Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora
Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...

 and fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...

, and for specific restoration-preservation processes in native habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

s, with several definitions.
  • The first definition, the most used, applies to non-indigenous species, or "non-native", plants or animals that adversely affect the habitat
    * Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

    s and bioregions they invade economically, environmentally, and/or ecologically. They disrupt by dominating a region, wilderness areas
    Wilderness or wildland is a natural environment on Earth that has not been significantly modified by human activity. It may also be defined as: "The most intact, undisturbed wild natural areas left on our planet—those last truly wild places that humans do not control and have not developed with...

    , particular habitat
    * Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

    s, and/or wildland-urban interface
    Wildland-urban interface
    A wildland–urban interface refers to the zone of transition between unoccupied land and human development. Communities that are within of the zone may also be included...

     land from loss of natural controls (i.e.: predators
    In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

     or herbivore
    Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

    s). This includes non-native invasive plant species labeled as exotic pest plants and invasive exotics, in restoration parlance, growing in native plant communities. It has been used in this sense by government
    Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

     organizations as well as conservation groups such as the International Union for Conservation of Nature (IUCN) and the California Native Plant Society
    California Native Plant Society
    The California Native Plant Society is a California not-for-profit organization that seeks to increase understanding of California's native flora and to preserve that flora. Its "paramount purpose is to preserve wild plants".-History:...

    . The European Union
    European Union
    The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

     defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution area, and secondly, threaten biological diversity. It is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds. The kudzu vine
    Kudzu is a plant 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. Its name comes from the Japanese name for the plant, . It is a weed that climbs over trees or shrubs and grows so...

     (Pueraria lobata), Andean Pampas grass
    Cortaderia jubata
    Cortaderia jubata is a species of grass known by several common names, including Purple pampas grass and Andean pampas grass. It is similar to its more widespread relative, the Pampas Grass C...

     (Cortaderia jubata), and yellow starthistle (Centaurea solstitialis) are examples.

  • The second definition includes the first, but broadens the boundaries to include indigenous or native species, with the non-native ones, that disrupt by a dominant colonization of a particular habitat or wildlands area from loss of natural controls (i.e.: predators or herbivores). Deer
    Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...

     are an example, considered to be overpopulating their native zones and adjacent suburban gardens, by some in the Northeastern
    Northeastern United States
    The Northeastern United States is a region of the United States as defined by the United States Census Bureau.-Composition:The region comprises nine states: the New England states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont; and the Mid-Atlantic states of New...

     and Pacific Coast
    West Coast of the United States
    West Coast or Pacific Coast are terms for the westernmost coastal states of the United States. The term most often refers to the states of California, Oregon, and Washington. Although not part of the contiguous United States, Alaska and Hawaii do border the Pacific Ocean but can't be included in...

     regions of the United States.

  • The third definition identifies invasive species as a widespread nonindigenous species. This one can be too broad, as not every nonindigenous or "introduced" species has an adverse effect on a nonindigenous environment. A nonadverse example is the common goldfish (Carassius auratus), though common outside its native range globally, it is rarely in harmful densities to a native habitat.

Because of the variability of its definition, and because definitions are often from a socio-economic perspective, the phrase invasive species is often criticized as an imprecise term for the scientific field of ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

. This article concerns the first two definitions; for the third, see Introduced species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...


Conditions that lead to invasion

Scientists propose several mechanisms to explain invasive species, including species-based mechanisms and ecosystem-based mechanisms. It is most likely a combination of several mechanisms that cause an invasive situation to occur, since most introduced plants, biotic and animals do not become invasive.

Species-based mechanisms

Species-based characteristics focus on competition. While all species compete to survive, invasive species appear to have specific traits or combinations of specific traits that allow them to outcompete native species. Sometimes they just have the ability to grow and reproduce more rapidly than native species; other times it is more complex, involving a number of traits and interactions.

Studies seem to indicate certain traits mark a species as potentially invasive. One study found that of a list of invasive and noninvasive species, 86% of the invasive species could be identified from the traits alone. Another study found invasive species tended only to have a small subset of the invasive traits, and that many of these invasive traits were found in noninvasive species, as well indicating that invasiveness involves complex interaction not easily categorized. Common invasive species traits include:
  • The ability to reproduce both asexually
    Asexual reproduction
    Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

     and sexually
    Sexual reproduction
    Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...

  • Fast growth
  • Rapid reproduction
  • High dispersal
    Biological dispersal
    Biological dispersal refers to 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...

  • Phenotypic plasticity
    Phenotypic plasticity
    Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

     (the ability to alter one's growth form to suit current conditions)
  • Tolerance of a wide range of environmental conditions (Ecological competence
    Ecological competence
    Ecological competence is the ability of an organism, often a pathogen, to survive and compete in new habitats. In the case of plant pathogens, it is also their ability to survive between growing seasons. For example, peanut clump virus can survive in the spores of its fungal vector until a new...

  • Ability to live off of a wide range of food types (generalist
    Generalist and specialist species
    A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...

  • Association with humans
  • Other successful invasions

Typically an introduced species must survive at low population densities before it becomes invasive in a new location. At low population densities, it can be difficult for the introduced species to reproduce and maintain itself in a new location, so a species might be transported to a location a number of times before it becomes established. Repeated patterns of human movement from one location to another, such as ships sailing to and from ports or cars driving up and down highways, allow for species to have multiple opportunities for establishment (also known as a high propagule pressure
Propagule pressure
Propagule pressure is a composite measure of the number of individuals of a species released into a region to which they are not native. It incorporates estimates of the absolute number of individuals involved in any one release event and the number of discrete release events...


An introduced species might become invasive if it can outcompete native species for resources, such as nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s, light, physical space, water or food. If these species evolved under great competition
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...

 or predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

, the new environment may allow them to proliferate quickly. Ecosystems in which all available resources are being used to their fullest capacity by native species can be modeled as zero-sum
In game theory and economic theory, a zero-sum game is a mathematical representation of a situation in which a participant's gain of utility is exactly balanced by the losses of the utility of other participant. If the total gains of the participants are added up, and the total losses are...

 systems, where any gain for the invader is a loss for the native. However, such unilateral competitive superiority (and extinction of native species with increased populations of the invader) is not the rule. Invasive species often coexist with native species for an extended time, and gradually the superior competitive ability of an invasive species becomes apparent as its population grows larger and denser and it adapts to its new location.

An invasive species might be able to use resources previously unavailable to native species, such as deep water sources accessed by a long taproot
A taproot is an enlarged, somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally.Plants with taproots are difficult to transplant...

, or an ability to live on previously uninhabited soil types. For example, barbed goatgrass (Aegilops triuncialis
Aegilops triuncialis
Aegilops triuncialis native to Palestine and the Levant....

) was introduced to California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 on serpentine soil
Serpentine soil
A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle....

s, which have low water-retention, low nutrient levels, a high Mg/Ca ratio, and possible heavy metal toxicity. Plant populations on these soils tend to show low density, but goatgrass can form dense stands on these soils, crowding out native species that have not adapted well to growing on serpentine soils.

Ecological facilitation
Facilitation describes species interactions that benefit at least one of the participants and cause harm to neither. Facilitations can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one species benefits and the other is unaffected...

 is the mechanism by which some species can alter their environment using chemicals or manipulating abiotic factors, allowing the species to thrive, while making the environment less favorable to other species with which it competes. One such facilitative mechanism is allelopathy
Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms...

, also known as chemical competition or interference competition. In allelopathy, a plant will secrete chemicals which make the surrounding soil uninhabitable, or at least inhibitory, to competing species.

Examples of this in Centaurea
Centaurea is a genus of between 350 and 600 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding regions are particularly species-rich...

 are Centaurea solstitialis (yellow starthistle) and Centaurea diffusa (diffuse knapweed
Diffuse knapweed
Diffuse Knapweed , also known as White Knapweed or Tumble Knapweed, is a member of the genus Centaurea in the family Asteraceae. It is native to Asia Minor , the Balkans, , Ukraine, and southern Russia. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm...

). These Eastern Europe
Eastern Europe
Eastern Europe is the eastern part of Europe. The term has widely disparate geopolitical, geographical, cultural and socioeconomic readings, which makes it highly context-dependent and even volatile, and there are "almost as many definitions of Eastern Europe as there are scholars of the region"...

an noxious weeds have spread their way through the western
Western United States
.The Western United States, commonly referred to as the American West or simply "the West," traditionally refers to the region comprising the westernmost states of the United States. Because the U.S. expanded westward after its founding, the meaning of the West has evolved over time...

 and West Coast states
West Coast of the United States
West Coast or Pacific Coast are terms for the westernmost coastal states of the United States. The term most often refers to the states of California, Oregon, and Washington. Although not part of the contiguous United States, Alaska and Hawaii do border the Pacific Ocean but can't be included in...

. Experiments show that 8-hydroxyquinoline
8-Hydroxyquinoline is an organic compound with the formula C9H7NO. It is a derivative of the heterocycle quinoline by placement of an OH group on carbon number 8...

, a chemical produced at the root of C. diffusa, has a negative effect only on plants that have not co-evolved with C. diffusa. Such co-evolved native plants have also evolved defenses, and C. diffusa and C. solstitialis do not appear in their native habitats to be overwhelmingly successful competitors. This shows how difficult it can be to predict if a species will be invasive just from evaluating its behavior in its native habitat, and demonstrates the potential for novel weapons to aid in invasiveness.

Changes in fire regimens are another form of facilitation. Bromus tectorum, originally from Eurasia, is highly fire-adapted. It not only spreads rapidly after burning, but also increases the frequency and intensity (heat) of fires, by providing large amounts of dry detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...

 during the dry fire season in western North America. In areas where it is widespread, it has altered the local fire regimen so much that native plants cannot survive the frequent fires, allowing B. tectorum to further extend and maintain dominance in its introduced range.

Facilitation also occurs when one species physically modifies a habitat and that modification is advantageous to other species. For example, zebra mussel
Zebra mussel
The zebra mussel, Dreissena polymorpha, is a small freshwater mussel. This species was originally native to the lakes of southeast Russia being first described in 1769 by a German zoologist Peter Simon Pallas in the Ural, Volga and Dnieper rivers. They are still found nearby, as Pontic and Caspian...

s increase habitat complexity on lake floors, providing crevices in which invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s live. This increase in complexity, together with the nutrition provided by the waste products of mussel filter-feeding
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

, increases the density and diversity of benthic
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...

 invertebrate communities.

Ecosystem-based mechanisms

In ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s, the amount of available resources and the extent to which those resources are used by organisms determines the effects of additional species on the ecosystem. In stable ecosystems, equilibrium exists in the use of available resources. These mechanisms describe a situation in which the ecosystem has suffered a disturbance which changes the fundamental nature of the ecosystem.
When changes occur in an ecosystem, like forest fires in an area, normal succession would favor certain native grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

es and forb
A forb is a herbaceous flowering plant that is not a graminoid . The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory.-Etymology:...

s. With the introduction of a species that can multiply and spread faster than the native species, the balance is changed and the resources that would have been used by the native species are now used by an invader. This has an impact on the ecosystem and changes its composition of organisms and their use of available resources. Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 and phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 are often the limiting factors in these situations.

Every species has a role to play in its native ecosystem; some species fill large and varied roles, while others are highly specialized. These roles are known as niche
Ecological niche
In 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 pod if the members of these pods utilize significantly different food...

. Some invading species are able to fill niches that are not used by native species, and they also can create niches that did not exist.

When changes occur to ecosystems, conditions change that impact the dynamics of species interaction and niche development. This can cause once rare species to replace other species, because they now can use greater available resources that did not exist before; an example would be the edge effect
Edge effect
The edge effect in ecology is the effect of the juxtaposition or placing side by side of contrasting environments on an ecosystem.This term is commonly used in conjunction with the boundary between natural habitats, especially forests, and disturbed or developed land. Edge effects are especially...

. The changes can favor the expansion of a species that would not have been able to colonize areas and niches that did not exist before.


Although an invasive species is often defined as an introduced species that has spread widely and causes harm, some species native to a particular area can, under the influence of natural events, such as long-term rainfall changes or human modifications to the habitat, increase in numbers and become invasive.

All species go through changes in population numbers, in many cases accompanied by expansion or contraction of range. Human alterations of the natural landscape
Natural landscape
A natural landscape is a landscape that is unaffected by human activity. A natural landscape is intact when all living and nonliving elements are free to move and change. The nonliving elements distinguish a natural landscape from a wilderness. A wilderness includes areas within which natural...

 are especially significant. This anthropogenic
Human impact on the environment or anthropogenic impact on the environment includes impacts on biophysical environments, biodiversity and other resources. The term anthropogenic designates an effect or object resulting from human activity. The term was first used in the technical sense by Russian...

 alteration of an environment may enable the expansion of a species into a geographical area where it had not been seen before, and thus that species could be described as invasive. In essence, one must define "native" with care, as it refers to some natural geographic range of a species, and is not coincident with human political boundaries. Whether noticed increases in population numbers and expanding geographical ranges is sufficient reason to regard a native species as "invasive" requires a broad definition of the term, but some native species in disrupted ecosystems can spread widely and cause harm, and in that sense become invasive. For example, the Monterey cypress is an endangered endemic, naturally occurring only in two small stands in California. They are being exterminated as exotic invasive species less than 50 miles (80.5 km) from their native home.

Traits of invaded ecosystems

In 1958, Charles S. Elton argued ecosystems with higher species diversity
Species diversity
Species diversity is an index that incorporates the number of species in an area and also their relative abundance. It is a more comprehensive value than species richness....

 were less subject to invasive species because of fewer available niches. Since then, other ecologists have pointed to highly diverse, but heavily invaded ecosystems and have argued ecosystems with high species diversity seem to be more susceptible to invasion. This debate seems largely to hinge on the spatial scale
Scale (spatial)
Spatial scale provides a "shorthand" form for discussing relative lengths, areas, distances and sizes. A microclimate, for instance, is one which might occur in a mountain valley or near a lakeshore, whereas a megatrend is one which involves the whole planet....

 at which invasion studies are performed, and the issue of how diversity affects community susceptibility to invasion remains unresolved. Small-scale studies tend to show a negative relationship between diversity and invasion, while large-scale studies tend to show a positive relationship. The latter result may be an artifact of invasive or non-native species capitalizing on increased resource availability and weaker overall species interactions that are more common when larger samples are considered.

Invasion is more likely if an ecosystem is similar to the one in which the potential invader evolved. Island ecosystems may be prone to invasion because their species are “naïve” and have faced few strong competitors and predators throughout their existence, or because their distance from colonizing species populations makes them more likely to have “open” niches. An example of this phenomenon is the decimation of the native bird populations on Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

 by the invasive brown tree snake
Brown tree snake
The brown tree snake is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia....

. Alternatively, invaded ecosystems may lack the natural competitors and predators that keep introduced species in check in their native ecosystems, a point that is also seen in the Guam example. Lastly, invaded ecosystems have often experienced disturbance, usually human-induced. This disturbance may give invasive species, which are not otherwise co-evolved with the ecosystem, a chance to establish themselves with less competition from more adapted species.


Non-native species have many vectors, including many biogenic ones, but most species considered "invasive" are associated with human activity. Natural range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...

 extensions are common in many species, but the rate and magnitude of human-mediated extensions in these species tend to be much larger than natural extensions, and the distances species can travel to colonize are also often much greater with human agency.

One of the earliest human-influenced introductions involved prehistoric humans introducing the Pacific rat (Rattus exulans) to Polynesia. Today, non-native species come from horticultural
Horticulture is the industry and science of plant cultivation including the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant breeding and genetic...

 plants either in the form of the plants themselves or animals and seeds carried with them, and from animals and plants released through the pet trade. Invasive species also come from organisms stowed away on every type of transport vehicle. For example, ballast water taken up at sea and released in port is a major source of exotic marine life. The invasive freshwater zebra mussel
Zebra mussel
The zebra mussel, Dreissena polymorpha, is a small freshwater mussel. This species was originally native to the lakes of southeast Russia being first described in 1769 by a German zoologist Peter Simon Pallas in the Ural, Volga and Dnieper rivers. They are still found nearby, as Pontic and Caspian...

s, native to the Black
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

, Caspian
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

 and Azov seas
Sea of Azov
The Sea of Azov , known in Classical Antiquity as Lake Maeotis, is a sea on the south of Eastern Europe. It is linked by the narrow Strait of Kerch to the Black Sea to the south and is bounded on the north by Ukraine mainland, on the east by Russia, and on the west by the Ukraine's Crimean...

, were probably transported to the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern 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 by total surface, coming in second by volume...

 via ballast water from a transoceanic vessel. The arrival of invasive propagule
In horticulture, a propagule is any plant material used for the purpose of plant propagation. In asexual reproduction, a propagule may be a woody, semi-hardwood, or softwood cutting, leaf section, or any number of other plant parts. In sexual reproduction, a propagule is a seed or spore...

s to a new site is a function of the site's invasibility.

Species have also been introduced intentionally. For example, to feel more "at home", American colonists formed "Acclimation Societies" that repeatedly released birds that were native to Europe until they finally established along the east coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

. In 2008, U.S. postal workers in Pennsylvania noticed noises coming from inside a box from Taiwan; the box contained more than two dozen live beetles. U.S. Customs and Border Protection
U.S. Customs and Border Protection
U.S. Customs and Border Protection is a federal law enforcement agency of the United States Department of Homeland Security charged with regulating and facilitating international trade, collecting import duties, and enforcing U.S. regulations, including trade, customs and immigration. CBP is the...

 sent the beetles to the Agricultural Research Service
Agricultural Research Service
The Agricultural Research Service is the principal in-house research agency of the United States Department of Agriculture . ARS is one of four agencies in USDA's Research, Education and Economics mission area...

 (ARS) to be expertly identified. The ARS entomologists identified them as rhinoceros beetle
Rhinoceros beetle
The Rhinoceros Beetles or Rhino Beetles are a subfamily of the scarab beetle family . Other common names – some for particular groups of rhino beetles – are for example Hercules beetles, unicorn beetles or horn beetles...

, hercules beetle
Hercules beetle
The Hercules beetle, Dynastes hercules, is the most famous and largest of the rhinoceros beetles. It is native to the rainforests of Central America, South America, and the Lesser Antilles . Their title is well deserved, with some males reaching 6.75 inches in length...

, and king stag beetle
Phalacrognathus muelleri
Phalacrognathus muelleri MacLeay, 1885 is a beetle of the Family Lucanidae.- List of subspecies :* Phalacrognathus muelleri muelleri Origin: Queensland, Australia* Phalacrognathus muelleri fuscomicans Origin: New Guinea-External links:*...

. Because these beetles are not native to the U.S., they could pose a threat to native ecosystems, agriculture, and the environment. To prevent exotic species from becoming a problem in the U.S., special handling and permits are needed when insects and other living materials are shipped from foreign countries. Programs such as Smuggling Interdiction and Trade Compliance
Smuggling Interdiction and Trade Compliance
The Smuggling Interdiction and Trade Compliance Program is a component of the United States Department of Agriculture Animal and Plant Health Inspection Service , Plant Protection and Quarantine...

 (SITC) have also been set up by the USDA
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...

 in an effort to prevent exotic species outbreaks in America.

Economics play a major role in exotic species introduction. The scarcity and demand for the valuable Chinese mitten crab
Chinese mitten crab
The Chinese mitten crab, Eriocheir sinensis is a medium-sized burrowing crab, named for its furry claws that look like mittens, that is native in the coastal estuaries of eastern Asia from Korea in the north to the Fujian province of China in the south...

 is one explanation for the possible intentional release of the species in foreign waters.

Impacts of wildfire

Invasive species often exploit disturbances to an ecosystem (wildfires, roads, foot trails) to colonize an area. Large wildfires are capable of sterilizing soils and removing any trace of life from their path, while adding a variety of nutrients to the soil. In the resulting ecological free-for-all, invasive species can easily dominate native plants, and quickly become established.

Many invasive plant species have the ability to regenerate from their roots. This means if a low intensity fire burns through an area and removes surface vegetation, native species will have to rely on seeds for propagation, while a well-established invasive species with intact roots can regrow as soon as the ecosystem recovers from the fire, and often completely shade out any native vegetation.

Impact of wildfire suppression on spreading

Wildfires often occur in remote areas, requiring fire suppression crews to travel through pristine forest to reach the site. The crews can unwittingly be the bearers of invasive seeds. Should any of these stowaway seeds become established along the way, a new thriving concentration of invasive weeds can be present in as few as six weeks, at which point controlling the outbreak will require years of continued attention to prevent further spread. Also, the disturbance of the soil surface, such as firebreaks for fire prevention, destroying the native cover and exposing open soil, can accelerate 'invasive exotic' plants spreading. In suburban and wildland-urban interface
Wildland-urban interface
A wildland–urban interface refers to the zone of transition between unoccupied land and human development. Communities that are within of the zone may also be included...

 areas, the vegetation clearance and brush removal ordinances of municipalities for defensible space
Defensible space (fire control)
In the context of fire control, Defensible Space is the natural and landscaped area around a structure that has been maintained and designed to reduce fire danger, sometimes called Firescaping. "Defensible space" is also used in the context of wildfires, especially in the wildland-urban interface...

 can result in excessive clear-cutting of native shrubs and perennials that exposes the soil to more light and less competition for invasive plant species.

Fire suppression vehicles are often the major culprits of such outbreaks, as the vehicles are frequently driven on back roads often overgrown with invasive plant species. The undercarriage of the vehicle becomes a prime vessel of transport. In response, on large fires, vehicle washing stations are set up, and it is required that vehicles be "decontaminated" prior to engaging in suppression activities. In addition when suppressing large wild fires, personnel from around the country are often used, further increasing the potential for transport of seeds across the country, thus showing the importance of "cleaning stations".

Ecological impacts

Land clearing and human habitation put significant pressure on local species. Disturbed habitats are prone to invasions that can have adverse effects on local ecosystems, changing ecosystem functions. A species of wetland plant known as aeae in Hawaii (the indigenous Bacopa monnieri
Bacopa monnieri
Bacopa monnieri is a perennial, creeping herb whose habitat includes wetlands and muddy shores...

) is regarded as a pest species in artificially manipulated water bird refuges because it quickly covers shallow mudflats established for endangered Hawaiian stilt (Himantopus mexicanus knudseni
Black-winged Stilt
The Black-winged Stilt or Common Stilt is a widely distributed very long-legged wader in the avocet and stilt family . Opinions differ as to whether the birds treated under the scientific name H. himantopus ought to be treated as a single species and if not, how many species to recognize...

), making these undesirable feeding areas for the birds.

Multiple successive introductions of different non-native species can have interactive effects; the introduction of a second non-native species can enable the first invasive species to flourish. Examples of this are the introductions of the amethyst gem clam
Amethyst gem clam
The amethyst gem clam, Gemma gemma, is a small species of marine bivalve mollusk. It is a member of the family Veneridae, the Venus clams.It is one of the smaller species of marine clam, reaching a length of only 5 mm...

 (Gemma gemma) and the European green crab (Carcinus maenas
Carcinus maenas
Carcinus maenas is a common littoral crab, and an important invasive species, listed among the 100 "world's worst alien invasive species". It is native to the north-east Atlantic Ocean and Baltic Sea, but has colonised similar habitats in Australia, South Africa, South America and both Atlantic and...

). The gem clam was introduced into California's Bodega Harbor
Bodega Bay
Bodega Bay is a shallow, rocky inlet of the Pacific Ocean on the coast of northern California in the United States. It is approximately across and is located approximately northwest of San Francisco and west of Santa Rosa...

 from the East Coast of the United States a century ago. It had been found in small quantities in the harbor but had never displaced the native clam species (Nutricola spp.). In the mid 1990s, the introduction of the European green crab, found to prey preferentially on the native clams, resulted in a decline of the native clams and an increase of the introduced clam populations.

In the Waterberg
Waterberg Biosphere
The Waterberg Biosphere is a massif of approximately 15,000 square kilometers in north Limpopo Province, South Africa. Waterberg is the first region in the northern part of South Africa to be named as a Biosphere Reserve by UNESCO. The extensive rock formation was shaped by hundreds of millions of...

 region of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, cattle grazing over the past six centuries has allowed invasive scrub and small trees to displace much of the original grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...

, resulting in a massive reduction in forage
Fodder or animal feed is any agricultural foodstuff used specifically to feed domesticated livestock such as cattle, goats, sheep, horses, chickens and pigs. Most animal feed is from plants but some is of animal origin...

 for native bovids and other grazers. Since the 1970s, large scale efforts have been underway to reduce invasive species; partial success has led to re-establishment of many species that had dwindled or left the region. Examples of these species are giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...

, blue wildebeest
Blue Wildebeest
The Blue Wildebeest , also called the Common Wildebeest, is a large antelope and one of two species of wildebeest. It grows to 115–145 cm shoulder height and attains a body mass of 168–274 kg. They range the open plains, bushveld and dry woodlands of Southern and East Africa, living for...

, impala
An impala is a medium-sized African antelope. The name impala comes from the Zulu language meaning "gazelle"...

, kudu
The kudus are two species of antelope of the genus Tragelaphus:*Lesser Kudu, Tragelaphus imberbis*Greater Kudu, Tragelaphus strepsiceros- Etymology :...

 and white rhino.

Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regimen (cheatgrass, Bromus tectorum
Drooping Brome
Drooping brome or Cheat Grass, Bromus tectorum, is a grass native to Europe, southwestern Asia and northern Africa.-Description:...

), nutrient cycling (smooth cordgrass Spartina alterniflora
Spartina alterniflora
Spartina alterniflora is a perennial deciduous grass which is found in intertidal wetlands, especially estuarine salt marshes. It grows 1-1.5 m tall, and has smooth, hollow stems which bear leaves up to 20-60 cm long and 1.5 cm wide at their base, which are sharply tapered and bend down...

), and hydrology (Tamarix
The genus Tamarix is composed of about 50-60 species of flowering plants in the family Tamaricaceae, native to drier areas of Eurasia and Africa...

) in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass, Spartina alterniflora, threatens the existence of California cordgrass (Spartina foliosa
Spartina foliosa
Spartina foliosa is a species of grass known by the common name California cordgrass. It is native to the salt marshes and mudflats of coastal California and Baja California, especially San Francisco Bay. It is a perennial grass growing from short rhizomes. It produces single stems or clumps of...

) in San Francisco Bay.

Genetic pollution

Natural, wild species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 can be threatened with extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 through the process of genetic pollution
Genetic pollution
Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. This gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.-Usage:...

. Genetic pollution is uncontrolled hybridization and introgression
Introgression, also known as introgressive hybridization, in genetics is the movement of a gene from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species...

, which leads to homogenization or replacement of local genotypes as a result of either a numerical or fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...

 advantage of the introduced species. Genetic pollution can bring about a form of extinction either through purposeful introduction 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, creating hybrids and swamping the entire rarer gene pool, thus driving the native species to extinction. Attention has to be focused on the extent of this problem, it is not always apparent from morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 observations alone. Some degree of gene flow
Gene flow
In 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, all constellations of gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s and genotypes can be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.
An example of this is the interbreeding of migrating coyotes with the red wolf, in areas of eastern North Carolina where the red wolf has been reintroduced.


Non-native species can have benefits. Asian oysters, for example, are better at filtering out water pollutants than native oysters. They also grow faster and withstand disease better than natives. Biologists are currently considering releasing the mollusk in the Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

 to help restore oyster stocks and clean up the bay's pollution. A recent study by the Johns Hopkins School of Public Health found the Asian oyster could significantly benefit the bay's deteriorating water quality.


Economic costs from invasive species can be separated into direct costs through production loss in agriculture and forestry, and management costs of invasive species. Estimated damage and control cost of invasive species in the U.S. alone amount to more than $138 billion annually. In addition to these costs, economic losses can occur through loss of recreational and tourism revenues. When economic costs of invasions are calculated as production loss and management costs, they are low because they do not consider environmental damage; if monetary values were assigned to the extinction of species, loss in biodiversity, and loss of ecosystem services, costs from impacts of invasive species would drastically increase. The following examples from different sectors of the economy demonstrate the impact of biological invasions.

Economic opportunities

For many invasive species, there are commercial benefits, either existent or capable of being developed. For instance, silver carp
Silver carp
The silver carp is a species of freshwater cyprinid fish, a variety of Asian carp native to north and northeast Asia. It is cultivated in China....

 and common carp
Common carp
The Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...

, where heavy metals are not excessive in their flesh, can be harvested for human food and exported to markets already familiar with the product, or into pet foods, or mink
There are two living species referred to as "mink": the European Mink and the American Mink. The extinct Sea Mink is related to the American Mink, but was much larger. All three species are dark-colored, semi-aquatic, carnivorous mammals of the family Mustelidae, which also includes the weasels and...

 feed. Numerous vegetative 'invasives' like water hyacinth
Water hyacinth
The seven species of water hyacinth comprise the genus Eichhornia. Water hyacinth are a free-floating perennial aquatic plant native to tropical and sub-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...

, when in sufficient quantities to be harvestable, can be turned into fuel by methane digesters if no other better use can be determined. The depletion or exploitation of any unwanted species is dependent on officials who recognize the need for a solution. Commercial enterprises need assurances the exploitation can continue long enough for a reasonable profit to be generated and that taxation of the 'resource' is given a sufficiently long period of grace that an enterprise is attracted to the proposition.


Weeds cause an overall reduction in yield, though they often provide essential nutrients for sustenance farmers. Weeds can have other useful purposes: some deep-rooted weeds can "mine" nutrients from the subsoil and bring them to the topsoil, while others provide habitat for beneficial insects and/or provide alternative foods for pest species. Many weed species are accidental introductions with crop seeds and imported plant material. Many introduced weeds in pastures compete with native forage plants, are toxic (e.g., leafy spurge, Euphorbia esula) to young cattle (older animals will avoid them) or unpalatable because of thorns and spines (e.g., yellow starthistle). Forage loss from invasive weeds on pastures amounts to nearly US$1 billion in the U.S. alone. A decline in pollinator services and loss of fruit production has been caused by the infection of honey bees (Apis mellifera, another invasive species to the Americas) by the invasive varroa mite. Introduced rats (Rattus rattus and R. norvegicus) have become serious pests on farms, destroying stored grains.

In many cases, one could consider the overabundant invasive plant species as a ready source of biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 in the perspective of biogas
Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung, and kitchen waste can be converted into a gaseous fuel called biogas...

 production. See Eichhornia crassipes
Eichhornia crassipes
Eichhornia crassipes, commonly known as Common Water Hyacinth, is an aquatic plant native to the Amazon basin, and is often considered a highly problematic invasive species outside its native range.-Ecology:...



The unintentional introduction of forest pest species and plant pathogens can change forest ecology
Forest ecology
Forest ecology is the scientific study of the interrelated patterns, processes, flora, fauna and ecosystems in forests. The management of forests is known as forestry, silviculture, and forest management...

 and negatively affect the timber industry. The Asian long-horned beetle (Anoplophora glabripennis) was first introduced into the U.S. in 1996, and is expected to infect and damage millions of acres of hardwood trees. Thirty million dollars have already been spent in attempts to eradicate this pest and protect millions of trees in the affected regions.

The woolly adelgid inflicts damage on old-growth spruce fir forests and negatively affects the Christmas tree
Christmas tree
The Christmas tree is a decorated evergreen coniferous tree, real or artificial, and a tradition associated with the celebration of Christmas. The tradition of decorating an evergreen tree at Christmas started in Livonia and Germany in the 16th century...

 industry. The chestnut blight fungus (Cryphonectria parasitica
Chestnut blight
The pathogenic fungus Cryphonectria parasitica is a member of the ascomycota category, and is the main cause of chestnut blight, a devastating disease of the American chestnut tree that caused a mass extinction in the early 1900s of this once plentiful tree from its historic range in the eastern...

) and Dutch elm disease (Ophiostoma novo-ulmi
Dutch elm disease
Dutch elm disease is a disease caused by a member of the sac fungi category, affecting 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...

) are two plant pathogens with serious impacts on forest health.

Tourism and recreation

Invasive species can have impacts on recreational activities, such as fishing, hunting, hiking, wildlife viewing, and water-based recreation. They negatively affect a wide array of environmental attributes that are important to support recreation, including, but not limited to, water quality and quantity, plant and animal diversity, and species abundance. Eiswerth goes on to say that "very little research has been performed to estimate the corresponding economic losses at spatial scales such as regions, states, and watersheds." Eurasian Watermilfoil (Myriophyllum
Myriophyllum is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The center of diversity for Myriophyllum is Australia with 43 recognized species...

) in parts of the US, fill lakes with plants making fishing and boating difficult.

Health impacts

An increasing threat of exotic diseases exists because of increased transportation and encroachment of humans into previously remote ecosystems. This can lead to new associations between a disease and a human host (e.g., AIDS virus
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...

). Introduced birds (e.g. pigeons), rodents and insects (e.g. mosquito, flea, louse and tsetse fly
Tsetse fly
Tsetse , sometimes spelled tzetze and also known as tik-tik flies, are large biting flies that inhabit much of mid-continental Africa between the Sahara and the Kalahari deserts. They live by feeding on the blood of vertebrate animals and are the primary biological vectors of trypanosomes, which...

 pests) can serve as vectors and reservoirs of human diseases. The introduced Chinese mitten crabs are carriers of the Asian lung fluke. Throughout recorded history, epidemics of human diseases, such as malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

, yellow fever
Yellow fever
Yellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....

, typhus
Epidemic typhus is a form of typhus so named because the disease often causes epidemics following wars and natural disasters...

, and bubonic plague
Bubonic plague
Plague is a deadly infectious disease that is caused by the enterobacteria Yersinia pestis, named after the French-Swiss bacteriologist Alexandre Yersin. Primarily carried by rodents and spread to humans via fleas, the disease is notorious throughout history, due to the unrivaled scale of death...

, have been associated with these vectors. A recent example of an introduced disease is the spread of the West Nile virus
West Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...

 across North America, resulting in the deaths of humans, birds, mammals, and reptiles. Waterborne disease agents, such as cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...

 bacteria (Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...

), and causative agents of harmful algal blooms are often transported via ballast water. The full range of impacts of invasive species and their control goes beyond immediate effects and can have long term public health implications. For instance, pesticides applied to treat a particular pest species could pollute soil and surface water.

Threat to global biodiversity

Biotic invasion is considered one of the five top drivers for global biodiversity loss and is increasing because of tourism and globalization
Globalization refers to the increasingly global relationships of culture, people and economic activity. Most often, it refers to economics: the global distribution of the production of goods and services, through reduction of barriers to international trade such as tariffs, export fees, and import...

. This may be particularly true in inadequately regulated fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...

 systems, though quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....

s and ballast water rules have improved the situation.

As noted above, invasive species may drive local native species to extinction via competitive
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...

 exclusion, niche
Ecological niche
In 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 pod if the members of these pods utilize significantly different food...

 displacement, or hybridisation with related native species. Therefore, besides their economic ramifications, alien invasions may result in extensive changes in the structure, composition and global distribution of the biota of sites of introduction, leading ultimately to the homogenisation of the world’s fauna and flora and the loss of biodiversity. Nevertheless, it is difficult to unequivocally attribute e.g., extinctions, to an invasive species, and the few scientific studies that have done so have been with animal (see examples above) rather than plant taxa. Concern over the impacts of invasive species on biodiversity must therefore consider the actual evidence (either ecological or economic), in relation to the potential risk.

Scientific definition

Stage Characteristic
0 Propagules residing in a donor region
I Traveling
II Introduced
III Localized and numerically rare
IVa Widespread but rare
IVb Localized but dominant
V Widespread and dominant

In an attempt to avoid the ambiguous, subjective, and pejorative vocabulary that so often accompanies discussion of invasive species even in scientific papers, e.g., Colautti and MacIsaac have proposed a new nomenclature system based on biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

 rather than on taxa.

By removing taxonomy, human health, and economic factors from consideration, this model focuses only on ecological factors. The model evaluates individual populations, and not entire species. This model does not attribute detrimentality to invasive species and beneficiality to native species. It merely classifies a species in a particular location based on its growth patterns in that particular microenvironment. This model could be applied equally to indigenous and to non-native species.

See also

External links

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