Do snow-adapted prey facilitate coexistence of the Sierra Nevada red fox with sympatric carnivores?

The Sierra Nevada red fox (SNRF; Vulpes vulpes necator) is an endangered
subspecies restricted to high-elevation habitats. Competition with
larger-bodied coyotes (Canis latrans) limits red fox abundance throughout
their sympatric ranges.  Because SNRF were isolated and have
evolved solely within subalpine ecosystems, we hypothesized that
specialized adaptations, including low foot loading to more efficiently
hunt snow-adapted lagomorphs in deep snow conditions, facilitate
coexistence with coyotes.  Because subalpine lagomorphs are
themselves in decline, understanding the contribution of these and other
prey to the SNRF diet and those of coyotes and other sympatric
mesocarnivores is fundamental to SNRF conservation. We used metabarcoding
to investigate the diets and niche relationships of these carnivores,
along with martens (Martes caurina) and bobcats (Lynx rufus) using 789
scats collected from sites of two SNRF populations (Lassen, Sierra
Nevada). As predicted, SNRFs exhibited high dietary overlap with coyotes
but showed greater specialization for white-tailed jackrabbits (Lepus
townsendii) and American pika (Ochotona princeps). In both populations,
SNRF diet consisted primarily of small rodents and lagomorphs. Dietary
overlap was higher with coyotes (Pianka's index: 0.89) than with
martens (0.56) and bobcats (0.59). SNRFs more frequently than coyotes
consumed lagomorphs (p ≤ 0.005). We also observed a high frequency of
pine, most likely whitebark pine (Pinus albicaulus) seeds, in SNRF scats,
particularly during winter. Our findings suggest that subalpine specialist
prey species may play a major role in facilitating SNRF coexistence with
coyotes, and underscore the need for data on the current status and trends
of these sensitive lagomorph populations.