Diversity Patterns and Associations of Brasilian Lotic Fish Species

Biological diversity, frequently measured by species richness, is a common social goal and management objective that is measured at a local or site scale and extrapolated to landscape, basin, or riverscape scales.  However, increasingly the insufficiencies of such extrapolations are being recognized.  In this study, we sampled 24 to 80 randomly or stratified-randomly selected stream or reservoir sites in 7 river basins through use of multiple gears, depending on site characteristics.  After identifying each individual collected to species, we calculated alpha (mean site), gamma (basin), and beta (gamma-alpha, or turnover) species richness.  We also collected landscape and site environmental data for all sites.  Gamma (and alpha) species richness in the basins ranged from 20(4) in a highland savanna ecoregion to 111(22) in an eastern lowland Amazon basin.  Beta species richness was 2 to 8 times, but typically 4 times, alpha richness.  Estimated gamma richness and sampling effort curves indicated that more than 40 sites and site sampling distances greater than 40 times mean stream widths were needed to reach sampling effort asymptotes.  Natural landscape, land use/cover, site, and combined models explained 20%, 11%, 32%, and 47% of the variability in savanna fish species, respectively.