Comparing biodiversity between protected areas and adjacent rangeland in xeric succulent thicket, South Africa: arthropods and reptiles.
Although it is widely assumed that protected areas conserve species that would not survive elsewhere, this assumption is seldom tested. The aim of the study was to determine the respective roles of a nature reserve and commercial and subsistence rangeland in preserving terrestrial arthropods and reptiles in xeric succulent thicket in the Eastern Cape, South Africa. Faunal diversity on a nature reserve (the Great Fish River Reserve Complex) was compared with a historically overgrazed commercial farm, an intensively managed, conservatively stocked commercial farm and a communal grazing area. Terrestrial arthropods and reptiles were caught in paired pitfall traps inside and outside the nature reserve, specimens being sorted into recognizable taxonomic units (RTU). The taxa occurring in each land management unit were compared using RTU diversity, a hierarchical richness index (HRI), community similarity and uniqueness. The nature reserve contained more RTU and a greater HRI than adjacent land for most arthropod groups, and also supported more unique taxa than the other study localities. Snakes and lizards, in contrast, were almost twice as abundant in the communal grazing area as elsewhere, although reptile species diversity was similar at all localities. Each individual locality contained fewer than 62% of the total number of arthropod RTU and 55% of the total reptile RTU; the communal grazing area contained only 37% of the total number of arthropod RTU collected in the study area. Nineteen (73%) of the ant, 18 (69%) of the weevil, 60 (70%) of the spider and 12 (60%) of the grasshopper RTU and 10 (66%) of the reptiles were shared by the three land uses. Six new weevil species and probably several new arachnid species were collected, but all the new weevils were confined to the nature reserve. The communal grazing area differed most from the nature reserve in richness and community composition, followed by the conservatively stocked commercial farm. The historically overgrazed commercial farm was most similar to the nature reserve. The communal grazing area was characterized by xeric-adapted reptiles and predatory arthropods whose ranges are centred in the semi-arid parts of South Africa. In contrast, the nature reserve and commercial farms supported more mesic-adapted reptiles and herbivorous arthropods. Synthesis and applications. The data show how protected areas are key to conserving those species that decrease under heavily grazed and disturbed conditions. However, they also illustrate that diverse land-use mosaics promote gamma diversity in the xeric succulent thicket of South Africa. Conservation policies that include protected space in the wider environment and conserve habitat diversity are likely to both promote regional richness and support scarce species.