Demographic projections of the Apennine brown bear population Ursus arctos marsicanus (Mammalia: Ursidae) under alternative management scenarios

Abstract

Apennine brown bears are a very small, isolated population of central Italy, consisting of about 50 individuals and under a severe risk of extinction. We performed a population viability analysis (PVA) for this population, contrasting a deterministic model and an individual-based stochastic model, using a set of demographic parameters estimated for the same population during the last decade. We also built a set of simulated management scenarios, in which we compared the effectiveness of alternative conservation measures and assessed the susceptibility of the population to catastrophic mortality events. The deterministic model produced an estimate of the asymptotic population growth rate r = 0.001, corresponding to an asymptotically stable population. The stochastic model produced an estimate of r = − 0.013 (standard deviation = 0.103), corresponding to an annual population decrease of 1.3%, a 17% extinction risk in 100 years, an average population of 27 bears for non-extinct populations, and an average time to extinction of 81 years for those gone extinct. Extinction probability increased to more alarming levels (> 0.4) when at least one catastrophic event occurred during a 100-year period. Current vital rates of the population are not compatible with a more than negligible numerical increase, and this bear population is likely to remain small and exposed to a relatively high risk of extinction, if the average survival or reproductive rates do not increase. Management efforts aimed to increase food availability generated minimal to moderate variations in population growth rate and in the associated risk of extinction, whereas interventions meant to reduce adult female mortality were highly effective in increasing persistence probability. We propose that the general objectives of the action plan for the conservation of the Apennine brown bear for the incoming decade should explicitly contemplate quantitative demographic goals, focusing in particular on adult female and cub mortality.

Keywords

• Extinction risk
• small populations
• individual-based stochastic simulation models
• viability analysis
• VORTEX