Date of Award
Doctor of Philosophy
The life-history tactics of Clethrionomys gapperi and Microtus pennsylvanicus were examined at two elevations (1450m; 2240m) in southwestern Alberta (Kananaskis Country) to test the hypothesis that females in environments with shorter breeding seasons should produce fewer but larger litters and survive less well than those in environments with longer breeding seasons (Spencer and Steinhoff 1968). Other life-history traits such as body weights and the energetics of reproduction were also compared between elevations.;Life-history data were collected by mark-recapture techniques, kill-trapping and from laboratory colonies.;The high elevation was colder, had fewer frost-free days and more precipitation than the low elevation. The length of the breeding season of C. gapperi averaged two days longer at the low elevation than at the high elevation. The length of the breeding season of M. pennsylvanicus averaged 27 days longer at the low elevation than at the high elevation. The shorter breeding season of M. pennsylvanicus at the high elevation may have been related to spring flooding and colder temperatures compared to the low elevation.;As predicted, the lack of a difference in the lengths of the breeding seasons of C. gapperi between elevations was not associated with any differences in the number of litters, litter size or female survival. Contrary to the hypothesis, the differences in the lengths of the breeding seasons of M. pennsylvanicus did not limit the number of opportunities for breeding for the average female, yet litter size was greater at the high elevation than at the low elevation and there was no difference in female survival between elevations. The average number of litters per season was slightly less than two in all populations; the average female did not survive long enough to produce young over the entire length of the season. Data from the literature also suggested that the length of the breeding season is not associated with litter size and the maximum number of litters per season within these species.;Few traits showed differences between elevations and these were not necessarily the same ones in both species. The maximum weights of over-wintered males, the age when young opened their eyes and one index of reproductive effort showed differences in C. gapperi between elevations. Litter size, nestling survival, maximum weights of over-wintered males, mean weights of mature, young-of-the-year males and the relative fat content of males showed differences in M. pennsylvanicus between elevations. These differences are probably phenotypic responses to environmental conditions such as food quality. Alternatively, some differences may have been fixed at random by genetic drift.
Innes, Duncan Gordon, "The Life-history Tactics Of The Voles, Clethrionomys Gapperi And Microtus Pennsylvanicus, At Two Elevations" (1984). Digitized Theses. 1371.