Spatial distribution and composition of waterbirds in relation to limnological conditions in the Amazon basin

The main hypothesis is that waterbird richness in Amazonian lakes differs between white- and black-waters, and has gradients in species composition relating to lake-to-lake differences in shape, depth, water transparency, habitat richness, and productivity. I tested a complementary hypothesis that bird assemblages respond to variations in lake characteristics over a regional scale, and to neighboring aquatic components, called water body richness, including rivers, channels, and ponds. Bird surveys were conducted by circumnavigating 70 lakes along 1,000 km of Amazon River floodplains. To test these hypotheses, a non-metric multiple-dimensional scaling ordination complemented by multiple linear models was used to determine relationships between bird richness and assemblage composition, and biotic and abiotic lake characteristics. At a local scale, lake shape, water transparency, and trophic status influence bird assemblages. At a regional scale, differences among sites in water body richness, produced by Amazon River tributaries, and the two water types, are determinants of variation in composition of waterbird assemblages. The results indicate that waterbird assemblage composition within Amazonian floodplains does result from links in processes operating at both spatial scales as predicted by neutral theory or influenced by local ecological factors as predicted by niche theory.