What is biodiversity?
Biodiversity (biological diversity) refers to the variety of life on Earth at all its levels, from genes to ecosystems. The term was popularised by sociobiologist Edward Wilson. Biodiversity encompasses not only the variety of species but also the variation within species (genetic diversity) and the variety of ecosystems they inhabit.
The Earth is estimated to harbour about 1.5 million formally described species, though the true total may be anywhere from 5 to 50 million. The majority remain undiscovered, particularly insects, fungi, marine invertebrates, and microorganisms.
India as a megadiversity country
India harbours 8.1% of global species on only 2.4% of Earth's land area. India has ~45,000 plant species (ranks 10th globally), ~90,000 animal species (ranks 7th in endemism), and 4 of the world's 34 biodiversity hotspots.
Three levels of biodiversity
Genetic diversity
Variation in genes within a species. Allows populations to adapt to changing environments. The basis of evolution.
Example: India has >50,000 genetically distinct rice (Oryza sativa) varieties; >1,000 varieties of mango. Genetic diversity also occurs between geographically isolated populations of the same species.
Species diversity
Variety of species within a community or region. Measured by species richness (number of species) and species evenness (relative abundance).
Example: Western Ghats have greater amphibian species diversity than the Eastern Ghats. India: ~45,000 plant species and ~90,000 animal species formally described.
Ecosystem diversity
Variety of ecosystems in a region. Includes tropical forests, grasslands, wetlands, deserts, mangroves, coral reefs, rivers, and lakes.
Example: India has a remarkable diversity of ecosystems: tropical rainforests of the Western Ghats, cold deserts of Ladakh, mangroves of Sunderban, coral reefs of Lakshadweep, and the high-altitude grasslands of the Deccan.
Global patterns: latitudinal gradient
One of the most striking patterns in nature is that species richness is highest in tropical regions near the equator and decreases progressively toward the poles. This is called the latitudinal biodiversity gradient.
Why are tropics more biodiverse?
- Evolutionary time: tropical regions have remained undisturbed for millions of years, allowing more speciation. Polar and temperate regions were periodically disrupted by glaciation, resetting species composition.
- Climate stability: tropical environments are constant and predictable. This allows highly specialised niches to evolve, promoting diversity. Temperate and polar environments are harsh and unpredictable.
- Solar energy and productivity: tropics receive more solar energy, leading to higher primary productivity, which supports more complex food webs and higher species richness.
Key fact
Tropical rainforests cover only about 2% of Earth's land surface but harbour over 50% of all known species. Amazon rainforest alone is estimated to contain 1 in 10 of all species on Earth.
Species-area relationship
Alexander von Humboldt first observed that within a region, species richness increases with increasing explored area but only up to a point. This relationship was later formalised mathematically by Robert McArthur and Edward Wilson as the species-area relationship.
The equation
log S = log C + Z log A
Equivalently: S = C × A^Z
- S = species richness
- A = area of the region
- Z = regression coefficient (slope): 0.1 to 0.2 for small areas; 0.6 to 1.2 for large continents
- C = Y-intercept (related to species richness when area = 1 unit)
Species-area relationship: log S = log C + Z log A
Adjust the C value and area type to see how species richness changes with area. Understand the difference between Z values for small islands (0.1 to 0.2) and large continents (0.6 to 1.2).
Z = 0.15 | Small island / isolated patch
Z = 0.1 to 0.2. Gentle slope: doubling area adds relatively fewer new species. Typical for habitat islands within a larger landscape (e.g. forest patches).
log C (Y-intercept): 1.5 (C = 32 species at unit area)
NEET key: species-area relationship
- Equation: log S = log C + Z log A (or S = C × A^Z)
- S = species richness; A = area; Z = slope (regression coefficient); C = Y-intercept
- Z = 0.1 to 0.2 for small areas / islands within a continent
- Z = 0.6 to 1.2 for large areas / separate continents
- Proposed by Alexander von Humboldt; formalised by McArthur and Wilson
- Larger areas have more habitats, supporting greater species richness
Try this
- Switch to "Large continent" (Z = 0.85): the curve becomes much steeper. Doubling area adds far more species for continents than for small islands.
- The species-area relationship explains why deforestation is so damaging: destroying 90% of a habitat causes extinction of roughly 50% of its species (depending on Z value).
Importance of biodiversity
Narrow utilitarian value
Direct, economic use of biodiversity: food (crops, livestock, fish), fibre (cotton, jute, silk), timber, medicine (most drugs derived from plants or microbes), and fuel. More than 25% of all drugs prescribed globally are derived from plants. For example, quinine from Cinchona bark, morphine from Opium poppy, artemisinin from Artemisia.
Broad utilitarian value (ecosystem services)
Indirect benefits from ecosystem functions: pollination (crucial for agriculture), pest control, water purification (wetlands), flood regulation, climate regulation (forests sequester carbon), soil formation and nutrient cycling. The total economic value of ecosystem services globally is estimated at over USD 33 trillion per year.
Ethical value
Every species has intrinsic value regardless of its utility to humans. All species have a right to exist. Causing extinction is ethically unacceptable even for species with no known utility.
Rivet-popper hypothesis (Paul Ehrlich)
Paul Ehrlich compared an ecosystem to an airplane held together by rivets (species). Removing rivets (species going extinct) weakens the structure. Some rivets (keystone species) are more critical than others. But even removing seemingly unimportant rivets progressively weakens the plane (ecosystem), and eventually it will crash. This is why we must prevent ALL species extinctions, not just charismatic ones.
Threats to biodiversity (HIPPO + co-extinctions)
The current rate of species extinction is estimated at 100 to 1,000 times the background (natural) extinction rate. We are in the midst of the sixth major mass extinction event, but unlike the previous five (which were caused by natural events), this one is driven entirely by human activities.
H
Habitat loss and fragmentation
MOST IMPORTANT cause globally. Deforestation (especially tropical), agricultural expansion, urbanisation, mining, wetland drainage. Fragmentation isolates populations, reducing gene flow. Example: Amazon deforestation for soy farming and cattle ranching.
Examples: Amazon deforestation; mangrove destruction for shrimp farming; wetland drainage for agriculture
I
Invasive species
Alien species introduced (accidentally or deliberately) that outcompete, predate, or displace native species. Often thrive without natural predators. Second most important cause.
Examples: Nile perch in Lake Victoria (200+ cichlid extinctions); Water hyacinth in India; Lantana and Parthenium in India
P
Pollution
Air, water, and soil pollution kill organisms or disrupt reproduction. Pesticides (e.g. DDT) accumulate in food chains (biomagnification). Acid rain kills forest trees and aquatic life. Nutrient pollution causes eutrophication.
Examples: Pesticide biomagnification; eutrophication from agricultural runoff; plastic pollution in oceans
P
Population growth
Human population growth drives all other threats: increased demand for food (agriculture), land (habitat loss), water, and resources (overexploitation). Urbanisation rapidly converts natural habitats.
Examples: 8 billion humans demand ever-expanding footprint; agricultural land now covers 50% of habitable land
O
Overexploitation
Hunting, poaching, overfishing, and unsustainable harvesting of species for trade (bushmeat, traditional medicine, pet trade, exotic leather). Even some plant species are overharvested for medicinal use.
Examples: Dodo (hunted to extinction by 1662); Passenger pigeon; Overfishing of Bluefin tuna; Rhinoceros poaching for horn
+
Co-extinctions
Extinction of one species causes extinction of another that depends on it for survival. Food web and mutualistic relationships mean extinction cascades can affect many species. Example: obligate pollinator goes extinct when its only host plant disappears.
Examples: Fig wasp if fig tree extinct; parasites of extinct host; pollinators of extinct endemic flowers
Biodiversity hotspots
A biodiversity hotspot is a region that is both extremely species-rich (high endemism) AND is under significant threat of habitat loss. The concept was introduced by Norman Myers. Currently there are 34 biodiversity hotspots globally.
Criteria for a hotspot
- Must have at least 1,500 endemic vascular plant species (endemic = found nowhere else in the world)
India's 4 biodiversity hotspots
Western Ghats + Sri Lanka
Coastal mountains of South India + Sri Lanka. Rich in endemic frogs, fish, plants, and birds. High rainfall creates exceptional diversity.
Notable species: Endemic frogs (>200 sp.), Nilgiri tahr, lion-tailed macaque
Eastern Himalayas (Indo-Burma)
Parts of NE India, Nepal, Bhutan, Myanmar. High altitudinal gradient creates diverse habitats from tropical to alpine.
Notable species: Snow leopard, red panda, one-horned rhino (in foothills)
Indo-Burma
Partially overlaps with Eastern Himalayas. Covers parts of NE India, Myanmar, Laos, Cambodia, Vietnam, Thailand, southern China.
Notable species: Giant softshell turtles, Asian elephants, many endemic plants
Sundaland
Includes the Andaman and Nicobar Islands, plus Malaysia, Indonesia (Borneo, Sumatra), the Philippines. Coral reefs and rainforests.
Notable species: Orangutans, Sumatran rhino, many endemic birds and plants
Together, all 34 hotspots cover less than 2% of Earth's land but contain more than 50% of all known endemic plant species and ~42% of all endemic vertebrate species.
In situ conservation
In situ (on-site) conservation involves protecting species within their natural habitat. This is the most effective form of conservation because species can continue their natural behaviours, interactions, and evolutionary processes.
- National Parks (89 in India):areas where all human economic activities (grazing, farming, logging, mining) are prohibited. Only scientific study is permitted. Boundaries are fixed by legislation. Jim Corbett National Park (1936) was India's first. Other important ones: Kaziranga (one-horned rhino), Kanha (tiger, barasingha), Gir Forest (Asiatic lion), Sundarban (Royal Bengal tiger).
- Wildlife Sanctuaries (440+ in India): less strict than national parks. Limited human activities like collection of forest produce and grazing are permitted. Bharatpur (Keoladeo Ghana) Bird Sanctuary, Chilika Lake, Vedanthangal are examples.
- Biosphere Reserves (14 in India): large protected areas with three concentric zones: Core zone (complete protection, no human activity), Buffer zone (research and limited tourism allowed), Transition/Manipulation zone (human settlements and sustainable use allowed). Three are part of UNESCO World Biosphere Reserve Network: Nilgiri (first, 1986), Gulf of Mannar, Sunderban.
Conservation strategies: in situ vs ex situ
Click each conservation strategy to see what it protects, where it is, and examples. Test yourself with the scenario classifier.
Select a strategy:
National Parks
Areas where no human activity (including grazing, farming, logging) is allowed except for scientific study. Highest level of protection. Managed by government.
89 national parks in India
Examples:
- Jim Corbett NP (India's first, 1936) — tigers
- Kaziranga NP — one-horned rhinoceros
- Kanha NP — barasingha (swamp deer)
- Sundarban NP — Royal Bengal tiger
- Periyar NP — elephants, tigers
Scenario (1/6) — Which conservation strategy?
A forest area where no farming, grazing, or tree-felling is allowed except for scientific study.
Try this
- Key NEET distinction: National parks = most strict (no human activity); Wildlife sanctuaries = less strict; Biosphere reserves = 3 zones (core/buffer/transition).
- Biosphere reserves in UNESCO World Network: Nilgiri, Gulf of Mannar, and Sunderban. Nilgiri was India's first biosphere reserve (1986).
Ex situ conservation
Ex situ (off-site) conservation involves protecting species outside their natural habitat. It is a last resort when species cannot be protected in their natural environment, or as a supplement to in situ conservation.
- Zoological Parks (Zoos): living animal collections maintained for conservation, education, and research. Captive breeding programs aim to maintain viable populations of endangered species. Examples: breeding programs for Amur leopard, giant panda, Arabian oryx. Delhi Zoo maintains white tigers and rhinoceros.
- Botanical Gardens: living plant collections maintained for research, conservation, and education. Often maintain rare and threatened plant species. Royal Botanic Gardens Kew (UK), Indian Botanical Garden at Howrah (Kolkata), National Botanical Research Institute (Lucknow), Lalbagh (Bangalore).
- Seed Banks:long-term storage of seeds from diverse plant varieties, especially crop wild relatives and traditional varieties. Seeds are dried to very low moisture content and stored at low temperatures (-20°C). The National Bureau of Plant Genetic Resources (NBPGR) in New Delhi maintains India's plant genetic resources. The Svalbard Global Seed Vault (Norway) is the world's largest seed bank.
Worked problems
NEET-style problem · Species-area relationship calculation
Question
Use: log S = log C + Z log A
Solution
Step 1: Find log C from the first patch.
log 80 = log C + 0.2 × log 100
1.903 = log C + 0.2 × 2
1.903 = log C + 0.4
log C = 1.503; C ≈ 31.8
Step 2: Use C and Z to find S for A2 = 10,000 km2.
log S2 = 1.503 + 0.2 × 4 = 1.503 + 0.8 = 2.303
S2 = 10^2.303 ≈ 201 species
NEET-style problem · Hotspot criteria
Question
Solution
Biodiversity hotspot criteria: (1) At least 1,500 endemic vascular plant species, AND (2) More than 70% of original habitat lost (i.e. less than 30% remaining).
- Region X: 2,000 endemic plant species (criteria 1 met: 2,000 greater than 1,500). Only 15% forest cover remaining = 85% lost (criteria 2 met: 85% greater than 70%). Region X qualifies as a biodiversity hotspot.
Key takeaway: BOTH criteria must be satisfied simultaneously. High threat alone or high endemism alone is not sufficient.
Biodiversity and Conservation NEET quiz: 12 questions
12-question scored quiz covering biodiversity types, hotspots, species-area relationship, conservation strategies (in situ vs ex situ), threats (HIPPO), and key facts.
Question 1/12
Score: 0
How many biodiversity hotspots are there globally (as per current count)?
18
25
34
50
Quick-recall cheat sheet
Biodiversity types
- Genetic: variation within species (>50,000 rice varieties in India)
- Species: variety of species in an area
- Ecosystem: variety of ecosystems
- India: 8.1% global species on 2.4% of land; 4 hotspots
Species-area relationship
- log S = log C + Z log A (or S = C × A^Z)
- Z = 0.1 to 0.2 for small areas/islands
- Z = 0.6 to 1.2 for large areas/continents
- Proposed by Humboldt; formalised by McArthur-Wilson
- Higher Z = steeper rise in diversity with area
Biodiversity hotspots
- 34 hotspots globally
- Criteria: >1,500 endemic vascular plants AND >70% habitat lost
- India has 4: Western Ghats + Sri Lanka, Eastern Himalayas, Indo-Burma, Sundaland
- All 34 hotspots = <2% land but >50% endemic species
Threats (HIPPO)
- H: Habitat loss (MOST IMPORTANT)
- I: Invasive species (Nile perch, water hyacinth)
- P: Pollution (biomagnification, eutrophication)
- P: Population growth
- O: Overexploitation (hunting, poaching)
- Co-extinctions: chain of dependent extinctions
In situ conservation
- National parks: 89 in India; no human activity
- Wildlife sanctuaries: 440+ in India; limited activity
- Biosphere reserves: 14 in India; 3 in UNESCO World Network (Nilgiri, Gulf of Mannar, Sunderban)
- Sacred groves: community-managed, religious protection
Ex situ conservation
- Zoological parks: captive breeding programs
- Botanical gardens: rare plant collections
- Seed banks: NBPGR New Delhi; seeds at -20°C
- Cryopreservation: gametes/embryos at -196°C (liquid nitrogen)
- Svalbard Global Seed Vault: world's largest seed bank
Frequently asked questions
How often does Biodiversity and Conservation appear in NEET?
Biodiversity and Conservation typically contributes 2 to 4 questions per NEET paper. High-yield topics include: types of biodiversity (genetic, species, ecosystem), biodiversity hotspots (criteria, Indian hotspots), in situ vs ex situ conservation methods, threats (HIPPO), species-area relationship (equation and Z values), and the rivet-popper hypothesis. NEET 2022 had 3 questions from this chapter.
What are the criteria for a biodiversity hotspot?
A region qualifies as a biodiversity hotspot if it meets two criteria: (1) it must have at least 1,500 endemic vascular plant species (endemic means found nowhere else in the world), AND (2) it must have already lost more than 70% of its original habitat. There are 34 biodiversity hotspots globally. India has 4 hotspots: Eastern Himalayas (Indo-Burma), Western Ghats + Sri Lanka, Sundaland (includes Andaman-Nicobar Islands), and Indo-Burma (partially overlapping).
What is the species-area relationship and what do Z values mean?
The species-area relationship (described by Alexander von Humboldt, formulated by McArthur and Wilson) states that species richness increases with area in a predictable way. The equation is: log S = log C + Z log A, where S = species richness, A = area, Z = slope of the regression line (regression coefficient), and C = Y-intercept. Z values: 0.1 to 0.2 for small areas (like islands within a continent), 0.6 to 1.2 for very large areas or separate continents. The slope Z is steeper for larger, more isolated areas because larger regions support more habitat types and more species can speciate.
What is the difference between in situ and ex situ conservation? Give examples.
In situ conservation (on-site) means protecting species in their natural habitat. Examples: National parks (no human activity allowed), Wildlife sanctuaries (limited human activity allowed), Biosphere reserves (have a core zone, buffer zone, and transition zone), Sacred groves (community-protected forest patches). Ex situ conservation (off-site) means protecting species outside their natural habitat. Examples: Zoological parks (animals), Botanical gardens (plants), Seed banks (dried seeds, e.g. NBPGR in New Delhi), Gene banks, Cryopreservation (gametes and embryos in liquid nitrogen at -196°C). Both approaches are complementary and needed.
What is the HIPPO threat framework for biodiversity loss?
HIPPO is an acronym for the major threats to biodiversity: H = Habitat loss and fragmentation (most critical threat globally; tropical deforestation causes most species loss), I = Invasive species introduction (alien species that outcompete native species; examples: Nile perch in Lake Victoria causing extinction of 200 cichlid fish species; water hyacinth, Parthenium, Lantana in India), P = Pollution (air, water, soil pollution kills organisms), P = Population growth (human overpopulation drives all other threats), O = Overexploitation (hunting, poaching, overfishing). Co-extinctions (also mentioned in NCERT) are when the loss of one species leads to extinction of another dependent species (e.g. fig wasp when fig tree goes extinct).
Why are tropical rainforests more biodiverse than temperate and polar regions?
Multiple hypotheses explain the latitudinal biodiversity gradient: (1) Tropics have undisturbed stable climate for millions of years, allowing time for greater speciation. (2) Tropical environments are constant and predictable (no harsh winters), allowing highly specialised niche differentiation. (3) Greater solar energy input to tropics allows greater primary productivity, which supports more complex food webs and more species. (4) The tropics have been free from glaciation disturbances that reset species composition in temperate and polar regions. Tropical rainforests cover only 2% of Earth's land but harbour 50% of all species.
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