Micro scale heterogeneity of spiders (Arachnida: Araneae) in the Soutpanberg, South Africa: a comparative survey and iventory in representative habitats

Abstract

Coarse-scale studies that focus on species distributions and richness neglect heterogeneity that may be present at finer scales. Studies of arthropod assemblage structure at fine (1 x 1 km) scales are rare, but important, because these are the spatial level at which real world applications are viable. The study investigates fine-scale variation in spider assemblages, comparing five representative vegetation types in the western Soutpansberg, Limpopo Province, South Africa. We assess these vegetation type in terms of their family and species composition, as well as levels of endemicity, relating these differences with vegetation structure. The study inventoried 297 species (9752 individuals), representing 158 genera, and 50 families in an area less than 450 ha were collected during the three sampling periods, namely May 2004 (late) Autumn, November 2004 (late) Spring and March 2005 (late) Summer as part of the South African National Survey of Arachnida database (SANSA).

Analyis of the results suggests spider abundance and richness was highest in November as compared to Marchin five habitat types with 34% of the spiders caught in spring being adults decreasing to 25% later in the season. Endemie taxa are associated with Tall Forest and, to a lesser extent, Woodland. The Woodland had the highest species diversity, and much of the variation observed in spider assemblage structure is explained by these two vegetation types. Inventory completeness was more than 70% for all the habitats except the Mo aic Grassland. Twenty three species had significant lndVals > 70 and majority of indicators were associated with the Woodland (13), followed by Tall Forest (8), which was dominated by web builders such as Nephila pilipes, Leucauge decorata and Glenognatha sp. The re tricted distribution of taxa at the local scale, often overlooked at the broader regional scale, is confirmed by the observation that only 27.4% of the species were found in all the habitats, at a scale less than 2 km in extent. Based on vegetation structure variables that e plained significant ,variation in spider assemblages, human influence through bush encroachment will result in a change of spider assemblages to that of Short Forest and Mosaic Woodland vegetation types, with implications for biodiversity maintenance and heterogeneity. Beating targeted the most species, followed by ground collecting and leaf litter sifting.