- For a list of extraterrestrials in fiction, see List of alien species.
An
introduced,
alien,
exotic,
non-indigenous, or
non-native species, or simply an
introduction, is a
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
living outside its
nativeIn biogeography, a species is defined as indigenous or native to a given region or ecosystem if its presence in that region is the result of only natural resources, with no human intervention. Every natural organism has its own natural range of distribution in which it is regarded as native...
distributional range, which has arrived there by human activity, either deliberate or accidental. Some introduced species are damaging to the ecosystem they are introduced into, others negatively affect agriculture and other human uses of natural resources, or impact on the health of animals and humans. A
list of introduced species is given in a separate article. Introduced species and their effects on natural environments is a controversial subject and one that has gained much scrutiny by scientists, governments, farmers and others.
Terminology
The terminology associated with introduced species is presently in flux for a variety of reasons. Other terms that are used sometimes interchangeably (having the same or similar meanings) with
introduced are
acclimatized,
adventive,
naturalized,
immigrant, and
xenobiotic. Nonetheless, distinctions can and should be made between some of these terms.
In the broadest and most widely used sense, an introduced species is synonymous with
non-native and therefore applies as well to most garden and farm organisms; these adequately fit the basic definition given above. However, some sources add to that basic definition: "...and are now reproducing in the wild", which removes from consideration as
introduced all of those species raised or grown in gardens or farms that do not survive without tending by people. With respect to plants, these latter are in this case defined as either
ornamental or
cultivated plants.
The following definition from the
United States Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to regulate chemicals and protect human health by safeguarding the natural environment: air, water, and land...
, although perhaps lacking ecological sophistication, is more typical:
introduced species are .."[s]pecies that have become able to survive and reproduce outside the habitats where they evolved or spread naturally". However, introduction of a species outside its native range is often all that is required to be qualified as an "introduced species" such that one can distinguish between introduced species that may only occur in cultivation, under domestication or captivity whereas other become established outside their native range and reproduce without human assistance. Such species might be termed "naturalized", "established", "wild non-native species", or "invasive". The transition from introduction, to establishment and invasion has been described by 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..
An
invasive species'Invasive species' is a phrase with several definitions. The first definition expresses the phrase in terms of non-indigenous species that adversely affect the habitats they invade economically, environmentally or ecologically...
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".
Although some argue that "invasive" is a loaded word and harm is difficult to define, the fact of the matter is that organisms have and continue to be introduced to areas where they are not native, sometimes with, usually without, much regard to the harm that could result.
From a regulatory perspective, it is neither desirable nor practical to simply list as undesirable or outright ban all non-native species (although the
State of HawaiiHawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August...
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.
In
Great BritainGreat Britain is an island lying to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island. With a population of about 59.6 million people, it is the third most populated island on Earth. Great Britain is surrounded by over 1000 smaller...
the
Wildlife and Countryside Act 1981The Wildlife and Countryside Act 1981 is an Act of Parliament in the United Kingdom which aims to protect the wildlife and countryside of the United Kingdom...
prevents the introduction of any animal not naturally occurring in the wild, and also any of a list of both animals or plants which have been introduced previously and have proved to be invasive.
Table of terms related to "Introduced Species"
NATIVE |
NON-NATIVE
INTRODUCED (broad definition) |
INDIGENOUS
or ENDEMIC |
CULTIVATED
and
LIVESTOCK |
Established in the wild
INTRODUCED
(narrow definition) |
INVASIVE
(pest) |
All others
not listed* |
*Not listed in any "official" source as a pest species
Nature of introductions
By
definitionThe terminology in this page contains definitions for invasion biology terms in common usage today, taken from accessible publications. References for each definition are included...
, 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 believe that the newly introduced species will be in some way beneficial to humans in its new location. 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.
Perhaps the most common motivation for introducing a species into a new place is that of economic gain. Examples of species introduced for the purposes of benefiting
agricultureAgriculture is the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of human civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and...
,
aquacultureAquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
or other economic activities are widespread. Eurasian carp was first introduced to the United States as a potential food source. The apple snail was released in Southeast Asia with the intent that it be used as a protein source, and subsequently to places like Hawaii to establish a food industry. In Alaska, foxes were introduced to many islands to create new populations for the fur trade. The timber industry promoted the introduction of Monterey Pine (
Pinus radiata) from California to Australia and New Zealand as a commercial timber crop. These examples represent only a small subsample of species that have been moved by humans for economic interests.
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) that threatens the endemic California salamander (
Ambystoma californiense) was introduced to California as a source of bait for fishermen. Pet animals have also been frequently transported into new areas by humans, and their escapes have resulted in several successful introductions, such as those of feral cats and parrots.
Many plants have been introduced with the intent of aesthetically improving public recreation areas or private properties. The introduced
Norway MapleAcer platanoides is a species of maple native to eastern and central Europe and southwest Asia, from France east to Russia, north to southern Scandinavia and southeast to northern Iran....
for example occupies a prominent status in many of Canada's parks. The transport of ornamental plants for landscaping use has and continues to be a source of many introductions. Some of these species have escaped horticultural control and become
invasiveInvasive may refer to:*A military invasion*An invasive species*An invasive medical procedure*The invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer...
. Notable examples include
water hyacinthThe seven species of water hyacinth comprise the genus Eichhornia. Water hyacinth is a free-floating perennial aquatic plant native to tropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as 1 meter in height. The leaves...
, salt cedar, and
purple loosestrifeLythrum salicaria is a flowering plant belonging to the family Lythraceae, native to Europe, Asia, northwest Africa, and southeastern Australia. The name is commonly cited unhyphenated as purple loosestrife, but it should not be confused with other plants sharing the name loosestrife that are...
.
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 starlings to North America by Englishman
Eugene SchieffelinEugene Schieffelin belonged to the and the New York Zoological Society. He was responsible for introducing the starling to North America, where it has become a serious pest.-Starling release:In 1890, he released 60 starlings into New York City’s Central Park...
, a lover of the works of Shakespeare, 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 is the introduction of the
European rabbitThe European Rabbit is a species of rabbit native to south west Europe . It has been widely introduced elsewhere often with devastating effects on local biodiversity...
to
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
by one
Thomas AustinThomas Austin was a pioneer settler in Van Diemen’s Land and Winchelsea, Victoria, Australia, and is generally credited with the introduction of rabbits into Australia in 1859....
, a British landowner who had the rabbits released on his estate in Victoria because he missed hunting them. A more recent example is the introduction of the
wall lizardThe common wall lizard is a species of lizard with a large distribution in Europe and well-established introduced populations in North America, where it is also called the European wall lizard...
to North America by a
CincinnatiCincinnati is a city in the U.S. state of Ohio and the county seat of Hamilton County. The municipality is located north of the Ohio River at the Ohio-Kentucky border. The population within city limits was estimated to be 333,336 in 2008, making it the state's third largest city...
boy, George Rau, in the 1950s after a family vacation to Italy.
Intentional introductions have also been undertaken with the aim of ameliorating environmental problems. A number of fast spreading plants such as
Garlic MustardGarlic mustard is a biennial flowering plant in the Mustard family, Brassicaceae. It is native to Europe, western and central Asia, and northwestern Africa, from Morocco, Iberia and the British Isles, north to northern Scandinavia, and east to northern India and western China...
and
kudzuKudzu, Pueraria lobata is one of about 20 species in the genus Pueraria in the pea family Fabaceae, subfamily Faboideae. It is a climbing, coiling, and trailing vine native to southern Japan and southeast China...
have been introduced as a means of
erosionErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
control. Other species have been introduced as biological control agents to control invasive species and 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 ParkYellowstone National Park, established by the U.S. Congress as a national park on March 1, 1872 , is located primarily in the U.S. state of Wyoming, though it also extends into Montana and Idaho. The park was the first of its kind, and is known for its wildlife and its many geothermal features,...
in the U.S., and the
Red kiteThe Red Kite is a medium-large bird of prey in the family Accipitridae, which also includes many other diurnal raptors such as eagles, buzzards and harriers. The species is currently endemic to the Western Palearctic region in Europe and northwest Africa, though formerly also occurred just outside...
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.
The above examples highlight the intent of humans to introduce species as a means of incurring some benefit. While these benefits have in some cases been realized, introductions have also resulted in unforeseen costs, particularly when introduced species take on characteristics of invasive species.
Non-native species can become such a common part of an environment, culture, and even diet that little thought is given to their geographic origin. For example, soybeans, kiwi fruit, wheat and all livestock except the
llamaThe llama is a South American camelid, widely used as a pack animal by the Incas and other natives of the Andes mountains. In South America llamas are still used as beasts of burden, as well as for the production of fiber and meat....
and the
turkeyA turkey is either of two living species of large birds in the genus Meleagris. One species, Meleagris gallopavo, commonly known as the Wild Turkey, is native to the forests of North America...
are non-native species to North America. Collectively, non-native crops and livestock comprise 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.
Accidental introductions
Unintentional introductions occur when species are transported by human vectors. For example, three species of
ratRats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
(the Black, Norway and Polynesian) have spread to most of the world as hitchhikers on ships. There are also numerous examples of marine organisms being transported in
ballast waterBallast water discharge typically contains a variety of biological materials, including plants, animals, viruses, and bacteria. These materials often include non-native, nuisance, exotic species that can cause extensive ecological and economic damage to aquatic ecosystems. Ballast water discharges...
, one being the
zebra musselThe zebra mussel, Dreissena polymorpha, is a species of small freshwater mussel, an aquatic bivalve mollusc. This species was originally native to the lakes of southeast Russia...
. Over 200 species have been introduced to the
San Francisco BaySan Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...
in this manner making it the most heavily invaded estuary in the world. Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native.
Introduced plants and algae
Many non-native plants have been introduced into new territories, initially as either
ornamental plantOrnamental plants are typically grown in the flower garden or as house plants. Most commonly they are grown for the display of their flowers. Other common ornamental features include leaves, scent, fruit, stem and bark. In some cases, unusual features may be considered ornamental, such as the...
s or for
erosionErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
control, stock feed, or forestry. Whether an exotic will become invasive is seldom understood in the beginning, and many non-native ornamentals languish in the trade for years before suddenly naturalizing and becoming invasive.
Peaches, for example, originated in Persia, and have been carried to much of the populated world. Tomatoes are native to the Andes. Squash (pumpkins), maize, and tobacco are native to the Americas, but were introduced to the Old World. Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously
competeInterspecific competition, in ecology, is a form of competition in which individuals of different species vie for the different resource in an ecosystem...
with natives, but simply increase the biodiversity of the area.
Dandelions are also introduced species to North America.
A very troublesome marine species in southern Europe is the
seaweedSeaweedSeaweed has antioxidents. Is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
Caulerpa taxifoliaCaulerpa taxifolia is a species of seaweed, an alga of the genus Caulerpa. Native to the Indian Ocean, it has been commonly used as ornamentation in aquarium installations around the world...
.
Caulerpa was first observed in the
Mediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by Africa, and on the east by the Levant. The sea is technically a part of the Atlantic Ocean, although it...
in 1984, off the coast of
MonacoMonaco , officially the Principality of Monaco , is a small sovereign city-state located in South Western Europe on the northern central coast of the Mediterranean Sea, having a land border on three sides only with France, and being about away from Italy. Its size is just under 2 km² with an...
. By 1997, it had covered some 50 km². It has a strong potential to overgrow natural
biotopeBiotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. Biotope is almost synonymous with the term habitat, but while the subject of a habitat is a species or a population, the subject of a biotope is a biological...
s, and represents a major risk for sublittoral
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s. The origin of the alga in the Mediterranean was thought to be either as a migration through the
Suez CanalThe Suez Canal is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened on November 1869, it allows water transportation between Europe and Asia without navigating around Africa...
from the Red Sea, or as an accidental introduction from an aquarium.
Japanese knotweedJapanese Knotweed is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea...
grows profusely in many nations. Human beings introduced it into many places in the 19th century. It is a source of
resveratrolResveratrol is a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi. Resveratrol has also been produced by chemical synthesis and is sold as a nutritional supplement derived primarily from Japanese knotweed...
, a dietary supplement.
Introduced animals
One example of introducing an exotic animal was carried out by a lover of the works of
ShakespeareWilliam Shakespeare was an English poet and playwright, widely regarded as the greatest writer in the English language and the world's preeminent dramatist. He is often called England's national poet and the "Bard of Avon"...
, who wanted to introduce all of the birds mentioned in Shakespeare's plays into the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
. He deliberately released eighty
starlingsThe European Starling, Common Starling or just Starling is a passerine bird in the family Sturnidae.This species of starling is native to most of temperate Europe and western Asia...
into
Central ParkCentral Park is a large public, urban park that occupies over a square mile in the heart of Manhattan in New York City. It is host to approximately twenty-five million visitors each year...
in
New York CityNew York is the most populous city in the United States, and the center of the New York metropolitan area, which is among the most populous urban areas in the world. A leading global city, New York exerts a powerful influence over worldwide commerce, finance, culture, fashion and entertainment...
in 1890, and another forty in 1891. The starling had been introduced previously into
OhioOhio is a Midwestern state of the United States. The thirty-fourth largest state by area in the U.S., it is the seventh-most populous with nearly 11.5 million residents...
and had failed to survive.
Other examples of introduced animals include the
gypsy mothThe gypsy moth, Lymantria dispar, is a moth in the family Lymantriidae of Eurasian origin. Originally ranging from Europe to Asia, it was introduced to North America in the late 1860s and has been expanding its range ever since.-Eggs:...
in eastern
North AmericaNorth America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...
, the
zebra musselThe zebra mussel, Dreissena polymorpha, is a species of small freshwater mussel, an aquatic bivalve mollusc. This species was originally native to the lakes of southeast Russia...
and
alewifeThe alewife is a species of herring. There are anadromous and landlocked forms. The landlocked form is also called a sawbelly or mooneye...
in the
Great LakesThe Great Lakes are a collection of freshwater lakes located in eastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth. They are sometimes referred to as the "Third...
, the
Canada GooseThe Canada Goose is a wild goose belonging to the genus Branta, which is native to Arctic and temperate regions of North America, having a black head and neck, white patches on the face, and a brownish-gray body...
and
Gray SquirrelThe Eastern Gray Squirrel , or the Grey Squirrel, depending on region, is a tree squirrel native to the eastern and midwestern United States and to the southerly portions of the eastern provinces of Canada...
in Europe, the
MuskratThe muskrat , the only species in genus Ondatra, is a medium-sized semi-aquatic rodent native to North America, and introduced in parts of Europe, Asia, and South America. The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats...
in Europe and Asia, the
Cane ToadThe cane toad , also known as the Giant Neotropical Toad or Marine Toad, is a large, terrestrial true toad native to Central and South America. It is a member of the subgenus Chaunus of the genus Bufo, which includes many different true toad species found throughout Central and South America...
and
Red foxThe red fox is a mammal of the order Carnivora. It has the widest range of any terrestrial carnivore, being native to Canada, Alaska, almost all of the contiguous United States, Europe, North Africa and almost all of Asia, including Japan. In Ireland and the UK, where there are no longer any other...
in Australia, Nutria in North America, Eurasia, and
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
, and the
Common Brushtail PossumThe Common Brushtail Possum is a nocturnal, semi-arboreal marsupial of the family Phalangeridae, and the largest of the possums....
in
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
.
Invasive exotic diseases
History is rife with the spread of exotic diseases, such as the introduction of
smallpoxSmallpox is an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning spotted, or varus, meaning "pimple"...
into the Americas, where it obliterated entire
Native AmericanThe indigenous peoples of the Americas are the pre-Columbian inhabitants of the Americas, their descendants, and many ethnic groups who identify with those peoples...
civilizations before they were ever even seen by Europeans.
Problematic exotic disease introductions in the past century or so include the
chestnut blightThe chestnut blight fungus, Cryphonectria parasitica , virtually eliminated the once-widespread American chestnut tree....
which has virtually extinguished the
American chestnutThe American Chestnut is a large, deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range...
, and
Dutch elm diseaseDutch elm disease is a fungal disease of elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native populations of elms which had not had the opportunity...
, which has severely damaged the
American elmUlmus americana, generally known as the American Elm or, less commonly, as the White Elm or Water Elm, is a species native to eastern North America, occurring from Nova Scotia west as far as British Columbia, from northern Alberta at the top of its range, south to Florida and central Texas...
.
Most commonly introduced species
Some species, such as the
Brown RatThe brown rat, common rat, sewer rat, Hanover rat, Norway rat, Norwegian rat, or wharf rat is one of the best known and most common rats. One of the largest muroids, it is a brown or grey rodent with a body up to long, and a similar tail length; the male weighs on average and the female...
,
House SparrowThe House Sparrow is a member of the Old World sparrow family Passeridae, considered by some to be a relative of the Weaver Finch Family.It occurs naturally in most of Europe and much of Asia...
,
Ring-necked PheasantThe Common Pheasant , is a bird in the pheasant family . It is native to Asia and has been widely introduced elsewhere as a game bird. In parts of its range, namely in places where none of its relatives occur such as in Europe , it is simply known as the "pheasant"...
and
European StarlingThe European Starling, Common Starling or just Starling is a passerine bird in the family Sturnidae.This species of starling is native to most of temperate Europe and western Asia...
, have been introduced very widely. In addition there are some
agriculturalAgriculture is the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of human civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and...
and
petA pet is an animal kept for companionship and enjoyment or a household animal, as opposed to livestock, laboratory animals, working animals or sport animals, which are kept for economic reasons. The most popular pets are noted for their loyal or playful characteristics, for their attractive...
species that frequently become
feralA feral organism is one that has escaped from domestication and returned, partly or wholly, to a wild state. The introduction of feral animals or plants to their non-native regions, like any introduced species, can disrupt ecosystems and may, in some cases, contribute to extinction of indigenous...
; these include
rabbitRabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genera in the family classified as rabbits, including the European rabbit , Cottontail rabbit , and the Amami rabbit...
s,
dogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
s,
goatThe domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep: both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s,
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
,
pigPigs are a genus of even-toed ungulates within the family Suidae. The name hog most commonly refers to the domestic pig in everyday parlance, but technically encompasses several distinct species, including the wild boar...
s and
catThe cat , also known as the domestic cat or housecat to distinguish it from other felines and felids, is a small carnivorous mammal that is valued by humans for its companionship and its ability to hunt vermin and household pests...
s.
Introduced species on islands
Perhaps the best place to study problems associated with introduced species is on islands. Depending upon the isolation (how far an island is located from continental biotas), native island biological communities may be poorly adapted to the threat posed by exotic introductions. Often this can mean that no natural predator of an introduced species is present, and the non-native spreads uncontrollably into open or occupied
nicheIn ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different school if the members of these schools utilize significantly different...
.
An additional problem is that birds native to small islands may have become flightless because of the absence of predators prior to introductions, and cannot readily escape danger. The tendency of rails in particular to evolve flightless forms on islands has led to the disproportionate number of extinctions in that family.
The field of
island restorationThe ecological restoration of islands, or island restoration, is the application of the principles of ecological restoration to islands and island groups. Islands, due to their isolation, are home to many of the world's endemic species, as well as important breeding grounds for seabirds and some...
has developed as a field of
conservation biologyConservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction. It is an interdisciplinary subject drawing on sciences, economics, and the practice of natural...
and ecological restoration, a great deal of which deals with the eradication of introduced species.
New Zealand
In
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
the largest commercial crop is
Pinus radiata, the Monterey Pine from
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
, which grows better in New Zealand than in California. However, the pine forests are also occupied by
deerDeer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Animals from related families within the order Artiodactyla are often also considered to be deer – these include muntjac and water deer...
from
North AmericaNorth America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...
and
EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
and by
possumA possum is any of about 69 small to medium-sized arboreal marsupial species native to Australia, New Guinea, and Sulawesi . The name derives from their resemblance to the opossums of the Americas...
s from
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
. All are exotic species and all have thrived in the New Zealand environment. The pines are seen as beneficial while the deer and possums are regarded as serious pests.
Common
gorseGorse, furze, furse or whin is a genus of about 20 species of spiny evergreen shrubs in the subfamily Faboideae of the pea family Fabaceae, native to western Europe and northwest Africa, with the majority of species in Iberia.Gorse is closely related to the brooms, and like them, has green stems...
, originally a hedge plant in
ScotlandScotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, was introduced to New Zealand for the same purpose. Like the radiata pine, it has shown a favour to its new climate and is regarded as a noxious plant which threatens to obliterate native plants in much of the country and is hence routinely eradicated, though it can also provide a nursery environment for native plants to reestablish themselves.
RabbitRabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genera in the family classified as rabbits, including the European rabbit , Cottontail rabbit , and the Amami rabbit...
s, introduced as a food source by sailors in the 1800s, have become a severe nuisance to farmers, notably in South Island. The
myxomatosisMyxomatosis is a disease which affects rabbits. It is caused by the Myxoma virus. First observed in Uruguay in the late 1800s, it was deliberately introduced into Australia in 1950 in an attempt to control rabbit infestation and population there; see rabbits in Australia...
virusA virus is an infectious agent too small to be seen directly with a light microscope. They are not made of cells and can only replicate inside the cells of another organism . Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
was illegally imported and illegally released but it had little lasting effect upon the rabbit population other than to make it more resistant to the virus.
Rats, brought either by the first humans to arrive in New Zealand (the
MaoriThe Māori are the indigenous Polynesian people of New Zealand . The group probably arrived in southwestern Polynesia in several waves at some time before 1300...
) or by Europeans have had a devastating effect upon native birdlife, particularly as many New Zealand birds are flightless. Feral cats and dogs which were originally brought as pets are also known to kill large numbers of birds. A recent (2006) study in South Island has shown that even domestic cats with a ready supply of food from their owners may kill hundreds of birds in a year, including natives.
Sparrows, which were brought to control insects upon the introduced
grainGRAIN is an international non-governmental organization based in Barcelona, Spain, which works toward sustainable agriculture. It was formed upon the realization that the genetic diversity of the world's food crops are being drastically eliminated...
crops, have displaced native birds as have
Rainbow LorikeetThe Rainbow Lorikeet, Trichoglossus haematodus is a species of Australasian parrot found in Australia, eastern Indonesia , Papua New Guinea, New Caledonia, Solomon Islands and Vanuatu. In Australia, it is common along the eastern seaboard, from Queensland to South Australia and northwest Tasmania...
s and cockatoos (both from Australia) which fly free around areas west of
AucklandThe Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with a population approaching 1.4 million residents, percent of the country's population. Demographic trends indicate that it will continue to grow faster than the rest...
City such as the
Waitakere RangesThe Waitakere Ranges are a chain of hills generally running approximately 25 km from north to south, 25 km west of central Auckland, New Zealand. The maximum elevation within the ranges is 474 m . The ranges and surrounding areas were traditionally known to local Māori as Te Wao Nui a Tiriwa...
.
In much of the New Zealand the Australian
black swanThe Black Swan is a large waterbird which breeds mainly in the southeast and southwest regions of Australia.-Taxonomy:The black swan was first described by English naturalist John Latham in 1790...
has effectively eliminated the existence of the previously introduced
mute swanThe Mute Swan is a species of swan, and hence in turn a member of the duck, goose and swan family Anatidae. It is native to much of Europe and Asia, and the far north of Africa. It is also an introduced species in North America, Australasia and southern Africa...
.
Two notable varieties of spiders have also been introduced: the white tail spider and the
black widow spiderLatrodectus mactans, the Black widow, is a species of spider in the genus Latrodectus. They are well known for the distinctive black and red coloring of the female of the species and for the fact that she will occasionally eat her mate after reproduction. The highly venomous species is native to...
. Both may have arrived inside shipments of fruit. Prior to this the only spider (and the only poisonous animal) dangerous to humans was the native
katipoLatrodectus katipo, the katipo, is an endangered species of spider native to New Zealand. A member of the genus Latrodectus, it is related to the Australian redback spider, and the North American black widow spiders. The species is venomous to humans, capable of delivering a comparatively...
which is very similar to the black widow and which is known to successfully interbreed with the more aggressive North American variety.
Genetic pollution
Purebred naturally evolved region specific wild
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
can be threatened with
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
in a big way through the process of
genetic pollutionGenetic pollution is undesirable gene flow into wild populations. The term is usually associated with the gene flow from a genetically engineered organism to a non GE organism; however, conservation biologists and conservationists are using it to describe gene flow from a domestic, feral,...
i.e. uncontrolled hybridization,
introgressionIntrogression, in genetics , is the movement of a gene from one species into the gene pool of another by backcrossing an interspecific hybrid with one of its parents. Introgression is a long-term process; it may take many hybrid generations before the backcrossing occurs...
and genetic swamping which leads to homogenization or replacement of local genotypes as a result of either a numerical and/or
fitnessFitness is a central concept in evolutionary theory. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation...
advantage of introduced plant or animal. Nonnative species can bring about a form of extinction of native plants and animals by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones where the abundant ones can interbreed with them swamping the entire rarer gene pool creating hybrids thus driving the entire original purebred native stock to complete extinction. Attention has to be focused on the extent of this under appreciated problem that is not always apparent from
morphologicalIn biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
(outward appearance) observations alone. Some degree of
gene flowIn population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
may be a normal, evolutionarily constructive process, and all constellations of
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
s and genotypes cannot be preserved however, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.
See also
- Avian range expansion
Avian range expansion describes how birds expand their habitat. Because of the activities of birdwatchers these range expansions are well documented. Throughout the last century a number of birds have expanded their range...
- Biodiversity
Biodiversity is the variation of life forms within a given ecosystem, biome, or for the entire Earth. Biodiversity is often used as a measure of the health of biological systems...
- Biological dispersal
Biological dispersal refers to a species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
- Genetic pollution
Genetic pollution is undesirable gene flow into wild populations. The term is usually associated with the gene flow from a genetically engineered organism to a non GE organism; however, conservation biologists and conservationists are using it to describe gene flow from a domestic, feral,...
- Invasion biology terminology
The terminology in this page contains definitions for invasion biology terms in common usage today, taken from accessible publications. References for each definition are included...
- Invasive species
'Invasive species' is a phrase with several definitions. The first definition expresses the phrase in terms of non-indigenous species that adversely affect the habitats they invade economically, environmentally or ecologically...
- List of introduced bird species
- List of introduced species
External links