Alien (biology)

An introduced, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its native distributional range, which has arrived there by human activity, either deliberate or accidental. Non-native species can have various effects on the local ecosystem. Introduced species that become established and spread beyond the place of introduction are called invasive species. The impact of introduced species is highly variable. Some have a negative effect on a local ecosystem, while other introduced species may have no negative effect or only minor impact. Some species have been introduced intentionally to combat pests. They are called biocontrols and may be regarded as beneficial as an alternative to pesticides in agriculture for example. In some instances the potential for being beneficial or detrimental in the long run remains unknown. A list of some introduced species is given in a separate article.

The effects of introduced species on natural environments have gained much scrutiny from scientists, governments, farmers and others.

Formal definition from the United States Environmental Protection Agency: A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species."

There are many terms associated with introduced species that represent subsets of introduced species, and the terminology associated with introduced species is now in flux for various reasons. Examples of these terms are acclimatized, adventive, naturalized, and immigrant species but those terms refer to a subset of introduced species. The term "invasive" is used to describe introduced species when the introduced species causes substantial damage to the area in which it was introduced.

Subset descriptions:

1.Acclimatized species: Introduced species that have changed physically and/or behaviorally in order to adjust to their new environment. Acclimatized species are not necessarily optimally adjusted to their new environment and may just be physically/behaviorally sufficient for the new environment.

2.Adventive Species

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