NEET BiologyNCERT Class 12Chapter 13

Biodiversity and Conservation: NEET notes

This chapter measures the variety of life and asks why it is worth keeping. It defines biodiversity at the genetic, species and ecological levels, counts the species recorded worldwide and in India, explains why the tropics are richer and why species rise with area (log S = log C + Z log A), links diversity to ecosystem stability through Tilman's plots and the rivet popper analogy, lists the extinctions and the four human causes behind them, and closes with the reasons for conservation and its in situ and ex situ methods.

What NEET asks

NEET asks for the three levels of biodiversity with their examples, the global and Indian species figures (about 1.5 million described, Robert May's 7 million, India's 2.4 per cent of land and 8.1 per cent of species), the bird counts along the latitudinal gradient, the Z ranges 0.1-0.2 and 0.6-1.2, the evil quartet with its examples, the 34 hotspots and the three in India, the counts of protected areas, and which methods are in situ and which ex situ. Marks are lost by swapping the Z ranges, by naming over-exploitation as the chief cause of extinction, and by putting sacred groves or seed banks on the wrong side of in situ and ex situ.

1. What biodiversity is

NCERT §13.1

Life is staggeringly varied. Known species include more than 20,000 kinds of ants, about 3,00,000 kinds of beetles, 28,000 of fishes and nearly 20,000 of orchids.
Diversity exists at every level of biological organisation, from macromolecules inside cells up to biomes. The sociobiologist Edward Wilson popularised the word biodiversity for this combined diversity.
Genetic diversity: one species can vary widely at the genetic level across its range. Rauwolfia vomitoria from different Himalayan ranges differs in the potency and concentration of the reserpine it makes.
Two examples of genetic diversity from India: over 50,000 genetically distinct rice strains, and 1,000 varieties of mango.
Species diversity: the Western Ghats hold a greater diversity of amphibian species than the Eastern Ghats.
Ecological diversity: India holds deserts, rain forests, mangroves, coral reefs, wetlands and estuaries, and alpine meadows too, so its ecosystem diversity is greater than that of a Scandinavian country such as Norway.
Millions of years of evolution built this diversity, yet at the present rate of species loss it could be gone in less than two centuries, which makes its conservation a matter of international concern.

2. How many species on Earth

NCERT §13.1.1

We know how many species have been recorded, because every named species is published, but not how many exist.
According to the IUCN (2004), slightly more than 1.5 million plant and animal species have been described so far.
Species lists are more complete for temperate than for tropical countries, and most undiscovered species are in the tropics.
To estimate the total, biologists take the temperate-to-tropical ratio of species richness in a thoroughly studied insect group and extrapolate it to other groups of plants and animals.
Some extreme estimates run from 20 to 50 million species; the more conservative, scientifically sound estimate by Robert May is about 7 million.
Of the recorded species, animals are more than 70 per cent. Plants, counting algae, fungi, bryophytes, gymnosperms and angiosperms together, are no more than 22 per cent.
Insects are the most species-rich animal group, more than 70 per cent of all animals: 7 of every 10 animal species are insects.
Fungi have more species than fishes, amphibians, reptiles and mammals put together.
These estimates leave out prokaryotes. Standard taxonomic methods do not suit microbes and many cannot be cultured; by biochemical or molecular criteria their diversity alone might run into millions.

3. Biodiversity of India

NCERT §13.1.1

India covers just 2.4 per cent of the Earth's land, yet it holds 8.1 per cent of the world's species diversity.
That share places India among the world's 12 mega diversity countries.
About 45,000 plant species have been recorded from India, and roughly double that number of animal species.
By May's global estimate, only 22 per cent of all species have been recorded so far.
Applying that proportion to India's lists, probably over 1,00,000 plant species and over 3,00,000 animal species are still undiscovered and undescribed.
Finishing this inventory would need a great many trained taxonomists and a long time, and many species may go extinct before they are ever found: nature's biological library is burning before its books are catalogued.

4. Latitudinal gradients

NCERT §13.1.2

Diversity is spread unevenly over the Earth. A widely known pattern is the latitudinal gradient: species diversity generally falls from the equator towards the poles.
With very few exceptions, the tropics (23.5° N to 23.5° S) hold more species than temperate or polar regions.
Birds: Colombia, near the equator, has nearly 1,400 species; New York at 41° N has 105; Greenland at 71° N has only 56. India, mostly tropical, has more than 1,200.
A tropical forest in Ecuador can hold up to 10 times as many vascular plant species as an equal area of temperate forest in the Midwest of the USA.
The Amazonian rain forest, largely tropical, holds the greatest biodiversity on Earth. Its counts: plants over 40,000 species, fishes 3,000, birds 1,300, mammals 427, amphibians 427, reptiles 378, and invertebrates over 1,25,000. At least two million insect species there may still await discovery.
Hypothesis 1: speciation is a function of time. Temperate regions went through frequent glaciations, while the tropics stayed relatively undisturbed for millions of years, giving more time for diversification.
Hypothesis 2: tropical environments are less seasonal, more constant and predictable, which promotes niche specialisation and so greater species diversity.
Hypothesis 3: the tropics receive more solar energy, which raises productivity and may indirectly add to diversity.

5. Species-area relationship

NCERT §13.1.2

Exploring South American jungles, Alexander von Humboldt saw that within a region, species richness rose as the explored area grew, but only up to a limit.
For many taxa (angiosperm plants, birds, bats, freshwater fishes) species richness against area is a rectangular hyperbola.
On logarithmic scales the relationship becomes a straight line: log S = log C + Z log A, where S is species richness, A is area, Z is the slope (regression coefficient) and C is the Y-intercept.
Z lies between 0.1 and 0.2 whatever the taxonomic group or region: plants in Britain, birds in California and molluscs in New York state give remarkably similar slopes.
For very large areas such as whole continents the line is much steeper, with Z between 0.6 and 1.2.
For frugivorous (fruit-eating) birds and mammals in tropical forests of different continents, Z is 1.15.
A steeper slope means species richness climbs much faster with area, so losing area costs more species.

6. Diversity and ecosystem stability

NCERT §13.1.3

Whether the number of species matters to how an ecosystem works is a question ecologists have not answered definitively. For decades they held that species-rich communities tend to be more stable.
A stable community does not vary too much in productivity from year to year, is resistant or resilient to occasional natural or man-made disturbances, and resists invasion by alien species.
David Tilman's long-term experiments on outdoor plots gave tentative answers: the richer a plot was in species, the less its total biomass varied from one year to the next.
In the same experiments, greater diversity also raised productivity.
Rich biodiversity is essential for ecosystem health and imperative for the survival of humans, even though exactly how richness helps is not fully understood.
Paul Ehrlich's rivet popper hypothesis: an airplane (the ecosystem) is held together by thousands of rivets (species). Passengers popping rivets one by one (extinctions) may not affect flight safety at first, but the plane grows dangerously weak as more go.
Which rivet goes also matters. Rivets on the wings stand for key species that drive major ecosystem functions; losing them is far more serious than losing a few from the seats or windows.

7. Loss of biodiversity

NCERT §13.1.4

It is doubtful whether speciation is adding new species today, but species are certainly being lost, and human activities are clearly to blame.
When humans colonised the tropical Pacific Islands, over 2,000 native bird species are said to have gone extinct.
The IUCN Red List (2004) records the extinction of 784 species in the last 500 years: 338 vertebrates, 359 invertebrates and 87 plants.
Recent extinctions: the dodo of Mauritius, the quagga of Africa, the thylacine of Australia, Steller's sea cow of Russia, and three tiger subspecies (Bali, Javan, Caspian). In the last twenty years alone, 27 species have disappeared.
Extinctions are not random across taxa; some groups, such as amphibians, appear more vulnerable.
More than 15,500 species worldwide face the threat of extinction: 12 per cent of bird species, 23 per cent of mammal species, 32 per cent of amphibian species and 31 per cent of gymnosperm species.
Over more than 3 billion years of life there have been five mass extinctions. The 'Sixth Extinction' now under way differs in rate: 100 to 1,000 times faster than in pre-human times, because of human activities. If trends continue, nearly half of all species could be lost within the next 100 years.
Losing biodiversity in a region can cause (a) a fall in plant production, (b) weaker resistance to environmental perturbations such as drought, and (c) greater variability in ecosystem processes: plant productivity, water use, and the cycles of pests and diseases.

8. The evil quartet

NCERT §13.1.4

Today's accelerated extinctions are largely caused by humans. The four major causes are nicknamed 'The Evil Quartet'.
Habitat loss and fragmentation is the most important cause. Tropical rain forests, which once covered over 14 per cent of the land surface of the Earth, now cover no more than 6 per cent; 1000 more hectares are lost in the time it takes to read this chapter.
The Amazon rain forest, called the 'lungs of the planet' and home to probably millions of species, is being cleared to grow soya beans or to make grassland for beef cattle. Pollution also degrades many habitats.
When large habitats are broken into small fragments, mammals and birds that need large territories, and animals with migratory habits, are badly hit and their populations decline.
Over-exploitation: when 'need' turns to 'greed', species are harvested to extinction. Steller's sea cow and the passenger pigeon were lost this way in the last 500 years, and many marine fish populations are over-harvested today.
Alien species invasions: introduced species can turn invasive. After the Nile perch was introduced into Lake Victoria in east Africa, over 200 species of cichlid fish, an ecologically unique group, eventually went extinct.
In India, the invasive weeds carrot grass (Parthenium), Lantana and water hyacinth (Eichhornia) damage the environment, and the illegally introduced African catfish Clarias gariepinus threatens native catfishes in our rivers.
Co-extinctions: when a species dies out, species bound to it in an obligatory way die too. A host fish takes its unique parasites with it, and in a coevolved plant-pollinator mutualism the loss of one leads to the loss of the other.

9. Why conserve biodiversity

NCERT §13.2.1

The reasons fall into three groups: narrowly utilitarian, broadly utilitarian and ethical.
Narrowly utilitarian: nature gives direct economic benefits such as food (cereals, pulses, fruits), firewood, fibre and building material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines.
More than 25 per cent of the drugs sold worldwide come from plants, and 25,000 plant species contribute to the traditional medicines of native peoples.
Bioprospecting means searching diversity at the molecular, genetic and species levels for economically important products; countries rich in biodiversity stand to gain enormously from it.
Broadly utilitarian: biodiversity drives ecosystem services. By one estimate, the photosynthesis of the Amazon forest supplies 20 per cent of all the oxygen in Earth's atmosphere.
Pollination, without which plants give no fruits or seeds, is a service provided by bees, bumblebees, birds and bats. There are also intangible benefits such as the pleasure of a walk in thick woods or a bulbul's song at dawn.
Ethical: every species has an intrinsic value, even with no present economic use. We have a moral duty to care for the species we share the planet with and to pass our biological legacy on in good order.

10. In situ conservation

NCERT §13.2.2

In situ (on site) conservation protects the whole ecosystem, and with it biodiversity at every level: save the entire forest to save the tiger.
Ex situ (off site) conservation is the right approach when a plant or animal is endangered or threatened, meaning it runs a very high risk of dying out in the wild in the near future, and must be rescued urgently.
Species needing protection far outnumber conservation resources, so conservationists picked biodiversity hotspots for maximum protection: regions with very high species richness and a high degree of endemism (species found only there).
Initially 25 hotspots were identified; nine more were added, making 34. Hotspots are also regions of accelerated habitat loss.
Three hotspots cover India's richest regions: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.
All 34 hotspots together occupy under 2 per cent of the Earth's land, yet hold a very large number of species; strictly protecting them could cut the ongoing mass extinctions by almost 30 per cent.
India gives legal protection to its biodiversity-rich regions. Its protected network counts 448 wildlife sanctuaries, 90 national parks and 14 biosphere reserves.
Sacred groves are forest tracts set aside by religious and cultural tradition, where every tree and animal is venerated and fully protected. Examples: the Khasi and Jaintia Hills of Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghats in Karnataka and Maharashtra, and Sarguja, Chanda and Bastar in Madhya Pradesh.
In Meghalaya, sacred groves are the last refuges of many rare and threatened plants.

11. Ex situ conservation

NCERT §13.2.2

Ex situ conservation takes threatened plants and animals out of their natural habitat into special settings where they are protected and cared for.
Zoological parks, botanical gardens and wildlife safari parks do this job. Many animals now extinct in the wild survive only in zoos.
Modern methods go beyond enclosures: gametes of threatened species can be kept viable and fertile for long periods by cryopreservation.
Eggs can be fertilised outside the body (in vitro), and plants can be multiplied by tissue culture.
Seed banks store seeds of different genetic strains of commercially important plants for long periods.
Biodiversity knows no political boundaries, so its conservation is the collective responsibility of all nations.
The Convention on Biological Diversity ('The Earth Summit') at Rio de Janeiro in 1992 called on all nations to conserve biodiversity and use its benefits sustainably.
At the follow-up World Summit on Sustainable Development in Johannesburg, South Africa, in 2002, 190 countries pledged to achieve a significant reduction in the rate of biodiversity loss by 2010, at global, regional and local levels.

Must-know facts

Edward Wilson popularised the term biodiversity; its three key levels are genetic, species and ecological.
Genetic diversity: Rauwolfia vomitoria (reserpine) across the Himalaya; India's 50,000+ rice strains and 1,000 mango varieties.
Species diversity: Western Ghats have more amphibian species than the Eastern Ghats. Ecological: India more than Norway.
IUCN (2004): slightly more than 1.5 million species described; Robert May's estimate about 7 million; extreme estimates 20-50 million.
Recorded species: animals more than 70 per cent, plants no more than 22 per cent; insects more than 70 per cent of animals.
Fungi outnumber fishes, amphibians, reptiles and mammals combined in species.
India: 2.4 per cent of world land, 8.1 per cent of species; one of 12 mega diversity countries; about 45,000 plant species and twice as many animal species.
Birds: Colombia nearly 1,400, New York (41° N) 105, Greenland (71° N) 56, India more than 1,200.
Tropics are richer: more evolutionary time, a constant environment, more solar energy.
log S = log C + Z log A; Z is 0.1-0.2 within regions, 0.6-1.2 for continents, 1.15 for frugivorous birds and mammals.
Tilman: more species, less year-to-year variation in biomass and higher productivity.
Rivet popper hypothesis: Paul Ehrlich; wing rivets are key species.
IUCN Red List (2004): 784 extinctions in 500 years (338 vertebrates, 359 invertebrates, 87 plants); 27 species lost in the last twenty years.
More than 15,500 species threatened: 12 per cent birds, 23 per cent mammals, 32 per cent amphibians, 31 per cent gymnosperms.
The Sixth Extinction is 100 to 1,000 times faster than pre-human rates.
Evil quartet: habitat loss and fragmentation (most important), over-exploitation, alien species invasions, co-extinctions.
Nile perch in Lake Victoria: more than 200 cichlid species extinct.
34 hotspots, three covering India: Western Ghats and Sri Lanka, Indo-Burma, Himalaya.
India: 14 biosphere reserves, 90 national parks, 448 wildlife sanctuaries.
Ex situ: zoos, botanical gardens, safari parks, cryopreservation, in vitro fertilisation, tissue culture, seed banks. Earth Summit Rio 1992; Johannesburg 2002 with 190 countries.

Common traps

Giving Z = 0.6-1.2 for small regions.

Within a region Z is 0.1-0.2; only very large areas such as whole continents give the steeper 0.6-1.2.

Naming over-exploitation as the most important cause of extinction.

Habitat loss and fragmentation is the most important of the evil quartet.

Calling a sacred grove ex situ conservation.

A sacred grove protects the forest where it stands, so it is in situ; zoos, seed banks and cryopreservation are ex situ.

Saying plants make up most recorded species.

Animals are more than 70 per cent of recorded species and plants no more than 22 per cent.

Writing that India holds 8.1 per cent of the world's land.

India has 2.4 per cent of the land and 8.1 per cent of the species.

Listing four hotspots in India or naming the Eastern Ghats.

Three: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.

Thinking the species-area curve is a straight line on ordinary axes.

It is a rectangular hyperbola; it becomes straight only on logarithmic scales.

Saying the current extinction rate equals past mass extinctions.

It is 100 to 1,000 times faster than pre-human rates, driven by humans.

Key terms

Biodiversity: The combined variety of life at every level of biological organisation, from genes to biomes.
Genetic diversity: Variation within one species across its range, as in the reserpine content of Rauwolfia vomitoria.
Species diversity: The variety of species in a region, such as amphibians in the Western Ghats.
Ecological diversity: The variety of ecosystems in a region, such as India's deserts, forests, mangroves and reefs.
Mega diversity country: One of the 12 countries holding an exceptionally large share of the world's species; India is one.
Latitudinal gradient: The fall in species diversity from the equator towards the poles.
Species-area relationship: Species richness rises with area to a limit; log S = log C + Z log A.
Z (regression coefficient): Slope of the log S against log A line; 0.1-0.2 within regions, 0.6-1.2 for continents.
Rivet popper hypothesis: Paul Ehrlich's analogy of species as rivets holding an airplane (the ecosystem) together.
Evil quartet: The four main causes of biodiversity loss: habitat loss and fragmentation, over-exploitation, alien invasions, co-extinctions.
Co-extinction: Extinction of species tied obligatorily to one that has gone extinct.
Bioprospecting: Exploring molecular, genetic and species diversity for products of economic importance.
Endemism: Species being confined to one region and found nowhere else.
Biodiversity hotspot: A region of very high species richness and endemism, chosen for maximum protection; there are 34.
In situ conservation: Protecting species in their natural habitat by protecting the whole ecosystem.
Ex situ conservation: Protecting threatened species away from their habitat, in zoos, gardens, seed banks or by cryopreservation.
Sacred grove: A forest tract protected by religious and cultural tradition, with all its trees and wildlife.
Cryopreservation: Keeping gametes viable and fertile for long periods at very low temperature.

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