Amphibian occurrence and abundance patterns across a modified floodplain ecosystem

Amphibian populations have experienced unprecedented decline over the past few decades. River regulation, water diversions and reductions in the frequency of reconnections between rivers and floodplains have contributed to decreased floodplain inundation and overall wetland degradation, contributing to regional declines in amphibians. Hydrological modifications coupled with invasive exotic fish also have had a significant impact on inland floodplain frog communities. Using an eight-year study of 21 wetlands across a nationally important inland floodplain system, we quantified occurrence and abundance patterns in six frog species (adults and tadpoles) to a range of landscape-scale and site-scale hydrological and vegetation-related variables. Occurrence and abundance models for adult frogs and tadpoles were characterised by different suites of predictor variables and effect directions for each species. The occurrence of some frog species, such as the inland banjo frog (Limnodynastes interioris), was negatively related to distance to the main river and area of inundation, whereas the abundance of most species was positively related to mean daily discharge. Tadpoles of species such as the plains froglet (Crinia parinsignifera) had contrasting relationships to introduced common carp (Cyprinus carpio) and eastern gambusia (Gambusia holbrooki). Our findings suggest factors that lead to a particular species occurring at a wetland may differ from those that make them abundant once conditions necessary for occurrence have been met. Thus, management interventions to improve amphibian diversity across inland floodplain systems will need to consider watering actions that benefit a range of frog species, particularly endangered species, across their developmental stages.