Niche Relationships of Dipodomys agilis and D. stephensi: Two Sympatric Kangaroo Rats of Similar Size

Abstract

-Congeneric heteromyid rodent species of similar size rarely occur in sympatry and use distinct habitats when they do. We characterized habitat use by two such species, Dipodomys stephensi and D. agilis, at two sites in western Riverside Co., California, and compared their selection of seeds and seed patches in the laboratory. At both localities, D. agilis.and D. stephensi were segregated spatially; D. agilis captured in areas with significantly greater cover of shrubs at both sites. In the laboratory, the species were very similar in choice of seed sizes and native seed species. Substrate use also was similar, but D. agilis avoided heavy substrates more than D. stephensi, and discriminant analysis correctly classified all individuals to species. The species differed significantly in response to light and artificial shrubs; D. agilis foraged under shrub canopies and avoided lighted open areas more than D. stephensi. Dipodomys stephensi consumed significantly more commercial seed with high oil and protein content. These differences suggest that the basis for divergent habitat selection in this case could involve a suite of factors related to effects of habitat on predation risk, water balance and, perhaps, foraging efficiency.