Selection of Seed Distribution Types by Dipodomys Merriami and Perognathus Amplus

Laboratory experiments were conducted to investigate the foraging responses of kangaroo rats (Dipodomys merriami) and pocket mice (Perognathus amplus) to aggregates of seeds which differed in size, depth, and degree of clumping. Kangaroo rats effectively used clumps of seeds, whereas the pocket mice did not differentially select clumps of seeds over a scattered distribution of seeds. In addition to distribution, clump size and depth were important criteria for both species in determining foraging efforts. These data, coupled with recent information which suggests wide arrays of seed distribution types in the desert, lead us to propose that rodents select seeds on the basis of spatial distribution of the resource. This is an attractive hypothesis because it can accommodate both of the primary mechanism previously suggested for desert rodent coexistence, seed size selection and habitat selection.