The El Niño Southern Oscillation (ENSO) is the main source of variation for the gamma diversity of plankton communities in subtropical shallow lakes.

We determined the variation in the composition of plankton communities (zooplankton, phytoplankton, and ciliates) in subtropical lakes at different temporal scales, in relation to the seasons (dry and rainy seasons), as well as at finer (among months) and broader (ENSO—among El Niño, La Niña, and normal climate events) scales. Using a 16-year time-series dataset, we tested the hypothesis that seasonal variation would explain most of the gamma diversity of these plankton communities. We also investigated the environmental and temporal factors responsible for the variations in composition and species turnover. The scale related to dry and rainy seasons explained a considerable percentage of the gamma diversity and variation partitioning, showed that compositional changes occurred mainly over broader temporal scales. Environmental factors varying among seasons and ENSO events explained changes in composition, although some communities did not respond to the environment. Our results suggest that niche and stochastic processes operating at temporal scales correlated with ENSO climate events contributed to changes in species composition. Hence, climate anomalies might be important to maintain diversity in areas with reduced or loss of the natural variations in environmental conditions. Our results also suggest that, although communities show similar patterns of variation in composition, they might respond in a different degree to environmental and temporal factors. Thus, while niche-associated (environment) and stochastic (time) processes drove the phytoplankton, stochastic processes were more important for zooplankton, whereas neither were important for ciliates. [ABSTRACT FROM AUTHOR]