From the UK Independent, by By Mark Rowe
Rare plants and creatures face extinction as vigorous invaders devour everything in their path, conservationists warn
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Scientists have identified the world's 100 deadliest invasive species, which
are responsible for the extinction of hundreds of other species and causing
havoc to ecosystems and the birds and mammals that inhabit them. Fish, ants,
snails and even seaweed are named for their aggressive growth, biological
pollution and catastrophic impact on habitats around the world.
The species are published in a new and updated booklet compiled by the World
Conservation Union (IUCN), one of the world's leading conservation agencies.
It will be distributed this week at the IUCN's world conservation congress
in Bangkok, where delegates will be warned of the urgent need to curb
invasive species or face a world where only "hardened survivors" such as
pigeons exist, at the expense of parrots and other exotic creatures.
Among the leading culprits in the booklet, entitled One Hundred of the
World's Worst Species, is the Nile perch, which has contributed to the
extinction of more than 200 endemic fish species in Africa by eating not
only their food but also the fish themselves. Another is caulerpa, a seaweed
in the Mediterranean that smothers the beds of native sea grass which act as
nurseries for many species. The IUCN considers caulerpa to be a threat to
the whole of the Mediterranean.
Many invasive species initially appear benign: the water hyacinth's large
purple and violet flowers make it a popular ornamental plant for ponds but
it is fast-growing and can quickly block waterways, limiting boat traffic,
swimming and fishing.
Britain also has its share of invasives in the booklet, including Japanese
knotweed, the grey squirrel and Dutch elm disease. Even the humble domestic
cat takes its place in the list, for its role in killing both familiar
garden birds in the developed world and exotic bird species further afield.
An invasive species is an animal or plant that has been taken from its
native habitat and introduced to another area. Though the international
trade in species is responsible for many invasives, some instances can be
accidental. Caulerpa is believed to have been emptied into the Mediterranean
as waste from the Monaco aquarium. On other occasions it is deliberate:
rabbits and stoats were introduced to New Zealand in the 19th century with
catastrophic results. Birds in New Zealand had evolved for millions of years
without predators and many had lost the need to fly: several species,
including the kakapo, a flightless parrot, and the yellowed- eyed penguin,
the world's rarest penguin, have been brought to the point of extinction by
stoats and feral cats.
Invasives are invariably aggressive and hardened to their new habitat. "This
booklet really spells out what the dangers and impacts are," said Dr Maj de
Poorter, co-ordinator of the IUCN's invasive species specialist group.
"Invasives are taken out of the ecosystem that evolved with them and put in
a new ecosystem which may have none of the tough predators or pests they
evolved to fight. The ecosystem into which they are introduced has never had
a need to deal with them. In New Zealand, nothing had evolved to cope with
stoats."
But invasive plants and animals have wider implications for humans and the
planet, according to Jeffrey McNeely, the IUCN's chief scientist. "Climate
change is altering our ecosystems at a great pace." he said. " Invasive
species adapt to new and quick-changing environments and so they are likely
to respond most quickly to climate change. Our biodiversity is going to
become homogenised and the richness of our planet will be lost.
"Do we want pigeons or parrots? People like diversity, they like lots of
flowers in their garden. In the end, it's a matter of how we want to live."
The 10 most destructive
1 Nile perch: introduced to Lake Victoria, Africa, in 1954 to counteract the
drastic drop in native fish stocks caused by over-fishing. Instead, it has
contributed to the extinction of more than 200 endemic fish species through
predation and competition for food.
2 Water hyacinth: this South American native is one of the most insidious
aquatic weeds in the world. Its flowers make it a popular ornamental plant
for ponds but it is now found in more than 50 countries on five continents,
infesting waterways and making fishing impossible.
3 Caulerpa: introduced to the Mediterranean around 1984, it is thought, as
waste from the Monaco aquarium. Hardier than most tropical seaweeds, it has
adapted well to cold waters and smothers habitats.
4 Crazy ant: so named because of their frenetic movements, crazy ants have
invaded native ecosystems and caused environmental damage from Hawaii to the
Seychelles and Zanzibar. On Christmas Island in the Indian Ocean they have
formed supercolonies in all habitats of the rainforest.
5 Small Indian mongoose: this voracious and opportunistic predator is native
to areas as widespread as Iran and the Malay Peninsula. It was introduced to
Mauritius, Fiji, the West Indies and Hawaii to control rats but has caused
the local extinction of endemic birds, reptiles and amphibians.
6 Feral pig: introduced to many parts of the world, it damages crops, stock
and property and transmits many diseases such as leptospirosis and foot and
mouth. Diet includes juvenile land tortoises, sea turtles and sea birds.
7 Dutch elm disease: deadly fungus, spread by the elm bark beetle, which can
kill an elm in three weeks by clogging its water-conducting vessels. Spread
in the UK in 1968 from imported Canadian timber to deadly effect, killing
more than a third of southern England's 23 million elms.
8 Grey squirrel: the American grey has devastated Britain's native
population of red squirrels, which are barely half the size. First appeared
in the English countryside between 1876 and 1929, possibly after having been accidentally released from London Zoo.
9 Japanese knotweed: introduced from Asia to Europe in the mid-19th century
as an ornamental and fodder plant. Grows rapidly, prevents native seeds from
germinating and thrives on being uprooted - can even regrow after being
rooted out and washed downstream.
10 Giant African snail: introduced to the islands of the Pacific and Indian
oceans as a food source for humans but has a voracious appetite and has been
recorded as attacking more than 500 different kinds of plants. Has spread to
parts of South America. Tropical in origin, but copes comfortably with snow
at other latitudes.
