The pulsed effects of reintroducing wolves on the carnivore community of Isle Royale

Large carnivores are being globally reintroduced with the goal of restoring ecological interactions. However, the extent that competitive interactions are restored within communities is often unclear. In a before–after study within Isle Royale National Park (in the US state of Michigan), we quantified the spatial, behavioral, trophic, and demographic effects of the reintroduction of a large carnivore (gray wolf; Canis lupus) on meso-carnivores (red fox; Vulpes vulpes) and small carnivores (American marten; Martes americana). The wolf reintroduction produced a phase-dependent pulse perturbation: wolves constrained the distribution of foxes, thereby benefiting martens, yet foxes altered their behavior, notably using human-provided resource subsidies (campsites and food) more frequently, which buffered demographic consequences. Once wolf packs coalesced, all observed changes subsided, and competitive interactions returned to their pre-wolf values. Our results show that some predicted—and often desired—consequences of large carnivore reintroductions may not be permanent due to the transitory dynamics of social carnivores and the presence of humans, even within a “pristine wilderness”.