Density dependence impacts our understanding of population resilience

Current metrics of demographic resilience (e.g., resistance, recovery) summarize the potential responses of populations to the frequent, varied disturbances that ecological systems experience. Much of the application of these metrics has focused on the potential response of time-invariant, density-independent structured population models to hypothetical disturbances. Here, we examine such resilience measures in a flexible structured model with five vital rate parameters. Making one vital rate density-dependent at a time, we show that density dependence has profound and complex impacts on our understanding of resilience. Depending on which vital rate was subject to density effects, existing measures of demographic resilience (compensation, resistance, and recovery time) either increased or decreased with population density. Moreover, the density-independent model under-predicted the recovery time of the corresponding density-dependent model, with a greater offset for species with longer generation times and higher iteroparity. Our findings demonstrate the importance of underlying non-linear processes when examining demographic resilience.