The impact of a run-of-the-river hydroelectric dam on a non-volant small-mammal assemblage in Brazilian Amazonia

There are few scientific studies evaluating the impact of the loss of wetlands on the banks of tropical rivers on assemblages of small non-flying mammals. To understand the possible deleterious effects of hydroelectric construction in tropical forests on this group of mammals, we used data from 2 years of monitoring carried out during the period before the filling of a hydroelectric plant reservoir in the Brazilian Amazon, and related them to vegetation, soil and topography. We captured 659 individuals of 20 small-mammal species. The species assemblage composition in the flooded areas was a subset of species that occurred in both floodable and non-floodable areas, and only one species was captured exclusively in the flooded area. Species composition was influenced by the proportion of sand, by soil nutrient concentration and distance from water bodies. We conclude that there is no evidence that the flooding of low-lying areas along the Madeira River would negatively affect the assemblage of non-flying small mammals in the short term because the remaining areas have similar assemblages of small mammals as those destined for flooding. Whether the area lost will be important for population dynamics will depend on the conservation of the remaining areas.