Effects of hydrological, environmental and spatial factors on fish diversity and community structure in oxbow lakes from the Amazon floodplain

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Effects of flood pulses on lakes are mediated by the hydrological connectivity between environments in floodplain systems. Thus, hydrological connectivity along with other environmental filters are essential for structuring aquatic communities. Besides, it can also drive ecological changes in local diversity and species composition of numerous organisms. In this context, we characterize the hydrological connectivity in oxbow lakes to evaluate the influence of connectivity on alpha and beta diversity, as well as the local and spatial factors on the structure of fish metacommunities in different hydrological periods (flood, ebbing and drought). The study was conducted in oxbow lakes located in the Middle Purus River, western Amazon. The dynamics of hydrological periods was the primary factor in the variation of alpha diversity, and the different connectivity levels determined the increase in fish beta diversity. We found that even during biotic homogenization stemming from increased water levels, the beta diversity of fish remained high, since a region with varied connectivity levels between environments may contribute to the variation in species composition. In terms of metacommunities, the importance of connectivity was reduced during the flood, where the environment mainly structured metacommunities, which is consistent with species sorting. Thus, the contribution of connectivity increased during the disconnection of some lakes in the drought, especially for the most common and intermediate species, which may have influenced the dispersal and environmental pressures on these communities. For rare fish species, space and connectivity were the factors determining community structure, being influenced by factors of dispersal limitation during the flood and mass effect during the ebbing. Thus, the present study showed important processes that can lead to the structuring of fish communities in floodplains. This process induced different connectivity levels between rivers and lakes, and the action of environmental and spatial factors on species distribution, providing important information to encourage efforts for conservation and restoration of these ecosystems.