18.3.5—Invasive alien species

An invasive species is a species that has moved into an ecosystem where it was previously unknown and then disrupts the balance of the ecosystem. Most recorded introductions are linked to human transport, trade or deliberate release.

1. Identify the introduced species, the route by which it arrived and the native species or ecosystem processes affected.
2. Monitor its spread and population increase, together with competition, predation, disease and changes in biodiversity or productivity.
3. Prevent further introduction or spread by controlling the human pathways that transport species between ecosystems; deliberate biological-control introductions also require evidence because a non-native species may become invasive.
4. If control is considered, judge the intervention against reduction of the invasive population and recovery of native species, while checking non-target effects, ecosystem disruption, cost and ethical acceptability.
5. Continue long-term monitoring: a short-term fall in numbers is not the same as lasting recovery of the native community.

The risk chain is: few natural predators, competitors or pathogens → rapid population increase → competition for prey, nutrients, light or space, successful predation or introduction of disease → native-population decline and reduced biodiversity/productivity. Human health, travel and economic costs can also be affected.

Do not call every non-native species invasive, and do not assume that one control action is automatically effective or harmless. The matched SME page does not specify a physical, chemical or biological control protocol, so no named treatment, dose or non-target claim is added here. Assisted reproduction and IUCN/CITES roles are separate cards.