Predator foraging response to a resurgent dangerous prey

Prey switching occurs when a generalist predator kills disproportionately more of an abundant prey species and correspondingly spares a rarer species. Although this behaviour is a classic stabilizing mechanism in food web models, little is known about its operation in free-living systems which often include dangerous prey species that resist predation. We used long-term (1995–2015) data from a large mammal system in northern Yellowstone National Park, USA, to understand how prey preference of a wild, generalist predator (Canis lupus) responds to a shift in prey species evenness involving rising numbers of dangerous prey (Bison bison) and dropping numbers of relatively safer prey (Cervus elaphus). Contrary to the prey switching hypothesis, wolves attacked and killed disproportionately more of the rarer, but safer, species. Wolves maintained a strong preference against bison even when this species was more than twice as abundant as elk. There was also evidence that wolves were increasin...