It is the term biodiversity refers to the totality of genes, species, and ecosystems of a region.

·         Types of biodiversity described by Edward Wilson:

o    Genetic diversity: A single species might show high diversity at the genetic level over its distributional range.

§  Medicinal plant Rauwolfia vomitoria of Himalayan range produces active chemical reserpine shows genetic variation.

§  India has more than 50000 different strain of rice.

§  1000 varieties of mango.


·         Species diversity: different species of a single animal like frog.

·         Ecological diversity: diversity in the ecosystem level like desert, rain forest, mangroves, coral reef, wetlands, estuaries etc.

How many species are there on Earth and How many in India?

·         According to IUCN (2004), 1.5 million of plants and animals are in our biosphere.

·         Robert May places global species diversity at about 7 millions.

·         More than 70 percent of all the species recorded are animals.

·         All plants constitute about 22 percent.

·         Among animals insects constitute 70 percent.

·         India has only 2.4 percent of the world’s land area; its share of global species diversity is impressive 8.1 percent.

·         India is considered one of the mega diversity countries of the world.

Pattern of Biodiversity:

Latitudinal gradients:

·         Species diversity decreases as we move away from the equator towards the pole.

·         Tropic (23.5o N to 23.5o S) harbors more species than temperate and pole

·         The largely tropical Amazonian rain forest in South America has the greatest biodiversity on earth:

·         40,000 species of plants.

·         3000 species of fishes.

·         1300 of birds.

·         427 amphibians

·         378 reptiles

·         More than 1, 25,000 invertebrates.

Why tropical rain forest has greater biodiversity:

·         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.

·         Tropical environments. Unlike temperate ones, are less seasonal, relatively more constant and predictable, promotes niche specialization and lead to greater species diversity.

·         There is more solar energy available in the tropics, which contribute to higher productivity.

Species area relationship:

·         ALEXANDER  VON  HUMBOLDT  observed  within  a  region  species  richness  increased  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 describe by the equation  LogS = logC +Z log A

Where S= species richness, A = Area, Z = slope of the line (regression coefficient), C = Y- intercept.

·         It has been noted that regardless of the taxonomic group or region the slope of the regression line are amazingly similar.  However,  for  a  very  large  area  like  the  entire  continent  the  slope  of  the  line  is steeper.

Importance of species diversity to the Ecosystem:

·         Community with more species generally tends to be more stable than those with less species.

·         A stable community should not show too much variation in productivity from year to year; it must be resistant or resilient to occasional disturbances (natural or man-made)

·         Stable community must be resistant to invasion by alien species.

·         David Tillman’s long-term field experiment finds that:

o    Plots with more species showed less year to year variation in biomass

o    Increased diversity contributed to higher productivity.


·         The rivet popper hypothesis:

o    In an airplane (ecosystem) all parts are joined together by thousands of rivets (species).

o    If every passenger starts popping a rivet to take home (species extinct), it may not affect flight safety initially but as more and more rivets are removed the plane becomes dangerously weak.

o    Furthermore which rivet is removed may also be critical.

o    Loss of rivets on the wings (key species) 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:

·         The IUCN Red List (2004) documents the extinction of 784 species.

·         Recent extinction includes:

o    Dodo (Mauritius).

o    Quake (Africa)

o    Thylacine (Australia)

o    Stiller’s cow (Russia)

o    Three subspecies of tiger (Bali, Java, Caspian).


·         Since the origin and diversification of life on earth there were five episodes of mass extinction of species.

·         The sixth mass Extinctions in progress now.

How the’ sixth Extinction’ is different from the previous five extinctions.

·         The current extinction rate is 100 to 1000 times faster.

·         All others are pre-human period, this one is anthropogenic.


Effect of biodiversity loss:

  • Decline in plant production.
  • Lowered resistance to environmental perturbations such as drought.
  • Increased variability in certain ecosystem processes such as plant productivity, water use, and pest and disease cycle.

Causes of biodiversity loss:

  • The present loss is all due to human activity (anthropogenic)
  • There are four major causes “The Evil Quartet” are as follows:

Habitat loss and fragmentation:

  • Most important cause driving animals and plants to extinct.
  • The tropical rain forest reduced to 6 % from 14 % of earth land surface.
  • The Amazonian rain forest is called as ‘lungs of the planet ‘is being cut cleared for cultivating soya beans.
  • Degradation of many habitat by pollution is also threatens the loss of diversity.
  • Large areas are broken into figments also the cause of diversity loss.


  • When ‘need’ turns to ‘greed’ it leads to over-exploitation of natural resources.
  • Many species extinctions in the last 500 years (Stiller’s cow, passenger pigeons) were due to over-exploitation.
  • Many marine fish populations around the world are over harvested.

Alien species invasion:

  • The alien species became invasive and cause decline or extinction of indigenous species.
  • Nile perch introduced into Lake Victoria in east Africa led to extinction of 200 species of cichlid fish in the lake.
  • Parthenium, (carrot grass), Lantana, and water hyacinth (Eichornia) posed a thread to indigenous species.
  • African cat fish Clarias gariepinus for aquaculture purposed is posing a threat to indigenous catfishes in our rivers.


  • When a species becomes extinct, the plant and animal species associated with it an obligatory way also become extinct.
  • Extinction of Host species leads to extinction of the parasite also.
  • Co-evolved plant-pollinator mutualism where extinction of one invariably lead to the extinction of the other.

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