Biodiversity and Conservation

2.1 Core concepts

• Biodiversity is the term popularised by sociobiologist Edward Wilson to describe combined diversity at all levels of biological organisation — from macromolecules within cells to biomes — and the biosphere shows immense diversity (heterogeneity) at every level, not just the species level (NCERT §13.1, p. 216–217).
• There are three key levels of biodiversity: (i) Genetic diversity — variation within a species over its distributional range; e.g., Rauwolfia vomitoria in different Himalayan ranges shows differing potency and concentration of the active chemical (reserpine); India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango (NCERT §13.1, p. 217).
• (ii) Species diversity — diversity at the species level; e.g., the Western Ghats have a greater amphibian species diversity than the Eastern Ghats (NCERT §13.1, p. 217).
• (iii) Ecological / ecosystem 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 (NCERT §13.1, p. 217). It has taken millions of years of evolution to accumulate this wealth, but the present rate of species losses could erase it in less than two centuries (NCERT §13.1, p. 217).
• How many species exist? According to IUCN (2004), slightly more than 1.5 million plant and animal species have been described so far; how many are yet to be discovered is unclear. Robert May's scientifically sound conservative estimate puts global species diversity at about 7 million; extreme estimates range from 20 to 50 million (NCERT §13.1.1, p. 217).
• Taxonomic share of described species: more than 70 per cent are animals; plants (algae, fungi, bryophytes, gymnosperms, angiosperms) make up ≤22 per cent. Among animals, insects are the most species-rich group (more than 70 per cent of the total animals) — out of every 10 animals on the planet, 7 are insects. The number of fungi species is more than the combined total of fishes, amphibians, reptiles and mammals (NCERT §13.1.1, p. 218, Figure 13.1).
• Prokaryotes are excluded from these counts because conventional taxonomy fails (many are unculturable). On molecular criteria, prokaryote diversity alone might run into millions (NCERT §13.1.1, p. 218).
• India's share: India has only 2.4 per cent of the world's land area but 8.1 per cent of the global species diversity — making it one of the 12 mega-diversity countries. Nearly 45,000 species of plants and twice as many animals have been recorded; applying May's 22% recovery proportion, India probably has >1,00,000 more plant species and >3,00,000 more animal species awaiting discovery (NCERT §13.1.1, p. 219).
• Latitudinal gradient — species diversity decreases as we move from the equator to the poles. Tropics (between 23.5°N and 23.5°S) harbour 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 has more than 1,200. A tropical forest in Ecuador has up to 10× more vascular plant species than a temperate forest of equal area in the Midwest USA. The Amazon rain forest holds the greatest biodiversity — >40,000 plants, 3,000 fishes, 1,300 birds, 427 mammals, 427 amphibians, 378 reptiles and >1,25,000 invertebrates — with possibly two million insect species yet to be described (NCERT §13.1.2 (i), p. 219).
• Three hypotheses for greater tropical richness: (a) Speciation is a function of time — unlike temperate regions subjected to frequent glaciations, tropical latitudes have remained relatively undisturbed for millions of years and had a long evolutionary time for diversification; (b) tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable, which promotes niche specialisation; (c) more solar energy is available in the tropics, which contributes to higher productivity and indirectly to greater diversity (NCERT §13.1.2 (i), pp. 219–220).
• Species–Area relationship (Alexander von Humboldt) — within a region, species richness increases with explored area but only up to a limit; the relationship is a rectangular hyperbola described by S = CA^Z, which on a log–log scale becomes log S = log C + Z log A, where S = species richness, A = area, Z = slope of the line (regression coefficient) and C = Y-intercept. Z values lie between 0.1 and 0.2 regardless of taxon (plants in Britain, birds in California, molluscs in New York). Across very large areas like entire continents the slopes are much steeper, Z = 0.6 to 1.2; for frugivorous birds and mammals in the tropical forests of different continents Z = 1.15 (NCERT §13.1.2 (ii), p. 220, Figure 13.2).
• Importance of species diversity to ecosystems — communities with more species generally tend to be more stable than those with fewer species. A stable community shows little year-to-year variation in productivity, is resistant/resilient to disturbances (natural or human-made) and resists invasions by alien species. David Tilman's long-term outdoor-plot experiments showed that plots with more species had less year-to-year biomass variation, and that increased diversity contributed to higher productivity (NCERT §13.1.3, p. 220–221).
• The rivet popper hypothesis of Paul Ehrlich uses an analogy — an airplane (ecosystem) is held together by thousands of rivets (species); losing a few may not affect flight safety initially, but progressive loss weakens the plane, and the loss of rivets on the wings (key species driving major ecosystem functions) is far more serious than loss on the seats or windows (NCERT §13.1.3, p. 221).
• Loss of biodiversity — the IUCN Red List (2004) documents the extinction of 784 species (338 vertebrates, 359 invertebrates, 87 plants) in the last 500 years; recent examples are the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's Sea Cow (Russia) and three subspecies (Bali, Javan, Caspian) of tiger; the last 20 years alone saw 27 species disappear (NCERT §13.1.4, p. 221).
• More than 15,500 species are currently threatened with extinction — 12% of all bird species, 23% of mammals, 32% of amphibians and 31% of gymnosperms (NCERT §13.1.4, p. 222).
• Earth has seen five mass extinctions over >3 billion years; the present "Sixth Extinction" differs in rate — currently 100 to 1,000 times faster than pre-human rates and human-driven. Ecologists warn that nearly half of all species on Earth could be wiped out within the next 100 years (NCERT §13.1.4, p. 222).
• Causes — The Evil Quartet: (i) Habitat loss and fragmentation — the most important cause; tropical rain forests have shrunk from 14% to 6% of land surface; the Amazon (the "lungs of the planet") is being cleared for soya cultivation and cattle ranching; large habitats broken into small fragments badly hurt mammals and migratory birds; (ii) Over-exploitation — Steller's sea cow and passenger pigeon were exterminated this way; many commercially important marine fish populations are presently over-harvested; (iii) Alien species invasions — the Nile perch introduced into Lake Victoria led to extinction of >200 cichlid fish species; Parthenium (carrot grass), Lantana and water hyacinth (Eichhornia) damage native plants; illegal introduction of African catfish Clarias gariepinus threatens indigenous catfish; (iv) Co-extinctions — when a host fish becomes extinct so does its assemblage of parasites; coevolved plant–pollinator mutualisms collapse together (NCERT §13.1.4, p. 222–223).
• Why conserve — three arguments: (a) 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% of drugs currently sold are derived from plants; 25,000 plant species contribute to traditional medicines); bioprospecting promises further gains. (b) Broadly utilitarian — biodiversity drives ecosystem services: the Amazon produces 20% of the Earth's total atmospheric oxygen; pollination by bees, bumblebees, birds and bats is irreplaceable; aesthetic and intangible benefits exist too. (c) Ethical — every species has intrinsic value; we owe a moral duty to pass on our biological legacy to future generations (NCERT §13.2.1, p. 223–224).
• In-situ conservation protects the whole ecosystem (you save the entire forest to save the tiger); globally, biodiversity hotspots — regions of very high species richness and very high endemism (species confined to that region) — were identified for maximum protection. Initially 25 were named; now there are 34 hotspots worldwide. Three of these — Western Ghats and Sri Lanka, Indo-Burma, and Himalaya — cover India's exceptionally rich regions. Although hotspots together cover <2% of land, strict protection of them could reduce ongoing mass extinctions by about 30% (NCERT §13.2.2, p. 224).
• India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries as legally protected areas. Many cultural and religious traditions also protect nature — sacred groves in Khasi and Jaintia Hills of Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra, and Sarguja, Chanda and Bastar areas of Madhya Pradesh; Meghalaya sacred groves remain the last refuge for many rare and threatened plants (NCERT §13.2.2, p. 225).
• Ex-situ conservation takes threatened animals and plants out of their natural habitat into special settings — zoological parks, botanical gardens, wildlife safari parks; recent advances include cryopreservation of gametes in viable/fertile condition, in-vitro fertilisation of eggs, tissue culture propagation of plants, and seed banks for genetic strains of commercially important plants (NCERT §13.2.2, p. 225).
• International cooperation: The historic Convention on Biological Diversity ("The Earth Summit") was held in Rio de Janeiro, 1992; in follow-up, the World Summit on Sustainable Development at Johannesburg, 2002, saw 190 countries pledge to achieve by 2010 a significant reduction in the current rate of biodiversity loss at global, regional and local levels (NCERT §13.2.2, p. 225).

2.2 Definitions to memorise

2.3 Diagrams / processes to remember

• Figure 13.1 (p. 218) — Pie charts of global biodiversity: Invertebrates (insects dominate, then molluscs, crustaceans, other animal groups), Vertebrates (fishes largest, then birds, reptiles, amphibians, mammals), Plants (angiosperms largest, then fungi, algae, mosses, ferns & allies, lichens). Memorise that insects are >70% of animals and fungi outnumber the combined total of fishes, amphibians, reptiles and mammals.
• Figure 13.2 (p. 220) — Species–Area curve: rectangular hyperbola on linear axes (S = CA^Z); straight line on log–log axes (log S = log C + Z log A). Remember Z range: 0.1–0.2 (small/within-region) vs 0.6–1.2 (continental); 1.15 for frugivorous birds and mammals.
• Rivet popper analogy (p. 221) — visualise airplane parts as species; wing rivets = key species; losing a few seat rivets may be tolerated, but losing wing rivets is catastrophic.
• Process flow — Evil Quartet (p. 222–223): habitat loss → over-exploitation → alien species invasions → co-extinctions.
• Process flow — conservation tiers (p. 224–225): In-situ (hotspots → biosphere reserves → national parks → wildlife sanctuaries → sacred groves) and Ex-situ (zoos → botanical gardens → seed banks → cryopreservation → in-vitro fertilisation → tissue culture).

2.4 Common confusions / NTA trap points

• Edward Wilson popularised the term "biodiversity" — NOT Humboldt (who studied species–area) and NOT Robert May (who estimated global species number).
• Z value confusion: 0.1–0.2 is for small areas/within a region; 0.6–1.2 is for very large areas/continents. Specifically 1.15 for frugivorous birds & mammals across tropical forests.
• Threatened percentages (memorise exact numbers): 12% birds, 23% mammals, 32% amphibians, 31% gymnosperms.
• India's protected-area counts: 14 biosphere reserves, 90 national parks, 448 wildlife sanctuaries — easy to confuse the three figures.
• Hotspots: initially 25, now 34. Three Indian hotspots — Western Ghats & Sri Lanka, Indo-Burma, Himalaya (NOT "Eastern Ghats" or "Sundarbans" as standalone hotspots).
• Earth Summit = Rio de Janeiro 1992 (Convention on Biological Diversity); Johannesburg 2002 is the World Summit on Sustainable Development — students mix these up.
• Robert May's estimate is 7 million (conservative). Extreme estimates 20–50 million. Described species ~1.5 million.
• Amazon produces ~20% of Earth's atmospheric oxygen — not 100%, and not "all" oxygen.
• IUCN Red List 2004 extinction figure = 784 (338 vertebrates + 359 invertebrates + 87 plants); 15,500 is the currently threatened count, NOT extinct count.

2.5 Numbers and classifications grounded in NCERT