Community Structure in Sympatric Rodents

Species diversity, microhabitat separation, microhabitat shifts and body size patterns are examined in seven sympatric rodent species. Habitat separation and seasonal shifts are identified by multiple—group discriminate analysis on microhabitat variables representing shrub structure and substrate patchiness. The rodents form two functional groups. Four permanent, year—round residents (Peromyscus eremicus, Neotoma lepida, Neotoma fuscipes, and Dipodomys agilis) show significant separation on habitat structure and some temporal habitat shifts. Three seasonal residents (Peromyscus maniculatus, Peromyscus, and Reithrodontomys megalotis) show no microhabitat shifts and have a greater frequency of microhabitat overlap with one another and with permanent residents. There is no relationship between niche breadth and population density for any given species; however, as a group, seasonal residents show reduced breadth with increased population density. The significance of this pattern is discussed with respect to ecological opportunism of seasonal residents. The pattern of body size differences within the fauna is examined in light of habitat structure. Pairwise differences in habitat structure and body size are positively correlated. The data show that permanent residents are more different from one another in body size and structural habitat than pairs in which at least one species is a seasonal resident. Increased similarity in body size and microhabitat structure may not favor year—round coexistence in some pairs of species. The most similar—sized pair of species are congeneric deer mice (P. eremicus and P. maniculatus), and in addition to seasonal separation, they show niche difference by habitat structure.