Canada lynx foraging strategies: Facultative specialists become obligate generalists toward the distribution edge

Abstract

Spatial and temporal variation in prey availability can affect predator foraging strategies, but it is unclear how large‐scale gradients in prey availability shape predator diets in space and time. The facultative specialist hypothesis predicts that niche expansion by specialist predators is advantageous when preferred prey are limited and alternate prey are available, as might be expected following the collapse of primary prey populations in species‐poor environments or at range margins where species assemblages shift. Canada lynx (Lynx canadensis) are broadly distributed and prey predominantly on snowshoe hares (Lepus americanus), with other species serving as alternate prey when hares are limited. We used stable isotope analysis of lynx, snowshoe hare, and red squirrel hair during periods of high/low snowshoe hare availability from five regions throughout their distribution, to measure spatiotemporal changes in diet and test the facultative specialist hypothesis. Hares were the primary food item in all lynx diets, irrespective of space and time. Core lynx populations consumed the greatest proportion of hares overall and increased the use of alternate prey when hares were limited. Despite fluctuations in hare availability, lynx toward the southeastern extent of their distribution invariably consumed alternate prey in similar proportions to those exhibited by core populations during hare lows. The temporal consistency of lynx diets in these regions indicates that broader diets are obligate along this distribution edge. Our results provide new evidence for the facultative specialist hypothesis across a broad spatial scale and emphasize that, as specialist–generalist paradigms operate along a continuum, so too can obligate–facultative strategies depending on environmental context.

Dietary flexibility of the greater bamboo lemur (Prolemur simus), a specialized feeder, in eastern Madagascar

“…Like obligate specialists, facultative specialists have narrow dietary niches and may have adaptations to process difficult foods. Where they differ is that facultative specialists can expand their diet to include less difficult foods when conditions allow, resulting in a broader fundamental niche (Shipley et al, 2009; Szumski et al, 2023). The fundamental niche is defined by a species’ physiology associated with, for example, tolerances to plant secondary metabolites or nutritional requirements (Hutchinson, 1965; Roughgarden, 1974).…”

“…Therefore, it is critical to assess data from across the distribution of P. simus to adequately gauge its degree of specialization and develop a more accurate understanding of the species’ fundamental niche. As some species can shift from being an obligate to a facultative specialist depending on resource availability (Apostolico et al, 2016; Szumski et al, 2023), long‐term data on P. simus should be used to create a species‐specific spectrum of specialization upon which populations can be assessed. Doing so would open doors to explore the drivers of dietary specialization and their implications on species viability in changing environments.…”