Biodiversity dynamics in the Anthropocene: how human activities change equilibria of species richness

We are living in a time of rapid environmental changes caused by anthropogenic pressures. Besides direct human exploitation of plant and animal populations and habitat transformation, biodiversity changes in the Anthropocene are affected by less trivial processes including rapid spreading of non-native species, emergence of novel communities and modifications of ecosystem functioning due to changing nutrient cycles and climate changes. These processes are so complex that confident predictions and effective biodiversity conservation cannot be obtained without a suitable theory of biodiversity dynamics. We argue that such dynamics have particular attractors, i.e. stable equilibria, that are determined by environmental conditions. These stable equilibria set biodiversity limits, i.e. carrying capacities for biodiversity, from local to global scales. We point out the evidence of such limits at various spatiotemporal scales and show, using the new equilibrium theory of biodiversity dynamics (ETBD), how dynamics of diversity depend on non-linear relationships between number of species, community abundance and population size-dependent processes of species extinction and origination (speciation or colonization). We show that non-linear effects of biodiversity on ecosystem functioning can lead to multiple biodiversity equilibria and tipping points. Various human activities, including species introductions, human appropriation of primary production and trophic downgrading, can change local, regional and global diversity equilibria by affecting processes that set equilibrium diversity levels. The existence of equilibrium and out-of-equilibrium states has important implications for conservation, restoration and reconciliation ecology. It highlights the need to more effectively and intentionally balance the historical focus on the preservation of natural habitats with management specifically directed towards the processes responsible for long-term maintenance of biodiversity equilibria. The Anthropocene represents a unique situation in which people make decisions concerning the dynamics of the natural world, and we argue that ecological restoration requires wisely deciding which of the alternative equilibria are worth maintaining.