How one creature drives so many species to extinction

Scores of animals and plants are being driven out of existence each year - and scientists say that mankind is almost always to blame

Planet Earth is going through its sixth and probably its most devastating period of mass extinction with scores, and possibly hundreds of species of animals and plants dying out each year. But unlike the previous five extinction waves, this time the culprit is just another lifeform, Homo sapiens.

A United Nations report on the environment, to be published tomorrow, will highlight the scale of a problem many conservationists believe is likely to rapidly worsen over 30 years as wildlife congregations are destroyed or invaded by a less diverse range of species.

Some scientists believe the "sixth wave" of mass extinction is between 1,000 and 10,000 times greater than the normal "background" rate at which species are lost naturally.

Such a dramatic fall in biological diversity is identified as one of the most pressing problems facing humanity, by the scientists who contributed to the Global Environment Outlook-3 (Geo-3) report of the United Nations Environment Programme (Unep).

The report will identify some 11,046 species of plants and animals known to face a high risk of extinction, including 1,130 mammals – 24 per cent of the total – and 12 per cent, or 1,183 species of birds.

Human activities, from habitat destruction to the introduction of alien species from one area to another, are listed as the main causes of this dramatic loss in biodiversity. In the report, scientists also identify 5,611 species of plants known to be on the verge of extinction. They say the true figure is likely to be far higher, given that only 4 per cent of the world's known plant species have been properly evaluated.

The Geo-3 report covers almost every aspect of environmental degradation, from forest destruction to water pollution. It is designed to set the framework for the world summit on sustainable development to be held this summer in Johannesburg.

Geo-3 looks back on the past 30 years of environmental degradation, since the 1972 Stockholm conference on the human environment, to assess the likely prospects for the next 30. It is likely to warn that many of the factors that led to the extinction of species in recent decades continue to operate with "ever-increasing" intensity.

Serious threats to life on Earth are over-exploitation of natural resources, pollution, habitat destruction, the introduction of alien species and global climate change, say the scientists who advised Unep.

They identify the loss of habitats by human encroachment as one of the most pervasive threats to wildlife. Habitat loss and fragmentation of breeding grounds are behind the precarious predicament of 89 per cent of threatened birds, 83 per cent of threatened mammals and 91 per cent of endangered plants, the Unep scientists say.

In addition to growing poverty and climate change caused by global warming, Unep has identified alien invasive species as another serious threat to biodiversity, affecting 30 per cent of threatened birds and 15 per cent of threatened plants.

The black rat, which since 1800 has stowed away on ships sailing to the remotest corners of the world, is held responsible for the biggest slaughter of birds, especially those on uninhabited islands.

Another of man's hitchhikers has caused havoc to native wildlife from Hawaii to the Seychelles and Zanzibar. The crazy ant, so called because of its frenetic movements, killed three million crabs in 18 months on Christmas Island alone.

A host of other invasive aliens have also inflicted enormous environmental and economic damage throughout the world. The list includes the brown tree snake, the small Indian mongoose, the Nile perch, the strawberry guava, the water hyacinth, the zebra mussel and the brushtail possum.

Several species of animals and plants in Britain are threatened by a similar invasion of aliens. The water vole is being killed off by the American mink, the eggs of rare wading birds nesting in the Outer Hebrides are being eaten by hedgehogs introduced from the mainland, and the wetland habitats of the Norfolk Broads suffered decades of destruction by the coypu, a South American rodent.

Jeff McNeely, chief scientist at the International Union for Conservation of Nature in Geneva, said the next 30 years could be the defining moment for life on Earth. Either we can finally recognise the problems and do something about them, or we do not, he said.

"It could go either way. It could be a golden age of nature conservation, or it could be a disaster scenario. If we assume a doomsday scenario then we're going to live in a greatly oversimplified world.

"Most of the remaining species are going to be widely dispersed and cosmopolitan. We will have lost many of the large mammals and birds, and life in general will be more homogeneous, with a smaller capacity to adapt to a changing environment."

Within the next 30 years, if the biodiversity crisis is not addressed, it is likely that the last tiger, rhinoceros, Asian elephant, cheetah and mountain gorilla will have been lost in the wild, Dr McNeely added.

Often it is the well-known animals and plants which are at greatest risk. The Chinese alligator is the most endangered crocodilian, with only 150 individuals in the wild. Half of the world's insect-eating pitcher plants are threatened and one, the green pitcher plant, is critically endangered because of the loss of its wetland habitat.

Scientists have identified and named about 1.5 million species but they believe that between 5 million and 15 million species have yet to be formally classified. It is now generally assumed that many unnamed animals, plants and micro-organisms are going extinct before they are even known to science.

Lord May, an Oxford zoologist, believes present extinction rates are likely to increase further over the next century. He said: "This represents a sixth great wave of extinction, fully compatible with the big five mass extinctions of the geological past, but different in that it results from the activities of a single other species rather than from external environmental changes."

This catalogue of extinction is in danger of going unrecorded as fewer scientists are being trained in the field of taxonomy, the science of systematic classification.

Last week, the House of Lords Select Committee on Science and Technology warned that a shortage of taxonomists and underfunding of the research centres for systematic biology was jeopardising efforts to protect wildlife. How can biodiversity be protected if no one is recording what is there? "We have a cultural and moral obligation, as well as a pragmatic economic need, to record and, as far as possible, conserve the diversity of life with which we share the planet," the committee said.

The Natural History Museum and Kew Gardens in London are two world-reknowned centres for animal and plant taxonomy yet the committee found that both were finding it difficult to provide a service because of financial constraints. "It has also placed the reference collections of specimens comprising a wide range of biodiversity, which are housed in these institutions, at considerable risk," the committee added.

Professor Paul Henderson, director of science at the Natural History Museum, said systematics and the description of species was critical to the preservation of animals and plants, and the key to economic prosperity for many of the poorer nations in the world. He said it was at the heart of the sustainable development theme of the forthcoming world summit.

"We helped to identify the screw-worm when it invaded African livestock from South America," Professor Henderson said. "Without recognising it early on, it would have wreaked havoc with enormous economic consequences,"

Yet being able to name species will not, in itself, stop the inexorable decline, he said. "In 30 years? We'll still be heading for very fast rates of extinction comparable to today simply because we're not doing anything about it," the professor said. "I have to be a bit gloomy on the 30-year time-scale. There's not been very much action to justify being optimistic."