Great Basin Naturalist


Some ecological relationships and interspecies interactions (i.e., habitat, foods, and reproduction) between Microtus pennsylvanicus pullatus, M. montanus nanus, M. longicaudus mordex, and Clethrionomys gapperi galei were investigated in Grand Teton National Park, Wyoming. Trapping was conducted from June–July, 1968 and May–July, 1969 yielding 110 M.p.p., 171 M.m.n., 17 M.l.n. and 41 C.g.g. Six plant communities were defined structurally; all communities contained voles but varied considerably in numbers of species and individuals. Analyses of stomach contents showed similar diets. Embryo counts indicated that there was no significant interspecies differences in litter sizes. Females of all species were pregnant in about equal proportions. Almost all adult males showed descended testes and were reproductively active. Testicular and seminal vesicle weights and lengths fluctuated. M.p.p. mean body weights were largest: M44.7g (N = 31). F38.1g (N = 29); this was nearly twice the mean weights of C.g.g.: M20.4g (N = 7), F23.3g (N = 3). Weights for M.m.n. and M.l.m. fell between these extremes and were similar to each other. Trends in differential habitat use were clearly demonstrated and evidence suggests the four microtines are at least partially incompatible.