BRITAIN: Butterflies on wane
Copyright 2001 Times (UK)
NOVEMBER 01 2001
BY MARK HENDERSON, SCIENCE CORRESPONDENT
MORE than half of Britain’s butterfly species are in decline even though the effects of global warming had been expected to provide them with a more favourable environment, scientists have discovered.
A survey covering 99 per cent of the land area of Britain has shown that habitat loss and intensive farming practices have led to sharp falls in butterfly numbers over the past two decades. The study, which examined 46 of the 64 species that are normally native to Britain, found that the populations of 34 species had fallen significantly since the last survey was taken between 1970 and 1982. Most varieties have declined by between 20 and 40 per cent, but the damage to some has been even greater. The high-brown fritillary, the worst affected species, has suffered a 77 per cent loss, and numbers of the marsh fritillary have fallen by 55 per cent.
The findings, which are published today in the journal Nature, are particularly surprising because average spring and summer temperatures have risen by up to 2F over the 30 years since the start of the last research period.
Because all 46 species studied are at the northern limit of their geographical range, such warming ought to have led to an improvement in their environment, and a rise in numbers. Instead, habitat degradation appears to have more than offset any benefits the butterflies might have gained from higher temperatures.
Christian Thomas, professor of biology at the University of Leeds, who led the research, said that the results revealed a crisis for many species of British butterfly. “On the basis of climate, we had expected to find many species increasing their geographical range and doing rather better,” he said. “Instead, we found that habitat loss is taking place at a faster rate than climate improvement, and the overall effect was the opposite.
Since 1940, intensified agriculture had eroded about 70 per cent of Britain’s semi-natural habitats, the researchers found. Pastures, for example, had changed from grazed meadows, with many types of grasses and wild flowers, to near-monocultures with a single grass variety. This was extremely bad news for butterflies, Professor Thomas said.