What controls tadpole richness and guild composition in ponds in subtropical grasslands?

Abstract

The community structure of pond systems is affected by resource competition, predation and degree of permanence of water. Here we evaluated the effect of the permanence–predation gradient in ponds on species richness and guild composition of tadpoles. The study was carried out at Caçapava do Sul in southern Brazil. Tadpoles and invertebrate predators were sampled in 38 ponds of different sizes and degrees of permanence. The collections were carried out twice, in spring 2007 and summer 2008. We ordinated guild composition in ponds in a single dimension through a non-metric multidimensional scaling.The relationships between tadpole richness and guild composition with environmental descriptors were tested through multiple regression. The species were classified into six guilds. Species richness increased with the abundance of predators and the mean water depth in summer. The ordination of guild composition was explained by permanence and mean depth in summer. Our results indicated a clear guild replacement through a permanence–depth gradient, confirming permanence as an important environmental filter. Therefore, most rich ponds would not contain species from all groups, and even very small, shallow and ephemeral ponds are important, given that some species groups are exclusive to such habitats.