Biodiversity and Conservation – Class 12 Biology Chapter 13 Notes & NCERT PDF

Class 12BiologyChapter 13NCERT book: Biology - Class 12

Notes and a simple summary of Chapter 13 of the NCERT Class 12 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 13: Biodiversity and Conservation

Introduction

The chapter opens with an imaginative line: an alien visiting Earth would be amazed by the enormous diversity of life — more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids. The chapter asks why there are so many species, why they are being lost and how to conserve them. Board questions focus on numbers, the Evil Quartet and conservation methods.

Key Concepts

13.1 Biodiversity

The term biodiversity was popularised by the sociobiologist Edward Wilson to describe the combined diversity at all levels of biological organisation. The most important levels are:

(i) Genetic diversity — variation within a species over its range. The medicinal plant *Rauwolfia vomitoria* in different Himalayan ranges varies in the potency and concentration of reserpine. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.

(ii) Species diversity — e.g. the Western Ghats have greater amphibian species diversity than the Eastern Ghats.

(iii) Ecological diversity — India, with deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, has greater ecosystem diversity than Norway.

13.1.1 How Many Species? According to IUCN (2004), slightly more than 1.5 million plant and animal species have been described. Biologists estimate the total by comparing the temperate–tropical species richness of an exhaustively studied group of insects and extrapolating the ratio to other groups. Extreme estimates range from 20 to 50 million; Robert May's conservative and scientifically sound estimate is about 7 million. More than 70% of recorded species are animals; plants (including algae and fungi) are no more than 22%. Insects are more than 70% of animals — out of every 10 animals, 7 are insects. Fungi species outnumber fishes, amphibians, reptiles and mammals combined. Prokaryotes are not included, as many are not culturable.

India: only 2.4% of the world's land area but 8.1% of global species diversity — one of the 12 megadiversity countries. Nearly 45,000 species of plants and twice as many animals are recorded. Using May's estimate that only 22% of species are recorded, India may have more than 1,00,000 plant and 3,00,000 animal species yet to be discovered.

13.1.2 Patterns of Biodiversity.

(i) Latitudinal gradients — diversity decreases from the equator to the poles; the tropics (23.5° N to 23.5° S) harbour more species. Colombia has nearly 1,400 bird species, New York (41° N) 105, Greenland (71° N) only 56; India has more than 1,200. A forest in Ecuador has up to 10 times as many vascular plant species as an equal area in the Midwest USA. The Amazonian rain forest has the greatest biodiversity on Earth (40,000+ plant species, 1,25,000+ invertebrates).

Three hypotheses for tropical richness: (a) speciation is a function of time — tropics were not disturbed by frequent glaciations and had long evolutionary time; (b) tropical environments are less seasonal, more constant and predictable, promoting niche specialisation; (c) more solar energy gives higher productivity, which may indirectly increase diversity.

(ii) Species–area relationships — Alexander von Humboldt observed that species richness increases with explored area but only up to a limit. The relation is a rectangular hyperbola; on a logarithmic scale it becomes a straight line: log S = log C + Z log A (S = species richness, A = area, Z = slope/regression coefficient, C = Y-intercept). Z lies between 0.1 and 0.2 regardless of taxon or region. For very large areas like entire continents, Z is 0.6 to 1.2; for frugivorous birds and mammals in tropical forests of different continents Z = 1.15. A steeper slope means species richness rises faster with area.

13.1.3 Importance of Species Diversity. A stable community should not vary much in productivity from year to year, should be resistant or resilient to disturbances and resistant to alien invasions. David Tilman's long-term outdoor plot experiments showed that plots with more species had less year-to-year variation in total biomass and that increased diversity gave higher productivity. Paul Ehrlich's 'rivet popper hypothesis': in an airplane (ecosystem), rivets are species; popping a few may not affect flight safety at first, but removing more makes the plane dangerously weak — and rivets on the wings (key species) matter more than those on seats.

13.1.4 Loss of Biodiversity. Human colonisation of tropical Pacific Islands led to 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, 87 plants). Recent extinctions: dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia) and three tiger subspecies (Bali, Javan, Caspian). More than 15,500 species face extinction: 12% of birds, 23% of mammals, 32% of amphibians, 31% of gymnosperms. There were five mass extinctions earlier; the ongoing 'Sixth Extinction' differs in rate — 100 to 1,000 times faster than in pre-human times, due to humans; nearly half of all species might vanish in 100 years. Loss of biodiversity lowers plant production, lowers resistance to perturbations like drought and increases variability of processes such as water use and pest cycles.

Causes — 'The Evil Quartet':

Habitat loss and fragmentation — the most important cause. Tropical rain forests once covered more than 14% of Earth's land surface, now no more than 6%. The Amazon ("lungs of the planet") is being cleared for soya beans and cattle.

Over-exploitation — when 'need' turns to 'greed'; Steller's sea cow and passenger pigeon; many marine fish are over-harvested.

Alien species invasions — the Nile perch in Lake Victoria led to extinction of more than 200 species of cichlid fish; invasive weeds *carrot grass (Parthenium), Lantana* and water hyacinth (Eicchornia); the illegally introduced African catfish Clarias gariepinus** threatens indigenous catfishes.

Co-extinctions — when a host fish goes extinct, its unique parasites also go; in coevolved plant–pollinator mutualism, extinction of one leads to extinction of the other.

13.2 Biodiversity Conservation

13.2.1 Why conserve? Three categories:

Narrowly utilitarian — direct economic benefits: food, firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines. More than 25% of drugs sold worldwide come from plants; 25,000 plant species are used in traditional medicine. Bioprospecting explores molecular, genetic and species-level diversity for economically important products.

Broadly utilitarian — ecosystem services: the Amazon produces an estimated 20% of the total oxygen in Earth's atmosphere; pollination by bees, birds and bats; aesthetic pleasures.

Ethical — every species has intrinsic value; we have a moral duty to pass on our biological legacy in good order.

13.2.2 How do we conserve?

In situ (on site) — protect the whole ecosystem: "save the entire forest to save the tiger." Biodiversity hotspots are regions with very high species richness and high endemism. Initially 25, now 34 hotspots. India has three: Western Ghats and Sri Lanka, Indo-Burma, Himalaya. All hotspots together cover less than 2% of Earth's land but their strict protection could reduce mass extinctions by almost 30%. India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. Sacred groves (Khasi and Jaintia Hills of Meghalaya, Aravalli Hills of Rajasthan, Western Ghats, Bastar) are last refuges for many rare and threatened plants.

Ex situ (off site) — threatened species are kept in special settings: zoological parks, botanical gardens, wildlife safari parks. Modern methods: cryopreservation of gametes, in vitro fertilisation, tissue culture propagation and seed banks.

International efforts: the Convention on Biological Diversity ('The Earth Summit'), Rio de Janeiro, 1992; the World Summit on Sustainable Development, Johannesburg, 2002, where 190 countries pledged to significantly reduce the rate of biodiversity loss by 2010.

Diagrams to Know

Figure 13.1 — Global biodiversity: proportionate number of species of major taxa; insects dominate the animal portion; fungi species outnumber fishes, amphibians, reptiles and mammals combined.

Figure 13.2 — Species–area relationship: a rectangular hyperbola on normal axes; a straight line on log–log axes with slope Z. Label S, A, Z and C.

Key-Facts Sheet

Described species > 1.5 million; May's estimate ≈ 7 million.

India: 2.4% land, 8.1% species; ~45,000 plants.

IUCN 2004: 784 extinctions; >15,500 threatened.

34 hotspots (3 in India); 14 biosphere reserves, 90 national parks, 448 sanctuaries.

Board Exam Focus

Components of biodiversity; estimating species number; three tropical hypotheses; significance of slope Z (Exercises 1–4).

The Evil Quartet; Tilman and the rivet popper hypothesis (Exercises 5–6).

Sacred groves; in situ versus ex situ; hotspots (Exercise 7).

Exercise 10: a species we might want extinct, e.g. a disease-causing pathogen — give a reasoned answer.

Key Terms

Biodiversity — जैव विविधता

Genetic diversity — आनुवंशिक विविधता

Species diversity — जातीय विविधता

Ecological diversity — पारिस्थितिक विविधता

Endemism — स्थानिकता

Megadiversity country — महाविविधता वाला देश

Species–area relationship — जाति-क्षेत्र संबंध

Co-extinction — सह-विलुप्तता

Biodiversity hotspot — जैव विविधता हॉटस्पॉट

In situ conservation — स्वस्थाने संरक्षण

Ex situ conservation — बहिःस्थाने संरक्षण

Sacred grove — पवित्र उपवन

Cryopreservation — निम्नताप परिरक्षण

Common Mistakes

Crediting the term biodiversity to Humboldt — it was popularised by Edward Wilson; Humboldt studied species–area relationships.

Reversing the latitudinal gradient — diversity decreases towards the poles.

Mixing Z values: 0.1–0.2 for regions, 0.6–1.2 for whole continents.

Listing pollution as one of the Evil Quartet — the four are habitat loss/fragmentation, over-exploitation, alien invasions and co-extinctions.

Calling zoos in situ — zoos, botanical gardens and seed banks are ex situ; national parks, sanctuaries, biosphere reserves and sacred groves are in situ.

💡 Key Learning Points

✓Biodiversity (a term popularised by Edward Wilson) exists at genetic, species and ecological levels; India, with 2.4% of land and 8.1% of species, is one of 12 megadiversity countries.
✓Diversity decreases from the equator to the poles, explained by longer evolutionary time, stable environments and more solar energy in the tropics.
✓The species–area relationship is log S = log C + Z log A, with Z of 0.1–0.2 for regions and 0.6–1.2 for continents.
✓Current extinction rates are 100–1,000 times pre-human rates, driven by the Evil Quartet: habitat loss and fragmentation, over-exploitation, alien invasions and co-extinctions.
✓Conservation is justified on narrowly utilitarian, broadly utilitarian and ethical grounds and done in situ (34 hotspots, protected areas, sacred groves) and ex situ (zoos, gardens, cryopreservation, seed banks).

👨‍🏫 Teaching Tips

→Open with the NCERT 'alien visitor' hook and the species counts of ants, beetles, fishes and orchids.
→Show a world map with latitudes and bird counts (Colombia 1,400, New York 105, Greenland 56) to make the gradient visual.
→Plot a species–area graph on normal and log–log axes so students see the hyperbola become a straight line.
→Act out Ehrlich's rivet popper hypothesis with a paper airplane made of clipped parts.
→Use the mnemonic 'HOAC' for the Evil Quartet: Habitat loss, Over-exploitation, Alien invasions, Co-extinctions.
→Make students mark India's three hotspots and local sacred groves on a map.
→Run a sorting activity: cards with national park, zoo, seed bank, sacred grove, cryopreservation — in situ or ex situ?
→Discuss Exercise 10 as a class debate to build reasoned answers.

📋 Assessment Questions

Can the student explain the three levels of biodiversity with NCERT examples?
Can the student give three hypotheses for high tropical diversity and interpret the species–area equation and slope Z?
Can the student explain the Evil Quartet with one example each?
Can the student distinguish in situ and ex situ conservation and name India's hotspots and protected-area numbers?
Can the student state narrowly utilitarian, broadly utilitarian and ethical reasons for conservation?

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