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Author Topic: How many species did you say?  (Read 1737 times)

Offline yor_on

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How many species did you say?
« on: 11/03/2011 15:19:05 »
"One of the most well-known objective assessment systems for declining species is the approach unveiled by the International Union for Conservation of Nature (IUCN) in 1994. It contains explicit criteria and categories to classify the conservation status of individual species on the basis of their probability of extinction.

   1. Extinct (EX), a designation applied to species in which the last individual has died or where systematic and time-appropriate surveys have been unable to log even a single individual'
   2. Extinct in the Wild (EW), a category containing those species whose members survive only in captivity or as artificially supported populations far outside their historical geographic range
   3. Critically Endangered (CR), a category containing those species that possess an extremely high risk of extinction as a result of rapid population declines of 80 to more than 90 percent over the previous 10 years (or three generations), a current population size of fewer than 50 individuals, or other factors

   4. Endangered (EN), a designation applied to species that possess a very high risk of extinction as a result of rapid population declines of 50 to more than 70 percent over the previous 10 years (or three generations), a current population size of fewer than 250 individuals, or other factors
   5. Vulnerable (VU), a category containing those species that possess a very high risk of extinction as a result of rapid population declines of 30 to more than 50 percent over the previous 10 years (or three generations), a current population size of fewer than 1,000 individuals, or other factors
   6. Near Threatened (NT), a designation applied to species that are close to becoming threatened or may meet the criteria for threatened status in the near future

   7. Least Concern (LC), a category containing species that are pervasive and abundant after careful assessment
   8. Data Deficient (DD), a condition applied to species in which the amount of available data related to its risk of extinction is lacking in some way. Consequently, a complete assessment cannot be performed. Thus, unlike the other categories in this list, this category does not describe the conservation status of a species.
   9. Not Evaluated (NE), a category used to include any of the nearly 1.6 millionspecies described by science but not yet assessed by the IUCN.

The IUCN system uses five quantitative criteria to assess the extinction risk of a given species. In general, these criteria consider:

   1. The rate of population decline
   2. The geographic range
   3. Whether the species already possesses a small population size
   4. Whether the species is very small or lives in a restricted area
   5. Whether the results of a quantitative analysis indicates a high probability of extinction in the wild

All else being equal, a species experiencing a 90 percent decline over 10 years (or three generations), for example, would be classified as critically endangered. Likewise, another species undergoing a 50 percent decline over the same period would be classified as endangered, and one experiencing a 30 percent reduction over the same time frame would be considered vulnerable.

It is important to understand, however, that a species cannot be classified by using one criterion alone; it is essential for the scientist doing the assessment to consider all five criteria to determine the status. Each year, thousands of scientists around the world assess or reassess species according to these criteria, and the IUCN Red List is subsequently updated with these new data once the assessments have been checked for accuracy to help provide a continual spotlight on the status of the world’s species. The IUCN Red List brings into focus the ongoing decline of Earth’s biodiversity and the influence humans have on life on the planet. It provides a globally accepted standard with which to measure the conservation status of species over time.

By 2008, 44,838 species had been assessed by using the IUCN Red List categories and criteria. Of these, 16,928 species of plants, animals, and others fell into the threatened categories (CR, EN, and VU), with 7,744 species considered either endangered or critically endangered. Today the list itself is an online database available to the public. Scientists can analyze the percentage of species in a given category and the way these percentages change over time; they can also analyze the threats and conservation measures that underpin the observed trends."


"One of the most threatened species group appears to be the amphibians, with 1,895 of the Earth’s 6,285 amphibian species currently in danger of extinction. The decline of the Kihansi spray toad , now classified as Extinct in the Wild, is symbolic of the situation of amphibians the world over." Of 2009 the results show that out of the 47,677 species assessed thus far, more than a third are threatened with extinction. Including amongst the 2,839 new additions 293 reptile species, and with another 510 species of the world’s freshwater fish making an addition to the Red List’s current tally of 3,120 freshwater fish endangered 2009. Frogs are seen as being very sensitive to pollution, so there's probably more than one reason to their declining numbers.

A photo montage. You can also search there for specific animals, like dolphins, polar bears, lions etc and see how they fare (at top of the link). It's difficult to asses how correct it is, but they have a very good reputation, with a lot of people contributing to the figures all over the world.
« Last Edit: 11/03/2011 15:37:32 by yor_on »


 

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How many species did you say?
« on: 11/03/2011 15:19:05 »

 

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