The
decline of species ...
By Tim Radford
19 March 19, 2004
The Guardian
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."