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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 biological classification, 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 individu ...

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 range, in geography, is a chain of hill A hill is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. Landforms together ...
, but which has arrived there by
human Humans (''Homo sapiens'') are the most abundant and widespread 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 speci ...

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 Rafting and whitewater rafting are recreational which use an inflatable to navigate a or other body of water. This is often done on or different degrees of rough water. Dealing with risk is often a part of the experience. This activi ...
. 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 Network, networking and networked may refer to: Science and technology * Network theory Network theory is the study of Graph (discrete mathematics), graphs as a representation of either symmetric relatio ...
(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 An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
), 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 such as s, s, s and . It relies on , , , or other natural mechanisms, but typically also involves an active human management role. It can be an important component of (IPM) programs. There a ...
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 agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...
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 any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
,
house sparrow The house sparrow (''Passer domesticus'') is a bird Birds are a group of warm-blooded vertebrates constituting the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * ...

house sparrow
s are well established since early
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory Prehistory, also known as pre-literary history, is the period of human history Human history, or world history, is the narrative of Human, humanity's pa ...
though they originated from
Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, Hemispheres. It shares the continental landmass of Eurasia with the cont ...

Asia
). 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 An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
". 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, 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, ...

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 An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll (), ...

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 ...
, 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.


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 A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Leg ...

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 Honey is a sweet, viscous food substance made by honey bees and some other Bee, bees. Bees produce honey from the sugary secretions of plants (floral nectar) or from secretions of other insects (such as honeydew (secretion), honeydew), by reg ...

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 predictabl ...
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 ...

American bison
and the
turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country located mainly on Anatolia Anatolia,, tr, Anadolu Yarımadası), and the Anatolian plateau. also known as Asia Minor, is a large peninsula in Western Asia an ...

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 sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
,
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the farming of fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct rel ...
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, s belonging to several of the family . They have a flattened skull, upright triangular ears, a pointed, slightly upturned , and a long bushy (or ''brush''). Twelve belong to the "true foxes" group of ge ...

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 Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...
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 An agrochemical or agrichemical, a contraction of ''agricultural chemical'', is a chemical A chemical substance is a form of matter having constant chemical composition and characteris ...

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 Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence for an individual, group or family ...

Cat
s and
Parrot Parrots, also known as psittacines , are birds of the roughly 398 species in 92 genus (biology), genera comprising the order (biology), order Psittaciformes , found mostly in tropics, tropical and subtropics, subtropical regions. The order is s ...

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 Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living a ...

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, (and also known as the "terror of Bengal"; generally in Bengali it is often called 'kochuripana') - is an aquatic plant native to the Amazon basin The Amazon Basin i ...

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 Great Britain and Ireland, is a medium-sized passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate ...

common starling
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 native to the Iberian Peninsula (including Spain, Portugal, and Geography of France, southwestern France). It has been widely introduced elsewhere, often with devasta ...
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, sma ...
.
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'' (common wall lizard) is a species of lizard Lizards (suborder Lacertilia) are a widespread group of Squamata, squamate reptiles, with over 6,000 species, ranging across all continents except Antarctica, as well as most ...
(''Podarcis muralis)'' to North America by a
Cincinnati Cincinnati ( ) is a city in the U.S. state In the , a state is a , of which there are currently 50. Bound together in a , each state holds al jurisdiction over a separate and defined geographic territory where it shares its with the ...

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 peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...

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 East Asia is the eastern region of Asia Asia () is Earth's largest and most po ...

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 natur ...
agents to control
invasive species An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
. 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 located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the U.S. Congress and signed into law by ...

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 ...

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 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 a ...

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 Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including hum ...

scorpion
s and exotic
spider Spiders (order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and the ...

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 In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specia ...

banana
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 liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is th ...
. Over 200 species have been introduced to the
San Francisco Bay San Francisco Bay is a shallow estuary An estuary is a partially enclosed Coast, coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zon ...

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 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 largest group of organisms i ...
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 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 Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cel ...

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 An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
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 ...

Peach
es, for example, originated in China, and have been carried to much of the populated world.
Tomato The tomato is the edible berry A berry is a small, pulpy, and often edible fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are ...

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 Sou ...

Andes
. 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 ''C ...

pumpkin
s),
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It can also be ...

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' ...

the Americas
, 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, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% o ...
. 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 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 continen ...

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 ''Chlorophyt ...

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 connected to the , surrounded by the and almost completely enclosed by land: on the north by and and , on the south by , and on the east by the . The Sea has played a central role in the . Although the Mediterrane ...
in 1984, off the coast of
Monaco Monaco (; ), officially the Principality of Monaco (french: Principauté de Monaco; Monégasque Ligurian: ''Prinçipatu de Mu̍negu''), is a sovereign Sovereign is a title which can be applied to the highest leader in various categories. 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 syst ...

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 Mean sea level (MSL) (often shortened to sea level) is an mean, average level of the surface of one or more of Earth's bodies of water from which hei ...
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 Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of ...

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 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 continen ...

North America
, the
zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is th ...
and alewife in the
Great Lakes 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 basin, surrounded by land Land ...

Great Lakes
, the
Canada goose The Canada goose (''Branta canadensis'') is a large wild goose A goose (plural geese) is a bird of any of several waterfowl Anseriformes is an order of bird Birds are a group of warm-blooded vertebrates constituting the class ...

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 interaction ...

beaver
in
Tierra del Fuego #REDIRECT Tierra del Fuego #REDIRECT 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 i ...

Tierra del Fuego
, the
muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecul ...

muskrat
in
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
and
Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, Hemispheres. It shares the continental landmass of Eurasia with the cont ...

Asia
, 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 cleanli ...

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, sma ...

Australia
,
nutria The nutria (''Myocastor coypus''), also known as the coypu, is a large, herbivorous A herbivore is an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an org ...

nutria
in
North America North America is a 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 continen ...

North America
,
Eurasia Eurasia () is the largest continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a ...

Eurasia
, and
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

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 ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
. In
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and N ...

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, is a country in Western Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part of a larger regio ...

Iran
and
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

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, in ...
and
Hawaii Hawaii ( ; haw, Hawaii or ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...

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 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 ...

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 domestication of animals, animals which are or may be currently undergoing the process of domestication and animals that have an exten ...
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' ...

the Americas
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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...

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 ...
.


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 Eusociality (from Greek Greek may refer to: Greece Anything of, fr ...

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 Rats are various medium-sized, long-tail ...
,
house sparrow The house sparrow (''Passer domesticus'') is a bird Birds are a group of warm-blooded vertebrates constituting the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * ...

house sparrow
,
ring-necked pheasant The common pheasant (''Phasianus colchicus'') is a bird in the pheasant family ( Phasianidae). The genus name comes from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European lang ...
, and
European 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 w ...

European starling
, have been introduced very widely. In addition there are some
agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors such as watching tele ...

agricultural
and
pet A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock or a laboratory animal. Popular pets are often considered to have attractive appearances, Animal cognitio ...

pet
species that frequently become
feral A feral animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ...
; these include
rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication ...

rabbit
s,
dog The dog or domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the ...

dog
s,
duck Duck is the common name for numerous species of waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anati ...

duck
s,
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
s,
goat The domestic goat or simply goat (''Capra hircus'') is a domesticated species of typically kept as . It was from the (''C. aegagrus'') of and . The goat is a member of the animal family and the subfamily , meaning it is closely related ...

goat
s,
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
,
pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and ani ...

pig
s, and
cat The cat (''Felis catus'') is a domestic Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence for an individual, group or famil ...

cat
s.


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 The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae Salmonidae is a Family (biology), family of ray-finned fish, the only living family currently placed in the Order (biology), order Salmoniformes ...

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 Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species In biology, a species is the basic unit of biological classificati ...
of the population which can increase the
adaptation In , adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits s to their environment, enhancing their . Secondly, it is a state reached by the population during that process. Thirdly, it is a or adapti ...

adaptation
ability of the population and increase the number of healthy individuals within a population. This was seen in the introduction of
guppies The guppy (), also known as millionfish and rainbow fish, is one of the world's most widely distributed tropical fish Tropical fish are generally those fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Lim ...
in
Trinidad Trinidad is the larger and more populous of the two major islands of Trinidad and Tobago Trinidad and Tobago (, ), officially the Republic of Trinidad and Tobago, is the southernmost island country in the Caribbean The Caribbean ( ...

Trinidad
to encourage
population growth Population growth is the increase in the number of people in a population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size ...
and introduce new
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
s into the population. The results of this introduction included increased levels of
heterozygosity Zygosity (the noun, zygote A zygote (from Greek ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke") is a eukaryotic cell formed by a fertilization event between two gamete A gamete ( /ˈ ...
and a larger
population size In population genetics and population ecology, population size (usually denoted ''N'') is the number of individual organisms in a population. Population size is directly associated with amount of genetic drift, and is the underlying cause of effects ...
.


On a planetary body

It has been hypothesized that
invasive species An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
of
microbial life A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties ...
could contaminate a
planetary body A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...
after the former is introduced by a
space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe may approach the Moon; travel through interplanetary space; planetary ...
or
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite alt=, A full-size model of the Earth observation satellite ERS 2 ">ERS_2.html" ;"title="Earth observation satellite ERS 2">Earth obse ...

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
habitable planets Planetary habitability is the measure of a planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is n ...
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 landing A Moon landing is the arrival of a spacecraft on the surface of the Moon. This includes both crewed and robotic missions. The first human-made object to touch the Moon was the Soviet Union's Luna 2, on 13 September 1959. The United St ...

moon landing
s in the 1960s.https://www.hou.usra.edu/meetings/deepspace2018/pdf/3032.pdf


See also

*
Archaeophyte An archaeophyte is a plant 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 energy tha ...
* Adventitious plant *
Biological dispersal Biological dispersal refers to both the movement of individuals (animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system ...
*
Biological hazard A biological hazard, or biohazard, is a biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientifi ...
*
Directed panspermia Directed panspermia is the deliberate transport of microorganisms in space to be used as introduced species (''Melilotus sp.''), introduced and naturalized in the Americas The Americas (also collectively called America) is a landmass co ...
*
Genetic pollution Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. It is defined as "the dispersal of contaminated altered genes from genetically engineered organisms to natural organisms, esp. by cross-pollination", but ha ...
* 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 Ecology terminology