A COMPARISON OF METHODS FOR STUDYING LIFE-HISTORY IN COLUMBIAN GROUND-SQUIRRELS

We reviewed data from three separate studies that examined the life-history characteristics of Columbian ground squirrels, Spermophilus columbianus, at different elevations in the Rocky Mountains of southwestern Alberta, Canada. One study used a static (vertical) life-table methodology, and the other two used a cohort (horizontal) life-table methodology. One of the latter studies also applied an experimental supplementation of food resources to two populations. Absolute values of characteristics measured by static and cohort methodologies were not directly comparable, but the pattern of change with elevation of litter size, adult survival, and body weight were similar. At high, relative to low elevations, litter size was lower, adult survival was higher, and body weight of adult females was lower. The two methodologies produced conflicting results regarding the proportion of females reproducing and juvenile survival at different elevations. The static methodology does not reveal the changes in life history that may occur in different years. An experimental method was required to demonstrate phenotypic plasticity of life-history characteristics. In two populations that received supplemental food, litter size, juvenile survival, and the body weight of adult females increased.