Biodiversity and its Conservation | ISC Class 12 Biology Notes

This note covers levels of biodiversity, global species diversity, latitudinal gradients, species-area relationships, ecosystem stability, extinction, causes of biodiversity loss, reasons for conservation, protected areas, hotspots, Ramsar sites, conservation techniques and international agreements.

What is biodiversity, and at which levels does it occur?

Definition: Biodiversity is the combined variety of life at all levels of biological organisation. Its three especially important levels are genetic diversity, variation within a species; species diversity, variety at the species level; and ecosystem diversity, variety of ecological settings.

The term biodiversity was popularised by Edward Wilson.

A species is a group of organisms sharing characteristic features and, in sexually reproducing organisms, capable of interbreeding to produce fertile offspring. An ecosystem includes organisms interacting with one another and with their physical environment.

How does genetic diversity differ from species diversity?

Genetic diversity means variation in inherited characteristics within a species. A single species might show considerable genetic variation across its geographical range. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.

The medicinal plant Rauwolfia vomitoria provides another example. Plants growing in different Himalayan ranges might differ in the potency and concentration of reserpine, the active chemical they produce. This is variation within one species, rather than a comparison of different species.

Species diversity is diversity at the species level. The Western Ghats have greater amphibian species diversity than the Eastern Ghats. Amphibians are the vertebrate group that includes frogs and toads; vertebrates are animals with a backbone.

What is ecosystem diversity?

Ecosystem diversity, also called ecological diversity, is the variety of ecosystems in a region. India's deserts, rain forests and other ecosystems give it greater ecosystem diversity than a Scandinavian country such as Norway.

These examples range from dry environments to forests. The comparison concerns different ecological settings. It does not mean that all the organisms within each setting belong to different species or have identical inherited characteristics.

The three levels are therefore related but distinct. Rice strains illustrate diversity within a species; amphibian species illustrate diversity between species; forests and deserts illustrate diversity between ecosystems. Conservation seeks to protect diversity at all three levels.

How is global biodiversity described and estimated?

Species richness is the number of species in an area or group. A species inventory records species that have been discovered and identified. Recorded richness must be distinguished from an estimate that also includes species awaiting discovery.

The International Union for Conservation of Nature and Natural Resources (IUCN) reported slightly more than 1.5 million described plant and animal species in its 2004 account. Robert May's more conservative estimate placed global species diversity at about 7 million.

Why are recorded totals incomplete?

For many groups, inventories are more complete in temperate countries than in tropical countries. An overwhelmingly large proportion of species awaiting discovery are in the tropics. Estimation therefore involves comparison and extrapolation, meaning extension of a measured relationship to less thoroughly studied groups.

1. Select an insect group that has been studied exhaustively enough to provide a useful comparison.
2. Compare its species richness in temperate and tropical regions.
3. Obtain the temperate-tropical richness ratio from that comparison.
4. Extrapolate the ratio to other plant and animal groups to obtain a gross estimate of global diversity.

In the species inventory described here, animals form more than 70 per cent of recorded species. Plants, grouped with algae, fungi and other listed groups, comprise no more than 22 per cent. Insects form more than 70 per cent of animal species.

Taxa are named biological groups; one group is a taxon. Invertebrates are animals without a backbone. Species proportions describe numbers of species, not numbers of individual organisms, their body mass or the area they occupy.

The labels include molluscs, soft-bodied invertebrates, and crustaceans, joint-legged invertebrates with a hard outer covering. Angiosperms are flowering plants. Reptiles, birds and mammals are vertebrate groups characterised respectively by scaly skin, feathers and milk-producing glands.

Algae are simple photosynthetic organisms, making organic food using light energy; most fungi absorb soluble organic matter from dead material, while others depend on living hosts; mosses are small non-vascular plants; and ferns are seedless vascular plants. Vascular plants contain specialised conducting tissues. Lichens are associations between a fungus and an algal partner.

Three pie charts compare invertebrates, vertebrates and plants. The invertebrate chart labels insects, molluscs, crustaceans and other animal groups. The vertebrate chart labels fishes, mammals, birds, reptiles and amphibians. The plant chart labels angiosperms, lichens, algae, fungi, mosses, and ferns and allies. No numerical percentages are printed inside these charts.

See Fig. 13.1 in your NCERT textbook

The chart labels identify biological groups. Their relative sizes are visual comparisons, rather than numerical subdivisions to be estimated by eye.

Prokaryotes, organisms whose cells lack a nucleus enclosed by a membrane, are excluded from these estimates. Conventional classification methods are unsuitable for identifying many microbial species, and many cannot be grown in laboratory conditions. Molecular or biochemical criteria might reveal diversity running into millions.

Why does biodiversity generally increase towards the tropics?

Latitude is angular distance north or south of the equator. The latitudinal gradient is the geographical pattern in which species diversity, in general, decreases from the equator towards the poles. This describes a broad tendency, rather than a rule without exceptions.

With very few exceptions, the tropics, between 23.5° north and 23.5° south, contain more species than temperate or polar areas. Temperate regions lie outside the tropics towards higher latitudes; polar regions surround the poles.

What comparisons illustrate the gradient?

Colombia, near the equator, has nearly 1,400 bird species. New York, at 41° north, has 105, while Greenland, at 71° north, has 56. India, with much of its area in tropical latitudes, has more than 1,200 bird species.

The Amazonian rain forest in South America is exceptionally rich in species. Its listed diversity includes more than 40,000 plant species, 3,000 fish species, 1,300 bird species, 427 mammal species, 427 amphibian species and 378 reptile species.

Which hypotheses explain tropical richness?

Speciation, the formation of new species, is generally a function of time. Unlike temperate regions subjected to frequent past glaciations, tropical latitudes remained relatively undisturbed for millions of years. They therefore had a long evolutionary period for diversification.

Tropical environments are less seasonal, relatively more constant and predictable than temperate ones. This promotes niche specialisation: organisms becoming adapted to particular ecological roles and resource requirements. Such specialisation leads to greater species diversity.

More solar energy is available in the tropics, contributing to higher productivity, the rate of production of organic matter. This in turn might contribute indirectly to greater diversity. The indirect, possible connection must be retained when explaining this hypothesis.

Note: The three explanations concern evolutionary time, environmental constancy and available energy. They are proposed explanations for a general pattern; none makes every tropical location richer than every temperate location.

How does species richness change with area?

Alexander von Humboldt observed that, within a region, species richness increased as the explored area increased, but only up to a limit. This species-area relationship occurs across widely different groups, including flowering plants, birds, bats and freshwater fishes.

Let S represent species richness, A the area explored, C the constant for the relationship, and Z the exponent that becomes the slope on a logarithmic plot. The relationship is written as S = CAᶻ.

A logarithm expresses a number as a power of a chosen base. Taking logarithms using the same base throughout gives log S = log C + Z log A. On this plot, log S is vertical and log A is horizontal.

What do the graph and slope show?

On ordinary axes, the relationship is a rising curve described as a rectangular hyperbola. On logarithmic axes, it is a straight line. Z, the regression coefficient or slope, describes how rapidly log species richness increases with log area.

For the straight-line equation, the vertical intercept is log C, the value of log S when log A is zero. The constant C determines the position of the relationship. An intercept is where a graph crosses its vertical axis.

Within regions, Z generally lies between 0.1 and 0.2. Across very large areas such as entire continents, the slope is much steeper, with Z between 0.6 and 1.2. For fruit-eating birds and mammals in tropical forests of different continents, Z is 1.15.

The vertical axis is species richness and the horizontal axis is area. A blue curve rises and becomes flatter, beside the formula S = CAᶻ. A red straight line labelled as a log-log scale accompanies the logarithmic equation.

See Fig. 13.2 in your NCERT textbook

How should the relationship be interpreted?

1. Identify whether the axes use ordinary values or logarithms before describing the graph's shape.
2. Identify S as species richness and A as explored area, rather than numbers of individual organisms.
3. Use Z as the slope of the logarithmic straight line, keeping the regional or continental scale in view.
4. Interpret a larger Z as a greater increase in log species richness for the same increase in log area.

Why can species diversity matter to ecosystem stability?

Community means the different species populations living together in an area. Ecologists have generally regarded communities with more species as tending to be more stable than communities with fewer species, but the relationship is not completely understood.

Stability includes limited variation in productivity from year to year, resistance or resilience to occasional disturbances, and resistance to invasion. Resistance means withstanding a disturbance; resilience means recovering after it. An alien species is one introduced outside its native region.

What did Tilman's experiments show?

David Tilman's long-term experiments used outdoor plots. Plots containing more species showed less variation between years in total biomass, the mass of living material. Increased diversity also contributed to higher productivity in those experiments.

These observations provide tentative answers about the connection between diversity and ecosystem functioning. They do not establish that every ecosystem response can be predicted simply by counting species. Both the number of species and their functional roles matter to the conservation question.

How does the rivet popper hypothesis explain the risk?

Paul Ehrlich's rivet popper hypothesis compares an ecosystem to an aeroplane and its species to rivets, the fasteners holding the aircraft together. Removing rivets represents species extinction. The analogy considers both accumulated losses and the importance of particular components.

1. Imagine an aeroplane whose different parts are held together by many rivets.
2. Passengers remove rivets, corresponding to species being lost from an ecosystem.
3. The first removals may not affect flight safety, just as initial losses may not visibly disrupt ecosystem functioning.
4. Continued removal makes the aircraft dangerously weak over time, illustrating the danger of cumulative species loss.
5. Removing wing rivets is more serious than removing some seat or window rivets, illustrating the importance of key functional species.

Sketch an aeroplane with labelled wing, seat and window rivets. Label the aircraft “ecosystem”, rivets “species”, and removed rivets “extinctions”. Emphasise the wing rivets as species driving major ecosystem functions. This is an analogy, not a measured extinction threshold.

What do extinction, endangerment and biodiversity loss mean?

Extinction is the disappearance of a species when no living individuals remain. Endangered organisms face the danger of extinction but still survive. Extinct in the wild describes organisms absent from their natural surroundings but still maintained under human care.

These distinctions matter because conserving an endangered species is different from recording a species already lost. Some animals have disappeared from the wild while continuing to survive in zoological parks. Their survival in captivity does not mean their natural populations remain intact.

Which losses illustrate the problem?

Examples of recent extinctions include the dodo of Mauritius, quagga of Africa, thylacine of Australia and Steller's sea cow of Russia. The Bali, Javan and Caspian tigers are extinct subspecies, distinctive groups within the tiger species.

The IUCN Red List's 2004 account documented 784 extinctions during the preceding 500 years: 338 vertebrates, 359 invertebrates and 87 plants. Extinctions are not randomly distributed across groups; amphibians appear to be more vulnerable.

The Red Data Book is a source book recording endangered plants and animals. India also maintains Red Data Books for its plants and animals. It concerns the conservation status of organisms, rather than being a catalogue of protected geographical areas.

How can biodiversity loss affect ecosystems?

Five earlier episodes of large-scale species extinction are recognised from fossil history. The present episode is often called the Sixth Extinction. Species extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, largely because of human activities.

In general, loss of biodiversity may reduce plant production and lower resistance to environmental disturbances such as drought. It may also increase variability in plant productivity, water use, and pest and disease cycles. These are possible ecological consequences, not identical outcomes in every affected region.

What are the four major causes of biodiversity loss?

The Evil Quartet is the collective name for four major causes of biodiversity loss: habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinction. The accelerated losses associated with these causes are largely due to human activities.

How do habitat destruction and excessive use cause losses?

A habitat is the natural environment in which an organism lives. Habitat loss and fragmentation are the most important cause driving plants and animals towards extinction. Fragmentation means breaking a large, continuous habitat into smaller, separated parts.

Amazon rain forest is cleared for soya bean cultivation and grasslands for beef cattle. Pollution also degrades habitats. Fragmentation badly affects mammals and birds requiring large territories and certain animals with migratory habits, leading to population declines.

Over-exploitation is excessive use of biological resources. Human over-exploitation caused the extinction of Steller's sea cow and the passenger pigeon. Overharvesting marine fish also endangers the continued existence of some commercially important species.

Why can introduced species and biological dependence be dangerous?

Some alien species become invasive, spreading in ways that cause decline or extinction of indigenous species. Indigenous means native to the region. Introduction may be deliberate or accidental; being introduced does not by itself mean that every alien species becomes invasive.

Nile perch introduced into Lake Victoria in east Africa eventually caused the extinction of more than 200 species of cichlid fishes. Invasive weeds include carrot grass, Parthenium, Lantana and water hyacinth. Introduced African catfish, Clarias gariepinus, threaten indigenous catfishes.

Co-extinction occurs when the extinction of one species causes the extinction of species obligatorily associated with it. An obligatory association is one on which survival depends. If a host fish species becomes extinct, parasites obligatorily dependent on that species also become extinct.

A parasite lives on or in a host and obtains resources from it. A second co-extinction example is a coevolved plant-pollinator mutualism: an association shaped by reciprocal evolution in which both partners benefit and depend on one another.

A pollinator transfers pollen between flowers. Where the plant and pollinator are obligatorily linked, extinction of one leads to extinction of the other. The essential condition is this dependence, rather than merely occurring in the same habitat.

Why should biodiversity be conserved?

Conservation means protecting biological diversity and maintaining it for the future. Arguments for conservation fall into three groups: narrowly utilitarian, broadly utilitarian and ethical. Utilitarian arguments concern benefits; ethical arguments concern moral responsibility and the value of life itself.

What are narrowly utilitarian benefits?

Narrowly utilitarian reasons concern direct economic benefits. Biodiversity supplies cereals, pulses, fruits, firewood, fibre and construction materials. It also supplies industrial products such as dyes and perfumes, together with substances of medicinal importance.

Bioprospecting means exploring molecular, genetic and species-level diversity for products of economic value. It connects conservation with the possibility of discovering useful biological materials. The full range of medicinally useful plants in tropical rain forests is not yet known.

What are broadly utilitarian benefits?

Broadly utilitarian reasons concern ecosystem services: benefits arising from the functioning of ecosystems. Pollination by bees, bumblebees, birds and bats is one example. Pest control, climate moderation and flood control are other services associated with biodiversity.

These benefits differ from directly collecting timber, fruit or a medicinal substance. The activity of living communities supports processes on which human life and production depend. Protecting biodiversity therefore protects more than the products immediately removed from nature.

Nature also provides aesthetic benefits, the pleasure associated with its beauty. Walking through woods, seeing flowers in bloom and hearing a bulbul's song are examples. Such experiences are valuable even when a simple market price cannot be assigned to them.

What is the ethical argument?

Intrinsic value is value belonging to something in itself. Every species has intrinsic value even if it has no present or potential economic use to humans. Conservation is therefore not restricted to organisms that people find commercially useful.

Humans share the planet with plants, animals and microorganisms and have a moral duty to care for their well-being. Passing this biological inheritance to future generations in good order is part of the ethical responsibility for conservation.

How does in situ conservation protect biodiversity?

In situ conservation means conserving organisms in their natural habitats. Protecting the whole ecosystem protects biodiversity at different levels. Saving the forest to save the tiger illustrates this approach: the species remains part of its ecological surroundings.

Protected areas include biosphere reserves, national parks and wildlife sanctuaries. Flora means the plants of an area; fauna means its animals. Protection can encompass organisms, their resources and the landscape in which their interactions occur.

How do the main forms of area protection compare?

These forms have different purposes and need not represent mutually exclusive areas. The Pachmarhi Biosphere Reserve contains Satpura National Park and the Bori and Pachmarhi wildlife sanctuaries. A larger conservation area can therefore include other protected areas within it.

Why conserve whole ecological settings?

The value of in situ conservation is its ecosystem approach. The target organism remains in its natural habitat alongside other species. Conservation is directed towards the setting that supports biodiversity, rather than merely maintaining a collection of individual organisms.

Protection remains important even when a species attracts most public attention. The forest contains plants, animals and microorganisms as well as the familiar animal being protected. Conserving that biological community retains the context in which its members live and interact.

Why are hotspots, sacred groves and Ramsar sites important?

Biodiversity hotspots are regions with exceptionally high species richness and a high degree of endemism that also face accelerated habitat loss. Endemism means restriction to a particular geographical region: endemic species do not occur naturally elsewhere.

Why prioritise hotspots?

Conservation resources are limited, while many species need protection. Hotspots help focus protection on places containing a great concentration of biological diversity under threat. High richness alone is not the complete description: endemism and habitat loss are also central.

The Western Ghats and Sri Lanka, Indo-Burma and Himalaya hotspots cover exceptionally diverse regions of India. Their significance lies in the species and habitats they contain. A hotspot is a regional conservation priority, rather than another name for every national park.

How do sacred groves contribute?

Sacred groves are forest patches whose trees and wildlife receive protection through cultural or religious traditions. Examples occur in the Khasi and Jaintia Hills of Meghalaya, the Aravalli Hills of Rajasthan, and Western Ghat regions of Karnataka and Maharashtra.

In Meghalaya, sacred groves are the last refuges for a large number of rare and threatened plants. Their conservation role arises from maintaining living habitat. The tradition protects organisms in place rather than transferring them into artificial collections.

What is a Ramsar site?

A wetland is an area where water covers or saturates the ground permanently or seasonally. A Ramsar site is a wetland recognised as internationally important under the Ramsar Convention, the international agreement concerning wetlands.

Chilika Lake in Odisha and Keoladeo National Park at Bharatpur are examples protected as waterfowl habitats under this convention. Waterfowl are birds associated with water habitats. These examples show the conservation importance of aquatic and wetland settings alongside forests.

A Ramsar designation concerns a site, whereas the Red Data Book concerns endangered organisms. Neither term means “extinct species”. Keeping the unit of conservation clear helps distinguish a habitat designation, a regional priority and a record of species at risk.

How does ex situ conservation preserve threatened organisms?

Ex situ conservation means conserving organisms outside their natural habitats under special care. It is desirable where a threatened plant or animal needs urgent measures to prevent extinction. Zoological parks, botanical gardens and wildlife safari parks provide such settings.

What techniques are used?

Gametes are reproductive cells that fuse during fertilisation. Viable material remains living; fertile gametes retain the ability to participate in reproduction. Cryopreservation therefore concerns preservation of biological function, rather than simply keeping a non-living specimen for display.

In vitro fertilisation means fertilisation outside the body under laboratory conditions. Eggs can be fertilised in this way. Plant propagation means producing new plants; tissue culture allows plants to be propagated from small amounts of living material.

How does this differ from habitat protection?

Ex situ methods provide special care for selected organisms or reproductive material. In situ methods conserve organisms within the ecosystems where they naturally occur. A zoo and a wildlife sanctuary can both protect animals, but they do so in different ecological settings.

Seed storage, gamete preservation and tissue culture extend conservation beyond keeping whole organisms in enclosures. The material preserved differs between techniques: seeds, reproductive cells and plant tissues serve different biological roles and should not be treated as interchangeable.

How do international agreements support conservation?

Biodiversity crosses political boundaries, making its conservation a collective responsibility. Species, ecosystems and the benefits they provide cannot be understood solely within national borders. International cooperation connects local and national conservation efforts with wider commitments.

What was the purpose of the Earth Summit?

The Earth Summit was held at Rio de Janeiro in 1992. The Convention on Biological Diversity called upon nations to take appropriate measures to conserve biodiversity and use its benefits sustainably. Sustainable utilisation means use that can be maintained without exhausting the biological resource.

The conservation purpose was therefore linked with the way biological resources are used. Protecting diversity and maintaining its benefits were connected responsibilities. This relationship brings together the protection of life and the continuing human dependence on biological resources.

What commitment followed at Johannesburg?

The World Summit on Sustainable Development took place in Johannesburg, South Africa, in 2002. At this meeting, 190 countries pledged to achieve a significant reduction in the rate of biodiversity loss by 2010, at global, regional and local levels.

The year 2010 was the target attached to that historical pledge. The pledge itself does not establish that the target was achieved. Its object was a significant reduction in the rate of loss, rather than a promise that all extinction would stop immediately.

The two meetings should be distinguished by place, year and purpose. Rio de Janeiro in 1992 concerned conservation and sustainable use of biodiversity; Johannesburg in 2002 included the commitment to reduce its rate of loss by a stated target year.

Glossary

• Biodiversity — The combined variety of life at genetic, species and ecosystem levels of biological organisation.
• Genetic diversity — Variation in inherited characteristics within a species across its populations or geographical range.
• Species richness — The number of different species present in an area or biological group.
• Ecosystem diversity — The variety of ecosystems and ecological settings represented within a geographical region.
• Latitudinal gradient — The general pattern of decreasing species diversity from the equator towards the poles.
• Endemism — Restriction of a species to a particular region, without natural occurrence elsewhere.
• Fragmentation — The breaking of a large continuous habitat into smaller and separated habitat patches.
• Co-extinction — Loss of a species following extinction of another species on which it obligatorily depends.
• Bioprospecting — Exploration of molecular, genetic and species diversity for products with potential economic importance.
• In situ conservation — Protection of organisms within their natural habitats through conservation of the surrounding ecosystem.
• Ex situ conservation — Protection of organisms or biological material outside natural habitats under specially managed conditions.
• Cryopreservation — Preservation of living biological material at very low temperatures for later use.
• Sacred grove — A forest tract whose trees and wildlife receive protection through religious or cultural traditions.
• Ramsar site — A wetland recognised as internationally important under the international convention concerning wetland conservation.
• Red Data Book — A source book that records endangered plants and animals for conservation purposes.

Common errors and misconceptions

• Misconception: Rice varieties demonstrate different species. Correct: Genetically different rice strains illustrate variation within a species and therefore genetic diversity.
• Misconception: Species richness measures the number of individual organisms. Correct: It measures how many different species occur, regardless of the total number of individuals counted.
• Misconception: Every alien species becomes invasive. Correct: Some introduced species become invasive and cause native species to decline or disappear.
• Misconception: Z is the intercept on a logarithmic species-area graph. Correct: Z is the slope; in log S = log C + Z log A, the vertical intercept is log C.
• Misconception: Endemic means endangered. Correct: Endemic describes geographical restriction; endangered describes risk of extinction. These terms answer different biological questions.
• Misconception: Any association produces co-extinction. Correct: The relevant association is obligatory, as in a parasite dependent on a particular host species.
• Misconception: Seed banks conserve plants in their natural habitats. Correct: Seed storage is ex situ conservation; protection within natural habitats is in situ conservation.
• Misconception: The Johannesburg pledge proves biodiversity loss stopped in 2010. Correct: It set a target for a significant reduction in the rate of loss, not evidence of its achievement.

Exam-style questions with model answers

Q1. Define genetic diversity and species diversity, giving one example of each. [2 marks]

1. Genetic diversity is inherited variation within a species, illustrated by India's genetically different rice strains.
2. Species diversity is diversity at the species level, illustrated by the greater amphibian diversity of the Western Ghats compared with the Eastern Ghats.

Q2. Explain three hypotheses for the greater species richness of tropical regions. [3 marks]

1. Tropical regions remained relatively undisturbed for millions of years, unlike temperate regions exposed to frequent glaciations. This provided a long evolutionary time for species diversification.
2. Tropical environments are less seasonal, relatively more constant and predictable. Such conditions promote niche specialisation and lead to greater species diversity.
3. Greater solar energy contributes to higher productivity in the tropics. This in turn might contribute indirectly to greater diversity.

Q3. For the relationship log S = log C + Z log A, S is species richness, A is area, C is a constant, Z is slope and log means logarithm. Regional Z values are 0.1 to 0.2; continental values are 0.6 to 1.2. Describe the graph, identify its intercept, compare the slopes and explain the steeper slope. [4 marks]

1. A plot of log S vertically against log A horizontally is a straight line, expressing the species-area relationship on logarithmic axes.
2. Its vertical intercept is log C, because when log A equals zero, the equation gives log S equal to log C.
3. The continental relationship is steeper: its given Z range of 0.6 to 1.2 exceeds the given regional range of 0.1 to 0.2.
4. A steeper slope means a larger increase in log species richness for the same increase in log explored area.

Q4. Explain each of the four major causes of biodiversity loss, with one example or affected group for each. [4 marks]

1. Habitat loss and fragmentation remove or divide natural habitat. Breaking large habitats into fragments badly affects mammals and birds requiring large territories.
2. Over-exploitation means excessive use of biological resources. Human exploitation caused extinction of the passenger pigeon and Steller's sea cow.
3. Alien species invasion occurs when some introduced species harm native diversity. Nile perch introduced into Lake Victoria caused extinctions among its cichlid fishes.
4. Co-extinction is loss caused by obligatory dependence on a disappearing species. Parasites obligatorily dependent on a host fish species also become extinct when that host species becomes extinct.

Q5. Explain the rivet popper hypothesis through five points covering its author, its analogy, initial losses, cumulative losses and the importance of particular species. [5 marks]

1. Paul Ehrlich proposed the rivet popper analogy to explain why loss of species can threaten ecosystem functioning even when its immediate consequences are not obvious.
2. The aeroplane represents an ecosystem, and the rivets holding its parts together represent species. Removal of rivets corresponds to the extinction of species.
3. Removing a few rivets may not affect flight safety initially. Similarly, initial species losses may not immediately produce a visible failure of ecosystem functioning.
4. As more rivets are removed, the plane becomes dangerously weak over time. Continued species losses can therefore undermine the functioning of the ecosystem.
5. Wing rivets are more critical than some seat or window rivets. Likewise, losing species that drive major ecosystem functions can be particularly serious.

Q6. Define in situ and ex situ conservation. Then explain how protected areas, sacred groves, cryopreservation and seed banks contribute to conservation. [6 marks]

1. In situ conservation protects organisms in their natural habitats, conserving the surrounding ecosystem and its biodiversity at different levels together.
2. Ex situ conservation protects organisms or biological material outside natural habitats, providing special care when threatened species require urgent protective measures.
3. Protected areas such as national parks, wildlife sanctuaries and biosphere reserves conserve natural habitats. Satpura National Park is an example of such protection.
4. Sacred groves protect forest patches through religious and cultural traditions. Meghalaya's groves provide last refuges for many rare and threatened plants.
5. Cryopreservation preserves living material at very low temperatures. Gametes of threatened species can remain viable and fertile for long periods.
6. Seed banks store seeds of different genetic strains of commercially important plants for long periods, preserving material that can be used later.

Q7. Distinguish narrowly utilitarian, broadly utilitarian and ethical reasons for conserving biodiversity, giving an example or implication of each. [3 marks]

1. Narrowly utilitarian reasons concern direct economic benefits such as food, firewood, fibre and medicinal products obtained from biological resources.
2. Broadly utilitarian reasons concern ecosystem services such as pollination, pest control and climate moderation, together with aesthetic benefits associated with experiencing nature.
3. Ethical reasons recognise the intrinsic value of every species, even without economic use, and our responsibility to pass biodiversity to future generations in good order.

Q8. State the place, year and main conservation purpose of the Earth Summit and the World Summit on Sustainable Development. [2 marks]

1. The Earth Summit at Rio de Janeiro in 1992 called for biodiversity conservation and sustainable utilisation of its benefits.
2. The World Summit at Johannesburg in 2002 secured a pledge by 190 countries to significantly reduce biodiversity loss rates by 2010 at global, regional and local levels.

Key takeaways

• Biodiversity includes genetic variation within species, diversity between species and variety among ecosystems within a region.
• Recorded species totals are incomplete, and estimated diversity must be distinguished from species already discovered and named.
• Species diversity generally decreases towards the poles; tropical richness has explanations involving time, environmental constancy and solar energy.
• The species-area relationship becomes a straight line on logarithmic axes, with Z representing its slope.
• The rivet analogy highlights both the cumulative danger of species losses and the importance of particular functional species.
• Habitat loss, over-exploitation, alien species invasion and co-extinction are four major human-associated causes of biodiversity loss.
• Conservation protects direct resources, ecosystem services and the intrinsic value of species for present and future generations.
• In situ conservation protects natural habitats, while ex situ methods maintain organisms or reproductive material under special care.
• Hotspots prioritise threatened regions rich in endemic species; sacred groves and Ramsar sites protect important habitats.

Test yourself

Why are mango varieties an example of genetic diversity?

They represent inherited variation within a species, rather than a comparison between different species or ecosystems.

Why are prokaryotes excluded from the stated global species estimates?

Conventional classification methods are unsuitable for many microbial species, and many cannot be cultured under laboratory conditions.

What does a larger Z mean on a logarithmic species-area graph?

A larger Z means a steeper slope and a larger increase in log species richness for the same increase in log area.

What two findings came from Tilman's outdoor experiments?

More diverse plots showed less year-to-year variation in total biomass, and increased diversity contributed to higher productivity.

Why does the disappearance of a host sometimes cause another extinction?

If a parasite depends obligatorily on that host species, it also becomes extinct when the host species becomes extinct.

How does a Ramsar site differ from the Red Data Book?

A Ramsar site is an internationally important wetland; the Red Data Book records endangered plants and animals.

What biological condition should cryopreserved gametes retain?

They should remain viable and fertile, retaining life and their ability to participate in reproduction.

Why does an ethical argument extend beyond useful species?

Every species has intrinsic value, even without economic usefulness, and humans have a moral responsibility to care for biodiversity.