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

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.

Automated summary

This study used stable isotope analysis to show that Canada lynx primarily feed on snowshoe hares in all regions, but will switch to alternate prey when hare availability is low. These findings support the facultative specialist hypothesis, suggesting that specialist predators expand their diets when preferred prey are limited.