Arthropod species of the Mariepskop Summit, Mpumalanga Province, South Africa : Affinities with Afromontane Natal Drakensberg fynbos and Cape fynbos

Abstract

Mountains have been identified as areas with unique biodiversity, due to the diverse range of habitats and micro-environments present on the summits. The heterogenic montane habitats are important for sheltering arthropods from severe climatic circumstances, and the conditions present provide the potential for an array of ecological investigations along different gradients. As arthropods are sensitive to their abiotic and biotic environments, they easily reflect ecological change in ecosystems and are thus effective in determining the effect of changing conditions in community composition and species distribution patterns. Six different collecting methods were used to collect true bug (Heteroptera) and spider (Araneae) species on the Mariepskop Summit, a semi-inselberg, which forms part of the Great Escarpment Mountain range system. Seventeen study sites spread across four plant communities were sampled, during three surveys. Sampling was undertaken in three distinct vegetation communities on the summit, namely Panicum ecklonii–Watsonia cf. pulchra Grassland (Grassland community), Erica woodii–Passerina montana Shrubland (Shrubland community) and Dryopteris athamantica–Podocarpus latifolius Forest (Forest community). A fourth community was added due to the area`s major terrain difference. These areas consisted of the Rocky expanses of the summit, with some small pockets of grass and shrubs between the rocks and boulders. After collection, specimens were preserved in 70% alcohol. Collected specimens were then identified by taxonomic experts in their respective fields to ensure accurate results. The focus of this study was to establish a list of genera and species above 1800 m.a.s.l. on the summit of Mariepskop; the species composition patterns of the recorded spiders and true bugs sampled in the different vegetation communities was explored and the larger scale geographical distribution of these species investigated to determine if any affinities exist with the fauna of the Natal Drakensberg Afromontane (NDA) fynbos and the Cape Floristic Region (CFR) fynbos? An extensive list of species for both spiders and true bugs was established, which led to a considerably improved knowledge of the arthropod diversity present on Mariepskop. The publication of species lists is important for ecological assessments and evaluating species distribution patterns. A rich diversity of species was recorded, with a total of 127 true bug species and 127 species of spiders. A rather sizeable proportion could not be identified to species or genus level, whereas others are undescribed, with nothing known about their distribution and habitat association. These are possibly new to science. Community composition patterns were examined using non-metric multidimensional scaling (nMDS) analysis based on Bray-Curtis dissimilarity in PRIMER 5. Analysis of similarities (ANOSIM) and similarity percentage (SIMPER) analysis was used to test for significant differences between nMDS communities. One of the major findings is the apparent rich diversity within the Shrubland vegetation, compared to the other vegetation communities, for both true bug and spider species. The structural habitat characteristics and plant species present in the Shrubland vegetation are possibly an important factor determining the arthropod diversity. With much still to explore, the species found on Mariepskop provide a better understanding of the faunal links along the Afromontane fynbos of the Great Escarpment. The results of the geographical distributions indicated that the majority of both the spider and true bug species on the summit of Mariepskop have a wide distribution, inhabiting a range of vegetation types. Differences were, however, evident between different trophic levels. Some degree of similarity was found between the Heteroptera species of the Mariepskop Summit and those of the fynbos of the NDA and the CFR, most probably because Heteroptera generally tend to be phytophagous, with high levels of host plant specificity. However, these taxa are not exclusively shared with fynbos areas, and have been recorded in other non-montane plant communities. Several spider species have been recorded in fynbos vegetation; however, none are known to be regional fynbos endemics. With several unknown species recorded and two known spider endemics present on Mariepskop, the consensus of research suggests that the area is rich in invertebrate diversity and should be conserved.