Biodiversity is the diversity of biological organisation ranging from cellular macromolecules to biomes.
Edward Wilson popularized the term ‘biodiversity’.
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.
According to Robert May’s Global estimate about 7 million species would have on earth. (He considered the species to be discovered in the tropics. i.e. only 22% of the total species have been recorded so far).
Animals are more diverse (above 70%) than plants including Plantae and Fungi (22%).
Most species rich taxonomic group among animals are insects (70%, i.e. out of every 10 animals, 7 are insects).
Number of fungi species is more than the combined total of the species of fishes, amphibians, reptiles & mammals.
Biologists are not sure about total number of prokaryotic species because
Applying May’s global estimates, India would have more than 1 lakh plant species and 3 lakh animal species.
Tropics (latitudinal range of 23.5o N to 23.5o S) have more species than temperate or polar areas.
E.g. Number of bird species in different latitudes is given below:
Tropical Amazonian rain forest (South America) is the greatest biodiversity on earth. It contains
Where, S= Species richness A= Area C= Y-intercept
Z= slope of the line (regression co-efficient)
Z value 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.
Rich biodiversity is essential for ecosystem health and imperative for the very survival of the human race.
‘Rivet popper hypothesis’:
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.
Fragmentation badly affects animals requiring large territories and migratory animals.
Nile Perch introduced in Lake Victoria (East Africa) caused extinction of more than 200 species of cichlid fish.
Invasive weed species like Parthenium (carrot grass), Lantana and Eicchornia (water hyacinth) caused damage to our native species.
Illegal introduction of the African Catfish (Clarias gariepinus) for aquaculture is posing a threat to the indigenous catfishes in our rivers.
More than 25% of the drugs are derived from plants.
25,000 species of plants have medicinal value.
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 ecosystems for conservation and sustainable use.
Sacred forests (Sacred groves): E.g.
Hotspots
These are the regions with very high species richness, high degree of endemism (species confined only to a specific region) but most threatened.
There are 34 hotspots in the world.
3 hotspots (Western Ghats and Sri Lanka, Indo-Burma and Himalaya) cover India’s biodiversity regions.
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)
According to International Union for Conservation of Nature (IUCN, 2004) more than 1.5 million species described so far.According to Robert May’s Global estimate about 7 million species would have on earth. (He considered the species to be discovered in the tropics. i.e. only 22% of the total species have been recorded so far).
Animals are more diverse (above 70%) than plants including Plantae and Fungi (22%).
Most species rich taxonomic group among animals are insects (70%, i.e. out of every 10 animals, 7 are insects).
Number of fungi species is more than the combined total of the species of fishes, amphibians, reptiles & mammals.
Biologists are not sure about total number of prokaryotic species because
- Conventional taxonomic methods are not suitable for identifying microbial species.
- Many species are not culturable under laboratory conditions.
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.
E.g. Number of bird species in different latitudes is given below:
- Colombia (near equator): about 1400 species.
- India (tropical latitudes): > 1200 species.
- New York (41o N): 105 species.
- Greenland (71o N): 56 species.
Tropical Amazonian rain forest (South America) is the greatest biodiversity on earth. It contains
- > 40000 species of plants
- 3000 species of fishes
- 1300 species of birds
- 427 species of mammals
- 427 species of amphibians
- 378 species of reptiles
- > 1,25,000 species of invertebrates
Biodiversity (species richness) is highest in tropics because
Relation between 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
- Tropics had more evolutionary time.
- Relatively constant environment (less seasonal).
- 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 between species richness and area for a wide variety of taxa gives a rectangular hyperbola.
Log S = log C + Z log A
Where, S= Species richness A= Area C= Y-intercept
Z= slope of the line (regression co-efficient)
Z value 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.
THE IMPORTANCE OF SPECIES DIVERSITY TO THE ECOSYSTEM
David Tilman conducted some long-term ecosystem experiments using outdoor plots. He found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.Rich biodiversity is essential for ecosystem health and imperative for the very survival of the human race.
‘Rivet popper hypothesis’:
It is an analogy used to understand the importance of biodiversity. It is proposed by Stanford ecologist Paul Ehrlich. In an airplane (ecosystem) all parts are joined together using thousands of rivets (species). If every passenger starts popping a rivet (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially. But as more and more rivets are removed, the plane becomes dangerously weak. Loss of rivets on the wings (key species that drive major ecosystem functions) is a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.
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 - 1000 times faster than in the pre-human times. If this trend continues, nearly 50% species might be extinct within next 100 years.
LOSS OF BIODIVERSITY
IUCN Red List (2004) says that 784 species (338 vertebrates, 359 invertebrates & 87 plants) were extinct 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 - 1000 times faster than in the pre-human times. If this trend continues, nearly 50% species might be extinct within next 100 years.
Impacts of Loss of biodiversity
- Decline in plant production.
- Environmental perturbations such as drought.
- 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:
It is the most important cause of biodiversity loss.
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.
Fragmentation badly affects animals requiring large territories and migratory animals.
2. Over-exploitation:
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.
Nile Perch introduced in Lake Victoria (East Africa) caused extinction of more than 200 species of cichlid fish.
Invasive weed species like Parthenium (carrot grass), Lantana and Eicchornia (water hyacinth) caused damage to our native species.
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
There are 3 categories of reasons for conservation.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 etc.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 ecosystems for conservation and sustainable use.
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).
b. Ex situ conservation (off site)
It is the conservation of organisms outside their habitats. E.g. genetic resource centres, zoological parks, wildlife safari parks, botanical gardens, gene banks, cryopreservation etc.Hotspots
These are the regions with very high species richness, high degree of endemism (species confined only to a specific region) but most threatened.
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):
It had 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):
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):
In this summit, 190 countries pledged to reduce the current rate of biodiversity loss.