Do frogs bounce, and if so, by how much? Responses to the 'Big Wet' following the 'Big Dry' in south-eastern Australia

Abstract

Aim: We assessed the resistance and resilience of anuran amphibians to an abrupt change in weather conditions in 2010-12 (the 'Big Wet') following the most pronounced drought in eastern Australia's records (1997-2010, the 'Big Dry'). Location: Five pairs of landscapes (each of 19.6 km2) spread across 30,000 km2 in temperate, inland Australia. One in each pair was eucalypt woodland while the other was cleared agricultural land; there were eight representative waterbodies in each landscape. Methods: We collected data on anuran abundances, species richness and breeding by using aural surveys and visual searches. We surveyed six times during the austral winter-springs of 2006 and 2007 (the Big Dry) and six times in the corresponding seasons of 2011 and 2012 (the Big Wet); our results refer only to species breeding in the winter-spring season. Results: Mean species richness, total numbers of calling males and numbers of the five most common species of anurans increased in the Big Wet compared with the Big Dry, but the least common species did not. Proportions of waterbodies with eggs or tadpoles increased in the Big Wet, but the occurrence of eggs and tadpoles was still low (evidence of presence in <50% of waterbodies). The most common species had relatively high resistance to the first 5 years of the Big Dry, but all declined sharply after a decade of drought. Four of the common species showed some resilience, but reporting rates fell much below the peak values prior to the Big Dry. There were virtually no records for seven other species that had been recorded previously in the region. Main conclusions: The pressure of drying, warming climates, even when broken by shorter wet periods, seems to be sufficient to induce regional-scale declines even among species that, from global analyses of risk factors, might be expected to be relatively immune from such effects. © 2013 John Wiley & Sons Ltd.