Introduced species

Cattle Bos primigenius taurus introduced worldwide
Sweet clover (Melilotus sp.), introduced and naturalized to the Americas from Europe as a forage and cover crop.

An introduced species (alien species, exotic species, non-indigenous species, or non-native species) is a species living outside its native distributional range, but 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.[1]

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

Terminology: introduced species and subsets

The formal definition of an introduced species, from the United States Environmental Protection Agency, is A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species.[2]

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:

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.
Adventive species
Naturalized species (plants): A naturalized plant species refers to a non-native plant that does not need human help to reproduce and maintain its population in an area that it is not native to.

General description of introduced species:

In the broadest and most widely used sense, an introduced species is synonymous with non-native and therefore applies as well to most garden and farm organisms; these adequately fit the basic definition given above. However, some sources add to that basic definition "and are now reproducing in the wild",[3] which removes from consideration as introduced species that were raised or grown in gardens or farms that do not survive without tending by people. With respect to plants, these latter are in this case defined as either ornamental or cultivated plants.

Invasive species

Introduction of a species outside its native range is all that is required to be qualified as an "introduced species" such that one can distinguish between introduced species that may not occur except in cultivation, under domestication or captivity whereas others become established outside their native range and reproduce without human assistance. Such species might be termed "naturalized", "established", "wild non-native species". If they further spread beyond the place of introduction and cause damage to nearby species, they are called "invasive". The transition from introduction, to establishment and to invasion has been described in the context of plants.[4] Introduced species are essentially "non-native" species. Invasive species are those introduced species that spreadwidely or quickly and cause harm, be that to the environment,[5] human health, other valued resources or the economy. There have been calls from scientists to consider a species "invasive" only in terms of their spread and reproduction rather than the harm they may cause.[6]

According to a practical definition, an invasive species is one that has been introduced and become a pest in its new location, spreading (invading) by natural means. The term is used to imply both a sense of urgency and actual or potential harm. For example, U.S. Executive Order 13112 (1999) defines "invasive species" as "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health".[7] The biological definition of invasive species, on the other hand, makes no reference to the harm they may cause, only to the fact that they spread beyond the area of original introduction.

Although some argue that "invasive" is a loaded word and harm is difficult to define,[3] the fact of the matter is that organisms have and continue to be introduced to areas in which they are not native, sometimes with but usually without much regard to the harm that could result.

From a regulatory perspective, it is neither desirable nor practical to list as undesirable or outright ban all non-native species (although the State of Hawaii has adopted an approach that comes close to this). Regulations require a definitional distinction between non-natives that are deemed especially onerous and all others. Introduced pest species that are officially listed as invasive, best fit the definition of an invasive species. Early detection and rapid response is the most effective strategy for regulating a pest species and reducing economic and environmental impacts of an introduction [8]

In Great Britain, the Wildlife and Countryside Act 1981 prevents the introduction of any animal not naturally occurring in the wild or any of a list of both animals or plants introduced previously and proved to be invasive.

Other Languages
Alemannisch: Neobiota
العربية: نوع مستقدم
asturianu: Especie invasora
bosanski: Uvedena vrsta
čeština: Nepůvodní druh
Deutsch: Neobiota
eesti: Võõrliik
Frysk: Eksoat
한국어: 도입종
Bahasa Indonesia: Spesies pendatang
қазақша: Интродукция
Kreyòl ayisyen: Espès egzotik
Lëtzebuergesch: Neobiota
Nederlands: Exoot
日本語: 帰化植物
norsk nynorsk: Framande artar
Plattdüütsch: Neobiota
polski: Introdukcja
Seeltersk: Neobiota
Simple English: Introduced species
slovenčina: Nepôvodný druh
slovenščina: Alohtona vrsta
srpskohrvatski / српскохрватски: Introducirane vrste
suomi: Vieraslaji
Türkçe: Egzotik tür
Tiếng Việt: Loài du nhập
中文: 外來物種