Nowhere to hide: Pumas, black bears, and competition refuges

Abstract

One hypothesis for how carnivores with overlapping ecology coexist in natural systems is through heterogeneous competition landscapes, in which subordinates utilize "competition refuges" to mitigate risks associated with dominant competitors. We tested for the effects of American black bear (Ursus americanus) kleptoparasitism on puma (Puma concolor) foraging in 2 systems in North America. We also tested whether partial prey consumption exhibited by pumas in the presence of bears was better explained by rules of optimal foraging or by kleptoparasitism by black bears, and whether pumas utilized spatial competition refuges to mitigate competition with bears over carcass remains. Puma kill rates in ungulates/wk were equivalent across study systems, but 48% greater in the bear season than the no-bear season. Our analyses of handling time did not support the notion that partial prey consumption exhibited by pumas followed patterns of optimal foraging. Rather, puma handling time and prey consumption were better explained by the presence of bears. Surprisingly, pumas did not utilize spatial competition refuges to mitigate competition with black bears, and instead our results suggested they increase their kill rates to compensate for losses. Our results linking high seasonal kill rates of a top predator with kleptoparasitism by a dominant competitor provide strong evidence that the effects of predation can only be understood within a community framework. In particular, we propose that future predation studies should differentiate between relative contributions of predators and competitors on prey dynamics. Further, our results suggest kleptoparasites may indirectly impact prey populations through their effects on top predators.