Bipedal Hopping and Seed‐dispersion Selection by Heteromyid Rodents: The Role of Locomotion Energetics

Selection of seeds with different dispersion patterns, facilitated by the energetic differences between bipedal—hopping and quadrupedal heteromyid rodents, has been proposed as a mechanism of resource allocation for microsympatric species. To test several aspects of this hypothesis, field observations of foraging behavior and laboratory measurements of locomotion costs were made for several species of heteromyids. Neither the field observations nor the laboratory measurements supported predictions generated by the seed—dispersion hypothesis. Locomotion costs of the bipedal—hopping Dipodomys deserti and D. merriami were similar to those predicted for quadrupeds of equal mass. At low speeds, the cost of quadrupedal locomotion was not greater for a small, hopping biped than would be expected for a similar—sized quadruped. Free—living Dipodomys deserti, D. merriami, and Perognathus longimembris spent most of their foraging time either stopped or moving at slow speeds. High—speed locomotion, at which energetic "savings" by bipeds should be greatest, was rare. These results led to the conclusion that the energetic costs of different locomotory modes do not play a major role in resource allocation for Mojave Desert heteromyids.