Biodiversity is the diversity of biological organisation ranging from cellular macromolecules to biomes.
Edward Wilson popularized the term ‘biodiversity’.
LEVELS OF BIODIVERSITY
1. Genetic diversity: Diversity shown by a single species at genetic level. E.g. Rauwolfia vomitoria (Himalaya) shows genetic variation in the potency & concentration of the chemical reserpine. India has more than 50,000 different strains of rice and 1000 varieties of mango.
2. Species diversity: Diversity at species level. E.g. Western Ghats have greater amphibian species than Eastern Ghats.
3. Ecological diversity: Diversity at ecosystem level.
E.g. In India, deserts, rain forests, mangroves, coral reefs, wet lands, estuaries & alpine meadows are seen.
TOTAL NUMBER OF SPECIES ON EARTH (GLOBAL SPECIES DIVERSITY)
o According to IUCN (2004): More than 1.5 million species described so far.
o According to Robert May’s Global estimate: About 7 million (considering the species to be discovered in the tropics. i.e. only 22% of the total species have been recorded so far).
o Animals are more diverse (above 70%) than plants including Plantae and Fungi (22%).
o Most species rich taxonomic group among animals: Insects (70%, i.e. out of every 10 animals, 7 are insects).
o Number of fungi species is more than the combined total of the species of fishes, amphibians, reptiles & mammals.
o Biologists are not sure about total number of prokaryotic species because conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions.
o India has only 2.4% of world’s land area, but has 8.1% of the species diversity. India is one of the 12 mega diversity countries of the world. Nearly 45,000 species of plants and twice as many of animals have been recorded from India.
o Applying May’s global estimates, India would have more than 1 lakh plant species and 3 lakh animal species.
PATTERNS OF BIODIVERSITY
i. Latitudinal gradients
- Species diversity decreases from the equator to the poles.
- Tropics (latitudinal range of 23.5o N to 23.5o S) have more species than temperate or polar areas.
o Colombia (near equator) has about 1400 species of birds.
o New York (41o N): 105 species of birds
o Greenland (71o N): 56 species of birds
o India (tropical latitudes): > 1200 species
- Equador (Tropical forest region) has up to 10 times as many species of vascular plants as a forest of equal area in Midwest of USA (temperate region).
- Greatest biodiversity on earth: Tropical Amazonian rain forest in South America (> 40000 species of plants, 3000 fishes, 1300 birds, 427 mammals, 427 amphibians, 378 reptiles and more than 1,25,000 invertebrates.
- Biodiversity (species richness) is highest in tropics because
o Tropics had more evolutionary time.
o Relatively constant environment (less seasonal).
o They receive more solar energy which contributes to greater productivity.
ii. Species- Area relationship
According to the study of Alexander von Humboldt (German naturalist & geographer) in South American jungles, within a region, species richness increases with increasing explored area, but only up to a limit. Relation b/w species richness and area for a wide variety of taxa gives a rectangular hyperbola.
On a logarithmic scale, the relationship is a straight line described the equation Log S = log C + Z log A
Where, S= Species richness A= Area C= Y-intercept
Z= slope of the line (regression co-efficient)
The value of Z lies in the range of 0.1 to 0.2
In species-area relationship among the large areas like entire continents, slope of the line is steeper (Z value: 0.6 to 1.2).
E.g. for frugivorous birds and mammals in the tropical forests of different continents, the slope is 1.15.
LOSS OF BIODIVERSITY
Different species have been extinct due to human activities.
- IUCN Red List (2004) documents extinction of 784 species (338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years. E.g. Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Stellar’s sea cow (Russia) and 3 subspecies (Bali, Javan, Caspian) of tiger.
- 27 species have been disappeared in the last 20 years.
- More than 15,500 species are facing threat of extinction.
- 12% birds, 23% mammals, 32% amphibians, 31% gymnosperm species face the threat of extinction.
- The current extinction rate is 100 to 1000 times faster than in the pre-human times. If this trend continues, nearly 50% species on earth might be wiped out within next 100 years.
Impacts of Loss of biodiversity:
o Decline in plant production
o Environmental perturbations such as drought.
o Increased variability in ecosystem processes such as plant productivity, water use and pest and disease cycles.
Causes of Biodiversity losses (‘The Evil Quartet’)
1. Habitat loss and fragmentation: Most important cause.
- E.g. Tropical rain forests (loss from 14% to 6%). Thousands hectares of rain forests is being lost within hrs.
- The Amazon rain forest is being cut for cultivating soya beans or for conversion of grass lands for cattle.
- Due to fragmentation, animals requiring large territories and migratory animals are badly affected.
2. Over-exploitation: Many species like Stellar’s sea cow, Passenger pigeon etc extinct due to over exploitation.
3. Alien species invasions: Alien species cause decline or extinction of indigenous species. E.g.
- The Nile Perch introduced in Lake Victoria (East Africa) caused extinction of more than 200 species of cichlid fish.
- Invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia) caused damage to our native species.
- The illegal introduction of the African Catfish (Clarias gariepinus) for aquaculture is posing a threat to the indigenous catfishes in our rivers.
4. Co-extinction: When a species becomes extinct, the plant and animal species associated with it also extinct. E.g.
- Extinction of the parasites when the host is extinct.
- Co-evolved plant-pollinator mutualism where extinction of one leads to the extinction of the other.
BIODIVERSITY CONSERVATION
Reasons for conservation are 3 categories.
a. Narrowly utilitarian arguments
- Human derive economic benefits from nature such as food, firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines.
- More than 25% of the drugs are derived from plants.
- 25,000 species of plants have medicinal value.
b. Broadly utilitarian arguments
Biodiversity has many ecosystem services. E.g.
· Amazon forest (‘lung of the planet’) produces 20% of total O2 in the earth’s atmosphere.
· Pollination through bees, bumblebees, birds and bats.
· Aesthetic pleasures.
c. Ethical arguments
Every species has an intrinsic value. We have a moral duty to care for their well-being.
Types of conservation
a. In situ conservation (on site)
It is the conservation of genetic resources within natural or human-made ecosystems in which they occur. E.g. Protected areas such as National Parks, Sanctuaries, Biosphere reserves, cultural landscapes, natural monuments.
- National Park: Strictly reserved for the welfare of the wildlife where private ownership, cultivation, grazing etc are prohibited. E.g. Eravikulam National Park in Kerala.
- Sanctuary: Here, protection is given only to the animals. Collection of timbers, minor forest products and private ownership are allowed so long as they do not harm the animals. E.g. Periyar wildlife sanctuary in Kerala.
- Biosphere Reserves: Areas of land or coastal environments to conserve ecosystem and genetic resources contained therein.
- Sacred forests (Sacred groves):E.g.
· Sacred groves in Khasi & Jaintia Hills in Meghalaya
· Aravalli Hills of Rajasthan
· Western Ghat regions of Karnataka & Maharashtra
· Sarguja, Chanda & Bastar areas (Madhya Pradesh).
India has 14 Biosphere Reserves, 90 National Parks and 448 wildlife sanctuaries.
b. Ex situ conservation (off site)
It is the conservation of organisms outside their habitats. E.g. genetic resource centres, zoological parks, botanical gardens, gene banks etc.
Hotspots:
- These are the richest and the most threatened reservoirs of plant and animal life on earth.
- There are 34 hotspots in the world.
- 3 hotspots (Western Ghats and Sri Lanka, Indo-Burma and Himalaya) cover India’s biodiversity regions.
International Efforts for conserving biodiversity
- The Earth Summit (Rio de Jeneiro, 1992) - 3 objectives:
a. Conservation of biodiversity
b. Sustainable use of biodiversity
c. Sharing of benefits in the utilization of genetic resources.
- The World Summit on Sustainable Development (Johannesburg, South Africa, 2002): 190 countries pledged to reduce the current rate of biodiversity loss.
