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Introduced species: causes, impacts, examples and management

An introduced species is a non-native organism brought to a new area by people. This article explains pathways, ecological and economic impacts, notable examples, and approaches to prevention and control.

Author: Leandro Alegsa Creation date: November 13, 2022 Last updated: April 26, 2026

simple.wikipedia.org · Public domain

Overview

An introduced species is a non-native organism established outside its natural range. Such organisms are not native to the place where they become established and owe their presence to direct or indirect human activity. Introductions may be intentional — for food, ornamental planting, or pest control — or accidental, for example via trade, transport or travel. The term introduced does not necessarily imply harm; only when a non-native species causes measurable ecological, economic or social damage is it commonly called invasive or a pest.

Pathways and reasons for introductions

People move species for many purposes. Some common pathways are deliberate release for agriculture, aquaculture and horticulture, the pet trade, and biological control; others are unintentional, such as transport in shipping ballast water, on vehicles, in packaging, or with traded plants and produce. Aquaculture and aquarium releases are especially important in freshwater systems: fish or plants stocked for production or kept as pets can escape or be released and then establish in rivers, lakes or wetlands. In some cases a species brought for one benefit later becomes a pest when it spreads beyond intended areas.

Typical ecological impacts

When a non-native species becomes abundant it can alter the receiving ecosystem in several ways. It may compete with native animals and plants for food, space or light; prey on native species; hybridize with closely related natives and reduce genetic diversity; or introduce diseases and parasites. Some introductions change nutrient cycling, water clarity or fire regimes, producing wider ecosystem effects. The severity of impacts depends on the characteristics of the introduced organism, the vulnerability of the recipient environment, and the availability of predators, competitors and disease in the new area.

Notable examples

Well-known examples illustrate typical pathways and impacts. Certain farmed or pet species have escaped and established wild populations with significant effects. The tilapia, a group of warm-water fishes native to parts of Africa and to regions of North and South America, as well as populations historically present in areas of India and Sri Lanka, has been widely moved for fish farming and sometimes sold as an aquarium species. In some regions tilapia reproduce rapidly, outcompete native fish, feed on eggs and juveniles, and alter water clarity or vegetation. Other introduced insects, such as aggressive ants and hybridized honeybee strains, have spread widely and altered local communities; certain aggressive ant species are a frequent example of insect introductions that become pests (see example).

Management, prevention and control

Responses to introduced species vary with context. Prevention — including biosecurity at borders, controls on trade and public education about pets and plants — is the most cost-effective approach. Early detection and rapid response can eradicate small, new populations before they spread. Where eradication is not feasible, management focuses on containment, control to reduce impacts, habitat restoration and monitoring. Measures include physical removal, targeted trapping, biological control (carefully tested), and legal restrictions on possession, transport or sale in affected jurisdictions.

Distinctions and notable facts

Introduced species differ from native species and from those that expand their ranges naturally in response to environmental change. Not every introduced species becomes invasive; many fail to establish or remain at low abundance. The outcome depends on ecological interactions, life-history traits and chance. Some introduced species provide benefits — crop plants, livestock, or food fish — while others cause costly losses to agriculture, native biodiversity and infrastructure. Management decisions therefore balance ecological risk, economic costs and social values, often requiring coordination among scientists, resource managers and the public.

Prevent new introductions by following local regulations and avoiding release of pets or garden plants.
Support early reporting of unexpected species so authorities can act quickly.
Learn about high-risk pathways such as ballast water, live-food trade and ornamental plantings.

Thick-stalked water hyacinth (Eichhornia crassipes), a worldwide spreading neophyte

Norway rat (Rattus norvegicus), a worldwide successful neozoon

Sargassum muticum , an invasive seaweed belonging to the brown algae group.

Terms

The terminology of invasion biology is very inconsistent. In the English-speaking world, terms such as invasive species or similar are mainly used, which are interpreted differently and do not differentiate between different animal groups or characteristics of the species. The International Union for Conservation of Nature and Natural Resources (IUCN) distinguishes in its definitions between alien species and invasive alien species. Alien species are species that have been introduced into a foreign area through human influence. The attribute invasive is attributed to species that displace already native species in their new habitat.

In addition to the inconsistency, the military or even xenophobic connotation of invasive and alien has also been criticized. The value-neutral term neobiota unites all species that have colonized new areas through human influence. However, the terms with neo are not used in a completely uniform manner:

According to one view, the terms neobiota or neophytes or neozoa apply regardless of when a species was introduced.
According to another understanding, these designations apply only to species carried over from 1492. The year of Columbus' discovery of America was chosen as the boundary because it marks the beginning of the intensive exchange of living organisms between Europe and America. Previously displaced species, such as crops displaced during the Neolithic Revolution, are called archaeobiota, archaeophytes (plants) or archaeozoa (animals). These terms are mainly used in the German-speaking world.

Numerous other categories exist for alien species, see Kühn & Klotz (2002). Archaeobiota and neobiota are grouped under the term adventive species (for plants: adventive plants). Depending on the (unconscious) mode of introduction or (conscious) mode of introduction and the subsequent degree of establishment, there are further differentiations among adventitious plants.

The term neophyte goes back to the accepted definition of 1918 by Albert Thellung, which was later modified many times. The corresponding zoological definition (neozoa) is much more recent (Ragnar Kinzelbach 1972) and is not as widespread and generally accepted. The term neomycetes was introduced by Markus Scholler in 1999.

Opuntias originating from America at an ancient Greek temple in Selinunte, Sicily

Biological invasions

→ Main article: Biological invasion

Probably the most important vector for neobiota at present is global trade; its steady growth increases the number of new neobiota considerably. Among the most important vectors are cargo ships, where neobiota can be introduced hidden in containers or cargo, for example. Aviation also further spreads neobiota. Spread through trade routes is mostly unintentional. At the country level, there is a correlation between economic strength and the number of neobiota. In the past, and less frequently today, neobiota have also been deliberately released, e.g. as biological control agents or game. Similarly, neozoa can escape from human care and establish stable populations, and crops can become established in the wild. Invasive species are considered a significant part of globalization.

When humans influence the environment, organisms can spread indirectly and migrate to a new area as neobiota. For example, canal constructions allow aquatic organisms access to a new area. However, it is not always possible to clearly determine whether the species have spread due to anthropogenic environmental changes and are therefore to be classified as neobiota. The spread of the Eurasian Collared Dove (Streptopelia decaocto), for example, could be due to the creation of agricultural landscapes as a food supply for the dove on the one hand, and to genetic adaptations of the dove on the other.

According to a 2015 study published in Nature, at least 13,186 plant species have been shown to have been transported from their original habitats to other regions and become native there due to human influence; the largest increase was in North America, and the main source for all other continents was Europe.

Ballast and bilge water are among the most important vectors for aquatic neobiota.

Author

AlegsaOnline.com - Introduced species - Leandro Alegsa

Creation date: November 13, 2022
Last updated: April 26, 2026

URL: https://en.alegsaonline.com/art/47878