Patterns of larval amphibian distribution along a wetland hydroperiod gradient

Abstract

We investigated the response of pond-breeding amphibian assemblages to wetland hydroperiod and associated predator changes (invertebrates (abundance and richness) and fish (presence/absence)) in relatively undisturbed landscapes in southern New Hampshire, U.S.A. We sampled 42 wetlands for larval amphibians in 14 spatial blocks (each with a short-, intermediate-, and permanent-hydroperiod wetland) in 1998 and 1999. Assemblages in short-hydroperiod wetlands (<4 months) were depauperate (4 species only) compared with intermediate-hydroperiod (non-permanent but >4 months) and permanent wetlands, which included 7 and 9 species, respectively. Total amphibian abundance did not vary among hydroperiod categories. Species distributions along the hydrological gradient also differed. Rana sylvatica dominated wetlands with short and intermediate hydroperiods, whereas Rana catesbeiana, Bufo americanus, Rana clamitans, and Pseudacris crucifer dominated in those with a longer hydroperiod. Among permanent wetlands, amphibian species richness and abundance did not differ with respect to the presence of predatory fish, although there were species-compositional differences. Amphibian species richness and abundance were positively correlated with the abundance and richness of predatory invertebrates, suggesting that both amphibian and macroinvertebrate predator assemblages may be responding similarly to differences in wetland characteristics (e.g., dissolved oxygen concentration). Overall, our results indicate that wetland hydroperiod has an important influence on amphibian distribution and should be incorporated into regulations and legislation designed to protect biologically diverse isolated wetlands.