Habitat preferences of three sympatric lacertid lizards in the arid Tankwa Karoo Basin of South Africa

Four lacertid lizards, Pedioplanis laticeps, P. lineo-ocellata, Meroles knoxii and Nucras tessellata, occur sympatrically on the arid plains of the Tankwa Karoo Basin in South Africa. The aim of this study was to determine whether the four species are spatially separated in terms of the microhabitat each species occupies, allowing them to occur in sympatry in this structurally simple system with a limited number of potential niches. The habitat preferences of the four species were investigated on the farm Gansfontein in the southwestern parts of the Tankwa Karoo Basin. The area was surveyed by walking transects through different habitat types and recording all active lizards. For each lizard observed, the species was identified and a photograph was taken of its microhabitat. At the end of the sampling period the microhabitats in which lizards were found were sorted into distinct types on the basis of substrate composition. During the survey, only one individual of N. tessellata was recorded, but sample sizes for the other three species were sufficiently large to provide a clear perspective of habitat segregation among the three species. The results showed that the three species are spatially separated at the study site, with P. lineo-ocellata being restricted to rocky areas, P. laticeps preferring gravel substrates and M. knoxii frequenting sandy areas. Although only anecdotal information is available, all indications are that the observed spatial separation of the three species is mainly the result of historical adaptation to the different substrate types.