Gradients Of Biodiversity

Biodiversity of Class 12

What is Gradients Of Biodiversity

Change in latitude or altitude leads to change in biodiversity. Biodiversity increases from poles to equator (from high to low latitude).

Number of species increase in area with favourable environmental conditions (e.g. in tropical rain forests).

In temperate regions, plants grow for shorter period due to adverse climatic conditions. For example vascular plants in tropic rain forests are 118-236 per 0.1 ha sample area when compared with temperate zones (only 21-48 species). It has been found to be true with other taxonomic groups like ants, birds, butterflies, etc. can be noticed.

On mountains, decrease in species diversity takes place from lower to higher altitude. Higher seasonal variations and fall in temperature leads to reduction in biodiversity with 1000 m increase in altitude lead to temperature drop of about 6.5°C.

Biodiversity has great importance to mankind due to its many uses :

Ecosystem services :

All the living organisms are so closely interlinked (through food chain, food webs, material cycling, energy flow, etc.) that destruction of one kind of wildlife on the earth may upset the ecological balance in nature.


destruction of snakes will lead to increase in the rat population which will destroy crops.

Similarly, killing of carnivores will increase the population of herbivores which will damage the vegetation and disturb the ecological balance. Species of plants and animals keep a check on their numbers through food chains, so the wildlife helps to preserve the environment as self-sustaining system. Biodiversity is required for maintaining and sustainable use of goods and services from ecosystems.

These services are maintenance of gaseous composition in atmosphere, pollination, formation of soil, nutrient cycling, climate control by forests and oceanic systems.

Scientific importance :

Wildlife acts as a source of gene bank for breeding programmes in agriculture, animal husbandry, fisheries, etc. e.g. fruit flies, frogs, rats, rabbit, guinea pigs, rhesus monkeys and many other wild animals are used as research materials on which drugs are tested before applying to mankind. Plant breeders have produced a number of high-yielding and disease-resistant varieties from their wild relatives by genetic modifications. So there is an urgent need to protect wildlife for breeding experiments. The wildlife acts as a source for new varieties. The protection of wild life becomes of paramount importance for their survival and propagation of race, so man is constantly in search of ways and means of preserving natural areas in their natural conditions to promote the development of wildlife.

e.g. man was able to save the high-yielding varieties of rice to protect them from a new rice pest Nilaparvata lugens (brown plant hopper) by introducing pest-resistant gene in them from a few wild varieties found in Kerala.

Similarly, wild rice (Oryza nivara) provided resistance against grassy stunt virus in 1970s when virus-resistant gene was incorporated in IR-36 rice variety; Wild Thatch Grass (Saccharum spontaneum) provided resistant gene to sugarcane against red rot disease; similarly in potato, resistant gene against late blight disease has been incorporated from a wild variety -Solanum demissum. Thus the production of high-yielding, disease-resistant crops,livestocks and fish cannot withstand the changes of the surrounding withouttheir wild relatives.

Drugs and medicine.

Some examples of drugs and medicines extracted from plants are :

  1. Morphene (Papaver somniferum) is used as analgesic.

  2. Quinine (Chinchona ledgeriana) for treatment of malaria.

  3. Taxol extracted from bark of Taxus brevifolia and T. baccata is used as anticancer drug.

  4. Plants are also useful for making many synthetic products called botanochemicals.

Commercial importance :

Wildlife is a renewable source and is beneficial to mankind in many ways :

Food and improved varieties. Fresh-water and marine fishes provide large amount of food.

Biodiversity in modern agricultural is beneficial due to :

  • For breeding, biodiversity provides source material.
  • As a source of new biodegradable pesticides.
  • As a source of new crops.

Plants provide food not only for themselves but also for other organisms including man. About twenty plant species are used which provide about 85 percent of world’s food.

  •  Fur, skin and other products like musk, leather, honey, lac, cochineal (a red pigment), guano, pearls, etc. obtained from wild animals are sources of trade.
  • Several wild plants provide useful products like timber, paper, gums, resins, tannins, dry fruits, fibres (cotton,jute), drinks (tea, coffee) distillation products like wood alcohol, acetic acid, oxalic acid, charcoal, and medicines, etc.

Aesthetic importance.

  • Due to their beauty, many birds, variously colourful butterflies, mammals, green forests etc.have great aesthetic value to human beings.
  • Many plants are considered sacred and even worshipped in India. e.g. Ficus religiosa (Peepal), Ocimum sanctum (Tulsi) and Prosopis cineraria (Khejri).

Unknown benefits :

A wild species may have certain benefits which are still not known to us and may become known in future. So the conservation of even non-beneficial species is equally significant e.g. isolation of penicillin from Penicilliumnotatum (blue-green mould); anti-malarial drug-quinine from the bark of Cinchona plant of Peru; and natural silk from the silk moth-Bombyx mori, etc. were not known from the very beginning.

Sport and Enjoyment :

Wildlife is also important in games so are hunted upon while some of them are even worshipped. A visit to the sanctuaries and national parks is a thrilling experience. Some animals are used for recreation of people in circus shows.

Economic importance :

Wildlife has following uses :

Economic importance of plants :
  1. The plants act as producers in the ecosystem and form the basis of biotic system.

  2. These produce a number of useful products like resins, fibres (cotton, jute), gums, food, tannins, drugs, wood, organic acids, etc.

  3. These produce oxygen as a by-product of photosynthesis for aerobic respiration of animals.

  4. These bind the soil particles and prevent soil erosion, floods and advancement of deserts.

  5. These act as habitat for a variety of animals.

Economic importance of animals :

  1. These act as consumers in the ecosystem and help in homeostasis.

  2. These produces carbon dioxide in aerobic respiration. CO2 is released in atmosphere for its reuse in photosynthesis by the plants.

  3. These produce a number of useful products like food, fur, hide, leather, feathers, ivory, musk, lac, honey, cochineal (a red pigment), pearls, shells, etc.

  4. Some animals like honey bee help in pollination.

  5. Some animals help in seed and fruit dispersal e.g. frugivorous animals.

  6. Fossorial animals like earthworms, rats, rabbit, etc. make the soil porous for the better growth of plant roots.

  7. Some animals are used for transport and agricultural operations.

Economic Importance of Microbes :

  1. The decomposers (e.g. bacterial and fungi) decompose the dead bodies and wastes for material cycling in the ecosystem.

  2. Some microbes help in nitrogen fixation e.g. bacteria like Azotobacter, Rhizobium, Clostridium; and cynobacteria like Nostoc, Anabaena etc.

  3. Some microbes have industrial uses e.g. Lactobacillus in milk industry; Saccharomyces in baking and brewing industries; Acetobacter in vinegar industry, etc. These are also used in industries producing vitamins and antibiotics;in retting of fax and hemp, in curing of tea and tobacco and in preparing leather; etc.

  4. Some microbes help in symbiotic digestion of cellulose e.g. Trichonympha (a protozoan) in intestine of Termite; Ruminococcus in rumen stomach of ruminants (cud-chewingmammals), etc.

Ethical needs.

The present wild life is the result of organic evolution which started about 3.5 billion years ago. So it is our ethical duty to conserve the wildlife for the utilization of coming generations.

Religious importance.

Different animals are symbolized as the vahanas of Hindu gods/goddesses e.g. garuda for Lord Vishnu; bull for Ishwara; mouse for Ganpathy; peacock for Subramaniyam; tiger for Goddess Durga, etc. There are many animal gods as well like Matsya, Narsimha and Hanuman.


Extinction is the complete elimination of a wild species :It is a natural but slow process but due to unplanned activities of man, the rate of decline of wild life has been particularly rapid in the last one hundred years. There are a number of causes which are known to cause extinction of wildlife :

Destruction of habitats and fragmentation. It is the most serious threat to wildlife. It is the most serious threat to wildlife.

It is due to :

  1.  Environmental pollution due to automobiles etc. leading to degradation of a number of important habitats.

  2. Deforestation leads to decrease in the area of movement so decreasing their reproductive powers. In Tripura, deforestation of dense forests is posing a serious threat to the precious barbe’s leaf monkey, better known as “spectacled monkey” or “lajvanti bandar” (shy monkey). Main causes of its facing extinction are increasing destruction of its habitat by deforestation coupled with jhum and shifting cultivation.

  3. Soil erosion.

  4. Agricultural expansion.

  5. Overgrazing.

  6. Increasing urbanisation.

  7. Forest fires due to certain human activities or by chance.

  8. Development works like dams, reservoirs, roads, railway lines, croplands, industries, mines, etc. Dams block spawning and migration of certain fishes.

  9. Cleanliness drives adversely affect the natural scavengers like Cathartes californianus California candox (a shy scavenger and largest fly bird of today).

  10. Destruction of habitat is very serious threat to our life because :

    1. It decreases the hiding places of animals, and

    2. It increases the chances of their predation.

  11. A forest area surrounded by urban colonies, orchards, plantations, cropland represent fragmented habitats.

Due to this species present in deeper areas start disappearing.

Indiscriminate hunting for various uses of animals like food, hide, musk, tusk, horn, fur, plumage, recreation, etc.

Other causes of indiscriminate hunting of wild animals are their increased demand as museum specimens and increased trade for the animal products like hides, skins, fur, leather, feathers, horns, ivory, meat, etc. Excessive hunting is known to cause.

  1. Extinction of Dodo bird (Didus ineptus-extensively killed due to its beautiful feathers) of Mauritius.

  2. Extinction of Cheetah (Acinomyx jubatus), the test mammal of India. (Last live cheetah died in Zoo in 1994).

  3. Many species of fish, molluscs, sea-turtles, sea-cows and whales are facing extinction.

According to a report of WPSI (Wildlife Protection Society of India), more than 60 tigers have been poached in different parts of the country during the year 1994-95. A London based international conservation organisation has stated that poaching of tigers for Chinese medicines, responsible for the death of at least one tiger in India every day.

According to another report, rhino poaching in and around Kaziranga National Park has increased and 25 rhinos have been poached in 1995. In Orissa, many wildlife species including Asian elephant face imminent danger of extermination because of poaching and lack of concern by the Government to check trafficking of wild animals. Wildlife Society of Orissa has reported that 57 elephants have been shot dead by poachers for ivory between 1992-96. Strict action by Rajasthan Government coupled with quick judicial pro¬nouncements (in October, 1998) in the cases related to two black bucks by cine star Salman Khan and his accomplices has dearly sent a message that howsoever highly placed one might be, no one can escape the due process of law when it comes to the crime of killing the wild animals. Between 1995 and 2000, about 175 lions and 226 tigers died in Indian zoos as against 46 lions and 142 tigers in the ‘protected areas’.Introduction of exotic species are known to threaten the survival of many native species.

  1. Periplaneta americana (American cockroach) is threatening the existence of native oriental cockroach.

  2. Exotic trout and bass are affecting many species in USA.

  3. Large scale killing of American chestnut tree by an exotic fungus species, Endothia parasitica (chestnut blight) of China. The fungus was accidentally introduced into the United States in 1904.

  4. Goats and rabbits introduced in the islands of Pacific and Indian Oceans are destroying the habitats of several plants, birds and reptiles.

  5. Eupatorium odoratum replaced Tectona grandis in N.E. India.

  6. Parthenium hysterophorus has replaced herbs and shrubs in open spaces.

  7. Eichhornia crassipes (water hyacinth) has become dominant species in pools and ponds.

  8. Nile perch, an exotic predatory fish introduced in Lake Victoria of South Africa has eliminated several native small cichlid fish species which were endemic to this lake.

  9. Lantana camara, a plant now has entered into forests and seriously competing with native species growing there. These exotic species are known to adversely affect the native species through factors like competition for food and space, predation, habitat destruction, transmission of diseases and parasites.

Over-exploitation of natural resources e.g. over-fishing, mechanical catching of animal species, etc. is a serious threat to the wildlife.

Disturbance in migratory routes of animals like fishes due to construction of dams, etc., so these are not able to reach their spawning grounds and face extinction.

International trade in increasingly scarce animal products like medicines, perfumes, cosmetics, decoration, museum specimens,etc. is the cause of destruction of many species e.g. musk-deer (Moschus moschiferus) and great one-horned rhinoceros(Rhinoceros unicornis) in India are being extensively killed for the medicinal importance of their musk and rhino-horn respectively.

Highways. A number of wild animals get confused and are run-over by the vehicles on the highways so decreasing their number.

Lack of education. Majority of Indian people are not aware of the importance of wildlife and ill effects of its destruction. So the people must be educated to save the wildlife.

Official laxity in the implementation of Wildlife (Protection) Act. Most of the destruction of wildlife is avoidable.


Natural extinction (Background extinction): Some species disappear due to change in environment and still others appear,which are adapted to changed environment. This is called natural extinction, which is a gradual continuous process and has occured in geological past.

Mass extinction: Many times, several species disappeared due to catastrophes. This has occurred number of times in geological history.

Anthropogenic extinction: Due to human interference, loss of biodiversity is taking place. This leads to disappearance of number of species and it takes place within short span of time.It has been estimated at World Conservation Monitoring Centre that about 384 plant species (mostly phanerogams) and 533 animal species (mostly vertebrates have become extinct since year 1600. This rate of extinction of species is 1000 to 10,000 times higher than earlier rate.

Few interesting points for extinction of species noticed are:

  1. Tropical forests are losing 14000 - 40000 species per year i.e. at the rate of 2-5 species per hour.

  2. Near about 50 per cent species may become extinct at the end of 21st century, if present rate does not retards.

  3. Loss of 17000 endemic plant species and 350,000 endemic animals may take place in near future from 10 high diversity localities in tropical forests.

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