POPULATION-DYNAMICS OF THE COLLARED LEMMING AND THE TUNDRA VOLE AT PEARCE-POINT, NORTHWEST-TERRITORIES, CANADA

From 1987 to 1989 we monitored population changes during summer of the collared lemming (Dicrostonyx groenlandicus) and the tundra vole (Mic rotus oeconomus) at Pearce Point, Northwest Territories, Canada (69 de grees 48' N, 122 degrees 40' W). Populations on four study areas did n ot cycle but remained at low density (<3/ha) each year and continued a t low numbers for the following 3 years (Reid et al. 1995). Lemming nu mbers often declined throughout the summer in spite of continuous repr oduction, and population recovery occurred overwinter. Heavy predation losses of radio-collared lemmings occurred each summer and this lemmi ng population may be trapped in a predator-pit. Collared lemmings bree d in winter and only because of winter population growth do these popu lations persist. Tundra vole numbers increased rapidly in most summers but usually declined overwinter. Tundra voles do not seem able to sus tain winter reproduction in this extreme environment and this prevents them from reaching high density because of the short summer. Populati on growth in both these rodents could be prevented by poor food or by predation losses, and landscape patchiness may also help to prevent po pulation growth. For lemmings we do not think that a shortage of shelt er or intrinsic limitations could be restricting population increase a t Pearce Point. This is the first detailed study of a non-cyclic colla red lemming population.