Padrões Espaço-Temporais da comunidade planctônica do complexo lacustre do Médio Rio Doce

Abstract

During ten years the Brazilian The Long Term Ecological Research Program (LTER-site4) collected data from planktonic communities of several lakes belonging to the Vale do Rio Doce lacustrine system. In this study, we used four studies which evaluated the community structure of these lakes focusing on different temporal and spatial scales, which are: inter- and intra-annual variation, daily variation, variation between and within the lakes (vertical and horizontal). The objective of this thesis was to evaluate which scales explain variation in community structure the most and what are the main generation mechanisms of this variation. We used a technique called variance partitioning where the coefficient of determination of the multiple regression of biotic variables was partitioned between the spatio-temporal scales, making it possible to compare them with each other. Initially, the random residuals corresponded to the larger fraction of the variance (69%). This result was expected, since several other scales and sources of variation were not considered in this analysis. The variation between the lakes was the scale with the largest explanation of variability of plankton community structure (18%), followed by inter-annual variation (8%). The intra-annual variation, or seasonal, and intra-lake, both vertically and horizontally, showed the lowest explanations (2%). Regarding the generating mechanisms of variation, the mixture patterns of the lakes is the main mechanism that determines the community structure in both time and space. Other factors affect the community structure indirectly by influencing the mixing pattern. Seasonal and inter-annual variations in weather variables determine the mixture pattern, as well as their inter-annual variations. The vertical attenuation coefficient acts together with the depth of the lake, determining the strength of the thermal stratification and the circulation pattern (e.g. monomitic or polymitic), thus determining the differences in community structure between lakes. Biotic factors, such as top-down control by introductions of exotic piscivorous fish species are also capable of generating long-term variations in community structure, but further studies are still necessary to prove the exact mechanism by which this trophic cascade occurs.