Exercises

1. Name the three important components of biodiversity.

1. Genetic Diversity: Variation in genes within a single species.
2. Species Diversity: Variation in the number and variety of species in a region.
3. Ecological Diversity: Variation in ecosystems (deserts, forests, etc.) in a geographical area.

2. How do ecologists estimate the total number of species present in the world?

• By making a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects.
• The ratio obtained is then extrapolated to other groups of animals and plants to calculate a gross estimate of the total species on Earth.
• Robert May’s estimate of 7 million is considered a scientifically sound figure.

3. Give three hypotheses for explaining why tropics show greatest levels of species richness.

1. Time Hypothesis: Tropical latitudes have remained relatively undisturbed for millions of years, allowing more time for species diversification.
2. Climate Stability: Tropical environments are less seasonal and more predictable, promoting niche specialization.
3. Energy Hypothesis: Tropics receive more solar energy, leading to higher productivity and indirectly supporting greater diversity.

4. What is the significance of the slope of regression in a species – area relationship?

• The slope (Z) indicates how species richness increases with area.
• For small areas, Z values are similar (0.1 to 0.2) regardless of the taxon or region.
• For very large areas (continents), the slope is much steeper (0.6 to 1.2), indicating that species richness increases more rapidly as the area becomes immense.

5. What are the major causes of species losses in a geographical region?

• (The Evil Quartet):
  1. Habitat loss and fragmentation: Destroys homes and isolates populations.
  2. Over-exploitation: Harvesting beyond the capacity of the species to replenish itself.
  3. Alien species invasions: Non-native species outcompeting indigenous ones.
  4. Co-extinctions: Loss of one species leading to the loss of dependent species.

6. How is biodiversity important for ecosystem functioning?

• A diverse community is more stable, showing less year-to-year variation in productivity.
• It is more resistant or resilient to occasional natural or man-made disturbances.
• It provides resistance to invasions by alien species.
• According to the Rivet Popper Hypothesis, every species plays a specific role, and losing them weakens the entire system.

7. What are sacred groves? What is their role in conservation?

• Sacred groves are forest patches that are set aside and protected by religious or cultural traditions.
• Role: They act as the last refuges for many rare and threatened plants and animals, effectively serving as an indigenous form of in situ conservation.

8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?

• Plant roots bind the soil, preventing it from being washed away by water or wind (preventing erosion).
• Vegetation acts as a physical barrier and absorbs excess rainwater, reducing the speed and volume of runoff into rivers (controlling floods).

9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations?

• Animals have evolved more complex nervous systems and sensory organs, allowing them to adapt to diverse environments and niches.
• Mobility allows animals to escape unfavorable conditions and colonize new habitats.
• Diverse feeding habits and specialized ecological niches lead to greater speciation in animals.

10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?

• Situation: Pathogenic organisms that cause deadly human diseases, such as the Smallpox virus or Polio virus.
• Justification: The primary goal is to ensure the health and survival of the human race. Eradicating such pathogens eliminates suffering and death on a global scale.