Introduced species (also called invasive species) are those that have been released by humans into an area to which they are not native. These releases can occur accidently, from places such as the cargo holds of ships. They can also occur intentionally, and species have been introduced for a range of ornamental and recreational uses, as well as for agricultural, medicinal, and pest control purposes.

Introduced species can have dramatically unpredictable effects on the environment and native species. Such effects can include overabundance of the introduced species, competitive displacement, and disease-caused mortality of the native species. Numerous examples of adverse consequences associated with the accidental release of species or the long term effects of deliberately introduced species exist in the United States and around the world. Introduced species can be beneficial as long as they are carefully regulated. Almost all the major varieties of grain and...