Competition and Habitat Selection: Test of a Theory Using Small Mammals

Abstract
Two hypotheses about community structure were examined for the small mammals occupying a wet grassland in southwest North Dakota, USA. The possibility of competition and the possible relationship between competition and habitat selection was studied. Relative densities of Microtus pennsylvanicus, Zapus hudsonius, Spermophilus tridecemlineatus and Peromyscus maniculatus were determined by live-trapping in July and Sept. 1976. Species interactions and patterns of habitat occupancy were examined using regression analysis. Microtus, Zapus and Spermophilus were each competitively dominant to Peromyscus. No competitive effects were observed among Microtus, Zapus and Spermophilus. The 4 spp. differed markedly in habitat utilization. Microtus, Zapus and Spermophilus were each specialized on different habitats. Peromyscus was a habitat generalist and its distribution was determined primarily by competitive interactions with the other species.