Read this article to learn about categories and census of threatened species.
Categories of Threatened Species:
The major IUCN threatened categories (IUCN Red List Categories, 1995) currently recognised, together with their definitions!
(i) Extinct (EX):
Species not definitely located in the wild during the past fifty years but which may survive in cultivation (e.g. Franklinia aloetamha). Some authors suggest that ‘Extinct’ should denote those taxa that have been totally lost and that the terminology ‘Extinct in the wild’ should be used to refer to species lost in the wild, while living under cultivation (dubbed by IUCN as EW).
(ii) Endangered (EN):
Species in danger of extinction (within a few decades) and whose survival is unlikely if the causal factors continue to operate (Areca concinna, Euphorbia obdelkuri). In this category are included those taxa whose numbers have been reduced to a critical level or whose habitats have been so drastically reduced that they are deemed to be in immediate danger of extinction.
Also included are taxa that may now be extinct even though seen in the wild in the past 50 years. The other criteria are 50% decline in the last 10 years; <5,000 km2 area of occupancy or <500 km2 in fragmented areas; 2,500 individuals or subpopulation of 250 mature individuals.
The category Critically Endangered (CR) includes species that face an extremely high risk of extinction in the wild in the immediate future. These are characterized by 80% decline in the last 10 years, 100 km2 occupancy or 10 km2 in fragmented areas.
(iii) Vulnerable (VU):
Taxa likely to move into the endangered category in near future if the causal factors continue to operate (Ranunculus ophioglossifolius). Included in this category are taxa in which most or all populations decrease in size because of overexploitation, extensive destruction of habitat or other environmental disturbances.
Also included are taxa with populations that are still abundant but under threat from severe adverse factors throughout their distribution range. The other criteria include 50% decline in last 20 years; < 20,000 km2 occupancy or < 2,000 km2 in fragmented populations; 10,000 individuals or subpopulation of 1,000 mature individuals.
(iv) Rare (R):
Taxa with small populations that are not endangered or vulnerable at present but are at risk are included under this category (Lactuca saligna, Salvia saxicola). A species may be rare because of restricted geographical range, high habitat specificity and small local population size, or thinly scattered over a more extensive range, or due to a combination of two or more of these characteristics. Rare species have a population of less than 20,000 individuals. Some species are naturally rare and have never occurred in greater numbers, yet they are able to maintain these numbers. Other species become rare through man’s action or other natural forces.
(v) Indeterminate (I):
Species considered definitely to be endangered, vulnerable or rare but for which information is insufficient to categorically assign them to any of these three categories.
Census of Threatened Species:
Raven (1987) mentioned that of the 300,000 species of vascular plants, 170,000 are tropical and subtropical; of the 130,000 tropical plant species, some 60,000 are threatened and at risk of extinction within the next half- century. Of the 80,000 temperate plant species, about 8,000 are threatened.
In a more recent estimate, a total of 26,106 species of plants were considered threatened by the World Conservation Monitoring Centre (WCMC, 1994). This number account for 8% of the world’s plant species. Of these, 3,632 species of plants belong to the category Endangered, 5,687 to Vulnerable, 11,485 to Rare and 5,302 to Indeterminate (WCMC 1994). Table 6 provides data on the total number of threatened species in the major countries of the world.