Shifting biodiversity equilibria in the Anthropocene

Understanding current rapid biodiversity changes requires a robust and versatile theoretical framework that enables to model and conceptualize biodiversity dynamics under various conditions and settings. Recently proposed Equilibrium Theory of Biodiversity Dynamics (ETBD) postulates the existence of regional and local biodiversity equilibria (i.e. the attractors of biodiversity dynamics) which are determined by the balance of population-size dependent species origination and extinction and a feedback between total community abundance and species richness. According to the ETBD, diversity equilibria may shift due to three principally different reasons: (1) change of the total resource level that affects maximum community abundance, (2) change of the factors that directly affect species origination or extinction rates, e.g. the existence of geographic barriers or the temporal stability of the environment, (3) change of the function that links species richness to community abundance via the effect of diversity on ecosystem functioning and resource acquisition (e.g. due to change of the presence of keystone species or ecosystem engineers). We argue that human activities may change biodiversity equilibria via all these three effects. However, it is crucial to distinguish diversity changes due to the change of the equilibria or due to the movement out of the equilibria, as this has profound consequences for biodiversity management. In contrast to the out-of-equilibrium dynamics, the equilibrium level can be modulated by intentional human activities, and due to the three prinicpally different ways of equilibria shifts, there are alternative options which equilibria can be maintained and how. This theoretical framework thus opens new possibilities for ecological restoration and rewilding.