Northern Yellowstone Elk survival and competing risks

Prey vulnerability to predation can vary by life history stage, and prey population stage structure determines the strength a predator species wields on their community. Prey population stage structure can vary over time, yet little is known about how temporal change in prey stage structure influences predator-prey interactions. We used data of wolves hunting adult female elk in Yellowstone National Park to demonstrate that stage-selective wolf predation of old individuals (>11 years old) was more additive than wolf predation of young individuals (2–11 years old). Additive predation of older elk coupled with an aging female elk population increased the strength of wolf predation over time. When vulnerable prey comprise an increasing proportion of a population, their early demise may decrease population growth. Accounting for temporal variation in predation risk across a prey population is therefore critical to understanding the community-level consequences of predator-prey interactions.