The word biodiversity is derived from bios meaning life and diversity meaning variety. It refers to a wide variety of life on Earth- to all plants, animals and microorganisms which exist on this beautiful planet, to the various species and the ecosystem they live in. It is, thus the sum total of genes, species and ecosystems.
In other words, Biodiversity or Biological Diversity is that part of nature which includes the differences in genes among the individuals of a species; the variety and richness of all the plant and animal species at different scales in space- locally, in a region, in the country and the world; and the type of ecosystems, both terrestrial and aquatic, within a defined area.
In the Convention of Biological Diversity (1992), biodiversity has been defined as the variability among living organisms from all sources including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are apart; this includes diversity within species and of ecosystems.
Levels of Biodiversity:
Units of biodiversity may range from the genetic level within a species to the biota in a specific region and may extend up to the great diversity found in different biomes.
It is the basic source of biodiversity. The genes found in organisms can form an enormous number of combinations each of which gives rise to some variability. Genes are the basic units of hereditary information transmitted from one generation to other. When the genes within the same species show different versions due to new combinations, it is called genetic variability. For example- all rice varieties belong to the species Oryza sativa, but there are thousands of wild and cultivated varieties of rice which show variations at the genetic level and differ in their colour, size, shape, aroma and nutrient content of the grain. This is the genetic diversity of rice.
The number of species of plants and animals that are present in a region constitutes its species diversity. This diversity is seen both in natural ecosystems and in agricultural ecosystems. Some areas are richer in species than others.
For example- natural undisturbed tropical forests have much greater species richness than monoculture plantations developed by the Forest Department for timber production.
A natural forest ecosystem provides a large number of non-timber forest products (NTFPs) that local people depend on, such as fruit, fuelwood, fodder, fiber, gum, resin and medicines. Timber plantations do not provide a large variety of goods that are essential for local consumption.
In the long-term, the economic sustainable returns from NTFPs is said to be greater than the returns from felling a forest for its timber. Thus, the commercial value of a natural forest, with all its species richness, is much greater than a plantation. Modern intensive agricultural ecosystems have a relatively lower diversity of crops than traditional agro-pastoral farming systems, where multiple crops were planted.
Shannon-Wiener index and Simpson index are the popular indices used for measuring species diversity.
Ecosystem Diversity relates to the diversity and health of the ecological complexes within which species occur. Ecosystems provided natural cycles of nutrients (from production to consumption to decomposition), of water, of oxygen and carbon. Ecological processes govern primary and secondary production (i.e energy flow), mineralization of organic matter in the soils and sediments, and storage and transport of minerals and biomass. Efforts to conserve species must therefore also conserve the ecosystem of which they are apart. Ecosystem Diversity thus shows variations in ecological niches, trophic structure, food webs, nutrient cycling etc., and also in physical parameters such as moisture, temperature altitude, precipitation etc. A familiar example is the variety of habitats and environmental parameters that constitute the Bay of Bengal- Godavari Delta ecosystems grasslands, wetlands, rivers, estuaries, fresh and saltwater and mangrove ecosystems.
A global quantitative evolution of ecosystem diversity is not possible. Generally ecosystem diversity is assessed in terms of the global or continental distribution of broadly defined ecosystem types, or in terms of the species diversity within ecosystems. This assessment may include estimation of richness in particular groups and evaluation of their relative abundance.