Functional nestedness of anuran communities along gradients of pond area and permanence

Abstract

Turnover in community composition is expected when species are restricted to parts of environmental or biotic gradients. In contrast, nestedness emerges when some parts of a gradient allow many species to co-occur, while other parts restrict presence to generalist species. This leads to communities in diversity-poor areas of the gradient to be subsets of those in the richer areas. Anurans that develop in ponds are strongly affected by water availability, with small and ephemeral habitats harbouring species with traits adapted to desiccation risk. We hypothesized that water availability, estimated by pond area and permanence, will generate a nested pattern in anuran trait diversity. We tested this hypothesis using data from two anuran metacommunities in tropical and subtropical regions of Brazil. The first metacommunity comprised 1514 adult anurans from 23 species distributed in 11 ponds, whereas the second one included 10,852 tadpoles from 21 species in 38 ponds. We estimated functional diversity using body variables, habitat use and reproductive modes and tested our hypothesis using a nestedness metric based on functional data (treeNODF). We found that small ponds and with low permanence included not only lower functional diversity, but diversities that were subsets of those present in larger, more permanent ponds. The results suggest that, even in tropical and subtropical regions and regardless of life stage, anuran traits are more diverse in large habitats with prolonged water permanence. Small and temporary ponds severely restrict species and their traits, thus favouring few species with specific sets of traits.