All plant and animal species cannot occur at one place. Whether or not a species can occur on a site is determined by environmental conditions of site and range of tolerance of species. Biologically rich and unique habitats are being perished, fragmented and degraded due to increasing human activities, resource consumption and pollution. Biodiversity loss is now one of the most pressing crises. How to check the loss of species and erosion of gene pool is one of the major challenges to science.
Systemic work on identifying and naming species has been in progress for the last two centuries. But still, the numbers of species collected, described and named so far are much less than the actual number of species present. The known and described number of species of all organisms on earth is between 1.7 and 1.8 million, which is fewer than the 15 per cent of the actual number. The predicted number of total species varies from 5 to 50 million and averages at 14 million. There are many more species that have not yet been described, especially in the tropical regions.
There is fascinating variety in organism’s complex ecological relationship among organisms, genetic diversity within species and a great variety of ecological systems. Biodiversity consists of three hierarchical levels:
1. Genetic diversity; 2. Species diversity 3. Community and ecosystem diversity
Every species, varying from bacteria to higher plants and animals, stores an immense amount of genetic information. For example, the number of genes is about 450-700 in mycoplasma, 4000 in E. coli, 13000 in Drosophila melanogaster,