Effects of body size, seed density, and soil characteristics on rates of seed harvest by heteromyid rodents.

Although it is well established that coexisting heteromyid rodent species forage in different microhabitats, we do not yet know the basis for divergent microhabitat choice. One possibility is that seed harvest rates differ among microhabitats, and each species forages where it can extract seeds most efficiently. Microhabitats vary in several factors that could affect heteromyid foraging efficiency, including seed density, soil organic content and particle size distribution. We have explored the effect of each of these variables on harvest rates of several species feeding from petri dishes containing known densities of millet seeds embedded in soil of known particle size and density. Results indicate that the number of seeds harvested per second increases uniformly with seed density and soil density and decreases with soil particle size. Body size affects these relationships: larger animals have higher harvest rates for a given set of conditions and experience a greater relative change in harvest rate for a give change in conditions. This implies that heteromyids can be expected to exhibit species-specific microhabitat preferences while foraging in nature.