Chapter 13: Biodiversity and Conservation | Summary

According to the IUCN (2004), about 1.5 million species have been described so far. Robert May's conservative estimate places global species diversity at about 7 million. More than 70 per cent of all recorded species are animals; among them, insects are the most species-rich group, comprising over 70 per cent. The number of fungi species exceeds the combined total of fishes, amphibians, reptiles and mammals.

India covers only 2.4 per cent of the world's land area yet accounts for 8.1 per cent of global species diversity, making it one of the 12 mega diversity countries. About 45,000 plant species and nearly 90,000 animal species have been recorded. Applying Robert May's estimate that only 22 per cent of species have been described, India likely has over 1,00,000 undiscovered plant species and over 3,00,000 undiscovered animal species.

Species diversity is not uniformly distributed; it generally decreases from the equator towards the poles. Tropics (23.5° N to 23.5° S) harbour far more species than temperate or polar regions. Colombia, near the equator, has about 1,400 bird species; New York at 41° N has 105; Greenland at 71° N has only 56. India has over 1,200 bird species. The Amazonian rainforest hosts 40,000 plant species, 3,000 fish species, 1,300 bird species, 427 mammal species and more than 1,25,000 invertebrate species.

Three key hypotheses explain tropical species richness: (a) Tropical latitudes have been relatively undisturbed for millions of years, providing a long evolutionary time for speciation; (b) Tropical environments are less seasonal, more constant and predictable, promoting niche specialisation; (c) Higher solar energy availability in the tropics leads to greater productivity, which indirectly supports greater diversity.

Alexander von Humboldt observed that species richness increased with increasing explored area, but only up to a limit. For a wide variety of taxa, this relationship is a rectangular hyperbola, which on a logarithmic scale becomes a straight line described by: log S = log C + Z log A, where S = species richness, A = area, Z = slope (regression coefficient) and C = y-intercept.

For smaller areas, ecologists have found that the value of Z lies between 0.1 and 0.2, regardless of the taxonomic group or region. For very large areas such as entire continents, the slope is much steeper, with Z values ranging from 0.6 to 1.2. For example, frugivorous birds and mammals in tropical forests across different continents show a slope of 1.15. Steeper slopes indicate that species richness increases more rapidly with area at continental scales.

A stable community must not show excessive year-to-year variation in productivity, must be resistant or resilient to disturbances, and must resist invasions by alien species. David Tilman's long-term outdoor plot experiments showed that plots with more species had less year-to-year variation in total biomass and that increased diversity contributed to higher productivity.

Paul Ehrlich's 'rivet popper hypothesis' illustrates ecosystem functioning: an airplane (ecosystem) is held together by thousands of rivets (species). Removing rivets gradually weakens the structure. Loss of key species — those driving major ecosystem functions, like rivets on wings — poses the greatest threat. While we may not understand all mechanisms, rich biodiversity is essential for ecosystem health and human survival.

Human activities are the primary driver of accelerating biodiversity loss. The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years, including the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's Sea Cow and three tiger subspecies. Currently, 12 per cent of all bird species, 23 per cent of mammal species, 32 per cent of amphibian species and 31 per cent of gymnosperm species face extinction threats.

Although five episodes of mass extinction occurred in Earth's geological past, current extinction rates are 100 to 1,000 times faster than pre-human rates. Loss of biodiversity may lead to decline in plant production, lowered resistance to environmental perturbations, and increased variability in ecosystem processes. The four major causes — the 'Evil Quartet' — are habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions.

Habitat loss and fragmentation is the most important cause of species extinction. Tropical rainforests, once covering 14 per cent of Earth's land area, now cover only 6 per cent. The Amazon rainforest is being cleared for soya cultivation and beef cattle ranches. Fragmentation especially affects large mammals, birds requiring wide territories, and migratory animals. Over-exploitation is the second cause; species like Steller's sea cow and the passenger pigeon were hunted to extinction. Many marine fish populations are currently over-harvested.

Alien species invasions are a third cause. Introduced species like Nile perch in Lake Victoria led to the extinction of over 200 cichlid fish species. In India, invasive plants like Parthenium, Lantana, and water hyacinth (Eichhornia) threaten native species. The African catfish Clarias gariepinus, illegally introduced for aquaculture, threatens indigenous catfishes. Co-extinctions occur when a species becomes extinct and dependent species — such as parasites of a host fish or pollinators of a specific plant — also disappear due to obligatory relationships.

Arguments for conserving biodiversity fall into three categories. The narrowly utilitarian argument highlights direct economic benefits: food, firewood, fibre, construction materials, industrial products (tannins, dyes, resins, perfumes), and medicines. Over 25 per cent of drugs worldwide are derived from plants, and 25,000 plant species contribute to traditional medicines. Bioprospecting — exploring biodiversity for economically valuable products — promises further benefits.

The broadly utilitarian argument emphasises ecosystem services: the Amazon forest produces 20 per cent of atmospheric oxygen through photosynthesis; pollinators (bees, bumblebees, birds, bats) enable fruit and seed production; biodiversity provides flood control, pest regulation, climate moderation, and aesthetic pleasures. The ethical argument holds that every species has intrinsic value regardless of economic utility, and humans have a moral duty to preserve biodiversity for future generations.

In situ conservation involves protecting species in their natural habitat — saving the entire forest to save the tiger. Biodiversity hotspots are regions with very high species richness and high endemism that are also facing accelerated habitat loss. Initially 25 hotspots were identified; the number has grown to 34. Three hotspots — Western Ghats and Sri Lanka, Indo-Burma, and Himalaya — are in India. Though hotspots together cover less than 2 per cent of Earth's land area, strict protection could reduce ongoing mass extinctions by nearly 30 per cent.

India legally protects biodiversity-rich regions through 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. Sacred groves — tracts of forest protected by religious and cultural traditions — are found in the Khasi and Jaintia Hills of Meghalaya, Aravalli Hills of Rajasthan, Western Ghats of Karnataka and Maharashtra, and Sarguja, Chanda and Bastar areas of Madhya Pradesh. In Meghalaya, sacred groves serve as the last refuges for many rare and threatened plants.

Ex situ conservation involves removing threatened organisms from their natural habitat and maintaining them under protected conditions in zoological parks, botanical gardens or wildlife safari parks. Some species now extinct in the wild continue to survive in zoological parks. Modern ex situ techniques include cryopreservation of gametes, in vitro fertilisation, tissue culture propagation of plants, and seed banks where seeds of commercially important plants are stored for long periods.

Biodiversity conservation is a global responsibility. The Convention on Biological Diversity ('The Earth Summit') held in Rio de Janeiro in 1992 urged all nations to conserve biodiversity and use its benefits sustainably. At the World Summit on Sustainable Development in Johannesburg in 2002, 190 countries pledged to significantly reduce the rate of biodiversity loss by 2010 at global, regional and local levels.

Biodiversity — the variety of life at genetic, species and ecosystem levels — is essential for the health and stability of the biosphere and for human survival. Earth hosts an estimated 7 million species, of which only about 1.5 million have been described. Species richness is highest in the tropics due to greater evolutionary time, more stable environments, and higher solar energy. Current extinction rates, driven by habitat loss, over-exploitation, alien species invasions and co-extinctions, are 100–1,000 times faster than natural rates. Conservation, both in situ and ex situ, backed by international agreements, is the urgent need of the hour.

For CBSE board examinations, this chapter carries significant weightage. Students should thoroughly understand the three levels of biodiversity, patterns such as the latitudinal gradient and species-area relationship (including the Z value ranges), the Evil Quartet of biodiversity loss, and the distinction between in situ and ex situ conservation with examples. Numerical data — hotspot count (34), India's protected areas (14 biosphere reserves, 90 national parks, 448 sanctuaries), percentage of species threatened — are frequently tested. The rivet popper hypothesis and reasons for tropical diversity are common analytical questions.