Fearlessness towards extirpated large carnivores may exacerbate the impacts of naïve mesocarnivores
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By suppressing mesocarnivore foraging, the fear large carnivores inspire can be critical to mitigating mesocarnivore impacts. Where large carnivores have declined, mesocarnivores may quantitatively increase foraging, commensurate with reductions in fear. The extirpation of large carnivores may further exacerbate mesocarnivore impacts by causing qualitative changes in mesocarnivore behavior. Error management theory suggests that, where predators are present, prey should be biased towards over-responsiveness to predator cues, abandoning foraging in response to both predator cues and benign stimuli mistaken for predator cues (false-positives). Where predators are absent, prey may avoid these foraging costs by becoming unresponsive (naïve) to both predator cues and false-positives. If naiveté occurs in mesocarnivores where large carnivores have been extirpated, it could substantively exacerbate their impacts, as "fearless" mesocarnivores may engage in virtually unrestricted foraging. We tested the naiveté of raccoons (Procyon lotor) to extirpated large carnivores in the context of a larger experiment demonstrating that fear of large carnivores can mediate mesocarnivore impacts. Raccoon responsiveness to playbacks of their extirpated large carnivore predators (cougars, Puma concolor; bears, Ursus americanus) was significantly less than to the only extant large carnivore predator (dogs), and was no greater than to non-predators ("seals"; Phoca vitulina, Eumetopias jubatus). Raccoons failed to recognize their now extirpated predators as threatening, spending as much time foraging as when hearing non-predators, which we estimate has substantive impacts, based on results from the larger experiment. We discuss the potentially powerful role of "fearlessness" in exacerbating mesocarnivore impacts in systems where large carnivores have been lost.