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Biological Diversity: Islands Beat Mainland Nine to One

New world maps for nature conservation / study also investigates impacts of climate change

The islands located in the oceans are around nine times as valuable as an equally large piece of mainland for maintaining global biological diversity. Researchers at the University of Bonn have come to this conclusion in a recent joint project carried out with colleagues from the University of California San Diego and the University of Applied Sciences Eberswalde. For this they compiled the largest collection of data on the global occurrence of plant and vertebrate animal species. On this basis they calculated an index reflecting the number of species and their rarity. They have presented the results in the form of world maps. The study will be published in the next edition of the renowned US journal PNAS.

The island of New Caledonia ranks first on the biodiversity list. Covering an area comparable to the State of New Jersey, it is home to 3,270 plant species, 2,432 of which only occur on the island. These include Amborella, for example, the most primordial of all living flowering plants. But even unique bird species can be found here, such as the Kagu, the only surviving representative of an entire major group of animals. 'Maps such as ours only previously existed for individual continents,' Dr. Gerold Kier, project leader at the University of Bonn, says. 'With them you can calculate our "ecological footprint", for example, or ascertain which regions are particularly important for nature conservation in a worldwide comparison.'

Dr. Holger Kreft, an ecologist from the University of California in San Diego and one of the two main authors of the study, points out another important innovation: 'Although islands have been known since Darwin's day for their unique flora and fauna, until now there was no global analysis comparing their value for nature conservation with continents.' However, some mainland areas also have remarkably high values on the index, above all the southern tip of Africa, known as Capensis. Moreover, many mountains, especially in the tropics, are among the most valuable areas from the point of view of biological diversity. These are followed by areas with a Mediterranean climate.

'We now have new and important data in our hands, but still have no simple solutions for nature conservation,' Holger Kreft emphasises, adding: 'In particular, we need to answer the question how protected areas with their flora and fauna can complement each other in the best way. The part played by ecosystems, e.g. their ability to bind the green-house gas carbon dioxide or their contributions to the regional water budget should be increasingly taken into account.'

According to the study, more than 70,000 plant species are native on oceanic islands, i.e. almost a quarter of the approximately 315,000 species worldwide. Considering the fact that islands cover less than four per cent of the total land area, this is a substantial percentage. "However, it would in fact not make any sense now for protective measures to simply focus on islands because three quarters of all plant species are nevertheless found on the continental mainland." Kreft comments.
The researchers also investigated the threats due to human impact. The scenarios they have calculated for 2100 warn that flora and fauna on islands will be affected more drastically than on the mainland. The reason for this is expected to be the change in land use in particular, i.e. the expansion of farmland and the deforestation associated with this. Invasive plant and animal species also have particularly drastic effects on islands by displacing the indigenous species. However, the opposite is true of the predicted effects of climate change. Here islands seem to be less affected due to the buffering effect of the oceans, if the effect of rising sea levels is ignored, which can literally lead to many smaller islands being swamped. Gerold Kier urges that action is needed: 'Climate change remains one of the main threats to the biodiversity of the earth. If we cannot slow it down significantly, protected areas will not be much help.'

This means that biodiversity worldwide is exposed to many new dangers. Historically, by contrast, it was mainly the direct influence of humans that led to the extinction of species. 'Madagascar, the second largest island on earth, is a particularly dramatic example,' Professor Wilhelm Barthlott from the Nees Institute for Biodiversity of Plants in Bonn explains. 'The elephant bird, the Roc of the Arabian Nights, is one of many species that have become extinct here during the past centuries.' As early as 1996, Barthlott's group published a world map of the diversity of plant species which was adopted by many textbooks. It was only several years later, after their request for funds had been accepted by the Academy of Sciences and Literature in Mainz, the Federal Ministry of Research and the Wilhelm Lauer Foundation, that they were able to begin with this new work, which also focuses on the rarity of species.

Gerold Kier, Holger Kreft, Tien Ming Lee, Walter Jetz, Pierre L. Ibisch, Christoph Nowicki, Jens Mutke & Wilhelm Barthlott: A global assessment of endemism and species richness across island and mainland regions. PNAS (doi: 10.1073/pnas.0810306106), soon available free at or


Dr. Holger Kreft
Tel. +1-858-534-6659
Email: [Email protection active, please enable JavaScript.]

Dr. Gerold Kier
Telephone: +49 (0)172 57 14007
Email: [Email protection active, please enable JavaScript.]

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