Debate over hotspots gets warmer

Life on earth is not evenly spread. Some areas are richer than others, particularly tropical rainforests.

Such patchy distribution inspired conservationists to draw up a list of "hotspots" where the species' diversity was greater than normal.

If we could concentrate our conservation efforts here, so the theory went, we might be able to stem the rapid rate of extinctions.

It was a reasonable assumption. A hotspot with the greatest biodiversity is also likely to be at the greatest risk of species loss.

But new research doesn't completely support the central tenets behind hotspot ecology, and instead raises questions about how wise it is to focus conservation on them.

A study has drawn up the first detailed global map of the world's bird species.

It reveals that the areas where most avian species can be found do not always overlap with the areas where they are most threatened.

Professor Ian Owens of Imperial College London, who led the study published in the journal Nature, says in terms of species richness, the world's bird hotspots are in the mountains of South America and Africa, but in terms of extinction risk they are in Madagascar, New Zealand and the Philippines.

"In the past, people thought that all types of biodiversity showed the same sort of pattern, but that was based on small-scale analyses," he says.

"Different types of diversity don't map in the same way. A variety of mechanisms are therefore responsible for biodiversity, and this points to the need to base conservation on more than one measure."

The study looked at three different measures of diversity - species richness, the richness of threatened species - a measure of extinction risk - and the number of endemic species in the region (those that do not breed or cannot be found elsewhere).

To their surprise, the researchers found that the measures overlapped to a significant extent only in the Andes.

"Birds are a model for this type of work," says Professor Owens. "There is a wealth of historical information about them, and they are also large, colourful and can be seen in the daytime. It's very difficult to do at this scale for other organisms."

The team spent five years collating all the information and the result was the most detailed analysis of the hotspot concept since it was devised.

"We must now act decisively to avoid losing these storehouses of the earth's life forms," says Conservation International president Russell Mittermeier.

"By concentrating on hotspots, we are not only protecting species, but deep lineages of evolutionary history."

And yet not all scientists appear to be entirely happy with the biodiversity hotspot concept.

"[There is] an alarming lack of congruence between hotspots defined using different metrics," say Australian scientists Hugh Possingham and Kerry Wilson, referring to the Owens study.

And yet, the idea that identifying species hotspots can help conservation is not discredited.

Professor Possingham and Kerry Wilson point out that all 10 threatened bird-species hotspots identified by Professor Owens are on the Conservation International list.

Hotspots

* Concept introduced in 1988 by ecologist and environmental campaigner Norman Myers.

* He identified 10 tropical forest hotspots that he characterised as having exceptional levels of plant endemism and uncommon rates of habitat loss.

* Conservation International took up the idea and has now identified 34 hotspots.

* The sites today cover about 2.3 per cent of the earth's land surface - they once covered 15.7 per cent - and are home to 75 per cent of the planet's most threatened species.

- INDEPENDENT