Alien Invaders Aren't Just Science Fiction
According to The Nature Conservancy, about 4,000 species of nonindigenous plants and at least 2,300 species of nonnative animals now live in the United States. Also called "exotic," "alien," "introduced," and "invader" species, they are plants and animals that have been introduced to areas outside their natural habitats.
Why Introduced Species Can Make Trouble
Most people are aware of water and air pollution but have never given a thought to biological pollution, of which introduced species are a form. "Alien invasion is the least recognized threat to wildlife today," says David S. Wilcove, senior ecologist for the Environmental Defense Fund. "People don't realize that alien plant and animal species are everywhere, growing in our forests and grasslands, swimming in our lakes and rivers, and driving native species to the brink of extinction."
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