Determinantes da diversidade beta e variabilidade temporal da comunidade fitoplanctônica em um reservatório tropical

Abstract

Understanding how the patterns of communities are structured in nature is one of the main interests of ecologists. Beta diversity and persistence are two ecological attributes that allow to assess how communities are structured. Thus, it is important to evaluate the temporal variation of communities to natural and anthropogenic environmental impacts, highlighting the potential drivers for compositional heterogeneity. In this context, the main objectives of this study were to measure the influence of the construction of a reservoir on beta diversity and the persistence of phytoplankton checking the main drivers of the dissimilarity of communities; and to describe the temporal patterns of physical and chemical parameters. We selected six sites, along 25 months (between 2004 and 2013) for analysis of phytoplankton and quantification of limnological variables in the Peixe Angical reservoir, located on the Tocantins River. The land use in the reservoir area was also analyzed using satellite images. The calculation of beta diversity using multivariate dispersion revealed no difference over time. The beta diversity estimated by multiple dissimilarity index Simpson was given mainly by turnover component. Through model regressions, the main predictors of compositional dissimilarity highlighted the importance of the reservoir formation, precipitation, time (months) and environmental heterogeneity (the coefficient of variation of total phosphorus). We also found a value of 50.43% in the persistence of phytoplankton species after reservoir construction. Comparing both periods, there were major fluctuations in the persistence of the species before reservoir construction, with an average persistence of 47.46%, while after the construction the persistence of the community has an average of 52.93%. In relation to physical and chemical variables, the two main axes of the PCA explained 46.97% of the total variability of the data. This analysis showed that the sampling sites were mainly influenced by the seasonality of the region. Despite the transformation of a lotic environment in lentic, beta diversity of phytoplankton remained relatively high due primarily to environmental heterogeneity. Thus, the filling process of reservoir not homogenized the physical, chemical and biological characteristics of the affected environments. This environmental heterogeneity could also be the responsible for the results of species persistence (50.4%) after the reservoir construction. Probably, the residence time may result in the greatest changes in the community composition, near the dam.