Biodiversity, a term coined by Walter G. Rosen in 1985, refers to the variety of living organisms found on Earth. Biodiversity is the combined diversity at all levels of biological organisation, from genes and species to ecosystems. It represents the totality of genes, species and ecosystems in a region, and it is the very fabric of life on which all human welfare depends. The extraordinary richness of life on Earth, estimated to be about 1.7 million described species, is the result of billions of years of evolution.
The chapter explores the concept of biodiversity, its levels, the magnitude and distribution of biodiversity, its patterns and importance, the threats to biodiversity, and the strategies for its conservation. Biodiversity is not evenly distributed; some regions of the world, known as biodiversity hotspots, harbour an enormous number of species. The loss of biodiversity, driven by human activities such as habitat destruction, pollution and overexploitation, is one of the greatest environmental challenges of our time. The chapter emphasises both in situ and ex situ conservation methods, and highlights India's rich biodiversity heritage.
Biodiversity is the variety of living organisms in a given area. It can be studied at three levels: - Genetic diversity: The diversity in the genes and gene combinations within a species. For example, the genetic variation among the varieties of wheat, rice and other crops. Genetic diversity provides the raw material for evolution and crop improvement. - Species diversity: The diversity at the species level, such as the number of different species in a region. For example, the Western Ghats have greater amphibian species diversity than the Eastern Ghats. - Ecological diversity: The diversity of ecosystems, such as deserts, rainforests, mangroves, coral reefs and grasslands in a region. India has a rich ecological diversity, including deserts, rainforests, mangroves, coral reefs, wetlands and estuaries.
Biodiversity is not uniformly distributed on Earth. Several patterns have been observed:
Species diversity generally decreases from the equator to the poles. The tropics harbour more species than temperate or polar regions. For example, the number of species of mammals, birds, insects and plants is much higher in the tropics than in temperate regions. Colombia, located near the equator, has about 1,400 species of birds, while New York State, at a higher latitude, has about 105 species, and Greenland has about 56 species.
The number of species found in an area generally increases with the size of the area. The relationship between species richness and area can be represented as a rectangular hyperbola, and the logarithm of the number of species plotted against the logarithm of the area gives a straight line. The slope of the line (the value of the constant Z) is typically between 0.1 and 0.2 for most species, but for large areas such as whole continents, the value of Z can be in the range of 0.6 to 1.2.
The biodiversity of the world is not fully known. About 1.7 million species have been described so far, but the total number of species is estimated to be between 20 million and 50 million. The number of described species is dominated by insects, which constitute about 70 percent of all animal species.
India is one of the 12 mega-diversity countries of the world. About 45,000 plant species and about 90,000 animal species have been described in India. India contributes about 8.1 percent of the global species diversity. India also has about 47,000 species of plants and flowering plants, and it has a rich heritage of crop plants, including rice, wheat, maize and many spices and medicinal plants.
Biodiversity hotspots are regions with a high level of species richness and endemism (species found only in that region) that are under threat from human activities. The concept of biodiversity hotspots was proposed by Norman Myers. A region is a hotspot if it has at least 1,500 species of endemic vascular plants and has lost at least 70 percent of its original habitat. There are 34 biodiversity hotspots in the world. India has three hotspots: the Indo-Burma hotspot, the Himalayas and the Western Ghats and Sri Lanka.
Biodiversity provides humans with a vast array of benefits: - Food and medicines: A large number of wild plants and animals are used for food and medicine. - The Amazon forest is estimated to produce 20 percent of the total oxygen through photosynthesis, earning it the name the lungs of the planet.
The loss of biodiversity refers to the reduction in the number of species, the reduction in the abundance of species, or the extinction of species. The loss of biodiversity is caused by four main reasons, summarised by the acronym The Evil Quartet: - Habitat loss and fragmentation: The destruction of habitats is the most important cause of biodiversity loss. When large habitats are broken into small fragments, the species that require large areas are lost. - Overexploitation: The overuse of species for food, medicine and commerce, such as the overharvesting of the Steller's sea cow and passenger pigeon, which became extinct. - Alien species invasions: The introduction of foreign species that outcompete and displace native species. For example, the introduction of the African catfish (Clarias gariepinus) for aquaculture threatens the indigenous catfishes in Indian rivers, and the water hyacinth (Eichhornia crassipes) clogs water bodies. - Co-extinctions: When one species becomes extinct, the species that depend on it also become extinct. For example, when a host fish species becomes extinct, the parasites and species specialised on it also become extinct.
The extinction of species is a natural process; the fossil record shows that most of the species that ever lived are now extinct. However, the current rate of extinction is much higher than the natural rate, with some estimates suggesting that up to 10,000 times more species are becoming extinct than the natural background rate. The last 20 years alone have seen the extinction of 27 species. Extinct species include the dodo, quagga and many island species.
Conservation is the management of the environment and its resources to prevent the loss of biodiversity. The reasons for conservation are narrow utilitarian (food, fibre, medicine), broad utilitarian (ecosystem services like pollination and oxygen production) and ethical (every species has an intrinsic value, and we have a moral duty to preserve them).
In situ conservation is the conservation of biodiversity in its natural habitat, where the species occur naturally. The approaches include: - Protected areas: National parks, wildlife sanctuaries and biosphere reserves. - Sacred groves: Small forest patches protected by religious communities, which protect rare species. Sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghats, and Sarguja, Chanda and Bastar areas of Madhya Pradesh. - Biosphere reserves: Large areas that conserve biodiversity at all levels and protect the ecosystems, such as the Nilgiri Biosphere Reserve.
India currently has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
Ex situ conservation is the conservation of biodiversity outside its natural habitat. The approaches include: - Zoos: Conservation of animals in captivity. - Botanical gardens: Conservation of plants in managed gardens. - Wildlife safari parks: Conservation of animals in simulated natural environments. - Gene banks, seed banks and pollen banks: The storage of genetic material. The National Bureau of Plant Genetic Resources (NBPGR) in New Delhi stores plant genetic material, and the National Bureau of Animal Genetic Resources (NBAGR) stores animal genetic material.
The use of in vitro fertilisation, tissue culture and cryopreservation are also part of ex situ conservation. The IUCN Red List (International Union for Conservation of Nature) documents threatened species, and CITES (Convention on International Trade in Endangered Species) regulates the trade of endangered species.
| Level | Description | Example |
|---|---|---|
| Genetic diversity | Diversity within genes of a species | Varieties of wheat, rice |
| Species diversity | Number of species in a region | Western Ghats amphibians |
| Ecological diversity | Diversity of ecosystems | Deserts, rainforests, coral reefs |
| Threat | Description | Example |
|---|---|---|
| Habitat loss and fragmentation | Destruction of habitats | Most important cause |
| Overexploitation | Overuse of species | Steller's sea cow, passenger pigeon |
| Alien species invasion | Foreign species displace natives | African catfish, water hyacinth |
| Co-extinctions | Dependent species become extinct | Host-parasite extinctions |
| Type | Method | Examples |
|---|---|---|
| In situ | Natural habitat conservation | National parks, biosphere reserves, sacred groves |
| Ex situ | Outside natural habitat | Zoos, botanical gardens, seed banks |
Biodiversity is the richest inheritance of the living world, encompassing the diversity of genes, species and ecosystems that make life on Earth possible. The chapter has described the concept and levels of biodiversity, the latitudinal and species-area patterns that govern its distribution, and the enormous magnitude of undiscovered life, with India standing as one of the twelve mega-diversity countries. The loss of biodiversity, driven by the Evil Quartet of habitat destruction, overexploitation, alien species invasions and co-extinctions, threatens the very systems on which human survival depends. Conservation, both in situ in protected areas and sacred groves and ex situ in zoos, botanical gardens and gene banks, offers the means to halt this loss. The chapter reminds us that every species has intrinsic value and that preserving biodiversity is a moral and practical obligation, preparing us for the study of environmental issues in the final chapter.