The need for a clearly defined and consistent invasion biology terminology has been acknowledged by many sources. Invasive species, or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats. Invasion biology is the study of these organisms and the processes of species invasion.
The terminology in this article contains definitions for invasion biology terms in common usage today, taken from accessible publications. References for each definition are included. Terminology relates primarily to invasion biology terms with some ecology terms included to clarify language and phrases on linked articles.
Introduction Definitions of "invasive non-indigenous species have been inconsistent", which has led to confusion both in literature and in popular publications (Williams and Meffe 2005). Also, many scientists and managers feel that there is no firm definition of non-indigenous species, native species, exotic species, "and so on, and ecologists do not use the terms consistently." (Shrader-Frechette 2001) Another question asked is whether current language is likely to promote "effective and appropriate action" towards invasive species through cohesive language (Larson 2005). Biologists today spend more time and effort on invasive species work because of the rapid spread, economic cost, and effects on ecological systems, so the importance of effective communication about invasive species is clear. (Larson 2005)
Controversy in invasion biology terms exists because of past usage and because of preferences for certain terms. Even for biologists, defining a species as native may be far from being a straightforward matter of biological classification based on the location or the discipline a biologist is working in (Helmreich 2005). Questions often arise as to what exactly makes a species native as opposed to non-native, because some non-native species have no known negative effects (Woods and Moriarty 2001). Natural biological invasions, generally considered range expansions, and introductions involving human activities are important and could be considered a normal ecological process (Vermeij 2005). Non-native and native species may be sometimes considered invasive, and these invasions often follow human-induced landscape changes, with subsequent damage to existing landscapes a value judgment (Foster and Sandberg 2004). As a result, many important terms relevant to invasion biology, such as invasive, weed, or transient, include qualities that are "open to subjective interpretation" (Colautti and MacIsaac 2004). Sometimes one species can have both beneficial and detrimental effects, such as the Mosquito fish (Gambusia affinis), which has been widely introduced because of its suppression of larval mosquitoes, although it also has negative impacts on native species of insects, fish and amphibians (Colautti and MacIsaac 2004).
The large number and current complexity of terms makes interpretation of some of the invasion biology literature challenging and intimidating. Exotic, alien, transplanted, introduced, non-indigenous, and invasive are all words that have been used to describe plants and animals that have been moved beyond their native ranges by humans (Williams and Meffe 2005), along with other terms such as foreign, injurious, aquatic nuisance, pest, non-native, all with a particular implication. Even the use of what seem to be simple, basic terms to articulate ecological concepts "can confuse ideological debates and undermine management efforts" (Colautti and MacIsaac 2004). Attempts to redefine commonly used terms in invasion biology have been difficult because many authors and biologists are particular to a favorite definition (Colautti and MacIsaac 2004). Also, the status and identification of any species as an invader, a weed, or an exotic are "conditioned by cultural and political circumstances." (Robbins 2004)
Terminology Where words in a sentence are also defined elsewhere in this article, they appear in italics.
Adventive species (see casual)A species (usually a plant), that is introduced in a new environment and successfully reproduces without human intervention, but does not necessarily formed sustained populations.Definition of 'adventive' by Collins Dictionary. Retrieved February 2, 2025.adventive by Dictionary.com. Retrieved February 2, 2025. Alien species (See Introduced species) Less commonly used in scientific literature but often included in population publications, public information displays, and educational literature. This term refers to species that spread beyond their native range, not necessarily harmful, or species introduced to a new range that establish themselves and spread; similar terms include exotic species, foreign species, introduced species, non indigenous species, and non native species (Jeschke and Strayer 2005). Aquatic nuisance species Less commonly used in most literature. A nonindigenous species that threatens the diversity or abundance of native species or the ecological stability of infested waters, or commercial, agricultural, aquacultural or recreational activities dependent on such waters (EPA 1990). Aquatic species that causes economic or environmental harm to humans (Heutte and Bella 2003). An aquatic species with adverse effects on humans, either directly (e.g. species that produce toxins that are harmful to humans) or indirectly (e.g. species that infest nature reserves) (Colautti and MacIsaac 2004). Biological control or biocontrol (See Biological pest control) In general, the control of the numbers of one organism as a result of natural predation by another or others. Specifically, the human use of natural predators for the control of pests or weeds. Also applied to the introduction of large numbers of sterilized males of the pest species, whose matings result in the laying of infertile eggs (Allaby 1998). The release of one species to control another (Carlton 2001). The management of weeds using introduced herbivores (often insects) as biological control agents (Booth et al. 2003). Biological invasion or bioinvasion A broad term for both human-assisted introductions and natural range expansions (Carlton 2001). Biological diversity (See biodiversity) Used to describe species richness, ecosystem complexity, and genetic variation (Allaby 1998). Biological control (See Biological pest control) Control method involving a biological control agent that is a natural enemy of a target pest (Heutte and Bella 2003). Bioregion (See Ecoregion) A biological subdivision of the earth's surface delineated by the flora and fauna of the region (Allaby 1998). Biota The organisms (plants, animals, fungi, bacteria, algae, etc.) of a specific region or period, or the total aggregation of organisms in the biosphere (Allaby 1998). Casual species (see adventive) This term is becoming less common in usage. A non native species that does not form self-replacing populations (Booth et al. 2003). Similar terms include introduced species, non indigenous species, and non native species. Chemical control Control method that employs herbicides to control exotic plants (Heutte and Bella 2003). Community Any grouping of populations of different organisms that live together in a particular environment (Allaby 1998). Cryptogenic species Species that are neither clearly native nor exotic (Cohen and Carlton 1988). Cultivar A variety of a plant produced and maintained by horticultural techniques and not normally found in wild populations (Allaby 1998). Disturbance An event or change in the environment that alters the composition and successional status of a biological community and may deflect succession onto a new trajectory, such as a forest fire or hurricane, glaciation, agriculture, and urbanization (Art 1993). Ecosystem A discrete unit, or community of organisms and their physical environment (living and non-living parts), that interact to form a stable system (Allaby 1998). Endemic A species or taxonomic group that is restricted to a particular geographic region because of such factors as isolation or response to soil or climatic conditions; this species is said to be endemic to the region (Allaby 1998). Exotic species (See Introduced species) This term is commonly used in publications and literature, and is similar to the terms alien species, foreign species, introduced species, non indigenous species, and non native species (Heutte and Bella 2003). Other definitions include: An introduced, non native species, or a species that is the result of direct or indirect, deliberate or accidental introduction of the species by humans, and for which introduction permitted the species to cross a natural barrier to dispersal (Noss and Cooperrider 1994). In North America, often refers to those species not present in a bioregion before the entry of Europeans in the 16th century, or present in later parts of that region and later introduced to an ecosystem by human-mediated mechanisms (Cohen and Carlton 1988). Fauna The animal life of a region or geological period (Allaby 1998). Foreign species (See Introduced species) A species introduced to a new area or country. Similar terms include alien species, exotic species, introduced species, non indigenous species, and non native species. Flora Plant or bacterial life forms of a region or geological period (Allaby 1998). Habitat The place, including physical and biotic conditions, where a plant or an animal usually occurs (Allaby 1998). Herbicide Pesticide that specifically targets vegetation (Heutte and Bella 2003). Hybridization Production of novel genotypes, through mating between distinct species or ecotypes. Novel genotypes may be more invasive than parental genotypes. Indigenous (See Indigenous species) A species that occurs naturally in an area; a synonym for native species (Allaby 1998). Injurious species An introduced species that causes economic or environmental harm to humans. Similar terms include aquatic nuisance species, noxious weed, and invasive species (Heutte and Bella 2003). Intentional introduction A species that is brought to a new area, country, or bioregion for a specific purpose, such as for a garden or lawn; a crop species; a landscaping species; a species that provides food; a groundcover species; for soil stabilization or hydrological control; for aesthetics or familiarity of the species; or other purposeful reasons (Booth et al. 2003). Introduced species This term, along with the terms introduced species and nonindigenous species, is one of the most commonly used terms to describe a plant or animal species that is not originally from the area in which it occurs. This terms means those species that have been transported by human activities, either intentionally or unintentionally, into a region in which they did not occur in historical time and are now reproducing in the wild (Carlton 2001). Similar terms include alien species, exotic species, foreign species, non indigenous species, and non native species. Invasibility The ease with which a habitat is invaded (Booth et al. 2003). Invasion (See Introduced species and Invasive species) The expansion of a species into an area not previously occupied by it (Booth et al. 2003). Invasive species Generally, this term refers to a subset of plants or animals that are introduced to an area, survive, and reproduce, and expand beyond the original area of introduction. This is the biological definition. Practical definitions add that they cause harm economically or environmentally within the new area of introduction. An alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health (Executive Order 1999). An adjective for non native or nonindigenous species that have colonized natural areas;