AIM: The diversity of reproductive modes among amphibians provides a striking example of how differences in the biology of species furnish can provide important explanations for species distribution patterns on a broad scale. We hypothesized that sites with a higher humidity level will support more different modes of reproduction than drier sites and will consequently exhibit a higher phylogenetic diversity. Furthermore, we predict that if there is a gradient in the tolerance of reproductive modes to desiccation, there will be a nested pattern in the composition of reproductive modes among sites. LOCATION: Twenty-seven forest sites in the Brazilian Atlantic Forest. METHODS: Through a path analysis approach, we evaluated the direct and indirect effects of the humidity level on the number of reproductive modes as well as the relative importance of both variables on amphibian phylogenetic diversity. A nestedness analysis was used to quantify the extent to which the composition of both species and reproductive modes in drier sites correspond to non-random subsets of those in sites with higher annual precipitation. RESULTS: We found that the reproductive modes present in drier sites are non-random subsets of those present in sites with higher humidity levels. Because reproductive modes are phylogenetically conserved among amphibians, sites with a greater number of reproductive modes supported greater phylogenetic diversity. Sites with high precipitation throughout the year provided adequate environmental conditions for a larger number of reproductive modes, whereas sites with low precipitation and typical seasonal climates supported only those reproductive modes specialized to resist desiccation. MAIN CONCLUSIONS: Our results show that humidity-related variables are key environmental factors related to both the richness of reproductive modes and phylogenetic diversity. We hypothesized that the higher phylogenetic diversity found in moister sites reflects differences in the tolerance to desiccation among different reproductive modes. Given that reproductive modes are associated with susceptibility to desiccation, their incorporation into explanatory models may trigger a great advance in the understanding of the mechanisms regulating the species richness and composition of amphibian communities.