New insights into the formation of biodiversity hotspots of the Kenyan flora

Aim: Kenya intersects with the biodiversity hotspots Eastern Afromontane, Coastal Forests of Eastern Africa, and Horn of Africa. This study aims to investigate the distribution pattern of plant diversity in the low latitude arid area influenced by climatic fluctuation and orogeny at long historical period, and explore the formation of beta diversity pattern in Kenya.

Location: Kenya, East Africa.

Taxon: Angiosperms.

Methods: We quantified patterns of turnover and nestedness components of phylogenetic beta diversity among neighbouring sites for angiosperm species by using a well-resolved phylogenetic tree and extensive distribution records from public database and a set of books. We applied clustering methods to do biota delineation based on the pairwise similarities among multiple sites, and used a random assembly null model to assess the effects of species abundance distribution on phylogenetic beta diversity.

Results: Phylogenetic turnover for the Kenyan flora showed a non-monotonic pattern along the latitudinal gradient, which is strongly structured in volcanic and coastal areas. Whereas other areas were mainly dominated by phylogenetic nestedness, even in the eastern part of equatorial region which is parallel with volcanic area. Phylogenetic diversity and phylogenetic structure analyses elaborate the mechanism under the phylogenetic turnover or nestedness patterns we observed. We identified five phytogeographical regions in Kenya: the Mandera, Turkana, Volcanic, Pan Coastal and West Highland Regions.

Conclusions: The variation extent of turnover gradient and the coexistence situation are highly dependent on the regional biogeographical history, that is, the process of climatic fluctuations and long-lasting orogeny jointly shaped the biodiversity pattern. The nestedness component dominated climatically unstable regions are presumed to be caused by heavy local species extinction and recolonization from the Volcanic Region. The high turnover component in climatically stable regions may preserve old lineages and the prevalence of endemic species within narrow ranges.