Aim: Human activities are causing massive increases in extinction rates but might also lead to drastic increases in speciation rates; for example, after human-mediated spread of species to otherwise unreachable landmasses. The long-term net anthropogenic effects on biodiversity therefore remain uncertain. Our aim was to assess the combined anthropogenic effects of extinctions and speciations on biodiversity over geological time-scales. Location: Global. Time period: Present and predicted future. Major taxa studied: Terrestrial mammals. Methods: We estimated known anthropogenic and predicted future extinctions based on Red List categories from the International Union for Conservation of Nature. We inferred potential anthropogenic speciations, assuming that all introductions to isolated landmasses would, over time, evolve into distinct species. We then estimated changes in regional and global species richness and phylogenetic diversity attributable to these extinctions and speciations. Results: We demonstrated that if all species introduced onto new landmasses develop into new species, the number of anthropogenic speciation and extinctions eventually become similar. However, even after accounting for an anthropogenic increase in speciation, our estimates suggest recovery times for phylogenetic diversity of several millions of years. Main conclusions: Our results highlight that although humans are causing drastic biodiversity losses, human-driven speciation could eventually counterbalance these losses in species numbers, whereas phylogenetic diversity, at least within our simulation scenarios, would remain permanently reduced. This conclusion, however, requires our pressures on biodiversity to cease soon and requires us to consider geological time-scales rather than changes over this century.
