The importance of spatial scales to analysis of fish diversity in Amazonian floodplain lakes and implications for conservation

The Amazon River Basin has the highest fish species diversity of any region in the world, but is under threat from anthropogenic perturbations including overharvesting, alien species and drought. We asked whether species diversity in this region is more a function of within-lake species richness (i.e., alpha diversity) or differences among lakes (beta diversity). Although many studies have reported on species richness and diversity in single habitats, the importance of measuring diversity at different spatial scales is not yet well established. We collected fish in 10 floodplain lakes along the Solimoes River (Brazil), divided evenly between two lake types: those on islands in the river channel (island lakes) and those on the margins of the river (coastal lakes) during 2006. We partitioned fish diversity into three spatial scales: alpha = within each lake; beta(1) = among lakes of the same type (coastal or island) and beta(2) = between the two types of lakes, and compared their relative contributions to regional (gamma) diversity. beta(1) + beta(2) contributed as much or more to gamma diversity than did alpha. Although many of the 116 fish species were shared between lake types (S = 72), 32 species were found exclusively in coastal lakes and 12 species were found exclusively in island lakes. Coastal lakes, which were deeper and cooler than island lakes, consistently had higher fish species richness than island lakes. We suggest that it will be necessary to set areas large enough to contain multiple lakes of both types to preserve regional fish diversity.