Microhabitat Use by Heteromyid Rodents: Effects of Artificial Seed Patches

Coexisting heteromyid rodent species differ in their affinities for foraging microhabitats. Bipedal forms (Dipodoyms, Microdipodops) use open spaces preferentially, while quadrupedal forms (Perognathus) use spaces under or near vegetation. Despite consistent reports that these preferences occur in heteromyid assemblages throughout North American deserts, and despite frequent speculation about the importance of foraging economics and predation risk in producing them, few experimental analysis of microhabitat use exist. Here we describe studies showing that (1) microhabitats distinguished by heteromyids in nature differ in seed abundance, soil particle size, and soil density, all of which are features that have been shown to influence heteromyid foraging efficiency; (2) four coexisting species differ in their preferences for artificial seed patches in a large laboratory foraging arena, and differences in the properties of preferred and nonpreferred patches correspond qualitatively to differences in the attributes of preferred and nonpreferred microhabitats in nature; and (3) microhabitat use in nature, as measured by livetrapping, can undergo rapid shifts that track the location of preferred artificial seed patches placed either in open spaces or under vegetation. These results suggest that divergent microhabitat specializations of coexisting heteromyids are in part functions of divergent preferences for the particular combinations of seeds and soils found in various microhabitats. Further experimental studies are needed, however, to determine whether these preferences can be predicted accurately from knowledge of the economics of foraging, and to what extent other factors may also influence microhabitat choice.