Introduced species

An introduced species, alien species, exotic species, adventive species, immigrant species, foreign 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, directly or indirectly, and either deliberately or accidentally. Non-native species can have various effects on the local ecosystem. Introduced species that become established and spread beyond the place of introduction are considered naturalized. The process of human-caused introduction is distinguished from biological colonization, in which species spread to new areas through "natural" (non-human) means such as storms and rafting. The Latin expression neobiota captures the characteristic that these species are new biota to their environment in terms of established biological network (e.g. food web) relationships. Neobiota can further be divided into neozoa (also: neozoons, sing. neozoon, i.e. animals) and neophyta (plants). The impact of introduced species is highly variable. Some have a substantial negative effect on a local ecosystem (in which case they are also classified more specifically as an invasive species), while other introduced species may have little or no negative impact (no invasiveness), integrate well into the ecosystem they have been introduced to, and are generally not considered to be invasive. 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. The effects of introduced species on natural environments have gained much scrutiny from scientists, governments, farmers and others.

Terminology 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". 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 means that species growing in a garden, farm, or house may not meet the criteria unless they escape and persist.

Subset descriptions A wide range of terms is used to describe specific subsets or categories of introduced species, and the terminology continues to evolve for conceptual and practical reasons. Common examples include "invasive", "acclimatized", "adventive", "naturalized", and "immigrant" species. The term "invasive" refers to introduced species that cause ecological, economic, or other forms of damage within the area to which they have been introduced. Acclimatized species are introduced taxa that have undergone physical and/or behavioural changes that allow them to adjust to the new environment. Such species are not necessarily optimally adapted, but have characteristics sufficient for survival under the new conditions. Adventive species are often treated as synonymous with "introduced species", although the term is sometimes used specifically for introduced species that are not yet permanently established. Naturalized species are typically introduced species that can reproduce and maintain self-sustaining populations outside their native range without ongoing human assistance (i.e. they are no longer adventive). The term can also apply to populations that have migrated and become established in a novel environment without direct human introduction; for example, in Europe, house sparrow populations have been well established since the early Iron Age despite originating in Asia. Immigrant species are species that move between habitats, sometimes under their own power but often with unintentional human assistance. Invasiveness is not implied or required.

Invasive species

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