Insect deaths add to extinction fears

British survey hints that species are crashing worldwide.

19 March 2004 - MICHAEL HOPKIN


   The 'large blue' butterfly became
   extinct in Britain in 1979.
   © Robert Thompson/Butterfly
   Conservation caught by fishermen.
Ecologists have unveiled strong evidence that huge numbers of the world's species are disappearing. A survey of British wildlife suggests that insects - thought to be among the most resilient species - are suffering similar extinction rates to larger, better-studied animals.

If the same is happening worldwide, we may be witnessing the largest die-off since the mass extinction that killed the dinosaurs, says Jeremy Thomas of the Centre for Ecology and Hydrology in Dorset, UK, who led the study in this week's Science¹.

Thomas's team analysed surveys of British birds, plants and butterflies stretching back 40 years. The statistics, collected by 20,000 amateur naturalists, form an unprecedented census of insects. "No dataset approaches this detail and scale anywhere in the world," Thomas says.

The researchers divided Britain into 10-kilometre squares and counted the number of squares occupied by each species. Of 58 butterfly species, 71% have declined or disappeared over the past 20 years, alongside 54% of birds. The past 40 years has seen declines in 28% of plants studied.

Experts had assumed that the sheer number of insects would safeguard them against mass extinction. "The gloomy result is that this group has declined massively," says Thomas. As insects comprise more than 50% of the planet's species, a large die-off would be bad news for global diversity, he adds.

The sixth extinction?

"This study provides further evidence that the world is facing another major extinction crisis," warns Michael Rands, director of UK conservation group BirdLife International.

There have been five such events since the birth of multicellular life 600 million years ago. In each, 65-95% of the world's species died out. No one is claiming that current species loss has reached this rate, Thomas concedes. "But it's accelerating," he warns. "If nothing is done, we're going lose a lot more species."

   Birds, plants and butterflies were
   surveyed over 40 years.
   © Derek Belsey/BTO
Thomas and his team attribute the British trend to habitat loss. Across the world, Thomas says, habitat preservation will be the first line of defence against species loss.

A second study in Science² shows that another reason for species decline, in Britain at least, is nitrogen pollution. A team led by Carly Stevens of the Open University in Milton Keynes, UK, examined 68 grasslands around the British Isles and found that higher nitrogen pollution means fewer species.

Soils in Britain and Central Europe receive an average of 17 kilograms of nitrogen compounds per hectare per year, mostly from fossil-fuel burning and intensive livestock farming. This pollution could kill 20% of grassland species, Stevens warns.

We need to act now to reduce this, says Stevens. Once biodiversity begins to decline, it is very difficult to prevent it crashing, she says: "If you keep taking enough bricks out of the wall, the wall's going to fall down."