O papel de ribeirões para a manutenção da diversidade no alto São Francisco
Fish conservation; freshwater fish; migratory fish; river size; juvenile fish; São Francisco basin
In the tropical region, among the lotic freshwater ecosystems, the medium-sized rivers are little known compared to headwaters and large rivers. They seem to play a crucial role in the life cycle of migratory fishes and possibly harbor an important part of the fish community in their basin. However, few studies have investigated these matters for different river sizes and recent publications are absent. Therefore, my study aimed to assess if the river size influences the juveniles of migratory species (chapter one) and the diversity patterns (alpha and beta diversity) of the region (chapter two). We analyzed fish communities from 16 and 48 rivers for chapters one and two, respectively, in the upper São Francisco River basin. We found that smaller rivers, especially when draining regions close to floodplains, seem to be the first places where juveniles of migratory species move after leaving the floodplain lagoons. We have also raised information indicating that individuals move downstream as they grow, being found in increasingly larger rivers. The analyzed rivers showed high values for alpha and beta diversities, with turnover being the main process leading to species variation among the rivers of all sizes. The alpha diversity showed an increase with the size of the river while the beta diversity does not seem to have a clear pattern related to the river size. We also added 34 additional species from lotic stretches that had not been registered yet for this region and indicated that several additional species can still be recorded in this basin. We concluded that intermediate-sized rivers, despite little studied, are essential in maintaining biodiversity, including for large species, such as migratory.