The measurement of species diversity is its richness, i.e. the number of species per unit area. The greater is the species richness the more will be the species diversity. In nature, the number and kind of species, as well as the number of individual per species, vary, and this leads to greater diversity.
It is the diversity at community level. It can be of 3-types
It is the diversity of organisms within the same community or habitat.
It is the diversity between communities or different habitats. Higher the heterogenecity in the altitude, Humidity and Temperature of a region, the greater will be the dissimilarity between communities, and higher will be the β diversity.
It is the diversity of organisms over the entire geographical area, covering several ecosystems or habitats and various trophic levels and food webs. Such diversity is most stable and productive.
Number of species on earth
It is diffi cult to believe that there are 20,000 species of orchids, 20,000 species of ants, 28,000 species of fi shes and about 3,00,000 species of beetles on earth. According to IUCN (International Union for Conservation of Nature and Natural resources) estimates, the total number of animal and plant species, described so far, is more than 1.5 million. Due to project ‘Species 2000’ aand ‘Global Biodiversity Information’, the new species are being discovered faster than ever before. However, the discovery and description of species is more complete in temperate than in tropical countries. A large number of species are waiting to be discovered from tropics.
According to estimates of Robert May
• The global species diversity is about 7 million (1.5 million, i.e. 22% reported till now and 78% are yet to be discovered).
• More than 70% of all the species recorded are animals. Plants are not more than 22% of the total.
• Among animals also, about 70% are insects.
• The Fungi have more species than all the vertebrates species combined.
• In case of vertebrates, the species of fi shes are more than that of birds, and of latter, more than reptiles.
• In case of plant species, the species of fungi > species of angiosperms > species of algae.
The all above estimates do not give any idea for the number of species of prokaryotes, whose species diversity may run in millions.
Number of species in India
India is one of the 12 mega divesity country of the world. It has 2.4%, i.e., 1/40 of world land area, but global species diversity is 8.1 %, i.e. 1/12. In India the number of animal and plant species recorded so far is 90,000 and 45,000 respectively.
According to May’s global estimates, about 3,00,000 animal species and 1,00,000 plant species are yet to be discovered from India.
(A large number of species are facing the threat of extinction even before they are discovered, i.e. ‘Nature’s biological library is burning even before we catalogue the titles of all the books stocked there’).
