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The Decline of Species ...

British Study Covering Last 40 Years Points to Worldwide Mass Extinction of Wildlife and Plants
Tim Radford, The Guardian, Friday March 19, 2004

  Scientists have produced the first comprehensive evidence that the diversity of butterflies, birds and plants is in decline in the UK. They say their research supports the argument that mass extinction threatens life on Earth.

In the past 20 years, according to a study in the US journal Science today, about 70% of all butterfly species in Britain have shown signs of decline. About 28% of plant species and 54% of bird species also declined in areas studied over long periods. The finding comes from government-funded scientists using data painstakingly amassed over the past 40 years by 20,000 skilled naturalists.Sandra Knapp, a botanist at the Natural History Museum, said the UK survey gave a crucial message for the world: "The lesson and the warning are there for all to see. Britain, by virtue of its well-known and well-studied biodiversity, is the canary for the rest of the globe.

"This adds enormous strength to the hypothesis that the world is approaching its sixth major extinction event," said Jeremy Thomas of the Natural Environment Research Council, who led the study of butterfly populations.

"The others appear to have been cosmic events, either from outer space coming in or some major perturbation - volcanoes, whatever - within the Earth. So they are believed to be physical events.

"You could say this latest one is an organic event: that one form of life has become so dominant on Earth that through its over-exploitation and its wastes, it eats, destroys, or poisons the others."

There have been five episodes of mass extinction in the last 500m years.

The Ordovician period ended about 439m years ago with the loss of an estimated 84% of species. In the Late Devonian about 367m years ago, 79% of life was wiped out. At the close of the Permian period some 245m years ago, 95% of species disappeared in a cataclysmic event. Half of all marine life vanished about 208m years ago, at the end of the Triassic. The Cretaceous era ended abruptly 65m years ago along with the death of the dinosaurs and the loss of up to 70% of all species.

The 600m-year fossil record shows a pattern of continuous evolution and extinction. But naturalists now think that extinction rates are at least 100 times greater than the natural "background" rate because of pollution, habitat destruction, hunting, agriculture, global warming and population growth.

Hard evidence, however, has been based only on research into a small number of species, mainly birds. But birds make up less than 1% of all species, while insects make up more than 50% of life on Earth.

Dr Thomas and his colleagues analysed six surveys recording the presence of almost all of Britain's native plant, bird and butterfly populations in the past 40 years in 10km grid squares.

One third of plant, bird and butterfly species have disappeared from one of the squares they occupied 20 or 40 years ago. About 70% of butterflies show some decline and two species have become extinct.

"We are going to lose a lot of species, there is no doubt about that. It is accelerating, this decline, for a lot of species and we are going to lose more than we have lost in the last 20 years. And it is just going to go on and on. But it is not all bad news, because the conservation bodies have done wonders," Dr Thomas said.

A second study in Science showed that pollution by nitrogen compounds, from industry and agriculture, could be linked to the loss of species from native grasslands.

Carly Stevens, a PhD student from the Open University and the NERC centre for ecology and hydrology in Huntingdon, examined 68 sites and found that rising levels of pollution by oxides of nitrogen and ammonia threatened 40% of selected native grassland plants.

Where nitrogen levels were low - in the Scottish Highlands and Lundy island in the Bristol Channel - plant variety increased. Where they were high - for instance, in the Peak District and Staffordshire - the number of species in any patch of grass was reduced.

Although nitrogen is a fertiliser, many plants flourish best in poor nutrient conditions, and these were most threatened by increasing nitrogen levels from car exhausts and intensive livestock farming.

"I studied the same type of grassland in different sites. Plants that were particularly sensitive were heather, hare bell, eyebright, purple moor grass, mountain fern moss and ribwort plantain," she said. "We all drive cars. We all use fossil fuels. We all eat food grown with fertiliser."

Lord Robert May, president of the Royal Society and a distinguished ecologist, said: "If this pattern holds more generally, then estimates of global extinction rates - which are mainly based on birds and mammals - although already alarming, could err on the optimistic side.