Distribution of anuran amphibians in massively altered landscapes in south-eastern Australia: effects of climate change in an aridifying region

Aim We explored whether the anuran amphibian faunas differed among landscapes that are relatively intact (largely covered in forests and woodlands) and others that are completely converted to agriculture. We also used historical data sets to assess the current condition of the anuran fauna in a region predicted to experience, and experiencing, severe drying and warming. Location Five pairs of landscapes (each of c. 20 km(2)) - one in each pair being almost completely wooded and the other cleared for agriculture - across a 30,000 km(2) region of northern Victoria, Australia. Methods Sites were repeatedly surveyed in the austral winter-spring breeding seasons of 2006 and 2007, with records collected of numbers of calling males and the presence of egg masses and tadpoles. We characterized the sites using static (e.g. dimensions, surrounding physiognomic characteristics such as tree cover) and labile (e.g. pH, dissolved oxygen) variables. Data were analysed using hierarchical Bayesian models. Results For calling males, landscape type did not affect densities or species richness measures. The availability of a grassy verge around water bodies was an important predictor for most species, but other labile and static variables seemed not to be important. Fewer than half of the species historically known from the region were recorded. There were no important predictors of occurrence of egg masses or tadpoles. Reproduction effectively may have failed over the period, with fewer than one in four sites showing evidence of egg masses or tadpoles. Main conclusions The proportion of sites at which some well-studied species (e.g. Crinia signifera, Limnodynastes dumerilii) were recorded has dropped substantially since the 1970s, as have average densities of calling males of Crinia spp. The remnant anuran fauna appears to be dominated by resilient and hardy species with low current diversity. The on-going (12+ years) drought in these landscapes suggests a bleak long-term prognosis for the few remaining species of anuran amphibians.