Data from: Competition between apex predators? Brown bears decrease wolf kill rate on two continents

Trophic interactions are a fundamental topic in ecology, but we know
little about how competition between apex predators affects predation, the
mechanism driving top-down forcing in ecosystems. We used long-term
datasets from Scandinavia (Europe) and Yellowstone National Park (North
America) to evaluate how grey wolf (Canis lupus) kill rate was affected by
a sympatric apex predator, the brown bear (Ursus arctos). We used kill
interval (i.e. the number of days between consecutive ungulate kills) as a
proxy of kill rate. Although brown bears can monopolize wolf kills, we
found no support in either study system for the common assumption that
they cause wolves to kill more often. On the contrary, our results showed
the opposite effect. In Scandinavia, wolf packs sympatric with brown bears
killed less often than allopatric packs during both spring (after bear den
emergence) and summer. Similarly, the presence of bears at wolf-killed
ungulates was associated with wolves killing less often during summer in
Yellowstone. The consistency in results between the two systems suggests
that brown bear presence actually reduces wolf kill rate. Our results
suggest that the influence of predation on lower trophic levels may depend
on the composition of predator communities.