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Ecosystems under threat: Invasion of the alien species Whether by accident

or design, humankind has been responsible for the creation of monsters right

across the world. Some are big, some are small - but all of them are scary.

Steve Connor reports Published: 10 November 2006 **

 

*One of the greatest threats to the world's biodiversity - the richness of

its wildlife - is the spread of alien species that have been deliberately or

unwittingly introduced into new habitats where they can thrive. *

 

*In many ways, the movements of plants and animals around the world by human

activity has been an inevitable consequence of the globalised economy in

which we now live. Without such movement, we would not enjoy many of the

benefits of modern life - but the consequences have been severe for fragile

ecosystems.*

 

*What makes an alien species able to invade and then damage the biodiversity

of its new home ultimately comes down to its ability to outperform resident

lifeforms. Alien animals and plants become invasive and damaging because

they can grow faster, breed more profusely, disperse more widely, tolerate a

wider range of conditions or simply grow bigger than the resident species of

the invaded ecosystem.*

 

*But of course, there is another factor at work in deciding whether an

introduced species becomes invasive. It is whether the animal or plant in

question is able to form some sort of close association with man - arguably

the most destructive invasive species on earth. After all, the oldest

invasive species are the animals and plants that have been either

domesticated by humans for many centuries, or, in the case of the mouse and

rat, have lived in close proximity to man.*

 

*Cats, pigs and goats are especially destructive when introduced into remote

islands, such as the Galapagos. Distant islands are vulnerable because life

on them has evolved largely in isolation from the rest of the terrestrial

world. The consensus is that island species tend to be naïve in terms of

Darwinian competitiveness, having not been subjected to intense competition.

*

 

*Islands exist on land as well, if you are a fish. Lake Victoria in Africa

has been largely isolated from the rest of the aquatic world for thousands

of years, which accounted for the 400 or so species of cichlid fish that had

evolved there. It was the deliberate introduction of the Nile perch that

abruptly upset a fine balance. The perch has eaten its way through half of

the 400 or so species of indigenous cichlids.*

 

*Giant African snails Barbados*

 

*Snails are rarely regarded as the most agile of creatures but one species,

the giant African snail, has proved to be a remarkably intrepid traveller.

Originally from east Africa, this large gastropod has turned up in countries

as far apart as Thailand and Brazil. Most recently it sneaked into the

Caribbean island of Barbados, probably on a cargo ship, much to the

consternation of local farmers who say it is wreaking havoc on the local

cane-sugar and banana crops.*

 

*The secret of the giant African snail's ability to travel lies in the

peculiar way it incubates inside its shell during food shortages, known as

aestivation. The snail can incubate for years until the moist, warm

conditions it favours return. Tourists to east Africa have often picked up

seemingly empty shells and taken them back to their country, not knowing

that once warm the snail will emerge from its shell, feeling particularly

hungry.*

 

*Cane toad Australia*

 

*In 1935, 100 cane toads were introduced to Australia following reports

about their role in controlling beetles in the sugar cane fields of central

and South America. They quickly multiplied and now number more than 100

million - their leathery skin and high-pitched mating call can be seen and

heard across New South Wales and the Northern Territory. However, the

voracious appetite and ducts full of poisonous bile that make the cane toad

such an effective predator have had a disastrous effect on indigenous fauna

in Australia. A Northern Territory politician sparked controversy last year

when he said a cricket bat was the best weapon against the toads. Animal

rights groups were aghast, instead recommending they be frozen. Meanwhile,

Western Australia has " active control and management " plans to stop the

toads crossing the border. An ingenious entrepreneur is now selling assorted

cane toad leather products, including purses, mobile phone cases and caps

via the internet.*

 

*Tiger mosquito Spain*

 

*The aggressive Asian tiger mosquito that invaded Spain two years ago has

established itself in Barcelona where it is " spreading like an oil slick "

and set to expand throughout the country, scientists warned yesterday. Aedes

albopictus, 5mm long, with a white-striped body, long legs and vicious

sting, " cannot be eradicated " , admits Roger Eritja, a biologist from

Barcelona's Mosquito Control Service. The creature travels by hiding under

car seats, an ideal cool and sheltered habitat and at the end of its journey

it seeks pools of stagnant water. Such haunts are the perfect humid habitat

for eggs to grow into larvae and pupae, a process that takes about a week.

Old tyres are a favourite incubation site, and a Barcelona tyre-recycling

company was recently found to be infested. Catalans are being urged to

discard containers that might harbour stagnant rainwater. But scientists

warn that only the country's desert regions are likely to escape the plague.

*

 

*Nomura's jellyfish Japan*

 

*They look more like something out of Doctor Who than the jellyfish seen in

European waters. But since last year Japan's coastline was invaded by the

massive sea creatures which can grow up to 6.5 feet (2 metres) wide and

weigh up to 450lb (220kg). The creatures, which are normally found further

south in the waters off China and Korea, have caused problems with local

fishermen by clogging their nets and poisoning their catches. One theory is

that the plague has been caused by heavy rains which swept the giants from

China's Yangtze river delta to Japan, but others believe that, because of

global warming, seas have been warmed and are better suited for breeding

jellyfish. In addition to this, scientists blame over-fishing of natural

predators that feed on jellyfish and pollution along the continent's coasts.

Human injury is rare but a few unlucky swimmers have been killed.*

 

*Yellowjackets America*

 

*For a long time, the name yellowjackets referred simply to Ohio's state

basketball team. Now the mere mention of the insects is enough to bring

Americans out in goosepimples. Giant yellowjackets, or German wasps (Vespula

germanica), introduced by early European settlers, are invading the Deep

South. In previous years, nests have been rarely larger than a basketball,

but this new strain of yellowjackets are so adept at home improvements that

nests the size of a Chevrolet, above, have been found. The largest nest to

date was found in Alabama this summer. At first no bigger than a car tyre,

seven weeks later, it had expanded to the size of the barn. Such a nest

would house as many as 100,000 workers plus multiple queens. Mild winters

are blamed.*

 

*Nile perch Africa*

 

*The introduction of the Nile perch to Lake Victoria in the 1950s has become

an ecological cautionary tale, after the silver- skinned predator decimated

hundreds of native fish species. Best chronicled in the award-winning

documentary Darwin's Nightmare, the perch has stimulated a fishing industry

worth more than £100m a year, but the arrival of cash and regular flights

prompted an arms industry that has spread conflict within the region. The

Nile perch (Lates niloticus), a species of freshwater fish in the

Centropomidae family, is now found in Lake Chad, Congo, the Nile, Senegal,

Volta, Lake Turkana and other river basins, but overfishing has driven

stocks in Lake Victoria low enough for native species to make a comeback.*

 

*Water hyacinth Africa and Asia*

 

*Water hyacinth (Eichhornia crassipes) has caused havoc in more than 50

countries since being exported by Brazilian horticulturists in the late 19th

century, initially to Africa and then Asia. The floating weeds, which

flourish on tropical lakes and waterways, have one of the highest growth

rates of any plant in the world and are able to double their population in

just 12 days. Vast blankets of hyacinth starve the water below of oxygen and

sunlight, decimating fish stocks. The thick, tightly entwined mats render

shipping all but impossible and governments around the world have spent vast

sums of money trying to control the weed with varying degrees of success.

One of the most effective and inexpensive ways has been to introduce

hyacinth-eating weevils.*

 

*Harlequin ladybird United Kingdom*

 

*First introduced to North America from Asia to control plant pests, the

harlequin ladybird made its British debut in September 2004 and has since

established colonies in Derby and the South-east of England. Harlequins are

such effective aphid predators that they pose a serious threat to the

survival of Britain's 46 resident species of ladybird. With a longer

reproductive period than other species, their larvae can be found as late as

October, long after most other ladybird species have gone into hibernation.

Their propensity to tuck into grapes has caused havoc in French vineyards.

The rotund brown-legged specimen is easily recognisable by its colour; it is

most commonly orange with 15 to 21 black spots or black with two large red

spots. *