Biodiversity And Conservation Chapter 15 Class 12 Biology NCERT Textbook PDF

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Biodiversity and Conservation

Chapter 15: Biodiversity and Conservation

15.1 Biodiversity

In our biosphere immense diversity (or heterogeneity) exists not only at the species level but at all levels of biological organization ranging from macromolecules within cells to biomes.

Biodiversity is the term popularized by sociobiologist Edward Wilson to describe the combined diversity at all the levels of biological organization.

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 have 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 is now a vital environmental issue of international concern as more and more people around the world begin to realize the critical importance of biodiversity for our survival and well-being on this planet.

15.1.1 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 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 is in the tropics.

biologists make a statistical comparison of the temperate-tropical species and the 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 of earth’s biodiversity based on the currently available species inventories.

More than 70 percent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) comprise no more than 22 percent of the total.

Among animals, insects are the most species-rich taxonomic group, making up more than 70 percent 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. In Figure 15.1, biodiversity is depicted showing the species number of major taxa.

Language English
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NCERT Solutions Class 12 Biology Chapter 15 Biodiversity and Conservation

1. Name the three important components of biodiversity.


The variety of living forms found in different ecosystems is referred to as biodiversity which includes variability in life forms from all possible sources such as air, water, and land.

The three significant components of biodiversity are as follows:

(i) Species diversity

(ii) Genetic diversity

(iii) Ecosystem diversity

2. How do ecologists estimate the total number of species present in the world?


Living entities exhibit a vast diversity on Earth. Researchers estimate it to be close to seven million.

Ecologists can estimate the total number of species on Earth through a statistical comparison between species richness of a well-studied group of insects in tropical and temperate regions. Later these ratios are extrapolated with groups of other plants and animals to estimate the net species richness found on Earth.

3. Give three hypotheses for explaining why tropics show the greatest levels of species richness.


Three hypotheses used by scientists to explain species richness in the tropics are as follows:

(i) As tropical latitudes receive more solar energy compared to temperature regions, it results in high species diversity and high productivity

(ii) Tropical regions have less seasonal variations and a more or less constant environment promoting specialization and hence high species richness

(iii) In the ice age, temperate regions were subjected to glaciations whereas tropical regions were unchanged leading to an increase in the species diversity in that region.

4. What is the significance of the slope of regression in a species-area relationship?


The slope is very helpful in finding the species-area relationship. An analysis of the species-area relationship in smaller regions reveals that the values of slopes of regression are the same irrespective of the taxonomic assemblage or the region.

But, when the same analysis is carried out in large areas, the slope of regression was found to be much steeper.

5. What are the major causes of species losses in a geographical region?


Biodiversity is referred to the variety of living forms found in different ecosystems including variability observed in life forms from different sources such as air, water, and land. However, biodiversity all around the globe is fast declining. Following are the major causes:

(i) Habitat loss and fragmentation – uncontrolled and unsustainable human activities such as slashing, deforestation, mining, burning agriculture, and urbanization cause habitats of different entities to be destructed or altered.

This leads to the breakup of habitat into smaller pieces affecting the migration of animals and also a decline in the genetic exchange between populations resulting in a decline in the species.

(ii) Co-extinction – One species is connected to the other in its native habitat in an intricate network.

Hence, the extinction of one species causes the extinction of the other wherein they are associated with each other in an obligatory connection. For instance, the extinction of the host would cause the extinction of its parasites.

(iii) Over-exploitation – Humans have caused species to get extinct or endangered due to over-exploitation and over-hunting of different plants and animals. (extinction of passenger pigeons and tigers)

(iv) Alien species invasions – Intentional introduction of non-native species into a particular habitat causes the extinction of indigenous species.

Example – Nile perch caused the extinction of more than two hundred species of native fish of Lake Victoria in Kenya when they were introduced into the lake.

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