Predator community and prey dynamics : a case study of roe deer and re-colonizing fox, lynx and wolf

Abstract: The role of predation is a central question in ecology and population dynamics. In South-central Sweden, the predator community has gone through drastic changes over the last fifty years with the progressive recovery of three large predators: the fox (Vulpes vulpes), recovering after a sarcoptic mange (Sarcoptes scabiei) outbreak, the lynx (Lynx lynx) and the wolf (Canis lupus), the two latter re-colonizing the region after a massive population persecution at the beginning of the 20th century. These three species potentially prey upon roe deer (Capreolus capreolus). Although it is one of the most common ungulate species in Europe, the combined effect of several predators on its survival is poorly documented. The objective of this study was therefore to infer how roe deer responds to the changes in a gradually increasing multipredator system, and to estimate the consequences for population growth rate. I used long-term (37 years) series based on telemetry data to analyze annual survival rates of 458 knownaged roe deers captured in Grimsö Wildlife Research Area (GWRA) between 1975 an 2012. Two complementary methods, the Cumulative Incidence Function and Cox Proportional Hazards were used to generate accurate estimates under a competing-risk framework. Predation was found to be largely additive to natural and human-related mortality causes, making the total mortality to increase by 40%. The compensatory or additive nature of each predation risk (fox, lynx or wolf) was unclear, but wolf is suspected to play an increasingly important role in the future. Monte-Carlo simulations with projection matrices corresponding to the four risk regimes experienced by roe deer confirmed the synergistic effect of the three predators on roe deer population growth rate as it decreased by more than 17% in the presence of the three predators, a pattern that could explain the recent drop in roe deer densities by 80% in GWRA in the 10-15 recent years.