Abstract

Topic: Predator-prey interactions

Hiding among your competitors: Predator preference as a prey shield

Brendan Carswell¹, Christina Prokopenko², Tal Avgar³, Garrett Street⁴, Katrien Kingdon⁵, Allyson Menzies⁶, Eric Vander Wal⁵

University of Calgary, Memorial University of Newfoundland and Labrador, Calgary, Canada
University of Manitoba, Winnipeg, Canada
University of British Columbia, Canada
Mississippi State University, USA
Memorial University of Newfoundland and Labrador, Canada
University of Calgary, Canada

Nearly 50 years ago ecologists introduced the idea of apparent competition—where the interaction between two species are primarily mediated through a shared predator. Predators, however, also have unequal preference for their prey. Predator preference can be influenced by prey vulnerability and individual and joint density of prey species, such that, competing prey may exploit the preference of their shared predator to mitigate their own risk of being depredated. We test the ‘prey shield hypothesis’, which predicts that less preferred prey will capitalize on space used by their more preferred competitors to reduce their predation risk. We test the hypothesis in a wolf, elk, and moose system. Because elk are more vulnerable, they are the preferred prey of wolves. Elk, however, are less abundant in our study system than moose and thus, moose represent a higher proportion of wolf diets. We predict that moose will be less risk-averse when they share space with higher densities of more vulnerable elk. We use time-to-event modelling from n = 104 camera traps, and over 88,000 observations, to show that at locations where both prey species are more catchable by wolves, i.e., riskier, and where elk are more abundant, moose tend to return to camera sites sooner following a wolf presence. That is, moose are less risk averse in risky habitats and when there are relatively more elk present. Though prey have typically been considered passive agents in apparent competition, we illustrate that prey can exploit the spatial dynamics of their competitors to reduce their own predation risk.