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Before You Read
Ask students: Do you know what the term invasive species means? Why do some insects and animals from outside the United States become a threat when they arrive in this country? What are some ways those species end up in the United States? Invasive species can also be plants; do you know of any nonnative plants in your community?
ecosystem--a group of plants, animals, and other living organisms that live together in the same area
native species--a plant or an animal that naturally lives in an area or region
* North America has 20 percent more plant species than it did before European colonization, biologists say.
* Ninety percent of immigrant species do no obvious harm to their new home environment.
* The Nature Conservancy estimates that 4,000 species of nonnative plants and 2,300 species of nonnative animals now live in the United States.
* Invasive species include everything from kudzu vines from Asia that is common in the South, to the West Nile virus, which comes from Africa. West Nile virus has been …