**7.1 Hybridisation**

For the DAC, Hillard and Burtt (1987) list 21 hybrid taxa of which three (two *Senecio* crossed species and one *Cephalaria*) are exclusive to high altitude DAC records, and do not occur on Platberg, while the *Protea roupelliae* x *P. subvestita* cross has both species growing in the vicinity of Platberg. Of the remaining 17 hybrids it could be that some or all of them may occur on Platberg. This level of taxonomic expertise must wait for future detailed analysis. Hillard & Burtt (1987) do not offer an explanation for the occurrence of these 21-recorded hybrids (it is possible there are more). However, hybridisation breaks down species boundaries. Linden (2003) reports for the Cape flora, where species co-occur, such as *Moraea* hybrids, these are frequently found. This is the case also for *Romulea* with artificial hybrids cultivated for *Sparaxis, Watsonia* and *Ixia* of which *Watsonia* and *Morea* occur on Platberg (Linden 2003). Most of these Cape hybrids are sterile, however, hybridisation, sterile or not, is an environmental response to selection forces, which, in the case of Cape flora, limit gene flow (Linden 2003).

For the higher areas of the DAC, and Platberg as an inselberg, a degree of geographical isolation occurs which allows for edaphic and microclimatic, as well as larger, longer climatic and geological processes, to provide for geographical isolation of species (MacArthur & Wilson 2001; Porembski & Brown 1995; Gröger & Barthlott 1996; Linden 2003). This isolation has allowed for speciation and to quote from Linden (2003, page 623): " … factors that allow (and drive?) speciation may be very similar to those that allow species to co-exist. These factors could be expected to include those that limit gene flow between sister species, as well as those that result in differential selection. Reproductive isolation is needed to prevent the ecological specialisation from being lost…."

This may offer a partial explanation for the high numbers of hybrids recorded, as well as the speciation and high numbers of endemics or near-endemics observed within the DAC and by extension, Platberg. Hybrids and rare species do not contribute to community patterns (beta-diversity), but are important for maintenance of biological diversity (Mutke et al. 2001; Cowling & Lombard 2002).

### **7.2 Pollination: Birds, insects and wind 7.2.1 Birds**

For the central and southern Drakensberg, Hillard & Burtt (1987) have recorded bird pollination for *Protea, Kniphofia, Watsonia, Pelargonium schlecterii, Sutherlandea montana, Halleria lucida* and *Leonotis.* Most *Protea* species have a specalised feeding connection with Sugar birds *(Promerops* spp.) and Sunbirds (*Nectariania* species) detailed by Kingdom (1989) as well as the Cape Canary (*Serinus leucopterus*) and a beetle specialists which also feeds on Protea nectar. Except for *Protea*, all the other plant species occur on Platberg. This form of pollination, where a single pollinator will visit different, but close-by species with similar flower morphology and physiology, may also be responsible for the phytosociological associations of some plants. On Platberg, such community assemblage corresponds to the *Leonotis ocymifolia–Watsonia lepida* and *Halleria lucida* plant associations (Brand et al., 2009). Limited empirical research has been done to establish the connection between bird/plant community associations and is a subject for future investigation.
