Biodiversity is the term popularised by the sociobiologist Edward Wilson to describe the combined diversity at all levels of biological organisation. The three most important levels are:

• Genetic Diversity: A single species might show high diversity at the genetic level over its distributional range. For example, the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges shows variation in the potency and concentration of the active chemical reserpine. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.

   

• Species Diversity: The diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.

   

• Ecological Diversity: At the ecosystem level, India (with deserts, rain forests, mangroves, coral reefs, etc.) has a greater ecosystem diversity than a Scandinavian country like Norway.

   

Global and Indian Biodiversity Estimates:

According to the IUCN (2004), the total number of plant and animal species described is slightly more than 1.5 million. A more conservative and scientifically sound estimate by Robert May places the global species diversity at about 7 million.

• Animals make up more than 70% of all species, while plants comprise no more than 22%. Among animals, insects are the most species-rich group (making up >70%).

   

• The number of fungi species is more than the combined total of fishes, amphibians, reptiles, and mammals.

   

• India has only 2.4% of the world’s land area, but its share of global species diversity is an impressive 8.1%. This makes India one of the 12 mega diversity countries of the world.

Patterns of Biodiversity:

1. Latitudinal Gradients: Species diversity generally decreases as we move away from the equator towards the poles. Tropics harbour more species than temperate or polar areas. The Amazonian rain forest in South America has the greatest biodiversity on earth.

   • Reasons for high tropical diversity:

     • Speciation is a function of time: Tropics have remained relatively undisturbed for millions of years, allowing for a long evolutionary time.

        

     • Stable Environment: Tropical environments are less seasonal, relatively more constant, and predictable, promoting niche specialisation.

        

     • Solar Energy: More solar energy is available in the tropics, contributing to higher productivity.

        

2. Species-Area Relationships: German naturalist Alexander von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit. The relationship is a rectangular hyperbola described by the equation log S = log C + Z log A, where S is Species richness, A is Area, Z is slope of the line (regression coefficient), and C is Y-intercept .

   • The value of Z lies in the range of 0.1 to 0.2 for most groups. However, for very large areas like entire continents, the slope is steeper (Z = 0.6 to 1.2). For frugivorous birds and mammals in tropical forests, the slope is 1.15.

      
     Importance of Species Diversity:  David Tilman’s experiments showed that plots with more species showed less year-to-year variation in biomass and that increased diversity contributed to higher productivity.

• Rivet Popper Hypothesis: Proposed by Stanford ecologist Paul Ehrlich. He compared the ecosystem to an airplane and species to rivets. Removing rivets (extinction) may not initially affect flight safety, but losing key rivets on the wings (key species that drive major ecosystem functions) is a serious threat .

Loss of Biodiversity: 

The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years. Recent extinctions include the Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s Sea Cow (Russia), and three subspecies of tiger (Bali, Javan, Caspian). Amphibians appear to be more vulnerable to extinction.

The Evil Quartet (Causes of Biodiversity Loss):

1. Habitat Loss and Fragmentation: The most important cause. The Amazon rain forest (lungs of the planet) is being cut for cultivating soya beans or raising beef cattle. 

2. Over-exploitation: “Need” turning to “greed” led to the extinction of Steller’s sea cow and passenger pigeon.

3. Alien Species Invasions: The Nile perch introduced into Lake Victoria led to the extinction of >200 species of cichlid fish. Invasive weeds like carrot grass (Parthenium), Lantana, and water hyacinth (Eicchornia) pose threats. The illegal introduction of African catfish (Clarias gariepinus) threatens indigenous catfishes.

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., host fish and its parasites, coevolved plant-pollinator mutualism). 

Biodiversity Conservation:

• Why Conserve?

  • Narrowly Utilitarian: Humans derive direct economic benefits (food, firewood, fibre, industrial products, medicines). More than 25% of drugs are derived from plants.

  • Broadly Utilitarian: Ecosystem services. Amazon forest produces 20% of the earth’s oxygen. Pollination is another crucial service.

  • Ethical: Every species has an intrinsic value, and we have a moral duty to care for them.

     

• How to Conserve?

  • In situ (On site) Conservation: Protecting the whole ecosystem.

    • Biodiversity Hotspots: Regions with very high levels of species richness and high degree of endemism (species confined to that region). There are 34 hotspots in the world. Three cover India: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.

    • Protected Areas: India has 14 biosphere reserves, 90 national parks, and 448 wildlife sanctuaries.

    • Sacred Groves: Tracts of forest set aside where all trees and wildlife are venerated. Found in Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka/Maharashtra), and Sarguja, Chanda, Bastar areas (Madhya Pradesh).

  • Ex situ (Off site) Conservation: Threatened animals and plants are taken out from their natural habitat and placed in special settings (Zoological parks, botanical gardens, wildlife safari parks).

    • Advanced methods include Cryopreservation of gametes, in vitro fertilization, tissue culture, and Seed banks. 

International Conventions:

• The Earth Summit (1992): Held in Rio de Janeiro, called for conservation of biodiversity and sustainable utilisation.

• World Summit on Sustainable Development (2002): Held in Johannesburg, South Africa; 190 countries pledged to significantly reduce the rate of biodiversity loss by 2010.