Introduced Species - Terminology

Terminology

The terminology associated with introduced species is presently in flux for a variety of reasons. Other terms that are used sometimes interchangeably (having the same or similar meanings) with introduced are acclimatized, adventive, naturalized, immigrant, and xenobiotic. Nonetheless, distinctions can and should be made between some of these terms.

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", which removes from consideration as introduced all of those species 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.

The following definition from the United States Environmental Protection Agency, although perhaps lacking ecological sophistication, is more typical: introduced species are .."pecies that have become able to survive and reproduce outside the habitats where they evolved or spread naturally". However, introduction of a species outside its native range is often all that is required to be qualified as an "introduced species" such that one can distinguish between introduced species that may only occur in cultivation, under domestication or captivity whereas other become established outside their native range and reproduce without human assistance. Such species might be termed "naturalized", "established", "wild non-native species", or "invasive". The transition from introduction, to establishment and invasion has been described by in the context of plants. Introduced species are essentially "non-native" species. Invasive species are those introduced species that spread-widely or quickly, and cause harm, be that to the environment, 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.

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".

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

From a regulatory perspective, it is neither desirable nor practical to simply 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.

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

*Not listed in any "official" source as a pest species.