Biodiversity and Conservation

This is the thirteenth and last chapter of NCERT's Class 12 Biology textbook (pages 216–227 of the 2026-27 reprint) and the third of Unit X, Ecology. It has two sections — 13.1 Biodiversity (levels, numbers, patterns, importance and loss) and 13.2 Biodiversity Conservation (why and how) — with Figures 13.1 and 13.2, a summary and 10 exercises. It is short on figures but long on numbers and terms, and it is one of the most heavily examined NCERT chapters for the Prelims environment questions. This page splits it into ten concept sections.

• Neighbouring chapters: Ecosystem (Chapter 12) gave the functions — productivity, energy flow — that biodiversity keeps running; Organisms and Populations (Chapter 11) covered predation, competition and co-evolved mutualisms (fig–wasp), the links behind co-extinction; Evolution (Chapter 6) explains how species arise; Biotechnology and its Applications (Chapter 10) covers biopiracy and the protection of genetic resources. The geography book's Biodiversity and Conservation (Class 11, Fundamentals of Physical Geography, Chapter 14) covers the same ground with more on IUCN categories and hotspot lists; Natural Vegetation (Class 11, India: Physical Environment, Chapter 5) and Forest and Wildlife Resources (Class 10, Contemporary India II, Chapter 2) cover India's protected areas.
• Prelims — environment and ecology: hotspots (1996, 2009, 2010, 2011), what threatens biodiversity (1993, 2012), latitudinal and altitudinal gradients (2011), the size of global biodiversity (1993, 1996), in situ vs ex situ (2011), Red Data Books (2011), ecosystem services (2011), the sixth extinction (2018), co-extinction via the dodo (1998), water hyacinth (1988) and the Johannesburg summit (2002).
• GS3 — Environment and conservation: Mains 2018 asked how biodiversity varies in India and how the Biological Diversity Act, 2002 helps conserve it. GS1/GS2 touch-points: forest dwellers and protected areas, the Forest Rights Act, and international environmental conventions.

• Biodiversity (term popularised by Edward Wilson): diversity at all levels of organisation. Three most important: genetic (Rauwolfia reserpine potency; India > 50,000 rice strains, 1,000 mangoes), species (Western Ghats richer in amphibians than Eastern Ghats), ecological (India's many ecosystem types vs Norway).
• Numbers: ≈ 1.5 million species described (IUCN 2004); Robert May ≈ 7 million; extremes 20–50 million. Animals > 70% (insects > 70% of animals), plants ≤ 22%; fungi outnumber fishes + amphibians + reptiles + mammals. India: 2.4% of land, 8.1% of species; ≈ 45,000 plants, twice as many animals; one of 12 megadiversity countries (NCERT).
• Patterns: latitudinal gradient — Colombia ≈ 1,400 bird species, New York 105, Greenland 56; tropics richer because of more evolutionary time, constant environment, more solar energy. Species–area (Humboldt): log S = log C + Z log A; Z = 0.1–0.2 in regions, 0.6–1.2 for continents (frugivores 1.15).
• Why diversity matters: stability = little year-to-year change, resistance or resilience, resistance to invasions. Tilman: more species → less variation in biomass, higher productivity. Ehrlich's rivet popper: species are rivets; wing rivets are key species.
• Loss: IUCN 2004 — 784 extinctions in 500 years (338 vertebrates, 359 invertebrates, 87 plants); > 15,500 threatened; amphibians 32%, gymnosperms 31%, mammals 23%, birds 12% threatened. Sixth extinction: rates 100–1,000× pre-human. Evil Quartet: habitat loss and fragmentation (top), over-exploitation, alien invasions (Nile perch → 200+ cichlids), co-extinctions.
• Conserve — reasons: narrowly utilitarian (food, drugs: > 25% of drugs from plants; bioprospecting), broadly utilitarian (ecosystem services: oxygen, pollination), ethical. In situ: 34 hotspots (3 cover India), 14 biosphere reserves, 90 national parks, 448 sanctuaries, sacred groves. Ex situ: zoos, botanical gardens, cryopreservation, IVF, tissue culture, seed banks. CBD (Rio, 1992); WSSD (Johannesburg, 2002).

Diversity (heterogeneity) exists not only among species but at all levels of biological organisation, from macromolecules within cells to biomes. Biodiversity is the term popularised by the sociobiologist Edward Wilson for this combined diversity. NCERT names three levels as the most important:

• Genetic diversity — variation within a single species over its range. The medicinal plant Rauwolfia growing in different Himalayan ranges varies in the potency and concentration of its active chemical, reserpine. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
• Species diversity — diversity at the species level: the Western Ghats have greater amphibian species diversity than the Eastern Ghats.
• Ecological diversity — diversity at the ecosystem level: India, with deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, has greater ecosystem diversity than a Scandinavian country such as Norway.

It took millions of years of evolution to build this diversity; NCERT warns that at present rates of species loss it could be lost in under two centuries, which is why biodiversity is now an environmental issue of international concern.

We know how many species have been recorded, but not how many exist. According to the IUCN (2004), slightly more than 1.5 million plant and animal species have been described. Inventories are more complete in temperate than in tropical countries, and most undiscovered species are in the tropics, so biologists compare the temperate–tropical species richness of an exhaustively studied group of insects and extrapolate that ratio to other groups. Extreme estimates run from 20 to 50 million; a more conservative and scientifically sound estimate by Robert May is about 7 million.

From current inventories: more than 70 per cent of recorded species are animals and no more than 22 per cent are plants (NCERT includes algae, fungi, bryophytes, gymnosperms and angiosperms). Insects are the most species-rich group, more than 70 per cent of animals — 7 of every 10. Fungi have more species than fishes, amphibians, reptiles and mammals combined. These estimates give no figures for prokaryotes: conventional taxonomy cannot identify many of them and many cannot be cultured; by biochemical or molecular criteria their diversity alone might run into millions.

India has only 2.4 per cent of the world's land area but 8.1 per cent of global species diversity — about 3.4 times its share by area — which makes it one of the 12 megadiversity countries in NCERT's count. Nearly 45,000 plant species and twice as many animal species have been recorded. If, as May's estimate implies, only 22 per cent of species have been recorded, India probably has more than 1,00,000 plant and more than 3,00,000 animal species still undescribed. NCERT's image: nature's biological library is burning before we have catalogued the titles.

Diversity is not spread evenly. The best-known pattern is the latitudinal gradient: species diversity generally decreases from the equator towards the poles. With very few exceptions, the tropics (23.5° N to 23.5° S) hold more species than temperate or polar areas. Colombia, near the equator, has nearly 1,400 bird species; New York (41° N) has 105 and Greenland (71° N) only 56. India, with much of its land in tropical latitudes, has more than 1,200. A tropical forest in Ecuador has up to 10 times as many vascular plant species as an equal area of temperate forest in the US Midwest.

The largely tropical Amazonian rain forest has the greatest biodiversity on Earth. Why are the tropics so rich? NCERT gives three hypotheses: (a) time — speciation is a function of time; temperate regions suffered frequent glaciations, while the tropics stayed relatively undisturbed for millions of years; (b) constancy — tropical environments are less seasonal, more constant and predictable, promoting niche specialisation; (c) energy — more solar energy gives higher productivity, which might indirectly support greater diversity.

Exploring South American jungles, the German naturalist and geographer Alexander von Humboldt observed that within a region species richness increases with explored area, but only up to a limit. For many taxa — angiosperms, birds, bats, freshwater fishes — the relation is a curve NCERT calls a rectangular hyperbola (Figure 13.2). On a logarithmic scale it becomes a straight line:

log S = log C + Z log A, where S = species richness, A = area, Z = slope of the line (regression coefficient) and C = the Y-intercept. (Equivalently, S = C·A^Z.)

Ecologists find Z = 0.1 to 0.2 regardless of taxonomic group or region — plants in Britain, birds in California and molluscs in New York state all give similar slopes. But across very large areas such as whole continents, the slope is much steeper, Z = 0.6 to 1.2; for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, Z = 1.15. NCERT asks what steeper slopes mean: species richness rises much faster with area, because distant continents hold largely different species — each new continent adds many new species instead of repeating the old ones.

Does the number of species really matter to how an ecosystem functions? Ecologists have no definitive answer, but for decades believed that communities with more species tend to be more stable. A stable community should not vary too much in productivity from year to year; it must be resistant or resilient to occasional disturbances, natural or man-made; and it must resist invasion by alien species. David Tilman's long-term experiments in outdoor plots gave tentative answers: plots with more species showed less year-to-year variation in total biomass, and increased diversity contributed to higher productivity.

NCERT's answer to the ‘naïve’ question — would the Western Ghats be less functional if one tree frog species were lost? — is Paul Ehrlich's rivet popper hypothesis. In an aeroplane (the ecosystem) all parts are held by thousands of rivets (species). If every passenger popped a rivet to take home (a species going extinct), flight safety (ecosystem function) might not suffer at first, but the plane would grow dangerously weak over time. And which rivet goes matters: rivets on the wings (key species that drive major ecosystem functions) are far more critical than a few on the seats or windows.

It is doubtful whether new species are being added through speciation at any meaningful rate, but losses are certain, and the accusing finger points at human activities. Human colonisation of the tropical Pacific islands is said to have caused the extinction of more than 2,000 native bird species. The IUCN Red List (2004) documents 784 extinctions in the last 500 years — 338 vertebrates, 359 invertebrates and 87 plants. Recent examples: the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia) and three subspecies of tiger (Bali, Javan, Caspian); the last twenty years alone saw 27 species disappear. Extinctions are not random: amphibians appear more vulnerable.

More than 15,500 species face the threat of extinction worldwide: 12% of bird species, 23% of mammals, 32% of amphibians and 31% of gymnosperms. Fossils show five earlier episodes of mass extinction over more than 3 billion years, before humans existed. The ‘Sixth Extinction’ now in progress differs in its rate — 100 to 1,000 times faster than in pre-human times — and in its cause, human activity; if trends continue, nearly half of all species might be wiped out within 100 years. Loss of biodiversity in a region may lead to (a) decline in plant production, (b) lowered resistance to perturbations such as drought, and (c) increased variability in processes such as plant productivity, water use and pest and disease cycles.

(i) Habitat loss and fragmentation — the most important cause. Tropical rain forests once covered more than 14 per cent of the Earth's land surface and now cover no more than 6 per cent; NCERT says 1,000 more hectares are lost in the time it takes to read the chapter. The Amazon (‘the lungs of the planet’) is cleared for soya beans and for grassland for beef cattle. Pollution degrades many habitats too. When large habitats are broken into fragments, mammals and birds needing large territories, and migratory animals, are badly affected.

(ii) Over-exploitation — when ‘need’ turns to ‘greed’. Many extinctions of the last 500 years (Steller's sea cow, passenger pigeon) were due to over-exploitation; many marine fish populations are over-harvested today. (iii) Alien species invasions — introduced species, deliberately or not, may turn invasive. The Nile perch introduced into Lake Victoria eventually caused the extinction of an ecologically unique assemblage of more than 200 cichlid species; in India, carrot grass (Parthenium), Lantana and water hyacinth (Eichhornia) are invasive weeds, and the illegal introduction of the African catfish Clarias gariepinus for aquaculture threatens native catfishes. (iv) Co-extinctions — when a species dies out, species tied to it in an obligatory way go too: a host fish's unique parasites, or one partner of a co-evolved plant–pollinator mutualism.

NCERT groups the reasons into three categories. Narrowly utilitarian: direct economic benefits — food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines. More than 25 per cent of drugs sold worldwide are derived from plants, and 25,000 plant species contribute to traditional medicines used by native peoples. With more investment in bioprospecting, biodiversity-rich nations can expect enormous benefits.

Broadly utilitarian: biodiversity drives ecosystem services. NCERT states that the Amazon forest produces, through photosynthesis, 20 per cent of the oxygen in Earth's atmosphere, and asks what that would cost at a hospital's oxygen-cylinder price; pollination by bees, bumblebees, birds and bats is another service, without which plants give no fruits or seeds; and there are intangible pleasures — walking through thick woods, spring flowers, a bulbul's song. The Summary adds pest control, climate moderation and flood control. Ethical: every species has intrinsic value, even with no current economic value; we have a moral duty to care for the millions of species we share the planet with and to pass on our biological legacy in good order.

Protecting a whole ecosystem protects biodiversity at all its levels — ‘we save the entire forest to save the tiger’ — and is called in situ (on site) conservation. When an animal or plant is endangered or threatened (at very high risk of extinction in the wild in the near future) and needs urgent rescue, ex situ (off site) conservation is the desirable approach (section 10).

Biodiversity hotspots. Faced with the conflict between development and conservation, and with far more species to save than resources, conservationists identified for maximum protection certain biodiversity hotspots — regions with very high species richness and a high degree of endemism. Initially 25 were identified; 9 more were added, making 34. They are also regions of accelerated habitat loss. Three cover India's exceptionally rich regions: Western Ghats and Sri Lanka, Indo-Burma and Himalaya. All hotspots together cover less than 2 per cent of Earth's land, yet hold an extremely high number of species, and strict protection of them could reduce the ongoing mass extinctions by almost 30 per cent.

Protected areas in India. Ecologically unique, biodiversity-rich regions are legally protected as biosphere reserves, national parks and sanctuaries; NCERT's reprint gives 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. Sacred groves: many cultures set aside tracts of forest in which all trees and wildlife were venerated and given total protection. NCERT locates them in the Khasi and Jaintia Hills (Meghalaya), the Aravalli Hills (Rajasthan), the Western Ghat regions of Karnataka and Maharashtra, and the Sarguja, Chanda and Bastar areas; in Meghalaya the sacred groves are the last refuges for a large number of rare and threatened plants.

In ex situ conservation, threatened animals and plants are taken out of their natural habitat and placed in special settings where they can be protected and given special care: zoological parks, botanical gardens and wildlife safari parks. Many animals that are extinct in the wild survive in zoos. Ex situ methods now go beyond enclosures: gametes of threatened species can be stored viable and fertile for long periods by cryopreservation, eggs can be fertilised in vitro, plants can be propagated by tissue culture, and seeds of different genetic strains of commercially important plants can be kept for long periods in seed banks.

International action. Biodiversity knows no political boundaries, so its conservation is a collective responsibility of all nations. The historic Convention on Biological Diversity (Rio de Janeiro, 1992) called on all nations to conserve biodiversity and use its benefits sustainably. At the follow-up World Summit on Sustainable Development (Johannesburg, South Africa, 2002), 190 countries pledged to achieve by 2010 a significant reduction in the current rate of biodiversity loss at global, regional and local levels.

Debates around protected areas. How far people should be kept out of protected areas is contested. The positions below are set out side by side with no verdict.

The table records positions, not a verdict.

The chapter asks a string of questions in its running text; here are short answers.

Numbers

One-liners

• Biodiversity is the combined diversity at all levels of biological organisation.
• Edward Wilson popularised the term biodiversity.
• Genetic diversity is variation within one species.
• About 1.5 million species have been described.
• Robert May estimated about 7 million species on Earth.
• Insects are the most species-rich group of organisms.
• Fungi outnumber fishes, amphibians, reptiles and mammals combined.
• India holds 8.1% of species on 2.4% of the world's land.
• Species diversity decreases from the equator towards the poles.
• Humboldt found that species richness rises with area up to a limit.
• On a log scale the species-area relation is a straight line of slope Z.
• Z is 0.1 to 0.2 for regions and 0.6 to 1.2 for continents.
• Tilman found that more species meant less variation in biomass.
• Ehrlich's rivet popper hypothesis compares species to rivets in an aeroplane.
• Today's extinction rates are 100 to 1,000 times pre-human rates.
• Habitat loss and fragmentation is the most important cause of extinction.
• The Nile perch wiped out over 200 cichlid species in Lake Victoria.
• Co-extinction takes obligate partners along with a lost species.
• Pollination and oxygen production are broadly utilitarian values.
• Hotspots combine high species richness, high endemism and habitat loss.
• Three hotspots in NCERT's list cover India.
• Sacred groves are the last refuges of many rare plants in Meghalaya.
• Botanical gardens and seed banks are ex situ methods.
• The Convention on Biological Diversity was signed at Rio in 1992.

Traps to avoid

• Many rice strains are genetic diversity, not species diversity.
• 1.5 million is described; 7 million is estimated.
• Insects, not fungi or bacteria, are the largest identified group.
• Z is the slope; C is the intercept.
• Steeper slopes belong to whole continents, not small regions.
• The sixth extinction differs in rate and human cause.
• Endemic means restricted range; endangered means high extinction risk.
• Habitat loss, not over-exploitation, is the top cause of species loss.
• An alien species is not always invasive.
• Pollination is a broadly, not narrowly, utilitarian value.
• Botanical gardens are ex situ, not in situ.
• Hotspots are not only tropical.
• NCERT's 34 hotspots and protected-area counts are dated.
• The text says 784 extinctions; the Summary says nearly 700.
• Red Data Books list threatened species, not protected sites.

Prelims — what UPSC asks

• Hotspots and conservation: Western Ghats as a hotspot (1996); which regions are hotspots (2009); hotspots not only tropical and India's list (2010); criteria — species richness, endemism, threat (2011); botanical gardens are not in situ (2011); Red Data Books list threatened species (2011); the Johannesburg summit of 2002 (2002).
• Numbers, patterns and loss: best estimate of global biodiversity (1993); insects the largest identified group (1996); latitude and altitude gradients (2011); habitat destruction as the chief threat (1993); global warming, fragmentation and invasions as threats (2012); biodiversity's services — soil, erosion, waste, pollination (2011); the sixth extinction (2018); the dodo and a Mauritian tree (1998); water hyacinth is Eichhornia (1988).
• Key notes: 1993 (best estimate) keys ‘about ten million species, no more than half a million identified’ — far below NCERT's 1.5 million described; a flawed, dated question. 2009 (hotspots) keys ‘Eastern Himalayas only’, but the Mediterranean Basin hotspot takes in the eastern Mediterranean, so ‘1 and 2’ is arguable — disputed; north-western Australia is not a hotspot (south-western is). 1998 rests on a co-extinction story later questioned by botanists — the key (dodo) stands.
• Likely next: the three levels with examples, May's 7 million vs 1.5 million described, India's 2.4% vs 8.1%, Z values and what a steeper slope means, Tilman vs Ehrlich vs Humboldt, IUCN categories, the Evil Quartet and its examples (Nile perch, Clarias gariepinus), narrowly vs broadly utilitarian, hotspot criteria and counts (34 vs 36), sacred groves' locations, in situ vs ex situ methods, CBD and its protocols.

Mains — where it appears and how to answer

• GS3 2018 (how biodiversity varies in India; the Biological Diversity Act, 2002): open with the three levels and India's 8.1% of species on 2.4% of land; explain variation by latitude (tropical south and north-east), altitude, rainfall and ecosystem type, naming the Western Ghats, Himalaya and Indo-Burma hotspots; then the Act — the NBA, State Biodiversity Boards and Biodiversity Management Committees, regulated access and benefit-sharing, and local registers of biodiversity.
• GS3 environment answers on deforestation, invasive species, wetlands or protected areas: use the Evil Quartet as the frame, the species–area relationship for how many species habitat loss costs, the three utilitarian–ethical arguments for why it matters, and in situ plus ex situ for what to do; present the protected-area debates (strict protection vs community rights, relocation) as attributed positions.

Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.

Open any question to attempt it in the Question bank — your attempt is saved to your progress.