CHAPTER 13 - BIODIVERSITY AND CONSERVATION

 

Biodiversity

  • In biodiversity, a variety of different form of organism live together and interact each other in a given area.
  • According to Edward Wilson, biodiversity is described as combined diversity at all the levels of biological organisation.

Forms of Biodiversity

  • The most important forms of them are–
    • (i) Genetic diversity -
      • A single species might show high diversity at the genetic level over its distributional range.
      • The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.
      • India has more than 50,000 genetically different strains of rice, and 1,000 varieties of mango.
    • (ii) Species diversity -
      • The diversity at the species level, e.g., the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
    • (iii) Ecological diversity -
      • At the ecosystem level, India, e.g., with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway.

Global Biodiversity

  • According to the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), the total number of plant and animal species described so far is slightly more than 1.5 million.
  • A more conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million.
  • More than 70% of all the species recorded are animals.
    • Among animals, insects are the most species-rich taxonomic group, making up more than 70% of the total. That means, out of every 10 animals on this planet, 7 are insects.
  • Plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22% of the total.
  • The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles and mammals.
  • Problems to estimate exact number of species on the earth
    • The problem is that conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions.
    • If we accept biochemical or molecular criteria for delineating species for this group, then their diversity alone might run into millions.

Biodiversity in India

  • Although India has only 2.4 per cent of the world’s land area, its share of the global species diversity is an impressive 8.1 per cent.
    • That is what makes our country 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.
  • If we accept May’s global estimates, only 22 per cent of the total species have been recorded so far. Applying this proportion to India’s diversity figures, we estimate that there are probably more than 1,00,000 plant species and more than 3,00,000 animal species yet to be discovered and described.
  • Consider the immense trained manpower (taxonomists) and the time required to complete the inventory of the biological wealth of our country.
    • The situation appears more hopeless when we realise that a large fraction of these species faces the threat of becoming extinct even before we discover them.
  • Nature’s biological library is burning even before we catalogued the titles of all the books stocked there.

Patterns of Biodiversity

Latitudinal gradients

  • The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution.
  • For many group of animals or plants, there are interesting patterns in diversity, the most well- known being the latitudinal gradient in diversity.
  • In general, species diversity decreases as we move away from the equator towards the poles.
  • With very few exceptions, tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas.
  • Colombia located near the equator has nearly 1,400 species of birds while New York at 41° N has 105 species and Greenland at 71° N only 56 species.
  • India, with much of its land area in the tropical latitudes, has more than 1,200 species of birds.
  • A forest in a tropical region like Equador has up to 10 times as many species of vascular plants as a forest of equal area in a temperate region like the Midwest of the USA.
  • The largely tropical Amazonian rain forest in South America has the greatest biodiversity on earth- it is home to more than 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates.
  • Scientists estimate that in these rain forests there might be at least two million insect species waiting to be discovered and named.
  • Ecologists and evolutionary biologists have proposed various hypotheses; some important ones are
    • (a) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification,
    • (b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity and
    • (c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.

Species-Area relationships

  • During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit.
  • In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.
  • 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)
    C = Y-intercept
  • Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region (whether it is the plants in Britain, birds in California or molluscs in New York state, the slopes of the regression line are amazingly similar).
  • But, if we analyse the species-area relationships among very large areas like the entire continents, we find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2).
  • For example, for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.

Importance of Biodiversity

  • A stable community should not show too much variation in productivity from year to year. it must be either resistant or resilient to occasional disturbances (natural or man-made), and it must also be resistant to invasions by alien species. We don’t know , but
  • David Tilman's experiments -
    • David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers how the attributes are linked to species richness in a community.
      • Tilman found that plots with more species showed less year-to-year variation in total biomass.
      • He also showed that in his experiments, increased diversity contributed to higher productivity.
  • The ‘rivet popper hypothesis’ -
    • This is used by Stanford ecologist Paul Ehrlich.
    • In an airplane (ecosystem) all parts are joined together using thousands of rivets (species).
    • If every passenger travelling in it starts popping a rivet to take home (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 over a period of time.
    • Furthermore, which rivet is removed may also be critical.
    • Loss of rivets on the wings (key species that drive major ecosystem functions) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.

Loss of Biodiversity

  • If any new species are being added (through speciation) into the earth’s treasury of species, there is no doubt about their continuing losses.
  • The biological wealth of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities.
  • The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds.
  • The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
  • Some examples of recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s Sea Cow (Russia) and three subspecies (Bali, Javan, Caspian) of tiger.
  • The last twenty years alone have witnessed the disappearance of 27 species.
  • Careful analysis of records shows that extinctions across taxa are not random; some groups like amphibians appear to be more vulnerable to extinction.
  • Adding to the grim scenario of extinctions is the fact that more than 15,500 species world-wide are facing the threat of extinction.
  • Presently, 12 per cent of all bird species, 23 per cent of all mammal species, 32 per cent of all amphibian species and 31per cent of all gymnosperm species in the world face the threat of extinction.
  • From a study of the history of life on earth through fossil records, we learn that large-scale loss of species like the one we are currently witnessing have also happened earlier, even before humans appeared on the scene.
  • During the long period (> 3 billion years) since the origin and diversification of life on earth there were five episodes of mass extinction of species.
  • This is the ‘Sixth Extinction’ presently in progress different from the previous episodes.
  • The difference is in the rates; the current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates.
  • Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years.
  • In general, loss of biodiversity in a region may lead to
    • (a) decline in plant production,
    • (b) lowered resistance to environmental perturbations such as drought and
    • (c) increased variability in certain ecosystem processes such as plant productivity, water use, and pest and disease cycles.

Causes of biodiversity losses

  • The accelerated rates of species extinctions that the world is facing now are largely due to human activities.
  • There are four major causes ( ‘The Evil Quartet’ ) -
    1. Habitat loss and fragmentation -
      • This is the most important cause driving animals and plants to extinction.
      • The most dramatic examples of habitat loss come from tropical rain forests.
      • Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent.
      • They are being destroyed fast.
      • By the time we finish reading this chapter, 1000 more hectares of rain forest would have been lost.
      • The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.
      • Besides total loss, the degradation of many habitats by pollution also threatens the survival of many species.
      • When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to population declines.
    2. Over-exploitation -
      • Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over -exploitation of natural resources.
      • Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.
      • Presently many marine fish populations around the world are over harvested, endangering the continued existence of some commercially important species.
    3. Alien species invasions -
      • When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species.
      • The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.
      • Around us, the environmental damage caused and threat posed to our native species by invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia).
      • The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.
    4. Co-extinctions -
      • When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.
      • When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate.
      • Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

Biodiversity Conservation

  • It is the practice of protecting as well as preserving the variety of species alongwith their habitat and ecosystem which are at risk of extinction.

Reasons to Conserve Biodiversity

  • They can be grouped into three categories:
    • narrowly utilitarian
    • broadly utilitarian
    • ethical.
  • The narrowly utilitarian argument -
    • The narrowly utilitarian arguments for conserving biodiversity are obvious.
    • Humans derive countless direct economic benefits from nature-food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes ) and products of medicinal importance.
    • More than 25 per cent of the drugs currently sold in the market worldwide are derived from plants and 25,000 species of plants contribute to the traditional medicines used by native peoples around the world.
    • Nobody knows how many more medicinally useful plants there are in tropical rain forests waiting to be explored.
    • With increasing resources put into ‘bioprospecting’ (exploring molecular, genetic and species-level diversity for products of economic importance), nations endowed with rich biodiversity can expect to reap enormous benefits.
  • The broadly utilitarian argument -
    • The broadly utilitarian argument says that biodiversity plays a major role in many ecosystem services that nature provides.
    • The fast-dwindling Amazon forest is estimated to produce, through photosynthesis, 20 per cent of the total oxygen in the earth’s atmosphere.
    • Pollination (without which plants cannot give us fruits or seeds) is another service, ecosystems provide through pollinators layer – bees, bumblebees, birds and bats.
    • There are other intangible benefits – that we derive from nature–the aesthetic pleasures of walking through thick woods, watching spring flowers in full bloom or waking up to a bulbul’s song in the morning.
  • The ethical argument -
    • The ethical argument for conserving biodiversity relates to what we owe to millions of plant, animal and microbe species with whom we share this planet.
    • Philosophically or spiritually, we need to realise that every species has an intrinsic value, even if it may not be of current or any economic value to us.
    • We have a moral duty to care for their well-being and pass on our biological legacy in good order to future generations.

Methods of Biodiversity Conservation

  • When we conserve and protect the whole ecosystem, its biodiversity at all levels is protected - we save the entire forest to save the tiger. This approach is called in situ (on site) conservation.
  • However, when there are situations where an animal or plant is endangered or threatened (organisms facing a very high risk of extinction in the wild in the near future) and needs urgent measures to save it from extinction, ex situ (off site) conservation is the desirable approach.
  • In situ conservation -
    • The number of species waiting to be saved from extinction far exceeds the conservation resources available.
    • On a global basis, this problem has been addressed by eminent conservationists.
    • They identified for maximum protection certain ‘biodiversity hotspots’ regions with very high levels of species richness and high degree of endemism (that is, species confined to that region and not found anywhere else).
    • Initially 25 biodiversity hotspots were identified but subsequently nine more have been added to the list, bringing the total number of biodiversity hotspots in the world to 34.
    • These hotspots are also regions of accelerated habitat loss.
    • Three of these hotspots – Western Ghats and Sri Lanka, Indo-Burma and Himalaya – cover our country’s exceptionally high biodiversity regions.
    • Although all the biodiversity hotspots put together cover less than 2 per cent of the earth’s land area, the number of species they collectively harbour is extremely high and strict protection of these hotspots could reduce the ongoing mass extinctions by almost 30 per cent.
    • In India, ecologically unique and biodiversity-rich regions are legally protected as biosphere reserves, national parks and sanctuaries.
    • India now has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
    • India has also 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 were venerated and given total protection.
    • Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra and the Sarguja, Chanda and Bastar areas of Madhya Pradesh.
    • In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants.
  • Ex situ Conservation -
    • In this approach, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care.
    • Zoological parks, botanical gardens and wildlife safari parks serve this purpose.
    • There are many animals that have become extinct in the wild but continue to be maintained in zoological parks.
    • In recent years ex situ conservation has advanced beyond keeping threatened species in enclosures.
    • Now gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques,
      • eggs can be fertilised in vitro, and
      • plants can be propagated using tissue culture methods.
    • Seeds of different genetic strains of commercially important plants can be kept for long periods in seed banks.
    • Biodiversity knows no political boundaries and its conservation is therefore a collective responsibility of all nations.
    • The historic Convention on Biological Diversity (‘The Earth Summit’) held in Rio de Janeiro in 1992, called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits.
    • In a follow-up, the World Summit on Sustainable Development held in 2002 in Johannesburg, South Africa, 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.

One Mark Questions

Q1. Define biodiversity.

Ans. In biodiversity, a variety of different form of organism live together and interact each other in a given area.

Q2. Define biodiversity Conservation.

Ans. Biodiversity conservation is the practice of protecting and preserving variety of species, habitats, ecosystems, and genetic diversity on the planet.

Q3. When life originated on earth?

Ans. Nearly 3.8 billion years ago.

Q4. Define bioprospecting.

Ans. It is the method of exploring molecular, genetic and species-level diversity for products of economic importance.

Q5. What is biodiversity hotspots?

Ans. It is the regions with very high levels of species richness and high degree of endemism (that is, species confined to that region and not found anywhere else). e.g. Wild ass in western ghats.

CHAPTER 12 - ECOSYSTEM

CHAPTER 1 – SEXUAL REPRODUCTION IN FLOWERING PLANTS

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