Can the loss of forest habitat cause changes in local communities? The results of our study of anuran assemblages in the southern Amazon indicate that the conversion of forest into open environments results in the substitution of species and the reduction of beta diversity. The increasing loss of tropical forests to agricultural development, especially in the Amazon, has resulted in the extensive modification of the natural landscape, transforming once-continuous forests into a mosaic of modified habitats. Our data indicate that this process resulted in the substitution of forest species by generalists, which are more typical of open environments. Also, this process has a homogenizing effect, making different areas more similar to one another, resulting in a decrease in beta diversity. This substitution–homogenization process may become increasingly common through the ongoing advance of agricultural frontiers, resulting in the local extinction of an important component of the biodiversity of tropical forests.