British Study Suggests New Mass Extinctions

Why Britain’s disappearing butterflies may be
early victims of the sixth mass extinction

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By Steve Connor, Science Editor
Independent (UK)
19 March 2004

A milestone study of British birds,
butterflies and wild flowers has revealed the
strongest evidence yet that we are on the verge of a
mass extinction of global wildlife - the sixth mass
extinction in the history of life on Earth.

Scientists have accumulated the most detailed data to
date indicating that human activity is systematically
stripping the planet of its rich biodiversity. Nearly
a third of native British plants have significantly
decreased in 40 years, more than half of native birds
have declined in just two decades and nearly three-
quarters of British butterflies have fallen in numbers
in 20 years.

The study involved about 20,000 naturalists who
inspected the entire British landscape to compile
three atlases of native birds, butterflies and wild
plants. The information they gathered on the presence
or absence of more than 1,500 species in each 10-
kilometre (six-mile) square of countryside they
surveyed was compared directly with similar atlases
compiled 20 or 40 years previously.

In the relatively short period between the past and
present surveys, the scientists found a dramatic
decline of all three major groups of wildlife, with
one-third of all species studied disappearing from at
least one part of the UK they had occupied 20 or 40
years ago.

Jeremy Thomas, the leader of the study from the Centre
for Ecology and Hydrology in Dorset, said the decline
in butterflies was much worse than expected and far
worse than that of birds or plants. "The results are
appalling," he said. "In Britain 71 per cent of all
butterfly species have declined in the last 20 years.
"For the first time we can say that in the UK one
group of insects has suffered as badly as birds or
plants - this adds enormous strength to the hypothesis
that the world is approaching its sixth major
extinction event."

For more than a decade scientists have constructed
computer models of the rate at which species are going
extinct. Such models suggested a rate of anywhere
between a hundred to many thousands of times greater
than normal "background" rates. The information used
for these models was based on the fossil record and
what little was known about the rate of extinction
within certain well-studied but rather
unrepresentative groups, such as birds, fish, certain
mammals and palm plants. but Britain has good records
of wildlife that could help to fill many of the gaps.

"There are simply no data sets that approach this
detail and scale anywhere in the world," Dr Thomas
said.

"Even though UK butterflies are a tiny proportion of
the world’s insects, and although the UK is a small
country, this is the first time it has been possible
to compare for any group of insects with the better
recorded groups [of animals and plants]. "The gloomy
result is that this group has indeed declined as
rapidly as plants and birds and it’s because of this
we believe it provides tentative support of the sixth
mass extinction event," he added.

In 1999, Lord May of Oxford, the president of the
Royal Society and the Prime Minister’s former chief
scientific adviser, estimated that the current
extinction rate could be up to 10,000 times higher
than it should be under normal circumstances. In a
speech at the time to the World Conservation Union, he
said: "This represents the 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 [humans] rather than from external
environmental changes."

Yesterday, Lord May said the latest study, showing a
28 per cent decline of native plants, a 54 per cent
decrease in abundance of native birds and a 71 per
cent decline of butterflies, supported the belief that
the world was on the cusp of another mass extinction.
"These are dismaying trends," he said. "If this
pattern holds more generally then estimates of global
extinction rates - which are mainly based on birds and
mammals - could err on the optimistic side."

The study, funded by the Natural Environment Research
Council and published in the journal Science, is
important because of its focus on a major group of
insects.

Dr Thomas said: "Past assumptions about extinctions
were based on just a small number of species studied,
mainly birds. But birds make up only 0.6 per cent of
all species on Earth. An obstacle to this conclusion
[of sixth mass extinction] is that really no reliable
information has existed for insects and insects
comprise over half the species on Earth.

"Butterflies have declined by an order of magnitude
greater than either birds or plants. This was an
unexpected result and it has implications both
nationally and globally. We tentatively suggest that
this provides the first objective support for any
group of insects for the hypothesis that the world is
experiencing the sixth major extinction event in the
history of life."

Since the last British butterfly survey 20 years ago,
two species - the large blue and the large
tortoisehell - have gone extinct in the UK. Of the 58
native species studied, the high brown fritillary has
declined most, down by 71 per cent.

Dr Thomas said this was probably because of changes in
the way woodlands are managed, which have made
woodland floors shadier places, hampering the survival
of caterpillars that live on forest violets. Lost of
habitat is the overwhelming reason for the decline of
both wild animals and plants.

The ploughing of heathland and the draining of
wetlands have resulted in complete destruction of some
habitats, while others have become degraded as a
result of other forms of human activity, such as
pollution.

Professor Georgia Mace, director of science at the
Institute of Zoology in London, who has studied
extinction rates, said that the latest study suggests
the problem could be far worse than previously
imagined. "According to the results here, we could be
seriously underestimating the severity of the
problem," Professor Mace said.

THE END OF THE WORLD, BACK THEN

Cretaceous-Tertiary extinction (about 65 million years
ago) The last mass extinction wiped out the dinosaurs
and nearly half of the main groups of marine animals.
Most likely cause was a collision with a large
asteroid.

Triassic extinction (199m to 214m years ago) Killed
nearly half of the major groups of marine wildlife.
Believed to have been caused by undersea volcanoes.

Permian-Triassic extinction (about 251m years ago) The
worst mass extinction, wiping out up to 95 per cent of
species. Probably caused by volcanic eruptions or an
asteroid.

Late Devonian extinction (about 364m years ago) Death
toll estimated to be 22 per cent of marine families
and 57 per cent of marine genera. No one knows why it
happened.

Ordovician-Silurian extinction (about 439m years ago)
Killed a quarter of marine families, including some
bizarre creatures such as Hallucigenia (right).
Believed to have been caused by a fall in sea levels
as glaciers formed, then rising sea levels as glaciers
melted.

Genevieve Roberts

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