Population responses of naive roe deer to the recolonization of the French Vercors by wolves

Abstract

In a context of rapidly changing carnivore populations worldwide, it is crucial to understand the consequences of these changes for prey populations. The recolonization by wolves of the French Vercors mountain range and the long-term monitoring (2001-2017) of roe deer populations provided us a unique opportunity to assess both lethal and non-lethal effects of wolves on these populations. We compared roe deer population abundance and growth, fawn body mass, and browsing intensity in two contrasted areas: a central area (core of a wolf pack territory characterized by an intense use by wolves) and a peripheral area (used more occasionally). Both populations of roe deer strongly dropped after an extremely severe winter but the population of the central area facing with wolves was slower to recover (due to a much lower growth rate the following year) and remained at lower abundance levels for 5 years. Fawn body mass was lower in the central area during that period and was not influenced by weather conditions or population abundance. The browsing index in the forests in presence of wolves decreased for a longer period, suggesting that possible habitat shifts have occurred. Altogether, the effects of wolves on the roe deer population in the central area occurred mainly during a 5-year period following the establishment of wolves, with effects at the population level in the first years only through the interplay between wolf predation (before wolves started preying on red deer), harsh winter conditions and naivete of prey to this recolonizing predator.