Understanding Biodiversity
Biodiversity, or biological diversity, is not a monolithic entity. It encompasses the variety of life on Earth at multiple levels of biological organization and exhibits distinct patterns across geographical scales. Understanding these intricacies is crucial for appreciating its value and for formulating effective conservation strategies, especially in a megadiverse country like India.
Levels of Biodiversity
Biodiversity manifests at three fundamental hierarchical levels:
Genetic Diversity
The variety of genes within a single species, encompassing all different alleles and their combinations.
Significance:
Crucial for adaptation, resilience, agriculture (crop/livestock improvement), and medicine.Examples: Different dog breeds, numerous rice (50,000+ strains) and mango (1000+ varieties) types in India, varying potency of Rauwolfia vomitoria.
Threats:
Small population size, habitat fragmentation, selective breeding (genetic erosion).
Species Diversity
The variety of different species (plants, animals, fungi, microorganisms) in a region. Most commonly understood level.
- Species Richness: Total number of species.
- Species Evenness: Relative abundance of species.
- Taxonomic Diversity: Variety of higher taxonomic groups.
Significance:
Contributes to ecosystem stability, productivity, and services. Each species has a unique niche.Examples: High amphibian diversity in Western Ghats, immense species richness in tropical rainforests and coral reefs.
Ecosystem Diversity
The variety of different ecosystems or habitats within a geographical region (e.g., forests, deserts, wetlands, coral reefs).
Significance:
Provides unique habitats, supports a wider range of species, and offers diverse ecosystem services.India's Ecosystem Diversity: Deserts (Thar), rainforests (Western Ghats, NE), mangroves (Sundarbans), coral reefs (Andaman), alpine meadows (Himalayas).
Levels within Ecosystem Diversity:
Alpha: Local diversity. Beta: Species turnover between habitats. Gamma: Overall regional diversity.
Patterns of Biodiversity (Gradients)
Biodiversity is not uniformly distributed; it follows predictable patterns influenced by various factors.
Observation: Species diversity generally increases from poles towards the equator. Tropical regions are richest.
Example: Colombia (equatorial) has ~1,400 bird species vs. New York (41°N) with 105, and Greenland (71°N) with 56.
Hypotheses:
- Solar Energy & Climate Stability: More energy, stable climate allow specialization.
- Longer Evolutionary Time: Tropics as "cradles" (more speciation) or "museums" (lower extinction).
- Greater Niche Specialization: Stable environments allow narrower niches.
- Higher Predation Pressure: Prevents competitive exclusion.
Observation: Species diversity generally decreases from lower to higher altitudes on mountains.
Reason: Harsher conditions at higher altitudes (lower temperature, shorter growing season, etc.).
Example: Himalayan vegetation changes from tropical forests at foothills to alpine meadows and barren rock/ice at high altitudes.
The Mid-Domain Effect sometimes causes a peak in diversity at mid-altitudes.
Observation: Larger areas generally contain more species (Alexander von Humboldt).
Represented by the equation:
(S = Species richness, A = Area, c = Y-intercept, z = slope)
On a logarithmic scale: log S = log c + z log A
Reasons:
- Greater habitat diversity in larger areas.
- Larger populations are less prone to local extinction.
- Increased likelihood of colonization by new species.
- Depth Gradient (Aquatic): Diversity often decreases with depth (less light, temp, food), though exceptions like hydrothermal vents exist.
- Productivity Gradient: Higher primary productivity often supports higher diversity, but not always linear.
- Disturbance Gradient: Intermediate disturbance levels can promote higher diversity (Intermediate Disturbance Hypothesis).
- Structural Complexity: Habitats with greater structural complexity (e.g., multi-layered forests) tend to support more species.
Biodiversity Variation in India
India, a megadiverse country, showcases remarkable variation in biodiversity due to its diverse geography, climate, and biogeographic location.
Latitudinal & East-West Variation
Southern India (Western Ghats, Andaman & Nicobar) shows higher richness for tropical species. Eastern Himalayas (higher rainfall) are generally richer than Western Himalayas.
Coastal & Marine Biodiversity
Rich mangroves (Sundarbans), vibrant coral reefs (Andaman, Lakshadweep), productive estuaries (Chilika Lake).
Arid & Semi-Arid Regions
Thar Desert and Deccan rain shadow areas host unique, drought-adapted flora and fauna with significant endemism.
Island Biodiversity
Andaman & Nicobar and Lakshadweep islands have unique ecosystems with high endemism, but are vulnerable.
Altitudinal Zonation in the Himalayas
Foothills (up to ~1000m)
Tropical and subtropical forests (e.g., Sal, moist deciduous).
Temperate Zone (~1000m - 3500m)
Temperate broadleaf (oaks, maples) and coniferous forests (pine, deodar).
Alpine Zone (~3500m - 4500m/5000m)
Alpine meadows with herbaceous plants, dwarf shrubs.
Nival Zone (>4500m/5000m)
Snow-covered, very sparse or no vegetation.
Species diversity generally decreases with increasing altitude; high endemism is characteristic.
Biogeographic Zones of India
India is divided into 10 biogeographic zones by the Wildlife Institute of India, each with distinct biodiversity:
- Trans-Himalayan Zone
- Himalayan Zone
- Desert Zone
- Semi-Arid Zone
- Western Ghats Zone (Hotspot)
- Deccan Peninsula Zone
- Gangetic Plain Zone
- North-East India Zone (Hotspot)
- Islands (Andaman & Nicobar, Lakshadweep)
- Coastal Zone
The Western Ghats and North-East India are global biodiversity hotspots, exceptionally rich in species.
UPSC Relevance
Prelims:
- Definitions: Genetic, Species, Ecosystem diversity.
- Concepts: Species richness/evenness, Alpha/Beta/Gamma diversity.
- Gradients: Latitudinal, Altitudinal (reasons, examples).
- Species-Area Relationship.
- Biodiversity patterns in India (Himalayas, Western Ghats, NE, Coasts, Islands).
- Biogeographic zones of India.
Mains (GS Paper III - Environment, GS Paper I - Geography):
- Questions like "How does biodiversity vary in India?" (UPSC Mains 2018).
- Explaining latitudinal and altitudinal gradients.
- Essential for topics on conservation, protected areas, climate change impacts.
Example PYQ (Prelims - conceptual):
"Species diversity generally increases when moving from: (a) Equator to Poles (b) Poles to Equator (c) Low altitude to High altitude (d) Larger area to Smaller area".
Correct Answer: (b)
Example PYQ (Mains):
"How does biodiversity vary in India? How is the Biological Diversity Act, 2002 helpful in conservation of flora and fauna?" (UPSC Mains 2018, GS III).