New biodiversity hotspots revealed

Five years ago, conservationists identified 25 sites around the world where plant and animal species are most abundant. Now there are six more.

It was a reasonable assumption. A hotspot with the greatest biodiversity is also likely to be at the greatest risk of species loss. New research, however, does not 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 last month, says that 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 biodiversity, and this points to the need to base conservation on more than one measure."

The study carried out by the scientists looked at three different measures of diversity. These were species richness, the richness of threatened species - a measure of extinction risk - and the number of endemicspecies in the region (those that do not breed or can't be found elsewhere). To their surprise, the researchers found that the measures only overlapped to a significant extent 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." It took five years for the team to collate all the information for analysis, and the result was the most detailed analysis of the hotspot concept since it was devised.

The idea of hotspots first surfaced in 1988 in a scientific paper by the ecologist and environmental campaigner, Norman Myers. Myers identified 10 tropical forest hotspots that he characterised as having exceptional levels of plant endemism and uncommon rates of habitat loss.

Conservation International, the environmental body, took up the idea and launched a quest to identify more. To qualify, a region had to contain at least 1,500 species of endemic vascular plants, and had to have 30 per cent or less of its original vegetation remaining.

This analysis resulted in the identification of 25 hotspots. Collectively they were home to 44 per cent of the world's plants and 35 per cent of its terrestrial vertebrates, in an area that formerly covered only 11.8 per cent of the earth's land surface. This had been reduced by about 90 per cent by human activity, meaning that this wealth of biodiversity was now restricted to 1.4 per cent of the earth's land surface.

Since then, Conservation International has further refined its criteria and found six new hotspots, making 34 in total, as some existing sites were split into two. Details are published this month in a book called Hotspots Revisited. The sites today cover about 2.3 per cent of the earth's land surface - once they covered 15.7 - and are home to 75 per cent of the planet's most threatened species.

"We must now act decisively to avoid losing these storehouses of the earth's life forms," says Russell Mittermeier, the president of Conservation International. "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 in Nature. "[There are] also concerns about the notion that species-richness hotspots should overlap with those identified using other diversity metrics."

And yet, the idea that identifying species hotspots can help conservation is not discredited. Possingham and Wilson point out that all 10 threatened bird-species hotspots identified by Professor Owens are on the Conservation International list. The debate about biodiversity hotspots is not over, it has just got hotter.

'Hotspots Revisited',Conservation International, £45 www.conservation.org

The new regions

Madrean Pine-Oak Woodland, south-west US and northern Mexico

Includes about 40 mountain tops, or "sky islands". Pine and oak are the characteristic vegetation. Includes about 5,300 species of flowering plants and 1,500 vertebrate animals, such as the volcano rabbit and the endangered maroon-fronted parrot (pictured right).

Maputaland- Pondoland-Albany region, southern Africa

Consists of ancient sand dunes, low-lying plains and rugged terraces. It is Africa's second richest region for flowering plants, including the endemic bird-of-paradise flower (Strelitzia reginae). Threatened animals include the giant golden mole and white rhinoceros.

Horn of Africa

Includes the Ethiopian highland and Socotra Archipelago off Somalia, all of Djibouti and parts of Ethiopia, Eritrea, Kenya, Yemen, Oman and Sudan. One of only two hotspots in the world that is entirely arid. Home to about 5,000 known species of vascular plants and rare antelopes, such as the beira, dibatag, Speke's gazelle and gerenuk.

Irano-Anatolian region

Crossed by the ancient silk route, this hotspot's highest point is 18,000 feet, and it includes forest steppe as well as alpine vegetation. Globally threatened birds that breed in the area include the white-headed duck and imperial eagle. The region's most important flagship species is the Asiatic cheetah.

Mountains of Central Asia

Includes two of Asia's major mountains, the Pamir and the Tien Shan. About 1,500 of the known 5,500 plants in the region are endemic. There are 16 endemic tulips, including the rare, orange-red Greig's tulip, the "king of tulips". Some 500 species of birds regularly visit or breed here, including the Himalayan griffon.

Japan

In addition to the main islands, this hotspot includes about 3,000 smaller islands. Some 73 per cent of the region is mountainous. Japan is home to some 5,600 species of vascular plants, about a third of which are endemic. About 90 mammals live in the island region, half of which are endemic. Japan has 65 reptiles, half of them endemic.