Theory: Biodiversity & Conservation
1. The Evil Quartet — Details
📌 Habitat loss & fragmentation: Most important cause. Amazon deforestation, wetland drainage. Forest fragmentation isolates populations → inbreeding → extinction. Tropical forests (14% of land) hold 50%+ of species.
📌 Over-exploitation: Hunting, poaching, overfishing beyond sustainable limits. Steller's sea cow, passenger pigeon, dodo — all hunted to extinction.
📌 Alien species invasions: Introduced species outcompete native species. Nile perch in Lake Victoria → extinction of 200 cichlid species. Water hyacinth (Eichhornia crassipes) in Indian water bodies.
📌 Co-extinctions: When one species goes extinct, dependent species also go extinct. Coevolved plant-pollinator pairs; parasites lose their host species.
2. Biodiversity — Types and Measurement
Three levels of biodiversity: (1) Genetic diversity — variety of genes within a species. India has 50,000 rice varieties, 1000 mango varieties. (2) Species diversity — number and variety of species in an area. Western Ghats have more amphibian species than Eastern Ghats. (3) Ecosystem diversity — variety of ecosystems (deserts, rainforests, coral reefs). Species richness = number of species in an area. Alpha diversity = within a community. Beta diversity = between communities. Gamma diversity = total diversity over a large region.
3. Biodiversity Hotspots
A biodiversity hotspot must have: (1) ≥1500 species of endemic vascular plants, (2) ≥70% of original habitat already destroyed. There are 34 hotspots worldwide. Two in India: Western Ghats + Sri Lanka, and Indo-Burma (includes Northeast India). Hotspots cover only 2.4% of Earth's land area but contain >50% of world's endemic plants and ~42% of endemic terrestrial vertebrates. Norman Myers first identified hotspots in 1988.
4. IUCN Red List Categories
📌 Extinct (EX): No reasonable doubt that last individual has died. Dodo, Steller's sea cow, passenger pigeon.
📌 Extinct in the Wild (EW): Only survives in captivity. Garamba white rhino.
📌 Critically Endangered (CR): Extremely high risk. Tiger, Indian rhino, Gangetic dolphin.
📌 Endangered (EN): Very high risk. Snow leopard.
📌 Vulnerable (VU): High risk. Nilgiri tahr.
📌 Near Threatened (NT): Close to qualifying as threatened.
📌 Least Concern (LC): Not threatened. Humans!
5. In-situ vs Ex-situ Conservation
In-situ (on-site) conservation: protecting species in their natural habitat. Examples: National parks, Wildlife sanctuaries, Biosphere reserves, Sacred groves (sacred forests in India). India has 104 national parks, 565 wildlife sanctuaries, 18 biosphere reserves. Project Tiger (1973) — saved Bengal tiger from extinction. Ex-situ (off-site) conservation: protecting species outside their natural habitat. Examples: Zoological parks (zoos), Botanical gardens, Wildlife safari parks, Seed banks, Cryopreservation, Pollen banks, DNA banks. Tissue culture banks preserve plant germplasm. Seed bank in Svalbard, Norway — global backup.
6. Alien/Invasive Species — Examples
📌 Nile perch (Lates niloticus): Introduced into Lake Victoria, East Africa → caused extinction of >200 cichlid fish species.
📌 Water hyacinth (Eichhornia crassipes): Introduced in India → grows rapidly → blocks waterways → kills aquatic life → "Terror of Bengal". Native of Amazon.
📌 Lantana camara: Invasive shrub in Indian forests — outcompetes native plants.
📌 Parthenium (Congress grass): Invasive weed in India from Central America.
📌 Cane toad: Introduced in Australia for pest control → now itself a major pest, toxic to native predators.
📌 Africanised honey bee: Released in Brazil, spread to North America — outcompetes native bees.
7. Species Area Relationship
Alexander von Humboldt observed: species richness increases with area (species-area relationship). S = CA^Z, where S = species richness, A = area, Z = slope of line (regression coefficient), C = Y-intercept. For smaller areas (islands, continents within a region): Z ≈ 0.1–0.2. For large areas (continents): Z ≈ 0.6–1.2. log S = log C + Z log A (linear on log-log scale). If forest area reduces to 10%: species richness drops to 50% (for Z = 0.3). This is why habitat destruction causes mass extinctions.
8. Arguments for Biodiversity Conservation
Narrowly utilitarian: direct benefits — food (rice, wheat), fibres (cotton), medicines (25% drugs from plants: morphine, quinine, taxol), industrial products (rubber, timber). Broadly utilitarian: ecosystem services — pollination (bees), water purification (wetlands), oxygen production, climate regulation (forests), soil formation, nutrient cycling. Ethical argument: every species has intrinsic value independent of human use — we have a moral obligation to preserve all life forms. Rivet-popper hypothesis (Paul Ehrlich): losing species is like popping rivets from an airplane — too many lost = catastrophic failure.
Frequently Asked Questions
1. Who coined the term "Evil Quartet"? ⌄
Jared Diamond coined the term "Evil Quartet" in 1989 to describe four major causes of biodiversity loss. His paper identified: (1) Habitat destruction and fragmentation, (2) Over-exploitation, (3) Introduced species (alien species), (4) Chains of extinction (co-extinctions). This framework is widely cited in conservation biology. Diamond is also known for the "species equilibrium model" of island biogeography (with Robert MacArthur) and the book "Guns, Germs and Steel."
2. Why is habitat loss the most important cause? ⌄
Habitat loss and fragmentation is considered the single most important cause of biodiversity loss worldwide. Reasons: (1) Tropical rainforests (harboring 50%+ of species) are being cleared at alarming rates for agriculture, logging, and urbanisation. (2) Fragmentation isolates populations — small isolated populations suffer inbreeding, reduced gene flow, and increased extinction risk. (3) Even without complete destruction, fragmentation disrupts migration routes and disrupts ecosystem functions. Amazon deforestation for soybean cultivation is a prime example.
3. What is co-extinction? Give an example. ⌄
Co-extinction occurs when the extinction of one species leads to the extinction of other dependent species. Examples: (1) Fig trees and fig wasps — highly coevolved mutualism. If fig trees go extinct, fig wasps (which exclusively pollinate and reproduce in figs) also go extinct. (2) A parasitic plant that depends exclusively on one host plant will go extinct if the host goes extinct. (3) Coral reef bleaching — corals die → hundreds of fish species that depend on coral habitat also disappear. (4) Dodo extinction → Calvaria tree seeds stopped germinating (the dodo was needed to crack the seed coat).
4. How does the Nile perch cause co-extinction? ⌄
The Nile perch (Lates niloticus) was introduced into Lake Victoria in East Africa in the 1950s for sport fishing and to boost the local food industry. Being a large predatory fish, it began eating and outcompeting the native cichlid fish (which were highly diverse — >200 endemic species). The cichlids had evolved unique feeding niches over millions of years. The Nile perch drove over 200 cichlid species to extinction. This is considered one of the worst human-caused freshwater biodiversity disasters. The remaining cichlid species are now under constant pressure.
5. What is the current global biodiversity status? ⌄
Earth has approximately 1.5 million described species, but estimated total is 5-50 million (true number unknown). Fungi: 70,000 known. Plants: ~2,50,000. Insects: ~7,50,000 (largest group). Vertebrates: ~45,000. India has only 2.4% of world's land area but 8.1% of global species diversity — one of 12 megadiversity countries. Current extinction rates are 100-1000× the natural background rate. We are in the 6th mass extinction (Holocene extinction), the first caused by a single species (humans). Previous 5 mass extinctions were caused by asteroid impacts, volcanic eruptions, etc.
6. What is the difference between a National Park and a Wildlife Sanctuary? ⌄
National Park: strictly protected area. No human activity (including grazing, collection of timber) permitted. Boundaries are fixed by legislation. Examples: Jim Corbett (first NP in India, 1936), Kaziranga, Bandipur. Wildlife Sanctuary: private ownership may be allowed. Limited human activities (grazing, collection of minor forest produce) may be permitted. Boundaries may not be fixed by legislation. Examples: Bharatpur Bird Sanctuary. Biosphere Reserve: larger areas including human habitation. Has three zones: core (strictest protection), buffer (limited use), transition (human settlements). Examples: Nilgiri, Gulf of Mannar, Sunderbans.
7. What is sacred grove and its significance? ⌄
Sacred groves (Dev vans/Dev vanas) are forest patches around religious sites that are traditionally protected by local communities due to religious/cultural beliefs. No logging, hunting, or disturbance allowed — enforced by community taboos. Examples: Khasi and Jaintia Hills (Meghalaya), Western Ghats, Rajasthan, Uttarakhand. Many rare and endangered species survive in sacred groves that have been cleared elsewhere. They represent traditional in-situ conservation. Some sacred groves in Meghalaya have survived for over 1000 years. They provide refugia for biodiversity in otherwise disturbed landscapes.
8. What is the Convention on Biological Diversity (CBD)? ⌄
The Convention on Biological Diversity (CBD) was adopted at the Earth Summit in Rio de Janeiro (1992) and came into force in 1993. Three main objectives: (1) Conservation of biological diversity. (2) Sustainable use of its components. (3) Fair and equitable sharing of benefits arising from genetic resources. India ratified CBD in 1994. India enacted the Biological Diversity Act, 2002 and established the National Biodiversity Authority (NBA). The Nagoya Protocol (2010) operationalised the benefit-sharing objective. Access and Benefit Sharing (ABS) ensures communities get fair share when their genetic resources are commercially used.