The impacts of altered flooding regimes on the endangered Southern Bell Frog (Litoria raniformis)
In south eastern Australia, flow regulation and flood mitigation measures have led to substantial changes in the frequency, timing and extent of flood events. The impacts of these changes on amphibian populations are difficult to predict because the relationship between flooding, local population processes and spatial dynamics are poorly understood. We investigated the relationship between flooding, habitat occupancy, movement and breeding behaviour of the endangered Southern Bell Frog (Litoria raniformis), using a combination of population surveys and radio-tracking before, during and after a flood event. Analysis of the survey and radio-tracking data enabled the following observations: (1) the pattern of habitat occupancy changed significantly following flooding as individuals moved out of permanent waterbodies into newly flooded habitats, (2) movement patterns changed significantly in response to flooding, specifically radio-tracked individuals moved further over 24hours and had lower levels of site fidelity while occupying flooded habitat patches, and (3) the number of tadpoles and recently metamorphosed individuals were significantly higher in newly flooded patches compared to permanent habitat patches. These observations suggest that flooding plays an important role in the movement patterns and recruitment of L. raniformis. A reduction in the area inundated by flood waters as a result of flow regulation has the potential to limit movement across the floodplain, thereby reducing opportunities for recolonisation following local extinctions. In addition, a reduction in the frequency of flood events is likely to result in a decrease in the number of successful breeding and recruitment events leading to reductions in local population numbers.