Facilitating a trophic cascade from wolves through coyotes to foxes: How much wilderness is enough?

Background/Question/Methods

Many of the world’s largest carnivores are experiencing declines in their populations and geographic ranges around the world. These declines are driven by habitat destruction and active persecution of large predators by humans. This has renewed interest in determining how large carnivores shape and drive community structure. It has also led to widespread predictions that the loss of large carnivores will release populations of smaller carnivores, as depicted by the mesopredator release hypothesis. The ecological effects of mesopredator release, via predation and competition, can be dramatic and affect a wide range of faunal elements. It is therefore crucial to fully understand how top-down processes, via the direct and indirect effects of competition, can potentially influence the spatial distribution of terrestrial predators.

In North America, wolves have been largely restricted to intact wilderness areas due to widespread predator control throughout much of the 20^thcentury. The presence of wolves within these wilderness areas provides a unique opportunity to explore how a top-predator can influence the spatial distribution of mesopredators such as the coyote and red fox. Herein, we use long term time series of fur return data, from eight jurisdictions in North America, to test the hypothesis that the presence of wolves has caused a continent-wide shift in coyote and red fox density.

Results/Conclusions

Across multiple jurisdictions and years our results suggest that red foxes outnumber coyotes in areas where wolves are present. In the absence of wolves, coyotes outnumber red foxes. These results support the existence of a continent-wide among-carnivore cascade from wolves through coyotes to red foxes. However, for a distance of up to 200 km from the edge of wolf range, there is a transition zone where the effects of top-down control are weakened, possibly due to the rapid dispersal and reinvasion capabilities of coyotes. We conclude that wolves may need to occupy large continuous areas to facilitate among-carnivore cascades. This presents a challenge because much of the land set aside under the 1964 Wilderness Act is isolated and small in size. Successful strategies to minimise human-wolf conflicts are therefore urgently required to provide opportunities for wolves to deliver widespread ecological benefits.