BIODIVERSITY
In our biosphere immense diversity (or heterogeneity)
exists not only at the species level but at all levels of
biological organisation ranging from macromolecules
within cells to biomes. Biodiversity is the term popularised
by the sociobiologist Edward Wilson to describe the
combined diversity at all the levels of biological organisation.
The most important 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, for example,
the Western Ghats have a greater amphibian species diversity than
the Eastern Ghats.
(iii) Ecological diversity: At the ecosystem level, India, for instance,
with its deserts, rain forests, mangroves, coral reefs, wetlands,
estuaries, and alpine meadows has a greater ecosystem diversity
than a Scandinavian country like Norway.
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.
How Many Species are there on Earth and How
Many in India?
Since there are published records of all the species discovered and named,
we know how many species in all have been recorded so far, but it is not
easy to answer the question of how many species there are on earth.
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, 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.
Let us look at some interesting aspects about earth’s biodiversity based
on the currently available species inventories. 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. That
means, out of every 10 animals on this planet, 7 are insects. Again, how
do we explain this enormous diversification of insects? The number of
fungi species in the world is more than the combined total of the species
of fishes, amphibians, reptiles and mammals. biodiversity
is depicted showing species number of major taxa.
Representing global biodiversity: proportionate number of
species of major taxa of plants, invertebrates and vertebrates
FigureIt should be noted that these estimates do not give any figures for
prokaryotes. Biologists are not sure about how many prokaryotic species
there might be. 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.
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. How many living species are actually there waiting
to be discovered and named? 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. Would we ever be able to complete
the inventory of the biological wealth of our country? Consider the immense
trained manpower (taxonomists) and the time required to complete the
job. 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.
