Stochastic metapopulation dynamics of a threatened amphibian to improve water delivery

Water extraction and climate change are altering the availability of surface water globally, thereby contributing to amphibian population declines. The managed delivery of water to benefit environmental values (environmental watering) is a promising conservation technique that can support amphibian recruitment and maintain viable populations. Environmental water can be delivered in various spatial patterns and with different frequencies, but comparing the effectiveness of competing strategies is complicated by variable and interactive environmental processes. We built a spatially explicit, stochastic, hydroecological metapopulation model to compare the effects of five environmental-watering scenarios on the probability of persistence of threatened southern bell frogs (Litoria raniformis) in a major river reach in southern Australia. We compared a no-intervention control to two managed watering frequencies (moderate and frequent) delivered in two spatial designs (managed wetlands grouped or spread across the reach). More frequent water provision to intervention sites improved the reach-wide (metapopulation) probability of persistence, and spreading intervention sites across the reach improved persistence more than grouping intervention sites together. When re-examined under severe drought conditions, L. raniformis had a 0.04 probability of persistence without intervention, which improved to 0.56 with high watering frequency. Model-guided environmental water provision can improve reach-wide persistence of amphibian metapopulations by guiding spatial and temporal delivery patterns to reduce the risk of extinction.