COS 160-2 - CANCELLED - Empirical evidence for optimal prey switching

Background/Question/Methods

For at least 45 years, wolves (Canis lupus) have subsisted predominantly on elk (Cervus elaphus) in Riding Mountain National Park. Then wolves switched to a more dangerous alternative, moose (Alces alces). Generalist predators are ubiquitous but testing mechanisms of population-level prey switching in large vertebrates is rare. While the population density of prey appears to be the simplest factor to explain the composition of predator diets, recent theory has shown that antipredator traits can govern predator decisions. We populated a published model with empirical estimates of predator success rates, injury rates, and handling times for moose and elk. We integrated data from long term monitoring at Riding Mountain National Park that tracked changes in wolf diets and prey abundance to test two main predictions.

Results/Conclusions

First, predators prefer more vulnerable prey, consuming them disproportionately more than expected by their density (P1: Qualities over quantities). Second, predators exhibit a stronger preference when total prey abundance is high but are less discerning when total prey abundance is low (P2: Necessity rejects no prey). In agreement with these predictions, wolves preferred elk and there was stronger preference for elk when both prey were more abundant. This work illustrates feasible applications of a model that dissolves species boundaries and places animals on a quantifiable energetic continuum.