Biology: Class 12 — Chapter 13: Biodiversity and Conservation

• Genetic diversity: High diversity shown by a single species at the genetic level over its distributional range. E.g., 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: Diversity at the species level. E.g., the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
• Ecological diversity: Diversity at the ecosystem level. E.g., India, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, has a greater ecosystem diversity than a Scandinavian country like Norway.

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

• More than 70 per cent of all recorded species are animals, while plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) comprise no more than 22 per cent of the total.
• Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total (7 out of every 10 animals on Earth are insects).
• The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles, and mammals.
• Prokaryotic species numbers are not definitively known because conventional taxonomic methods are not suitable for identifying microbial species, and many species are not culturable under laboratory conditions.
• India's Diversity: India has only 2.4 per cent of the world's land area, but its share of global species diversity is an impressive 8.1 per cent, making it one of the 12 mega diversity countries of the world. Nearly 45,000 species of plants and twice as many animals have been recorded from India.

• Latitudinal gradients: Species diversity is not uniform but decreases as we move away from the equator towards the poles. Tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas. E.g., Colombia near the equator has nearly 1,400 species of birds, while New York at 41° N has 105, and Greenland at 71° N has only 56. The largely tropical Amazonian rain forest in South America has the greatest biodiversity on Earth.
• Hypotheses for Greater Tropical Diversity:
  1. Speciation is a function of time; unlike temperate regions subjected to frequent glaciations, tropical latitudes remained relatively undisturbed for millions of years.
  2. Tropical environments are less seasonal, relatively more constant, and predictable, promoting niche specialisation.
  3. More solar energy is available in the tropics, contributing to higher productivity.
• Species-Area relationships: German naturalist and geographer Alexander von Humboldt observed that within a region, species richness increases with increasing explored area, but only up to a limit. On a logarithmic scale, the relationship is a straight line described by the equation:$$\log S = \log C + Z \log A$$Where $S$ = Species richness, $A$ = Area, $Z$ = slope of the line (regression coefficient), and $C$ = Y-intercept. The value of $Z$ lies in the range of 0.1 to 0.2 regardless of taxonomic group or region, but for very large areas like entire continents, the slope is much steeper ($Z$ values in the range of 0.6 to 1.2).

Communities with more species tend to be more stable than those with fewer species. A stable community should not show too much variation in productivity from year to year, must be resistant or resilient to occasional disturbances, and must be resistant to invasions by alien species.

• David Tilman's Experiments: Long-term ecosystem experiments using outdoor plots showed that plots with more species showed less year-to-year variation in total biomass and contributed to higher productivity.
• Rivet Popper Hypothesis: Proposed by Stanford ecologist Paul Ehrlich. It compares the ecosystem to an airplane and its species to rivets. Popping rivets (causing species extinction) may not affect flight safety (ecosystem function) initially, but as more rivets are removed, the plane becomes dangerously weak. Loss of key rivets on the wings (key species driving major ecosystem functions) is a more serious threat than loss of rivets inside the cabin.

The biological wealth of our planet has been declining rapidly due to human activities. The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) 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).

The Evil Quartet (Four Major Causes of Biodiversity Loss):

1. Habitat loss and fragmentation: The most important cause driving extinction. E.g., tropical rain forests once covered 14% of Earth's land surface but now cover no more than 6%. The Amazon rain forest is being cut and cleared for cultivating soya beans or grasslands for raising beef cattle. Fragmentation of large habitats badly affects mammals and birds requiring large territories.
2. Over-exploitation: When human 'need' turns to 'greed', leading to over-exploitation of natural resources. E.g., Steller's sea cow and passenger pigeon.
3. Alien species invasions: Introduction of non-native species causes decline or extinction of indigenous species. E.g., the Nile perch introduced into Lake Victoria led to the extinction of more than 200 species of cichlid fish. Invasive weeds like carrot grass (Parthenium), Lantana, and water hyacinth (Eichhornia) cause severe damage. The illegal introduction of the African catfish Clarias gariepinus poses a threat to indigenous catfishes.
4. Co-extinctions: When a species becomes extinct, the plant and animal species obligatorily associated with it also become extinct. E.g., coevolved plant-pollinator mutualisms.

• Narrowly utilitarian: Humans derive direct economic benefits from nature, including food, firewood, fibre, construction material, industrial products, and medicines. More than 25% of drugs are derived from plants. Bioprospecting (exploring molecular, genetic, and species-level diversity for products of economic importance) offers immense potential benefits.
• Broadly utilitarian: Biodiversity plays a major role in ecosystem services. E.g., the Amazon forest produces 20% of the total oxygen in Earth's atmosphere. Other services include pollination (by bees, birds, bats) and aesthetic pleasures.
• Ethical: Every species has an intrinsic value, and humans have a moral duty to care for their well-being and pass on the biological legacy in good order.

• In situ conservation (On-site): Protecting the whole ecosystem to save biodiversity.
  • Biodiversity hotspots: Regions with very high levels of species richness and high degree of endemism (species confined to that region and not found anywhere else). There are 34 hotspots globally; three cover India's high biodiversity regions: 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 and given total protection. E.g., Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra, and Sarguja, Chanda, and Bastar areas of Madhya Pradesh.
• Ex situ Conservation (Off-site): Threatened animals and plants are taken out of their natural habitats and placed in special settings for protection and care.
  • Includes zoological parks, botanical gardens, and wildlife safari parks.
  • Advanced techniques include cryopreservation of gametes in viable and fertile conditions, in vitro fertilisation, tissue culture propagation, and seed banks.
• International Initiatives:
  • The Earth Summit: Held in Rio de Janeiro in 1992, calling upon nations to take measures for conservation and sustainable utilisation of biodiversity.
  • World Summit on Sustainable Development: Held in Johannesburg in 2002, where 190 countries pledged to achieve a significant reduction in the current rate of biodiversity loss by 2010.