Of wolves and bears: Seasonal drivers of interference and exploitation competition between apex predators

Competition between apex predators can alter the strength of top-down forcing, yet we know little about the behavioral mechanisms that drive competition in multipredator ecosystems. Interactions between predators can be synergistic (facilitative) or antagonistic (inhibitive), both of which are widespread in nature, vary in strength between species and across space and time, and affect predation patterns and predator-prey dynamics. Recent research suggests gray wolf (Canis lupus) kill rates decrease where they are sympatric with brown bears (Ursus arctos), however, the mechanisms behind this pattern remain unknown. We used data from two long-term research projects in Scandinavia (Europe) and Yellowstone National Park (North America) to test the role of interference and exploitation competition from bears on wolf predatory behavior, where altered wolf handling and search time of prey in the presence of bears are indicative of interference and exploitation competition, respectively. Our results suggest the mechanisms driving competition between bears and wolves were dependent on the season and study system. During spring in Scandinavia, interference competition was the primary mechanism driving decreased kill rates for wolves sympatric with bears; handling time increased, but search time did not. In summer, however, when both bear and wolf predation focused on neonate moose, the behavioral mechanism switched to exploitation competition; search time increased, but handling time did not. Interference competition, however, did affect wolf predation dynamics in Yellowstone during summer, where wolves prey more evenly on neonate and adult ungulates. Here, bear presence at a carcass increased the amount of time wolves spent at carcasses of all sizes and wolf handling time for small prey, but decreased handling time for the largest prey. Wolves facilitate scavenging opportunities for bears, however, bears alter wolf predatory behavior via multiple pathways and are primarily antagonistic to wolves. Our study helps clarify the behavioral mechanisms driving competition between apex predators, illustrating how interspecific interactions can manifest into population-level predation patterns.The readme file contains an explanation of each of the variables in the dataset and their measurement units. Please see the full write-up in the Ecological Monographs article for the methods on dataset collection and processing. Funding provided by: Marie-Claire Cronstedts StiftelseCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010732Award Number: Funding provided by: Norges ForskningsrådCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100005416Award Number: Funding provided by: MiljødirektoratetCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100008776Award Number: Funding provided by: Office of Environmental Affairs in Hedmark County*Crossref Funder Registry ID: Award Number: Funding provided by: Svenska JägareförbundetCrossref Funder Registry ID: http://dx.doi.org/10.13039/100009588Award Number: Funding provided by: NaturvårdsverketCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004357Award Number: Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB‐0613730 & DEB‐1245373Funding provided by: Yellowstone Forever*Crossref Funder Registry ID: Award Number: Funding provided by: Office of Environmental Affairs in Hedmark CountyCrossref Funder Registry ID: Funding provided by: Yellowstone ForeverCrossref Funder Registry ID:This data set was collected by two long-term research projects in Scandinavia and Yellowstone National Park. This data was cleaned and processes for a manuscript accepted into Ecological Monographs