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Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Biodiversity Biodiversity Conservation Conventions on Biodiversity Biodiversity is inherent in the occurrence of various types of environmental conditions in different parts of an area as well as earth and the presence of various forms of life adapted to these different environmental regimes. The common man would find it hard to believe that there are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids. Biodiversity is not uniform. It is tremendous in some places, moderate in others and low in certain regions. BIODIVERSITY The term biodiversity was popularised by sociobiologist Edward Wilson to describe the combined diversity (or heterogeneity) at all the levels of biological organisation right from macromolecules within the cells, genes, species, ecosystems and biomes. There are three most important hierarchial levels of biodiversity: (i) Genetic diversity: A single species might show high diversity at the genetic level over its distributional range. It means genetic diversity is a measure of variety in genetic information contained in the organisms. Within a species, genetic diversity occurs in the differences of alleles, entire genes and chromosomal structures. Genetic diversity enables a population to adapt to its environment and the changes occurring in the environment. It results in variation in potency and concentration of the active chemical (reserpine) being present in medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges. It helps in formation of ecotype and plays a key role in process of speciation. More than 50,000 genetically different strains of rice, and 1,000 varieties of mango occur in India due to genetic variations. Chapter 20 Biodiversity and Conservation
82 Biodiversity and Conservation NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 (ii) Species diversity: It refers to the variety of species within a region. For example, Western Ghats have greater amphibian species diversity as compared to Eastern Ghats. (a) Species diversity is product of species richness and species evenness. (b) Species richness is the number of species present within a unit area. (c) Species evenness or species equitability is the proportionate number of individuals of different species (taxonomic groups). Communities where species are represented by more or less equal number of individuals exhibit evenness. Others where one or more species have more individuals than others show dominance or unevenness. (d) Maximum taxonomic diversity occurs where species of taxonomically different groups occur in almost equal abundance. (iii) Ecological diversity (Community diversity) : It is the variety of ecosystems which indicate diversity in the number of niches, trophic levels, food webs, nutrient cycles and ecological processes sustaining energy flow. For example, ecosystem diversity is high in India because of the occurrence of a large number of ecosystems like deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows. It is quite low in small countries e.g., Scandinavian country like Norway. Alpha diversity of a community Beta diversity between communities Gamma diversity of a region Fig.: Types of ecological diversity (community diversity) How many Species are there on Earth and How many in India? According to the International Union of Conservation of Nature and Natural Resources (IUCN, 2004), the total number of plant and animal species described so far is slightly more than 1.5 million, but we have no clear idea of how many species are yet to be discovered and described. Estimates of species vary widely and many of them are only educated guesses. Scientists estimate the number of species present in tropics by comparing species richness between tropical and temperate areas. For many taxonomic groups, species inventories are more complete in temperate than in tropical countries. Estimates are made of their number in tropics on the basis of temperate tropical species richness of some exhaustively studied groups like insects.
NEET Biodiversity and Conservation 83 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 On this basis, scientists have calculated that the total number of species in the world ranges from 20 to 50 million. Robert May, with his conservative and scientifically sound estimate, places the number of global species diversity at about 7 million. Some interesting aspects about earth’s biodiversity based on the currently available species inventories: (1) Number of animal species is more than 70 percent. Plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) account for nearly 22% of the total. (2) Among animals, insects are the most species-rich taxonomic group, making more than 70 percent of the total. It means, out of every 10 animals on this planet, 7 are insects. (3) Number of fungi species (72,000) in the world is more than the combined total of the species of fishes (28,000), amphibians (4780), reptiles (7150) and mammals (4650). Invertebrates Vertebrates Fishes Mammals Birds Reptiles Amphibians Other animal groups Crustaceans Molluscs Insects Angiosperms Plants Mosses Ferns and allies Algae Lichens Fungi Fig.: Representing global biodiversity: Proportionate number of species of major taxa of invertebrates, vertebrates and plants Estimates (1-3), mentioned above, do not give any figures for prokaryotes. Biologists are not sure about how many prokaryotic species there might be. The possible reasons are as follows: (i) Conventional taxonomic methods are not suitable for identification and characterisation of microbial species. (ii) Many species are simply not culturable under laboratory conditions. If biochemical or molecular criteria are employed for distinguishing species for prokaryotes, then their diversity may run into millions. Biodiversity in India : India is divided into 10 bio-geographical regions. India with only 2.4% of the world’s land area possesses 8.1% species diversity of the world due to varying physical conditions and species grouping. It is because India is one of the 12 mega diversity countries of the world. There are nearly 45,000 species of plants and twice as many animal species. If we accept May’s global estimates, only 22% of the total species have been recorded so far. Applying this proportion to India’s diversity figures, we estimate that there are probably more than 1,00,000 plant species and more than 3,00,000 animal species yet to be discovered and described. It will require a large trained manpower of taxonomists and lot of time to complete the inventory of the biological
84 Biodiversity and Conservation NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 wealth of our country. However, a very large number of species that are yet to be discovered are facing the threat of becoming extinct even before we discover them. Nature’s biological library is burning even before we catalogued the titles of all the books stocked there. Patterns of Biodiversity The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution. There are many interesting patterns in diversity like latitudinal, altitudinal, geographical, topographical, humidity gradients but most well - known being the latitudinal gradient in diversity. (i) Latitudinal gradients: As we move from low to high latitude i.e. from the equator to the poles, the biodiversity decreases. In other words, the biodiversity is minimum in the arctic region, moderate in temperate area and maximum in tropical regions (latitudinal range of 23.5° N to 23.5° S). Examples of high diversity in tropical regions: (a) Colombia located near the equator (tropical region) has about 1,400 species of birds. New York (41° N) in temperate area has 105 species and Greenland (71° N) in arctic area possess 56 species of birds. (b) India has more than 1,200 species of birds because most of the land area of our country lies in tropics. (c) A forest in a tropical region like Equador has 10 times more species of vascular plants as compared to a forest of equal area in a temperate region like the Midwest of the USA. (d) Tropical Amazonian rain forest in South America has the greatest biodiversity on earth. Table: Biodiversity in Amazonian rain forest Taxa Number of species Plant species More than 40,000 Mammals 427 Birds 1,300 Reptiles 378 Amphibians 427 Fishes 3,000 Invertebrates More than 1,25,000 These rain forests might have atleast 2 million insect species yet to be discovered and named. Why biodiversity is rich in tropics? Ecologists and evolutionary biologists have proposed various hypothesis to explain the cause of high diversity in tropics. Some important ones are as follows: (a) Speciation is a function of time. Temperate areas have undergone frequent glaciations in the past. It killed most of the species. No such diversification occurred in tropics where species continued to flourish and evolve undisturbed for millions of years. (b) Warm temperatures and high humidity in tropical areas provide favourable conditions throughout the year. Therefore, tropical environments unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant and favourable environment has helped tropical organisms to gain more niche specialisation and lead to a greater species diversity. (c) Tropical areas receive more solar energy over the year as they are near to equator. Thus tropical communities are more productive that can support a wider range of species.