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.