Isolated wetlands lack permanent stream connections to adjacent bodies of water. They are ecologically important because they can be the most abundant type of wetland in a region and can harbor unique biological communities. Despite this, isolated wetlands are rarely protected by federal and state legislation, and federal agencies do not assess their abundance when reporting national trends in wetland losses. We will present the results from a field study that illustrates how the presence of small and isolated wetlands is important in maintaining populations of pond-breeding amphibians across the Delaware Water Gap National Recreational Area (New Jersey, USA). We surveyed 44 wetlands for nine species of amphibians and developed occupancy models based on a wetland’s size, stream connection, degree of spatial isolation, and surrounding forest canopy. We then used occupancy models to predict the occurrence of amphibian species at all 175 wetlands in our study area.
Species occupancy models suggested that stream connections at wetlands strongly influenced the occurrence patterns of five out of nine amphibian species, and models generated relatively accurate predictions of species occurrence (% correct classification ranged from 62.5% to 90.6%) when validated using observations at 32 model validation sites. Predictions of species presence throughout our study area suggested that six species would lose at least half of their breeding sites if either: 1) all wetlands less than 0.30 ha or 2) wetlands lacking permanent stream connections were removed from the landscape. We correlated the relative times of year a species bred with the median size of their predicted breeding sites to illustrate that early-breeding species use smaller wetlands more often than later-breeding species. Furthermore, early-breeding species had a larger proportion of their breeding sites, and breeding wetland area, among wetlands that lack stream connections. This study illustrates how legislation that protects only large wetlands and those with permanent stream connections can fail to protect amphibian species that breed earlier in the year and contain a large fraction of their breeding populations in small and hydrologically isolated wetlands.