Abstract
Life history characteristics were studied experimentally in Columbian ground squirrels (Spermophilus columbianus) at two elevations in the Rocky Mountains of southwestern Alberta, Canada, from 1981 to 1984. In two populations with supplemented food resources, survival of young increased, age at maturity of females decreased, litter size increased, and spring body weight increased in comparison with an initial unmanipulated period and with two populations monitored for reference. For individual ground squirrels, litter size and spring body weight increased under supplementation. Thus, life history characteristics exhibited phenotypically plastic responses to experimental manipulation of food resources. Life history patterns changed among natural ground squirrel populations at different elevations and these changes were likely due to changes in food resources. A general prediction of life history theory that reproductive effort should be highest in years favorable for juvenile survivorship was supported by the experimental results. The results did not support predictions from interspecific studies of changes in life history characteristics that scale to body weight.
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