Category : 12th Class

The term 'biodiversity' refers to 'the variety and variability among living organisms and the ecological complexes in which they occur'. If you observe a patch of forest, you may find a wide variety of plant and animal life. The plant life may range form a small herb to a large tree, and animal life may vary from a tiny insect to a large mammal. Apart from plants and animals, numerous microorganisms, which cannot be seen with naked eyes also occur in the soil. This shows biological diversity or biodiversity of a forest patch. Thus, biodiversity can be defined as 'the totality of genes, species and ecosystem of a region'

Biodiversity differs from place to place as each habitat has its distinct biota. However, many biologically rich and unique habitats are being destroyed, degraded and fragmented.

The major factors that tend to decrease biodiversity are increasing human population, higher resource consumption and pollution. Loss of biodiversity reduces gene pool of species, number of interactions in the biota and ability of species to adapt themselves to changes in the environment. It not only checks evolutionary advancements but also put the surviving species to dangers of extinction.

(1) Magnitude of biodiversity : Biologists are enganged in the identification and naming of species for the last 250 years. Still, they are able to name and describe for less number of species than the actual number present. Presently, the known and described number of species of all organisms on the earth is between 1.7 and 1.8 million, which is fewer than 15% of the actual number. It is predicted that the number of total species varies from 5 to 50 million. Approximately 61% of the known species are insects. About 2,70,000 species of plants and only 4650 species of mammals are known to science. Only fragmentary information is available about bacteria, viruses, protists and Archaea. The major area where numerous species are believed to be unknown to science are tropics and coral reefs.

Presently, efforts are being made to discover and describe new species more rapidly. The projects like 'Global Biodiversity Information Facility and the Species 2000’, are attempting to discover new species faster than ever before.

(2) Levels of biodiversity : The biological diversity include three interrelated hierarchical levels, viz. Genetic diversity, Species diversity and Community and ecosystem diversity.

(i) Genetic diversity : It is the diversity in the number and types of genes as well as chromosomes present in different species and the variations in the genes and their alleles in the same species. For instance, the number of genes is about 450-700 in Mycoplasma, 4000 in Escherichia coli, 13000 in Drosophila melanogaster, 32000-50000 in Oryza sativa and 35000 to 45000 in Homo sapiens sapiens.

'The genetic variation existing within a species is called genetic diversity’. The genetic variation may be in alleles (different variants of same genes), in entire genes (the traits determining particular characteristies) or in chromosomal structures.

Genetic diversity is useful in adaptation to changes in environmental conditions. It helps in speciation or evolution of new species. Lower genetic diversity within a species or variety may be useful for uniformity in yield as well as higher yield. However, it is liable to undergo degradation and prone to mass scale destruction at the hands of fungal or insect attacks.

(ii) Species diversity : It is the variety in the number and richness of the species of a region. The number of species per unit area is called species richness. Number of individuals of different species represent species evenness or species equitability. 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. Species diversity is product of both species richness or evenness or equitability, i.e., species richness weighed by species evenness.

Odum et al (1960) calculate species diversity (d) as number of species per thousand individuals while Menhinick (1964) calculates it as number of species in relation to square root of total number of individuals. Diversity index commonly used in ecological studies is Shannon index.

(iii) Community and ecosystem diversity : Community diversity refers to the variations in the biological communities in which species live. There are three perspectives of diversity at the level of community. These are alpha diversity, beta diversity and gamma diversity.

(a) Alpha diversity (a-index Diversity, Within-Community Diversity) : It indicates diversity within the community. It refers to the diversity of organisms sharing the same community or habitat. A combination of species richness and equitability/evenness is used to represent diversity within a community or habitat.

(b) Beta diversity (b-index Diversity, Between-Community Diversity) : It is biodiversity which appears in a range of communities due to replacement of species with the change in community/habitat due to presence of different microhabitats, niches and difference in environmental conditions.

(c) Gamma diversity (g-index Diversity) : It refers to the diversity of the habitats over the total land scape or geographical area.

Ecosystem diversity refers to the variation in the structure and functions of the ecosystem. It describes the number of niches, trophic levels and various ecological processes that sustain energy flow, food webs and the recycling of nutrients. It has focus on various biotic interactions and the role and function of keystone species (Species determining the ability of large number of other species to persist in the community). Diversity helps in producing more productive and stable ecosystems/communities which can tolerate various stresses like prolonged drought.

(3) Gradients of biodiversity : Biodiversity is not uniform on the earth. It varies with change in latitude or altitude. Biodiversity increase, when we move from high to low latitude (i.e. from the poles to the equator). The temperate region has severe climate with short growing period for plants. On the other hand tropical region has favourable conditions for the growth throughout the year. The favourable environmental conditions favour speciation (i.e. origin of new species) and make it possible for a larger number of species to occur and grow. Therefore, tropical regions are rich in biodiversity.

Similarly, the species diversity decreases from lower to higher altitude on a mountain. The temperature drops about 6.5oC with increase in altitude by 1000 m. The drop in temperature and greater seasonal variability at higher altitudes are the two major factors that reduce diversity.

It should not be confused with complexity and heterogenecity of the physical environment which tends to increase complexity and diversity of flora and fauna of an area.

(4) Benefits of biodiversity : Biodiversity provides numerous direct and indirect services to human beings, e.g., :

(i) Diversity of plants and animals provide a vast variety of foods and fabrics.

(ii) Maintenance of ecological balance or ecosystems stability.

(iii) Preserving biodiversity provides economic benefits which include improving the desirable characteristics of crops, making plants more pest resistant, providing medicines to treat and curve illness, supporting ecotourism and providing enjoyment to individuals.

(iv) Biodiversity enriches the lives of people in industrialized world and developed countries provides the means of survival to people in developing countries.

(5) Threats to biodiversity

(i) Destruction of habitats : Destruction of natural habitat is the primary threat to the biodiversity. Natural habitats, which protect natural flora and fauna are being converted to human settlements, harbours, dams, reservoirs, crop-lands, grazing grounds and mining sites. Deforestation deprive animal life of shelter and food. This decreases the population of many species. Migratory animals are also affected by deforestation because of the disturbance in their routes. Some of the dams are blocking, spawning and migration of fishes by inundating the habitats and by changing the physical environment. Sometimes human cleanliness destroy the habitat of scavengers such as vultures, kites, etc. The California condor (Cathartes californianus) a shy scavanger, which is the largest flying bird of today, has been severely affected by human cleanliness.

(ii) Disturbance and degradation of habitats : They are of two types, natural and man-made. Natural disturbance and degradation are caused by spontaneous jungle fire, pest infestation, defoliation by insects, locust attack, etc. Man-made disturbance and degradation are more severe. They include felling of trees, use of fire for clearing forest areas, collection of litter, and over-exploitation for other economically important products. Disturbance and degradation result in loss of biodiversity.

(iii) Pollution : The most subtle form of habitat degradation is environmental pollution. Pollution may reduce and eliminate populations of sensitive species. The populations of fish eating birds and falcons have declined due to excessive use of pesticides in crop fields. Lead poisoning is another major cause of mortality of many aquatic birds like ducks, swans and cranes. These birds often swallow the spent shotgun pellets that fall into lakes and marshes. The nutrient enrichments (eutrophication) also drastically reduce biodiversity.

(iv) Introduction of exotic species : New species entering a geographical region are called exotic or alien species. Introduction of exotic species may cause significant loss to the biological communities. The great majority of the exotic species do not become established in the introduced new places. However, some of the species are able to establish in new area. Such successful exotic species may kill or eat native species to the point of extinction, or may so alter the habitat that many natives are no longer able to persist. Island ecosystems are most vulnerable due to small size and small number of species.

A few examples of introduction of exotic species and their effects are : (a) Introduction of Nile perch (an exotic predatory fish) into lake Victoria (South Africa) threatened the entire ecosystem of the lake by eliminating several native species of the small Cichlid fish species that were endemic to this fresh water ecosystem. (b) In several tropical countries including India, water hyacinth (A free floating exotic water weed) clogs rivers and lakes, and threatens the survival of many aquatic species in lakes and rivers. (c) Lantana camara (An exotic shrub) strongly competes with the native species and eliminate many of them. The exotic shrub has invaded many forests in different parts of our country.

(6) Extinction of species : The most serious aspect of the loss of biodiversity is the extinction of species. Once a species goes extinct, its chances for further evolution are lost. A species is considered extinct, when no member of the species remains alive anywhere in the world. If individuals of a species remain alive only in captivity or other human-controlled conditions, the species is said to be extinct in the wild. In both of these situations, the species would be considered globally extinct.

A species is considered to be ecologically extinct, if it persists at such reduced numbers that its effects on other species in its community are negligible. Extinction is a natural process.

Types of extinction : Species become extinct through three types of extinction processes.

(i) Natural extinction : It is the extinction of species slowly from the earth due to change in environmental conditions. Some species disappear and the others which are more adapted to changed conditions, take their place. Many species have lost in the geological past by natural extinction. The extinction of species in the geological past is also called background extinction.

(ii) Mass extinction : It refers to the extinction of large number of species due to catastrophe. There have been several periods in the earth's geological history, when large number of species became extinct because of catastrophes. Mass extinction occurred in millions of years.

(iii) Anthropogenic extinction : They are extinctions abetted by human activities like settlements, hunting, over exploitation and habitat destruction. The World Conservation Monitoring Centre has found out that since 1600 A.D., the earth has lost 533 animal species (mostly vertebrates) and 384 plant species (mostly flowering plants). 75% of these extinctions are caused by direct human interference. It is almost documented that Dodo (Raphus cucullatus) and Taswania Wolf (Thylacinus cyanocephalus) have been hunted to extinction by humans.

(7) Susceptibility of extinction : All species are not equally susceptible to extinction. The characteristics which make a species susceptible to extinction are listed below

(i) Large body size e.g. Bengal tiger, lion and elephant.

(ii) Small population size and low reproductive rate e.g. Blue whale and Giant Panda.

(iii) Feeding at high tropic levels in the food chain e.g. Bengal tiger and Bald eagle.

(iv) Fixed migratory routes and habit. e.g. Blue whale and whooping crane.

(v) Localized and narrow range of distribution. e.g. Woodland caribou and Island species.

(8) Red data book and IUCN : IUCN is International Union of Conservation of Nature and Natural Resources which is now called World Conservation Union (WCU). It has its headquarters at Morges, Switzerland. It maintains a red data book or red list which is a catalogue of taxa facing risk of extinction. Threatened species is the one which is liable to become extinct if not allowed to realise its full biotic potential by providing protection from exotic species/human exploitation/habitat deterioration/depletion of food. Red data book or red list was initiated in 1963.


Red list has eight categories


Red list category




A taxon is Extinct when there is no reasonable doubt that the last individual has died. e.g. Dodo.


Extinct in the wild

A taxon is Extinct in the wild when exhaustive surveys in known and/or expected habitats, have failed to record an individual.


Critically endangered

A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future. e.g. Sus salvanius (Pigmy hog) Berberis nilghiriensus.



A taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future. e.g. Ailurus fulgens (Red panda), Blue whale, Largest Lemur Idri-Idri of Madagascar, etc.



A taxon is Vulnerable when it is not Critically Endangered or Endangered, but is facing a high risk of extinction in the wild in the medium-term future. e.g. Antilope cervicapra (Black Buck).


Lower risk

A taxon is Lower Risk when it has been evaluated and does not satisfy the criteria for Critically Endangered, Endangered or Vulnerable.


Data deficient

A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction.


Not evaluated

A taxon is Not Evaluated when it has not yet been assessed.


Out of these, four categories of species are included threatened species - critically endangered, endangered, vulnerable and lower risk species. Two more categories are also added to them. They are (i) Rare Species (R): They are species with naturally small population, either localised or thinly scattered, which are always at risk from pests/pathogens/predators/exotic species. Clouded Leopard (Neofelis nebulosa). Hawaiian Monk Seal (Monochus schauinslandii). Great Indian Bustard (Ardeotis nigriceps). (ii) Indeterminate Species : The species are in danger of extinction but the reason is not known, e.g., 3-banded Armadillo of Brazil, Short Eared Rabbit of Sumatra, Mexican Prairie Dog.

The main objectives of Red lists are listed below :

(i) Identification and documentation of endangered species.

(ii) Providing a global index of the decline of biodiversity.

(iii) Developing awareness about the importance of threatened biodiversity.

(iv) Defining conservation priorities at the local level and guiding conservation action.

(9) Conservation of biodiversity : Conservation of biodiversity is protection, uplift and scientific management of biodiversity so as to maintain it at its optimum level and derive suitainable benefit for the present as well as future strategies.

Conservation strategies : There are two basic strategies of biodiversity conservation – in-situ (on site) and ex-situ (off site).

(i) In-situ conservation : It is protection and management of important components of biological diversity through a network of protected areas.

(a) Protected areas : They are ecological/biogeographical areas where biological diversity alongwith natural and cultural resources are protected, maintained and managed through legal or other effective measures. National Parks and Wild life Sactuaries are the examples of protected areas. The World Conservation Monitoring Centre (WCMC) has recognised 37,000 protected areas around the world. As of September 2002, India has 581 protected areas (89 National parks and 492 Wildlife Sanctuaries). These areas cover 4.7 per cent of the land surface as against 10 per cent internationally suggested norm. The protected areas provide following benefits.

  • Maintain viable populations of all native species and sub-species.
  • Maintain the number and distribution of communities and habitats, and conserve the genetic diversity of all the present species.
  • Prevent man made introduction of alien species.
  • Make it possible for species/habitats to shift in response to environmental changes.

(b) Biosphere reserves : The Man and Biosphere (MAB) programme of UNESCO formulated the concept of Biosphere in 1975, which deals with conservation of ecosystems and genetic resources contained therein. "The Biosphere Reserves are a special category of protected areas of land/or coastal environments, wherein people are an integral component of the system'. These are representative examples of natural biomes and contain unique biological communities.

A biosphere reserve has three zones :

  • Core or natural zone : It comprises an undisturbed and legally protected ecosystem.
  • Buffer zone : It surrounds the core area, and is managed to accommodate a greater variety of resource use strategies, and research and educational activities.
  • Transitional zone or manipulation zone : It is the outer most part of the biosphere reserve. It serves as an area of active cooperation between reserve management and the local people, wherein activities like settlements, cropping, forestry and recreation and other economic uses continue in harmony with conservation goals.

Importance of biosphere reserve

Restoration : Biosphere reserves help in restoration of degraded ecosystems and habitats.

Conservation : Biosphere reserves ensure the conservation of landscapes, ecosystems, species and genetic resources. These reserves also encourage the traditional resource use.

Development : The biosphere reserves promote culturally, socially and ecologically sustainable economic development.

Scientific research, monitoring and education : The biosphere reserves provide support for research monitoring, education and information exchange related to local, national and global issues of conservation and development.

(c) Sacred forests and Scared lakes : Sacred forests are forest patches around places of worship which are held in high esteem by tribal communities. They are the most undisturbed forest patches (Island of pristine forests) which are often surrounded by highly degraded landscapes. They are found in several parts of India, e.g., Karnataka, Maharashtra, Kerala, Meghalaya, Temples built by tribals are found surrounded by Deodar forests in Kumaon region, Jaintias and Khasias in Meghalaya. Not a single branch is allowed to be cut from these forests. As a result many endemic species which are rare or have become extinct elsewhere can be seen to flourish here. Similarly aquatic flora and fauna is also protected in sacred water bodies. e.g. Khaeheopalri lake in Sikkim.

(ii) Ex-situ conservation : It is conservation of selected rare plants/animals in places outside their natural homes. Ex situ conservation includes offsite collections and gene banks.

(a) Offsite collections : They are live collections of wild and domesticated species in botanical gardens, zoos, arboreta, etc. Currently, there are more than 1500 botanical gardens and arboreta (Gardens with trees and shrubs) having more than 80,000 species. Many of them have seed banks, tissue culture facilities and other ex-situ technologies. The number of zoos/zoological parks is more than 800. They have about 3000 species of mammals, birds, reptiles and amphibians. Most of them have well managed captive breeding programmes.

Therefore, offsite collections can be used to restock depleted populations, reintroduce species in the wild and restore degraded habitats.

(b) Gene banks : A gene bank or germ plasm bank is an institution where valuable plant material is preserved in a viable condition. These are stored either in the form of seeds or dormant vegetative organs or in the form of frozen gametes.

  • Seed banks : Plant germplasm in live state is the viable seed. In a seed the embryo is present in a dormant state. The moisture contents of seeds is kept low (5-15%) and they are stored at low temperature (\[{{10}^{o}}C\] to\[{{20}^{o}}C\]) with supply of little oxygen. With these conditions there is reduced enzyme activity and reduced respiration. From time to time at definite intervals these seeds are sown to produce new plants and fresh seeds are obtained. Such seeds are called Orthodox seeds as they can withstand the reduction in moisture and prolonged exposure to low temperature. Seeds of trees and shrubs usually get killed on drying and freezing. Such seeds are called Recalcitrant seeds e.g., tea, litchi. In such cases plants are kept in orchards and maintained through in-situ conservation.
  • Orchards : Plants with recalcitrant seeds are grown in orchards where all possible strains and varieties are maintained, e.g., litchi, oil Palm, rubber tree, etc.
  • Tissue Culture : It is carried out through callus formation, embryoids, pollen grain culture and shoot tip culture for those plants which are either seedless, have recalcitrant seeds, variable seed progeny or where clone is to be maintained. The method is useful in maintaining a large number of genotypes in small area, rapid multiplication of even endangered species and for hybrid rescue. Shoot tip culture maintains virus free plants. It is used for international exchange of germplasm in vegetatively multiplied cultivars, e.g., banana, potato.
  • Cryopreservation : Preservation at \[{{196}^{o}}C\](liquid nitrogen) can maintain tissue culture, embryos, animal cells/tissues, spermatozoa indefinitely. The cryopreserved material is revived through special technique when required.

(10) Hot spots of biodiversity : They are the areas with high density of biodiversity or megadiversity which are also the most threatened one. To designate priority areas for in situ conservation, Norman Myers developed the 'hot spots' concept in 1988. 'The hot spots are the richest and the most threatened reservoirs of plant and animal life on earth'.

Ecologically hot spots are determined by four factors.           

(i) Number of species/species diversity. (ii) Degree of endemism. (iii) Degree of threat to habitat due to its degradation and fragmentation. (iv) Degree of exploitation.

Over the world 25 terrestrial hot spots have been identified for the conservation of biodiversity. Out of these 15 hot spots have tropical forests, 5 occur in Mediterranian-type zones and 9 hot spots are present in tropics. The hot spots together occupy 1.4 per cent of the earth's land area. About 20 per cent of the human population lives in the hot spots.

Hot spots in India : Out of the 25 hot spots of the world, two are found in India. These are Western Ghats and Eastern Himalayas, and these extend to the neighboring countries also. These areas show high degree of endemism and are inhabited by a wide variety of flowering plants, swallow tailed butterflies, amphibians, reptiles and mammals.

(i) Western Ghats : It lies parallel to the Western Coast of Indian peninsula for almost 1600 km, spread over in Maharashtra, Karnataka, Tamil Nadu and Kerala. The evergreen forests are found at low elevation (i.e. 500 m above mean sea level), whereas semi-evergreen forests occur at 500-1500 m height. The two main centres of biological diversity are : (i) the Agastryamalai hills and Silent valley and (ii) the new Amambalam Reserve.

(ii) Eastern Himalaya : It extend to the north eastern India and Bhutan. Many deep and semi isolated valleys are found in this region. These valleys are exceptionally rich in endemic plant species. There occur temperate forests at altitudes of 1780 to 3500 m in this region. The eastern Himalaya is an active centre of evolution and exhibits a rich diversity of flowering plants. Numerous primitive angiosperm families (e.g., Magnoliaceae and Winteraceae) and primitive genera of plants like Magnolia and Betula and found in this region.

(11) International efforts for conserving biodiversity : Earth summit of Rio de Janeiro (1992), Brazil, promoted Convention of Biological Diversity (CBD) which was signed by 152 nations. Its recommendations came into effect on 29th Dec. 1993. India became a party to this Convention on Biological Diversity in May, 1994.

The convention has three key objectives

(i) Conservation of biological diversity

(ii) Sustainable use of biodiversity

(iii) Fair and equitable sharing of benefits arising out of the utilization of genetic resources.

A number of projects for the conservation and appropriate development of Biosphere Reserves, are being supported by the World Conservation Union and the World Wide Fund for Nature (WWF).

(12) Biodiversity conservation in India : India is a centre of rich biological diversity and has contributed significantly of the global biodiversity.

India is a home land of 167 cultivated species and 320 wild relatives of crop plants. It is a centre of diversity of animal species (e.g. zebu, mithun, chicken, water buffalo, camel); crop plants (e.g. edible diascoreas, alocasia, colocasia); species and condiments (e.g., cardamom, black pepper, ginger, turmeric), bamboos, brassicas and tree cotton. India also represents a secondary centre of domestication for some animals (e.g. horse, goat, sheep, cattle, yak and donkey) and plants (e.g. tobacco, potato and maize).

Because of the abundant diversity present in the country, its conservation is very important not only for the country but also for the rest of the world. Both in situ and ex situ conservation measures are being undertaken.



The National parks, Wildlife sanctuaries and other protected areas maintained by the Ministry of Environment and Forests provide in situ conservation of biodiversity. The joint forest management systems involve forest departments and local communities to enable tribal and local people to have access to non-wood forest products (such as lac, silk, honey, wax, tendu leaves, etc.) and at the same time protect the forest resources.

Major ex situ conservation of biodiversity is being managed by National Bureau of Plant, Animal and Fish Genetic Resources. There is an International Crop Research Institute for Semi-Arid Tropics (ICRISAT) in Hydrabad for conserving germplasm of Groundnut, Pigeon Pea, Chick Pea, Pearl Millet and Sorghum. A number of other centres in India are maintaining hundred and thousands of present and past varieties of crop plants. Thus germplasms of plants and animals are being conserved in vitro in gene/seed banks, field gene banks, botanical gardens and zoological gardens. Being spread over different parts of the country, the various institutes are conserving regional variants of all types of important plants and animals.

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