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Question : Describe the number of species found on the earth. |
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Answer» Solution :According to International Union of Conservation of Nature (IUCN) 2004, the total number of plants and animals species described so far is more than 1.5 million. For many taxonomic groups, species inventories are more complete in temperate than in TROPICAL countries. Assuming that a large number of species are undiscovered in the tropics, biologists make a statistical comparison of the temperate - tropical species RICHNESS of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants. This leads to a gross estimate of the total number of species on earth ranges from 20 to 50 million. A more conservative and scientifically sound estimate by Robert May places the global species diversity at about 7 million. More than `70%` of all the species recorded are animals while plant comprise not more than `22%` of the total. Insects are the most species rich taxonomic group in animal kingdom making more than `70%` of the total animals. It means out of every 10 animals, 7 are insects on the earth. Number of fungi species in the world is more than the total number of species of fishes, amphibians, reptiles and mammals. But biologist are still not sure about the diversity of prokaryotic species like prostists, orchaea bacteria etc. This is because of the following reasons : (i) The conventional taxonomic methods are not sufficient for identifying these microbial species, (ii) Most of the species can not be cultured under LABORATORY conditions. (iii) If molecular and BIOCHEMICAL criteria are adopted for delineating the microbial species, this would put the diversity into MILLIONS. 
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