Ecological Distributin of Mice in the Medicine Bow Mountains of Wyoming

The distribution of six species of native mice with regard to plant communities, vegetative ground cover, and proximity of water was studied in the Medicine Bow Range of Southern Wyoming. The eight types of plant communities sampled were: mountain mahogany, sagebrush, aspen, subalpine meadow, willow—alder bog, lodgepole pine, spruce—fir, and alpine tundra. The western jumping mounse (Zapus princeps) and long—tailed vole (Microtus longicaudus) both reached their greatest densities in three habitats: Willow—alder, aspen forest, and subalpine meadows. Both species preferred sites adjacent to water and having dense ground cover. The montane vole (Microtus montanus) was most abundant in meadow situations as exemplified by alpine tundra and subalpine forb—sedge meadows. This species preferred moderate to dry situations and dense to intermediate ground cover. The redbacked vole (Clethrionomys gapperi) was by far the most abundant species taken in lodgepole pine and spruce—fir communities. This species occurred commonly at a distance from water and was equally abundant in areas of dense, intermediate, or sparse vegetative ground cover. The heather vole (Phenacomys intermedius) was not trapped in great numbers at any locale but was most frequently taken in subalpine meadows, spruce—fir forest, and alpine tundra, indicating the species is primarily a high altitude form. Heather voles exhibited no preferences with regard to proximity of water or density of ground cover. The deer mouse (Peromyscus maniculatus) was the most widely distributed species studied, but displayed particularly high densities in mountain mahogany and sagebrush communities. The habitats yielding the highest overall mouse production were those located at lower elevations in the mountains, i.e. the sagebrush, mountain mahogany, aspen, and subalpine meadows; while those habitats yielding the lowest number of mice were at highest elevations, i.e. lodgepole pine, spruce—fir, and alpine tundra. The proximity of water seemed to have no clearcut effect on the overall production of mice, although areas of dense cover were on the average twice as productive as those with sparse cover.