Class 12 Biology Notes Chapter 15 (Biodiversity and Conservation) – Examplar Problems Book

Detailed Notes with MCQs of Chapter 15: Biodiversity and Conservation. This is a crucial chapter, not just for your board exams but also frequently tested in various government competitive exams. Pay close attention to the definitions, examples, and data points.

Biodiversity and Conservation: Detailed Notes

1. What is Biodiversity?

• The term was popularized by sociobiologist Edward Wilson.
• It refers to the variety of life forms at all levels of biological organisation, ranging from macromolecules within cells to biomes.
• Levels of Biodiversity:
  • Genetic Diversity: Variation in genes within a species. This allows species to adapt to environmental changes.
    • Example: Rauwolfia vomitoria growing in different Himalayan ranges produces different concentrations and types of the active chemical reserpine.
    • Example: India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
  • Species Diversity: Variety of species within a region. Measured by species richness (number of species) and species evenness (relative abundance of species).
    • Example: Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
  • Ecological Diversity: Variety of ecosystems (habitats, communities, ecological processes) in a region.
    • Example: India has diverse ecosystems like deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, leading to greater ecological diversity than a country like Norway.

2. Magnitude of Biodiversity on Earth and in India

• Global Estimates:
  • According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million.
  • A more conservative and scientifically sound estimate by Robert May places the global species diversity at about 7 million.
  • More than 70% of all recorded species are animals; plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) account for no more than 22%.
  • Among animals, insects are the most species-rich group, making up more than 70% of the total animal species.
  • The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles, and mammals.
  • Estimating prokaryotic diversity is difficult because conventional taxonomic methods are unsuitable, and many species cannot be cultured in the lab.
• India's Biodiversity:
  • India has only 2.4% of the world's land area but shares 8.1% of the global species diversity.
  • This makes India one of the 12 mega-diversity countries of the world.
  • India has about 45,000 species of plants and twice as many species of animals recorded.
  • Applying May's global estimates, India likely has over 1,00,000 plant species and over 3,00,000 animal species yet to be discovered and described.

3. Patterns of Biodiversity

• Latitudinal Gradients:
  • Species diversity generally decreases as we move away from the equator towards the poles.
  • The tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas.
  • Example: Colombia (near the equator) has nearly 1,400 bird species, while New York (41° N) has 105 species, and Greenland (71° N) has only 56 species.
  • The tropical Amazonian rainforest in South America has the greatest biodiversity on Earth.
  • Reasons for higher tropical diversity:
    • Speciation is a function of time: Tropical latitudes have remained relatively undisturbed for millions of years, allowing longer evolutionary time for species diversification. Temperate regions faced frequent glaciations.
    • Less seasonal environment: Tropical environments are relatively constant and predictable, promoting niche specialisation and higher species richness.
    • More solar energy: Higher solar energy availability contributes to higher productivity, which might support greater diversity indirectly.
• Species-Area Relationships:
  • Observed by German naturalist and geographer Alexander von Humboldt.
  • Within a region, species richness increases with increasing explored area, but only up to a certain limit.
  • The relationship is a rectangular hyperbola expressed as: S = CA^Z
    • Where S = Species richness, A = Area, Z = Slope of the line (regression coefficient), C = Y-intercept.
  • On a logarithmic scale, the relationship is a straight line described by: log S = log C + Z log A
  • The value of Z (slope) generally lies in the range of 0.1 to 0.2, regardless of the taxonomic group or region (e.g., plants in Britain, birds in California, molluscs in New York).
  • However, for very large areas like entire continents, the slope (Z value) is much steeper, ranging from 0.6 to 1.2.
    • Example: For frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the Z value is found to be 1.15.

4. Importance of Species Diversity to the Ecosystem

• Ecologists believe that communities with more species tend to be more stable than those with fewer species.
• Characteristics of a stable community:
  • Should not show too much variation in productivity from year to year.
  • Must be resistant or resilient to occasional disturbances (natural or man-made).
  • Must be resistant to invasions by alien species.
• David Tilman's long-term ecosystem experiments using outdoor plots confirmed that plots with more species showed less year-to-year variation in total biomass (increased stability) and demonstrated increased productivity.
• Rivet Popper Hypothesis (Paul Ehrlich): Compares an ecosystem to an airplane and species to rivets. Loss of a few rivets (species) might not affect flight safety initially, but as more rivets are removed, the plane becomes dangerously weak. Loss of 'key' rivets (keystone species) is obviously a more serious threat.

5. Loss of Biodiversity

• Current species extinction rates are estimated to be 100 to 1,000 times faster than pre-human, natural background rates, largely due to human activities (Anthropogenic extinction).
• Recent Extinctions: Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller's Sea Cow (Russia), three subspecies of Tiger (Bali, Javan, Caspian).
• IUCN Red List (2004): Documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) in the last 500 years.
• More than 15,500 species worldwide are facing the threat of extinction. Currently, 12% of bird species, 23% of mammal species, 32% of amphibian species, and 31% of gymnosperm species face the threat.
• Causes of Biodiversity Loss (The 'Evil Quartet'):
  • Habitat Loss and Fragmentation: This is the most important cause. Due to deforestation (e.g., tropical rainforests reduced from 14% to 6% of land), conversion of forests to agricultural land (e.g., Amazon rainforest cleared for soybean cultivation or cattle ranching), urbanization, mining, etc. Fragmentation breaks large habitats into smaller ones, affecting migratory animals and those needing large territories.
  • Over-exploitation: Harvesting renewable resources faster than they can regenerate. Examples: Steller's sea cow, Passenger pigeon were driven to extinction. Many marine fish populations are declining due to overfishing.
  • Alien Species Invasions: Introduction of non-native species (intentionally or unintentionally) that invade and negatively impact native species, sometimes leading to their extinction.
    • Examples: Nile Perch introduced into Lake Victoria (East Africa) led to the extinction of >200 species of cichlid fish. Invasive weeds like Parthenium (carrot grass), Lantana, and Eichhornia (water hyacinth) threaten native species. Introduction of the African catfish Clarias gariepinus for aquaculture is posing a threat to indigenous catfishes.
  • Co-extinctions: When a species becomes extinct, plant and animal species associated with it in an obligatory way also become extinct.
    • Examples: Extinction of a host fish leads to the extinction of its unique parasites. Coevolved plant-pollinator mutualism where extinction of one leads to the extinction of the other.

6. Why Should We Conserve Biodiversity?

• Arguments for conservation are grouped into three categories:
  • Narrowly Utilitarian: Humans derive direct economic benefits from nature.
    • Food (cereals, pulses, fruits), firewood, fibre, construction material.
    • Industrial products (tannins, lubricants, dyes, resins, perfumes).
    • Medicinal products (More than 25% of drugs are derived from plants; e.g., Quinine from Cinchona, Digitalis from Foxglove).
    • Bioprospecting: Exploring molecular, genetic, and species-level diversity for products of economic importance.
  • Broadly Utilitarian: Biodiversity plays a major role in providing ecosystem services.
    • Oxygen production (Amazon rainforest estimated to produce 20% of total oxygen).
    • Pollination (by bees, bumblebees, birds, bats).
    • Climate regulation.
    • Flood and erosion control.
    • Nutrient cycling.
    • Aesthetic pleasures, recreation, ecotourism.
  • Ethical: Every species has an intrinsic value, regardless of its economic value to us. We have a moral duty to care for their well-being and pass on our rich biological legacy to future generations.

7. How Do We Conserve Biodiversity?

• In-situ Conservation (On-site): Protecting species in their natural habitat. This involves protecting the entire ecosystem.
  • Biodiversity Hotspots: Concept developed by Norman Myers. These are regions with very high levels of species richness and high degree of endemism (species found only in that region and nowhere else).
    • Criteria: Must have at least 1500 species of vascular plants (>0.5% of world total) as endemics AND must have lost ≥ 70% of its original habitat.
    • Initially 25 hotspots were identified; now there are 34 (some sources say 36).
    • These hotspots cover less than 2% of the Earth's land area but harbour an extremely high number of species. Strict protection could reduce ongoing mass extinctions by almost 30%.
    • India's Hotspots: Western Ghats & Sri Lanka, Indo-Burma, Himalaya, Sundaland (includes Nicobar Islands).
  • Protected Areas: Legally protected areas like National Parks, Sanctuaries, and Biosphere Reserves.
    • National Parks: Strict protection, no human activity like grazing, forestry, cultivation allowed. Primarily for wildlife and habitat conservation. (India has 106 NPs as of recent data).
    • Sanctuaries: Protection given mainly to fauna (animals). Some human activities like timber collection, grazing might be permitted if they don't interfere with wildlife. (India has 567 WLSs as of recent data).
    • Biosphere Reserves: Large tracts of land with zoning (Core, Buffer, Transition) allowing varying degrees of human activity, focusing on conserving biodiversity with sustainable human use. (India has 18 BRs).
  • Sacred Groves: Tracts of forest set aside, protected by local communities based on religious beliefs. All trees and wildlife within are venerated. Found in Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka, Maharashtra), Sarguja, Chanda, Bastar areas (Madhya Pradesh). Often serve as refugia for rare and threatened plants.
• Ex-situ Conservation (Off-site): Protecting threatened animals and plants outside their natural habitat.
  • Zoological Parks (Zoos), Botanical Gardens, Wildlife Safari Parks: Maintain threatened species, often for breeding programs.
  • Cryopreservation: Preservation of gametes, seeds, tissues, embryos of threatened species in viable condition at very low temperatures (-196°C in liquid nitrogen). Used for gene banks and seed banks. Seeds of commercially important plants can be kept viable for long periods in seed banks.
  • Tissue Culture / Micropropagation: Can be used to propagate rare or endangered plants.

8. International Efforts for Conservation

• The Earth Summit (UNCED): Held in Rio de Janeiro, Brazil, in 1992. Called upon all nations to take appropriate measures for:
  • Conservation of biodiversity.
  • Sustainable utilization of its benefits.
  • Fair and equitable sharing of benefits arising from the utilization of genetic resources (Convention on Biological Diversity - CBD).
• World Summit on Sustainable Development: Held in 2002 in Johannesburg, South Africa. 190 countries pledged their commitment to achieve, by 2010, a significant reduction in the current rate of biodiversity loss at global, regional, and local levels. (Note: This target was not fully met).

Multiple Choice Questions (MCQs)

1. Which of the following represents the maximum number of species among global biodiversity?
   (a) Fungi
   (b) Mosses and Ferns
   (c) Algae
   (d) Insects

2. The concept of 'Biodiversity Hotspots' was developed by:
   (a) Edward Wilson
   (b) Paul Ehrlich
   (c) Norman Myers
   (d) Alexander von Humboldt

3. Which of the following is NOT a cause for biodiversity loss under the 'Evil Quartet'?
   (a) Alien species invasion
   (b) Co-extinction
   (c) Habitat fragmentation
   (d) Bioprospecting

4. The species-area relationship on a logarithmic scale is represented by the equation:
   (a) S = CA^Z
   (b) log S = log C + Z log A
   (c) log C = log S + Z log A
   (d) S = C + ZA

5. Cryopreservation of gametes of threatened species in viable and fertile condition can be referred to as:
   (a) In-situ conservation by sacred groves
   (b) Ex-situ conservation of biodiversity
   (c) In-situ conservation of biodiversity
   (d) Advanced ex-situ conservation of biodiversity

6. Which region in India is NOT listed as a biodiversity hotspot?
   (a) Western Ghats
   (b) Indo-Burma
   (c) Aravalli Hills
   (d) Himalaya

7. The narrowly utilitarian argument for conserving biodiversity focuses on:
   (a) Ecosystem services like pollination
   (b) Ethical responsibility towards species
   (c) Direct economic benefits like food, medicine, and industrial products
   (d) Aesthetic and recreational value

8. The introduction of Nile Perch into Lake Victoria led to the extinction of:
   (a) Indigenous catfish
   (b) Cichlid fish
   (c) Water hyacinth
   (d) Steller's sea cow

9. According to Robert May's estimate, the global species diversity is about:
   (a) 1.5 million
   (b) 7 million
   (c) 20 million
   (d) 50 million

10. Sacred groves are examples of:
    (a) Ex-situ conservation
    (b) In-situ conservation
    (c) Cryopreservation
    (d) Botanical gardens

Answer Key for MCQs:

1. (d) Insects
2. (c) Norman Myers
3. (d) Bioprospecting (This is exploring biodiversity for useful products, not a direct cause of loss, though unsustainable bioprospecting can be harmful).
4. (b) log S = log C + Z log A
5. (d) Advanced ex-situ conservation of biodiversity (Cryopreservation is a specific technique within ex-situ conservation). Option (b) is also correct but (d) is more specific to the technique mentioned. In exams, look for the most appropriate answer. If (d) wasn't an option, (b) would be correct. Let's refine option 5 to be less ambiguous. Let's rephrase Q5.

Revised MCQ 5:
Cryopreservation techniques involving storing gametes or tissues at very low temperatures (-196°C) fall under which category of conservation strategy?
(a) In-situ conservation
(b) Ex-situ conservation
(c) Ecological restoration
(d) Community-based conservation

Revised Answer Key:

1. (d)
2. (c)
3. (d)
4. (b)
5. (b) Ex-situ conservation
6. (c) Aravalli Hills (Sacred groves are found there, but it's not a designated global hotspot)
7. (c)
8. (b)
9. (b)
10. (b) In-situ conservation

Make sure you revise these notes thoroughly. Understand the concepts behind the facts and figures. Good luck with your preparation!