Prey selectivity of wolves in Banff National Park. I. Prey species
I examined the components generating selectivity in wolves preying on five ungulate species in Banff National Park, Alberta. Overall selectivity for elk and deer species, and apparent avoidance of bighorn sheep and mountain goats, were due primarily to lower habitat overlap of wolves with the latter two species, and therefore lower encounter rates. For social ungulates, I argue that the herd should be considered the unit of encounter, with encounter rates proportional to the number of herds rather than the number of individuals. However, large herds predictably associated with certain areas may be visited intentionally by wolves, increasing effective encounter rates. Foraging theory suggests that all ungulate prey should be equally profitable to wolves upon encounter and therefore the factors affecting encounter rates are critical in determining prey selectivity. A simple model incorporating different habitat overlap, herd sizes, and predictable herds predicts qualitatively different functional responses of wolves to changes in density of the different prey types. The model also demonstrates how apparent selectivity for a prey type can result from the different ways in which prey are encountered.