Speciation Rates of Freshwater Fish Across the Americas Vary With Environmental Heterogeneity and Dispersal Ability

Abstract

Aims

Species richnesses show marked spatial trends, but the contribution of speciation rates (SpecRates) to these trends is less clear. The roles of environmental heterogeneity (topography and climate), glaciation, dispersal ability, times to colonise, and to speciate to large-scale variation in SpecRates of freshwater fish faunas are assessed.

Location

Atlantic and Pacific coast drainages in North, Central, and South America.

Taxon

Fish.

Methods

Published information was compiled on SpecRates, phylogenies, colonisation times, species geographic distributions, and migratory behaviour of fishes in 582 catchments. The effects of topographic and climatic factors, including glaciation and vagility, on three speciation rate metrics were examined using boosted regression tree models.

Results

Mean SpecRates differ five-fold across drainage regions and with glaciation. Pacific coast drainage SpecRates are highest in the Nearctic and decline southwards, but in Atlantic drainages, rate trends differ between Nearctic and Neotropical basins. Assemblage SpecRates vary with the percentage of migratory species, glaciation, environmental heterogeneity, colonisation time, and species age. High Nearctic rates are associated with postglacial recolonisation by rapidly speciating diadromous species, but rates in the Neotropics for resident and potamodromous species are higher than for diadromous species. Species dispersing into an area are more migratory, occur further north, and have wider distributions than species diversifying in situ. Endemicity in the more recently colonised Nearctic increases with colonisation time to Neotropical levels.

Main Conclusions

Spatial and temporal variation in topography and climate generate differences in connectivity which, coupled with differences in species abilities to overcome these barriers, result in differences in speciation rates in different areas.