Invasive species

A species occurring outside its natural range is often called non-native or alien in that place. It is not automatically invasive: under the Convention on Biological Diversity's definition, an invasive alien species is one whose introduction or spread threatens biological diversity. Conservation and policy frameworks may also take account of impacts on ecosystem services, economies, health and human well-being. Definitions and legal thresholds can differ, so the setting and the kind of harm being assessed matter.

Invasions commonly involve a sequence of transport, introduction, establishment and spread. People move organisms deliberately—for example, as pets or aquarium species—or unintentionally as hitchhikers in transport and trade. Arrival alone does not make a population invasive: an organism must survive in its new surroundings and establish a population, and the consequences depend on local ecological conditions. Impacts can emerge well after an initial introduction, which makes surveillance and knowledge of introduction pathways important.

Invasive organisms can alter ecosystems in several ways. They may compete with native species, prey on them, introduce disease, or change habitats and ecological relationships. The result can include declining native populations and disruption of ecosystem functions, although the scale and type of impact vary by species and place. Biological invasions can also affect economic activity, food security, health and livelihoods, making them an environmental and social concern as well as a conservation issue.

Preventing an introduction and preparing to respond are generally more effective and less costly than dealing with a widely established population. Measures can focus on pathways such as trade and transport, risk assessment and biosecurity. When prevention fails, monitoring can help detect a new population early enough for rapid response; depending on feasibility and ecological risk, managers may seek eradication, containment or longer-term control. The appropriate response depends on evidence about the organism, the affected ecosystem and the interests of local communities. The Convention on Biological Diversity calls on parties, as far as possible and appropriate, to prevent, control or eradicate alien species that threaten ecosystems, habitats or species.

IPBES's 2023 assessment reported that more than 37,000 alien species had been recorded worldwide, including more than 3,500 invasive alien species. These are assessment-era global counts, not a complete or permanent inventory: records and impacts continue to change, and biological invasions are monitored unevenly. IPBES identifies invasive alien species as one of the main direct drivers of biodiversity loss and emphasizes prevention, preparedness and cooperation—including engagement with Indigenous Peoples and local communities—as parts of effective responses.