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Alien invaders, a global environment under attack
By Camille Feanny
CNN
Friday, December 31, 2004 Posted: 1730 GMT (0130 HKT)
ATLANTA,
Georgia (CNN) -- They're not from the sci-fi show "X-Files," but
scientists are sounding the alarm that aliens have invaded the planet.
A
recently updated report from the World Conservation Union (IUCN) titled
"100 of the World's Worst Invasive Alien Species" (Report: http://www.issg.org/booklet.pdf
)
warns that if left unchecked, these invasive species could eventually
destroy global biodiversity and irreversibly alter the health of the
natural environment.
Invasive, or alien species, are plants,
animals, or other organisms that have been introduced into an area
where they don't belong. Without natural predators to curb their
population, alien species pose real dangers to the long-term health of
the native ecosystems they inhabit.
Maj de Poorter, a scientist
with the IUCN's invasive species specialist group, says that
"worldwide, invasive species are the second biggest threat to any
native bio-diversity after habitat destruction."
Experts from the
World Bank also warn that introduced plant, animal and other species
now pose severe threats to the world's food supply.
Unwanted entry
The
transfer of invasive species into a region can be accidental, as was
the case with brown tree snakes in Guam. Native to Indonesia, the
snakes are believed to have initially arrived in the country by
hitching a ride aboard cargo vessels.
Biologists with the U.S.
Geological Survey (USGS) say the snakes have devoured a majority of the
bird, bat, and other native species on the island.
Other species
biologists consider noteworthy for their destructive potential and
difficulty to control are zebra mussels, that have stifled aquatic
systems, and cost millions of dollars in damage to the Mississippi
River Basin.
The Asian long-horned beetles have decimated many of
the maple, elm and other hardwood trees across the United States.
Experts suspect the insect came into the country in wood packing crates.
History
points to many "natural experiments" gone awry, and countless reports
highlight the substantial risks of using biological control methods to
rid an area of a problem species; decisions that proved to create much
larger environmental problems than they were enlisted to solve.
The
Indian mongoose, for example, was initially introduced to the Caribbean
islands to control the rodent population on sugar cane plantations. In
time, their varied diet of birds, insects, reptiles, fish and fruit
wrought havoc on the region's sensitive bio-diversity, and led to the
extinction of several species throughout the region.
Costly decisions
Biologists
from the IUCN and other organizations assert that a major contributor
to the spread of invasive species was the result of the robust
international trade in ornamental plants and exotic pets.
Unwanted animals and plants that were released into the wild have virtually crippled some ecosystems around the globe.
Wildlife
officials in Everglades National Park in Florida have reported that
Burmese pythons have been found throughout the area, and could pose a
threat to local species. They suspect the original snake was a former
pet that was released into the park. But new hatchlings recovered by
rangers reveal that the reptiles are making a home in south Florida
waters.
Feral pigs, introduced to nations around the world, now
spread disease, damage crops, and devour native animals with wild
abandon.
Caluerpa Taxifolia, found mostly in private aquariums
around the world, has smothered vast areas of native aquatic vegetation
throughout the Mediterranean, and has now been found in the waters off
southern California. Researchers say that as the algae becomes
established in various regions, it continues to cause massive economic
and environmental damage.
South American Water Hyacinth, popular
in backyard ponds for its large violet flowers -- is choking the life
out of waterways in more than 50 countries on five continents, the IUCN
reports.
Natural causes
Although
scientists from the IUCN and other organizations say the global trade
of animals and plants is a principal reason that invasive species "hot
spots" can now be found all around the world, it is not the only cause.
Degradation
and weakening of the natural habitat, the explosive rise in
international travel and tourism, and the current global marketplace
give safe passage to diverse organisms eager to hitch daily rides from
country to country.
A 2001 IUCN report indicates that "North
American nursery catalogs [alone] offer nearly 60,000 plant species to
a global market."
Other reports show that the trafficking of
species for medicinal, personal, or professional uses accounts for the
transfer of thousands of species, that involve almost every nation on
the planet.
Counting the losses
Around
the globe, the urgency to stem the spread of invasive species is a top
priority that is costing countries dearly in lost crops, lowered
property values, endangered ecosystems, and in the development of
countless control programs.
Scientists scour the world armed with research as they experiment with toxins and traps. And still there is no end in sight.
According
to the 2001 IUCN report, the economic costs to humans, plants and
animals in the United States alone exceeds $130 billion per year, with
billions more being spent worldwide.
"In addition to being very
detrimental to biodiversity, the invasive species also do a lot of
economic damage," says de Poorter. "If you look at some species that
affect the rice industries in the Philippines, where the golden apple
snail has been introduced, so far the cumulative impact there has been
more than billions of dollars."
Scientists from the IUCN say that
while their list includes 100 significant alien species, there are
others that deserve to be mentioned. "There are many, many more
damaging invasive species which are not on the list. The reason why we
pick a hundred of them is to really get across to people how much
variety there is in the species," de Poorter says.
Experts
caution that as larger numbers of species span the continental divide,
more effort is needed to keep invasive species from taking hold. They
say that international cooperation and collaboration is a critical step
toward achieving this goal.
"There are many ways to fight back
against the problem of invasives," says de Poorter. "It can't be
stressed how important it is to do something about the invasive species
you already have, as well as prevent more from coming in."
