1. Biodiversity
n The occurrence of different types of genes, gene pools, species, habitats and ecosystems in a particular place and various parts of earth is called biodiversity.
n The term ‘biodiversity’ was given by Edward Wilson.
n Biodiversity is divided into three levels of biological organisation:
(i) Genetic diversity
l It is the measure of variety in genetic information contained in the organisms over its distributional range.
l It enables a population to adapt to its environment.
l For example, medicinal plant Rauwolfia vomitoria growing in Himalayan ranges shows variation in potency and concentration of the active chemical reserpine that it produces.
l There are more than 50,000 genetically different strains of rice and 1,000 varieties of mango in India.
(ii) Species diversity
l It is a measure of the variety of species and their relative abundance present within a region.
l For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
(iii) Ecological diversity
l It is a measure of the diversity at community and ecosystem levels. They represent the local, unique habitat and regional components of species diversity.
l For example, ecological diversity is greater in India than a Scandavian country like Norway due to presence of large number of ecosystems like deserts, rainforests, coral reefs, wetlands, estuaries and alpine meadows.
2. Global Species Diversity
n According to the International Union for Conservation of Nature and natural resources or IUCN (2004), the total number of plant and animal species is over 1.5 million.
n A more conservative and scientifically sound estimate made by Robert May, places the global species diversity at about 7 million.
n More than 70 per cent of all the species are animals, while plants account for about 22 per cent of the total.
n Amongst animals, insects comprise more than 70 per cent that means, out of every 10 animals on this planet, 7 are insects on this earth.
n India has only 2.4 per cent of world’s land area and 8.1 per cent global species diversity. There are nearly 45,000 plants and twice as many animals. So, India is one of 12 megadiversity countries of the world.
n Large number of species are facing threat of becoming extinct even before we discover them.
n We cannot estimate diversity of prokaryotes because conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions. If we accept biochemical or molecular criteria for delineating species of prokaryotes, then their diversity might run into millions.
3. Patterns of Biodiversity
n Biodiversity is not uniform throughout the world because it is affected by two factors— latitudinal gradients and species–area relationship.
(i) Latitudinal gradients
l Biodiversity increases from poles to equators, i.e., from high to low latitude.
l Tropics (23.5°N to 23.5°S) have more species than temperate or polar regions. For example, Columbia located near the ecuator has 1,400 species of birds while New York (41.5°N) has 105 species and Greenland (71°N) has only 56 species. India has more than 1200 species of birds.
l Forest in tropical region like Ecuador has up to 10 times as many species of vascular plants as forest of equal area in temperate region like midwest of USA.
l Tropical rain forests of Amazon in South America possess the greatest biodiversity on earth with more than 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals,427 of amphibians, 378 of reptiles and more than 1,25,000 of invertebrates.
l Greater biological diversity is observed in tropics because:
(a) Temperate regions have been subjected to frequent glaciations in the past but tropical regions remained undisturbed. Therefore, tropics had a longer evolutionary time for species diversification.
(b) Temperate environment unlike the tropics are more seasonal, less constant and unpredictable, resulting in less niche specialisation and lesser species diversity.
(c) Tropics have greater solar energy exposure which contributes to higher productivity and greater diversity.
(ii) Species–area relationship
l German naturalist and geographer Alexander von Humboldt observed that within a region, species richness increased with increasing explored area but up to a limit.
l The relationship between species richness and area for a wide variety of taxa (like vascular plants, birds, bats and freshwater fishes) appears as a rectangular hyperbola.
l On a logarithmic scale, the relationship is a straight line described by the following equation:
log S = log C + Z log A
where S = Species richness
A = Area
Z = Slope of the line (regression coefficient)
C = Y-intercept.
l The value of Z lies in the range of 0.1–0.2 regardless of taxonomic group or the region. Whether it is plants in Britain, birds in california or malluscs in New York State, slopes of regression are similar.
l However, the analysis in a very large area like the whole continent gives a Z value that ranges from 0.6 to 1.2. For example, for frugivorous (fruit eating) birds and mammals in the tropical forest of different continents, the slope is 1.15.
4. Importance of Species Diversity to the Ecosystem
n Ecologists believe that communities with more species tend to be more stable than those with less species. This was confirmed by David Tilman.
n Characteristics of a stable community:
(i)Productivity should not vary too much from year to year.
(ii) It should be resistant to occasional natural and man-made disturbances.
(iii) It should be resistant to invasions by alien species.
n Importance of biodiversity for survival of species can be explained by the ‘rivet popper hypothesis’ proposed by Paul Ehrlich.
n This hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.
n If every passenger pops a rivet to take home (resulting in species extinction), it may not affect the flight safety initially (proper ecosystem functioning) but with time as more rivets are removed the plane becomes dangerously weak and fatal to the life of other species.
5. Loss of Biodiversity
n It is caused by over-population, urbanisation and industrialisation.
n The colonisation of tropical Pacific Islands by humans has led to the extinction of more than 2,000 species of native birds.
n 15,500 species are facing the threat of extinction worldwide.
n IUCN Red list (2004) documents extinction of 784 species including 338 vertebrates, 359 invertebrates and 487 plants in last 500 years.
n At present, 31 per cent of gymnosperms, 32 per cent of amphibians, 12 per cent of bird species and 23 per cent of mammals face the threat of extinction.
n Some recently extinct species are dodo (Mauritius), quagga (Africa), thylacine (Australia), Stellar’s sea cow (Russia) and three tiger species (Bali, Java, Caspian).
n In last 20 years, 27 species have disappeared.
n There has been five episodes of mass extinction of species and the sixth extinction is going on, but it is 100–1000 times faster than the earlier ones.
n Loss of biodiversity in a region may lead to
(i) decrease in plant production.
(ii) less resistance to environmental disturbances such as drought.
(iii) increased variability in ecosystem processes like plant productivity, water use, pest and disease cycles.
6. Causes of Biodiversity Losses
n There are four major causes of biodiversity loss. These are also known as ‘The Evil Quartet’.
(i) Habitat loss and fragmentation
l Destruction of habitat is the primary cause of extinction of species.
l The tropical rainforests initially covered 14 per cent of the land surface of earth, but now cover only 6 per cent of land area.
l The Amazon rainforest (called the “lungs of the planet) is being cut and cleared for cultivation of soya beans and for conversion into grasslands for raising beef cattle.
l When large-sized habitats are broken or fragmented due to human settlements, building of roads, digging of canals, etc., the population of animals requiring large territories and some animals with migratory habitats declines.
(ii) Over-exploitation
l When biological system is over-exploited by man for the natural resources, it results in degradation and extinction of the resources.
l For example, Stellar’s sea cow, passenger pigeon and many marine fishes have become extinct due to over-exploitation by man.
(iii) Alien (exotic) species invasions
l Some alien (exotic) species when introduced unintentionally or deliberately, become invasive and cause harmful impact, resulting in extinction of the indigenous species.
l Nile perch, a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique assemblage of more than 200 species of Cichlid fish in the lake.
l Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and posed threat to our native species.
l Introduction of African catfish (Clarias gariepinus) for aquaculture purposes is posing a threat to the indigenous cat fishes of Indian rivers.
(iv) Co-extinctions
l When a species becomes extinct, the plant and animal species associated with it in an obligatory manner, also become extinct.
l For example, (a) if the host fish species becomes extinct, all those parasites exclusively dependent on it, will also become extinct; (b) in plant–pollinator mutualism also, extinction of one results in the extinction of the other.
7. Reasons for Biodiversity Conservation
n Biodiversity is important for ecosystem health and for survival of human race on earth. There are three main reasons for conserving the biodiversity which have been classified into the following categories:
(i) Narrowly utilitarian arguments
l Human beings derive direct economic benefits from nature, like food, firewood, fibre, construction material, industrial products (resins, gums, dyes, tannins, etc.) and medicinally important products.
l More than 25 per cent of the drugs are derived from plants and about 25,000 species of plants are used by native people as traditional medicines.
(ii) Broadly utilitarian arguments
l Biodiversity plays a major role in maintaining and sustaining supply of goods and services from various species as well as ecological systems.
l The different ecological services provided are:
(a) Amazon forest is estimated to contribute 20 per cent of the total oxygen in the atmosphere on earth by photosynthesis.
(b) Ecosystem provides pollinators like bees, bumble bees, birds and bats which pollinate plants to form fruits and seeds.
(c) Aesthetic pleasures like bird watching, spring flowers in full bloom, walking through the thick forest, waking up to a bulbul’s song, etc. are some other benefits of the ecosystem.
(iii) Ethical reasons
l There are thousands of plants, animals and microbes on this earth which are not useless. Every one has some intrinsic value even if it is not of any economic value to us.
l It is, therefore, our moral duty to ensure well-being of all the living creatures for the utilisation of future generations.
8. Conservation of Biodiversity
n Biodiversity can be conserved by protecting its whole ecosystem.
n There are two basic approaches for conservation of biodiversity.
(i) In situ conservation (On site conservation)
This approach involves protection of species in their natural habitat.
(a) Biodiversity hotspots
l These are regions of high levels of species richness and high degree of endemism.
l Endemic species are species confined only to a limited region.
l There are 34 hotspots in the world.
l In India, the three hotspots are Western Ghats and Sri Lanka, Indo–Burma and Himalaya.
l Biodiversity hotspots cover less than 2% of earth’s land area, but they harbour large number of species. Thus, they could reduce mass extinction by 30%.
(b) Protected areas
l India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
l Jim Corbett National Park was the first to be established in India.
(c) Ramsar sites
l Ramsar sites are wetlands which are considered to be of international importance.
l Ramsar Convention (1971) is an international treaty for the conservation and sustainable utilisation of wetlands.
l Ramsar convention works for (a) conservation and use of wet lands, (b) recognition of fundamental ecological functions of wetlands and their cultural, economic, scientific and recreational value.
l There are 26 Ramsar sites in India. Some of these are Ashtamudi wetland (Kerala), Sambhar lake, Rudrasagar lake, Chilika lake, Bhitakanika wetland (Odisha).
l Wetlands include marshes, lakes, coral reefs, etc.
(d) Sacred groves
l These are forest patches set aside for worship. All the trees and wildlife within are given total protection by tribal people.
l Large number of rare and threatened plants can be found in these regions.
l Some of the sacred groves in India are as follows:
— Khasi and Jaintia Hills in Meghalaya
— Western Ghat regions of Karnataka and Maharashtra
— Aravalli Hills of Rajasthan
— Sarguja, Chanda and Bastar areas of Madhya Pradesh.
(ii) Ex situ conservation (Off-site conservation)
n This approach involves placing threatened animals and plants in special care units for their protection.
n India has 35 botanical gardens and 275 zoological parks where animals which have become extinct in wild are maintained.
n By using cryopreservation (preservation at –196°C) technique, sperms, eggs, animal cells, tissues and embryos can be stored for long period in genes banks, seed banks, etc.
n Plants are propagated in vitro using tissue culture methods (micropropagation).
n It is the desirable approach when urgent measures to save extinctiond are required.
S. No. | In situ conservation | Ex situ conservation |
(i) | It is the conservation and protection of biodiversity in its natural habitat. | It is the conservation of selected threatened plant and animal species in places outside their natural habitat. |
(ii) | Population is conserved in the surroundings where they have developed their distinctive features. | Population is conserved under simulated conditions that closely resemble their natural habitats. |
(iii) | E.g., national parks, biosphere reserves, wildlife sanctuaries, etc. | E.g., botanical gardens, zoological parks, wildlife safari, gene banks, etc. |
9. Conventions on Biodiversity
n The Earth Summit was held in Rio de Janeiro in 1992, which called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits.
n The World Summit on Sustainable Development was held in Johannesburg, South Africa in 2002 in which 190 countries pledged to reduce the current rate of biodiversity loss at global, regional and local levels by 2010.
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