Dietary niche expansion and recruitment of a specialist carnivore through a flux in preferred prey availability

Background/Question/Methods

Canada lynx (Lynx canadensis) typically exhibit 8-11 year population cycles that follow the abundance of their preferred prey, snowshoe hare (Lepus americanus). Lynx have been celebrated since the early 1900s for their oscillating population cycles and the associated predator-prey relationship; however, recent decades have noted diminished amplitudes and disrupted periodicity of snowshoe hare cycles in parts of their range. Some evidence suggests that lynx may be facultative specialists, using alternative prey when snowshoe hare densities are low, which could mitigate the stressor of changing snowshoe hare availability. Our objective was to understand intrapopulation variation in diet breadth of lynx through a low-amplitude snowshoe hare cycle to determine whether foraging habits differ among age classes, sexes, and animals of different body condition, and how these differences might influence population dynamics of lynx. Lynx carcasses were provided by trappers from within a 200 km range of each other in the Northwest Territories, Canada. We measured stable carbon and nitrogen isotope ratios in muscle tissue to assess winter diet and used fecal pellet plots to measure snowshoe hare density. We compared diet breadth among years, age classes, sexes, and the relationship to body condition using isotopic niche metrics.

Results/Conclusions

Decreasing diet specialization on snowshoe hare was linearly related to recruitment of juveniles, demonstrating for the first time the empirical link between diet and recruitment. The diet breadth of the population contracted and expanded with increasing and decreasing snowshoe hare density, supporting the facultative specialist hypothesis. Age classes differed in both diet and body condition, with 1- and 2-year old lynx exhibiting broader diets than kittens and adults, and younger lynx presenting low body fat more frequently. No sexual dimorphisms were observed in lynx diets; however males exhibited high body fat more frequently than females. Age class and sex differences in diet and body fat were present regardless of snowshoe hare density. Overall, we demonstrated that lynx are highly sensitive to even small changes in prey availability, responding in both diet breadth and juvenile recruitment. These responses are not enough to eliminate the cost of lynx dependency on snowshoe hare, but it does appear that a certain degree of dietary flexibility could mitigate risk of starvation during periods of limited snowshoe hare abundance.