Biodiversity and Conservation
This chapter explains what biodiversity is, how it is distributed across the globe and within India, why it matters to ecosystems and humans, and how human activity is driving an accelerating sixth mass extinction.
Biodiversity is a perennial UPSC favourite: Prelims repeatedly tests named concepts (Evil Quartet, rivet-popper hypothesis, species-area equation and Z-values, IUCN Red List figures, megadiversity status) and person-to-idea matches (Wilson, May, Tilman, Ehrlich, Humboldt). For Mains it anchors GS-III Environment & Ecology themes — conservation, ecosystem services, invasive species and India's megadiverse status — and connects to current affairs on extinctions and habitat loss.
Understand the chapter
What Biodiversity Means: Three Levels
Biodiversity, a term popularised by sociobiologist Edward Wilson, is the combined diversity of life at every level of biological organisation, from macromolecules to biomes. The three most important levels are genetic, species and ecological diversity. India illustrates all three richly, from thousands of rice strains to varied ecosystems.
- Genetic diversity: variation within a species across its range (e.g. reserpine potency in Rauwolfia vomitoria; India has 50,000+ rice strains, 1,000 mango varieties)
- Species diversity: variety of species in a region (Western Ghats have more amphibian species than Eastern Ghats)
- Ecological diversity: variety of ecosystems (India's deserts, rainforests, mangroves, coral reefs, wetlands, alpine meadows exceed Norway's)
How Many Species: Global and Indian Estimates
IUCN (2004) records slightly more than 1.5 million described species, but true totals are unknown because the tropics and microbes remain under-explored. Robert May's conservative, scientifically sound estimate places global diversity at about 7 million species; prokaryotes are excluded as conventional taxonomy cannot delineate them. India, despite only 2.4% of land area, holds 8.1% of global species, making it one of 12 megadiversity countries.
- Over 70% of recorded species are animals; plants (incl. algae, fungi, bryophytes, gymnosperms, angiosperms) are about 22%
- Insects are the most species-rich group — over 70% of animals, i.e. 7 of every 10 animals
- Fungi species outnumber the combined total of fishes, amphibians, reptiles and mammals
- India has ~45,000 plant and ~90,000 (twice as many) animal species recorded
Patterns: Latitudinal Gradient and Species-Area Relationship
Biodiversity is unevenly distributed. The latitudinal gradient shows species diversity declining from the equator towards the poles, so tropics (23.5 N to 23.5 S) are richest — the Amazon rainforest has the greatest biodiversity on Earth. Within a region, species richness rises with area as a rectangular hyperbola, becoming a straight line on a log scale.
- Three hypotheses for tropical richness: longer undisturbed evolutionary time, constant/predictable environment promoting niche specialisation, and higher solar energy and productivity
- Species-area equation (Alexander von Humboldt): log S = log C + Z log A
- Z (slope) = 0.1 to 0.2 for small areas regardless of taxon/region
- Z = 0.6 to 1.2 for very large areas/continents (1.15 for frugivorous birds and mammals)
Why Species Diversity Matters to Ecosystems
Communities with more species tend to be more stable — showing low year-to-year productivity variation and resistance/resilience to disturbance and invasion. David Tilman's long-term plot experiments showed greater diversity gives more stable biomass and higher productivity. Paul Ehrlich's rivet-popper hypothesis captures the danger of species loss.
- Stability = low productivity variation + resistance/resilience to disturbance + resistance to alien invasions
- Rivet-popper analogy (Ehrlich): ecosystem = airplane, species = rivets; losing key 'wing' rivets (keystone species) is far more dangerous than losing seat/window rivets
- Rich biodiversity is imperative for human survival, not merely desirable
Loss of Biodiversity and the Sixth Extinction
Biological wealth is declining rapidly, driven by human activity. The IUCN Red List (2004) documents 784 extinctions in 500 years and over 15,500 species currently threatened. Earth has seen five past mass extinctions; the ongoing 'Sixth Extinction' differs by its rate — 100 to 1,000 times faster than pre-human times — and could wipe out nearly half of all species within 100 years.
- 784 extinctions (500 yrs): 338 vertebrates, 359 invertebrates, 87 plants; e.g. dodo, quagga, thylacine, Steller's sea cow, three tiger subspecies
- Threatened today: 12% birds, 23% mammals, 32% amphibians, 31% gymnosperms; amphibians are most vulnerable
- Loss leads to declined plant production, lowered resistance to perturbations (drought), and greater variability in ecosystem processes
Causes: The Evil Quartet
Four major human-driven causes of extinction are collectively termed the Evil Quartet. Habitat loss and fragmentation is the single most important driver, dramatically seen in tropical rainforests, which shrank from over 14% to under 6% of land surface. Over-exploitation, alien invasions and co-extinctions complete the quartet.
- Habitat loss & fragmentation: most important; Amazon ('lungs of the planet') cleared for soya/cattle; fragmentation hits large-territory and migratory species
- Over-exploitation: 'need' to 'greed' (Steller's sea cow, passenger pigeon; over-harvested marine fish)
- Alien species invasions: Nile perch wiped out 200+ cichlid species in Lake Victoria; Parthenium, Lantana, water hyacinth (Eichhornia), African catfish (Clarias gariepinus)
- Co-extinctions: obligately associated species die together (host-parasite, plant-pollinator)
India's Conservation Framework (static anchor)
Although the chapter focuses on biodiversity science, India backs conservation with constitutional and statutory provisions flowing from the global Convention on Biological Diversity (CBD, 1992, Rio Earth Summit). These are the must-link static facts for answers on protecting India's megadiverse heritage.
- Constitutional: Article 48A (DPSP - protect environment) and Article 51A(g) (Fundamental Duty to protect natural environment)
- Statutory: Biological Diversity Act, 2002, enacted to give effect to the CBD
- Nodal body: National Biodiversity Authority (NBA), Chennai, with State Biodiversity Boards and BMCs
Key terms
- Biodiversity
- Combined diversity of life at all levels of organisation (genes to biomes); term popularised by Edward Wilson
- Genetic diversity
- Variation in genes within a single species across its distributional range
- Species diversity
- Variety and richness of species present in a given region or ecosystem
- Ecological diversity
- Diversity at the ecosystem level (forests, wetlands, deserts, reefs, etc.)
- Latitudinal gradient
- Pattern in which species diversity decreases from the equator towards the poles
- Species-area relationship
- Species richness rises with area as a rectangular hyperbola; log S = log C + Z log A
- Rivet-popper hypothesis
- Ehrlich's analogy: each species is a rivet in the ecosystem-airplane; cumulative loss, especially of key species, causes collapse
- The Evil Quartet
- The four causes of biodiversity loss: habitat loss/fragmentation, over-exploitation, alien invasions, co-extinctions
- Megadiversity country
- One of 12 nations holding a disproportionate share of global species; India has 8.1% on 2.4% of land
- Co-extinction
- Extinction of a species causing extinction of others obligately associated with it (host-parasite, plant-pollinator)
Must-know facts exam-ready
- Term 'biodiversity' was popularised by sociobiologist Edward Wilson
- IUCN (2004): ~1.5 million species described; Robert May's estimate of total global diversity ~7 million
- Over 70% of recorded species are animals; insects are 70%+ of animals (7 of every 10 animals)
- Plants comprise about 22%; fungi exceed combined fishes+amphibians+reptiles+mammals
- India: 2.4% of world's land area but 8.1% of global species; one of 12 megadiversity countries
- India has ~45,000 plant and ~90,000 animal species recorded
- Tropics span 23.5 N to 23.5 S; Amazon rainforest has Earth's greatest biodiversity
- Species-area: log S = log C + Z log A; Z = 0.1-0.2 (small areas), 0.6-1.2 (continents; 1.15 for frugivores)
- IUCN Red List (2004): 784 extinctions in 500 years (338 vertebrates, 359 invertebrates, 87 plants); 15,500+ threatened
- Threatened: 12% birds, 23% mammals, 32% amphibians, 31% gymnosperms; amphibians most vulnerable
- Sixth Extinction differs by RATE - 100 to 1,000 times faster than pre-human times; five past mass extinctions
- Tropical rainforests fell from over 14% to under 6% of land; Nile perch caused loss of 200+ cichlid species in Lake Victoria; Biological Diversity Act 2002 and NBA give effect to CBD (1992)
Memory tricks remember it for good
Traps to avoid
- Don't mix the scientists: Wilson popularised 'biodiversity', May estimated ~7 million, Tilman did stability experiments, Ehrlich gave the rivet-popper, Humboldt gave the species-area relation
- ~1.5 million is the number DESCRIBED (IUCN 2004); ~7 million is May's estimate of TOTAL - aspirants swap these
- NCERT says India is one of 12 megadiversity countries; do not write the Conservation International figure of 17
- Z-value is 0.1-0.2 for small areas but steeper 0.6-1.2 for continents - direction of difference is often reversed
- Latitudinal gradient: diversity is HIGHEST at the equator and falls towards poles, not the reverse
- Most important cause of extinction is habitat loss/fragmentation, NOT over-exploitation; 'lungs of the planet' is the Amazon
Exam focus
🧠 Prelims angles
- Match person to concept: Wilson (term), May (7 million), Tilman (stability/productivity), Ehrlich (rivet-popper), Humboldt (species-area)
- Evil Quartet components and identifying the single most important cause
- Species-area equation and the Z-value ranges (0.1-0.2 small vs 0.6-1.2 continental)
- IUCN Red List figures and threatened percentages (12/23/32/31; amphibians most vulnerable)
- Invasive/extinction examples: Nile perch-Lake Victoria-cichlids; Parthenium, Lantana, Eichhornia, Clarias gariepinus; dodo, quagga, thylacine, Steller's sea cow
- Megadiversity facts: India's 2.4% land vs 8.1% species, 12 megadiverse countries
✍️ Mains angles GS-III
- Examine the major drivers of biodiversity loss (the Evil Quartet) with Indian examples.Lead with habitat loss/fragmentation as foremost; substantiate each cause with examples (Amazon clearing, marine over-harvest, Lake Victoria cichlids/Parthenium, co-extinctions).
- Why is conserving biodiversity essential for human survival and ecosystem stability?Deploy the rivet-popper hypothesis and Tilman's stability-productivity findings; cite accelerating extinction rates and link to ecosystem services and India's conservation framework (CBD, Biodiversity Act 2002).
- Tropics harbour far greater biodiversity than temperate regions - explain why.Use the three hypotheses: longer undisturbed evolutionary time, constant/predictable (less seasonal) environments enabling niche specialisation, and greater solar energy raising productivity.
Last-minute revision tick as you recall
- Biodiversity = Genetic + Species + Ecological levels (popularised by Edward Wilson)
- India: 2.4% land, 8.1% species, 1 of 12 megadiverse nations; ~45,000 plants, ~90,000 animals
- Described ~1.5 million (IUCN 2004); May's total estimate ~7 million
- 7 of 10 animals are insects; plants ~22%; fungi beat fish+amphibians+reptiles+mammals combined
- Diversity falls equator to poles; Amazon richest; tropics = 23.5 N to 23.5 S
- Species-area: log S = log C + Z log A; Z 0.1-0.2 small, 0.6-1.2 continents (1.15 frugivores)
- Stability/productivity rise with diversity (Tilman); rivet-popper warns of cumulative loss (Ehrlich)
- Evil Quartet: Habitat loss (top) > Over-exploitation > Alien invasions > Co-extinctions
- Sixth Extinction: rates 100-1000x faster; amphibians most vulnerable; threatened 12/23/32/31 (birds/mammals/amphibians/gymnosperms)
Distilled from NCERT Class 12 · Biology (Class 12) for UPSC. Always cross-check facts with the original NCERT.