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An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
living outside its
native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...
distributional range, but which has arrived there by
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
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 Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the in ...
. 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 Rafting and whitewater rafting are recreational outdoor activities which use an inflatable raft to navigate a river or other body of water. This is often done on whitewater or different degrees of rough water. Dealing with risk is often a ...
. 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 A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
) 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 An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
), while other introduced species may have little or no negative impact (no invasiveness). Some species have been introduced intentionally to combat pests. They are called
biocontrol Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also in ...
s 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: introduced species and subsets

The formal definition of an introduced species from the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
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

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 "invasive", "acclimatized", "adventive", "naturalized", and "immigrant" species. The term "invasive" is used to describe introduced species that cause ecological, economic, or other damage to the area in which they were introduced. Acclimatized species are 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 are often considered synonymous with "introduced species", but this term is sometimes applied exclusively to introduced species that are not permanently established.
Naturalized species Naturalisation (or naturalization) is the ecological phenomenon through which a species, taxon, or population of exotic (as opposed to native) origin integrates into a given ecosystem, becoming capable of reproducing and growing in it, and proce ...
are often introduced species that do not need human help to reproduce and maintain their population in an area outside their native range (no longer adventive), but that also applies to populations migrating and establishing in a novel environment (e.g.: in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
house sparrow The house sparrow (''Passer domesticus'') is a bird of the Old World sparrow, sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale ...
s are well established since early
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age ( Paleolithic, Mesolithic, Neolithic) and the Bronze Age ( Chalcolithic). The concept has been mostly ...
though they originated from
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
). Immigrant species are species that travel, sometimes by themselves, but often with human help, between two habitats. Invasiveness is not a requirement.


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 Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the in ...
, "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 An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
". 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 (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". 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. Some argue that "invasive" is a loaded word and harm is difficult to define. 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 Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
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. In
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It ...
, the
Wildlife and Countryside Act 1981 The Wildlife and Countryside Act 1981 is an Act of Parliament in the United Kingdom implemented to comply with European Council Directive 79/409/EEC on the conservation of wild birds. In short, the act gives protection to native species (especia ...
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 definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories: intensional definitions (which try to give the sense of a term), and extensional definiti ...
, 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 (1) believe that the newly introduced species will be in some way beneficial to humans in its new location or, (2) 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.


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. 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 Biological globalization refers to the phenomenon where domesticated species are brought and cultivated in other favorable environments, facilitated by and for the benefit of humans. It has been defined as "the spread of plants domesticated in one ...
. 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.


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,
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu ...
s, kiwi fruit,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
honey bees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...
, and all
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to ani ...
except the
American bison The American bison (''Bison bison'') is a species of bison native to North America. Sometimes colloquially referred to as American buffalo or simply buffalo (a different clade of bovine), it is one of two extant species of bison, alongside the ...
and the
turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
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 Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
,
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
or other economic activities are widespread.
Eurasian carp The Eurasian carp or European carp (''Cyprinus carpio''), widely known as the common carp, is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia.Fishbase''Cyprinus carpio'' Linnaeus, 1758/ref>Arkive The ...
was first introduced to the United States as a potential food source. The
apple snail Ampullariidae, commonly known as the apple snails, is a family of large freshwater snails, aquatic gastropod mollusks with a gill and an operculum. These snails simultaneously have a gill and a lung as functional respiratory structures, which ...
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 Dung beetles are beetles that feed on feces. Some species of dung beetles can bury dung 250 times their own mass in one night. Many dung beetles, known as ''rollers'', roll dung into round balls, which are used as a food source or breeding cha ...
have established themselves in Australia after deliberate introduction by the
Australian Dung Beetle Project The Australian Dung Beetle Project (1965–1985), conceived and led by Dr George Bornemissza of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), was an international scientific research and biological control project with ...
in an effort to reduce the impact of livestock manure. The timber industry promoted the introduction of Monterey pine ('' Pinus radiata'') 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 organism A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. The exact definition of a genetically modified organism and what constitutes genetic engineering varies, wit ...
s has added another potential economic advantage to introducing new/modified species into different environments. Companies such as
Monsanto The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best known product is Roundup, a glyphosate-based herbicide, developed in ...
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.


= Human enjoyment

= Introductions have also been important in supporting recreation activities or otherwise increasing human enjoyment. Numerous fish and game animals have been introduced for the purposes of sport fishing and hunting. The introduced amphibian (''
Ambystoma tigrinum The tiger salamander (''Ambystoma tigrinum'') is a species of mole salamander and one of the largest terrestrial salamanders in North America. Description These salamanders usually grow to a length of with a lifespan of around 12–15 years. ...
'') that threatens the endemic California salamander (''
Ambystoma californiense The California tiger salamander (''Ambystoma californiense'') is a vulnerable amphibian native to California. It is a mole salamander. Previously considered to be a subspecies of the tiger salamander (''A. tigrinum)'', the California tiger salam ...
'') was introduced to California as a source of bait for fishermen. Pet animals have also been frequently transported into new areas by humans, and their escapes have resulted in several introductions, such as feral
Cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
s and
Parrot Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoide ...
s. Many plants have been introduced with the intent of aesthetically improving public recreation areas or private properties. The introduced
Norway maple ''Acer platanoides'', commonly known as the Norway maple, is a species of maple native to eastern and central Europe and western Asia, from Spain east to Russia, north to southern Scandinavia and southeast to northern Iran. It was introduced to ...
for example occupies a prominent status in many of Canada's parks. The transport of
ornamental plants Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...
for
landscaping Landscaping refers to any activity that modifies the visible features of an area of land, including the following: # Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal ...
use has and continues to be a source of many introductions. Some of these species have escaped horticultural control and become invasive. Notable examples include
water hyacinth ''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.salt cedar The genus ''Tamarix'' (tamarisk, salt cedar, taray) is composed of about 50–60 species of flowering plants in the family Tamaricaceae, native to drier areas of Eurasia and Africa. The generic name originated in Latin and may refer to the Tam ...
, and
purple loosestrife ''Lythrum salicaria'' or purple loosestrifeFlora of NW Europe''Lythrum salicaria'' is a flowering plant belonging to the family Lythraceae. It should not be confused with other plants sharing the name loosestrife that are members of the family Pr ...
. In other cases, species have been translocated for reasons of "cultural nostalgia", which refers to instances in which humans who have migrated to new regions have intentionally brought with them familiar organisms. Famous examples include the introduction of
common starling The common starling or European starling (''Sturnus vulgaris''), also known simply as the starling in Great Britain and Ireland, is a medium-sized passerine bird in the starling family, Sturnidae. It is about long and has glossy black plumage ...
s to North America by the American
Eugene Schieffelin Eugene Schieffelin (January 29, 1827 – August 15, 1906) was an American amateur ornithologist who belonged to the New York Genealogical and Biographical Society and the New York Zoological Society. In 1877, he became chairman of the American Acc ...
, a lover of the works of Shakespeare and the chairman of the
American Acclimatization Society The American Acclimatization Society was a group founded in New York City in 1871 dedicated to introducing European flora and fauna into North America for both economic and cultural reasons. The group's charter explained its goal was to introduce ...
, who, it is rumoured, wanted to introduce all of the birds mentioned in Shakespeare's plays into the United States. He deliberately released eighty starlings into Central Park in New York City in 1890, and another forty in 1891. Yet another prominent example of an introduced species that became invasive is the
European rabbit The European rabbit (''Oryctolagus cuniculus'') or coney is a species of rabbit native to the Iberian Peninsula (including Spain, Portugal, and southwestern France), western France, and the northern Atlas Mountains in northwest Africa. It has b ...
in
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
.
Thomas Austin Thomas Austin may refer to: *Thomas Austin (pastoralist) (1815–1871), English settler who introduced rabbits into Australia * Thomas Austin (American football) (born 1986), former American football center * Thomas Austin (cricketer) (1857–1941) ...
, a British landowner, had rabbits released on his estate in
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...
because he missed hunting them. A more recent example is the introduction of the
common wall lizard ''Podarcis muralis'' (common wall lizard) is a species of lizard with a large distribution in Europe and well-established introduced populations in North America, where it is also called the European wall lizard. It can grow to about in total ...
(''Podarcis muralis)'' to North America by a
Cincinnati Cincinnati ( ) is a city in the U.S. state of Ohio and the county seat of Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking and Ohio rivers, the latter of which marks the state line w ...
boy, George Rau, around 1950 after a family vacation to
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
.


= Addressing environmental problems

= Intentional introductions have also been undertaken with the aim of ameliorating environmental problems. A number of fast spreading plants such as
kudzu Kudzu (; also called Japanese arrowroot or Chinese arrowroot) is a group of climbing, coiling, and trailing deciduous perennial vines native to much of East Asia, Southeast Asia, and some Pacific islands, but invasive in many parts of the wor ...
have been introduced as a means of
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...
control. Other species have been introduced as
biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also i ...
agents to control
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
. This involves the purposeful introduction of a
natural enemy Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
of the target species with the intention of reducing its numbers or controlling its spread. A special case of introduction is the reintroduction of a species that has become locally endangered or extinct, done in the interests of conservation. Examples of successful reintroductions include wolves to
Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowst ...
in the U.S., and the red kite to parts of England and Scotland. Introductions or translocations of species have also been proposed in the interest of genetic conservation, which advocates the introduction of new individuals into genetically depauperate populations of endangered or threatened species.


Unintentional introductions

Unintentional introductions occur when species are transported by human vectors. Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native. For example, three species of rat (the black, Norway and Polynesian) have spread to most of the world as hitchhikers on ships, and
arachnids Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...
such as
scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always en ...
s and exotic
spider Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s are sometimes transported to areas far beyond their native range by riding in shipments of tropical fruit. This was seen during the introduction of '' Steatoda nobilis'' (Noble false widow) worldwide through
banana A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", disting ...
shipments. Further there are numerous examples of marine organisms being transported in
ballast water Ballast is used in ships to provide moment to resist the lateral forces on the hull. Insufficiently ballasted boats tend to tip or heel excessively in high winds. Too much heel may result in the vessel capsizing. If a sailing vessel needs to voy ...
, among them the invasive
comb jelly Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), an ...
''
Mnemiopsis leidyi ''Mnemiopsis leidyi'', the warty comb jelly or sea walnut, is a species of tentaculate ctenophore (comb jelly). It is native to western Atlantic coastal waters, but has become established as an invasive species in European and western Asian re ...
'', the dangerous bacterium ''
Vibrio cholerae ''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...
'', or the fouling
zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally introduced to numerous other areas and has become an invasive species in ma ...
. The Mediterranean and Black Seas, with their high volume shipping from exotic sources, are most impacted by this problem. Busy harbors are all potential hotspots as well: over 200 species have been introduced to the
San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water f ...
in this manner making it the most heavily invaded estuary in the world. There is also the accidental release of the Africanized honey bees (AHB), known colloquially as "killer bees") or
Africanized bee The Africanized bee, also known as the Africanized honey bee and known colloquially as the "killer bee", is a hybrid of the western honey bee (''Apis mellifera''), produced originally by crossbreeding of the East African lowland honey bee (''A. ...
to Brazil in 1957 and the Asian carp to the United States. The insect commonly known as the brown marmorated stink bug (''Halyomorpha halys'') was introduced accidentally in Pennsylvania. Another form of unintentional introductions is when an intentionally introduced plant carries a parasite or herbivore with it. Some become invasive, for example, the oleander aphid, accidentally introduced with the ornamental plant,
oleander ''Nerium oleander'' ( ), most commonly known as oleander or nerium, is a shrub or small tree cultivated worldwide in temperate and subtropical areas as an ornamental and landscaping plant. It is the only species currently classified in the ge ...
. Yet another unintentional pathway of introduction is during the delivery of
humanitarian aid Humanitarian aid is material and logistic assistance to people who need help. It is usually short-term help until the long-term help by the government and other institutions replaces it. Among the people in need are the homeless, refugees, and v ...
in the aftermath of natural disasters.{{cite journal , last1 = van den Burg , first1 = Matthijs P. , last2 = Daltry , first2 = Jennifer C. , last3 = Angin , first3 = Baptiste , last4 = Boman , first4 = Erik , last5 = Brisbane , first5 = Jeanelle L. K. , last6 = Collins , first6 = Katrina , last7 = Haakonsson , first7 = Jane E. , last8 = Hill , first8 = Arica , last9 = Horrocks , first9 = Julia A. , last10 = Mukhida , first10 = Farah , last11 = Providence , first11 = FitzGerald , last12 = Questel , first12 = Karl , last13 = Ramnanan , first13 = Naitram , last14 = Steele , first14 = Sophia , last15 = Vique Bosquet , first15 = Isabel M. , last16 = Knapp , first16 = Charles R. , title = Biosecurity for humanitarian aid , journal = Science , date = 7 May 2021 , volume = 372 , issue = 6542 , pages = 581–582 , issn = 0036-8075 , eissn = 1095-9203 , doi = 10.1126/science.abj0449 , pmid = 33958467 , bibcode = 2021Sci...372..581V , s2cid = 233872896 , url = {{cite journal , last1 = van den Burg , first1 = Matthijs P. , last2 = Brisbane , first2 = Jeanelle L. K. , last3 = Knapp , first3 = Charles R. , title = Post-hurricane relief facilitates invasion and establishment of two invasive alien vertebrate species in the Commonwealth of Dominica, West Indies , journal = Biological Invasions , date = 14 October 2019 , volume = 22 , issue = 2 , pages = 195–203 , issn = 1387-3547 , eissn = 1573-1464 , doi = 10.1007/s10530-019-02107-5 , pmid = , s2cid = 204460134 , url = This occurred during relief efforts for
Hurricane Maria Hurricane Maria was a deadly Category 5 hurricane that devastated the northeastern Caribbean in September 2017, particularly Dominica, Saint Croix, and Puerto Rico. It is regarded as the worst natural disaster in recorded history to affect ...
in
Dominica Dominica ( or ; Kalinago: ; french: Dominique; Dominican Creole French: ), officially the Commonwealth of Dominica, is an island country in the Caribbean. The capital, Roseau, is located on the western side of the island. It is geographical ...
, it was found that the common green iguana, the
Cuban tree frog The Cuban tree frog (''Osteopilus septentrionalis'') is a large species of tree frog that is native to Cuba, the Bahamas, and the Cayman Islands; but has become invasive in several other places around the Americas. Its wide diet and ability to ...
, and potentially the Venezuela snouted tree frog were introduced with the former two becoming established. Most accidentally or intentionally introduced species do not become invasive as the ones mentioned above. For instance, Some 179 coccinellid species have been introduced to the U.S. and Canada; about 27 of these non-native species have become established, and only a handful can be considered invasive, including the intentionally introduced ''
Harmonia axyridis ''Harmonia axyridis'' is a large lady beetle or ladybug species that is most commonly known as the harlequin, multicoloured Asian, or Asian lady beetle. This is one of the most variable species in the world, with an exceptionally wide range of col ...
'', multicolored
Asian lady beetle ''Harmonia axyridis'' is a large lady beetle or ladybug species that is most commonly known as the harlequin, multicoloured Asian, or Asian lady beetle. This is one of the most variable species in the world, with an exceptionally wide range of col ...
. However the small percentage of introduced species that become invasive can produce profound ecological changes. In North America, ''
Harmonia axyridis ''Harmonia axyridis'' is a large lady beetle or ladybug species that is most commonly known as the harlequin, multicoloured Asian, or Asian lady beetle. This is one of the most variable species in the world, with an exceptionally wide range of col ...
'' has become the most abundant
lady beetle Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as they ...
and probably accounts for more observations than all the native lady beetles put together.


Introduced plants

Many non-native plants have been introduced into new territories, initially as either
ornamental plant Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...
s or for
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...
control, stock feed, or forestry. Whether an exotic will become an
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
is seldom understood in the beginning, and many non-native ornamentals languish in the trade for years before suddenly naturalizing and becoming invasive.
Peach The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy fruits with various characteristics, most called peaches and others (the glossy-skinned, n ...
es, for example, originated in China, and have been carried to much of the populated world.
Tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
es are native to the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
. Squash (
pumpkin A pumpkin is a vernacular term for mature winter squash of species and varieties in the genus ''Cucurbita'' that has culinary and cultural significance but no agreed upon botanical or scientific meaning. The term ''pumpkin'' is sometimes use ...
s),
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American English, North American and Australian English), is a cereal grain first domesticated by indigenous peoples of Mexico, indigenous ...
(corn), and tobacco are native to
the Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...
, but were introduced to the
Old World The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by thei ...
. Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously
compete Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...
with natives, but simply increase the biodiversity of the area. One example would be
Dandelions ''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, which have become an essential source of early season nectar for both native and introduced pollinators, and do not meaningfully compete with native grasses or flowers. A very troublesome marine species in southern Europe is the
seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and '' Chlorophyta'' (green) macroalgae. Seaweed species such as ...
''
Caulerpa taxifolia ''Caulerpa taxifolia'' is a species of green seaweed, an alga of the genus ''Caulerpa'', native to tropical waters of the Pacific Ocean, Indian Ocean, and Caribbean Sea. The species name ''taxifolia'' arises from the resemblance of its leaf-lik ...
''. ''Caulerpa'' was first observed in the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
in 1984, off the coast of
Monaco Monaco (; ), officially the Principality of Monaco (french: Principauté de Monaco; Ligurian: ; oc, Principat de Mónegue), is a sovereign city-state and microstate on the French Riviera a few kilometres west of the Italian region of Lig ...
. By 1997, it had covered some 50 km2. It has a strong potential to overgrow natural
biotope A biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. ''Biotope'' is almost synonymous with the term "habitat", which is more commonly used in English-speaking countr ...
s, and represents a major risk for sublittoral
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s. The origin of the alga in the Mediterranean was thought to be either as a migration through the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popula ...
from the Red Sea, or as an accidental introduction from an aquarium. Another troublesome plant species is the terrestrial plant '' Phyla canescens,'' which was intentionally introduced into many countries in North America, Europe, and Africa as an ornamental plant. This species has become invasive in Australia, where it threatens native rare plants and causes erosion and soil slumping around river banks. It has also become invasive in France where it has been listed as an invasive plant species of concern in the Mediterranean region, where it can form monocultures that threaten critical conservation habitats. Japanese knotweed grows profusely in many nations. Human beings introduced it into many places in the 19th century. It is a source of
resveratrol Resveratrol (3,5,4′-trihydroxy-''trans''-stilbene) is a stilbenoid, a type of natural phenol, and a phytoalexin produced by several plants in response to injury or when the plant is under attack by pathogens, such as bacteria or fungi. Sourc ...
, a dietary supplement. It can grow in building foundations, threatening their stability, and spreads quite quickly.


Introduced animals

Most introduced species do not become invasive. Examples of introduced animals that have become invasive include the
gypsy moth ''Lymantria dispar'', also known as the gypsy moth or the spongy moth, is a species of moth in the family Erebidae. ''Lymantria dispar'' is subdivided into several subspecies, with subspecies such as ''L. d. dispar'' and ''L. d. japonica'' bei ...
in eastern
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, the
zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally introduced to numerous other areas and has become an invasive species in ma ...
and alewife in the
Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
, the
Canada goose The Canada goose (''Branta canadensis''), or Canadian goose, is a large wild goose with a black head and neck, white cheeks, white under its chin, and a brown body. It is native to the arctic and temperate regions of North America, and it is ...
and gray squirrel in Europe, the
beaver Beavers are large, semiaquatic rodents in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two extant species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers a ...
in
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...
, the muskrat in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
and
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
, the cane toad and red fox in Australia, nutria in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, Eurasia, and Africa, and the common brushtail possum in New Zealand. In Taiwan, the success of introduced bird species was related to their native range size and body size; larger species with larger native range sizes were found to have larger introduced range sizes. One notoriously devastating introduced species is the small Indian mongoose (''Small Indian mongoose, Urva auropunctata''). Originating in a region encompassing Iran and India, it was introduced to the West Indies and Hawaii in the late 1800s for pest control. Since then, it has thrived on prey unequipped to deal with its speed, nearly leading to the local extinction of a variety of species. In some cases, introduced animals may unintentionally promote the cause of Rewilding (conservation biology), rewilding.{{cite journal, last1= Lundgren, first1= E.J., last2= Ramp, first2= D., last3= Rowan, first3= J., last4= Middleton, first4= O., last5= Schowanek, first5= S.D., last6= Sanisidro, first6= O., last7= Carroll, first7= S.P., last8= Davis, first8= M., last9= Sandom, first9= C.J., last10= Svenning, first10=J.-C., last11= Wallach, first11= A.D., title= Introduced herbivores restore Late Pleistocene ecological functions, journal= Proceedings of the National Academy of Sciences, year= 2020, volume= 117, issue= 14, pages= 7871–7878, doi= 10.1073/pnas.1915769117, pmid= 32205427, pmc= 7148574, bibcode= 2020PNAS..117.7871L, s2cid= 214627869, doi-access= free For example, escaped horses and donkeys that have gone feral in
the Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...
may play ecological roles similar to those of the Equidae, equids that became Extinction, extinct there at the end of the Pleistocene.{{cite web , url= https://www.umass.edu/newsoffice/article/pablo-escobar%E2%80%99s-hippos-may-help-counteract , title= Pablo Escobar's hippos may help counteract a legacy of extinctions, last= Rowan, first= J., date= 2020, publisher= University of Massachusetts Amherst, U. Mass. Amherst, access-date= 2020-04-01 The exotic pet trade has also been a large source of introduced species. The species favored as pets have more general habitat requirements and larger distributions. Therefore, as these pets escape or are released, unintentionally or intentionally, they are more likely to survive and establish non-native populations in the wild. Among the popular exotic pets that have become alien or invasive species are parrots, frogs, terrapins, and iguanas.


Most commonly introduced species

Some species, such as the Western honey bee, brown rat,
house sparrow The house sparrow (''Passer domesticus'') is a bird of the Old World sparrow, sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale ...
, common pheasant, ring-necked pheasant, and European starling, have been introduced very widely. In addition there are some agriculture, agricultural and pet species that frequently become feral; these include rabbits, dogs, domestic duck, ducks, snakes, goats, fish, pigs, and cats.


Genetics

When a new species is introduced, the species could potentially breed with members of native species, producing hybrids. The effect of the creating of hybrids can range from having little effect, a negative effect, to having devastating effects on native species. Potential negative effects include hybrids that are less fit for their environment resulting in a population decrease. This was seen in the Atlantic Salmon population when high levels of escape from Atlantic Salmon farms into the wild populations resulted in hybrids that had reduced survival. Potential positive effects include adding to the genetic diversity of the population which can increase the adaptation ability of the population and increase the number of healthy individuals within a population. This was seen in the introduction of guppies in Trinidad to encourage population growth and introduce new alleles into the population. The results of this introduction included increased levels of heterozygosity and a larger population size. Wide-spread introductions of non-native iguanas are causing devastating effects on native ''Iguana'' populations in the Caribbean Lesser Antilles, as hybrids appear to have higher fitness than native iguanas, leading to competitive outcompetition and replacement.{{cite journal , last1 = Knapp , first1 = Charles R. , last2 = Grant , first2 = Tandora D. , last3 = Pasachnik , first3 = Stesha A. , last4 = Angin , first4 = Baptiste , last5 = Boman , first5 = Erik , last6 = Brisbane , first6 = Jeanelle , last7 = Buckner , first7 = Sandra D. , last8 = Haakonsson , first8 = Jane E. , last9 = Harlow , first9 = Peter S. , last10 = Mukhida , first10 = Farah , last11 = Thomas‐Moko , first11 = Nunia , last12 = Burg , first12 = Matthijs P. , last13 = Wasilewski , first13 = Joseph A. , title = The global need to address threats from invasive alien iguanas , journal = Animal Conservation , date = 6 November 2020 , volume = 24 , issue = 5 , pages = 717–719 , issn = 1367-9430 , eissn = 1469-1795 , doi = 10.1111/acv.12660 , pmid = , s2cid = 228838378 , url = {{cite journal , last1 = Vuillaume , first1 = Barbara , last2 = Valette , first2 = Victorien , last3 = Lepais , first3 = Olivier , last4 = Grandjean , first4 = Frédéric , last5 = Breuil , first5 = Michel , title = Genetic Evidence of Hybridization between the Endangered Native Species Iguana delicatissima and the Invasive Iguana iguana (Reptilia, Iguanidae) in the Lesser Antilles: Management Implications , journal = PLOS ONE , date = 5 June 2015 , volume = 10 , issue = 6 , page = e0127575 , eissn = 1932-6203 , doi = 10.1371/journal.pone.0127575 , pmid = 26046351 , pmc = 4457794 , bibcode = 2015PLoSO..1027575V , url = , doi-access = free Numerous populations have already become extinct and hybridization continues to reduce the number of native iguanas on multiple islands.


On a planetary body

{{Main, Interplanetary contamination {{Expand section, date=May 2021 It has been hypothesized that
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
of microbial life could contaminate a planetary body after the former is introduced by a space probe or spacecraft, either deliberately or unintentionally. It has also been hypothesized that the origin of life on earth is due to introductions of life from other planets billions of years ago, possibly by a sentient race. Projects have been proposed to introduce life to other lifeless but Planetary habitability, habitable planets in other star systems some time in the future. In preparation for this, projects have been proposed to see if anything is still alive from any of the feces left behind during the moon landings in the 1960s.https://www.hou.usra.edu/meetings/deepspace2018/pdf/3032.pdf {{Bare URL PDF, date=March 2022


See also

* Archaeophyte * Adventitious plant * Biological dispersal * Biological hazard * Colonisation (biology) * Directed panspermia * Genetic pollution * Hemerochory * Naturalisation (biology) * Invasive species


References

{{Reflist, refs= {{cite journal , last1=Occhipinti-Ambrogi , first1=Anna , last2=Galil , first2=Bella S. , title=A uniform terminology on bioinvasions: a chimera or an operative tool? , journal=Marine Pollution Bulletin , date=November 2004 , volume=49 , issue=9–10 , pages=688–694 , url=https://www.reabic.net/publ/Galil_et%20al_2004_alien%20species.pdf , doi=10.1016/j.marpolbul.2004.08.011 , pmid=15530511 , access-date=27 December 2020


Further reading

* {{cite book , title=Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction , author=Chris D. Thomas , publisher=PublicAffairs , year=2017 , isbn=978-1610397278


External links

{{Commons category, Introduced species {{Americana Poster, Immigrations, Animal and Vegetal
National Estuarine and Marine Exotic Species Information System (NEMESIS)

The Naked Scientists Invasive Species Articles
Ecologists challenge the categories that identify some species as natives and others as invaders. {{modelling ecosystems {{Pollution {{Authority control {{Portal bar, Earth sciences, Ecology, Environment, Gardening Introduced species, Ecology terminology