The faunistic diversity of spiders (Arachnida: Araneae) of the South African Grassland Biome

ABSTRACT

As part of the South African National Survey of Arachnida (SANSA), all available information on spider species distribution in the South African Grassland Biome was compiled. A total of 11 470 records from more than 900 point localities were sampled in the South African Grassland Biome until the end of 2011, representing 58 families, 275 genera and 792 described species. A further five families (Chummidae, Mysmenidae, Orsolobidae, Symphytognathidae and Theridiosomatidae) have been recorded from the biome but are only known from undescribed species. The most frequently recorded families are the Gnaphosidae (2504 records), Salticidae (1500 records) and Thomisidae (1197 records). The last decade has seen an exponential growth in the knowledge of spiders in South Africa, but there are certainly many more species that still have to be discovered and described. The most species-rich families are the Salticidae (112 spp.), followed by the Gnaphosidae (88 spp.), Thomisidae (72 spp.) and Araneidae (52 spp.). A rarity index, taking into account an endemicity index and an abundance index, was determined to give a preliminary indication of the conservation importance of each species. The endemicity index indicates that 58 species are endemic to the biome, while 38 species could be considered to be introduced, cosmopolitan, or having a distribution extending beyond the Afrotropical Region. Levels of endemism are highest for mygalomorph trapdoor spiders (7.14–50%) and selected araneomorph families with restricted dispersal capabilities (i.e. Archaeidae, Sicariidae and Scytodidae). A brief review of the published data of surveys from the biome and the patterns of spider assemblage structure in each is presented, together with information on the most species-rich spider families occurring in the biome.

Keywords:

• conservation
• diversity
• endemic
• habitat
• survey

ACKNOWLEDGMENTS

The Agricultural Research Council (ARC) and the South African National Biodiversity Institute (SANBI) Threatened Species Programme are thanked for generously funding SANSA Phase II. The National Research Foundation (NRF) also provided funding that facilitated fieldwork in the Grassland Biome. SHF acknowledges financial assistance from the DST-NRF Centre of Excellence for Invasion Biology. Cor Vink (AgResearch, New Zealand) is thanked for identifying the exotic Badumna longinqua specimens collected in South Africa. Louis Scott (University of the Free State, South Africa) kindly provided some useful botanical literature. The staff of the Arachnology section at the NCA (Connie Anderson, Petro Marais, Sma Mathebula, Almie van den Berg and Annette van den Berg), as well as several volunteers from the public, are thanked for their assistance with the sorting and databasing of specimens collected during the SANSA surveys. Various students, members of the public and members of the Spider Club of South Africa collected material for SANSA or provided photographs for the SANSA Virtual Museum, and their contributions are gratefully acknowledged. The three anonymous reviewers are thanked for their considerable inputs that helped improve the quality and presentation of this paper.