Stochasticity in social structure and mating system drive extinction risk

As anthropogenic activities continue to threaten species across the globe, many populations have seen dramatic reductions in abundance from historical values. While the underlying causes are varied, such long-term population declines greatly increase these species’ susceptibility to extinction via stochastic processes. Previous research has established that demographic stochasticity and environmental stochasticity play important roles in extinction risk, but few studies have investigated the role of stochasticity in social dynamics, such as group formation and mating systems. Here, we developed a suite of simulation models incorporating different combinations of stochastic processes, while also varying group size and mating system. Using these models, we evaluated the interacting effects of different mating systems coupled with varied sources of stochasticity on extinction risk. Extinction risk was generally higher for populations with mating systems more dependent on even sex ratios in groups (e.g., monogamy). However, in more flexible mating systems (e.g., polygynandry), stochasticity in the formation of individual groups actually reduced extinction risk in certain scenarios. By identifying the factors most important to the stochastic extinction risk of species with different mating systems and social structures, we provide insight into conservation and management strategies for such species facing population declines.