Subspeciation in the Meadow Mouse, Microtus montanus, in Wyoming and Colorado

University of Kansas Publications
Museum of Natural History
Volume 7, No. 7, pp. 489-506, 2 figures in text
July 23, 1954
University of Kansas Lawrence 1954
University of Kansas Publications, Museum of Natural History
Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Robert W. Wilson
Volume 7, No. 7, pp. 489-506, 2 figures in text Published July 23, 1954
University of Kansas Lawrence, Kansas
PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1954
25-3560
Microtus montanus reaches the eastern limits of its geographic distribution in Wyoming and Colorado. There the mountains, but in general not the lowlands, are occupied by this species. A certain minimum of moisture may be of direct importance to the mouse and certainly is indirectly important, because certain hydrophytic or mesophytic grasses used by the mouse for food, for protection from enemies, and for shelter from the elements are dependent on the moisture. Areas suitable for Microtus montanus are separated by deserts that are dominated by sagebrush and other xerophytic plants or by forests or rocky exposures at higher altitudes. A relatively small percentage, probably less than ten per cent, of the total area even in the more favorable parts of the range of the species is suitable for occupancy. In these mice, as in other microtines (Elton, 1942; Piper, 1909), there are seasonal, and irregularly multiannual fluctuations in population density, which sometimes are extreme. Consequently the mice at some times seem to be absent from suitable habitats, and at some other times occur there in amazingly large numbers.