Arboreal spider assemblages associated with four tree species in the Grassland Biome of central South Africa (Arachnida: Araneae)

ABSTRACT

Foliage-dwelling spiders (Arachnida: Araneae) were collected from four common tree species in the Grassland Biome of central South Africa by beat-sampling. The aim of the study was to assess possible differences in the assemblage structure and species composition of spiders that could be attributed to structural differences in the vegetation. In total, 1909 spiders representing 17 families and 54 species were collected. Four families were dominant in abundance, together accounting for more than 73% of the spider fauna: Miturgidae (23.1%) was most numerous, followed by Araneidae (17.7%), Thomisidae (16.7%) and Philodromidae (15.4%). Overall spider abundance and species richness did not differ significantly among the four tree species, decreasing slightly from Acacia karroo (n=495, 38 spp.) to Olea europaea africana (n=479, 32 spp.), Buddleja saligna (n=477, 36 spp.) and Searsia lancea (n=458, 37 spp.). However, significant seasonal differences were detected for each tree. Generally, abundance and species richness were lowest during winter and highest during summer on all four species. Our findings suggest that vegetative and habitat structure and complexity have a limited influence on the abundance and species richness of tree-dwelling spiders in grassland habitats, although these factors may affect the assemblage structure on different tree species.

Keywords:

• abundance
• habitat
• structure
• season
• species richness
• vegetation

ACKNOWLEDGEMENTS

This study was funded through a National Research Foundation of South Africa (NRF) grant in the NRF Thuthuka programme to the second author (TTK2008050500003). The staff of the Free State National Botanical Gardens, particularly Tshilidzi Netshisaulu and Elliot Lithudza, are thanked for their interest and support for the project and allowing access to the study site. The authors would like to thank Ansie Dippenaar-Schoeman (ARC – Plant Protection Research Institute, Pretoria) for assistance with the identification of some of the species. Carmen Luwes (Clinvet International, Bloemfontein) provided assistance in the field.