Anuran responses to pressures from high-amplitude drought–flood–drought sequences under climate change

We measured changes in the occurrence, abundances and evidence of breeding of frogs to a sequence of severe drought–extreme wet–drought in south-eastern Australia, which is projected to characterize the regional climate in the coming decades. We collected data on anuran abundances, species richness and breeding by using aural surveys and visual searches in 80 waterbodies in 10 landscapes. We surveyed six times during the austral winter-springs of 2006 and 2007 (9–10 years into the 13-year ‘Big Dry’ drought), six times in the corresponding seasons of 2011 and 2012 (the ‘Big Wet’) and another six times in 2014 and 2015, which had lapsed into another intense dry period (‘post-Big Wet’). The relatively small gains in species occupancy rates and evidence of breeding achieved during the Big Wet following the Big Dry were eroded and reversed in the years after the Big Wet period, with several biotic measures falling substantially below the values for the Big Dry. The global prognosis is for long-term drying and warming, notwithstanding much geographic variation in the degree and temporal patterns of drying. Longer droughts with short periods of wet/benign conditions are projected for many parts of the world. For water-dependent fauna such as most amphibians, our results signal widespread declines in lowland regions experiencing such patterns. If droughts exceed lifespans of frogs, then resistance to drought will be so low that populations will plunge to levels from which the short periods of more benign conditions will be insufficient to enable substantial recovery.