Prey size mediates interference competition and predation dynamics in a large carnivore community.

Direct competition for resources is especially fierce among predators, leading to disproportionately strong effects on fitness and functional roles. These competitive effects are exacerbated in complex predator guilds with dominance hierarchies that have clear winners and losers. The direct costs of losing these competitions are well understood, but the drivers of such interactions, and their indirect effects on prey, are not. We evaluate the drivers of interference competition for cougars, and how such competition affects cougar-prey dynamics, by leveraging 23 years of cougar predation data from Yellowstone National Park, USA. We show that the effect of prey size is context-dependent, negatively affecting how often cougars kill ungulate prey but positively affecting how often wolves/bears find and steal cougar kills. Further, cougars increasingly kill smaller prey as larger, primary prey density decreases. Handling time is shorter for smaller prey, leading to less kleptoparasitism by wolves and bears when primary prey density is lower. Our study counters the theory suggesting that interference competition should increase at kills when prey density declines, interspecific competitor density increases, or kill rates increase. We demonstrate that predator, competitor, and prey traits drive the strength of and even dampen interference competition, possibly increasing coexistence in complex communities.