Changes in body size in fluctuating populations of the collared lemming: age and photoperiod influences

Abstract

Paired wet lens weights of 115 laboratory-reared collared lemmings were plotted against known age, to assess the reliability of this parameter, as a means of estimating age. Approximately 85% of the total variability in In age (A) was accounted for by In paired wet lens weight (W) (equation of best fit; In A (days) = −0.9771 + 2.186 In W (milligrams). In addition, variation in gender and photoperiod did not influence lens weight, although other parameters such as body weight and pelage were significantly affected.Field data from Eskimo Point, N. W.T., indicated that animals were older and heavier during the peak year (1973). Reduced recruitment and length of breeding season were observed during high densities, and sexual maturation was delayed in the nonbreeding segment of the population. Fluctuations in body size during microtine cycles were discussed as influenced by age, photoperiod, and shifts in the breeding season.