Past Climate Change and the Generation and Persistence of Species Richness in a Biodiversity Hotspot, the Cape Flora of South Africa

Abstract

The physiognomically distinct Fynbos and Succulent Karoo Biomes are associated with the winter or all season rainfall region of southwestern South Africa. Fynbos (the more mesic) is co-dominated by small trees, shrubs and reed-like plants. Woody stemmed succulent shrubs, mainly small leaved, dominate the Succulent Karoo. Both biomes contain spectacular floristic richness. Have past climates determined present species richness in this region? We employed GIS-based bioclimatic modelling techniques to address this. After deriving bioclimatic envelopes for both Fynbos Biome (Fynbos Envelope; FYE) and Succulent Karoo (SKE), we used modelled paleoclimate reconstructions to map the distribution of the envelopes at 6, 12 and 18 kBP in the southern and western Cape. At the LGM, FYE possibly had a considerably greater extent along the west coast and the western interior, replacing much of the SKE. At 18 kBP SKE was limited to two separate areas, an extensive plain, the Knersvlakte (South) and montane Richtersveld (North). SKE expanded between 12 and 6 kBP to its present range, and FYE contracted into its current montane distribution. These reconstructions concur with the palynological record of indicator groups of both biomes, with current patterns of relictual Fynbos vegetation, and with Succulent Karoo centres of endemism. Climatic oscillations during the pleistocene probably shifted these biomes iteratively along a North/South axis on the west coast of southern Africa. Mutual vegetation replacements are likely to have accelerated sympatric and allopatric speciation, giving rise to high β and γ species turnover.