Patterns of Niche Shift in Mice: Seasonal Changes in Microhabitat Breadth and Overlap

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Abstract
Seasonal changes in niche overlap have been used as evidence for the importance of competition in structuring natural communities. Schoener (1982) reported less niche overlap in a lean season than in a fat season in 90% of 30 cases gleaned from the literature, and he argued that competition could account for this consistent pattern. Appropriate interpretation of such evidence depends on a knowledge of changes in the population densities of potentially competing species. In this study of microhabitat utilization by Peromyscus maniculatus (deer mouse) and P. truei (pinyon mouse) in a pinyon-juniper woodland, niche overlap was significantly less in winter and in the second summer period than in the first summer of the study. These seasonal differences were associated with changes in population densities of the two species. Evidence that competition is important in this system is that microhabitat niche overlap correlated negatively with pinyon mouse population density during the summer months, and particularly that the use by deer mice of the microhabitat preferred by both species (but especially by pinyon mice) was negatively correlated with pinyon mouse density. Pinyon mice were much more specializd than deer mice in microhabitat use, and the interactions of the two species are consistent with an included-niche model of interference competition.