Invasive species

Invasive species is a phrase with several definitions, but the term is most often used to describe non-indigenous species (e.g. plants or animals) that adversely effect the habitats they invade economically, environmentally or otherwise. It has been used in this sense by government organizations as well as conservation groups such as the IUCN. However, the term can also be extended to include both native and non-native species that heavily colonize a particular habitat. Yet another use of the word is for a widespread non-indigenous species, which is particularly misleading as not all non-indigenous species necessarily have an adverse effect on their adopted environment. An example of this use includes claims that the common goldfish (Carassius auratus) is invasive, but while it is common outside of its range globally, it almost never appears in harmful densities. Due to the ambiguity of the phrase, it is often criticized as an imprecise term within the field of ecology. This article concerns the first two definitions; for the third, see introduced species.