COMMUNITY ORGANIZATION OF ARVICOLINE RODENTS IN NORTHERN ALASKA

The community organization of arvicoline rodents was studied on 18 liv e-trapping grids near Toolik Lake on the North Slope of Alaska, At mod erate densities, tundra voles were more abundant on grids with more we t habitat, with more highly preferred food (cotton grass) and with les s shrub cover; singing voles were more abundant on grids with less wet habitat, with more highly preferred food (horsetail) and with more co ver;and collared lemmings were more abundant on grids with more highly preferred food (willow) and with less cover. Tundra vole and singing vole populations were negatively associated, probably because of their very different habitat preferences. At low densities, experimental ma nipulation of food, cover and competing species on the same 18 grids r evealed different effects on the arvicoline species. Abundance of tund ra voles increased with supplemental food, but singing voles and colla red lemmings showed no significant responses. Singing vole populations had a clear negative response, but tundra voles and collared lemmings had no significant response to removal of shrub cover. Similarly, col lared lemmings showed no response to removal of tundra voles or singin g voles, and tundra voles showed no response to removal of singing vol es, but singing voles showed a negative response to removal of tundra voles. The apparent mutualistic relationship between tundra voles and singing voles probably resulted from an indirect effect via predation, i.e., more predation on singing voles when tundra voles were removed. We conclude that the community organization of arvicoline rodents nea r Toolik Lake is strongly influenced by availability of preferred food s and by predation but less so by interspecific competition, at least when densities are low.