Biodiversity And Its Conservation Class 12 NCERT

Levels and Patterns of Biodiversity

Biodiversity refers to the combined diversity at all levels of biological organization. Sociobiologist Edward Wilson popularized this term. NCERT categorizes biodiversity into three key levels:

1. Genetic Diversity: Variation within a single species over its distributional range. For example, the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges shows variation in the potency and concentration of the active chemical reserpine. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
2. Species Diversity: Diversity at the species level. For example, the Western Ghats have greater amphibian species diversity than the Eastern Ghats.
3. Ecological Diversity: Diversity at the ecosystem level. India, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, has greater ecosystem diversity than a Scandinavian country like Norway.

Patterns of Biodiversity are not uniform across the globe. The most prominent pattern is the Latitudinal Gradient. Species diversity decreases as we move away from the equator towards the poles. Tropics (latitudinal range of 23.5° N to 23.5° S) harbor more species than temperate or polar areas. This is because tropical environments are relatively constant, less seasonal, historically undisturbed by glaciations (allowing millions of years for speciation), and receive more solar energy, which contributes to higher productivity.

Deriving the Species-Area Relationship

1. Observation by Alexander von Humboldt — During his pioneering explorations in South American jungles, German naturalist Alexander von Humboldt observed that within a region, species richness increases with increasing explored area, but only up to a limit.
2. Formulating the Mathematical Equation — On a logarithmic scale, the species-area relationship is a straight line described by the linear equation: log S = log C + Z log A. On a normal scale, this relationship is represented as a rectangular hyperbola: S = CA^Z (where S = Species richness, A = Area, Z = slope of the line/regression coefficient, and C = Y-intercept).
3. Analyzing the Slope (Z-value) — Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region. However, if you analyze the species-area relationship among very large areas like entire continents, the slope of the line is much steeper, with Z values ranging from 0.6 to 1.2 (e.g., frugivorous birds and mammals in tropical forests have a Z value of 1.15).

Board Exam Trap: In-Situ vs Ex-Situ Conservation

Students often lose marks by confusing In-situ and Ex-situ conservation methods. Remember this rule: In-situ is 'on-site' (protecting the whole ecosystem), while Ex-situ is 'off-site' (removing threatened organisms and keeping them in special, managed environments).

• In-situ Conservation: Biosphere Reserves (14 in India), National Parks (90 in India), Wildlife Sanctuaries (448 in India), Sacred Groves (e.g., Khasi and Jaintia Hills in Meghalaya, Aravalli Hills in Rajasthan).
• Ex-situ Conservation: Zoological Parks (Zoos), Botanical Gardens, Wildlife Safari Parks, Cryopreservation (freezing gametes at -196°C), In-vitro fertilization, Seed Banks.

Exam Tip: If a question asks where a threatened species is taken when it is at high risk of extinction in the wild, the answer is always Ex-situ (specifically zoological/botanical gardens or cryopreservation). If it asks how to protect an entire forest ecosystem containing a tiger, the answer is In-situ.

Practice Questions with Solutions

• Q: What is the 'Evil Quartet' in biodiversity loss? List and briefly explain each. A: Step 1: Identify the term. The 'Evil Quartet' refers to the four major causes of accelerated rates of species extinction. Step 2: List the four causes: 1. Habitat Loss and Fragmentation: This is the most important cause. E.g., the Amazon rain forest (called the 'lungs of the planet') is being cut down for soya bean cultivation. 2. Over-exploitation: Humans over-harvesting natural resources (e.g., Steller's sea cow, passenger pigeon became extinct due to human over-exploitation). 3. Alien Species Invasions: Introduction of non-native species causing extinction of indigenous species (e.g., Nile perch introduced in Lake Victoria led to the extinction of over 200 species of cichlid fish; invasive weeds like Lantana, Parthenium, and Eichhornia). 4. Co-extinctions: When a host species becomes extinct, its associated parasites/obligate mutualists also face extinction (e.g., co-evolved plant-pollinator mutualism). Final answer: The Evil Quartet consists of Habitat Loss, Over-exploitation, Alien Species Invasions, and Co-extinctions.
• Q: Explain Paul Ehrlich's 'Rivet Popper Hypothesis'. A: Step 1: Explain the analogy. Ehrlich compared an ecosystem to an airplane, and the species living in it to the thousands of rivets holding the plane's parts together. Step 2: Describe the consequences of losing rivets. If every passenger starts popping a rivet (causing a species to go extinct), the plane might not become unsafe immediately, but over time, as more rivets are removed, the plane becomes dangerously weak. Step 3: Analyze the critical rivets. Removing a rivet from key functional parts like the wings (representing key species that drive major ecosystem functions) is far more dangerous than removing a rivet from the passenger seats (minor species). Final answer: The Rivet Popper Hypothesis illustrates how the loss of individual species (especially key stone species) gradually destabilizes ecosystem function, leading to total collapse.
• Q: How do Sacred Groves play a role in conservation? A: Step 1: Define Sacred Groves. These are forest patches set aside where all wild plants and animals are venerated and given total protection due to cultural or religious beliefs. Step 2: Locate examples in India. Notable examples include Khasi and Jaintia Hills in Meghalaya, Aravalli Hills in Rajasthan, Western Ghat regions of Karnataka and Maharashtra, and Sarguja, Chanda, and Bastar areas of Madhya Pradesh. Step 3: State their conservation significance. In Meghalaya, sacred groves are the last refuges for a large number of rare, endemic, and threatened species of plants. Final answer: Sacred groves utilize traditional religious practices to create legally/culturally protected natural sanctuaries, preserving threatened endemic flora and fauna from deforestation.
• Q: Differentiate between Biosphere Reserves and National Parks. A: Step 1: Define Biosphere Reserve. It is a large, multipurpose protected area designed to conserve genetic diversity of representative ecosystems while permitting limited human activities like research and tribal settlement (divided into Core, Buffer, and Transition zones). Step 2: Define National Park. It is an area strictly reserved for the betterment of wildlife, where human activities like forestry, grazing, or cultivation are completely prohibited. Step 3: Contrast human involvement. Biosphere reserves incorporate human habitation and sustainable resource use in buffer/transition zones, whereas National parks have strictly protected boundaries with zero human exploitation. Final answer: Biosphere reserves protect larger regional landscapes and accommodate human research/tribal life, whereas National Parks are highly restricted zones dedicated exclusively to wildlife protection with zero human activity.

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