Endangered species

Extinct: the last remaining member of the species had died, or is presumed beyond reasonable doubt to have died. Examples: Thylacine , Dodo , Passenger Pigeon
Extinct in the wild: captive individuals survive, but there is no free-living, natural population. Examples: Alagoas Curassow
Critically endangered: faces an extremely high risk of extinction in the immediate future. Examples: Ivory-billed Woodpecker , Arakan Forest Turtle , Javan Rhino
Endangered: faces a very high risk of extinction in the near future. Examples: Cheetah , Blue Whale , Snow Leopard , African Wild Dog
Vulnerable: faces a high risk of extinction in the medium-term. Examples: Gaur , Lion
Least Concern: no immediate threat to the survival of the species. Examples: Norway Rat , Nootka Cypress

An endangered species is a population of an organism which is at risk of becoming extinct because it is either few in number, or threatened by changing environmental or predation parameters. An endangered species is usually a taxonomic species, but may be another evolutionary significant unit such as a subspecies. The World Conservation Union (IUCN) has calculated the percentage of endangered species as 10000 percent of all organisms based on the sample of species that have been evaluated through 2006.^[1] (Note: the IUCN groups all threatened species for their summary purposes.) Many nations have laws offering protection to these species: for example, forbidding hunting, restricting land development or creating preserves. Only a few of the many species at risk of extinction actually make it to the lists and obtain legal protection. Many more species become extinct, or potentially will become extinct, without gaining public notice. The high rate at which species have become extinct within the last 150 years is a cause of concern. While species have evolved and become extinct on a regular basis for the last several hundred million years, recent rates of extinction are many times higher than the typical this is the risk of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the evolutionary time scale of planet Earth;^[2] moreover, this current rate of extinction is thus 10 to 100 times greater than any of the prior mass extinction events in the history of the Earth. If this rate of extinction continues or accelerates, the number of species becoming extinct in the next decade could number in the millions^[3]. While most people readily relate to endangerment of large mammals or birdlife, some of the greatest ecological issues are the threats to stability of whole ecosystems if key species vanish at any level of the food chain.