Biodiversity and its Conservation — Notes

Biodiversity — a term popularised by the sociobiologist Edward Wilson — is the combined diversity at all levels of biological organisation.

• Genetic diversity: a single species may show high diversity at the genetic level over its distributional range. 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 about 1000 varieties of mango.
• Species diversity: 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 its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, has a greater ecosystem diversity than a Scandinavian country such as Norway.

How many species? According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million; Robert May placed the global species diversity at about 7 million. More than 70 percent of all recorded species are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) are no more than 22 percent. Among animals, insects are the most species-rich group, making up more than 70 percent — out of every 10 animals, 7 are insects. The number of fungus species is more than that of fishes, amphibians, reptiles and mammals combined.

India has only 2.4 percent of the world’s land area, but its share of global species diversity is an impressive 8.1 percent; it is one of the 12 mega-diversity countries, with nearly 45 000 species of plants and twice as many of animals.

Latitudinal gradients: species diversity decreases as we move away from the equator towards the poles. Tropics (23.5° N to 23.5° S) harbour more species than temperate or polar areas. Colombia, near the equator, has nearly 1400 species of birds, New York at 41° N has 105, and Greenland at 71° N only 56; India, largely in the tropics, has more than 1200. A tropical forest such as the Amazon has the greatest biodiversity on Earth (more than 40 000 plant species, 3000 fishes, 1300 birds, 427 mammals, 427 amphibians, 378 reptiles and more than 125 000 invertebrates). Reasons proposed: (a) the tropics have remained relatively undisturbed for millions of years, giving long evolutionary time for diversification; (b) tropical environments are less seasonal, relatively more constant and predictable, promoting niche specialisation; (c) there is more solar energy, contributing to higher productivity.

Species–area relationship: Alexander von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit. On a normal scale the relation is a rectangular hyperbola; on a logarithmic scale it is a straight line described by log S = log C + Z log A (S = species richness, A = area, Z = slope of the line (regression coefficient), C = Y-intercept), that is, S = CA^Z. The value of Z lies in the range 0.1 to 0.2, regardless of taxonomic group or region; for very large areas such as entire continents the slope is much steeper, 0.6 to 1.2 (for frugivorous birds and mammals in tropical forests of different continents, about 1.15).

Importance of species diversity: communities with more species tend to be more stable — David Tilman’s long-term 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: an ecosystem is like an aeroplane whose parts are joined by thousands of rivets (species). Removing a few rivets from the seats or windows (loss of minor species) may not affect flight safety, but as more rivets are removed the plane becomes dangerously weak; loss of rivets on the wings (key species that drive major ecosystem functions) is a serious threat.

Why conserve biodiversity?

• Narrowly utilitarian: humans derive countless direct economic benefits — food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines; more than 25 percent of drugs on the market are derived from plants; nations exploring molecular, genetic and species-level diversity for economically important products practise bioprospecting.
• Broadly utilitarian: biodiversity provides ecosystem services — the Amazon forest is estimated to produce through photosynthesis about 20 percent of the total oxygen in the Earth’s atmosphere; pollination by bees, bumblebees, birds and bats; aesthetic pleasures.
• Ethical: every species has an intrinsic value, even if it has no economic value to us; we have a moral duty to care for its well-being and pass on our biological legacy to future generations.

The colonisation of tropical Pacific islands by humans is said to have led to the extinction of more than 2000 species of native birds. The IUCN Red List (2004) documents the extinction of 784 species (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); in the last twenty years alone, 27 species have disappeared. More than 15 500 species worldwide face the threat of extinction, including 12 percent of birds, 23 percent of mammals, 32 percent of amphibians and 31 percent of gymnosperms. Loss of biodiversity in a region may lead to a decline in plant production, lowered resistance to environmental perturbations such as drought, and increased variability in ecosystem processes.

Causes — the “evil quartet”:

1. Habitat loss and fragmentation — the most important cause. Tropical rain forests once covered more than 14 percent of the Earth’s land surface but now cover no more than 6 percent; the Amazon rain forest (“lungs of the planet”) is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle. When large habitats are broken into small fragments, mammals and birds needing large territories and migratory animals are badly affected.
2. Over-exploitation — many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to over-exploitation by humans; many marine fish populations are over-harvested.
3. Alien species invasions — when alien species are introduced, some turn invasive and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria (East Africa) led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish. Invasive weeds such as carrot grass (Parthenium), Lantana and water hyacinth (Eichhornia) threaten native species; the illegal introduction of the African catfish Clarias gariepinus for aquaculture threatens indigenous catfishes.
4. Co-extinctions — when a species becomes extinct, plant and animal species obligately associated with it also become extinct: when a host fish species becomes extinct, its unique assemblage of parasites meets the same fate; co-evolved plant–pollinator mutualisms are another example.

In-situ (on site) conservation protects species in their natural habitat, together with the whole ecosystem.

Biodiversity hotspots — regions with very high levels of species richness and high degree of endemism (species confined to that region). Initially 25 hotspots were identified; the number now stands at 34. Three of them — Western Ghats and Sri Lanka, Indo-Burma, and the Himalaya — cover India’s exceptionally high biodiversity regions. Although all the hotspots together cover less than 2 percent of the Earth’s land area, they harbour an extremely high number of species; strict protection of these hotspots could reduce the ongoing mass extinctions by almost 30 percent.

Protected areas in India: ecologically unique and biodiversity-rich regions are legally protected as biosphere reserves, national parks and wildlife sanctuaries. A biosphere reserve has a strictly protected core zone, a surrounding buffer zone where limited activities (research, education, tourism) are permitted, and an outer transition zone where people live and use resources sustainably. National parks protect whole ecosystems strictly; sanctuaries protect particular species while allowing some human activities.

Sacred groves — India has a history of religious and cultural traditions that emphasised protection of nature. In many cultures, tracts of forest were set aside, and all the trees and wildlife within them were venerated and given total protection. Such sacred groves are found in the Khasi and Jaintia Hills in Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghat regions of Karnataka and Maharashtra, and the Sarguja, Chanda and Bastar areas of Madhya Pradesh. In Meghalaya, sacred groves are the last refuges for a large number of rare and threatened plants.

Ramsar sites — wetlands of international importance designated under the Ramsar Convention (signed at Ramsar, Iran, in 1971) for the conservation and wise use of wetlands.

Red Data Book — maintained by the IUCN (International Union for Conservation of Nature), it documents threatened species and classifies them into categories such as extinct, extinct in the wild, critically endangered, endangered and vulnerable, guiding conservation priorities.

Ex-situ (off site) conservation protects threatened animals and plants by taking them out of their natural habitat and placing them in special settings where they can be protected and given special care.

• Zoological parks, botanical gardens and wildlife safari parks serve this purpose; many animals that have become extinct in the wild continue to be maintained in zoos.
• Captive breeding of endangered species, with release into the wild where possible.
• Cryopreservation — gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques (storage in liquid nitrogen at −196 °C).
• In vitro fertilisation of eggs, and tissue culture methods for propagating plants.
• Seed banks — seeds of different genetic strains of commercially important plants can be kept for long periods. Ex-situ methods complement, but cannot replace, the protection of natural habitats.

Biodiversity knows no political boundaries, and conservation is a collective responsibility of all nations.

• The Earth Summit, held in Rio de Janeiro in 1992, called upon all nations to take appropriate measures for the conservation of biodiversity and the sustainable utilisation of its benefits; it produced the Convention on Biological Diversity (CBD), which also seeks fair and equitable sharing of benefits from genetic resources.
• The World Summit on Sustainable Development, held in Johannesburg, South Africa, in 2002: 190 countries pledged their commitment to achieve, by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and local levels.