Do the species with large geographic range diversify faster?

Range size is a universal characteristic of every biological species, and is often assumed to determine diversification rate. However, the relationship between range size and past and future diversification of species remains elusive. On one hand, there are strong theoretical arguments that large-ranged species should have higher rates of diversification. This theoretical view is challenged by observations that small-ranged species are often phylogenetically clustered and form spatially localized hotspots, claimed to be the cradles of biodiversity. The research of range-size evolution is a notoriously complex task, because the range sizes evolve not only anagenetically (range expansion or contraction), but also cladogenenetically (range size change between mother and daughter species during speciation). Here use a state-dependent diversification model covering both anagenetic and cladogenetic changes in range size, and apply it to the phylogeny and range size data of mammals. We show that in general, large-ranged species diversify faster, as theoretically expected, and that the phylogenetic clusters of small-ranged species reflect past fragmentation of large-ranged species, rather than ongoing radiations. However, the analysis of residual (concealed) variability of our models suggests that there are multiple mammalian taxa where this general pattern is reverted and small-ranged species indeed diversify faster. According to the ancestral state reconstructions, these ongoing radiations of small-ranged species typically take place in constantly insular landscapes, such as oceanic archipelagos. Our results suggest that, while range size is an important factor influencing species diversification, its effect in real-world systems is often locally modified or even inverted by idiosyncratic geographic setups.