Limitations to collared lemming population growth in winter

Abstract

We investigated the roles of ermine predation and temperature and snowfall regimes in limiting population growth of collared lemmings (Dicrostonyx kilangmiutak) at low densities (< 3/ha) in winters between 1987 and 1992 at Pearce Point, Northwest Territories, Canada. We estimated winter population growth, for four study populations, as the instantaneous weekly rate of population change from late August to early in the subsequent June. Population growth was not significantly related to the intensity of ermine predation, based on data from two winters. Variance in rates of growth among five winters was significantly explained by a combination of (i) cold intensity in autumn, i.e., the mean daily temperature in September and October, when lemmings change from summer to winter morphology, and (ii) the insulative potential of the snow, i.e., centimetre-days of snow cover per degree-day of frost from November through March, when lemmings potentially breed. Arvicoline winter nests were strongly associated with remnant snow in spring, indicating selection for areas with deepest snow. Low autumn temperatures and shallow winter snow appear to be strong limiting factors in winter, and may prolong the period of low density of Dicrostonyx populations.