Comparing the effects of landscape and local environmental variables on taxonomic and functional composition of phytoplankton communities

Landscape and local environmental factors are responsible for different structuring processes in aquatic communities. In this study, we evaluated the relative influence of local and landscape variables on the taxonomic and functional composition of phytoplankton. Samples were obtained from 29 floodplain lakes located in the Tocantins-Araguaia River Basin in Brazil. Taxonomic composition was assessed using densities of species, and functional composition was assessed using three classes of functional traits: morphological, physiological and behavioral. We used a partial redundancy analysis (pRDA) to evaluate the effect of local and landscape variables on taxonomic and functional phytoplankton composition. We found higher predictive power for environmental variables at the local scale for functional composition (physiological and behavioral traits) compared with their power for taxonomic composition. However, the type of land cover did not affect either taxonomic or functional composition. Phosphorus concentration and oxygen saturation were the main factors related to physiological traits, while zooplankton density and oxygen saturation to behavioral traits. These results indicate that local environmental variables act as determinants of the taxonomic and functional composition of phytoplankton in these lakes and that functional traits may be more appropriate than taxonomic composition for evaluating relationships between these communities and environmental factors.