Home - Species - Concepts - Categories of risk in the world
In order to be more objective, the definitions currently used by the IUCN are necesarily complex. Some of the conditions necessary for classification in the different categories are given below:
When there is no reasonable doubt that the last individual of a species has died.
When individuals of a species survive only in captivity or in populations outwith their historical range.
When a species faces a high risk of extinction in the wild due to:
A reduction in the size of its population (of more than 90%) over the past 10 years, and the causes of decline are understood and reversible.
A reduction in the size of its population (of more than 80%) over the past 10 years, and the causes of decline are not understood or are irreversible.
The outer limit of their distribution area being less than 100 km2.
The area occupied being less than 10 km2.
Their population being less than 250 mature individuals and in continuing decline.
Their population being less than 50 mature individuals, even if stable.
When a species faces a high risk of extinction in the wild due to:
A reduction in the size of its population (of more than 70%) over the past 10 years, and the causes of decline are understood and reversible
A reduction in the size of its population (of more than 50%) over the past 10 years, and the causes of decline are not understood or are irreversible
The outer limit of their distribution being less than 5000 km2
The area occupied being less than 500 km2
Their population being less than 2,500 mature individuals and in continuing decline.
Their population being less than 250 mature individuals, even if stable.
When a species faces a high risk of extinction in the wild due to:
A reduction in the size of its population (of more than 50%) over the past 10 years, and the causes of decline are understood and reversible
A reduction in the size of its population (of more than 30%) over the past 10 years, and the causes of decline are not understood or are irreversible
The outer limit of their distribution being less than 20,000 km2
The area occupied being less than 2000 km2
Their population being less than 10,000 mature individuals and in continuing decline
Their population being less than 1000 mature individuals, even if stable.
When a species has been evaluated under the criteria and, while not qualifying for the high risk categories, is very close and will probably qualify in the future.
When existing information is inadequate to assess risk of extinction of a species.
When a species has been assessed against the criteria but does not qualify for the high risk categories and would probably not qualify in the near future as it is abundant and has a wide distribution range.
A reduction in the size of its population (of more than 90%) over the past 10 years, and the causes of decline are understood and reversible.
