Habitat Selection and the Community Matrix of a Desert Small-Mammal Fauna

This study considers several questions about interspecific competition and habitat use by desert small mammals. From 1971 through 1973, rodent population data were collected by live—trapping on a creosote bush bajada located near Las Cruces, New Mexico, USA. At each trap station, measurements of the vegetation were taken to provide a description of the microhabitat surrounding each station. Multiple regression analysis was used to estimate the effects of competition and habitat selection in determining the local distributions and abundances of the rodent species in each year. The 10 species form four guilds: (1) Onychomys arenicola, (2) Neotoma albigula and N. micropus, (3) Dipodomys merriami and D. ordii, and (4) Perognathus intermedius, Pg. penicillatus, Peromyscus eremicus, P. maniculatus, and P. leucopus. None of the competition estimates for between—guild interactions was significantly negative, indicating that a species in one guild did not have any inhibitory effects on species in other guilds. Coexistence of the four guilds was attributable in some cases to differences in food and habitat preferences, and in others to differences in foraging methods related to body size. Competition was not observed within the Dipodomys guild because of the different microhabitat specializations of the two species. The three Peromyscus spp. appear to avoid competition with each other by complementary habitat use; competition was observed within the Perognathus—Peromyscus guild, but only among Perognathus intermedius, Pg. penicillatus, and Peromyscus eremicus. The magnitudes of the observed competitive interactions varied significantly from year to year with changes in both rodent densities and resource availabilities. The competitive relationships within the guild were consistent, however, and the three species were ranked in increasing competitive ability; Perognathus penicillatus < Perognathus intermedius < Peromyscus eremicus. Some evidence suggests that competitive ability increases with increasing habitat specialization.