Biodiversity and Conservation class 12 notes

Biodiversity and Conservation class 12 notes


The term biodiversity was coined by sociobiologist Edward Wilson who described biodiversity as the combined diversity (or heterogeneity) at all the levels of the biological organization right from macromolecules within the cells, genes, species, ecosystems and biomes.

Hierarchical Levels of Biodiversity

Genetic diversity

At the genetic level, a single species might show high diversity over its distributional range. The measure of variation in genetic information contained in the organisms is Genetic diversity. Eg.10-150 genes in a virus, 450-700 genes in mycoplasma, 32000-50000 genes in Oryza sativa. Genetic diversity occurs in the differences of alleles, entire genes and chromosomal structures within a species. Genetic diversity gives the population a chance to adapt to environmental changes occurring. Examples- it leads to variation in potency and concentration of the active chemical (reserpine) present in medicinal plant Rauwolfia vomitoria growing in Himalayan ranges. More than 1000 varieties of mango, 50000 different strains of rice occur in India due to genetic variations.

Species diversity

It is the variety of species within a region. For example, Western Ghats have greater amphibian species diversity as compared to the Eastern Ghats. The number of species per unit area is species richness, the number of individuals of different species represents species evenness or species equitability. Species diversity is the product of species richness and species evenness.

Ecological diversity

It is diversity at the level of communities and ecosystem. The variety of ecosystems indicate diversity in the number of niches, trophic levels, food webs, nutrient cycles and ecological processes sustaining energy flow. For example, in India, ecosystem diversity is high due to the presences of a large number of ecosystems like deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows. It is low in small countries like Norway.

Species Present on The Earth

According to the International Union of Conservation of Nature (IUCN, 2004), the total number of plant and animal species described is slightly more than 1.5 million, but there is no clear idea of species yet to be discovered. Scientists have calculated that the total number of species in the world ranges from 20 to 50 million on this basis. The number of global species diversity is about 7 million according to Robert May and his conservative and scientific studies.

Biodiversity and Conservation class 12 notes

Interesting aspects about the earth’s biodiversity based on the currently available species inventories:

The number of animal species is more than 70%.

Nearly 22% account for the total plants (including algae, fungi, bryophytes, gymnosperms and angiosperms).

Among animals, insects are the most species-rich taxonomic group, more than 70% of the total animal species. It means, 7 insects are present out of every 10 animals on this planet.

Biodiversity in India

India with only 2.4% of the world’s land area possesses 8.1% species diversity of the world due to varying physical conditions and species grouping. It is because India is one of the 12 megadiversity countries of the world. There are nearly 45000 species of plants and twice as many animal species. We estimate that there are probably more than 100000 plant species and more than 300000 animal species yet to be discovered and described according to May’s global estimates, only 22% of the total species have been recorded so far. However, a very large number of species that are yet to be discovered may be facing the threat of becoming extinct even before we discover them.

Patterns of Biodiversity

The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution. Different patterns in diversity are latitudinal, altitudinal, geographical, topographical, humidity gradients but most common is the latitudinal gradient in diversity.

Latitudinal Gradients

The biodiversity decreases as we move from low to high latitude i.e. from the equator to the poles. In other words, the biodiversity is maximum in tropical regions, moderate in temperate area and minimum in the Arctic region (latitudinal range of 23.5o N to 23.5o S).

Various examples of high diversity in tropical regions:

About 1400 species of birds are found in Colombia located near the equator (tropical region). About 105 species in New York (41o N) in the temperate area and about 56 species of birds Greenland (71o N) in arctic area. Most of the land area of our country lies in the tropics so India has more than 1200 species of birds. A tropical region forest like equator has 10 times more species of vascular plants as compared to temperate region forest of equal area like midwest of the USA. Tropical Amazonian rain forest (South America) has the greatest biodiversity on earth. At least 2 million insect species are yet to be discovered and named in these rainforests.

Species-Area Relationships

While exploring the South American jungles, German naturalist and geographer Alexander von Humboldt, found that within a region, species richness increased with increasing explored area but only up to a limit. The relationship between species richness and area is a rectangular hyperbola for a wide variety of organisms like angiosperm plants, birds, bats and freshwater fishes.

On a logarithmic scale, the relationship is a straight line described by the equation.

log S = log C + Z log A

S = Species richness
A = Area
Z = Slope of the line (regression coefficient)
C = Y-intercept

Biodiversity and Conservation class 12 notes

Ecosystem Health

If a few species become extinct it is often believed that little harm would occur to the ecosystem. There should not be much difference if one of the tree frog species is lost forever from Western Ghats ecosystems or the number of ant species is reduced from 20000 to 15000. However, rich biodiversity is important for ecosystem health but also for the survival of the human race on earth. Since a large number of species have a higher number of niches, more interactions and more inter-relationships.

Paul Ehrlich through Rivet popper hypothesis explained the effect of reduction in biodiversity. In an aircraft (ecosystem) all components are joined collectively by using thousands of rivets (species). If each and every passenger begins popping a rivet to take home (species extinct), it may not have an effect on the flight safety at the beginning but as more and more rivets are eliminated then the aircraft will become dangerously weak.

Furthermore which rivet is eliminated may also be critical. The loss of rivets in the wings (key species) is, of course, a more serious threat to flight safety than the loss of some rivets in the seats or interior windows of the aircraft.

Loss of Biodiversity

The IUCN Red List files the extinction of 784 species. The recent extinction includes Dodo in Mauritius, Quake in Africa, Thylacine in Australia, Stiller’s cow in Russia and three subspecies of tiger in Bali, Java, Caspian.

Since the origin and diversification of life on earth, there have been five episodes of mass extinction of species. The sixth mass Extinctions in progress now.

The “Sixth Extinction” is one of a kind from the preceding 5 extinctions.

The present-day extinction rate is 100 to 1000 times faster. All the others are prehuman times, this is anthropogenic.

Results of Loss of Biodiversity

Loss of biodiversity in a region may lead to:

Decline in plant production or productivity.
Reduced resistance to environmental perturbations like drought.
Increased variability of ecosystem processes like productivity, water use, and pest and disease cycles.

Causes of Loss of Biodiversity

The world is facing increased rates of species extinctions, due to human activities. There are four major causes of biodiversity losses, called as ‘The Evil Quarter’.

Habitat loss and fragmentation:

It is the most vital cause which drives animals and vegetation to extinction. The tropical rainforest decreased to 6 percent from 14 percent of earth land surface. The Amazonian rainforest is referred to as ‘lungs of the planet ‘is being cut cleared for cultivating soya beans.

Degradation of many habitats by means of pollution has also threatened the loss of diversity. Large areas are damaged into figments also the reason for diversity loss. Species diversity drastically reduces eutrophication (nutrient enrichment) of water bodies.

In habitat fragmentation large habitats are broken into small fragments due to various human activities like human settlements, building of roads, digging of canals etc. Forest patches having croplands, orchards, plantations and urban settlements on their outskirts are examples of fragmented habitats. Animals requiring large territories (e.g. mammals, birds) and migrating animals are badly affected, leading to population declines.


Humans have always dependent on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources. It means, beyond the degree of their renewability, biological systems should not be exploited. Overexploitation of a particular species reduces the size of its population to an extent so that it becomes vulnerable to extinction. Due to overexploitation by humans dodo, Steller’s sea cow and passenger pigeon have become extinct in the last 500 years. Some commercially important species are marine fishes are likely to become endangered because marine fish populations are being overharvested all over the world.

Alien species invasions:

New species entering a geographical region are called exotic or alien or non-native species. The disappearance of native or indigenous species through changed biotic interactions occur when alien species are introduced unintentionally or deliberately for whatever purpose.

A few examples of exotic species are as follows:

Nile perch, a large predator fish was introduced into Lake Victoria of East Africa. Nile perch killed and eliminated ecologically unique assemblage of over 200 species of cichlid fish that were endemic to this freshwater aquatic system.

Carrot grass (Parthenium) is a weed found in India as a contaminant with imported wheat. Many herbs and shrubs are exterminated and it has occupied all open areas.

Lantana is a straggling shrub of tropical America which got introduced in India accidentally. Today it has become a serious weed which as replaced many species in forests.

Water hyacinth (Eichhornia) was introduced by Europeans in India. It has clogged water bodies including wetlands at many placed resulting in the death of several aquatic plants and animals.


There are many obligate associations amongst different species in ecosystems. When a species will become extinct, the plant and animal species related to it also become extinct. The extinction of the parasite is due to the extinction of host species. Co-evolutionary mutualism of plant pollinators in which the extinction of one leads forever to the extinction of the other.

Biodiversity Conservation

Millions of years of evolution have resulted in this diversity in nature. If the present rates of species losses continue we could lose all that wealth in less than two centuries. Biodiversity and its conservation are important environmental issues of international concerns as it is of critical importance for our survival and well-being on this planet.

Due to several factors like pollution, invasive species, over-exploitation by humans, climate change etc. ecosystems are undergoing changes. Diversity at all levels-genetic, species and ecological is important and needs to be conserved.

Why Should We Conserve Biodiversity?

There are many reasons (all equally important). They can be grouped into three categories: narrowly utilitarian, broadly utilitarian, and ethical.

Narrowly utilitarian (Direct or economic uses):

Humans derive countless direct economic benefits from nature.

1. Food: All the food we eat comes from plants and animals e.g., cereals, pulses, fruits, eggs, meats etc.

2. Firewood: It is used as a source of energy for cooking and heating.

3. Fibre: Jute, flax, hemp, cotton, coir are the source of natural fibres.

4. Construction material: Wood is used as timber in construction work, furniture, sports goods,
musical instruments etc.

5. Industrial products: Tannins, lubricants, dyes, resins, perfumes, paper, and rubber are some of the industrial products obtained from plants.

6. Drugs: More than 25% of the drugs currently sold in the market worldwide are derived from a mere 120 species of plants. About 25000 species of plants contribute to the traditional medicines used by native peoples around the world. Many more medicinally useful plants especially in tropical rain forests, waiting to be explored.

Bioprospecting or exploring molecular, genetic and species-level diversity for products of economic importance is going on vigorously. Nations with rich biodiversity are expected to reap enormous benefits.

Broadly utilitarian (Ecosystem services):

Biodiversity plays a major role in many ecosystem services that nature provides.

Oxygen: Plants are replenishing O2 of the atmosphere due to their photosynthetic activity. Amazon rainforest is estimated to produce 20% of it.

Pollination: A number of organisms like bees, bumblebees, birds, bats and few other animals are involved in pollination of plants which is essential for the formation of fruits and seeds. If humans are made to do this duty, the cost would be many billions of dollars.

Aesthetic pleasure: Biodiversity has a lot of aesthetic and attraction value. It provides a lot of pleasures of walking through thick woods, fresh oxygen-rich air, watching flowers in full bloom, hearing the voices of various birds or waking up to a bulbul’s song in the mornings.

Flood and Erosion control: Plant roots hold the soil particles, moving wind and water and thus prevent soil erosion. Plants also increase the porosity of soil and thereby allow water to percolate down into the soil and then in the water table. It helps conservation of water by retaining water and preventing runoff of rainwater. Litter and humus of plants act as a sponge retaining most of the rainwater. As the soil is porous, the retained water downwardly and stored as underground water.


There are millions of plant, animal and microbial species who evolved just as we have evolved and are sharing the planet with us. No organisms are useless. Every species has an intrinsic value, though it may not be of direct use to us. It is, therefore, our moral and ethical duty not to destroy them. Instead, we should take care of their wellbeing so to pass the rich biological legacy to future generations.

How to Conserve Biodiversity

There are two basic strategies of biodiversity conservation, in-situ (on site) and ex-situ (off-site).

In-situ conservation:

Protection of whole natural ecosystem is emphasized in in-situ strategies, leading to biodiversity protected at all levels. It means we save the entire forest to save the tiger. In-situ conservation is of two types: hot spots and protected areas.

Hot spots

The richest and the most threatened reservoirs of plant and animal life on earth are the hot spots.

The key criteria for determining a hot spot are:
○ Very high levels of species richness.
○ High degree of endemism (species confined to that region and not found anywhere else).

Biodiversity hotspots in India:

1.Western Ghats and Sri Lanka: Occurring along the western coast of India through Maharashtra, Karnataka, Tamil Nadu and Kerala extending over to Sri Lanka.

2.Indo-Burma: Extending from Bhutan to Myanmar covering most of North-Eastern India.

3.Himalaya: One of the richest hotspot of biodiversity.

Protected areas

Areas of land and/or sea, especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources are protected areas. World Conservation Center has recognized nearly 37000 protected areas. India has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries covering 4.7% of the land surface, as against 10% internationally suggested norm.

Ex-situ conservation

Threatened animals and vegetation are taken out from their natural habitat and placed in a distinct setting where they can be protected and given specific care is Ex-situ conversation. Gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques and plants can be propagated using tissue culture methods. Seeds of different genetic strains of commercially important plants can be preserved in seeds banks.

Convention on Biodiversity:

In 1992, “The Earth Summit” that was held in Rio de Janeiro called upon all nations to take appropriate measures for conservation of biodiversity and the sustainable utilization of its benefits.

World Summit on Sustainable development held in 2002 in Johannesburg, South Africa, 190 nations pledged their commitment to achieving it by 2010 a considerable reduction in the present day rate of biodiversity loss at global, regional and local level.

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