Dung beetle conservation biogeography in southern Africa: current challenges and potential effects of climatic change

Abstract

Miocene, Pliocene and Pleistocene changes to the geomorphology, climate and vegetation of southern Africa are considered responsible for radical differences between southwest and northeast dung beetle assemblages (Coleoptera: Scarabaeidae: Scarabaeinae) leading to current endemism in Namibia, Botswana and South Africa. This bias is supported by distributional analysis of 437 species across vegetation regions and 2° × 2° squares of latitude and longitude using non-metric multidimensional scaling (NMDS) and minimum spanning trees (MST). The ordinal values for six NMDS dimensions showed significant correlations with annual rainfall, annual temperature, rainfall seasonality and altitude. Significant climatic differences were also shown between six regional centres defined and modelled for the subcontinent: winter/bimodal rainfall, southwest arid, southeast highlands, savanna, sandy savanna and east coast. Twenty-one, principal, subregional centres defined from further NMDS and MST analyses of regional data showed significant intra-regional differences in climatic attributes although published data suggest that soil, vegetation and dung type associations were frequent additional influences. Species showing the smallest ranges were centred primarily around the coast and bordering escarpments, which coincide with regions and subregions showing unique environmental conditions characterized by many endemic genera and species. Published land use data indicate that large parts of these regions are highly transformed or degraded, so that some species are facing strong current threats. Furthermore, published global climatic change data suggest that many endemic species could be further threatened, especially to the southwest where the late Cenozoic trend to unique climatic and environmental conditions could, potentially, be reversed in the future.