Seed caching by heteromyid rodents from two communities: Implications for coexistence

Diversity of species in communities of heteromyid rodents presents a classi c problem to ecologists, because species are similar ecologically and share a Limiting seed resource. Mechanisms of coexistence considered to date hav e focused on interspecific variation in ability to exploit heterogeneity in resources caused by environmental factors, An unexplored possibility is th at coexistence is promoted by heterogeneity among species in seed-caching b ehavior. To begin evaluating this possibility, we asked whether coexisting species differ in their propensity to cache and in types of caches made. In an indoor arena, we presented millet seeds to 8 species of kangaroo rats ( Dipodomys) and pocket mice (Perognathus and Chaetodipus) from 2 communities , 1 in California and 1 in Arizona. Species within communities differed in amounts of seed consumed and cached per night, Both consumption and caching increased with body mass in a manner similar to whole-animal metabolic rat e, suggesting that energetics underlie food storage behaviors. Species also differed significantly in propensity to cache in the home burrow (larderho ard) versus in small depots outside the burrow (scatterhoard); scatterhoard ing increased with body mass. Kangaroo rats scatterhoarded proportionally m ore than sympatric pecker mice, and species from California tended to scatt erhoard more than those of similar body size from Arizona. These interspeci fic differences are consistent with the possibility that caching promotes c oexistence. Our results appear to contradict those from a similar study of heteromyid caching behavior that used a different protocol for presenting s eeds. This discrepancy underscores the importance of understanding the exte nt to which caching behavior is sensitive to details of experimental protoc ol or animal state and of moving experimental caching studies into more nat ural situations.