NCERT Solutions

The three important components of biodiversity are:

1. Genetic Diversity: Diversity at the genetic level within a species (e.g., 50,000 genetically different strains of rice in India).
2. Species Diversity: Diversity at the species level (e.g., Western Ghats have greater amphibian species diversity than Eastern Ghats).
3. Ecological Diversity: Diversity at the ecosystem level (e.g., India has deserts, rain forests, mangroves, coral reefs, wetlands, etc.).

• Ecologists estimate the total number by making a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects.
• They extrapolate this ratio to other groups of animals and plants to calculate a gross estimate.
• According to the most widely accepted estimate by Robert May, the global species diversity is about 7 million.

1. Evolutionary Time: Speciation is a function of time. Unlike temperate regions subjected to frequent glaciations, tropical latitudes have remained relatively undisturbed for millions of years, allowing long evolutionary time for species diversification.
2. Stable Environment: Tropical environments are less seasonal, relatively more constant, and predictable. This promotes niche specialization and greater species diversity.
3. Solar Energy: There is more solar energy available in the tropics, which contributes to higher productivity, indirectly supporting greater diversity.

The slope of regression (represented by Z) indicates the relationship between species richness and area.

• In general, for small areas (like a country), the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or region.
• However, for very large areas like entire continents, the slope becomes much steeper (Z value 0.6 to 1.2). This signifies that species richness increases much more rapidly as the area increases on a continental scale.

These causes are collectively known as “The Evil Quartet”:

1. Habitat Loss and Fragmentation: The most important cause driving animals and plants to extinction (e.g., loss of Amazon rain forest).
2. Over-exploitation: Humans harvesting natural resources beyond sustainable limits (e.g., extinction of Steller’s sea cow, Passenger pigeon).
3. Alien Species Invasions: Introduction of non-native species causing decline of indigenous species (e.g., Water hyacinth, Nile perch).
4. Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct (e.g., Extinction of a host fish leads to extinction of its unique parasites).

• Stability: Ecosystems with more species are more stable. They show less year-to-year variation in total biomass (David Tilman’s experiments).
• Resilience: Rich biodiversity makes ecosystems more resistant to occasional disturbances (natural or man-made) and invasions by alien species.
• Rivet Popper Hypothesis: Proposed by Paul Ehrlich. Just as removing rivets (species) from an airplane (ecosystem) weakens it, loss of species (especially key species) threatens ecosystem safety and functioning.

• Sacred Groves: These are forest patches around places of worship that are held in high esteem by tribal communities. They are legally protected by communities due to religious beliefs.
• Role in Conservation: In these groves, nature is worshipped, and no trees are cut or animals killed. They serve as the last refuges for a large number of rare and threatened plants and animals in that area.
• Examples: Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka/Maharashtra).

This is achieved mainly by the Plant Cover (Forests and Vegetation):

• Soil Erosion Control: Plant roots bind the soil particles tightly, preventing topsoil from being washed away by wind or water.
• Flood Control: The forest canopy intercepts rain, breaking the force of falling water. The humus layer on the forest floor acts like a giant sponge, absorbing water and allowing it to percolate into the ground (recharging groundwater) rather than running off the surface rapidly, thus preventing flash floods.

Animals have achieved greater diversification due to:

1. Mobility: Unlike plants, animals are mobile. This allows them to move away from unfavorable conditions and find new habitats, leading to better survival and adaptation.
2. Complex Nervous System: Animals have evolved complex nervous and sensory systems, allowing them to receive stimuli and respond to environmental changes effectively (behavioral adaptation).
3. Co-evolution: Insects (the largest animal group) have co-evolved with angiosperms (plants) for pollination, leading to massive diversification in insect species.

Yes, humans deliberately try to eliminate certain species that are harmful or pathogenic.

• Disease-causing organisms: Smallpox virus (successfully eradicated), Polio virus (near eradication).
• Vectors: Mosquitoes (Vectors for Malaria, Dengue).

The extinction of these species is justified on the grounds of human welfare and health safety. These organisms cause immense suffering, mortality, and economic loss. Their elimination prevents deadly epidemics and improves the quality of human life.