Phytoplankton taxonomic and functional diversity in two shallow alluvial lakes with contrasting river connectivity

Abstract

The mechanisms behind phytoplankton diversity patterns in natural ecosystems still remain elusive. In two shallow lakes with contrasting river connectivity, we first explored how diversity within each sampling (alfa diversity, α), among samplings (beta diversity, β1), and among hydrological seasons (β2) contributed to the diversity registered throughout the whole year (gamma diversity, γ). Then we estimated the importance of several environmental and temporal factors as structuring factors of these diversity patterns. To do this, we sampled the two lakes—one laterally isolated and other laterally connected lake with the Paraná River System—during a complete hydrological year. For the analyses, we considered both the species and the functional group level. At the species level, temporal variation (β1 + β2) made the main contribution for gamma diversity at the connected lake, possibly related to the constant species input from the river system. For the isolated lake, however, α was the main contributor. Regarding functional groups, α was the most important for both lakes, although no element of gamma diversity was different from the null model. Environmental factors like conductivity, turbidity, nutrient availability, and flood phases appeared as more relevant for the connected lake. Temporal processes (e.g., succession, ecological drift) were critical for the observed diversity patterns in both lakes. These results were consistent particularly considering the taxonomical approach. Our main findings are that the environment influences phytoplankton diversity patterns; however, other dynamics occurring on temporal scales may be more relevant for the phytoplankton community.