Biodiversity

• If an alien from a distant galaxy were to visit our planet Earth, the first thing that would amaze and baffle him would most probably be the enormous diversity of life that he would encounter
• Even for humans, the rich variety of living organisms with which they share this planet never ceases to astonish and fascinate us
• The common man would find it hard to believe that there are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids
• Biodiversity

  • Diversity at all levels of biological organisation ranging from macromolecules within cells to biomes
• Levels of biodiversity

  • Genetic diversity
  • Species diversity
  • Ecological diversity
• It has taken millions of years of evolution, to accumulate this rich diversity in nature, but we could lose all that wealth in less than two centuries if the present rates of species losses continue
• Biodiversity and its conservation are now vital environmental issues of international concern as more and more people around the world begin to realise the critical importance of biodiversity for our survival and well-being on this planet
• According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million, but we have no clear idea of how many species are yet to be discovered and described
• Estimates vary widely and many of them are only educated guesses
• For many taxonomic groups, species inventories are more complete in temperate than in tropical countries
• Considering that an overwhelmingly large proportion of the species waiting to be discovered are in the tropics, biologists make a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the total number of species on earth
• Some extreme estimates range from 20 to 50 million, but a more conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million
• More than 70 per cent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total
• Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent 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
• Biologists are not sure about how many prokaryotic species there might be as 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
• 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
• 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
• The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution
• Latitudinal gradients in biodiversity

  • Species diversity decreases as we move away from the equator towards the poles
  • 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
• Hypotheses for greater biodiversity in tropics

  • Speciation is generally a function of time, and tropical latitudes have remained relatively undisturbed for millions of years
  • Tropical environments are less seasonal, relatively more constant and predictable, promoting niche specialisation
  • There is more solar energy available in the tropics, contributing to higher productivity
• Species-area relationship


  Within a region, species richness increases with increasing explored area, but only up to a limit
• The relation between species richness and area for a wide variety of taxa 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
• 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
• If you analyse the species-area relationships among very large areas like the entire continents, you will 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
• Steeper slopes mean that the rate of increase in species richness with increasing area is much higher for larger areas compared to smaller areas
• For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species
• Tilman found that plots with more species showed less year-to-year variation in total biomass and that increased diversity contributed to higher productivity
• Rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet
• The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years