Threat Categories For Species At Risk  

IUCN:

The World Conservation Union, is the world's largest conservation network. It's members include - many governmental organizations. IUCN has developed the red data book aimed at categorizing species at risk according to the severity of the threats facing them, and estimating the imminence of their extinction.

In order to Understand these, It is necessary to understand what a taxon is.
Taxon (plural taxa) is any group of organisms or population considered to be sufficiently distinct from other such groups to be treated as a separate unit.

Extinct (EX):

A taxon is extinct when there is no reasonable doubt that the last individual has died. For example , the Cheetah, Pink-headed Duck, Himalayan Quail are extinct in India.

Extinct in the wild (EW):

A taxon is Extinct in the wild when it is known only to survive in cultivation, in captivity or as a naturalized population (or populations) well outside the past range.

Critically Endangered (CR):

A taxon is critically Endangered when it is facing a very high risk of extinction in the wild in the near future. For example, Nicobar Tree shrew, Lion tailed Macaque, Tiger, Snow Leopard, Lesser Panda, Asian Elephant, Great Indian Rhinoceros, Nilgiri Tahr, Siberian Crane, Jerdon's Courser.

Endangered (EN):

A taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future. For example, Nicobar Tree shrew, Lion tailed Macaque, Tiger, Snow Leopard, Lesser Panda, Asian Elephant, Great Indian Rhinoceros, Nilgiri Tahr, Siberian Crane, Jerdon's Courser.

Vulnerable (VU):

A taxon is Vulnerable when it is not Critically Endangered or Endangered but is facing a high risk of extinction in the wild in the medium-term future. For example, Nilgiri Leaf Monkey, Dhole, Clouded Leopard, Sloth Bear, Gaur, Spot-Billed Pelican, Cheer Pheasant.

Lower Risk (LR):

A taxon is classified as lower Risk when it has been evaluated, does not satisfy the criteria for any of the categories-Critically Endangered or Vulnerable.

Taxa included in the Lower Risk category can be separated into three subcategories.

Conservation Dependent (cd):

Taxa which are the focus of a continuing taxon-specific or habitat-specific conservation programme targeted towards the taxon in question, the cessation of which would result in the taxon qualifying for one of the threatened categories above within five years. For example, Nilgai, Chinkara, Scaly Clam.

Near Threatened (nt):

Taxa which do not qualify for Conservation Dependent, but which are close to qualifying for Vulnerable. For example, Crab-eating Macaque, Fishing Cat, Indian Pangolin.

Least Concern (lc):

Taxa which do not qualify for the Conservation Dependent or Near Threatened.

Data Deficient (DD):

A taxon is Data Deficient when there is inadequate information to make a direct or indirect assessment of its risk of extinction based on its distribution and/or population status. a taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution could be lacking. Data Deficient is therefore not a category of threat or Lower Risk. It indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data is available. In many cases great care should be exercised in choosing between DD and threatened status, If the range of a taxon is suspected to be relatively circumscribed, and if a considerable period of time has elapsed since the last record of the taxon, threatened status may be well justified.
Examples : Hoolock Gibbon, Bengal Fox, Rusty spotted Cat, Indian Black Turtle.

Not Evaluated (NE):

A taxon is not evaluated when it has not yet been assessed against the criteria.

Source:

www.iucn.org