Do the drivers and levels of isolation in fish faunas differ across Atlantic and Pacific drainages in the Americas?

Abstract

Aim The roles of physical barriers to dispersal and species' abilities to cross barriers have in shaping freshwater fish distributions has been little explored at the macroscale. This study investigates how topography and species migratory behaviours and salinity tolerances (vagility) affect catchment isolation, species richness, large-scale distribution patterns and turnover across latitudes and coasts. Location North (NAm), Middle (MAm) and South (SAm) America. Taxon Fish. Methods From a large, published, dataset Pacific and Atlantic coast catchments in NAm, MAm and SAm were allocated to six georegions and species richness and composition correlated with information on catchment size, channel gradient and discharge. Catchment species richnesses, species–area relations (SAR), endemicity and turnover relationships were examined across coasts and latitude for species with different migratory behaviours and salinity tolerances. Results Pacific coast rivers are smaller, steeper, hydrologically more variable and have narrower marine shelves than Atlantic ones, except in MAm. Catchment isolation is greater in Pacific drainages but the barriers to species exchange differ across georegions. Species richnesses are greater in Atlantic drainages but the proportion of vagile species is smaller. SAR slopes are flatter in vagile species and endemicity less. Turnover varies with catchment topography, the relative contribution of vagile species and, in MAm, on evolutionary history. Main conclusions Tectonic and geomorphic processes influence catchment size and topography, and along with species differences in dispersal potential, affect how isolated catchments are, with consequences for species richness and composition.