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

Abstract

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.

Habitat segregation between brown bears and gray wolves in a human‐dominated landscape

“…However, evidence of interspecific competition between sympatric large carnivores with fine‐scale data (e.g. GPS data) and at the population level is just beginning to be documented, in terms of both kill rates (Elbroch et al., ; Tallian et al., ) and habitat selection (Ordiz et al., ). Our study took advantage of the long‐term monitoring with GPS collars of brown bears and wolves in Scandinavia.…”

“…The spring period (1 May–30 June) overlaps with wolf reproduction (Alfredéen, ; Nonaka, ; Mech & Boitani, ) and the bear mating season (Dahle & Swenson, ). The latter period also includes the birth of moose calves (Markgren, ), which are a highly utilized prey by both wolves and bears in several ecosystems, including our studied ecosystem (Rauset, Kindberg, & Swenson, ; Brockman, Collins, Welker, Spalinger, & Dale, , Tallian et al., ). During the late‐winter period, we only used GPS locations from one member of the pair (male or female, Supporting Information Table ), because both pair members usually travel together outside the reproduction period (Peterson, Jacobs, Drummer, Mech, & Smith, ; Zimmermann et al., ).…”

“…Then, we quantified habitat segregation between wolves and bears using a multivariate approach based on the niche concept. Because of the above-mentioned negative effects of bear density on the probability of establishment by wolf pairs (Ordiz et al, 2015) and the kleptoparasitism of wolf kills by bears in Scandinavia and elsewhere (Tallian et al, 2017), we hypothesize that wolves and bears will segregate more than expected by chance. Our study may advance current knowledge of the ecological mechanisms that drive interspecific interactions between apex predators and allow their coexistence in human-dominated landscapes.…”

“…Nevertheless, bears are also efficient predators of neonate moose (Dahle et al., ; Swenson et al., ), and they kleptoparasitize more than half of the wolf kills during spring in central Sweden (Milleret, ; Ordiz et al., ). Bear density has a negative effect on the probability of wolf pairs establishing in a given area (Ordiz et al., ), and wolf kill rates are lower when bears are present (Tallian et al., ). However, no effects of wolves have ever been documented on brown bears at the population level.…”

“…Bear density has a negative effect on the probability of wolf pairs establishing in a given area (Ordiz et al, 2015), and wolf kill rates are lower when bears are present (Tallian et al, 2017). However, no effects of wolves have ever been documented on brown bears at the population level.…”