Local environment and connectivity are the main drivers of diatom species composition and trait variation in a set of tropical reservoirs

Abstract

A metacommunity is defined as a set of local communities that are connected by dispersal and are controlled by environmental drivers operating at different spatial and temporal scales. Although diatom ecology has been studied extensively in temperate and lotic ecosystems, knowledge of tropical lentic systems is more limited. We evaluated how planktonic and surface-sediment diatom communities, including trait-based communities, were structured by environmental, spatial and land-use variables in tropical reservoirs. Diatoms were sampled in seven reservoirs (31 sites in total) in south-east Brazil, from the surface sediment and the plankton in summer and winter. Diatom communities responded primarily to a trophic gradient and secondarily to a light-availability gradient. Connectivity was also a strong predictor, whereas land use had a weaker influence on community variation. Our results further suggested that surface-sediment and planktonic diatom groups were structured by similar environmental variables. Trait-based analysis also indicated that these communities were related to environmental and spatial factors. We conclude that (1) trophic state, light availability and connectivity were the main drivers of diatoms in this set of tropical reservoirs, resulting in spatially structured communities; (2) patterns for surface-sediment diatoms resembled both summer and winter diatom communities in the plankton; and (3) the effects of the explanatory variables (local environment, connectivity and land use) varied among the different biological datasets (i.e. when organised taxonomically, or according to growth morphology, cell size or trophic preference). We emphasize that studies in tropical reservoirs should take spatial variables into account, due to the connectivity of the sites.