Predation Modifies Larval Amphibian Communities in Urban Wetlands

Fish introduced into wetlands can impact amphibian populations through predation on eggs and larvae. While relationships among hydroperiod, habitat complexity and predation on amphibian larvae have been examined in relatively natural freshwater ecosystems, they have not been explicitly considered in urban landscapes. We examined these relationships in 64 urban wetlands in southern Australia using non-native fish and aquatic invertebrates as predators. Larvae of three out of six frog species detected during our study were captured in wetlands containing fish. With other variables held constant, the mean number of tree frog (Litoria spp.) larvae in the wetland with the highest abundance of predatory fish was predicted to be only 0.8-3.2 % of the number of larvae in a fishless wetland. We also found a negative relationship between predatory invertebrates and larval abundance. The abundance of tree frog larvae was greatest in ephemeral wetlands where predatory fish were generally absent. Our results suggest that traditional models of amphibian distribution along pond-permanence gradients may not be applicable in urban ecosystems due to modified hydrology favoring permanent wetlands. To conserve amphibians in urban areas, we recommend draining wetlands periodically to remove exotic fish, and conserving or restoring ephemeral wetlands.