Biodiversity and Conservation: CBSE Class 12 Biology Chapter 13 Revision Notes

Biodiversity describes the combined heterogeneity of life at all levels of biological organization, from macromolecules within cells to entire biomes. Popularized by sociobiologist Edward Wilson, it is categorized into genetic, species, and ecological levels. While over 1.5 million species are documented, global estimates suggest around 7 million exist, with many facing extinction due to human activities. Biodiversity is highest in the tropics and decreases toward the poles. Conservation is critical for survival and involves in situ (on-site) and ex situ (off-site) strategies to protect our biological legacy.

1. Levels of Biological Diversity

Biodiversity is not limited to species; it exists at three primary levels:

2. Global Species Richness & Patterns

• Total Species: The IUCN (2004) records >1.5 million species; however, Robert May estimates the actual global diversity at 7 million.
• Taxonomic Proportions:
• Animals make up >70% of all recorded species; Plants (including fungi) comprise ~22%.
• Insects are the most species-rich group, accounting for 7 out of every 10 animals.
• The number of Fungi species exceeds the combined total of fishes, amphibians, reptiles, and mammals.
• India's Biodiversity: India holds 8.1% of global species diversity despite having only 2.4% of the world's land area, making it one of the 12 mega-diversity countries.

Latitudinal Gradients

Species diversity generally decreases as we move from the equator toward the poles.

• Why are Tropics more diverse?
• Time: Tropics remained undisturbed for millions of years, allowing more time for speciation (unlike glaciated temperate regions).
• Environment: Tropical climates are less seasonal, more constant, and predictable, promoting niche specialization.
• Solar Energy: Higher solar energy leads to higher productivity, indirectly supporting greater diversity.

3. Species-Area Relationship

Observed by Alexander von Humboldt, this concept states that species richness increases with increasing explored area, but only up to a limit.

• Mathematical Equation:
• log S=log C + Z log A
• S = Species richness; A = Area; Z = Regression coefficient (slope); C = Y-intercept.
• Z-Values:
• For small areas (e.g., a single state): 0.1 to 0.2.
• For large areas (e.g., entire continents): 0.6 to 1.2.

4. Loss of Biodiversity: "The Evil Quartet"

The current "Sixth Extinction" is occurring at a rate 100 to 1,000 times faster than pre-human times. The four major causes are:

• Habitat Loss and Fragmentation: The primary cause; e.g., Tropical rain forests have declined from 14% to 6% of Earth's land. The Amazon rain forest is being cleared for soya beans and cattle.
• Over-exploitation: When "need" turns to "greed"; e.g., extinction of Steller's sea cow and passenger pigeon.
• Alien Species Invasions: Non-native species outcompete indigenous ones; e.g., Nile perch in Lake Victoria, or invasive weeds like Parthenium (carrot grass) and Eicchornia (water hyacinth).
• Co-extinctions: When a host or partner species dies out, the species obligatorily associated with it also goes extinct (e.g., plant-pollinator mutualism).

5. Biodiversity Conservation

Comparison of Conservation Approaches

• Biodiversity Hotspots: Regions with very high species richness and endemism (species found nowhere else). There are 34 globally; three cover India: Western Ghats/Sri Lanka, Indo-Burma, and Himalaya.
• Sacred Groves: Forest tracts protected through religious/cultural traditions (e.g., Khasi and Jaintia Hills in Meghalaya).

Frequently Asked Questions:

1. What is Paul Ehrlich's 'Rivet Popper Hypothesis'?
   
   This analogy compares an ecosystem to an airplane and its species to rivets; initially, losing a few "rivets" (species) might not affect safety, but losing "key rivets" on the wings (key species) eventually causes the entire system to crash.
   
   
2. Why are "Broadly Utilitarian" arguments used for conservation?
   
   These arguments focus on indispensable ecosystem services that nature provides for free, such as the Amazon forest producing 20% of Earth's oxygen, pollination by insects, and the aesthetic/cultural value of nature.
   
   
3. What was the outcome of the 1992 Earth Summit?
   
   Held in Rio de Janeiro, the Convention on Biological Diversity (Earth Summit) called upon all nations to take appropriate measures for the conservation of biodiversity and the sustainable utilization of its benefits.