Spatial Patterns in Sizes of Seeds Collected by Four Species of Heteromyid Rodents

The results show that the difference between rodent species in the size of seeds they collect depends upon the difference in microhabitat selection of the species, and these two components of the niche reduce to a single dimension.

Abstract

This research was designed to provide information on the spatial variation in size of seeds collected by four species of heteromyid rodents. During summer 1975, rodents (Dipodomys merriami, Perognathus amplus, P. baileyi, and P. penicillatus) were live—trapped on several Sonoran Desert habitats at the Saguaro National Monument in southern Arizona, USA. In 1976 and 1977 a single study area containing all four rodent species was live—trapped to provide information on microhabitat and seed use among coexisting species. Any seeds contained in the cheek pouches of the rodents were identified and their linear dimensions were measured. Microhabitats were quantified by enumeration of shrubs and measurement of their size. Much of the variation in collection of different—sized seeds is attributable to habitat and microhabitat differences between rodent species. Not only do rodent species collect seeds of different size among different habitats, but within a habitat, locally coexisting rodent species collect seeds of different size. As a test of the concept of independent use of two resources (seed size and microhabitat) by coexisting species, seed size differences were compared to microhabitat differences between all pairs of heteromyid rodents. The results show that the difference between rodent species in the size of seeds they collect depends upon the difference in microhabitat selection of the species. Hence, these two components of the niche (seed size and microhabitat) of coexisting heteromyid rodents reduce to a single dimension.