Biodiversity and Conservation: Class 12 NCERT Biology Guide

Understanding Biodiversity: Levels and Importance

Biodiversity refers to the vast variety and variability of life on Earth. It exists at three main levels:

• Genetic Diversity: Variation of genes within a species. For example, different varieties of rice or mango in India.
• Species Diversity: The number and variety of species in a region, such as the rich amphibian diversity in the Western Ghats.
• Ecosystem Diversity: Variety of ecosystems like deserts, mangroves, coral reefs, and alpine meadows.

India is home to many ecosystems, making it a biodiversity hotspot. This diversity supports ecosystem functioning, human survival, and provides resources like medicines, food, and raw materials. Understanding biodiversity is essential for protecting these resources and maintaining ecological balance.

Estimating Species Richness: Methods and Significance

Estimating the total number of species on Earth or in India is challenging due to the vast diversity. Ecologists use several methods:

• Sampling and Extrapolation: Counting species in a small area and using statistical models to estimate larger areas.
• Species-Area Curve: Shows how species number increases with habitat area.
• Mark-Recapture Method: Used mainly for animals, capturing, marking, releasing, and recapturing to estimate population size.

Worked Example: If 50 species are found in 1 sq km, and the species-area relationship follows $S = cA^z$ where $S$ is species number, $A$ is area, $c=50$, and $z=0.25$, then for 16 sq km:

$$S = 50 imes (16)^{0.25} = 50 imes 2 = 100$$

This means species richness doubles when area increases 16 times, highlighting habitat importance.

Why Tropical Regions Have High Biodiversity

Tropical regions, including parts of India, show the greatest species richness due to:

• Historical Stability Hypothesis: Stable climate over millions of years allows species to diversify.
• Productivity Hypothesis: High solar energy and rainfall increase plant growth, supporting more species.
• Evolutionary Rate Hypothesis: Warm temperatures speed up mutation and speciation rates.

These factors create complex ecosystems with many niches, supporting diverse life forms. Conservation in tropical areas is critical to protect this rich biodiversity.

Major Threats to Biodiversity in India

Biodiversity in India faces several threats mainly caused by human activities:

• Habitat Destruction: Deforestation, urbanization, and agriculture fragment habitats.
• Pollution: Air, water, and soil pollution harm species directly or indirectly.
• Overexploitation: Excessive hunting, fishing, and plant collection reduce populations.
• Invasive Species: Non-native species outcompete native flora and fauna.
• Climate Change: Alters habitats and affects species survival.

These threats cause species extinction and ecosystem imbalance, making conservation urgent.

Conservation Strategies: In Situ and Ex Situ Approaches

Conservation aims to protect biodiversity and maintain ecological balance. Two main strategies are:

• In Situ Conservation: Protecting species in their natural habitats.
• National Parks (e.g., Jim Corbett)
• Wildlife Sanctuaries (e.g., Bharatpur)
• Biosphere Reserves (e.g., Nilgiri)

• Ex Situ Conservation: Protecting species outside their natural habitats.
• Botanical Gardens
• Zoos
• Seed Banks and Gene Banks

Both methods complement each other to preserve India's rich biodiversity.

Species-Area Relationship and Its Ecological Significance

The species-area relationship describes how the number of species ($S$) increases with habitat area ($A$) using the formula:

$$S = cA^z$$

Where:

• $c$ = constant related to habitat type
• $z$ = slope of regression (usually 0.2 to 0.35)

A steeper slope ($z$) means species richness increases rapidly with area, indicating high habitat heterogeneity. This relationship helps ecologists predict species loss when habitats shrink and plan conservation accordingly.

Worked Example: If a forest patch of 4 sq km has 80 species and $z=0.3$, estimate species in 1 sq km:

$$80 = c imes 4^{0.3} ightarrow c = \frac{80}{4^{0.3}} = \frac{80}{1.52} = 52.63$$

For 1 sq km:

$$S = 52.63 imes 1^{0.3} = 52.63$$

So, species count decreases as area reduces, showing habitat loss impact.