Cradles, museums, and disequilibria: reconciling biodiversity dynamics using equilibrium theory

Historical nonequilibrium processes are often considered the main drivers of global biodiversity patterns. We argue that while biodiversity is often out of equilibrium, the concept of equilibrium is still crucial for interpreting macroecological diversity patterns, and current confusion in the literature stems from misunderstandings concerning equilibrium dynamics. We demonstrate how an equilibrium-based framework, such as the 'Equilibrium Theory of Biodiversity Dynamics' (ETBD), illuminates diversity patterns in space and time, including the latitudinal diversity gradient, even in the out-of-equilibrium context. This framework has profound implications for understanding diversity dynamics during historical, current, and future climate changes, suggesting that while temperate diversity is probably below its equilibrium level, tropical biodiversity could be above its equilibrium, elevating extinction risk in tropical biomes.