Class 12 Biology Notes Chapter 15 (Biodiversity and conservation) – Biology Book

Detailed Notes with MCQs of a very crucial chapter for your exams – Chapter 15: Biodiversity and Conservation. This topic is not only important biologically but also holds significant relevance in current environmental discussions, making it a favourite for examiners.

Chapter 15: Biodiversity and Conservation - Detailed Notes

1. What is Biodiversity?

• The term 'biodiversity' was popularized by sociobiologist Edward Wilson.
• It refers to the variety and variability of life forms existing at all levels of biological organisation.
• Levels of Biodiversity:
  • Genetic Diversity: Variation in genes within a species. This allows species to adapt to environmental changes. Example: Different strains of rice or mangoes in India; Rauwolfia vomitoria growing in different Himalayan ranges shows variation in the potency and concentration of the active chemical (reserpine).
  • Species Diversity: Variety of different species within a region. Measured by:
    • Species Richness: Number of species per unit area.
    • Species Evenness: Relative abundance of different species. Example: Western Ghats have greater amphibian species diversity than Eastern Ghats.
  • Ecological Diversity: Variety of ecosystems (like deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, alpine meadows) in a region. Example: India has a greater ecosystem diversity than a Scandinavian country like Norway.

2. Magnitude of Biodiversity (Global and India)

• According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million.
• Robert May's Global Estimate: A more conservative and scientifically sound estimate places the global species diversity at about 7 million. He based this on extrapolating species richness ratios of insects between temperate and tropical regions.
• Distribution: More than 70% of all recorded species are animals, while plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) account for no more than 22%. Among animals, insects are the most species-rich taxonomic group, making up more than 70% of the total. Fungi species outnumber the combined total of fishes, amphibians, reptiles, and mammals.
• Prokaryotes: Conventional taxonomic methods are inadequate for identifying microbial species; many cannot be cultured. If we used biochemical or molecular criteria, their diversity might run into millions.
• India's Biodiversity:
  • India has only 2.4% of the world's land area.
  • It 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.
  • Applying May's global estimates, India might have 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.
  • Examples: Colombia (near equator) has nearly 1,400 bird species; New York (41° N) has 105 species; Greenland (71° N) has only 56 species. A forest in Ecuador (tropical) has up to 10 times as many vascular plant species as a forest of equal area in the Midwest of the USA (temperate). Amazonian rainforest has the greatest biodiversity on earth.
  • Reasons for Higher Tropical Biodiversity (Hypotheses):
    • 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, more constant environment: Tropics have relatively constant and predictable environments, promoting niche specialisation and leading to greater species diversity.
    • More solar energy: Higher solar energy availability contributes to higher productivity, which might support greater diversity indirectly.
• Species-Area Relationships: Within a region, species richness increases with increasing explored area, but only up to a limit.
  • Alexander von Humboldt observed this relationship.
  • The relationship is a rectangular hyperbola on a normal scale and a straight line on a logarithmic scale.
  • Equation: log S = log C + Z log A
    • S = Species richness
    • A = Area
    • Z = Slope of the line (regression coefficient)
    • C = Y-intercept
  • Value of Z: Generally lies between 0.1 to 0.2 regardless of taxonomic group or region (e.g., plants in Britain, birds in California). However, for very large areas like entire continents, the slope (Z value) is much steeper, ranging from 0.6 to 1.2. Example: Frugivorous birds and mammals in tropical forests of different continents have a Z value of 1.15.

4. Importance of Species Diversity to the Ecosystem

• Ecologists believe 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 showed that plots with more species showed less year-to-year variation in total biomass (increased stability). Increased diversity contributed to higher productivity.
• Rivet Popper Hypothesis (Paul Ehrlich): Compares an ecosystem to an airplane and species to rivets holding it together. Losing a few rivets (species) might not affect flight safety initially, but as more are lost, the plane becomes dangerously weak. Loss of key species ('rivets on the wings', analogous to keystone species) is obviously a more serious threat than loss of a few less critical species.

5. Loss of Biodiversity

• Accelerated rates of species extinction are largely due to human activities.

• IUCN Red List (2004): Documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) in the last 500 years.

• Recent Extinctions: Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s Sea Cow (Russia), and three subspecies of tiger (Bali, Javan, Caspian).

• More than 15,500 species worldwide are facing the threat of extinction. Currently, 12% birds, 23% mammals, 32% amphibians, and 31% gymnosperm species face this threat.

• Amphibians appear to be more vulnerable to extinction.

• The current extinction rate is estimated to be 100 to 1,000 times faster than pre-human times. If trends continue, nearly half of all species might be wiped out within the next 100 years.

• Consequences of Biodiversity Loss: Decline in plant production, lowered resistance to environmental perturbations (like drought), increased variability in ecosystem processes (like plant productivity, water use, pest and disease cycles).

• Causes of Biodiversity Loss ("The Evil Quartet"):

  • Habitat Loss and Fragmentation: Most important cause. Due to deforestation, urbanization, mining, conversion of forests to agriculture (e.g., Amazon rainforest cleared for soybean cultivation or cattle ranching). Fragmentation breaks large habitats into smaller ones, affecting animals requiring large territories and migratory species.
  • Over-exploitation: Humans have always depended on nature, but 'need' turning to 'greed' leads to over-exploitation. Examples: Steller’s sea cow, Passenger pigeon. Many marine fish populations are overharvested.
  • Alien Species Invasions: When alien (exotic/non-native) species are introduced, some turn invasive and cause decline or extinction of indigenous species. Examples:
    • Nile Perch introduced into Lake Victoria (East Africa) led to the extinction of >200 species of cichlid fish.
    • Invasive weeds like Carrot grass (Parthenium), Lantana, and Water hyacinth (Eichhornia) pose threats to native species.
    • Illegal introduction of African catfish (Clarias gariepinus) for aquaculture is posing a threat to indigenous catfishes in Indian rivers.
  • Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. Example: Extinction of a host fish leads to extinction of its unique parasites; coevolved plant-pollinator mutualism where extinction of one leads to the extinction of the other.

6. Biodiversity Conservation

• Why Conserve Biodiversity?

  • Narrowly Utilitarian Arguments: Humans derive direct economic benefits. Food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes), medicines. More than 25% of drugs are derived from plants. Bioprospecting: exploring molecular, genetic, and species-level diversity for products of economic importance.
  • Broadly Utilitarian Arguments: Biodiversity plays a major role in many ecosystem services. Examples:
    • Oxygen production (Amazon forest estimated to produce 20% of total oxygen).
    • Pollination (bees, bumblebees, birds, bats).
    • Climate regulation.
    • Flood and erosion control.
    • Nutrient cycling.
    • Aesthetic pleasures, recreation.
  • Ethical Arguments: Every species has an intrinsic value, even if not of direct economic use to us. We have a moral duty to care for their well-being and pass on our biological legacy intact to future generations.

• How to Conserve Biodiversity? (Strategies)

  • In situ (On-site) Conservation: Protecting endangered species in their natural habitat. Preferred strategy for conserving the entire ecosystem.
    • Biodiversity Hotspots: Regions with very high levels of species richness and high degree of endemism (species confined to that region and not found anywhere else).
      • Criteria: Must have at least 1500 species of vascular plants (>0.5% of world total) as endemics, and must have lost at least 70% of its original habitat.
      • Identified by Norman Myers. Initially 25 hotspots, now 34 hotspots identified globally.
      • These hotspots cover less than 2% of Earth's land area but harbour an extremely high number of species; protection could reduce ongoing mass extinctions by almost 30%.
      • India's Hotspots: Western Ghats & Sri Lanka, Indo-Burma, Himalaya. (Note: Sundaland is sometimes mentioned in context, but these three are primary).
    • Protected Areas: India has >100 National Parks, >500 Wildlife Sanctuaries, and 18 Biosphere Reserves.
    • Sacred Groves: Tracts of forest set aside, protected by local communities around places of worship. Found in Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghat regions (Karnataka, Maharashtra), Sarguja, Chanda, Bastar areas (Madhya Pradesh). Often the last refuges for many rare and threatened plants.
  • Ex situ (Off-site) Conservation: Protecting threatened animals and plants outside their natural habitat.
    • Zoological Parks (Zoos): Maintain threatened species, captive breeding programs.
    • Botanical Gardens: Maintain collections of living plants.
    • Wildlife Safari Parks: Larger areas allowing more natural behaviour than traditional zoos.
    • Cryopreservation: Preservation of gametes, tissues, embryos, seeds of threatened species in viable and fertile condition for long periods using liquid nitrogen (-196°C). Includes gene banks and seed banks. Seeds of commercially important plants can be kept for long periods in seed banks (using low temperature and reduced moisture). Orthodox seeds can be stored like this, but recalcitrant seeds cannot.

7. International Efforts for Conservation

• The Earth Summit (Rio de Janeiro, 1992): Called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilization of its benefits. (Convention on Biological Diversity - CBD).
• The World Summit on Sustainable Development (Johannesburg, South Africa, 2002): 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. (Target was not met).

Multiple Choice Questions (MCQs)

1. Which of the following represents the level of biodiversity dealing with the variety of ecosystems like deserts, rainforests, and mangroves?
   a) Genetic diversity
   b) Species diversity
   c) Ecological diversity
   d) Community diversity

2. According to Robert May's global estimate, the total number of species on Earth is approximately:
   a) 1.5 million
   b) 7 million
   c) 20 million
   d) 50 million

3. The pattern of biodiversity that shows a general decrease in species richness from the equator towards the poles is known as:
   a) Species-Area relationship
   b) Altitudinal gradient
   c) Latitudinal gradient
   d) Longitudinal gradient

4. In the species-area relationship equation, log S = log C + Z log A, what does 'Z' represent?
   a) Y-intercept
   b) Species richness
   c) Area
   d) Slope of the line (regression coefficient)

5. Which hypothesis, proposed by Paul Ehrlich, compares species to rivets in an airplane to explain the importance of species richness for ecosystem stability?
   a) Gaia Hypothesis
   b) Rivet Popper Hypothesis
   c) Red Queen Hypothesis
   d) Intermediate Disturbance Hypothesis

6. Which of the following is considered the MOST important cause driving animals and plants to extinction (part of the 'Evil Quartet')?
   a) Over-exploitation
   b) Alien species invasions
   c) Habitat loss and fragmentation
   d) Co-extinctions

7. The introduction of Nile Perch into Lake Victoria led to the extinction of numerous species of:
   a) Cichlid fish
   b) Amphibians
   c) Reptiles
   d) Aquatic birds

8. Which of the following is an example of in situ conservation strategy?
   a) Zoological Park
   b) Botanical Garden
   c) Biosphere Reserve
   d) Cryopreservation

9. Biodiversity hotspots are characterized by:
   a) Low species richness and high endemism
   b) High species richness and low endemism
   c) High species richness and high degree of endemism
   d) Low species richness and low endemism

10. Cryopreservation of gametes of threatened species in liquid nitrogen (-196°C) is an example of:
    a) In situ conservation
    b) Ex situ conservation
    c) Sacred groves protection
    d) Community reserve management

Answer Key for MCQs:

1. c) Ecological diversity
2. b) 7 million
3. c) Latitudinal gradient
4. d) Slope of the line (regression coefficient)
5. b) Rivet Popper Hypothesis
6. c) Habitat loss and fragmentation
7. a) Cichlid fish
8. c) Biosphere Reserve
9. c) High species richness and high degree of endemism
10. b) Ex situ conservation

Make sure you revise these points thoroughly. Pay special attention to the examples, numbers (like percentage of land area, species share, Z values, number of hotspots), the 'Evil Quartet', and the differences between in situ and ex situ conservation methods. Good luck with your preparation!