Functional responses of amazonian frogs to flooding by a large hydroelectric dam

River damming by hydroelectric plants interrupts the continuity of rivers and causes the flooding of adjacent terrestrial ecosystems. Assessments of the impacts of major hydroelectric dams on species and the functional responses of communities to flooding are scarce. We used data from eight years of forest monitoring around a - 100-km section of the Madeira River upstream of the Santo Antônio Dam in southwestern Brazilian Amazonia to investigate the effects of forest inundation on estimates of functional diversity and frequency of trait occurrence in pre- and post-flooding anuran assemblages. Lowland forests hosted higher functional diversity and more unique functional composition than unflooded areas sampled before and after reservoir filling. Functional richness was not affected by reservoir filling. Frequencies of arboreal anurans that lay their eggs in tree cavities or water and those that complete larval development in water were higher in flooded forest plots. In unflooded plots during the post-filling stage, there was an increase in the average frequency of nocturnal anurans and a decline in the abundance of fossorial and diurnal species. The average frequency of large-bodied anurans increased after river damming to levels similar to those of flooded plots. Our study indicates that anurans whose reproductive modes are associated with riparian and floodplain forests are most sensitive to permanent reservoir flooding. We recommend that efforts to mitigate the effects of hydropower infrastructure should include the protection of intact seasonally flooded lowland forests.