Résumé
The assessment of disturbance effects on wildlife and resulting mitigation
efforts are founded on edge-effect theory. According to the classical
view, the abundance of animals affected by human disturbance should
increase monotonically with distance from disturbed areas to reach a
maximum at remote locations. Here we show that distance-dependent movement
taxis can skew abundance distributions toward disturbed areas. We develop
an advection-diffusion model based on basic movement behavior commonly
observed in animal populations and parameterize the model from
observations on radio-collared caribou in a boreal ecosystem. The model
predicts maximum abundance at 3.7 km from cutovers and roads.
Consistently, aerial surveys conducted over 161,920 km2 showed that the
relative probability of caribou occurrence displays nonmonotonic changes
with the distance to anthropogenic features, with a peak occurring at 4.5
km away from these features. This aggregation near disturbed areas thus
provides the predators of this top-down-controlled, threatened herbivore
species with specific locations to concentrate their search. The
edge-effect theory developed here thus predicts that human activities
should alter animal distribution and food web properties differently than
anticipated from the current paradigm. Consideration of such nonmonotonic
response to habitat edges may become essential to successful wildlife
conservation.