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

Abstract

Diversity of species in communities of heteromyid rodents presents a classic problem to ecologists, because species are similar ecologically and share a limiting seed resource. Mechanisms of coexistence considered to date have focused on interspecific variation in ability to exploit heterogeneity in resources caused by environmental factors. An unexplored possibility is that coexistence is promoted by heterogeneity among species in seed-caching behavior. 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 rate, suggesting that energetics underlie food storage behaviors. Species also differed significantly in propensity to cache in the home burrow (larderhoard) versus in small depots outside the burrow (scatterhoard); scatterhoarding increased with body mass. Kangaroo rats scatterhoarded proportionally more than sympatric pocket mice, and species from California tended to scatterhoard more than those of similar body size from Arizona. These interspecific differences are consistent with the possibility that caching promotes coexistence. Our results appear to contradict those from a similar study of heteromyid caching behavior that used a different protocol for presenting seeds. This discrepancy underscores the importance of understanding the extent to which caching behavior is sensitive to details of experimental protocol or animal state and of moving experimental caching studies into more natural situations.