DNA metabarcoding reveals dietary diversity and prey partitioning in reintroduced fishers in the Washington Cascades

Abstract

Diet analyses can play a key role in ecological studies, and particularly in rare carnivore conservation, by revealing trophic interactions. Carnivore populations are often limited by access to prey and so limited knowledge of their foraging ecology can hinder recovery efforts. In recent years, diet analyses and the construction of food webs have been enhanced by DNA metabarcoding, which allows for the identification of prey species at a much finer scale than traditional identification methods. Limited prey availability may be a key factor hindering reintroduction success for small carnivores, thus investigating diet habits with modern techniques in reintroduction sites can provide insights into the role of prey choices in population establishment. Fishers (Pekania pennanti) are one of the most frequently reintroduced carnivores in North America, but their reintroduction success is variable. The reintroduction of fishers in Washington state offers an opportunity to assess diet variation across reintroduction areas using high-resolution, DNA metabarcoding methods, to evaluate factors affecting the success of population establishment. I assessed fisher diets in two reintroduction sites in the Washington Cascade Mountains, USA: the South Cascades and the North Cascades. I collected 300 fisher scats and gastrointestinal tracts and 167 scats of sympatric carnivores - bobcat (Lynx rufus), coyote (Canis latrans), and Pacific marten (Martes caurina) - using telemetry and scat detection dog teams. Snowshoe hares (Lepus americanus) were the most prevalent prey species in both fisher populations (North Cascades = 9%, South Cascades 68%), but there were substantial compositional differences between diets. Species richness was over three times greater in the North Cascades and no single prey exceeded 10% of sequence counts. I demonstrated that two geographically close and ecologically similar reintroduction sites can yield strikingly different diet profiles in fishers, highlighting the importance of localized diet analyses for carnivores whose foraging strategies can be strongly influenced by environmental factors. Additionally, DNA metabarcoding enabled us to detect important prey species that facilitate resource partitioning among fishers and competing mesocarnivores at a fine scale. I detected relatively high overlap among carnivores that generally increased as pairwise differences in body mass decreased. While dietary overlap was substantial for common prey items, I found strong compositional differences among diets. Consequently, restricted access of fishers to energetically efficient prey may slow recovery efforts in this region, highlighting the importance of investigating the role of competition in species restorations.