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" 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 relationships. Neobiota can further be divided into neozoa and neophyta.
The impact of introduced species is highly variable. Some have a substantial negative effect on a local ecosystem, while other introduced species may have little or no negative impact, 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. 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
Introduction of a species outside its native range is all that is required to be qualified as an "introduced species". Such species might be termed naturalized, "established", or "wild non-native species". If they further spread beyond the place of introduction and cause damage to nearby species, they are called "invasive species". The transition from introduction, to establishment and to invasion has been described 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.According to a practical definition, an invasive species is one that has been introduced and become a pest in its new location, spreading 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 defines "invasive species" as "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health". 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.
From a regulatory perspective, it is neither desirable nor practical to list as undesirable or outright ban all non-native species. 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. Management of invasion pathways are on the forefront of eliminating unwanted invasive species this would include preliminary steps; educating the public, cooperation from industries and government resources.
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.
Nature of introductions
By definition, a species is considered "introduced" when its transport into an area outside of its native range is human mediated. Introductions by humans can be described as either intentional or accidental. Intentional introductions have been motivated by individuals or groups who either: believe that the newly introduced species will be in some way beneficial to humans in its new location or, species are introduced intentionally but with no regard to the potential impact. Unintentional or accidental introductions are most often a byproduct of human movements and are thus unbound to human motivations. Subsequent range expansion of introduced species may or may not involve human activity.File:Wheat-haHula-ISRAEL.JPG|thumb|Wheat Triticum introduced worldwide from its place of origin
Intentional introductions
Species that humans intentionally transport to new regions can subsequently become successfully established in two ways. In the first case, organisms are purposely released for establishment in the wild. It is sometimes difficult to predict whether a species will become established upon release, and if not initially successful, humans have made repeated introductions to improve the probability that the species will survive and eventually reproduce in the wild. In these cases, it is clear that the introduction is directly facilitated by human desires.Image:Male Silver Pheasant.jpg|thumb|Male silver pheasant
In the second case, species intentionally transported into a new region may escape from captive or cultivated populations and subsequently establish independent breeding populations. Escaped organisms are included in this category because their initial transport to a new region is human motivated.
The widespread phenomena of intentional introduction has also been described as biological globalization.
Positive Introductions
Although most introduced species have negative impacts on the ecosystems they enter into, there are still some species that have affected the ecosystem in a positive way. For example, in New Hampshire invasive plants can provide some benefits to some species. Invasive species such as autumn olive, oriental bittersweet, and honeysuckle produce fruit that is used by a handful of fruit-eating bird species. The invasive plants can also be a source of pollen and nectar for many insects, such as bees. These invasive plants were able to help their ecosystem thriving, and increase the native animal's chances of survival. Several introduced exotic trees served as nest sites for resident waterbird species in Udaipur city, India.
Motivations for intentional introductions
Economic
Perhaps the most common motivation for introducing a species into a new place is that of economic gain. Non-native species can become such a common part of an environment, culture, and even diet that little thought is given to their geographic origin. For example, soybeans, kiwi fruit, wheat, honey bees, and all livestock except the American bison and the turkey are non-native species to North America. Collectively, non-native crops and livestock account for 98% of US food. These and other benefits from non-natives are so vast that, according to the Congressional Research Service, they probably exceed the costs.Other examples of species introduced for the purposes of benefiting agriculture, aquaculture or other economic activities are widespread. Eurasian carp was first introduced to the United States as a potential food source. The apple snail was released in Southeast Asia with the intent that it be used as a protein source, and subsequently to places like Hawaii to establish a food industry. In Alaska, foxes were introduced to many islands to create new populations for the fur trade. About twenty species of African and European dung beetles have established themselves in Australia after deliberate introduction by the Australian Dung Beetle Project in an effort to reduce the impact of livestock manure. The timber industry promoted the introduction of Monterey pine from California to Australia and New Zealand as a commercial timber crop. These examples represent only a small subsample of species that have been moved by humans for economic interests.
The rise in the use of genetically modified organisms has added another potential economic advantage to introducing new/modified species into different environments. Companies such as Monsanto that earn much of their profit through the selling of genetically modified seeds has added to the controversy surrounding introduced species. The effect of genetically modified organisms varies from organism to organism and is still being researched today, however, the rise of genetically modified organisms has added complexity to the conversations surrounding introduced species.