Using modern models to test Poynton's predictions

Abstract

In his seminal work ‘The Amphibia of southern Africa: a faunal study’, Poynton identified and contrasted two centres of amphibian importance, the temperate south-western Cape (“Cape”) and tropical northeast (“Tropical”). With reference to the dominant role of climate fluctuations resulting from Milankovitch forcing since the Pliocene, Poynton hypothesised: “These climatic fluctuations must have altered the faunal patterning very considerably, and they have probably left an impression on present distribution”. In this study we use modern methods of species distribution and palaeoclimatic models not available in the 1960s to further investigate Poynton's predictions on the importance of glacial–interglacial climatic changes on the distributions of southern Africa's amphibian assemblages. We constructed current distribution models based on presence data for 20 representative endemic anuran taxa from the two centres. We then used two paleoclimatic models (Model for Interdisciplinary Research on Climate: MIROC and Community Climate System Model: CCSM) to project the species’ current niches back to 6 and 21 Kya (Last Glacial Maximum: LGM) to reconstruct hypothetical historical distributions. Our results predict that 65% or 75% of species experienced a range reduction since the LGM, using MIROC and CCSM respectively, but this shrinking was significantly greater in the Cape (mean reduction since LGM = 18 099.6 ±5 894.27 km² MIROC) than Tropical areas, most of which expanded (mean = − 5 990.3±8 801.80 km² MIROC; F_1,18=5.074; P = 0.037. CCSM; F_1,18=15.65; P = 0.001.). Our results are discussed with reference to Poynton's predictions.