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(''Melilotus sp.''), introduced and
naturalized Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship Citizenship is the status of a person recognized under the law of a country (and/or local jurisdiction) of belongi ...
in the
Americas The Americas (also collectively called America) is a landmass comprising the totality of North and South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relativ ...
from
Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest ...

Europe
as a forage and cover crop 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 Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

species
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 entertain ...
distributional
range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to ...
, but which has arrived there by
human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only Extant taxon, ...

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 Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship Citizenship is the status of a person recognized under the law of a country (and/or local jurisdiction) of belongi ...
. 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 , Colorado Colorado (, other variants) is a U.S. state, state in the Mountain states, Mountain West region of the United States. It encompasses most of the Southern Rocky Mountains as well as the northeastern portion of the Colorado Platea ...
. The Latin expression neobiota captures the characteristic that these species are ''new'' biota to their environment in terms of established
biological network A biological network is any network that applies to biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different ...
(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 systems, consumer-resource system. Ecologists can broadly lump a ...

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). 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 insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. ...
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 Richard Milhous Nixon (January 9, 1913April 22, ...
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",Carlton, James T. 2002. ''Introduced Species in U.S. Coastal Waters''. Pew Oceans Commission. which means that species growing in a garden, farm, or house may not meet the criteria unless they escape and persist.


Subset descriptions


See also:

Glossary of Invasion Biology Terms The need for a clearly defined and consistent invasion biology terminology has been acknowledged by many sources. ''Invasive species'', or ''invasive Introduced species, exotics'', is a nomenclature term and categorization phrase used for flora ...

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 it was 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 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 continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest ...

Europe
,
house sparrow The house sparrow (''Passer domesticus'') and also known as the common bird or the common sparrow is a bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless ...

house sparrow
s are well established since early
Iron Age The Iron Age is the final epoch of the three-age system, three-age division of the prehistory and protohistory of Homo sapiens, humanity. It was preceded by the Stone Age (Paleolithic, Mesolithic, Neolithic, and Chalcolithic) and the Bronze Age ...
though they originated from
Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict crite ...
). Immigrant species are species that travel, often 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 Citizenship is the status of a person recognized under the law of a country (and/or local jurisdiction) of belongi ...
, "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 (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 U.S. state in the Western United States, in the Pacific Ocean about 2,000 miles (3,200 km) from the U.S. mainland. It is the only state outside North America, the only island state, and the only state in ...

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 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 List of European islands by area, largest European island, and the List of i ...

Great Britain
, the
Wildlife and Countryside Act 1981 The Wildlife and Countryside Act 1981 is an Act of Parliament Acts of parliament, sometimes referred to as primary legislation, are texts of law passed by the Legislature, legislative body of a jurisdiction (often a parliament or council). In most ...
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 In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical me ...
, 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. Male ''Lophura nycthemera'' (silver pheasant), a native of East Asia that has been introduced into parts of
Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest ...

Europe
for ornamental reasons 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.


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 and t ...

soybean
s, ,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'') ...

wheat
,
honey bees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles t ...

honey bees
, and all
livestock Livestock are the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable ...
except the
American bison The American bison or simply bison (''Bison bison''), also commonly known as the American buffalo or simply buffalo, is an American species In biology, a species is the basic unit of biological classification, classification and a taxonomic ...
and the
turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country located mainly on Anatolia in Western Asia, with a small portion on the Balkans in Southeast Europe. It shares borders with Greece and Bulgaria to the northwest; the B ...

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 Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentism, sedentary human civilization, whereby farming of domestication, domesticated species created food ...
,
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the farming of fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in ...
or other economic activities are widespread. Eurasian carp was first introduced to the United States as a potential food source. The
apple snail Ampullariidae, common name the apple snails, is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpos ...

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,
fox Foxes are small to medium-sized, omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, p ...

fox
es 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 beetle Beetles are a group of insects that form the Taxonomic rank, order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, Elytron, elytra, distinguishing them from mo ...
have established themselves in Australia after deliberate introduction by the
Australian Dung Beetle Project Australians, colloquially referred to as "Aussies", are the citizens Citizenship is the Status (law), status of a person recognized under the law of a country (and/or local jurisdiction) of belonging to thereof. In international law it i ...
in an effort to reduce the impact of livestock manure. The timber industry promoted the introduction of Monterey pine (''
Pinus radiata ''Pinus radiata'', the Monterey pine, insignis pine or radiata pine, is a species of pine A pine is any Pinophyta, conifer in the genus ''Pinus'' () of the family (biology), family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoi ...
'') 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 In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified ...
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. In 2018, it was acquired by Bayer as part of its crop science division. It was headquartered in Creve Coeur, Missouri. Monsanto ...

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.


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 240px, Biofluorescence in ''Ambystoma tigrinum'' These salamanders usually grow to a l ...
'') that threatens the endemic California salamander ('' Ambystoma californiense'') was introduced to California as a source of bait for fishermen. 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 In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined a ...
s and
Parrot Parrots, also known as psittacines , are bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled ...

Parrot
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 ''Acer'' is a genus of Tree, trees and Shrub, shrubs commonly known as maples. The genus is placed in the family Sapindaceae. There are approximately 132 species ...

Norway maple
for example occupies a prominent status in many of Canada's parks. The transport of
ornamental plants plant Ornamental plants are plants Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical en ...

ornamental plants
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 Flora is all the plant life present in a particular region or time, generally the naturally occ ...

landscaping
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'', commonly known as common water hyacinth, is an aquatic plant native to the Amazon basin, and is often a highly problematic invasive species outside its native range. It is the sole species of ''Pontederia'' subg. '' ...

water hyacinth
,
salt cedar The genus ''Tamarix'' (tamarisk, salt cedar) 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 Tambre River ...
, and
purple loosestrife ''Lythrum salicaria'' or purple loosestrifeFlora of NW Europe''Lythrum salicaria'' is a flowering plant The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of Embryophyte, land plants, with 64 Or ...

purple loosestrife
. 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 the British Isles, is a medium-sized passerine A passerine is any bird of the Order (biology), order Passeriformes (, Latin ''passer'' (“ ...
s to North America by Englishman Eugene Schieffelin, a lover of the works of Shakespeare and the chairman of the American Acclimatization Society, 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 Rabbits are small mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mamm ...
in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...
.
Thomas Austin Thomas Austin (181515 December 1871) was an English settler in Australia who is generally noted for the introduction of Rabbits in Australia, rabbits into Australia in 1859, even though rabbits had been brought previously to Australia by the First ...

Thomas Austin
, 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, Seychelles ...
because he missed hunting them. A more recent example is the introduction of the common wall lizard (''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, Ohio, Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking River (Kentucky), Licking and Ohio Rive ...

Cincinnati
boy, George Rau, around 1950 after a family vacation to
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a Northern Italy, continental part, delimited by the Alps, a Italian Peninsula, peninsula and List of islands of Italy, se ...

Italy
.


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 perennial vines native to much of East Asia, Southeast Asia Southeast Asia or Southeastern Asia is the United Nations geoscheme f ...

kudzu
have been introduced as a means of
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
control. Other species have been introduced as
biological control Biological control or biocontrol is a method of pest control, controlling pests such as insects, mites, weeds and phytopathology, plant diseases bioeffector, using other organisms. It relies on predation, parasitism, herbivory, or other natura ...
agents to control invasive species. This involves the purposeful introduction of a natural enemy 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#REDIRECT National park A national park is a park in use for Conservation (ethic), conservation purposes, created and protected by national governments. Often it is a reserve of natura ...

Yellowstone National Park
in the U.S., and the
red kite The red kite (''Milvus milvus'') is a medium-large bird of prey in the family Accipitridae, which also includes many other Diurnality, diurnal Bird of prey, raptors such as eagles, buzzards, and harrier (bird), harriers. The species currently br ...
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 Rats are various medium-sized, long-tailed rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area ar ...

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 animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, co ...
such as
scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs, and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve ...

scorpion
s and exotic
spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and rank se ...

spider
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 ''Steatoda nobilis'' is a spider in the genus ''Steatoda'', known in the United Kingdom as the noble false widow and is often referred to as the false widow. As the common name indicates, the spider superficially resembles and is frequently confus ...

Steatoda nobilis
'' (Noble false widow) worldwide through
banana A banana is an elongated, edible fruit – botanically a berry (botany), berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa (genus), Musa''. In some countries, Cooking banana, bananas used for c ...
shipments. There are also 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 boat/ship capsizing. If a sailing vessel should nee ...
, one being the
zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater Fresh water (or freshwater) is any naturally occurring water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorles ...
. Over 200 species have been introduced to the
San Francisco Bay San Francisco Bay is a shallow estuary in the US state of California. It is surrounded by a contiguous region known as the San Francisco Bay Area (often simply "the Bay Area"), and is dominated by the large cities of San Francisco, San Jose, ...

San Francisco Bay
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 The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 sp ...
to Brazil in 1957 and the
Asian carp upright=1.25, Grass carp Several species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the larg ...
to the United States. The insect commonly known as the (''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 , 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 genus ...

oleander
. 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'', most commonly known as the harlequin, multicolored Asian, or Asian ladybeetle, is a large coccinellid beetle. This is one of the most variable species in the world, with an exceptionally wide range of color forms. It is nat ...

Harmonia axyridis
'', multicolored Asian lady beetle. However the small percentage of introduced species that become invasive can produce profound ecological changes. In North America ''Harmonia axyridis'' has become the most abundant lady beetle 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 plant Ornamental plants or garden plants are plants that are grown for decorative purposes in gardens and landscape design projects. Many if not most are flowering plants, and garden varieties tend to be specially bred cultivars that improve on ...

ornamental plant
s or for
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
control, stock feed, or forestry. Whether an exotic will become an invasive species 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 In the fields of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists grow f ...

Peach
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 a tomato plant. The species originated in western South America South America is a continent entirely in the Western Hemisphere and mostly in the ...

Tomato
es are native to the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sout ...
. Squash (
pumpkin A pumpkin is a cultivar of winter squash that is round with smooth, slightly ribbed skin, and is most often deep yellow to orange in coloration. The thick shell contains the seeds and pulp. The name is most commonly used for cultivars of ''Cucu ...

pumpkin
s),
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples Indigenous peoples, also referred to as F ...

maize
(corn), and tobacco are native to
the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to East and West. ''North'' ...
, but were introduced to the
Old World The Old World consists of Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any ...
. Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously
compete Competition arises whenever 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 includes rivalry between entities such as organisms, ind ...
with natives, but simply increase the biodiversity of the area. One example would be
Dandelions ''Taraxacum'' () is a large genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may al ...

Dandelions
in
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
, 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 scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta ...

seaweed
''
Caulerpa taxifolia ''Caulerpa taxifolia'' is a species of seaweed Seaweed, or macroalgae, refers to thousands of species of Macroscopic scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta ...
''. ''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 the ...
in 1984, off the coast of
Monaco Monaco (; ), officially the Principality of Monaco (french: Principauté de Monaco; Monégasque dialect, Monégasque Ligurian: ''Prinçipatu de Mu̍negu''), is a Sovereign state, sovereign city-state and European microstates, microstate on the ...

Monaco
. 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 Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by plants a ...

biotope
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 syste ...

ecosystem
s. The origin of the alga in the Mediterranean was thought to be either as a migration through the
Suez Canal The Suez Canal ( ar, 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 canal is part of the Silk ...
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 ''Reynoutria japonica'', synonyms ''Fallopia japonica'' and ''Polygonum cuspidatum'', is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit o ...

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 In biochemistry, naturally occurring phenols refers to phenol functional group that is found in natural products. Phenolic compounds are produced by p ...

resveratrol
, 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 dispar'', commonly known as the gypsy moth, European gypsy moth, or North American gypsy moth, is a species of moth in the family Erebidae that is of Eurasian origin. It has a range that extends over Europe, Africa, and North A ...
in eastern
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
, the
zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater Fresh water (or freshwater) is any naturally occurring water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorles ...
and alewife in the
Great Lakes upright=1.3, Location in North America The Great Lakes also called the Great Lakes of North America or the Laurentian Great Lakes, is a series of large interconnected freshwater lake A lake is an area filled with water, localized in a ...

Great Lakes
, the
Canada goose The Canada goose (''Branta canadensis'') 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 its migration occasionally re ...

Canada goose
and
gray squirrelGray squirrel or grey squirrel may refer to several species of squirrel indigenous to North America: *The eastern gray squirrel (''Sciurus carolinensis''), from the eastern United States and southeastern Canada; introduced into Britain, Ireland, west ...

gray squirrel
in Europe, the
beaver Beavers are large, semiaquatic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions ...

beaver
in
Tierra del Fuego#REDIRECT Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", formerly also Fireland in English) is an archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of isl ...

Tierra del Fuego
, the
muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...

muskrat
in
Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest ...

Europe
and
Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict crite ...
, the
cane toad The cane toad (''Rhinella marina''), also known as the giant neotropical toad or marine toad, is a large, Terrestrial animal, terrestrial true toad native to South America, South and mainland Central America, but which has been Introduced specie ...

cane toad
and
red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanlin ...

red fox
in
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
,
nutria The nutria (''Myocastor coypus''), also known as the coypu, is a large, herbivorous File:Land_Snail_radula_tracks.jpg#, 250px, Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse ...

nutria
in
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
,
Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as contin ...

Eurasia
, and
Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are ...

Africa
, and the
common brushtail possum The common brushtail possum (''Trichosurus vulpecula'', from the Greek for "furry tailed" and the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was origina ...
in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and more than 700 List of islands of New Zealand, smaller islands, coveri ...

New Zealand
. In
Taiwan Taiwan (), officially the Republic of China (ROC), is a country in East Asia. Neighbouring countries include the China, People's Republic of China (PRC) to the northwest, Japan to the northeast, and the Philippines to the south. The main islan ...

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 ('' Urva auropunctata''). Originating in a region encompassing
Iran Iran ( fa, ایران ), also called Persia and officially the Islamic Republic of Iran ( fa, جمهوری اسلامی ایران ), is a country in Western Asia. It is bordered to the northwest by Armenia and Azerbaijan, to the north ...

Iran
and
India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populous country, the List of countries and dependencies by area, seventh-largest ...

India
, it was introduced to the
West Indies The West Indies are a subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inh ...
and
Hawaii Hawaii ( ; haw, Hawaii or ) is a U.S. state, state in the Western United States, located in the Pacific Ocean about 2,000 miles from the U.S. mainland. It is the only state outside North America, the only state that is an archipelago, a ...

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. For example, escaped
horse The horse (''Equus ferus caballus'') is a Domestication, domesticated odd-toed ungulate, one-toed ungulate, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two Extant taxon, extant subspecies of wild horse, ''Equus ferus' ...

horse
s and
donkey The donkey or ass is a domestic animal This page gives a list of domestic animals, also including a list of animals which are or may be currently undergoing the process of domestication Domestication is a sustained multi-generational relati ...
s that have gone feral in
the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to East and West. ''North'' ...
may play ecological roles similar to those of the
equids Equidae (sometimes known as the horse family) is the taxonomic family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship) ...
that became
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual of the species, although the Functional extin ...

extinct
there at the end of the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally c ...
.


Most commonly introduced species

Some species, such as the
Western honey bee The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to ...

Western honey bee
,
brown rat The brown rat (''Rattus norvegicus''), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown or g ...
,
house sparrow The house sparrow (''Passer domesticus'') and also known as the common bird or the common sparrow is a bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless ...

house sparrow
, 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.


On a planetary body

It has been hypothesized that invasive species 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


See also

* Archaeophyte * Adventitious plant * Biological dispersal * Biological hazard * Directed panspermia * Genetic pollution * Hemerochory


References


External links


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. {{Portal bar, Earth sciences, Ecology, Environment, Gardening Introduced species, Ecology terminology