Our dying bug-driven world

World Atlas of Biodiversity
June 20, 2003

Biodiversity sounds like the name of the latest detergent but is in fact a unique feature of our planet. It comprises not only species and their sub-units, such as races and populations, but also ecological processes that maintain life. It was designated one of five priority issues at the World Summit on Sustainable Development.

Creatures of one sort and another occur on the 8,848m peak of Everest and in the 11,000m depths of the Mariana Trench. Certain categories of species are remarkably numerous. There are at least 50 times as many individual birds, spread among 10,000 species, as there are humans, while there are at least 1,000 billion billion times as many bacteria, spread among at least 400,000 species. Ours is a "bug-driven" world.

The book opens with a review of what makes the biosphere tick, notably materials cycles, such as the carbon budget, and energy flows, such as plant growth. It surveys the emergence and proliferation of biodiversity throughout earth's history and documents biodiversity's distribution across the planet. At least half of all species occur in the tropical forests that cover less than one-20th of land.

We then read in admirable detail about how the main ecosystem types are faring under human impacts. Humans already utilise or waste half of all plant growth, while tropical forests have lost half of their expanse.

The over-exploitation of biodiversity by humans is all the more regrettable because, as the book spells out, we depend on it for food and other commodities, and, more importantly, for a lengthy list of environmental services, such as soil formation, watershed functions and regulation of weather and climate. All this is clearly presented, with references to both terrestrial and marine ecosystems. Finally, there is an assessment of conservation efforts.

Unfortunately, the book presents scant account, let alone analysis and evaluation, of what is surely the most remarkable aspect of biodiversity - that it is disappearing fast. Within just a few decades, there may well occur the most significant phenomenon in the history of biology - a mass extinction of species. There is a strong consensus among scientists that we are in the opening phase of an extinction spasm, and that processes of habitat loss - notably tropical deforestation - are working up so much momentum that we may soon find the grand-scale depletion of life's panoply all but impossible to slow, let alone to stop. Indeed, the upshot may soon be the demise of between one and two-thirds of all species, making for the biggest mass extinction since the elimination of the dinosaurs.

This dire démarche is covered in just a few pages that cite only one analyst and his findings of a decade ago. What about the abundant research of latest vintage? The reader is left with the impression that mass extinction is no big deal, or that it has not been sufficiently documented.

It is in this latter qualifier that the problem lies.

The authors focus on species that are known to exist - less than one-sixth of the planetary spectrum - and on species whose survival status has been assessed - a far smaller proportion. They also postulate that the best-known species of all - mammals and birds (0.15 per cent of all species) - reveal an extinction rate that has actually been slowing (grist to sceptics who proclaim that mass extinction is a fairy tale).

This curious lacuna apart, the book ranks as the best overview of biodiversity available. It is strongly recommended to all who care about life on earth - and who doesn't?

Norman Myers is a fellow of Green College, University of Oxford.

World Atlas of Biodiversity: Earth's Living Resources in the 21st Century

Author - Brian Groombridge and Martin D. Jenkins
ISBN - 0 520 23668 8
Publisher - University of California Press
Price - £36.95
Pages - 340

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