Gradient analysis of a tropical herpetofauna: distribution patterns of terrestrial reptiles and amphibians in Stage III of Kakadu National Park, Australia

The herpetofauna of Stage 111 of Kakadu National Park comprises 102 native reptile species and 24 native frog species. Distribution patterns of this herpetofauna are described in relation to derived environmental axes. Most species were associated with a gradient of substrate and moisture availability. Few species were associated with a gradient of vegetation structure. The reptile fauna included a distinctive assemblage restricted to rocky sandstone escarpment, a virtually ubiquitous group of species, an open-forest/woodland assemblage, a lowland wet forest assemblage, and several species with idiosyncratic ranges. Species richness was highest in rocky areas, and this was particularly so for geckos. The frog fauna also included a distinctive sandstone assemblage, as well as a lowland clay-flat assemblage, a wet forest assemblage and two species with idiosyncratic ranges. For most taxonomic subsets considered there is a pattern of species replacement along the derived environmental gradient. The herpetofauna of monsoon forests is depauperate.