# Biodiversity and Conservation (NEET Biology Class 12): Species-Area Relationship, Evil Quartet & Hotspots Source: https://tracknation.in/story/biodiversity-and-conservation-neet-biology-class-12-species-area-relationship-evil-quartet-hotspots (TrackNation — free UPSC notes with PYQs) > NEET Class 12 Biodiversity and Conservation, mined from NCERT: the three levels of biodiversity with their NCERT examples tabulated, a complete species-numbers table (global proportions and India's figures), the latitudinal gradient with bird-species counts by latitude and the three hypotheses for tropical richness, the species-area relationship with the full equation and every Z value, ecosystem stability (Tilman's experiments and the rivet popper hypothesis), the Sixth Extinction, the complete ## Levels of Biodiversity, Species Numbers & the Latitudinal Gradient 📌 **NEET priority: Important.** *2–3 questions a year, and almost all are **exact numbers** — the species proportions, the **species-area equation with its Z values**, the **Evil Quartet**, and India's **hotspot and protected-area counts**. Pure recall marks.* **Biodiversity** — a term popularised by the sociobiologist **Edward Wilson** — describes the combined diversity at all levels of biological organisation. ### The three levels of biodiversity | **Level** | **What it means** | **NCERT example** | | Genetic diversity | A single species showing high genetic diversity across its range | Rauwolfia vomitoria varies in the potency and concentration of RESERPINE across Himalayan ranges. 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 like NORWAY | ### How many species — the proportions NEET asks | **Fact** | **The number** | | Species described so far (IUCN 2004) | Slightly more than 1.5 million | | Robert May's conservative global estimate | About 7 million species | | Proportion of recorded species that are ANIMALS | More than 70 per cent | | Proportion that are PLANTS (incl. algae, fungi, bryophytes, gymnosperms, angiosperms) | No more than 22 per cent | | Proportion of ANIMALS that are INSECTS | More than 70 per cent — so 7 of every 10 animals is an insect | | Fungi species | MORE than the combined total of fishes, amphibians, reptiles and mammals | | India's plant species | About 45,000 — and TWICE as many animal species | | India's status | One of the 12 MEGA DIVERSITY countries of the world | These estimates give **no figures for PROKARYOTES** — conventional taxonomic methods are not suitable for identifying microbial species. ### The latitudinal gradient - **Species diversity DECREASES as we move away from the equator towards the poles.** The tropics (**23.5° N to 23.5° S**) harbour more species than temperate or polar areas. | **Region** | **Latitude** | **Bird species** | | Colombia | Near the equator | Nearly 1,400 | | India | Much land in tropical latitudes | More than 1,200 | | New York | 41° N | 105 | | Greenland | 71° N | 56 | The **Amazonian rain forest** has the greatest biodiversity on earth: **40,000 plant species, 3,000 fishes, 1,300 birds, 427 mammals, 427 amphibians, 378 reptiles and more than 1,25,000 invertebrates** — with an estimated **2 million insect species** still undiscovered there. **Why the tropics are so rich — three hypotheses:** (1) tropical latitudes remained **relatively undisturbed for millions of years**, giving **more evolutionary time** for speciation, unlike temperate regions subjected to frequent glaciation; (2) they provide a **relatively constant environment**; (3) they receive **more solar energy**, contributing to greater productivity. ## Species-Area Relationship, Stability & the Sixth Extinction ### Species-area relationship — the equation and its Z values - **Alexander von Humboldt**, the German naturalist and geographer, observed during South American exploration that species richness increases with area **but only up to a limit**. The relationship is a **RECTANGULAR HYPERBOLA**; on a **logarithmic scale it becomes a STRAIGHT LINE**: - **log S = log C + Z log A** where **S = species richness, A = area, Z = slope (regression coefficient), C = Y-intercept**. | **Scale of study** | **Value of Z** | **Note** | | Small areas — plants in Britain, birds in California, molluscs in New York | 0.1 to 0.2 | Amazingly similar REGARDLESS of taxonomic group or region | | Very large areas — entire continents | 0.6 to 1.2 | The slope is MUCH STEEPER | | Frugivorous birds and mammals in tropical forests of different continents | 1.15 | The specific NCERT example of a steep slope | ### Species diversity and ecosystem stability - A **stable community** must (1) not show much variation in productivity year to year, (2) be **resistant or resilient** to occasional disturbances, and (3) be **resistant to invasion by alien species**. - **David Tilman's** long-term outdoor plot experiments found that plots with **more species showed LESS year-to-year variation in total biomass**, and that **increased diversity contributed to HIGHER productivity**. - **Paul Ehrlich's 'rivet popper hypothesis':** an ecosystem is an aeroplane whose parts are joined by thousands of **rivets (species)**. Popping a few rivets may not affect flight safety at first, but as more are removed the plane weakens dangerously. Crucially, **WHICH rivet is removed matters** — losing rivets on the **wings** is far more serious than losing a few on the **seats**. ### The Sixth Extinction - There have been **FIVE previous episodes of mass extinction** in the >3 billion years since life began. The **'Sixth Extinction' now in progress differs in its RATE** — current extinction rates are estimated at **100 to 1,000 times faster** than pre-human times, and **human activities are responsible**. If trends continue, **nearly half of all species could be wiped out within the next 100 years**. - Loss of biodiversity leads to **declining plant production**, **lowered resistance to environmental perturbations** like drought, and **increased variability in ecosystem processes** (productivity, water use, pest and disease cycles). ## The Evil Quartet & Why We Conserve ### The Evil Quartet — the four causes of biodiversity loss | **Cause** | **What happens** | **The named example** | | 1. Habitat loss and fragmentation | THE MOST IMPORTANT cause. Tropical rain forests once covered more than 14 per cent of earth's land surface — now no more than 6 per cent. Fragmentation badly affects mammals and birds needing large territories, and migratory animals | The AMAZON rain forest — the 'lungs of the planet' — cleared for soya beans and beef cattle grasslands | | 2. Over-exploitation | When 'need' turns to 'greed'. Many marine fish populations are over-harvested | STELLER'S SEA COW and the PASSENGER PIGEON, both extinct in the last 500 years | | 3. Alien species invasions | Introduced species turn invasive and cause decline or extinction of indigenous species | NILE PERCH in Lake Victoria eliminated more than 200 species of CICHLID fish. Weeds: PARTHENIUM (carrot grass), LANTANA, EICCHORNIA (water hyacinth). The illegal African catfish CLARIAS GARIEPINUS threatens indigenous catfishes in Indian rivers | | 4. Co-extinctions | When a species goes extinct, species obligately associated with it follow | A host fish's unique assemblage of PARASITES dies with it. Also a coevolved PLANT-POLLINATOR mutualism — extinction of one causes extinction of the other | ### Why conserve biodiversity — three arguments | **Argument** | **The reasoning** | **The figures** | | Narrowly utilitarian | Direct economic benefits — food, 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; 25,000 plant species contribute to traditional medicines. 'BIOPROSPECTING' explores this diversity for economic products | | Broadly utilitarian | Biodiversity provides ecosystem SERVICES | The Amazon forest produces about 20 PER CENT of the total oxygen in earth's atmosphere. POLLINATION by bees, bumblebees, birds and bats. Plus intangible aesthetic benefits | | Ethical | What we owe to the millions of species we share the planet with — every species has intrinsic value | — | ## Hotspots, Conservation & Why This Matters for NEET ### Biodiversity hotspots & conservation - **Hotspots** are regions with **very high species richness AND a high degree of ENDEMISM** (species confined to that region and found nowhere else). Initially **25** were identified; **nine more** were added, bringing the world total to **34**. They are also regions of **accelerated habitat loss**. - **Three hotspots cover India:** **Western Ghats and Sri Lanka, Indo-Burma, and Himalaya**. All hotspots together cover **less than 2 per cent of earth's land area**, yet strict protection of them could **reduce ongoing mass extinctions by almost 30 per cent**. | **Conservation approach** | **What it involves** | **India's numbers / examples** | | IN SITU — protected areas | Protecting the species in its natural habitat | India has 14 BIOSPHERE RESERVES, 90 NATIONAL PARKS and 448 WILDLIFE SANCTUARIES | | IN SITU — sacred groves | Tracts of forest set aside and venerated, given TOTAL protection by religious and cultural tradition | KHASI and JAINTIA Hills (Meghalaya), ARAVALLI Hills (Rajasthan), Western Ghat regions of Karnataka and Maharashtra, and Sarguja, Chanda and Bastar (Madhya Pradesh). In Meghalaya these are the LAST REFUGES for many rare and threatened plants | | EX SITU | Threatened species taken OUT of their natural habitat into special protective settings | Zoological parks, botanical gardens, wildlife safari parks. Advanced methods: CRYOPRESERVATION of gametes in viable and fertile condition, IN VITRO fertilisation, TISSUE CULTURE propagation, and SEED BANKS for genetic strains of commercially important plants | ### Why this matters for NEET - High-value one-liners: biodiversity term popularised by **Edward Wilson**; **>70% animals, ≤22% plants**, and **>70% of animals are insects**; **log S = log C + Z log A** with **Z = 0.1–0.2** small scale, **0.6–1.2** continental, **1.15** for frugivorous birds/mammals; **Evil Quartet**; **34 hotspots**, **3 in India**, **<2%** of land but could cut extinctions by **30%**; **14 / 90 / 448** reserves, parks and sanctuaries; Amazon makes **20% of atmospheric oxygen**. - **Trap:** the **Sixth Extinction differs from the previous five in RATE, not in kind** — mass extinctions happened before humans; what is new is that it is **100–1,000 times faster** and human-caused. Also, **habitat loss and fragmentation is THE MOST IMPORTANT cause** of extinction — not over-exploitation, which is the intuitive but wrong answer. - **Second trap:** **IN SITU means in the natural habitat** (national parks, sanctuaries, biosphere reserves, sacred groves), while **EX SITU means removed from it** (zoos, botanical gardens, cryopreservation, seed banks). Sacred groves are **in situ** despite being culturally rather than legally protected. And the **rivet popper hypothesis** stresses that **which** species is lost matters — not merely how many. ## Test Yourself: MCQs, PYQs & Active Recall Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one. ## Practice Questions **Q1.** The term biodiversity was popularised by: - (a) David Tilman - (b) Edward Wilson - (c) Robert May - (d) Alexander von Humboldt **Answer: (b)** — The sociobiologist Edward Wilson popularised the term to describe combined diversity at all levels of biological organisation. **Q2.** India has more than how many genetically different strains of rice? - (a) 500 - (b) 5,000 - (c) 1,000 - (d) 50,000 **Answer: (d)** — India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango — an example of genetic diversity. **Q3.** According to IUCN (2004), the total number of species described so far is: - (a) About 500,000 - (b) Slightly more than 1.5 million - (c) About 20 million - (d) About 7 million **Answer: (b)** — Slightly more than 1.5 million species have been described; Robert May's conservative estimate of global diversity is about 7 million. **Q4.** What proportion of all recorded species are animals? - (a) About 30 per cent - (b) About 50 per cent - (c) More than 70 per cent - (d) About 22 per cent **Answer: (c)** — More than 70 per cent of all recorded species are animals; plants comprise no more than 22 per cent. **Q5.** Among animals, insects make up: - (a) About 30 per cent - (b) About 10 per cent - (c) More than 70 per cent - (d) About 50 per cent **Answer: (c)** — More than 70 per cent of animals are insects — meaning 7 out of every 10 animals on the planet is an insect. **Q6.** India is one of how many mega diversity countries in the world? - (a) 12 - (b) 17 - (c) 25 - (d) 6 **Answer: (a)** — India, with about 45,000 plant species and twice as many animal species, is one of the 12 mega diversity countries. **Q7.** The tropics are defined by the latitudinal range: - (a) 41° N to 41° S - (b) 66.5° N to 66.5° S - (c) 23.5° N to 23.5° S - (d) 0° to 10° **Answer: (c)** — The tropics span 23.5° N to 23.5° S and harbour more species than temperate or polar areas. **Q8.** Colombia, located near the equator, has approximately how many bird species? - (a) 1,200 - (b) 1,400 - (c) 105 - (d) 56 **Answer: (b)** — Colombia has nearly 1,400 bird species, compared to 105 in New York (41° N) and 56 in Greenland (71° N). **Q9.** The species-area relationship was first observed by: - (a) Robert May - (b) Alexander von Humboldt - (c) Edward Wilson - (d) Paul Ehrlich **Answer: (b)** — Von Humboldt observed during South American exploration that species richness increases with area, but only up to a limit. **Q10.** The species-area relationship on a normal scale is a: - (a) Rectangular hyperbola - (b) Straight line - (c) J-shaped curve - (d) Sigmoid curve **Answer: (a)** — The relationship is a rectangular hyperbola; on a logarithmic scale it becomes a straight line described by log S = log C + Z log A. **Q11.** For small areas, the value of Z in the species-area relationship lies between: - (a) 0.1 and 0.2 - (b) 0.6 and 1.2 - (c) 1.0 and 2.0 - (d) 0.01 and 0.05 **Answer: (a)** — Z is 0.1 to 0.2 for smaller areas regardless of taxonomic group; for entire continents it rises to 0.6 to 1.2. **Q12.** For frugivorous birds and mammals in tropical forests of different continents, the slope Z is: - (a) 0.5 - (b) 0.15 - (c) 2.15 - (d) 1.15 **Answer: (d)** — The slope for frugivorous birds and mammals across continents is 1.15 — a much steeper slope than for small areas. **Q13.** David Tilman's long-term experiments showed that plots with more species had: - (a) No difference - (b) Less year-to-year variation in biomass and higher productivity - (c) Lower productivity - (d) More year-to-year variation in biomass **Answer: (b)** — Tilman found plots with more species showed less year-to-year variation in total biomass, and increased diversity gave higher productivity. **Q14.** The rivet popper hypothesis emphasises that: - (a) WHICH species is removed also matters, not just how many - (b) Only plants matter - (c) All species are equally important - (d) Species loss has no effect **Answer: (a)** — Loss of rivets on the wings is far more serious than a few on the seats — so which species is lost is critical. **Q15.** The Sixth Extinction differs from the previous five mass extinctions mainly in its: - (a) Geographic extent - (b) Cause only - (c) Duration - (d) Rate — 100 to 1,000 times faster **Answer: (d)** — Current extinction rates are estimated to be 100 to 1,000 times faster than pre-human times, and human activities are responsible. **Q16.** The most important cause of biodiversity loss is: - (a) Habitat loss and fragmentation - (b) Alien species invasions - (c) Co-extinctions - (d) Over-exploitation **Answer: (a)** — Habitat loss and fragmentation is the most important cause driving animals and plants to extinction. **Q17.** The Nile perch introduced into Lake Victoria caused the extinction of more than: - (a) 20 species of cichlid fish - (b) 2 species of cichlid fish - (c) 200 species of cichlid fish - (d) 2,000 species of cichlid fish **Answer: (c)** — The Nile perch led to extinction of an ecologically unique assemblage of more than 200 species of cichlid fish. **Q18.** The total number of biodiversity hotspots in the world is now: - (a) 25 - (b) 12 - (c) 34 - (d) 50 **Answer: (c)** — Initially 25 hotspots were identified; nine more were added, bringing the world total to 34. **Q19.** Biodiversity hotspots cover what fraction of earth's land area? - (a) About 25 per cent - (b) About 50 per cent - (c) About 10 per cent - (d) Less than 2 per cent **Answer: (d)** — All hotspots together cover less than 2 per cent of earth's land area, yet protecting them could reduce mass extinctions by almost 30 per cent. **Q20.** Cryopreservation of gametes and seed banks are examples of: - (a) In situ conservation - (b) Biosphere reserves - (c) Ex situ conservation - (d) Sacred groves **Answer: (c)** — Ex situ conservation takes threatened species out of their natural habitat; it includes zoos, botanical gardens, cryopreservation and seed banks. ### NEET Previous Year Questions (PYQs) *Real NEET previous-year questions on this chapter, with explanations in our own words.* **Q21.** Which three biodiversity hotspots cover India? (NEET PYQ) - (a) Amazon, Congo and Himalaya - (b) Sundarbans, Thar and Deccan - (c) Western Ghats-Sri Lanka, Indo-Burma and Himalaya - (d) Only the Western Ghats **Answer: (c)** — Three hotspots — Western Ghats and Sri Lanka, Indo-Burma, and Himalaya — cover India's exceptionally high biodiversity regions. **Q22.** The Amazon rain forest is estimated to produce what proportion of earth's atmospheric oxygen? (NEET PYQ) - (a) 50 per cent - (b) 5 per cent - (c) 20 per cent - (d) 70 per cent **Answer: (c)** — The fast-dwindling Amazon forest is estimated to produce, through photosynthesis, 20 per cent of the total oxygen in earth's atmosphere. **Q23.** Steller's sea cow and the passenger pigeon became extinct due to: (NEET PYQ) - (a) Alien species invasion - (b) Over-exploitation - (c) Co-extinction - (d) Habitat loss **Answer: (b)** — Many species extinctions in the last 500 years, including Steller's sea cow and the passenger pigeon, were due to over-exploitation by humans. **Q24.** Tropical rain forests once covered more than 14 per cent of earth's land surface but now cover: (NEET PYQ) - (a) About 10 per cent - (b) Less than 1 per cent - (c) No more than 6 per cent - (d) About 12 per cent **Answer: (c)** — Tropical rain forests have shrunk from over 14 per cent to no more than 6 per cent of earth's land surface. **Q25.** Sacred groves are found in which of the following? (NEET PYQ) - (a) Only in Rajasthan - (b) Only in Meghalaya - (c) Only in national parks - (d) Khasi and Jaintia Hills, Aravalli Hills, Western Ghats and Bastar areas **Answer: (d)** — Sacred groves occur in Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghat regions and Sarguja, Chanda and Bastar (MP). **Q26.** More than what percentage of drugs sold worldwide are derived from plants? (NEET PYQ) - (a) 5 per cent - (b) 75 per cent - (c) 25 per cent - (d) 50 per cent **Answer: (c)** — More than 25 per cent of drugs currently sold worldwide are derived from plants, and 25,000 plant species contribute to traditional medicines. **Q27.** Parthenium, Lantana and Eicchornia are examples of: (NEET PYQ) - (a) Keystone species - (b) Invasive alien weed species - (c) Medicinal plants - (d) Endemic species **Answer: (b)** — These are invasive weed species causing environmental damage and threatening native species in India. **Q28.** India has how many biosphere reserves, national parks and wildlife sanctuaries respectively? (NEET PYQ) - (a) 14, 90 and 448 - (b) 14, 448 and 90 - (c) 25, 100 and 500 - (d) 34, 90 and 448 **Answer: (a)** — India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. **Q29.** Endemism, a defining feature of biodiversity hotspots, means: (NEET PYQ) - (a) Species confined to that region and found nowhere else - (b) Presence of migratory species - (c) High extinction rate - (d) High population density **Answer: (a)** — Endemism means species are confined to that region and not found anywhere else — a key criterion for hotspot designation. **Q30.** Which explanation is given for the greater species richness of the tropics? (NEET PYQ) - (a) They have a highly variable environment - (b) They remained relatively undisturbed for millions of years, giving more evolutionary time - (c) They experience frequent glaciation - (d) They have less solar energy **Answer: (b)** — Tropical latitudes remained relatively undisturbed unlike glaciated temperate regions, giving a long evolutionary time for speciation. ### Active Recall Prompt Write everything you can recall about **Biodiversity and Conservation**, naming each part first: the **three levels of biodiversity** with their NCERT examples; **how many species** exist (all the proportions and India's figures); the **latitudinal gradient** (with the bird-species numbers and the three hypotheses for tropical richness); the **species-area relationship** (Humboldt, the full equation, and every Z value); **species diversity and ecosystem stability** (Tilman, the rivet popper hypothesis); the **Sixth Extinction**; the **Evil Quartet** with each named example; the **three arguments** for conserving biodiversity; and **hotspots and conservation** (the counts, India's three hotspots, in situ vs ex situ, sacred groves). Begin each fact with its topic and end it with a full stop.