Climatic niche evolution and species diversification in the Cape flora, South Africa

Abstract

Aim
To evaluate the evolutionary dynamics of the ecological niche by quantifying the modes and rates of ecological niche evolution (with a particular focus on climatic parameters) and species diversification.
Location
Greater Cape Floristic Region, southern Africa.
Methods
Using the genus Babiana (Iridaceae) from the Cape flora, South Africa, we study the evolutionary dynamics of the ecological niche, which includes a characterization of the ecological niche, an assessment of phylogenetic signal, comparisons of different macroevolutionary models, and the estimation of rates of niche evolution (and their variation within and between clades) and lineage diversification, while accounting for phylogenetic uncertainty.
Results
A principal components analysis (PCA) identified mean annual precipitation and mean annual temperature as the most important climatic determinants differentiating species within Babiana. All parameters show significant phylogenetic signal, and the best-fit model of evolution is the Ornstein–Uhlenbeck process with two distinct precipitation optima for two neighbouring biomes: the Fynbos and the Succulent Karoo. Evolutionary rates of climatic niches vary by more than an order of magnitude over the phylogeny, and rates of niche evolution and lineage diversification are both higher in the Fynbos biome than in the Succulent Karoo.
Main conclusions
Our results show a possible link between rates of climatic niche evolution and rates of species diversification, indicating that rates of niche evolution might be driving diversification rates.