Biodiversity is comprised of the totality of genes, species and ecosystems of a region. The occurrence of various kinds of flora and fauna in a region reflects its biological diversity or biodiversity. In most parts of the world which are habitable, the living world abounds in biodiversity. In a patch of forest, there is a wide variety of insects, animals, plants and trees.
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, 32000 to 50000 in Oryza sativa, and 35000 to 45000 in Homo sapiens. The genetic diversity enables a population to adapt to its environment and to respond to natural selection. If a species has more genetic diversity, it can adapt better to the changed environmental conditions.
Species diversity refers to the variety of species within a region. The simplest measure of species diversity is species richness, i.e. number of species per unit area. The number of species increases with the area of the site. Generally, the greater the species richness, the greater is the species diversity. Diversity at the level of community and ecosystem has three perspectives, alpha diversity, beta diversity and gamma diversity.
(i) Alpha diversity is the diversity of organism sharing the same community/habitat. A combination of species richness and equitability/evenness is used to represent diversity within a community habitat.
(ii) Beta diversity is the rate of replacement of species along a gradient of habitats or communities.
(iii) Gamma diversity refers to the diversity of the habitats over the total landscape or geographical areas. Ecosystem diversity describes the number of niches, tropic levels and various ecological processes that sustain energy flow, food webs and recycling of nutrients.
Biodiversity varies with change in latitude or altitude. As we move from high to low latitudes, the biological diversity increases. While in temperate region the climate is severe with short growing period for plants in tropical rain forest, the conditions are favourable for growth throughout the year. Favourable environmental conditions favour speciation and make it possible for a larger number of species to occur and grow. A correlation is also found for a wide variety of taxonomic groups such as ants, birds, butterflies and moths.
Human derive severe direct and indirect benefits from living world. Biodiversity is the source of food, medicines, pharmaceutical drugs,...
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