Prey Partitioning in a Diverse Carnivore Community: Implications for Reintroduced Fishers in Washington

Competition for prey resources influences trophic community structure and carnivore population dynamics. Evaluating the impacts of competitive interactions on carnivore reintroductions is increasingly important, as anthropogenic activities have caused widespread restructuring of animal communities and potentially altered habitat quality for returning species. Here, we used fecal DNA metabarcoding to evaluate the diets of reintroduced fishers ( Pekania pennanti ) and sympatric coyotes ( Canis latrans ), bobcats ( Lynx rufus ), and Pacific marten ( Martes caurina ) in the North Cascades of Washington, a mountainous, forested region where fishers were reintroduced between 2018 and 2020. Diet samples were collected during October 2020 and July–August 2021. We assessed similarities in diet composition among species using relative read abundance and permutation‐based multivariate analyses, niche overlap indices, and null models. Niche overlap values ranged from 0.36 to 0.76 and generally increased as pairwise differences in body mass decreased; overlap was greatest between bobcats and coyotes and lowest between coyotes and martens, with fishers showing greatest similarity to bobcats. Whereas dietary overlap was substantial for common prey items, we found strong compositional differences among carnivore diets. DNA metabarcoding enabled us to detect important prey species that facilitate resource partitioning at fine taxonomic (genus‐ and species‐level) resolution. Consequently, restricted access of fishers to energetically efficient prey may slow recovery efforts in the North Cascades, highlighting the importance of investigating the role of competition in species reintroductions.