Question
Biodiversity exists at three hierarchical levels. Explain each level with Indian examples. Why is genetic diversity within a species important for its survival?
Biodiversity Levels Hierarchy
flowchart TD
A["Biodiversity"] --> B["Genetic Diversity"]
A --> C["Species Diversity"]
A --> D["Ecosystem Diversity"]
B --> E["Variation within a species"]
B --> F["Example: 50,000+ rice varieties in India"]
C --> G["Number of species in a region"]
C --> H["Example: Western Ghats has more amphibian species than Indo-Gangetic plains"]
D --> I["Variety of ecosystems in a region"]
D --> J["Example: India has deserts, rainforests, mangroves, coral reefs, alpine meadows"]Solution — Step by Step
Genetic diversity refers to the variation in genes and alleles within a single species. Different populations of the same species may carry different alleles due to mutations, natural selection, and genetic drift.
Indian example: India has over 50,000 genetically different strains of rice and 1,000 varieties of mango. These are all the same species but differ genetically — some rice varieties are drought-resistant, others are flood-tolerant, and some have higher protein content. This variation is the raw material for adaptation and crop improvement.
Species diversity has two components:
- Species richness — the total number of species in a given area
- Species evenness — how uniformly individuals are distributed among species
A region with 100 species, each represented by 10 individuals, has higher species diversity than a region with 100 species where one species has 900 individuals and the rest have 1 each.
Indian example: The Western Ghats is a biodiversity hotspot with about 7,402 species of flowering plants (of which 2,100+ are endemic). India as a whole has about 8.1% of the world’s recorded species.
Ecosystem diversity refers to the variety of ecosystems (habitats, biotic communities, and ecological processes) in a region. A country with deserts, forests, grasslands, wetlands, and coral reefs has higher ecosystem diversity than one with only forests.
Indian example: India has remarkable ecosystem diversity — tropical rainforests (Northeast and Western Ghats), deserts (Thar), mangroves (Sundarbans), coral reefs (Lakshadweep and Andaman), alpine meadows (Himalaya), and deciduous forests (Central India). This is why India is one of the 17 megadiversity nations.
Why This Works
The three levels are nested: genetic diversity supports species diversity, and species diversity contributes to ecosystem diversity. If a species loses genetic diversity, it becomes vulnerable to diseases and environmental changes — because every individual responds the same way. A genetically diverse population has a better chance that some individuals will survive any new stress.
The Irish Potato Famine (1845-49) is the classic example: Ireland grew mainly one variety of potato, and when a blight (Phytophthora infestans) struck, the entire crop was wiped out because there was no genetic diversity to resist it.
NEET often asks about India’s biodiversity statistics: 8.1% of world species, about 45,000 plant species and 91,000 animal species, 2 biodiversity hotspots (Western Ghats and Eastern Himalayas). These numbers have appeared repeatedly in PYQs from 2019-2024.
Alternative Method
A quick mnemonic: G-S-E from smallest to largest scale:
| Level | Scale | Measured By | Example |
|---|---|---|---|
| Genetic | Within species | Allelic variation | Rice varieties in India |
| Species | Within ecosystem | Species richness + evenness | Amphibians in Western Ghats |
| Ecosystem | Within region/country | Habitat variety | Deserts to rainforests in India |
Common Mistake
Students confuse species richness with species diversity. Richness is simply the count of species. Diversity includes both richness AND evenness (relative abundance). A tropical forest might have high richness (many species) and high evenness (no single species dominates), giving it very high diversity. NEET questions sometimes test this distinction explicitly.