Immediate effects of an Amazonian mega hydroelectric dam on phyllostomid fruit bats

Large losses of tropical forests result from the flooding of terrestrial ecosystems by mega hydroelectric dams. Because run-of-the-river dams operate based on smaller reservoirs with limited water storage, they have been generally considered less harmful to the environment, but their actual effects on biodiversity have been rarely measured. We herein estimate immediate impacts resulting from the flooding of the run-of-the-river Santo Antônio Hydroelectric on phyllostomid bat assemblages, based on the variation of their richness, abundance and species composition over the first two years after the establishment of the dam. We designed a standardized study integrating temporal sampling in areas that would and would not be flooded, before and after the establishment of the dam. We sampled 12 Pre-flood plots, and 34 plots that remained unflood. Among the non-flood plots, 25 were resampled after the river damming. We captured 3096 bats belonging to 59 species and found that the abundance of fruit bats decreased posterior to the formation of the dam. Moreover, the composition of fruit bats was different between the sampling periods, with a clear segregation of the várzea plots of the pre-flood period. Comparisons between pre- and post-unflood plots revealed that 60% of the plots decreased in abundance of bats, and 68% decreased in abundance of phyllostomid fruit bats. Our results demonstrate that the run-of-the-river dam altered the phyllostomid species composition in the non-flooded areas after the establishment of the dam, reducing the abundance of frugivorous bats. Also, the remaining unflood areas did not incorporate bat assemblages from the várzea forests that were permanently flooded by the reservoir. Based on our results, we suggest that environmental policies regulating the licensing processes for the implementation of large hydroelectric power stations should include orientation for the establishment of protected areas, as a condition for their operation. These areas can work as systematic instruments for biodiversity conservation, with special attention to the protection of the irreplaceable floodplain forests.