Key Points

Biodiversity, a term popularised by Edward Wilson, describes the combined diversity at all levels of biological organisation, from macromolecules within cells to biomes.

Biodiversity exists at three main levels: Genetic diversity (variation within a species), Species diversity (variety of species in a region), and Ecological diversity (variety of ecosystems like deserts and rainforests).

According to IUCN (2004), slightly more than 1.5 million species have been described. However, a more scientifically sound estimate by Robert May places the global species diversity at about 7 million.

More than 70 percent of all recorded species are animals, while plants comprise no more than 22 percent. Among animals, insects are the most species-rich group, making up over 70 percent of the total.

Although India has only 2.4 percent of the world's land area, its share of the global species diversity is an impressive 8.1 percent, making it one of the 12 mega diversity countries.

Species diversity generally decreases as we move away from the equator towards the poles. Tropical regions harbour more species than temperate or polar areas.

Three main hypotheses explain the high biodiversity in tropics: a long, undisturbed evolutionary time; relatively constant and predictable environments; and greater availability of solar energy leading to higher productivity.

Alexander von Humboldt observed that species richness increases with explored area up to a limit. The relationship is described by the equation $\log S = \log C + Z \log A$, where S is species richness, A is area, and Z is the slope of the line.

The value of Z (slope) typically lies in the range of 0.1 to 0.2 for smaller regions. For very large areas like entire continents, the slope is much steeper, with Z values in the range of 0.6 to 1.2.

According to David Tilman's experiments, communities with more species tend to show less year-to-year variation in total biomass and exhibit higher productivity. Rich biodiversity is essential for ecosystem health and stability.

Proposed by Paul Ehrlich, this analogy compares an ecosystem to an airplane and species to rivets. Losing a few rivets (species) may not affect safety initially, but losing too many, especially key ones (like on the wings), makes the system dangerously weak.

The four major causes of biodiversity loss are: Habitat loss and fragmentation (most important), Over-exploitation, Alien species invasions, and Co-extinctions.

Reasons for conservation are grouped into three categories: Narrowly utilitarian (direct economic benefits), Broadly utilitarian (ecosystem services like pollination and oxygen production), and Ethical (every species has intrinsic value).

This approach involves protecting endangered species in their natural habitat. Examples include national parks, wildlife sanctuaries, biosphere reserves, and sacred groves.

These are regions with very high species richness and a high degree of endemism that are under threat. There are 34 hotspots globally, including three in India: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.

This approach involves protecting threatened organisms outside their natural habitat. Methods include zoological parks, botanical gardens, cryopreservation of gametes, in vitro fertilization, and seed banks.

Key global initiatives include 'The Earth Summit' (Rio de Janeiro, 1992) and 'The World Summit on Sustainable Development' (Johannesburg, 2002), which called for global commitment to reduce biodiversity loss.