Biodiversity and Conservation Class 12 Notes जैव विविधता एवं संरक्षण — कक्षा 12 जीव विज्ञान अध्याय 13

Revise these first (prerequisites)

• Meaning of species and ecosystem (Chapters 11–12)
• Basic geography of latitude / equator / tropics
• Simple idea of a log graph (for species–area, optional)

1. What is biodiversity?

   The variety of life on Earth — from genes to species and ecosystems — is called biodiversity (जैव विविधता). The term was popularised by Edward Wilson. Think of a garden with different flowers, trees, insects and birds — that variety is biodiversity.

2. Three levels

   Genetic: variation within a single species (India has more than 50,000 varieties of rice and 1,000 varieties of mango). Species: number of different species (Western Ghats have more amphibian species than Eastern Ghats). Ecological: different ecosystems (India has deserts, rain forests, mangroves, coral reefs, wetlands…).

3. How rich is India?

   India has only 2.4% of the world's land area, but 8.1% of global species diversity. That is why India is one of the world's 12 mega-diversity countries. This is our heritage.

4. Greater diversity near the equator

   Generally, the number of species decreases as we move from the equator (tropics) towards the poles. The Amazon rain forest has the greatest biodiversity on Earth. A warm, humid and stable climate supports more organisms.

5. Why is biodiversity declining?

   Cutting forests (habitat loss), excessive hunting/use (over-exploitation), species brought in from outside (alien species), and the extinction of one species causing the extinction of another that depends on it (co-extinction) — together these are called the 'Evil Quartet'.

6. Two methods of conservation

   Protecting organisms in their own natural home — national parks, sanctuaries, biosphere reserves — is in-situ conservation. Protecting them in safe places outside their home — zoos, botanical gardens, seed banks — is ex-situ conservation.

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As per NCERT 2026-27 — every point you need for the board exam.

1. Levels of biodiversity

   Edward Wilson popularised the term. Genetic diversity (Rauwolfia vomitoria — reserpine; India has 50,000+ rice and 1000+ mango varieties), species diversity (Western Ghats have more amphibians), ecological diversity (India has deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, alpine meadows).

2. How many species?

   IUCN (2004): more than 1.5 million described species. Robert May's global estimate is ~7 million. More than 70% are animals; insects make up ~70% of animals. Fungi species outnumber fishes + amphibians + reptiles + mammals combined.

3. India's biodiversity

   Only 2.4% of the world's land area, but 8.1% of global species diversity — one of the 12 mega-diversity countries. ~45,000 plant species and about twice as many animal species recorded.

4. Latitudinal gradient

   Diversity decreases from the equator towards the poles. Colombia has ~1,400 bird species, New York 105, Greenland 56; India ~1,200. Amazon rain forest — the greatest biodiversity. Tropics: undisturbed for a long time, less seasonal, more solar energy.

5. Species–area relationship

   Alexander von Humboldt: species richness increases with increasing area (up to a limit). log S = log C + Z log A; Z (slope) is usually 0.1–0.2; for very large areas such as entire continents, 0.6–1.2.

6. Ecosystem stability

   David Tilman: plots with more species showed less year-to-year variation and higher productivity. Rivet popper hypothesis — Paul Ehrlich (rivets of an aeroplane = species).

7. Loss of biodiversity

   IUCN Red List (2004): 784 extinctions in the last 500 years. Examples: dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia), Bali, Javan and Caspian tigers. The present extinction rate is the 'Sixth extinction' — 100–1000 times faster than before.

8. Evil Quartet

   (1) Habitat loss & fragmentation — the most important cause; tropical rain forests, which once covered 14% of the land, now cover less than 6%; the Amazon ('lungs of the planet') is being cleared for soybean cultivation and cattle. (2) Over-exploitation — Steller's sea cow, passenger pigeon. (3) Alien species invasion — Nile perch wiped out 200+ cichlid fish species of Lake Victoria; Parthenium, Lantana, water hyacinth (Eichhornia); African catfish (Clarias gariepinus). (4) Co-extinctions — when a host goes extinct, its parasite also goes extinct.

9. Why conserve

   Narrowly utilitarian (food, medicine, timber, industrial products; bioprospecting), broadly utilitarian (ecosystem services — Amazon ~20% O₂; pollination), ethical (intrinsic value of every species).

10. In-situ conservation

    Biodiversity hotspots — 34 in total (initially 25); 3 in India: Western Ghats & Sri Lanka, Indo-Burma, Himalaya. Hotspots cover less than 2% of Earth's land area. India: 14 biosphere reserves, 90 national parks, 448 wildlife sanctuaries. Sacred groves: Khasi & Jaintia Hills (Meghalaya), Aravalli (Rajasthan), Western Ghats (Karnataka, Maharashtra), Sarguja, Chanda, Bastar (MP).

11. Ex-situ conservation

    Zoological parks, botanical gardens, wildlife safari parks; cryopreservation (gametes), in vitro fertilisation, tissue culture, seed banks.

12. International efforts

    Earth Summit — Rio de Janeiro, 1992 (Convention on Biological Diversity). World Summit on Sustainable Development — Johannesburg, 2002 (190 countries, target to reduce biodiversity loss by 2010).

The concept in depth — the why and the how. Everything stays within the NCERT syllabus.

1. Why is diversity greater in the tropics?

   Three main hypotheses: (1) tropical latitudes have remained relatively undisturbed for millions of years (they did not face repeated glaciations like temperate areas), so species had a long time for diversification; (2) the tropical environment is less seasonal, more constant and predictable, which promotes niche specialisation; (3) the tropics receive more solar energy, leading to higher productivity. Example: Colombia (near the equator) has ~1,400 bird species, New York (41°N) has 105, and Greenland (71°N) only 56.

2. Species–area relationship and Z

   Alexander von Humboldt observed that, within a limit, species richness increases with increasing area. On a log scale this is a straight line: log S = log C + Z log A, where Z is the slope (regression coefficient). For small areas, Z is usually 0.1–0.2, regardless of the taxonomic group or region; but for very large areas such as entire continents, Z becomes steeper, 0.6–1.2 (1.15 for frugivorous birds and mammals of tropical forests).

3. More species = more stable ecosystem?

   In David Tilman's outdoor plot experiments, plots with more species showed less year-to-year variation in total biomass, and greater diversity also increased productivity. Paul Ehrlich's rivet popper hypothesis: an ecosystem is like an aeroplane and species are its rivets. Removing a few rivets may not pose an immediate threat, but if rivets keep being removed, the plane becomes progressively weaker — and if the 'key' rivets on the wings (key species) are removed, the danger is serious.

4. Impact of alien species — real cases

   The Nile perch introduced into Lake Victoria in East Africa led to the extinction of more than 200 species of cichlid fish. Invasive weeds such as Parthenium (carrot grass), Lantana and water hyacinth (Eichhornia) are a threat to native species. The African catfish (Clarias gariepinus), introduced for aquaculture, is a threat to the indigenous catfishes of our rivers. This shows the competition and predation of Chapter 11 on a large scale.

5. Why conservation? Three types of arguments

   Narrowly utilitarian: food, timber, fibre, medicines — more than 25% of the world's drugs come from plants; bioprospecting yields new products. Broadly utilitarian: ecosystem services such as the Amazon forest producing ~20% of the oxygen in Earth's atmosphere, pollination, and the aesthetic pleasure of nature. Ethical: every species has its own intrinsic value, and we have a moral duty to conserve it for future generations.

6. Hotspots — small area, big benefit

   Biodiversity hotspots are regions with very high species richness, high endemism (species found only there) and a high level of threat. There are 34 hotspots in the world in total; India includes parts of three — Western Ghats and Sri Lanka, Indo-Burma, and the Himalaya. Together, all hotspots cover less than 2% of the Earth's land area, but strict protection of these can reduce current extinctions by almost 30%.

Common confusions — cleared up

1. In-situ vs Ex-situ

   In-situ = protection within the natural home (national parks, sanctuaries, biosphere reserves, sacred groves, hotspots). Ex-situ = outside the natural home (zoo, botanical garden, wildlife safari park, seed bank, cryopreservation).

2. Endemic vs Extinct

   Endemic species are found (living) only in one particular area. Extinct species are no longer found anywhere (e.g. dodo, quagga, thylacine, Steller's sea cow).

3. Genetic vs Species diversity

   Genetic = variation within a species (rice varieties). Species = how many different species there are (amphibians of the Western Ghats).

4. Co-extinction

   When a species becomes extinct, other species that are obligatorily dependent on it also become extinct — e.g., a host fish along with its unique parasites, or both partners in a plant–pollinator mutualism.

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