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Hyperdiverse flora in Cape region mainly caused by huge range of soil types

02 May 2011 Senckenberg Research Institute and Natural History Museum

Hardly any other place worldwide boosts such a hyperdiverse flora as is to be found on the southwestern tip of Africa. The flora is moreover quite unique with almost 70 % of the native species being endemic. An international team of scientists led by Dr Jan Schnitzler, Biodiversity and Climate Research Centre (BiK-F), Frankfurt am Main, Germany, has now established that the remarkable plant diversity is mainly due to the large range of different soils in this region. The study has been published online a few days ago in “Systematic Biology“.

The flora of the Cape Region comprises more than 9000 different types of plants. In comparison, the German flora amounts to rather little. Although Germany is about four times bigger in size than the Cape region, there are only around 3300 plant species. Much of the diversity in the Cape region is due to a few clades that have radiated substantially within this region. Emblematic species are magnificent flowering plants, such as Protea (sugar bush) of which there are more than a hundred different species.

Comprehensive analysis of the history of 470 species

Scientists have long wondered about the reasons for the high plant diversity here and have come up with a number of explanations. “The most accepted ideas are that it either results from the high diversity of soil types or from adaption to pollinators. This means many plant species have specialized on different pollinators, such as certain insects. Pollen will only be distributed by them.“ says Dr Jan Schnitzler, researcher at the Biodiversity and Climate Research Centre, (BiK-F), Frankfurt am Main, Germany. In order to test the main suggestions regarding the causes of the particular plant diversity he and his colleagues concluded the most comprehensive genetic analysis of plant species in the region so for and looked at about 470 native plant species, representing three of the seven largest plant families of the Cape region.

Soil is paramount factor for radiation

The researchers established the ways of plant species diversification by drawing up family trees using molecular genetic data and correlating it with information on ecology and geography of their habitat. Particular emphasis was placed on comparing differences in sister species. Jan Schnitzler sums up the results: "The Cape region comprises many different soil types on a relatively small space which turns out to be very important in the development of plant diversity. The reason is probably that it forced closely related species to develop adaptations to varied circumstances. Surprisingly for us, pollinator specialization is not a general factor that drives radiation here."

Taking the slow lane towards uniqueness

The scientists from the United States, Germany, United Kingdom and South Africa also found that the plant diversity is not a result of rapid radiation triggered by climatic changes. The development was rather a continuous process which took place over a long period of time. Furthermore, the relative climatic stability in the Cape may have resulted in lower extinction rates than in northern Europe which experienced several ice ages.

Universal pattern for the radiation of plant species?

The study is basic research in the field of biodiversity encompassing ten years of work. “We want to know, which factors contribute to a high biodiversity in the long-run.” says  Jan Schnitzler and adds “The next thing would be to test whether a large number of soil types is also the main cause for plant species radiation in other regions.“ Eligible regions that resemble those of the Cape region climate would be considered first. This applies, for example, to the Mediterranean, California and southwest Australia.

Attached files

  • The Cape Region is home to 9000 plant species. The picture shows a king protea, national flower of South Africa and one of the plant species on which the moleculargenetic analysis was performed. (Copyright: Jan Schnitzler)

  • Cape region: the high diversity in soil types is a paramount factor for the development of one of the world’s richest and most unique flora. (Copyright: Jan Schnitzler)

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