The new top dogs? Mesopredator densities increase with human habitat alteration, not with apex predator removal

Baily McCulloch, Robert Serrouya and Stan Boutin, Biological Sciences, University of Alberta, Edmonton, AB, Canada, Melanie Dickie, Alberta Biodiversity Monitoring Institute, Edmonton, AB, Canada

Background/Question/Methods
Top predators are disappearing worldwide as human activity continues to transform the natural world. These apex predators play a vital role in structuring ecosystems, and their absence can have complex consequences, including mesopredator release. However, because apex predators tend to be lost as a consequence of increasing human activity, human habitat alteration may confound studies of mesopredator release.
The wolf reduction program in Alberta provided an opportunity to study the effects of removing an apex predator, and the boreal ecosystem across Alberta and Saskatchewan offered a gradient of habitat alteration from Alberta, where industrial activity has reshaped the landscape, to less human-modified Saskatchewan.
We compared mesopredator densities between areas with and without wolf reduction and across a gradient of habitat alteration to determine which factor had a stronger effect on mesopredator populations. As the camera trap network was established before wolf reduction began, we were also able to compare mesopredator densities from before and after the implementation of wolf reduction.

Results/Conclusions
Using data from 1,785 camera traps established by the Alberta Biodiversity Monitoring Institute, we calculated mesopredator densities using the Random Encounter and Staying Time model.
Habitat alteration was associated with larger changes in mesopredator density than apex predator removal. We detected a significant increase in coyote and fox densities with increasing habitat alteration, whereas each mesopredator species was present at approximately equal densities both before and after wolf reduction, and both inside and outside of the wolf management area.
Coyotes were more abundant in areas with higher habitat alteration both before and after wolf reduction began, and red fox densities increased in areas with higher habitat alteration after wolf reduction was implemented.
Every km2 increase in the total area of surrounding habitat alteration before wolf reduction was implemented corresponded to an increase in coyote density of 0.24 coyotes per 1000 km2. After wolf reduction was implemented, every km2 increase in the total area of surrounding habitat alteration corresponded to an increase of 1.01 in coyote density per 1000 km2.
In the years after wolf reduction began, fox density was increased by 0.03 per 1000 km2 with every km2 increase in the total area of surrounding habitat alteration.
A more nuanced understanding of the circumstances under which mesopredator release may occur is essential to further our understanding of the future for all predators in a more and more human-dominated world.