Biodiversity is the term popularised by the sociologist Edward Wilson to describe the combined diversity at all the levels of biological organisation .
The most important of biodiversity are –
1 . Genetic diversity :-
A Single species might show high diversity at the genetic level over its distributional range . The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical that the plant produces . India had more than 50000 genetically different strains of rice and 1000 varieties of mango .
2 . Species diversity :-
The diversity at the species level . For example , the Western Ghats have a greater amphibian species diversity than the Eastern Ghats .
3 . Ecological diversity :-
At the ecosystem level , India for instance , with its deserts , rainforests , mangroves , coral reefs , wetlands , estuaries and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway .
- According to the IUCN ( 2004 ) , the number of 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 .
- Earth’s biodiversity based on the currently available species inventories . More than 70% of all the species recorded are animals , while plants ( including algae , fungi , bryophytes , gymnosperms and angiosperms ) comprise more than 22 % of the total .
- Among animals , insects are the most species rich taxonomic group , making up more than 70% of the total . that means out of every 10 animals on this planet , 7 are insects .
- The number of species in the world is more than the combined total of the species of fishes , amphibians , reptiles and mammals .
In figure ,biodiversity is depicted showing species number of major taxa .
Patterns of biodiversity
1 . Latitudinal gradients :-
The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution .
- For many group of animals or plants , there are interesting patterns in diversity , the most well-known being the latitudinal gradient in diversity .
- In general , species diversity decreases as we more away from the equator towards the poles .
- Columbia located near the equator has nearly 1,400 species of birds while New York at 41⁰ N has 105 species and Greenland at 71⁰ N only 56 species . India , with much of its land area in the tropical latitudes , has more than 1,200 species of birds .
- The largely tropical Amazonian rain forest in South America has the greatest biodiversity on Earth . it is home to 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 of more than 1,25,000 invertebrates .
2 . Species Area relationships :-
During his pioneering and extensive explorations In the wilderness of South America jungles , the German naturalist and geographer Alexander Von Humboldt observed that within a region species richness increased with increasing explored area , but only up to a limit .
- In fact , the relation between species richness and area for a wide variety of taxa ( angiosperm plants ,birds , bats , fresh water fishes ) turns out to be a rectangular hyperbola figure .
On a logarithmic scale , the relationship is a straight line described by the equation –
log S = log C + Z log A
where S = species richness , A = area , Z = slope of the line ( regression Coefficient ) , C = Y intersept
- Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2 , regardless of the taxonomic group or the reason ( where it is the plants in Britain , birds in California , the slopes of the regression line are amazingly similar ) .
Loss of Biodiversity :-
The biological wealth of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities .
- The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds .
- The IUCN Red list ( 2004 ) documents the extinction of 78 four species ( including 338 vertebrates , 359 invertebrates and 87 plants ) in the last 500 years .
Some examples of recent extinctions include the dodo ( Mauritius ) , quagga ( Africa ) , thylacine ( Australia ) , Steller’s Sea Cow ( Russia ) and three subspecies ( Bali , Javan , Caspian ) of tiger .
- The last 20 years alone have witnessed the disappearance of 27 species . Careful analysis of records shows that extinctions across taxa are not random , some groups like amphibians appear to be more vulnerable to extinction .
Adding to the grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction .
- Presently , 12% of all bird species , 23% of all mammal species , 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction .
- The current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre – human times and our activities are responsible for the faster rates .
- In general , loss of biodiversity in a region may lead to ( a )decline in plant production ( b ) lowered resistance to environmental perturbations such as drought and ( c ) increased variability in certain ecosystem processes such as plant productivity , water use , and pest and disease cycles .
Causes of biodiversity losses :-
The accelerated rates of species extinctions that the world is facing now are largely due to human activities . There are four major causes –
1 . Habitat loss and fragmentation :-
This is the most important cause driving animals and plants to extinction . The most dramatic examples of habitat loss come from tropical rain forests .
- Once covering more than 14 % of the earth’s land surface , these rain forests now cover no more than 6% . They are being destroyed fast .
- The Amazon rain forest ( it is so huge that it is called the lungs of the planet ) harbouring probably millions of species is being cut and cleared for cultivating Soya beans or for conservation to grasslands for raising beef cattle .
- Besides total loss , the degradation of many habitats by pollution also threatens the survival of many species .
2 . Over exploitation :-
Humans have always dependent on nature for food and shelter , but when need turns to greed , it leads to over exploitation of natural resources . many species extinctions in the last 500 years ( Steller’s sea cow , passenger pigeon ) where due to overexploitation by humans .
- Presently many marine fish populations around the World are over harvested , endangering the continued existence of some commercially important species .
3 . Alien species invasions :-
When Alien species are introduced unintentionally or deliberately for whatever purpose , some of them turn invasive , and cause decline for extinction of indigenous species .
- The Nile perch introduced into Lake Victoria in East Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake .
4 . Co – extinctions :-
When a species becomes extinct , the plant and animal species associated with it in an obligatory way also become extinct .
- When a host fish species becomes extinct , its unique assemblage of parasites also meets the same fate .
Another example is the case of a coevolved plant pollinator mutualism where extinction of one invariably leads to the extinction of the other .
Conservation of Biodiversity :-
When we conserve and protect the whole ecosystem , its biodiversity at all levels is protected , we save the entire forest to save the tiger . this approach is called in situ ( on site ) conservation .
- However , when there are situations where an animal or plant is endangered or threatened and needs urgent measures to save it from extinction , ex situ ( off site ) conservation is the desirable approach .
In situ conservation :-
Faced with the conflict between development and conservation , many nations find it unrealistic and economically not feasible to conserve all their biological wealth .
- Invariably , the number of species waiting to be saved from extinction far exceeds the conservation resources available .
- On a global basis , this problem has been addressed by eminent conservationists . they identified for maximum protection certain biodiversity hotspots regions with very high levels of species richness and high degree of endemism ( that is , species confined to that region and not found anywhere else ) .
- Initially 25 biodiversity hotspots were identified but subsequently 9 more have been added to the list , bringing the total number of biodiversity hotspots in the world to 34 . These hotspots are also regions of accelerated habitat loss . three of these hotspots – Western Ghats and Sri Lanka , Indo – Burma and Himalaya over our country’s exceptionally high biodiversity regions .
- Although all the biodiversity hotspots put together cover less than 2% of the earth’s land area , the number of species they collectively harbour is extremely high and strict protection of these hotspots could reduce the ongoing mass extinctions by almost 30% .
- In India , ecological unique and biodiversity rich regions are legally protected as Biosphere reserves , national parks and sanctuaries . India now has 14 Biosphere reserves , 90 national parks and 448 Wildlife sanctuaries . India has also history of religious and cultural traditions that emphasised protection of nature .
- In many cultures , tracts of forest were set aside , and all the trees and wildlife within were venerated and given total protection . Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya , Aravalli Hills of Rajasthan , Western Ghat regions of Karnataka and Maharashtra and Sarguja , Chanda and Bastar areas of Madhya Pradesh .
- In Meghalaya , sacred groves are the last refuges for a large number of rare and threatened plants .
Ex situ conservation :-
In this approach , threatened animals and plants are taken out from their natural habitat and placed special setting where they can be protected and given special care .
- Zoological parks , botanical gardens and wildlife Safari parks serve this purpose . There are many animals that have become extinct In The Wild but continue to be maintained in zoological parks .
- In recent years ex situ conservation has advanced beyond keeping threatened species in enclosures .
- Biodiversity known no political boundaries and its conservation is therefore a collective responsibility of all nations . The historic convention on biological diversity ( The Earth Summit ) held in Rio de Janeiro in 1992 , called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits .
- In a follow up the world summit on sustainable development and in 2002 in Johannesburg , South Africa , 190 countries pledge their commitment to achieved by 2010 , a significant reduction in the current rate of biodiversity loss at Global , regional and local levels .