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.