At the crossroads of two biodiversity hotspots : the biogeographic patterns of Shimba Hills, Kenya

At the crossroads of two biodiversity hotspots; the biogeographic patterns of Shimba Hills, Kenya
Beryl A. Bwong
The Shimba Hills of Kenya (SHK) is geographically located at the cross roads of two major biodiversity hotspots; the Coastal Forests of Eastern Africa (CFEA) and the Eastern Afromontane Biodiversity Region, specifically the neighbouring Eastern Arc Mountains (EAM). Results from old and recent collections of its flora and fauna indicate that Shimba Hills harbour species associated with EAM and CFEA as well as taxa that have affinity with West African Guineo-Congolian forest. However, the link between SHK and these biodiversity hotspots has never been tested appropriately using phylogenetic approaches. Using 16S mtDNA, demographic analysis and species distribution modelling, I sought to understand the phylogeographic affiliation of Shimba Hills with the neighbouring CFEA and EAM using its amphibian assemblage. Three main questions were explored, namely: a) Which are the closest relatives of SHK amphibian populations? b) Do amphibian species currently occurring in SHK have similar phylogeographic patterns to each other? c) Which historical processes, if any, account for the observed patterns of genetic diversity? I found that SHK and indeed the entire study area have a complex biogeographic history and no single pattern can explain the current amphibian assemblage in the area. Shimba Hills are more closely affiliated to the CFEA than to the EAM. Two previously undocumented putative phylogeographic breaks are recovered from the study area; one from the Kenya north coast and another in the Tanga region in Tanzania. Historical habitat stability and connectivity appear to play a significant role in species diversification in the area. Additionally, I also report on some fundamental findings on Shimba Hills amphibians during this study; Using a combination of molecular, morphological, spatial and bioacoustics methods the taxonomic status of the only endemic amphibian from Shimba Hills, Hyperolius rubrovermiculatus, is confirmed and description of a new species from the north eastern Tanzania is proposed. Secondly the taxonomic status of a Callulina rediscovered in Shimba Hills after 50 years is confirmed and I also propose the description of three new species of Callulina from the neighbouring Eastern Arc Mountains in Tanzania. Finally, I took the opportunity to compile the first ever annotated checklist of amphibians of Shimba Hills National Reserve where a new country record for the Ribbon Caecilian (Scolecomorphus vittatus) and other interesting discoveries are discussed. The reserve plus the entire SHK area contains the highest number of amphibian diversity for any known locality in Kenya. Therefore its continued conservation will ensure about 30% of Kenya’s amphibian species are preserved.
Key words: Coastal forests, Eastern Arc Mountains, Phylogeography, species distribution modelling, checklist, Amphibians.