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			Where do Invasive Species Come From? Ecological Society of America 02.23.01 Some nonnative species have been deliberately introduced in the U.S.-nonnative plants, like kudzu, were introduced to control soil erosion; European birds were introduced to make colonists feel more at home; and game fish have been widely transferred to stock sport fisheries. Some agricultural crops and trees have escaped plantations and become pests, and the importation of agricultural and forestry products has brought assorted pest species and diseases into new areas. Nonnative ornamental plants are used in landscaping around homes and businesses. Many have moved into natural landscapes, some with significant ecological or economic impacts. Increased trade in unusual pets introduces an increasing variety of species which may escape or be released by owners. The aquarium trade is the source of a large number of aquatic species accidentally or intentionally released into waterways. Aquaculture has also increased the spread of fish and other aquatic species and associated diseases. Huge metal containers used in shipping goods via boat, train, and truck provide entry for seeds and small animals to new locales. Thousands of species of marine organisms were and are moved around the world on ship bottoms, and hundreds more have been moved globally by the wholesale transfer of edible oysters for "replanting." It is estimated that more than 10,000 marine species each day may hitch rides around the globe in the ballast water of cargo ships (see Aquatic Hitchhikers). Flooding can also transport nonnative aquatic and marsh species to new regions. Human activities have improved the odds for many nonindigenous species. A rapidly increasing human population has led to greater land disturbance which favors the spread of invasive species. Increased demand for food and fiber and overuse of public lands for recreation and commercial purposes have also contributed to nonnative invasions.


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