Distributions of pond-breeding amphibians across wetland size and isolation gradients

In 2006, we sampled 41 potential amphibian breeding habitats in the Delaware Water Gap National Recreational Area for amphibian eggs and larvae.  Sites were stratified by wetland size and geographic isolation, and we used species occupancy models (MacKenzie et al. 2002) to examine relationships between amphibian species presence and wetland size, geographic isolation, and hydrologic connectivity.  While our initial analyses suggest that nine out of ten species were most likely to breed in larger sized wetlands, the presence of stream inputs/outflows at a breeding site (hydrologic connectivity) also significantly contributed to predicting presence for six of these species.  Furthermore, comparisons within the families Ambystomatidae, Ranidae, and Hylidae suggest that species with earlier breeding phenologies are more likely to occur in hydrologically isolated wetlands, while those that breed later in the year tend to breed in wetlands with more permanent stream inputs and outflows.  Thus, understanding relationships between species presence and wetland size must be framed in the context of hydrologic connectivity to anticipate the effects of future landscape changes on amphibian biodiversity.