Impacts of large dams on Amazonian floodplain bird communities

Abstract

Amazon river floodplains sustain distinct kinds of seasonally flooded habitats along with their specialized biota. River sediment load and geomorphology determine vegetation physiognomy and the occurrence of specialized taxa. Hydropower dams disrupt the annual flooding cycle, affecting the floodplain habitats and associated avifauna. Our goal was to understand how permanent flooding caused by large dams affects taxonomic, functional, and phylogenetic diversity of bird communities in two Amazonian rivers with distinct characteristics. We sampled 35 sites, including undisturbed sites and sites impacted by the permanent flooding caused by large dams operating on the Madeira and Xingu rivers since 2012 and 2016, respectively. We recorded 202 bird species through passive acoustic monitoring. We did not find differences in mean species richness between rivers or between impacted vs. undisturbed sites. However, we found species turnover between distinct river basins and between sites. Undisturbed sites were characterized by floodplain specialists and were more phylogenetically clustered and functionally more similar than impacted sites, which were occupied by more generalist species from different phylogenetic clades, with distinct functional traits. By assessing multiple dimensions of bird diversity, we show that permanent flooding leads to extensive changes in the floodplain avifauna, favoring generalist over specialist species and thus reducing the uniqueness of the affected communities. We demonstrate that alpha diversity metrics alone are insufficient to characterize the impacts of river damming on Amazonian floodplain avifauna. To properly monitor dams' environmental impacts, additional measures of community change should be standardized, with emphasis on species replacements in seasonally flooded environments.

Abstract in Portuguese is available with online material.