Herpetofauna and the catena: the effects of habitat variables on herpetofaunal community assemblages

Environmental variables such as vegetation and water availability are known to influence herpetofaunal diversity. The variation of abiotic and biotic factors along the catena are well researched; however, the effects of these factors on community composition and diversity remain unstudied. The aim of the project therefore was to assess the bottom-up controls of the differences in herpetofaunal communities along the catena. The species within these communities were divided up into functional guilds and life history groups to further explain the presence of species at certain positions along the catena. To sample herpetofaunal diversity, trap arrays were set up at the crest and valley bottom in four marula-knobthorn sites in the Skukuza landscape type, Kruger National Park, South Africa. In addition, active searching was done to further sample the presence of herpetofauna at each site. Soil characteristics and ground cover measures were collected at each site. Data from this study (November 2009) was pooled with data from biodiversity surveys carried out in January 2009. A total of 366 frogs frogs across 14 species and 43 reptiles across 12 species were captured in either the pitfall traps or identified during active searching. There was no difference in species richness, abundance, or Shannon-Weiner diversity indices between the crest and valley bottom, however a difference was found in community assemblages. It was found that soil type and depth influenced the presence of certain species along the catena. Of all the environmental factors used to describe amphibian community assemblages, tadpole requirements for growth and development tended to be the strongest driver of species distribution. No pattern was observed for reptiles possibly due to small sample size and time constraints. Our study suggests that investigating functional processes is relevant to explaining patterns of species diversity.