Why Study Biodiversity?
Biodiversity is the totality of genes, species, and ecosystems in a region. Edward Wilson coined the term “biodiversity.” India is one of 12 mega-diversity nations — with only 2.4% of the world’s land area, we have about 8.1% of global species.
This chapter matters beyond exams because we are currently in the sixth mass extinction — driven not by an asteroid, but by human activity. Understanding what biodiversity is, why it matters, and how to conserve it is both a NEET scoring chapter and genuinely important knowledge.
NEET dedicates 2-3 questions to this chapter. Focus on: levels of biodiversity, species-area relationship (equation), causes of biodiversity loss (HIPPO), and conservation strategies (in-situ vs ex-situ).
Key Terms & Definitions
Genetic diversity — variation in genes within a species. Example: India has more than 50,000 genetically different strains of rice.
Species diversity — variety of species in a region. Measured by species richness (number of species) and species evenness (relative abundance).
Ecological diversity — variety of ecosystems in a region. India has deserts, rainforests, mangroves, coral reefs, alpine meadows, wetlands — high ecological diversity.
Species-area relationship — larger areas support more species. Described by Alexander von Humboldt.
Endemism — species found exclusively in a particular geographic region and nowhere else. Western Ghats has high endemism.
Biodiversity hotspot — a region with high endemism and significant habitat loss. India has 4 hotspots: Western Ghats, Himalayas, Indo-Burma, and Sundaland (Nicobar Islands).
Patterns of Biodiversity
Latitudinal Gradients
Biodiversity generally increases from poles to the equator. Tropical regions (like the Amazon, Congo, Southeast Asia) have the highest species diversity.
Why? Three hypotheses:
- Tropical regions have had more evolutionary time — no glaciation events disturbed them.
- More solar energy → higher productivity → supports more species.
- Greater area — tropics cover a larger contiguous land area.
Colombia (near the equator) has about 1,400 bird species. India has about 1,200. New York (at 41°N) has about 105 breeding bird species. This gradient is dramatic and testable.
Species-Area Relationship
where = species richness, = area, = slope (regression coefficient), = y-intercept.
For small areas within a continent: ranges from 0.1 to 0.2. For islands or isolated areas: ranges from 0.2 to 0.35.
NEET has asked the Z-value range multiple times. Remember: 0.1-0.2 for mainland, 0.2-0.35 for islands. The equation is on a log-log scale — the relationship is a straight line on a log-log plot.
Species Diversity and Ecosystem Stability
David Tilman’s long-term studies showed that communities with more species are more stable — they show less year-to-year variation in productivity and can better resist disturbances. This is the rivet popper hypothesis — like rivets on an airplane, losing a few species (rivets) may not crash the system, but there is a threshold beyond which the ecosystem (airplane) fails.
Causes of Biodiversity Loss
The major causes can be remembered with HIPPO:
| Letter | Cause | Example |
|---|---|---|
| H | Habitat loss and fragmentation | Deforestation for agriculture |
| I | Invasive species | Water hyacinth in Indian lakes |
| P | Pollution | Pesticide bioaccumulation |
| P | Population growth (human overexploitation) | Overfishing, poaching |
| O | Over-harvesting / Climate change | Coral bleaching, Steller’s sea cow extinction |
flowchart TD
A[Biodiversity Loss Causes] --> B[Habitat Loss]
A --> C[Invasive Species]
A --> D[Pollution]
A --> E[Overexploitation]
A --> F[Climate Change]
B --> B1[Deforestation]
B --> B2[Fragmentation]
B --> B3[Urbanisation]
C --> C1[Water hyacinth]
C --> C2[Lantana camara]
C --> C3[African catfish]
E --> E1[Overfishing]
E --> E2[Poaching]
F --> F1[Coral bleaching]
F --> F2[Polar ice melting]
B1 --> G[Conservation Strategies]
G --> G1[In-situ: Protected areas]
G --> G2[Ex-situ: Zoos, seed banks]Habitat Loss — The Biggest Threat
Tropical rainforests once covered 14% of the Earth’s land surface — now reduced to about 6%. The Amazon alone loses thousands of square kilometres per year. Habitat fragmentation isolates populations, reduces genetic diversity, and makes species vulnerable to extinction.
Invasive Species
When exotic species are introduced (intentionally or accidentally) into a new habitat, they can outcompete native species. The Nile perch introduced into Lake Victoria caused the extinction of over 200 species of cichlid fish. In India, water hyacinth (Eichhornia) chokes water bodies and is called “Terror of Bengal.”
Co-extinctions
When a host species goes extinct, its obligate parasites and mutualists also perish. If a plant species goes extinct, all insects that depended exclusively on it for food also become extinct. This cascade effect multiplies the impact of every extinction.
Why Conserve Biodiversity?
Three categories of reasons:
Narrowly utilitarian — direct economic benefits. Food, medicines (25% of drugs derived from plants), industrial products (rubber, timber, fibre).
Broadly utilitarian — ecosystem services. Oxygen production, pollination, climate regulation, water purification, nutrient cycling. These are estimated at $33 trillion per year (Costanza et al.).
Ethical — every species has an intrinsic right to exist. We share the planet with millions of species — it is our moral responsibility to protect them.
Conservation Strategies
In-situ Conservation (In the natural habitat)
- Biosphere reserves — large areas for conservation of ecosystems (18 in India: Nilgiri, Nanda Devi, Sunderbans, etc.)
- National parks — protected areas with strict regulations (106 in India: Jim Corbett, Kaziranga, Ranthambore, etc.)
- Wildlife sanctuaries — protected, but some human activities allowed (over 550 in India)
- Sacred groves — patches of forest protected by religious communities. Found in Western Ghats, Meghalaya, Rajasthan.
- Biodiversity hotspots — priority areas for conservation based on endemism and threat level.
Ex-situ Conservation (Outside the natural habitat)
- Zoological parks (zoos) — captive breeding programs
- Botanical gardens — plant conservation (Royal Botanical Garden, Kew)
- Seed banks — storage of seeds under controlled conditions (National Bureau of Plant Genetic Resources, New Delhi)
- Cryopreservation — preserving gametes, embryos in liquid nitrogen (-196°C)
- Gene banks — storing genetic material for future use
In-situ conservation is always preferred because species evolve in their natural habitat. Ex-situ is a last resort for critically endangered species — like breeding the California condor or the Indian rhino in captivity before reintroducing them.
Important Conventions and Acts
| Convention/Act | Year | Purpose |
|---|---|---|
| Wildlife Protection Act | 1972 | Legal protection for Indian wildlife |
| CITES | 1975 | Regulates international trade in endangered species |
| Convention on Biological Diversity (CBD) | 1992 | Conservation, sustainable use, benefit-sharing |
| Biological Diversity Act (India) | 2002 | Implements CBD at national level |
| IUCN Red List | Ongoing | Categorises species by threat level (CR, EN, VU, NT, LC) |
Solved Examples
Example 1 (NEET Level — Easy)
Q: If , what is the Z value and what does it indicate?
A: Z = 0.2. Since Z is in the range 0.1-0.2, this represents a species-area relationship for a large mainland region (not an island).
Example 2 (NEET Level — Medium)
Q: Why are islands expected to have a higher Z value in the species-area relationship compared to mainland regions?
A: Islands have higher Z values (0.2-0.35) because they are isolated habitats. Immigration is low and species that go extinct on the island are not easily replaced from neighbouring areas. This makes species richness more sensitive to area changes. On mainlands, species can migrate between areas more freely, buffering the effect.
Example 3 (NEET Level — Medium)
Q: What is the rivet popper hypothesis?
A: Proposed by Paul Ehrlich. He compared species in an ecosystem to rivets on an airplane. Removing a few rivets (species) may not affect the airplane (ecosystem) noticeably. But there is a threshold — beyond which removal of one more rivet causes catastrophic failure. Similarly, each species loss weakens the ecosystem, and beyond a critical threshold, the ecosystem collapses.
Common Mistakes to Avoid
Mistake 1 — Confusing species richness with species diversity. Richness = just the number of species. Diversity = richness + evenness (relative abundance). A forest with 50 equally abundant species has higher diversity than one with 50 species where one species dominates 90% of the population.
Mistake 2 — Mixing up the Z-value ranges. Mainland: 0.1-0.2. Islands: 0.2-0.35. Students swap these values. Use the logic: islands are more sensitive to area, hence higher Z.
Mistake 3 — Thinking biodiversity hotspots have the MOST species. Hotspots are defined by high endemism (unique species) AND significant habitat loss — not by total species count. The Amazon has incredible biodiversity but the entire basin is not classified as a single hotspot.
Mistake 4 — Confusing in-situ and ex-situ conservation. In-situ = in natural habitat (national parks, sanctuaries). Ex-situ = outside natural habitat (zoos, seed banks). Sacred groves are in-situ conservation.
Mistake 5 — Forgetting co-extinctions. When a species goes extinct, its dependent species (obligate parasites, specialised pollinators) also face extinction. This cascading effect is underestimated by students.
Practice Questions
Q1. Name the three levels of biodiversity.
(1) Genetic diversity — variation within a species at the gene level. (2) Species diversity — variety of species in a community. (3) Ecological diversity — variety of ecosystems in a region.
Q2. India has four biodiversity hotspots. Name them.
(1) Western Ghats and Sri Lanka, (2) Himalayas, (3) Indo-Burma, and (4) Sundaland (includes the Nicobar Islands).
Q3. What is the “Evil Quartet” in biodiversity loss?
The four major causes of biodiversity loss identified by Jared Diamond: (1) Habitat destruction and fragmentation, (2) Overexploitation, (3) Alien species invasions, (4) Co-extinctions. This is often asked as a NEET match-the-following.
Q4. How do sacred groves help in biodiversity conservation?
Sacred groves are patches of forest that local communities protect due to religious or cultural beliefs. These groves serve as refugia for many native species, including rare and endemic ones. They are examples of traditional, community-based in-situ conservation that have existed for centuries.
Q5. Explain the significance of the species-area relationship in conservation.
The species-area relationship () tells us that reducing habitat area leads to species loss. If we destroy 90% of a habitat (reduce area to 10%), the species-area model predicts roughly 50% species loss. This quantitative prediction is critical for planning protected areas — we can estimate how many species will be lost for a given habitat reduction.
Q6. What is the difference between endangered and vulnerable species?
According to IUCN Red List categories: Endangered (EN) species face a very high risk of extinction in the wild. Vulnerable (VU) species face a high risk of extinction. Endangered is a more severe category than Vulnerable. Above Endangered is Critically Endangered (CR), and below Vulnerable is Near Threatened (NT).
Q7. Why is genetic diversity important for a species’ survival?
Greater genetic diversity means more variation within a population. This variation provides raw material for natural selection — some individuals are more likely to survive environmental changes (diseases, climate shifts). Populations with low genetic diversity (like cheetahs) are vulnerable because they lack the variation needed to adapt.
Q8. Name two examples of ex-situ conservation.
(1) Seed banks — like the National Bureau of Plant Genetic Resources in New Delhi, which stores seeds under controlled conditions. (2) Captive breeding in zoos — breeding endangered species in captivity for eventual reintroduction, such as the breeding program for the Indian rhino.
FAQs
What is the difference between a national park and a wildlife sanctuary? National parks have stricter protection — no human habitation, no grazing, no forestry allowed. Wildlife sanctuaries allow some human activities (like limited grazing, timber collection) with permission. Both are in-situ conservation methods.
Why are tropical regions more biodiverse? Three main reasons: longer evolutionary time (no glaciation), more solar energy supporting higher productivity, and larger contiguous area near the equator.
What is IUCN and what does it do? International Union for Conservation of Nature. It maintains the Red List — a comprehensive inventory of species categorised by extinction risk. Categories range from Least Concern (LC) to Extinct (EX).
How does habitat fragmentation affect biodiversity? Fragmentation breaks a large habitat into small, isolated patches. This reduces total area (supporting fewer species), creates edge effects (altered microclimate at boundaries), isolates populations (reducing gene flow), and prevents migration. Small fragmented populations are more prone to local extinction.
What are ecosystem services? Services provided by ecosystems that benefit humans — oxygen production, pollination, water purification, climate regulation, nutrient cycling, flood control, and recreational value. Robert Costanza estimated the value of ecosystem services at approximately $33 trillion per year.
**Why is the Amazon called the “lungs of the Earth”? The Amazon rainforest produces a significant portion of atmospheric oxygen through photosynthesis and absorbs large amounts of CO₂. It plays a critical role in global carbon cycling and climate regulation.