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From Cambridge University Press
Table 4: Information used to decide whether species fall into critically endangered, endangered or vulnerable IUCN categories (IUCN 1996).
A species falling within any of the categories A-E in the critically endangered column is defined as critically endangered. Similar rules apply to endangered and vulnerable.
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| Criteria (any one of A-E) |
Critically endangered
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Endangered
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Vulnerable
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| A. Actual or projected reduction in population's size |
80% decline over the last 10 years or 3 generations
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50%
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20%
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| B. Extent of occurrance or area of |
<100 km2
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5,000 km2
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20,000 km2
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| occupancy of |
<10 km2 and any two of
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500 km2
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2,000 km2
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(i) severely fragmented or known to exist at a single location
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5 locations
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10 locations
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(ii) continuing declines, and (iii) extreme fluctuations
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| C. Population numbering |
<250 mature individuals and an estimated continuing decline
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<2,500
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<10,000
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| D. Poulation estimated to number |
<50 mature individuals
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<250
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<1,000
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| E. Quantitative analysis showing the probability of extinction in the wild |
at least 50% within 10 years or 3 generations, whichever is the longer
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20% in 20 years or 5 generations
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10% in 100yrs
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Source: IUCN, 1996, IUCN Red List of Threatened Animals.
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