Small Mammal Distributions in Riparian and Adjacent Habitats of Grand Teton National Park, Wyoming

Abstract

Riparian ecosystems are among the most productive biological systems providing food, water, shade, and cover for wildlife (Thomas et al. 1979a). Furthermore, they may display a greater diversity of plant and animal species and vegetative structure than adjacent ecosystems (USDI 1986). Thomas et al. (1979a) provide a descriptive definition which characterizes riparian ecosystems by the presence of trees, shrubs, or herbaceous vegetation that require free or unbound water, or conditions that are more moist than those of the surrounding areas. They suggest that more wildlife species depend entirely on or spend disproportionally more time in riparian habitat than any other. Although the importance of riparian vegetation to wildlife has been apparent since the 1970's, its overall importance to vertebrate species has not been widely studied, especially in the western United States (Patton 1977). Elsewhere, there is a paucity of information on the ecological role of small mammals in riparian areas. Because small vertebrate species may serve as an especially important link in the food chain of threatened, endangered, or reintroduced species, and because small mammal species seem to be compacted in environmentally diverse areas, analysis of riparian vertebrate communities should provide important insights in mechanisms of habitat subdivision and utilization. Clearly, riparian areas contain a greater variety of species than adjoining forest or upslope habitats (Cross 1985). The effect of patch shape on the number of species occupying riparian habitats also has received limited attention (Patton 1975). Because riparian habitat consists of a narrow patch, the elongated shape of riparian areas produces a low interior-to­high-edge ratio which may facilitate or enhance ecological processes, especially the production and dispersal of small mammals. Unfortunately, no documentation exists about patterns of mammalian movement along stream corridors (Forman and Godron 1986). Thus, the importance of the relative use of the edge, riparian, and upland areas by small mammals needs to be investigated, especially in forested mountain land, where riparian areas tend to have smaller areal extent and economic value than upslope vegetation (Swanson et al. 1982). The principle objective of our study was to determine if consistent environmental and landscape features could be found in western riparian, edge, and upland communities, and if these features affected residency of small mammals in Grand Teton National Park. Three independent study sites were studied from June, 1991 through October, 1991 in preparation for a proposed long-term analysis of the role of riparian areas in production of small mammals.