|
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. Some have a negative effect on a local ecosystem. Some 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.〔Dov Sax, Aug 2008. (The Proceedings of the National Academy of Sciences )〕 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. == Terminology == The terminology associated with introduced species is now in flux for various reasons. Other terms with somewhat similar meanings) with ''introduced'' are ''acclimatized'', ''adventive'', ''naturalized'', and ''immigrant'' but those terms refer to a subset of introduced species: those that have become established and can reproduce without human assistance. The term invasive refers only to those species that become established and spread beyond the place of introduction. For practical purposes, this term is applied only to invasive species that cause damage. 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,"〔Carlton, James T. 2002. ''Introduced Species in U.S. Coastal Waters''. Pew Oceans Commission.〕 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 (EPA), although perhaps lacking ecological sophistication, is more typical: ''introduced species'' "A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species."〔U.S. Environmental Protection Agency. Mid-Atlantic Integrated Assessment. September 16, 2003. Introduced species. Web site at (US EPA )〕 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 they are called "invasive". The transition from introduction, to establishment and to invasion has been described in the context of plants.〔(Richardson et al. 2000 )〕 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,〔(biodiversity ) 〕 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.〔(Colautti and MacIsaac 2004 )〕 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".〔CEQ (1999). Web site page with (Executive Order 13112 ) text.〕 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,〔 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 〔2013. Invasive Species Program. Clemson University - DPI. http://www.clemson.edu/public/regulatory/plant_industry/invasive_exotic_programs/. Accessed 24 May 2013.〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「introduced species」の詳細全文を読む スポンサード リンク
|