Effects of Aspect and Altitude on Scorpion Diversity Along an Environmental Gradient in the Soutpansberg, South Africa

Journal of Arid Environments 113 (2015) 114e120 Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv Effects of aspect and altitude on scorpion diversity along an environmental gradient in the Soutpansberg, South Africa * Stefan Hendrik Foord a, , Vhuhwavho Gelebe b, Lorenzo Prendini c a Department of Zoology, South African Research Chair on Biodiversity Value & Change and Centre for Invasion Biology, School of Mathematical & Natural Sciences, University of Venda, Private Bag X5050, Thohoyandou 0950, South Africa b Department of Zoology, Centre for Invasion Biology, University of Venda, Private Bag X5050, Thohoyandou 0950, South Africa c Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, USA article info abstract Article history: Landforms with steep environmental gradients provide natural laboratories for studying regional dy- Received 15 November 2013 namics of diversity. The Soutpansberg range in South Africa presents contrasting habitats and climatic Received in revised form conditions on its northern and southern slopes. Scorpions are well adapted to arid environments, with 6 October 2014 greatest diversity in temperate deserts, but few studies have investigated the effects of aspect and Accepted 8 October 2014 altitude on scorpion diversity. We surveyed scorpion diversity along an altitudinal transect across the Available online Soutpansberg by actively searching for scorpions during the night and day. Patterns of scorpion diversity along the transect were compared to those of ants and woody plants. Unlike these taxa, scorpions Keywords: fi Scorpions exhibited a signi cant difference in species richness between slopes; higher on the arid northern slope, Richness and greater at lower than higher altitudes. Endemic taxa were restricted to mid-to higher altitudes of the Turnover northern slope. Species turnover decreased at higher altitudes and assemblage structure was influenced Ecomorphotypes by slope, altitude and rock cover. The Soutpansberg appears to be a hotspot of scorpion richness and Faunal elements mimics patterns of diversity in southern Africa. The richness and endemism of the scorpion fauna of the Transect arid northern slopes and foothills of the Soutpansberg emphasizes the need to prioritize the conservation of these areas. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The dispersal ability and longevity of a focal taxon may also confound the interpretation of patterns of diversity across a land- Habitat heterogeneity plays an important role in generating scape (Ozinga et al., 2005). As living fossils, with relatively limited biological diversity (Nevo, 1995) but assessing its influence may vagility and long lifespans among invertebrates, scorpions offer a depend on the scale of investigation and the focal taxon considered model system for studying the pattern and process of biological (Barton et al., 2010). Natural laboratories with strong abiotic and diversification (Prendini, 2001b; Bryson et al., 2013a, 2013b) and biotic contrasts, such as mountain ranges, provide unique oppor- the effect of spatiotemporal change on diversity. tunities to study the factors responsible for generating biological Scorpions reach their greatest diversity in temperate deserts. diversity at regional and global scales (Raz et al., 2009). Although Hotspots of scorpion species richness at continental or regional isolation and area usually exert disproportionately greater effects scales are associated with areas of climatic, topographic, and on biotic assemblages in mountains, differences in altitude and geological complexity (Prendini, 2005). At local scales, scorpion aspect may also generate rapid turnover across short distances assemblages are structured by temperature, precipitation, sub- (Longino and Colwell, 2011). In general, species richness decreases strate (soil hardness and texture; amount of stone or litter cover) with altitude (Rahbek, 1995) but there are exceptions, including and vegetation physiognomy (Prendini, 2001b, 2005; Druce et al., low altitude plateaus (McCain, 2009; Longino and Colwell, 2011) 2007). Different substrates exert different selection pressures on and mid-altitude peaks (Sanders et al., 2003; McCain, 2004; Bishop scorpions, resulting in the evolution of ecomorphotypes varying et al., 2014). from range-restricted stenotopic substrate specialists to more widespread eurytopic substrate generalists (Prendini, 2001b). Scorpions can respond to aspect at scales of less than 100 m and are more diverse on slopes facing the equator (Raz et al., 2009) * Corresponding author. E-mail addresses: [email protected], [email protected] (S.H. Foord). because of their ability conserve water (Hadley, 1970) and survive http://dx.doi.org/10.1016/j.jaridenv.2014.10.006 0140-1963/© 2014 Elsevier Ltd. All rights reserved. S.H. Foord et al. / Journal of Arid Environments 113 (2015) 114e120 115 high temperatures (Cloudsley-Thompson, 1962). Few studies have including two endemics, recorded on the mountain range or im- investigated the effects of aspect and altitude on scorpion diversity, mediate vicinity (Prendini, 2001a, 2005, 2006). however. The only such study conducted in Africa found a decrease We present the first quantitative survey of the scorpion diversity in scorpion species richness with increasing altitude on the of the Soutpansberg along an altitudinal transect from its arid Brandberg Massif, Namibia, and associated the high scorpion di- northern slopes to its mesic southern slopes. Diversity patterns of versity of the Massif with its heterogeneous climate, topography ants and woody vegetation along this transect have been the sub- and geology (Prendini and Bird, 2008). ject of continued, long-term study (Munyai and Foord, 2012). We The Soutpansberg range, a homoclinal ridge in the Limpopo assess patterns of scorpion diversity and assembly along this Province of South Africa (Fig. 1), presents an environmental transect, quantify the effect of altitude and aspect, and identify gradient with contrasting habitats, from arid savanna on its gentle environmental correlates of scorpion distribution. As scorpions are northern slopes to evergreen forest on its steeper southern slopes. adapted to arid environments, we predict higher scorpion species Its high plant diversity (over 2000 plant genera) results from diversity on the arid northern slopes of the Soutpansberg than on desert, savanna, temperate (grassland/forest), and tropical botan- its mesic southern slopes. We also predict greater turnover on the ical elements that overlap across its slopes (Van Wyk and Smith, northern slope, due to its steeper environmental gradient and 2001; Hahn, 2006). The fauna of the Soutpansberg, though far greater species diversity. We compare the patterns of diversity less studied than its flora, is similarly diverse. The Soutpansberg is a observed in scorpions, with those observed in ants and woody hotspot of scorpion richness in southern Africa, with 23 species, vegetation along the transect. Fig. 1. Study area for survey of scorpion diversity in the western Soutpansberg, Limpopo Province, South Africa, showing location of eleven sampling sites along altitudinal transect from northern (N) to southern (S) slopes of the mountain range. 116 S.H. Foord et al. / Journal of Arid Environments 113 (2015) 114e120 2. Methods night with ultraviolet light detection, the method of choice for collecting the greatest diversity and abundance of scorpions in a 2.1. Study area range of habitats (Sissom et al., 1990). Ten 1 ha quadrats were sampled per site. These were randomly The Soutpansberg range extends in a northeast to southwest located within a 1 km-stretch along the contour of each altitudinal orientation from Pafuri to Vivo (Fig. 1). The mountain range was zone, taking care not to cross more than 100 m in altitude. Each formed from an archaic group of basalt or sedimentary rocks and quadrat was sampled once only, sampling without replacement lava between 1800 and 1900 Ma. Extreme folds along the east- over time. ernewestern seams form parallel ridges and valleys (Hahn, 2006). In order to cover the transect within a reasonable time, sam- The geology of the Soutpansberg is dominated by erosion-resistant pling effort per site was limited to 30 min in the day and 30 min at quartzite and sandstone. Soils derived from the quartzite and night. Each site was sampled on ten occasions, during the dry sandstone are generally shallow, skeletal and well drained, with season (September) and wet season (January) over five years low nutrient content and acidic characteristics, those derived from (2008e2012), to avoid missing species with seasonal activity, the basalt and diabase dykes on the southern aspect in particular resulting in 10 h of search effort per site. are finely textured, clayey, well weathered and generally deep All specimens were collected, preserved in ethanol and depos- (Mostert et al., 2008). ited at the American Museum of Natural History, New York. Scor- The Soutpansberg borders the Limpopo Valley to the north, an pions were identified to species and classified into ecomorphotypes arid region, receiving about 350e400 mm of rainfall annually. The according to the criteria of (Prendini, 2001b). southern slope of the mountain range is more mesic, with an average annual rainfall of about 700e800 mm, twice that of the 2.4. Data analysis northern slope. The climate of the Soutpansberg

Load more