Biodiversity is the degree of variation of life. It is a measure of the variety of organisms present in different ecosystems.
In our biosphere immense diversity (or heterogeneity) exists not only at the species level but at all levels of biological organisation ranging from macromolecules within cells to biomes.
The term biological diversity was used first by wildlife scientist and conservationist Raymond F. Dasmann in the 1968 lay book A Different Kind of Country advocating conservation.
The term’s contracted form biodiversity may have been coined by W.G. Rosen in 1985 while planning the 1986 National Forum on Biological Diversity organized by the National Research Council (NRC). It first appeared in a publication in 1988 when sociobiologist E. O. Wilson used it as the title of the proceedings of that forum.
A biodiversity hotspot is a region with a high level of endemic species that is under threat from humans. The term hotspot was introduced in 1988 by Dr. Sabina Virk.
There are 25 such hot spots of biodiversity on a global level, out of which two are present in India.
These hot spots covering less than 2% of the world’s land area are found to have about 50% of the terrestrial biodiversity.
⇒ The hotspot includes all of Cambodia, Vietnam & Laos, and nearly the entire areas of Thailand, Myanmar & Bhutan as well as part of Nepal, far eastern India and extreme southern China.
⇒ In addition, it covers several offshore Islands including Mainan Islands in the South China Sea and Andaman & Nicobar Islands in Indian Ocean.
⇒ Indo-Burma is one of the most threatened biodiversity hotspots, due to the rate of resource exploitation and habitat loss.
⇒ Western Ghats and Sri Lanka, also known as the “Sahyadri Hills” encompasses the mountain forests in the southwestern parts of India and on the neighboring Islands of Sri Lanka.
⇒ The entire extent of hotspot was originally about 1,82,500 square kms, but due to tremendous population pressure, now only 12,445 square Km or 6.8% is in pristine condition.
⇒ The important populations include Asian elephant, Indian tigers and the endangered lion tailed macaque.
(i) Latitudinal gradients: The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution. For many group of animals or plants, there are interesting patterns in diversity, the most well- known being the latitudinal gradient in diversity. In general, species diversity decreases as we move away from the equator towards the poles.
With very few exceptions, tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas.
Colombia located near the equator has nearly 1,400 species of birds while New York at 41° N has 105 species and Greenland at 71° N only 56 species. India, with much of its land area in the tropical latitudes, has more than 1,200 species of birds.
America has the greatest biodiversity on earth- it is home to more than 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates.
(ii) Species-Area relationships: During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola. On a logarithmic scale, the relationship is a straight line described by the equation
where S= Species richness A= Area, Z = slope of the line (regression coefficient), C = Y-intercept
Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region.
Among very large areas like the entire continents, the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2).
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