Exotic Introductions

Exotic species are organisms introduced into habitats where they are not native, are severe world-wide agents of habitat alteration and degradation. A major cause of biological diversity loss throughout the world, they are considered biological pollutants.

Introducing species accidentally or intentionally, from one habitat into another, is risky business. Freed from the predators, parasites, pathogens, and competitors that have kept their numbers in check, species introduced into new habitats often overrun their new home and crowd out native species. In the presence of enough food and a favorable environment, their numbers will explode. Once established, exotics rarely can be eliminated.

Most species introductions are the work of humans. Some introductions, such as carp and purple loosestrife, are intentional and do unexpected damage. But many exotic introductions are accidental. The species are carried in on animals, vehicles, ships, commercial goods, produce, and even clothing. Some exotic introductions are ecologically harmless and some are beneficial. But other exotic introductions are harmful to recreation and ecosystems. They have even caused the extinction of native species — especially those of confined habitats such as islands and aquatic ecosystems.

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