The Significance of Limiting and Regulating Factors on the Demography of Moose and White-Tailed Deer

SUMMARY (1) I examined the significance of food competition, wolf predation (Canis lupus), and snow accumulation as limiting or regulating factors of moose (Alces alces) and white-tailed deer (Odocoileus virginianus). That is, I assessed the contribution of those factors in creating year-to-year variations in animal abundance, or in generating density dependence. (2) I used long-term data on the demography of moose on Isle Royale, Michigan, and deer in the National Superior Forest, north-eastern Minnesota. (3) Wolf predation and food competition explained 80% of the interannual variation of moose abundance. Snow accumulation had no quantifiable effect on moose numbers. Competition for food, but not wolf predation and snow, had a regulatory impact on moose. (4) Wolf predation was inversely related to moose density and the relationship differed between periods of moose expansion and reduction. The dual density relationship of wolf predation may explain population cyclicity of moose at elevated densities. (5) Significant inverse relationships were found between deer population growth and relative wolf density, as well as with deer density. Snow had no measurable effect on deer numbers, possibly because of extremely low deer densities and the predominant impact of wolf predation. (6) A previous suggestion that snow accumulation during consecutive winters creates a cumulative impact on the nutritional status of deer and moose was not supported.