Influence of Climate in Functional and Species Diversification in South African Pelargonium

Date of Completion

January 2010


African Studies|Biology, Botany|Biology, Ecology|Climate Change




With its more than 280 species Pelargonium is the third largest genus in the highly diverse Cape Floristic Region. Pelargonium is also well known by its morphological diversity: life form varies from geophytes and stem succulents to woody shrubs, with associated differences in stem structure and leaf architecture. Here I analyzed some of the ecological and historical factors that could have contributed to the large species and morphological diversification in the genus. ^ Biological diversity is generated and maintained through two main routes: niche based and neutral processes. In the niche based processes, the main focus of this work, niche differentiation and species divergence is product of a response to the biotic or abiotic environment. I specifically analyzed (1) if diversification in the genus has been accompanied by climate differentiation among closely related species; (2) the main climate drivers of species diversity in the genus and phylogenetic assemblage structure; (3) the role of species interactions on species accumulation pattern and; (4) how climate history might have influenced current ecological strategies in different Pelargonium clades. ^ I found that prevalence of intrasectional climate niche conservatism is clade dependent but generally low, suggesting that the steep climatic gradients in South Africa could have facilitated diversification in some Pelargonium clades. These differences in levels in climate niche conservatism among clades were parallel to divergent ecological strategies (drought avoidance vs. drought resistance). These strategies are most likely the result of adaptation to climate at early clade history and have facilitated diversification of each clade in its particular climate zone, but reduced success out of it. ^ Diversification in the genus was largely associated to a seasonal match of low environmental energy with high precipitation and therefore variation in species richness in Pelargonium did not follow the predictions of the species-energy hypothesis described for other regions. Geographical patterns of species richness closely matched phylogenetic assemblage structure and underlying assembly process; high prevalence of species interactions in the winter rainfall region and environmental filtering outside of it.^ Approaches incorporating phylogenetic information, climate and species traits are a powerful tool to determine the historical factors behind generation of biodiversity. ^