The term biological diversity or biodiversity refers to the variety of life forms and habitats found in a defined area. UNEP(1992) defines it as the variety and Variability of all animals and micro-organism and the ecological complexes of which they are a part. The term biodiversity was coined by W.C. Rosen(1985).Biological diversity defines biodiversity as the variability among living organism from all sources including, terrestrial, marine and other aquatic ecosystems and the epcological complexes of which they are a part. This includes Diversity within species, between species and of ecosystems. Biodiversity represents the totality of genes, species and ecosystems of a region.
LEVELS OF BIODIVERSITY
Ecological diversity: The diversity of ecological complexes or biotic communities found in a given area(McNeely et.al.1990).Indian ecosystem diversity is described at each of the three levels(Biogeographical region, biotic Province and biome).The enormous range of terrestrial and aquatic environments on earth has been classified into number of ecosystem. Few examples are:
- Tropical rain forests
Species diversity: Species diversity refers to variety of species in a region. Number of species per unit area is called species richness. Evenness or Equitability differs due to difference in number of individuals in an area.
Genetic diversity: The diversity of basic units of hereditary information(genes)which are passed down the generations, found within a species is genetic diversity. Genetic diversity refers to variation of genes within species. The genetic diversity within a species is expressed by many terms. Subspecies, breeds, races, Varieties and forms. This diversity arises from variations in the sequence of four Base pairs which as component of nucleic acids which constitute the genetic code. Genetic information is stored in genes. In Mycoplasma, there are about 450-700 Genes, in Escherichia coli 3200,in Drosophila melanogaster13000,in Oryza sativa 32000-50,000 and in Homo sapiens the number genes ranges in between 31000 and 45000.Due to genetic diversity, population adjusts in its environment and respond to natural selection. More the genetic diversity in an organism better is the adaptation to changed environmental conditions.
- Alpha diversity (with in community diversity)
It represents number of species in a given habitat. It represents the diversity of organisms sharing the same community/habitat.
- Beta diversity(between community diversity)
The rate of turnover or replacement of species while moving from one habitat to another within a given geographical area.
- Gamma diversity
This term is used for the rate of turnover or replacement of species between similar habitats in different geographical areas. For example: the differences in species, composition between the coral reef in the Gulf of kutch and in the Andaman Islands would be called as gamma diversity.
GRADIENTS OF BIODIVERSITY
Change in latitude or altitude leads to change in biodiversity. Biodiversity increases from poles to equator (from high to low latitude).Number of species Increase in area with favourable environmental condition(e.g. in tropical rain forests) on mountains, decrease in species diversity takes place from lower to higher altitude.
BIODIVERSITY OF INDIA
India has a great wealth of biodiversity in its forests, wetlands and marine areas. It has wide range of habitats ranging from tropical rainforest to alpine vegetation and from temperate forests to coastal wetlands. India consists of Fertile river plains and high plateaus and several major rivers including the Ganges, Brahmaputra and Indus. India shows a great diversity in climate, topography and geology hence very rich in biodiversity.
- Hot spots of biodiversity
Hot spots are areas that are extremely rich in species have high endemism (species confined to a particular region),and are under constant threat. Criteria for identifying the hot spots are:
- Number of endemic species(species confined only to that area).
- Degree of threat.
Out of 25 hot spots two are found in India. They are:
- Eastern Himalyan hot spot. It boundary extends from North eastern India to Bhutan.
- Western Ghat hot spot. Such evergreen forests lie at height of about 500-1500m in states like Karnataka, Maharashtra and kerela.
- BIOGEOGRAPHICAL REGIONS OF INDIA
Biogeography is the study of origin, environmental relationship and distribution of plants and animals. The larger the size of an area, the greater the number of Species found in it.