Ecology limits the diversity of the Cape flora: Phylogenetics and diversification of the genus Tetraria

abstract Understanding the ecology and evolution of the hyper-diverse Cape flora is dependent on developing anunderstanding of its component parts, best epitomized by the Cape floral clades that have diversified andare largely endemic to the region. Here we employ a new dated phylogenetic hypothesis for the sedgegenus Tetraria, one of the smaller Cape floral clades, to develop an understanding of timing and ratesof diversification in the group. Specifically, we test whether diversification in Tetraria slowed as the num-ber of extant lineages increased, suggesting that available ecological niche space has become increasinglysaturated through time. The radiation of Tetraria began approximately 18 million years ago, concordantwith that of many other Cape clades. Diversification rates in the genus showed no drastic shifts inresponse to major environmental changes, but declined as lineage diversity accumulated, indicative ofecological limitation on speciation rates. This allows the development of heuristic predictions aboutthe composition of Tetraria assemblages at various spatial scales, and suggests that closely related speciesshould either be ecologically differentiated or have non-overlapping geographic distributions. The ques-tion of whether ecological limitation of diversity is a common phenomenon in other Cape lineages hasimportant implications for our understanding of the evolution and ecology of the contemporary Capeflora as a whole. 2013 Elsevier Inc. All rights reserved.