Biodiversity and Conservation: Class 12 NCERT Biology Guide

Understanding Biodiversity: Components and Importance

Biodiversity refers to the variety of life on Earth and is classified into three main components:

• Genetic Diversity: Variation of genes within species, essential for adaptation and survival.
• Species Diversity: The number and variety of species in a particular region or habitat.
• Ecosystem Diversity: Different ecosystems like forests, grasslands, wetlands, each supporting unique life forms.

Biodiversity is crucial for ecosystem stability, providing resources like food, medicine, and raw materials. It also maintains ecological balance and supports human livelihoods. Class 12 NCERT Biology emphasizes these components to help students appreciate biodiversity’s role in sustaining life.

Patterns of Biodiversity Across the Globe

Biodiversity is not evenly spread across the Earth. Two major patterns explain this distribution:

1. Latitudinal Gradient: Species diversity is highest near the equator (tropics) and decreases towards the poles. For example:

• Colombia (near equator): ~1,400 bird species
• New York (41° N): 105 bird species
• Greenland (71° N): 56 bird species

India, mostly tropical, has over 1,200 bird species, illustrating rich biodiversity.

2. Species-Area Relationship: Species richness increases with the area of habitat but only up to a limit. This relationship is expressed as:

$$\log S = \log C + Z \log A$$

where $S$ = species richness, $A$ = area, $Z$ = slope, and $C$ = constant.

The slope $Z$ is 0.1–0.2 for small areas and 0.6–1.2 for large areas, meaning species accumulate faster in larger habitats.

These patterns help ecologists understand biodiversity distribution and guide conservation efforts.

Why Are Tropical Regions So Rich in Species?

Tropical regions have the greatest species richness due to several reasons:

• Historical Stability Hypothesis: Tropics have experienced fewer climatic disturbances over millions of years, allowing species to diversify.
• Productivity Hypothesis: High solar energy and rainfall increase primary productivity, supporting more organisms.
• Evolutionary Rate Hypothesis: Warm temperatures accelerate mutation and speciation rates, creating more species.

These factors combine to make tropical forests, like the Amazon and Western Ghats in India, biodiversity hotspots with tens of thousands of species.

Major Threats to Biodiversity in India and Worldwide

Biodiversity faces serious threats, especially in India, a megadiverse country. The main causes of species loss include:

• Habitat Destruction: Deforestation, urbanization, and agriculture reduce natural habitats.
• Habitat Fragmentation: Breaking habitats into smaller patches isolates populations.
• Pollution: Contaminants affect air, water, and soil quality, harming species.
• Overexploitation: Hunting, fishing, and trade reduce species numbers.
• Invasive Species: Non-native species outcompete native flora and fauna.

These threats lead to extinction and loss of ecosystem services, making conservation critical.

Conservation Strategies: Protecting Biodiversity Effectively

Conservation aims to protect and sustain biodiversity using two main approaches:

• In Situ Conservation: Protecting species in their natural habitats.
• Examples: National parks, wildlife sanctuaries, biosphere reserves.
• Benefits: Maintains ecological processes and evolutionary adaptations.

• Ex Situ Conservation: Conserving species outside their natural habitats.
• Examples: Zoos, botanical gardens, seed banks, tissue culture.
• Useful for endangered species needing special care.

India has many protected areas like Jim Corbett National Park and the Nilgiri Biosphere Reserve. Conservation also involves legal protection, community participation, and awareness programs.

Estimating Species Richness: Methods and Formulas

Ecologists estimate total species numbers using sampling and mathematical models:

• Sampling Methods: Counting species in a small area and extrapolating to larger regions.
• Species-Area Curve: Shows how species number increases with area.

The species-area relationship formula:

$$\log S = \log C + Z \log A$$

• $S$: Number of species
• $A$: Area sampled
• $Z$: Slope indicating rate of species accumulation
• $C$: Constant

Worked Example: If $Z=0.2$, $C=10$, and area $A=100$ sq km, then:

$$\log S = \log 10 + 0.2 \times \log 100 = 1 + 0.2 \times 2 = 1 + 0.4 = 1.4$$

$$S = 10^{1.4} = 25.12$$

So, approximately 25 species are expected in 100 sq km.

Comparison of Biodiversity Patterns and Conservation Approaches

Here is a comparison table summarizing biodiversity patterns and conservation methods:

This comparison helps students grasp key concepts efficiently for exams.