Biology Notes for Class 12

Chapter 15. Biodiversity and Conservation

Chapter Summary

          Since life originated on earth nearly 3.8 billion years ago, there had been enormous diversification of life forms on earth. Biodiversity refers to the sum total of diversity that exists at all levels of biological organisation. Of particular importance is the diversity at genetic, species and ecosystem levels and conservation efforts are aimed at protecting diversity at all these levels.

          More than 1.5 million species have been recorded in the world, but there might still be nearly 6 million species on earth waiting to be discovered and named. Of the named species, > 70 per cent are animals, of which 70 per cent are insects. The group Fungi has more species than all the vertebrate species combined. India, with about 45,000 species of plants and twice as many species of animals, is one of the 12 mega diversity countries of the world.

       Species diversity on earth is not uniformly distributed but shows interesting patterns. It is generally highest in the tropics and decreases towards the poles. Important explanations for the species richness of the tropics are: Tropics had more evolutionary time; they provide a relatively constant environment and, they receive more solar energy which contributes to greater productivity. Species richness is also function of the area of a region; the species-area relationship is generally a rectangular hyperbolic function.

           It is believed that communities with high diversity tend to be less variable, more productive and more resistant to biological invasions. Earth’s fossil history reveals incidence of mass extinctions in the past, but the present rates of extinction, largely attributed to human activities, are 100 to 1000 times higher. Nearly 700 species have become extinct in recent times and more than 15,500 species (of which > 650 are from India) currently face the threat of extinction. The causes of high extinction rates at present include habitat (particularly forests) loss and fragmentation, over -exploitation, biological invasions and co-extinctions.

          Earth’s rich biodiversity is vital for the very survival of mankind. The reasons for conserving biodiversity are narrowly utilitarian, broadly utilitarian and ethical. Besides the direct benefits (food, fibre, firewood, pharmaceuticals, etc.), there are many indirect benefits we receive through ecosystem services such as pollination, pest control, climate moderation and flood control. We also have a moral responsibility to take good care of earth’s biodiversity and pass it on in good order to our next generation.

        Biodiversity conservation may be in situ as well as ex situ. In in situ conservation, the endangered species are protected in their natural habitat so that the entire ecosystem is protected. Recently, 34 ‘biodiversity hotspots’ in the world have been proposed for intensive conservation efforts. Of these, three (Western Ghats-Sri Lanka, Himalaya and Indo-Burma) cover India’s rich biodiversity regions. Our country’s in situ conservation efforts are reflected in its 14 biosphere reserves, 90 national parks, > 450 wildlife sanctuaries and many sacred groves. Ex situ conservation methods include protective maintenance of threatened species in zoological parks and botanical gardens, in vitro fertilisation, tissue culture propagation and cryopreservation of gametes.


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

Ø  Types of biodiversity described by Edward Wilson:

Ø  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.

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

Ø  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?

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

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

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

Ø  All plants constitute about 22 percent.

Ø  Among animals insects constitute 70 percent.

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

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

Pattern of Biodiversity:

Latitudinal gradients:

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

Ø  Tropic (23.5°N to 23.5°S) harbors more species than temperate and pole

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

Ø  40,000 species of plants.

Ø  3000 species of fishes.

Ø  1300 of birds.

Ø  427 amphibians

Ø  378 reptiles

Ø  More than 1, 25,000 invertebrates.

Why tropical rain forest has greater biodiversity:

Ø  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.

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

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

Species area relationship:

Ø  ALEXANDER VON HUMBOLDT observed within a region species richness increased with increasing explored area but only up to a limit.

Ø  The relation between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola.

Ø  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.

Ø  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:

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

Ø  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)

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

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

  • Plots with more species showed less year to year variation in biomass
  • o    Increased diversity contributed to higher productivity.

Ø  The rivet popper hypothesis:

  • In an airplane (ecosystem) all parts are joined together by thousands of rivets (species).
  • 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.
  • Further more which rivet is removed may also be critical.
  • 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:

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

Ø  Recent extinction includes:

  • Dodo (Mauritius).
  • Quake (Africa)
  • Thylacine (Australia)
  • Stiller’s cow (Russia)
  • Three subspecies of tiger (Bali, Java, Caspian).

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

Ø  The sixth mass Extinctions in progress now.

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

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

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

Effect of biodiversity loss:

Ø  Decline in plant production.

Ø  Lowered resistance to environmental perturbations such as drought.

Ø  Increased variability in certain ecosystem processes such as plant productivity, water use, and pest and disease cycle.

Causes of biodiversity loss:

Ø  The present loss is all due to human activity (anthropogenic)

Ø  There are four major causes “The Evil Quartet” are as follows:

Habitat loss and fragmentation:

Ø  Most important cause driving animals and plants to extinct.

Ø  The tropical rain forest reduced to 6 % from 14 % of earth land surface.

Ø  The Amazonian rain forest is called as ‘lungs of the planet’ is being cut cleared for cultivating soya beans.

Ø  Degradation of many habitat by pollution is also threatens the loss of diversity.

Ø  Large areas are broken into figments also the cause of diversity loss.


Ø  When ‘need’ turns to ‘greed’ it leads to over-exploitation of natural resources.

Ø  Many species extinctions in the last 500 years (Stiller’s cow, passenger pigeons) were due to over- exploitation.

Ø  Many marine fish populations around the world are over harvested.

Alien species invasion:

Ø  The alien species became invasive and cause decline or extinction of indigenous species.

Ø  Nile perch introduced into Lake Victoria in east Africa led to extinction of 200 species of cichlid fish in the lake.

Ø  Parthenium, (carrot grass), Lantana, and water hyacinth (Eichornia) posed a thread to indigenous species.

Ø  African cat fish Clarias gariepinus for aquaculture purposed is posing a threat to indigenous catfishes in our rivers.


Ø  When a species becomes extinct, the plant and animal species associated with it an obligatory way also become extinct.

Ø  Extinction of Host species leads to extinction of the parasite also.

Ø  Co-evolved plant-pollinator mutualism where extinction of one invariably lead to the extinction of the other.


Why should we conserve Biodiversity?

Reason for conservation biodiversity is grouped into three categories.

Ø  Narrowly utilitarian.

Ø  Broadly utilitarian

Ø  Ethical

Narrowly utilitarian:

Ø  Human derive countless direct economic benefits from nature-

Ø  Food (cereals, pulses, fruits), firewood, fiber, construction material.

Ø  Industrial products (tannins, lubricants, dyes, resins, perfumes)

Ø  Products of medicinal importance.

Ø  Bioprospecting: exploring molecular genetic and species-level diversity for products of economic importance.

Broadly Utilitarian:

Ø  Amazonian forest along produce 20% of oxygen during photosynthesis.

Ø  Pollinator layer: bees, bumblebees, birds and bat that pollinate the plant without which seed cannot be produced by plants.

Ø  Aesthetic pleasure we get from the biodiversity.

How do we conserve biodiversity?

In situ conservation:

Ø  When we conserve and protect the whole ecosystem, its biodiversity at all level is protected – we save the entire forest to save the tiger. This approach is called in situ (on site) conservation.

Ø  Biodiversity hot spot: regions   with   very   high   levels   of   species   richness   and   high   degree of endemism. (species confined to that region and not found anywhere else)

Ø  Hot spot in biodiversity is also regions of accelerated habitat loss.

Ø  Out of 34 hot spot in the world, three hot spot located in India:

Ø  Western Ghats and Srilanka.

Ø  Indo-Burma.

Ø  Himalaya.

Ø  Other protected area under in situ conservations are:

Ø  14 biosphere reserve

Ø  90 national park

Ø  448 wild life sanctuary

Ø  Sacred groves: tract of forest were set aside, and all the trees and wildlife within were venerated and given total protection.

Ex situ conservation:

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.

Ø  Zoological Park.

Ø  Botanical garden

Ø  Wildlife safari.

Ø  Conservation of gamete by cryopreservation.

Ø  Genetic strains are preserved in seed bank.

Convention on Biodiversity:

“The earth Summit” held in Rio de Jeneiro in 1992 called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilization of its benefits.

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 level.

Disclaimer: All contents are originally prepared by Shri K C Meena Ji, Principal, KVS. 

Amazon Affiliate Disclaimer: is a part of Amazon Services LLC Associates Program, an affiliate advertising program  designed to provide a means for sites to earn advertising fees by advertising and linking to As an amazon associates we earn from qualifying purchases.

Notify of

Inline Feedbacks
View all comments
error: Content is protected !!
Would love your thoughts, please comment.x
Scroll to Top