Modelling effects of water regulation on the population viability of threatened amphibians

1. The regulation of river systems alters hydrodynamics and often reduces lateral connectivity between river channels and floodplains. For taxa such as frogs that rely on floodplain wetlands to complete their lifecycle, decreasing inundation frequency can reduce recruitment and increase the probability of local extinction. 2. We virtually reconstructed the inundation patterns of wetlands under natural and regulated flow conditions and built stochastic population models to quantify the probability of local extinction under different inundation scenarios. Specifically, we explored the interplay of inundation frequency, habitat size, and successive dry years on the local extinction probability of the threatened southern bell frog Litoria raniformis in the Murray River floodplains of South Australia. We hypothesised that the changes in wetland inundation resulting from river regulation are driving the decline of L. raniformis in this system. 3. Since river regulation began in the 1920s, the inundation frequency of many reliable breeding habitats has decreased to a point where they no longer support local populations. Increasing successive dry years drives the probability of local extinction, particularly in smaller wetlands. Larger wetlands and those with more frequent average inundation are less susceptible to these effects. 4. Synthesis and Applications . Although the availability of suitable habitats has reduced, environmental water provision is a promising tool to mitigate the negative impacts of river regulation on amphibian populations. Our modelling approach can be used to prioritise the delivery of environmental water (through pumping or the operation of flow-regulating structures) to minimise the probability of local extinction in L. raniformis and potentially many other frog species. By quantifying the extinction risk of amphibian populations, we can strategically manage environmental water to reduce successive catastrophic breeding failures and increase the probability of persistence. ### Competing Interest Statement We thank the Murraylands and Riverland Landscapes Board and the Nature Foundation SA for their generous support and the Murray-Darling Basin Authority for providing time-series data of natural flow.