Do small habitat size and isolation promote species richness in shallow lakes and ponds? A test of Scheffer et al.’s (2006) hypothesis in aquatic Amazonian ecosystems

Contemporary conservation planning is often based on the assumptions that small fragmented ecosystems support relatively few species. However, some recent evidences from small isolated aquatic systems have led ecologists to put in check the universality of this assumption. Scheffer et al’s (2006) second-order effects on biodiversity hypothesis states that, to some groups of organisms, small isolated aquatic habitats can harbor more species than large ones, with consequent maximization of the landscape-level biodiversity. Here we used data from a two-year field survey in 42 Amazonian lentic systems that varied widely in size, fish presence and aquatic vegetation cover to test if the Scheffer et al’s hypothesis works to high diverse tropical aquatic ecosystems. We observed that according Scheffer et al’s predictions small habitats were in general fishless and highly vegetated. Multivariate analysis (PCA) confirmed that in general small lakes sustained relatively more phytoplankton and zooplankton species. However, the same was not true to benthic invertebrate community, since the vegetation cover was positively correlated with low O₂ concentrations near the sediment surface. Preliminary analysis also suggest that according Scheffer et al’s hypothesis the higher local species richness in small lakes consistently increase the landscape-level aquatic biodiversity even in high species rich regions. Our data reinforce the needs to incorporate meta-community approach, which consider species interactions and indirect effects, into the classic island biogeography models when the targets of conservation are continental aquatic systems.