- An accelerating decline in species, in particular a fall
in butterflies, provides the first hard evidence that the Earth is on the
verge of a sixth mass extinction.
-
- There have been at least five over the past 500 million
years, with the biggest occurring 250 million years ago.
-
- Scientists report today that species diversity is falling
fast and, contrary to current opinion, insects are particularly hard hit.
This indicates that scientists may have underestimated the magnitude of
the pending extinction.
-
- If they are correct, the Earth is heading for the first
global wipeout with an organic cause, with humans the dominant agent of
destruction. Earlier extinctions were triggered by volcanism, cosmic impacts
and other physical causes.
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- "The warning is there for all to see - we are poised
on the verge of the sixth extinction crisis," said Dr Sandy Knapp
of the Natural History Museum. "Britain, by virtue of its well-known
and well-studied biodiversity, is the canary for the rest of the globe."
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- Around 28 per cent of our 1,254 native plant species
have significantly fallen in abundance in the past 40 years, 54 per cent
of the 201 native bird species over two decades, and 71 per cent of our
58 butterfly species over the same period, according to the milestone comparative
study published in the journal Science, led by Dr Jeremy Thomas of the
Natural Environment Research Council's Centre for Ecology and Hydrology,
Dorchester.
-
- "One form of life has become so dominant on Earth
that, through its over-exploitation and waste, it eats, destroys or poisons
the others," he said. "It is accelerating, this decline, and
we are going to lose more than we lost in the past 20 years."
-
- The team's study used data collected by scientists and
20,000 volunteers scouring the countryside and could only have been done
here, where more is known about diversity than anywhere else.
-
- Until now, the idea that the world is undergoing a sixth
mass extinction, with the loss of species rising to 100 times normal rates,
has rested on studies of a relatively small portion of the world's plants
and animals.
-
- Population information about insects, which make up approximately
half of all known species on Earth, has been particularly sparse and talk
of a mass extinction was "an enormous extrapolation", said Dr
Thomas.
-
- Now this gap has been filled, as Dr Thomas and colleagues
analysed six surveys covering virtually all of the native plant, bird and
butterfly populations over the last 40 years, including one he helped to
conduct 25 years ago, revealing the impact of pollution, habitat loss and
degradation.
-
- Dr Thomas said his team was surprised butterflies had
fared so poorly, a discovery with global implications. "This provides
the first objective support, for any group of insects, for the hypothesis
that the world is experiencing the sixth major extinction event."
-
- Over 20 years, the ranges of approximately 70 per cent
of all butterfly species declined to some degree, many severely. Shadier
woodland floors, resulting from changing management, have harmed caterpillars
of the high brown fritillary, causing a "frightening" 71 per
cent drop, for example. Loss of grasslands have harmed the blues, such
as the Large Blue.
-
- On average, these insects disappeared from 13 per cent
of areas they once occupied. "That's the opposite of what people thought
20 years ago: that insects were much more resilient because they could
fly about," Dr Thomas said.
-
- In a second study published today in Science, Carly Stevens,
a doctoral student at the Open University and the NERC Centre for Ecology
and Hydrology in Huntingdon, and colleagues recorded the abundance of plant
species in 68 grasslands in upland areas.
-
- She reports "strong evidence" of a decline
in species richness, for instance in species such as heather, harebells
and eye-bright.
-
- Nitrogen pollution is the most likely cause: excess nitrogen
can allow a few species, especially grasses, to grow fast and crowd or
shade out their neighbours. The nitrogen is the result of agricultural
fertilisation and fossil fuel combustion.
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- © Copyright of Telegraph Group Limited 2004.
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- Why Britain's disappearing butterflies may be early
victims of the sixth mass extinction
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- By Steve Connor, Science Editor
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- 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.
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- 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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- 19 March 2004 12:56
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