Home Range, Territoriality and Ecological Separation in Sympatric Shrews, Sorex vagrans and Sorex obscurus

Abstract

Spatial and temporal analyses of home ranges of sympatric Sorex vagrans and S. obscuras are made using an elliptical model. The occurrence of both intra- and interspecific territoriality is analyzed and discussed in context of competition and habitat preference. In both species, individual home range size increases significantly with the onset of reproductive activity, with males enlarging their home ranges to a greater extent than do females. Home range location tends to remain stationary throughout life, particularly in females. A territorial system is established among nonbreeding animals during their first summer. Territories are maintained only by the young of the year against members of their generation, and appear to be defended both intra- and interspecifically, although interspecific nonoverlap is attributable in part to different habitat preferences. Territorial systems break down with the onset of reproductive activity the following year. The establishment of territories early in life ensures successful individuals sufficient food during the limiting winter months, and acts as a density regulation mechanism at the population level. Individual success in overwintering, measured by attainment of sexual maturity the following year, is highly correlated with territorial success. The allotopic distribution of species and nonoverlap of individual home ranges between species are interpreted as functions of both interspecific territoriality resulting from competition as well as the ability of each species to compete more successfully in its preferred microhabitat. Possible factors allowing each species to be competitively superior in its habitat are suggested.