Negative frequency-dependent prey selection by wolves and its implications on predator–prey dynamics

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College of Forest Resources and Environmental Science


Many species exhibit selective foraging behaviour, where consumers use a nonrandom subset of available food types. Yet little is known about how selective foraging behaviour varies with environmental conditions and the community level consequences of such selection dynamics. We examined selective foraging by wolves preying primarily on elk in Yellowstone National Park (YNP) over a 12-year period and on moose in Isle Royale National Park (IRNP) over a 47-year period. Specifically, we assessed how selection for calves and senescent adults varied with their frequency in the environment, wolf abundance and winter severity. Selection for senescent adults decreased as the relative abundance of senescent prey increased (i.e. negative frequency-dependent selection) in both study sites. In IRNP, selection for calves was also negatively frequency dependent and declined with increasing wolf abundance. These results are inconsistent with the pattern of positive frequency-dependent selection expected under the prey-switching hypothesis. These results suggest that selection is primarily driven by intraspecific differences in prey vulnerability and wolves’ interest in minimizing their risk of injury, as opposed to maximizing intake rates. Lastly, we ran simulations to evaluate how predator–prey dynamics were influenced by dynamic patterns of selection, like those observed in YNP and IRNP. The simulations indicated that predators are more efficient (i.e. steeper slope of the numerical response) when selection for calves is negatively frequency dependent, which results in a lower mean abundance of prey. More importantly, predation is a stronger destabilizing force when selection for calves is negatively frequency dependent. That stronger destabilizing force is indicated by greater variability in the abundance of prey and predators, prey populations being less resilient and a steeper negative slope of the relationship between predation rate and prey population growth rate. As such, our simulation analyses suggest that some of the observed patterns of negative-frequency dependent selection may have important consequences for predator–prey dynamics.

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Animal Behaviour