Population ecology of caribou populations without predators: Southampton and Coats Island herds

Abstract: This paper is a review o f the ecology o f two caribou populations inhabiting predator-free northern islands, Coats and Southampton Island. Findings are analyzed in light o f the hypothesis that i n absence o f p réda t ion or high human harvest, food competit ion results in delayed puberty, reduced calf production, increased winter starvation o f caribou and regulates populations at high densities (>2 km " 2). Car ibou were hunted to extinction on Southampton Island (Northwest Territories, Canada) by mid-century. In 1967, 48 caribou were captured on neighbouring Coats Island and released on Southampton Island. Southampton Island is characterized by a high per capita winter food availa-bil i ty i n summer and i n winter. The population on Southampton Island has been increasing at a rapid rate o f growth since re-introduction (A, = 1.27). Fast population growth was possible because females invested early i n reproduction and over winter survival rate was high. The population on Coats Island is also characterized by high per capita food availa-bility in summer but l o w food availability i n winter. T h e population size has undergone some marked fluctuations, abrupt declines followed by relatively rapid recovery and, contrary to predictions, densities were always less than 1 km " 2. L o w population densities on Coats Island result primarily from l o w food availability. This review suggests that i n the absence o f p réda t ion or high human harvest competit ion for food regulates caribou population abundance. However