Sincronia e estabilidade de comunidades fitoplanctônicas

Abstract

Different population, community and ecosystem variables can vary synchronously. Spatial synchrony occurs when the abundances of different local populations vary in a similar way over time. Considering this concept, in the first chapter of this thesis, I tested whether aquatic mesocosms subjected to the same treatments – with and without gradual addition of nutrients – would exhibit higher levels of spatial synchrony of phytoplankton than those belonging to different treatments. The results indicated that this expectation was not confirmed and that, probably, even at small spatial scales, phytoplankton dynamics were controlled by local factors. In the second chapter, I tested the effects of gradual eutrophication on functional diversity, community synchrony and stability of the phytoplankton community. Only the stability of chlorophyll-a concentration was significantly reduced by eutrophication. These results indicate that eutrophication can decrease the stability of primary productivity, even without changes in functional diversity and community synchrony, probably through other stabilizing mechanisms. In the third chapter, I quantified the levels of interspecific synchrony in 12 phytoplankton communities in the Upper Paraná River floodplain. Furthermore, I tested whether the levels of synchrony depended on the trait dissimilarity. Despite the high environmental variability in the floodplain, low levels of interspecific synchrony were observed. The levels of interspecific synchrony were not correlated with trait dissimilarity. These results suggest that demographic stochasticity may be the main mechanism explaining the dynamics of phytoplankton populations in the Upper Paraná River floodplain.