Fine-scale bee species distribution models: Hotspots of richness and endemism in South Africa with species-area comparisons

Abstract

While global patterns of bee diversity have been modelled, our understanding of fine-scale regional patterns is more limited, particularly for under-sampled regions such as Africa. South Africa is among the exceptions on the African continent; its bee fauna (ca. 1253 species) has been well collected and documented, including mass digitising of its natural history collections. It is a region with high floral diversity, high habitat heterogeneity and variable rainfall seasonality. Here, we combine a South African bee species distributional database (877 bee species) with a geospatial modelling approach to determine fine-scale (~11 × 11 km grid cell resolution) hotspots of bee species richness, endemism and range-restricted species. Our analyses, based on the probabilities of occurrence surfaces for each species across 108,803 two-minute grid cells, reveal three bee hotspots of richness: Winter rainfall, Aseasonal rainfall and Early-to-late summer rainfall. These hotspots contain large numbers of endemic and geographically restricted taxa. Hotspots with particularly high bee diversity include the Fynbos, Succulent Karoo and Desert biomes; the latter showing 6–20 times more species per unit area than other biomes. Our results conform with global species-area patterns: areas of higher-than-expected bee density are largely concentrated in Mediterranean and arid habitats. This study further enhances our knowledge in identifying regional and global hotspots of richness and endemism for a keystone group of insects and enabling these to be accounted for when setting conservation priorities.