High species turnover of arthropod communities associated with distinct vegetation patches (“heuweltjies”) in an arid shrubland

Abstract

Dryland ecosystems are often characterized by their vegetation patchiness. The Succulent Karoo, a semi-arid region in South Africa is characterised by distinct vegetation patches surrounded by a homogenous vegetation matrix. These patches, locally known as heuweltjies, are naturally developed earthen mounds found throughout the region that contribute significantly to landscape heterogeneity. Arthropods are key for ecological functioning in semi-arid ecosystems. However, few studies have assessed the role that heuweltjies play in maintaining arthropod diversity in the landscape. This study investigates how arthropod abundance, species richness, beta-diversity and composition respond to heuweltjies at multiple spatial scales (biotope and site). Two sampling techniques (pitfall and vacuum sampling) were used to collect epigaeic (ground) and foliage-dwelling arthropods on heuweltjies and in the surrounding matrix, at three different sites in the Succulent Karoo during drought conditions. Heuweltjies had greater epigaeic and foliage alpha-diversity and abundance than the matrix. Additionally, epigaeic and foliage arthropod community composition were dissimilar at both the biotope and site scales. Beta diversity across the three sites was high and driven by species turnover. At the biotope scale, heuweltjie and matrix plots both showed high beta-diversity. This study took place during a prolonged drought with high plant mortality and relatively few foliage arthropods, but patterns in arthropod diversity between heuweltjies and the surrounding matrix were nevertheless still apparent. These results suggest that heuweltjies promote arthropod diversity and heterogeneity in the landscape, playing a vital role as refuges, providing food and nesting resources for various arthropod species.