5. Extinction-first described in 1750s. The possibility of extinction widely accepted before the 1800s. Georges Cuvier established extinction as a fact in 1796.
6. Extinction, in ecology refers to the end of a specific group of taxa. A taxon is extinct when there is no reasonable doubt that the last individual has died.
7. The IUCN-world conservation union has categorized species into different categories. Extinct species is the first category in it. A Taxon is presumed extinct when exhaustive surveys in known & expected habitat ,at appropriate times (diurnal, seasonal or annual) throughout its historic range have failed to record an individual.
8. 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.)
13. OVER EXPLOITATION is another reason for species extinction. Demands for items like tiger skin, tiger bones, rhinoceros horns etc.has led to over exploitation. Unrestricted whaling during the 20th century is another example for overexploitation.
16. They alter the natural habitat & cause a greater competition for food, since they are intruders.
17.
18. Major Extinction Events in the history of the planet 5 largest mass extinctions occurred. The late Ordovician period. The late Devonian period. At the end of the Permean period. The late Triassic period. At the Cretaceous period.
