As apex predators disappear worldwide, their role in structuring systems facing rapid anthropogenic change is a critical avenue of study. The absence of apex predators can have complex ecological consequences, such as mesopredator release – an increase in the number of smaller predators. Although global increases in mesopredator range and abundance are a conservation concern, it is uncertain whether this effect is driven primarily by apex predator loss, or by a changing landscape becoming more friendly to mesopredators; these factors have previously been challenging to test simultaneously. The wolf control program in Alberta provides a natural experiment to study mesopredator release, while neighbouring Saskatchewan offers a less human-modified baseline. Using a network of 275 camera traps established by the Alberta Biodiversity Monitoring Institute, paired with an emerging method for estimating the density of unmarked species, we compare mesopredator densities across different levels of wolf control and human disturbance. We estimate density using the ratio of the length of time that individuals are detected in any camera trap’s field of view to the product of the total amount of time all the cameras are operating and the area observed by each camera.
Results/Conclusions
We demonstrate that anthropogenic disturbance is associated with a larger change in mesopredator density than the top-down effect of apex predator loss. Preliminary results indicate that there are significantly more fishers and red foxes per 1000 km2 in areas with low human disturbance (95% CI of mean increase in density is 1.42, 33.75 for fishers and 0.35, 60.50 for red foxes). As the effect of human disturbance appears to outweigh any mesopredator release effect thus far, it may be a plausible explanation for disparities in studies of top-down effects on mesopredators where those two factors could have been confounded. Boreal mesopredators’ preference for areas with low human use illustrates the risk of grouping all mesopredators together as a conservation threat. This result also contrasts with the findings of previous work on mesopredators in more temperate agricultural areas. Moving forward, this work will advance our understanding of the effects of the loss of apex predators and the deepening human footprint on predator systems worldwide.