Age of primiparity and implications of early reproduction on life history in female Columbian ground squirrels

Abstract

Summary Factors leading to differences in age of primiparity and possible life‐history implications arising from these differences were studied in a population of Columbian ground squirrels (Spermophilus columbianus; Ord, 1815). We used data collected from 1992 to 2000 on two neighbouring colonies of ground squirrels in south‐eastern Alberta, Canada. Earlier born females were more likely to wean successfully a litter at the age of 2. Among 2‐year‐old females, those who emerged earlier and heavier from hibernation were more likely to wean offspring than those females who emerged later and lighter from hibernation. The presence of the mother had a significant positive impact on reproductive output in 2‐year‐old females. Although there was a positive correlation between lifetime reproductive success and age at death, there was no difference in lifetime reproductive success or in age at death, depending on age of primiparity. For individual females, litter size at weaning at 2 years old did not differ from that at 3 years old. We conclude that body condition, presence or absence of the mother and environmental conditions are the main factors leading to differences in age of first successful reproduction in Columbian ground squirrels. Previous breeding experience does not seem to play a role in determining reproductive success. Finally, differences in age of first successful reproduction do not seem to have an effect on lifetime reproductive success or longevity.