Biodiversity and Conservation

1. Chapter at a glance

• Biodiversity exists at genetic, species and ecological levels; Edward Wilson popularised the term for combined diversity at all levels of biological organisation.

• 1.5 million species described globally; Robert May’s estimate places total species diversity at ~7 million.

• India harbours 8.1 % of global species diversity despite 2.4 % land area (45 000 plant species, ~90 000 animal species) and is one of 12 mega-diversity countries.
• Latitudinal gradient: species richness highest in tropics (23.5° N–23.5° S) due to longer evolutionary time, stable climate and higher solar energy/productivity.
• Species-area relationship: log S = log C + Z log A (Z = 0.1–0.2 for small areas; steeper for continents).
• Present extinction rate (Sixth Extinction) is 100–1 000 times higher than pre-human rates; “Evil Quartet” causes are habitat loss & fragmentation, over-exploitation, alien species invasions and co-extinctions.
• Conservation: in situ (biodiversity hotspots, biosphere reserves, national parks, sanctuaries, sacred groves) and ex situ (zoos, botanical gardens, cryopreservation, tissue culture, seed banks).

2. Definitions and laws

• Biodiversity: “the combined diversity at all the levels of biological organisation” (popularised by Edward Wilson).
• Genetic diversity: diversity at the genetic level within a single species over its distributional range (example: Rauwolfia vomitoria, >50 000 rice strains, 1 000 mango varieties in India).
• Species diversity: diversity at the species level (example: greater amphibian diversity in Western Ghats than Eastern Ghats).
• Ecological diversity: diversity at the ecosystem level (example: India’s deserts, rain forests, mangroves, coral reefs, etc.).
• Species-area relationship (exact equation given): log S = log C + Z log A, where S = species richness, A = area, Z = slope (regression coefficient), C = Y-intercept.
• Evil Quartet: the four major causes of accelerated species extinctions – (i) habitat loss and fragmentation, (ii) over-exploitation, (iii) alien species invasions, (iv) co-extinctions.
• In situ conservation: “when we conserve and protect the whole ecosystem, its biodiversity at all levels is protected”.
• Ex situ conservation: “threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care”.
• Biodiversity hotspots: regions with very high levels of species richness and high degree of endemism (34 hotspots identified globally; three cover India – Western Ghats-Sri Lanka, Indo-Burma, Himalaya).

3. Important diagrams and activities

• Figure 13.1 – Representing global biodiversity: proportionate number of species of major taxa of plants, invertebrates and vertebrates (shows >70 % animals, insects >70 % of animals, fungi > all vertebrates combined).
• Figure 13.2 – Species-area relationship (rectangular hyperbola on arithmetic scale; straight line on log scale) demonstrating that species richness increases with area up to a limit.

4. Common misconceptions and exam pitfalls

• Confusing the three levels of biodiversity (genetic vs species vs ecological) or giving non-NCERT examples.
• Stating global species estimate as 20–50 million instead of Robert May’s conservative 7 million.
• Writing Z value 0.6–1.2 for small regions (correct only for continents).
• Mixing up in situ and ex situ examples or forgetting that sacred groves are a traditional in situ method.
• Claiming new species are being added at the same rate as losses; NCERT states speciation is doubtful while losses are rapid.
• Forgetting the exact “Evil Quartet” phrase or the rivet popper hypothesis analogy for ecosystem stability.

5. Formula sheet