Dissecting biodiversity in a global hotspot: Uneven dynamics of immigration and diversification within the Cape Floristic Region of South Africa

Aim Fragmented distributions should show immigration and diversification dynamics consistent with the predictions of island biogeography theory. We test whether this applies to the fragmented Cape fynbos vegetation. Location Southern Africa, Cape Floristic Region (CFR). Taxon Angiosperms, Restionaceae (restios). Methods We used a large occurrence dataset and environmental layers to characterize an existing regionalization and the intervals between the regions ecologically and spatially. We extended the available phylogeny for restios and inferred their historical biogeography using models implemented in BioGeoBEARS. We then measured the relative contribution of immigration and in situ speciation to the species richness of each region within the CFR. We used standard statistical methods to test the predictions of the island biogeography theory. Results The area and environmental heterogeneity of the seven regions of the CFR are positively correlated with in situ speciation rate. Furthermore, more isolated areas, and areas colonized more recently, have proportionally higher immigration rates, and more central and older areas proportionally higher in situ speciation rates. Main conclusions The variation in immigration and diversification dynamics among the regions within the CFR is extensive and consistent with the archipelago model of island biography theory. This dynamic may contribute significantly to the diversity of the Cape flora. Such a model could be generally useful for understanding the generation and maintenance of diversity in biodiversity hotspots, and may even scale up to explain continental biodiversity.