The IUCN Red List of Threatened Species provides a globally recognised system for classifying species according to their risk of extinction. This system is the international standard used by CITES, national governments and conservation organisations.
Species are ranked in order from most to least threatened:
| Category | Code | Definition |
|---|---|---|
| Extinct | EX | Last individual has died; no reasonable doubt |
| Extinct in the Wild | EW | Only survives in captivity, cultivation or naturalised outside native range |
| Critically Endangered | CR | Extremely high risk of extinction in the wild |
| Endangered | EN | Very high risk of extinction in the wild |
| Vulnerable | VU | High risk of extinction in the wild |
| Near Threatened | NT | Close to qualifying for threatened, or likely to qualify in near future |
| Least Concern | LC | Does not meet criteria for threatened categories; widespread and abundant |
| Data Deficient | DD | Insufficient information to assess risk |
| Not Evaluated | NE | Not yet assessed against criteria |
Species are assigned to categories based on five quantitative criteria (A–E):
| Criterion | Focus |
|---|---|
| A | Population size reduction (past or projected) |
| B | Geographic range size and fragmentation |
| C | Small and declining population size |
| D | Very small or restricted population |
| E | Quantitative analysis of extinction probability |
For Critically Endangered, the thresholds include:
- Population reduction of ≥80% over 10 years or 3 generations
- Extent of occurrence < 100 km²
- Population < 250 mature individuals
- Extinction probability ≥ 50% within 10 years or 3 generations
Australian legislation uses related but distinct categories:
- The Environment Protection and Biodiversity Conservation Act 1999 (Cth) uses categories: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Conservation Dependent
- The Flora and Fauna Guarantee Act 1988 (Vic) uses: Threatened, Critically Endangered, Endangered, Vulnerable
Examples of Australian species by category:
| Species | IUCN Status | Threat |
|---|---|---|
| Leadbeater’s possum | Critically Endangered | Logging, fire |
| Eastern quoll | Endangered | Introduced predators |
| Koala (VIC/SA/NSW) | Endangered | Habitat loss, disease |
| Common wombat | Least Concern | Widespread |
| Southern corroboree frog | Critically Endangered | Chytrid fungus |
Extinct in the Wild (EW) is a critical but often overlooked category:
- The species exists only in captivity or cultivation
- It cannot yet be declared Extinct but has no self-sustaining wild populations
- Conservation goal: reintroduce to the wild once threats are managed
Example: The Lord Howe Island stick insect (Dryococelus australis) was thought extinct for 80 years until rediscovered on Ball’s Pyramid. A captive breeding program at Melbourne Zoo is working toward wild reintroduction.
Conservation status:
- Triggers legal protection under national and state legislation
- Informs priority-setting for limited conservation funding
- Justifies zoning decisions in land-use planning
- Guides recovery planning: Critically Endangered species receive most urgent action
REMEMBER: The IUCN Red List and the Australian EPBC Act use similar but not identical category names. VCAA may ask you to name specific categories, explain what they mean, or apply criteria to a described scenario. Know the sequence: EW → CR → EN → VU → NT → LC.
