Main drivers of freshwater fish diversity across extra-tropical Southern Hemisphere rivers

Abstract

Many multi-regional studies investigating how available habitat area, energy availability, and historical refugia drive freshwater fish diversity have emphasized Northern Hemisphere and tropical areas. Furthermore, while many such studies have examined diversity drivers on basin-scale species richness (i.e., gamma diversity), they typically have not evaluated beta diversity or phylogenetic diversity nor included representative numbers of Southern Hemisphere basins unassociated with tropical rainforests. Here, we examine 784 basins and present the first comprehensive evaluation of the driving effects of gamma diversity and the patterns of beta and phylogenetic diversity across extra-tropical Southern Hemisphere (ETSH) freshwater fish communities. We find that ETSH gamma diversity does not show a strong historical legacy associated with glaciations, and is influenced more by factors related with habitat area and available energy. Additionally, ETSH regions show high beta and phylogenetic diversity and low levels of diadromy, except New Zealand, which shows narrow species diversity and cosmopolitan species dominance. Finally, phylogenetic diversity indicates how the endemism of the three ETSH Mediterranean-climate regions is characteristic of long-term isolation and persistence. These results demonstrate ETSH freshwater fish diversity to be distinct from both the tropics and their Northern Hemisphere latitudinal counterparts.