Friday 18 Apr 2014
Tue 28 Feb 12
Faunistic diversity of Spiders (Arachnida, Araneae) of the Savanna Biome in South Africa
During the second phase of the South African National Survey of Arachnida (SANSA) all available information on spider species distribution in the South African floral biomes was compiled. The Savanna Biome, the largest biome in the country, occupies over one third of the surface area. A total of 1270 localities in the Savanna Biome have been sampled since 1979. The rationale for this project was primarily to gather baseline information on diversity in an area that has been previously poorly sampled. Most sampling and taxonomic research on South African arachnids, undertaken between the periods 1820-1960, was based on the fauna of the coastal provinces, as most of the practicing arachnologists were stationed there. It was only in the late seventies that more intensive sampling started in the central and northern provinces of South Africa.

Data on spider species richness for the Savanna Biome of South Africa were obtained from existing data sets for this region supplied by the first Spider Atlas. The atlas was based on the SANSA database that is available in three formats: 1) information on all the preserved specimens housed in several natural history collections, worldwide and published in the primary literature (15 500 records); 2) primary data of specimens housed in the National Collection of Arachnida (NCA) at the ARC-Plant Protection Research Institute (PPRI), Pretoria (45 000 records), as well as 3) a digital photographic database containing images of species recorded by the public (2 300). This digital data is available on-line (www.arc.agric.za quick link SANSA, Virtual Museum). Also included were grey literature, i.e. unpublished MSc and PhD theses and longer term surveys that were undertaken since the seventies in the Savanna Biome. A total of 1230 spider species represented by 384 genera and 62 families are known from this biome. Thelast decade has seen an exponential growth in the knowledge of the group in South Africa, but there certainly are several more species that have to be discovered or described, and the distributions of those listed are largely unknown. At a large scale the eastern region is much better surveyed than the western parts, but at smaller scales throughout the region there is still very little information available for several areas.

A total of 928 spp. (75%) are free-living spiders with 571 spp. living on the soil surface, including those living in burrows (73 spp.), and 357 spp. that are associated with vegetation. The web dwellers are represented by 302 spp. with the largest number making orb-webs (123 spp.), followed by the retreat-web spiders (61 spp.) and the sheet-web spiders (39 spp.). The Salticidae is the most diverse family (159 spp.) and also has the most endemic Savanna species (42 s pp.), followed by Thomisidae (116 spp.). The Endemicity Index indicates that 308 species are endemic to the biome with 322 species that are near endemics, i.e. also occurring in an adjacent biome. The first checklist of all the Savanna spider species was published and a handbook on the spiders of the Savanna Biome is in preparation and will be released early next year.

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