Biodiversity and Conservation

Biodiversity refers to the variety of life on Earth — the total number of species, genes, and ecosystems. The term was popularised by sociobiologist Edward Wilson. Earth harbours an estimated 7 to 10 million species, of which only about 1.5 million have been formally described.

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Levels of Biodiversity

1. Genetic Diversity:
Variety in genes within a species. Different strains, varieties, or breeds of the same species represent genetic diversity (e.g., over 50,000 genetically distinct strains of rice in India; 1,000 varieties of mango). Genetic diversity provides the raw material for evolution and adaptation.

2. Species Diversity:
Variety of species within a region. Measured by species richness (number of species) and species evenness (abundance distribution). India has over 45,000 plant species and 91,000 animal species.

3. Ecosystem Diversity:
Variety of ecosystems in a region — tropical forest, wetlands, deserts, coral reefs, etc. A region with more diverse ecosystems has higher biodiversity.

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Patterns of Biodiversity

1. Latitudinal Gradient:
Species diversity generally increases from poles to the tropics — greatest at the equator. Tropical regions have had more stable climates for millions of years, allowing more time for speciation and niche differentiation.

Reasons for greater tropical diversity:
More solar energy → higher primary productivity → more ecological niches
Greater niche specialisation possible in stable environments
No historical glaciation events (unlike temperate regions) — uninterrupted evolution

2. Species-Area Relationship:
Alexander von Humboldt noticed that within a region, species richness increases with increasing explored area, up to a point.

Formula: log S = log C + Z × log A
Where: S = species richness, A = area, Z = slope (regression coefficient), C = Y-intercept

For smaller areas within a continent: Z = 0.1 to 0.2
For larger islands/continents: Z = 0.6 to 1.2
This relationship has critical implications for habitat conservation: reducing habitat area reduces species richness.

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Importance of Biodiversity (Arguments for Conservation)

1. Narrowly Utilitarian Arguments:
Direct economic benefits: food (rice, wheat, millets all from wild ancestors), industrial products (rubber, fibres, wood), medicines (25% of drugs are plant-derived; >40% of all pharmaceuticals originated from natural products), tourism (wildlife tourism).

2. Broadly Utilitarian Arguments:
Ecosystem services: pollination, purification of air and water, cycling of nutrients, climate regulation, flood control. The Amazon forest produces about 20% of total oxygen and sequesters vast amounts of CO2.

3. Ethical Arguments:
Every species has an intrinsic right to exist regardless of its utility to humans. We share the planet with millions of species; moral responsibility to preserve them. Paul Ehrlich's Rivet Popper Hypothesis: removing species from an ecosystem (like removing rivets from an aeroplane) eventually causes the whole system to fail.

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Loss of Biodiversity

The current species extinction rate is estimated to be 100 to 1,000 times higher than natural (background) extinction rates — an unprecedented mass extinction.

The Evil Quartet (four main causes of biodiversity loss):

1. Habitat Loss and Fragmentation:
The single greatest cause of biodiversity loss. Deforestation, conversion to agriculture, urbanisation, and dam construction destroy and fragment habitats. Fragmented patches cannot support viable populations of large animals (minimum viable population concept).

2. Over-Exploitation:
Humans have over-hunted and over-harvested many species to extinction or the brink of it: passenger pigeon (extinct 1914), dodo (extinct 1690s), Steller's sea cow — all hunted to extinction.

3. Alien (Invasive) Species Introductions:
Non-native species introduced to new regions may outcompete, predate on, or introduce disease to native species. Examples:
Nile perch introduced into Lake Victoria (Africa) → wiped out ~200 native cichlid fish species
Water hyacinth (Eichhornia crassipes): introduced in India, aggressively colonises water bodies, reduces biodiversity
Parthenium, Lantana: invasive weeds in India disrupting native plant communities

4. Co-extinctions:
When a keystone species or a host species goes extinct, all species that depend on it also go extinct. Example: if a host tree species goes extinct, all host-specific insects and plants dependent on that tree also go extinct.

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Conservation of Biodiversity

In-situ Conservation (On-site / In the habitat):
Conservation within the natural habitat. Preferred method because species are protected in their natural environment with natural ecosystem interactions.

Biosphere Reserves: large protected areas with core zones (no human activity), buffer zones, and transition zones (some human use). India has 18 Biosphere Reserves; internationally recognised by UNESCO.
National Parks: areas reserved for wildlife, no human activity permitted, have defined boundaries. India has 104 National Parks. Examples: Jim Corbett (first, 1936), Kaziranga (rhino), Gir (Asiatic lion).
Wildlife Sanctuaries: areas where wildlife is protected but some human activities like tourism and regulated grazing may be permitted. India has 543 Wildlife Sanctuaries.
Sacred Groves: forest patches protected by tribal/local communities for religious reasons — excellent in-situ conservation strategy. Found across India; known as "Dev van" or "Sacred groves."

Biodiversity hotspots (Norman Myers, 1988): Regions with exceptionally high species richness and endemism AND severe habitat threat. To qualify as a hotspot, a region must have >1,500 endemic vascular plant species and have lost >70% of its original habitat.

Originally 25 hotspots; now 34 biodiversity hotspots globally. India has 3 biodiversity hotspots:
Eastern Himalayas (Indo-Burma region)
Western Ghats (+ Sri Lanka)
Sundaland (Andaman & Nicobar Islands fall here)

Ex-situ Conservation (Off-site):
Conservation outside the natural habitat, used for critically endangered species or genetic resources.

Zoological parks (zoos) and botanical gardens: maintain living collections
Gene banks / Seed banks: long-term storage of genetic material at low temperature. National Bureau of Plant Genetic Resources (NBPGR) in New Delhi maintains seed banks.
Tissue culture banks: cryopreservation of cells, tissues, gametes, and embryos
DNA banks: storage of DNA from endangered species
National Zoological Parks, wild animal breeding centres

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Example 1

Why is genetic diversity important for a species' survival?
Genetic diversity provides the variation within a species on which natural selection can act. If all individuals are genetically identical (low genetic diversity), a single disease or environmental change could wipe out the entire population. Diverse gene pools buffer populations against such catastrophic losses.

Example 2

Explain the species-area relationship using the formula log S = log C + Z × log A.
This equation shows that as area (A) increases, species richness (S) increases in a power-law relationship. Z (slope) of 0.1-0.2 applies to small within-continent areas; 0.6-1.2 for islands. Practical implication: if forest area is halved, species richness does not halve — it drops by 10-50% depending on Z, but continued fragmentation can cause accelerating species loss.

Example 3

Explain how the introduction of Nile perch into Lake Victoria represents an alien species threat.
Nile perch (Lates niloticus) was deliberately introduced into Lake Victoria in the 1950s. Being a large, voracious predator with no natural enemies, it consumed and out-competed the native cichlid fish. Over 200 of the ~300 endemic cichlid species went extinct or are critically endangered — one of the greatest vertebrate species extinctions in recorded history.

Example 4

What is a biodiversity hotspot? Name the three biodiversity hotspots in India.
A biodiversity hotspot (Norman Myers) is a region with >1,500 endemic vascular plant species that has already lost >70% of its original habitat. It is rich in endemic species but severely threatened. India's three hotspots: (1) Eastern Himalayas / Indo-Burma region, (2) Western Ghats and Sri Lanka, (3) Sundaland (Andaman and Nicobar islands).

Example 5

Distinguish between in-situ and ex-situ conservation with one example each.
In-situ conservation: protecting species within their natural habitat. Example: Kaziranga National Park protects the one-horned rhinoceros in its natural floodplain habitat in Assam. Ex-situ conservation: protecting species outside their natural habitat. Example: Kanha National Park sends rescued tigers to breeding programmes; NBPGR seed bank stores crop plant seeds at -20 C for long-term preservation.

Example 6

What is the Rivet Popper Hypothesis? How does it justify species conservation?
Proposed by Paul Ehrlich, this hypothesis compares species in an ecosystem to rivets in an aeroplane. Losing one rivet (species) may have no immediate effect, but each subsequent loss weakens the structure until it fails catastrophically. This argues that even species that appear "unimportant" may be crucial, and we cannot predict which species are the vital "load-bearing" ones — so all should be conserved.

Example 7

Calculate the estimated species loss if a forest area is reduced from 10,000 km² to 1,000 km², given Z = 0.3 (assume C = 1 for simplicity).
Using log S = log C + Z × log A:
Original: log S1 = log 1 + 0.3 × log 10,000 = 0 + 0.3 × 4 = 1.2, so S1 = 10¹.2 ≈ 15.8 (relative units)
After reduction: log S2 = 0 + 0.3 × log 1,000 = 0.3 × 3 = 0.9, so S2 = 10⁰.9 ≈ 7.9
Species loss = (15.8 - 7.9)/15.8 ≈ 50% reduction in species richness when area is reduced by 90%.

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Summary

IUCN Red List categories: Extinct, Extinct in Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern
Biodiversity hotspots: 34 globally; 3 in India
Evil Quartet: Habitat loss, Over-exploitation, Alien invasive species, Co-extinctions
India's first National Park: Jim Corbett (1936, Uttarakhand)
Sacred groves in India: "Dev vans" — community-protected forest patches

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Common mistakes

Students confuse National Parks (strict protection, no human activity) with Wildlife Sanctuaries (some human activity allowed). Biodiversity hotspots are defined by BOTH high endemism AND high threat (loss of habitat) — a biodiverse area without habitat threat is NOT a hotspot. The species-area slope Z is not 1.0 for all regions — it varies. Co-extinction is often overlooked as a cause of biodiversity loss but is highly significant.

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