BIOGEOGRAPHIC BARRIERS IN A SUBDUED LANDSCAPE - THE DISTRIBUTION OF THE GEOCRINIA-ROSEA (ANURA, MYOBATRACHIDAE) COMPLEX IN SOUTH-WESTERN AUSTRALIA

The distribution of the four allopatric species of the Geocrinia rosea (Harrison, 1927) complex in south-western Australia is described in r elation to climate, landform and soils. A total of 221 positive distri bution records for the complex are correlated with climatic profiles g enerated by the computer program BIOCLIM. No additional sites were pre dicted for the complex, but each of the sixteen climatic variables exa mined were influential in separating the distributions of the four spe cies. Two rare species, G. alba (Wardell-Johnson & Roberts, 1989), whi ch occupies 190 ha over a range of 101 km2, and G. vitellina (Wardell- Johnson & Roberts, 1989), 20 ha over 6.3 km2, occur in permanently moi st sites in relatively dry and seasonal climatic zones and their distr ibutions are separated by 9 km of lateritic uplands and narrow valleys . The range limits of two more widespread and common species; G. rosea and G. lutea (Main, 1963), are separated by 39 km of broad swampy ter rain that is dry in summer. These two species pairs are separated by 4 7 km of muted topography which includes lateritic uplands, broad swamp y terrain and narrow stream channels in a relatively dry climatic enve lope. All calling sites of the complex examined, (fifteen), were on sl opes in sandy alluvial soils with a high organic content. Narrower mor e subtle geographic barriers than previously envisaged may have allowe d in situ speciation in the frog fauna in south-western Australia.