Population Structure and Density of Leopard Tortoises (Geochelone Pardalis) on Farmland in the Nama-karoo

Abstract The Leopard Tortoise (Geochelone pardalis) is the largest of the southern African species and has a wide distribution encompassing a variety of habitats. There is a paucity of ecological information about Leopard Tortoises in these habitats. The goal of this study was to determine the population density, biomass, sex and age distributions, and morphometrics of Leopard Tortoises on farmland in the semi-arid Nama-Karoo. Because previous studies have found that body size distributions vary between mesic and xeric habitats, we expected that these Leopard Tortoises would show an increased body size compared to those from more mesic areas. In addition, we expected lower densities of Leopard Tortoises compared to more mesic areas. In total, 92 tortoises were caught with a male to female sex ratio of 1:1.3 that was not significantly different from unity. Adult females were significantly larger than males with respect to all morphometric measurements. Leopard Tortoises (excluding juveniles) were larger than those from more mesic areas. A population estimate of 57.6 ± 4.0 tortoises in a 5500 ha area was obtained using a mark-recapture sampling method and radio-telemetry. Density of tortoises was extremely low at 0.017 tortoises ha−1, with a biomass of 0.002 kg ha−1. Population density and biomass were lower compared with Leopard Tortoise populations in more mesic areas. This has implications for the understanding of fitness parameters and conservation of this species in semiarid areas.

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