title: Topography as a driver of diversification in the Cape Floristic Region of South Africa.
abstract: The rugged topography of the Cape Floristic Region (CFR), South Africa, is frequently invoked to explain the spectacular radiation of the Cape flora, but the mechanisms involved remain unclear. Where recent authors emphasize the importance of elevation gradients as stimuli for ecological speciation, earlier workers stressed the role of topography as an isolating mechanism, particularly in montane lineages. Using six Cape plant lineages, we tested whether elevation niches are phylogenetically conserved. We then assessed whether high-elevation species are more consistently range-restricted than low-elevation species, and whether high-elevation sisters show stronger range exclusivity (allopatry) and weaker ecological and phenotypic differentiation, suggestive of nonecological speciation. Elevation niches tend to be phylogenetically conserved. Also, high-elevation species are more consistently range-restricted than low-elevation species, potentially explaining the generally stronger range exclusivity of high-elevation sisters. While the high-elevation zone is less homogeneous ecologically, more data are required to demonstrate that high-elevation sister species show generally weaker ecological and phenotypic differentiation. Topographic complexity promotes geographical isolation at high elevations, thereby providing opportunities for nonecological, vicariant speciation. While recognizing the need for additional data, we suggest that the upland and lowland floras of the CFR may differ with regard to predominant speciation mode.
authors.affiliation: Bolus Herbarium and Department of Biological Sciences, University of Cape Town, Private Bag, 7701, Rondebosch, South Africa.
authors.forename: G Anthony
authors.initials: GA
authors.lastname: Verboom
authors.affiliation: Compton Herbarium, South African National Biodiversity Institute, Private Bag X7, 7735, Claremont, South Africa.
authors.forename: Nicola G
authors.initials: NG
authors.lastname: Bergh
authors.affiliation: Bolus Herbarium and Department of Biological Sciences, University of Cape Town, Private Bag, 7701, Rondebosch, South Africa.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Haiden
authors.affiliation: Bolus Herbarium and Department of Biological Sciences, University of Cape Town, Private Bag, 7701, Rondebosch, South Africa.
authors.forename: Vera
authors.initials: V
authors.lastname: Hoffmann
authors.affiliation: Bolus Herbarium and Department of Biological Sciences, University of Cape Town, Private Bag, 7701, Rondebosch, South Africa.
authors.forename: Matthew N
authors.initials: MN
authors.lastname: Britton
mesh_terms: D000222:Adaptation, Physiological; D000531:Altitude; D044822:Biodiversity; D005075:Biological Evolution; D002980:Climate; D004463:Ecology; D017753:Ecosystem; D049810:Genetic Speciation; D055593:Geological Phenomena; D019684:Magnoliopsida / Q000235:genetics*; D010641:Phenotype; D010802:Phylogeny; D013019:South Africa
keywords: Cape Floristic Region; allopatry; ecological speciation; elevation; nonecological speciation; peripatry; topography; vicariance