About Invasive Species
What are Invasive Species?
The Federal Executive Order on Invasive Species defines an invasive species as "an alien species (plant, animal, insect, bacteria, and fungi) whose introduction does or is likely to cause economic or environmental harm or harm to human health". In turn, an alien species is defined with respect to a particular ecosystem and is considered any species "that is not native to that ecosystem" (Executive Order 13112, 1999). Alien species are also known as exotic, non-native, or introduced, however the term alien also applies to native species outside their natural range or ecological boundaries. The terms noxious, nuisance, or invasive characterize alien species when these organisms cause harm.
Since the time of settlement, plants, animals, and other organisms have traveled to places far beyond their likely natural dispersal ranges. The vast majority of these species transported to a place other than their native ecosystem, whether intentionally or accidentally, do not survive. Of those that do survive, scientists estimate that approximately 15% go on to become very harmful (OTA, 1993). The species that become invasive do succeed, in part, because the new ecosystem in which they find themselves offer favorable environmental conditions and lack the natural predators, competitors, and diseases that would normally keep their populations in check.
Invasive species are a significant threat to nearly half of the native US species currently listed under the federal Endangered Species Act (Wilcove et al, 1998). The cost of preventing, monitoring, and controlling invasive species in the United States, not to mention the costs of damage to crops, fisheries, forest, and other resources, are huge. The economic impact of invasive plants, alone, amount to $13 billion per year (Westbrooks, 1998).
Negative Effects of Invasives
The negative effects of invasive species on natural and managed ecosystems may be felt through one or more of the following:
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