Plant diversification in the Cape of South Africa
Research suggests that the high levels of biodiversity in the Cape of South Africa have been promoted by a combination of complex environmental conditions and climatic stability.
06 Mar 2012
Cape Eland amidst the diverse Fynbos vegetation at Cape Point, South Africa (image: Vincent Savolainen).
The Cape region of South Africa is one of the most remarkable biodiversity hotspots. Much of this diversity is due to an exceptionally large speciation of just a few plant lineages that radiated substantially within this region, but the causes behind this are poorly understood.
Comprehensive analyses of speciation
Research led by scientists from Kew and Imperial College London (Vincent Savolainen, Tim Barraclough, Jan Schnitzler and Martyn Powell), working with South African colleagues (John Manning, James Boatright and Tony Rebello) and Peter Goldblatt (Missouri Botanical Garden), presents one of the most comprehensive analyses of plant speciation in the region. By combining near complete species-level phylogenies of four major Cape clades (including more than 470 species) – the genus Protea, a tribe of legumes (Podalyrieae) and two speciose genera within the iris family (Babiana and Moraea) – with ecological and biogeographical information, the researchers tested various hypotheses that have been proposed to explain the radiation of the Cape flora.
Soil type and fire drive speciation
The results show that these radiations started throughout the Oligocene and Miocene and that net diversification rates have remained constant over time. Furthermore, by using sister species comparisons to assess the impact of different factors on speciation, the researchers identified changes in soil type as the most important cause of speciation in Babiana, Moraea and Protea, while shifts in fire-survival strategy is the most important factor for Podalyrieae. Contrary to previous findings in other groups, such as orchids, pollination syndromes show a high degree of phylogenetic conservatism, even in groups with a large number of specialised pollination syndromes like Moraea.
The study concludes that the combination of complex environmental conditions and relative climatic stability has led to high speciation and/or low extinction rates as the most likely cause of present-day patterns of hyper-diversity in the Cape.
Item from Prof. Vincent Savolainen (Professor of Organismic Biology, Imperial College London & Research Fellow, RBG Kew)
Kew Scientist, issue 40
Schnitzler, J., Barraclough, T. G., Boatwright, J. S., Goldblatt, P., Manning, J. C., Powell, M. P., Rebelo, T. & Savolainen*, V. (2011). Causes of plant diversification in the Cape biodiversity hotspot of South Africa. Systematic Biology 60: 343-357.
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