, animals once again tended to cache more clumped than scattered seeds in all but one paired combination of species: P. longimembris cached more scattered than clumped seeds when opposed by D. deserti. This suggests that the smaller species obtained a less preferred distribution of seeds in the face of competition. The two smaller species showed a great reduction in general foraging success in the presence of either of the two larger species. In general, a species cached less seeds when faced by larger opponent species.