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Alien invaders, a global environment under attack
By Camille Feanny
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.
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.
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.
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."