Biodiversity, a portmanteau of "bio" (life) and "diversity", generally refers to the variety and variability of life Earth. According to the United Nations Environment Programme (UNEP), biodiversity typically meausres variation at the genetic, the species, and the ecosystem level. Terrestrial biodiversity tends to be greater near the equator, which seems to be the result of the warm climate and high primary productivity. Biodiversity is not distributed evenly on Earth, and is richest in the tropics. These tropical forest ecosystem cover less than to percent of earth's surface, and contain about 90 percent of the world's species. Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature is highest, and in the mid-Iatitudinal band in all oceans. There are latitudinal gradients in species diversity. Biodiversity generally tends to cluster in hotspots, and has been increasing through time, but will be likely to slow in the future.
According to David Tilman's long term ecosystem experiments using outdoor plots provide some tentative answers. Tilman found that plots with more species showed less year to year variation in total biomass. He also showed.that in his experiments increased diversity contributed to higher productivity.
Although, we may not understand completely how species richness contributes to the well-bein of an ecosystem, know enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet. At a time when we are losing species at an alarming pace, one might ask does it really matter to us its a few species become extintct? Would Western Ghats ecosystems be less functional if one of its free frog species is lost forever ? How is our quality of life affected if, say, instead of 20,000 we have only 15,000 species of ants on Earth.
There are no direct answer to such native questions but we can develop a proper prospective through an analogy by 'Rovet popper hypothesis, used by Paul Ehrlich. In an airplane (ecosystem) all parts are joined together using thousands of rivets (species). Loss of rivets on the wings (Key species that drive major ecosystem functions) is obviously a more serious threat to flight safety than loss, of a few rivets on the seats or windows inside the plane.
Cause of depletion of biodiversity:
Pollution: Human activity influnces the natural enviroment producing negative direct indirect, effects that alter the flow of energy, the chemical and physical constitution of the environment and abundance of the species.
Climate change: For example, heating of the Earth's surface affects biodiversity because it endanger all the species that adapted to the cold due to the latitude (the polar species) or the altitude (mountain species).
Overexploitation of resources:
When the activities connected with capturing and harvesting (hunting fishing faming) a renewable natural resource in a particular area is excessively intences, the resource itself may become exhausted, as for example, is the case of sardines, herrings, cod, tuna and many other species that man captures without leaving enough time for the organisms to reproduce.
