INTRODUCTION
The word biodiversity refers to the variety of living organisms (flora and fauna). Biodiversity or Biological diversity is defined as the variability among all living organisms from all sources, including terrestrial, marine and other aquatic ecosystems and ecological complexes of which they are part. Wilson (1988) defined ‘Biological diversity’ or ‘biodiversity’ as 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 i.e. local, regional, country wise and global, and various types of ecosystems- both terrestrial and aquatic-within a defined area.
TYPES OF BIODIVERSITY:
Biological diversity deals with the degree of nature’s variety in the biosphere. This variety can be observed at three levels i.e., genetic, species and ecosystem.
Genetic diversity: Genetic diversity refers to the variation at the level of individual genes. Tremendous amount of genetic diversity exists within individual species. This genetic variability is responsible for the different characters in species. Genetic diversity is the raw material from which new species arise through evolution. Today, the genetic diversity is made use to breed new crop varieties, disease resistant crops.
Species diversity 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 ecosystem and in agricultural ecosystem. Some areas are richer in species than others. For example, natural undisturbed tropical forests have much greater species richness than mono culture plantations developed by the forest department for timber products. A natural forest ecosystem provides large number of non-timber forest products that local people depend on such as fruits, fuel, wood, fodder, fiber, gum, resin and medicines. Timber plantations do not provide the large variety of goods that are essential for local consumption. Modern intensive agro ecosystem have a relatively lower density of crops than traditional agropastoral farming systems, where multiple crops were planted. Areas that are rich in species diversity are called ‘hotspots’ of diversity and the countries with the highest species richness or have a relatively large proportion of these hot spots of diversity are referred to as ‘megadiversity nations’. India is among the world’s 15 nations that are exceptionally rich in species diversity. The earth’s biodiversity is distributed in specific ecological regions. There are over a thousand major eco-regions in the world. Of these, 200 are said to be the richest, rarest and most distinctive natural areas. These areas are referred to as the Global 200. It has been estimated that 50,000 endemic plants which comprise 20% of global plant life, probably occur in only 25 ‘hot spots’ in the world. These hotspots harbour many rare and endangered species. Two criteria help in defining hotspots namely rich endemism and the degree of threat. To qualify as hotspots an area must contain at least 0.5 per cent or 1500 of the worlds 3,00,000 plants species as endemics (Myers et al., 2000).
ECOSYSTEM DIVERSITY:
There are a large variety of different ecosystem on earth, each having their own complement of distinctive inter linked species based on differences in the habitat. Ecosystem diversity can be described for a specific geographical region or a political entity such as a country, a state or a taluk. Distinctive ecosystems include landscapes like forests, grasslands, deserts, mountains etc as well as aquatic ecosystems like rivers, lakes and seas. Each region also has man- modified areas such as farmland or grazing pastures. It refers to the variation in the structure and functions of the ecosystem. It describes the number of niches, trophic levels and various ecological processes that sustain energy flow, flood webs and the recycling of nutrients. It has focus on various biotic interactions and the role and functions of keystone species (species determining the ability of large number of other species to persist in the community).
METHODS OF MEASURING BIODIVERSITY:
There are three perspectives measuring of diversity at the level of community.
These are (i) Alpha diversity, (ii) beta diversity and (iii) gamma diversity. Community diversity refers to the variations in the biological communities in which species live.
(i) Alpha diversity indicates diversity within the community. It refers to the diversity of organisms sharing the same community or habitat. A combination of species richness and equitability / evenness is used to represent diversity within a community or habitat.
(ii) Beta diversity indicates diversity between communities. Species frequently change when habitat or community changes. There are differences in species composition of communities along environmental gradients, e.g, altitudinal gradient, moisture gradient, etc. the higher heterogeneity in the habitats ina region or greater dissimilarity between communities exhibit higher beta diversity.
(iii) Gamma diversity refers to the diversity of the habitats over the total land scope or geographical area. The sum of alpha and beta diversities of the ecosystems is an expression of the biodiversity of landscape, which is considered as Gamma Diversity. Higher diversity at community level provides stability and higher productivity. In temperate grasslands, it has been observed that diverse communities are functionally more productive and stable, even under environmental stresses such as prolonged dry conditions.
