THE best guess of biologists is that species are disappearing between 100 and
1000 times as fast as they were before Homo sapiens arrived. But our
impact is different from the mass extinctions of the past. They wiped out whole
groups of animals, notably the dinosaurs, whereas humans are picking off
individual species. In the past, biodiversity recovered as species spread into
new ecological niches, but humans are wiping out niches as well as organisms.
Wildlife will have a tough time regenerating.
The winners after the mass extinction that finished off the dinosaurs are
about to become the losers. One in four mammal species and one in eight bird
species face a high risk of extinction in the near future: the population of
each species is expected to fall by at least a fifth in the next 10 years.
Almost all are endangered by human activity. The invertebrates are tipped to
dominate the new world order. Only around 0.1 per cent of the 1.6 million known
species are thought to be threatened, though many undiscovered species are
likely to be dying out before we even know of their existence.
As global climate change shifts temperatures across the planet, species may
not be able follow fast enough. According to UNEP, they will have to migrate 10
times as fast as they did after the last ice age. Many won鈥檛 make it.
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Species that do up and leave will move at different rates, breaking up
existing communities. At high latitudes, entire forest types are expected to
disappear, to be replaced by new ones. During this transition, carbon will be
lost to the atmosphere faster than it can be replaced by new growth,
accelerating climate change.
The romantic notion of 鈥渨ilderness鈥� is fast becoming outmoded. Lee Hannah at
Conservation International in Washington DC found that human activity has
displaced the natural habitat over two-thirds of the habitable surface of the
planet. Much of the undisturbed land is merely rock, ice and blowing sand,
already shunned by wildlife.
After habitat destruction, the biggest threat to biodiversity is invasion by
alien species. These have arrived mainly through trade, tourism and biocontrol.
Invasive plant species already cover 400,000 square kilometres of the US, and
are spreading at 12,000 square kilometres a year. At that rate, the whole of the
US will fall to outside species within 750 years.
Darwin鈥檚 laboratory, the Galapagos Islands, now has almost as many introduced
species as native ones.
Biodiversity is good for humans. By destroying it, we could bring the axe
down on our own heads. Rural communities in more than 60 countries get much of
their meat from wild animals. Overpopulation, famine and the spread of
high-powered rifles are killing off these creatures. In many areas local people
are going hungry. In the Congo basin, conflict has forced people to sell wild
meat, putting the squeeze on creatures such as large antelopes, gorillas and
chimpanzees. This bush meat trade is growing so fast it will soon be
unsustainable, warns Douglas Williamson of the UN Food and Agriculture
Organization.
Fewer species will mean fewer potential medicines. Three-quarters of the top
150 prescription drugs in the US are lab versions of chemicals found in plants,
fungi, bacteria and vertebrates. The WHO estimates that more than 60 per cent of
the world鈥檚 population relies on plants for primary healthcare. There are 3000
plant species used in birth control alone.
Even if we stop killing species today, nobody reading this will see wildlife
restored to its former glory, says Anne Weil of Duke University in North
Carolina. Weil and James Kirchner from the University of California, Berkeley,
carried out the first comprehensive analysis of mass extinctions and recoveries.
The dent already made in biodiversity will take 10 million years to repair
itself.