Spider ecology in the Erfenis Dam Nature Reserve, Free State Province: (Arachnida: Araneae)

[摘要] English: Few spider studies have been done in the Grassland Biome of South Africa, even though it dominates the central part of South Africa. In September 2005, a study was initiated in Erfenis Dam Nature Reserve, Free State Province, to determine the impact of controlled burning on various faunal groups. Thus, the aim of this study was to determine the effect of controlled burning on ground-dwelling spider communities in the reserve. Pitfall traps were set out in six different sites in the reserve, with three sites located in the burned area and the other three sites in the unburned area. The traps were replaced every 30 days for one year between 21 September 2005 (day following burning) and 30 September 2006. During this period, a total of 5222 spiders representing 33 families and 121 species were collected. In the burned sites Gnaphosidae, Lycosidae, Caponiidae and Salticidae, were dominant in abundance, while Gnaphosidae, Lycosidae, Amaurobiidae and Corinnidae were dominant in the unburned sites. Monthly spider abundance and species richness were consistently lower in the burned grassland, suggesting that succession and colonisation processes are slow. Gnaphosidae and Lycosidae were present throughout the year in all six sites, indicating that they are either fire tolerant or fast colonisers.The potential was recognised to expand the study to the sampling of grass- and foliage-dwelling spiders as well. This study was conducted from November 2005 until August 2007, with sampling done in the last week of every third month. Foliage spiders were collected from three different tree species (Acacia karroo, Rhus lancea and Rhus ciliata) by beating. During the period of two years a total of 496 foliage spiders were collected that represented 17 families and 54 species. Sweeps were done in four different grasslands (uniform Themeda triandra, mixed, weedy and woodland grasslands). During the period of two years a total of 1649 spiders were collected that represented 15 families and 84 species. The families that dominate the Grassland biome in abundance are the Araneidae, Philodromidae, Salticidae and Thomisidae, due mainly because of the vegetation structure and complexity. More spider species as well as individuals were collected from the grasslands than from the tree layers, but the tree layers had a greater diversity of spider families.As part of the ground-dwelling spider study, the influence of termite activity on the activity of Ammoxenus amphalodes Dippenaar & Meyer (Ammoxenidae) was determined. A. amphalodes activity were concentrated in the two sites that had the greatest termite activity, especially that of Hodotermes mossambicus Hagen. Both A. amphalodes and H. mossambicus abundance were significantly influenced by soil type, which affects nest construction in H. mossambicus and foraging behaviour in A. amphalodes.While sorting the traps for the study on ground-dwelling spiders, a species of Calommata (Atypidae) known as the African purse-web spider was found. In South Africa the genus was last collected in the 1920's, when specimens were collected from several localities in Gauteng and the Soutpansberg. Subsequently, no material was collected until the recent discovery of a species in Groenkloof Nature Reserve in Gauteng in 2001, a male in the Blouberg Nature Reserve (Limpopo Province) and eight males found in pitfall traps in Erfenis Dam Nature Reserve. All of the material had previously been regarded as Calommata simoni Pocock, but examination of all available material indicated that at least six species occurred in the Afrotropical Region, four of which are described as new. Calommata transvaalica Hewitt is removed from synonymy with C. simoni and revalidated. C. meridionalis sp. n. showed a preference for soils with relative high clay content. Males of this species also showed most activity from October to November.

[发布机构] University of the Free State