The counteracting effects of human-driven speciation and extinction on mammal species richness and phylogenetic diversity

Human activities are causing massive increases in extinction rates, but
may also lead to drastic increases in speciation rates – for example
following the human-mediated spread of species to otherwise unreachable
landmasses. The long-term net anthropogenic effects on biodiversity,
therefore, remain uncertain. The aim of this paper is to assess the
combined anthropogenic effects of extinctions and speciations on
biodiversity over geological time scales. We estimate known anthropogenic
and predicted future extinctions based on Red List categories from the
International Union for Conservation of Nature. We infer potential
anthropogenic speciations assuming that all introductions to isolated
landmasses will over time evolve into distinct species. We then estimate
changes in regional and global species richness and phylogenetic diversity
due to these extinctions and speciations. We show that if all
species introduced into 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 million years. Our results highlight that while
humans are causing drastic biodiversity losses, human-driven speciation
could eventually counterbalance these losses in species numbers, while
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 timescales rather than changes over this century.