Chapter 13: Biodiversity and Conservation Case Study Questions | biology Class 12 CBSE

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Chapter 13: Biodiversity and Conservation Case Study Questions | biology Class 12 CBSE | ByteNotes.in

Case Study

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Case Set 1

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A group of students visited the Western Ghats as part of an ecology field trip. Their teacher pointed out that this region is considered one of the biodiversity hotspots of the world. The students observed a large number of amphibian species, several endemic plants, and unique insects that are not found anywhere else on Earth. The teacher explained that a biodiversity hotspot is a region with very high levels of species richness and a high degree of endemism. She also mentioned that these areas are undergoing accelerated habitat loss due to human activities. Although all biodiversity hotspots together cover less than 2% of Earth's land area, protecting them strictly could reduce ongoing mass extinctions by nearly 30%. Three such hotspots — Western Ghats and Sri Lanka, Indo-Burma, and Himalaya — cover India's exceptionally rich biodiversity regions.

Question 1: What is a biodiversity hotspot? Name any two biodiversity hotspots found in India.

A biodiversity hotspot is a region with very high levels of species richness and a high degree of endemism (species confined to that region and found nowhere else), and which is also undergoing accelerated habitat loss.
Two biodiversity hotspots in India: Western Ghats and Sri Lanka; Indo-Burma (Himalaya is also acceptable).

Question 2: Why is the Western Ghats region considered a biodiversity hotspot? Mention any two features that qualify it.

The Western Ghats has very high species richness — it shows greater amphibian species diversity than the Eastern Ghats.
It has a high degree of endemism, meaning many species found there are not found anywhere else in the world, and it is facing accelerated habitat loss due to human activities.

Question 3: Explain the significance of protecting biodiversity hotspots for global conservation. How does in situ conservation help in protecting these regions?

Biodiversity hotspots together cover less than 2% of Earth's land area but harbour an extremely high number of species, including many endemic ones.
Strict protection of these hotspots could reduce ongoing mass extinctions by almost 30%, making them critical targets for conservation investment.
In situ conservation involves protecting species within their natural habitats. In India, hotspot regions are protected through biosphere reserves, national parks, and wildlife sanctuaries, which safeguard the entire ecosystem including all the species within it, maintaining natural ecological processes.

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Case Set 2

Case Analysis

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Dr. Meena, a conservation biologist, was studying the impact of deforestation in the Amazon rainforest. She noted that the Amazon basin, often called the 'lungs of the planet,' once housed millions of species but is rapidly being cleared for soya bean cultivation and cattle ranching. Her team discovered that the loss of forest cover not only caused direct species extinction but also led to co-extinctions — when a host species goes extinct, its obligate parasites and mutualistic partners also disappear. She cited the example of coevolved plant-pollinator relationships where extinction of one partner invariably leads to the extinction of the other. Her report also highlighted how large-scale habitat fragmentation reduces population sizes of migratory birds and large mammals, ultimately leading to their decline.

Question 1: What is co-extinction? Give one example from the passage or your chapter.

Co-extinction occurs when a species becomes extinct, and the plant or animal species associated with it in an obligatory way also become extinct.
Example: When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate; or when one partner in a coevolved plant-pollinator mutualism goes extinct, the other also becomes extinct.

Question 2: How does habitat fragmentation contribute to biodiversity loss? Give two specific effects.

When large habitats are broken into small fragments, mammals and birds requiring large territories are badly affected, leading to population declines.
Animals with migratory habits are also severely impacted as fragmentation disrupts their movement corridors, isolating populations and reducing gene flow.

Question 3: Describe the 'Evil Quartet' of biodiversity loss. Why is habitat destruction considered the most important cause?

The 'Evil Quartet' refers to the four major causes of biodiversity loss: (i) Habitat loss and fragmentation, (ii) Over-exploitation, (iii) Alien species invasions, and (iv) Co-extinctions.
Habitat loss and fragmentation is considered the most important cause because it directly destroys the living space of species. Tropical rainforests that once covered more than 14% of Earth's land surface now cover only 6%, driving countless species to extinction.
The loss of habitat removes food, shelter, and breeding grounds simultaneously, making it impossible for species to survive, unlike other causes which may affect only certain species or certain aspects of their life cycle.

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Case Set 3

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In a biology class, students were discussing the species-area relationship observed by Alexander von Humboldt during his explorations in South America. He found that species richness increases with increasing area but only up to a limit. On a logarithmic scale, the relationship between species richness (S) and area (A) is represented as a straight line: log S = log C + Z log A. The teacher explained that the value of Z (slope of regression line) usually lies between 0.1 and 0.2 for smaller regions, but for very large areas like entire continents, Z values range from 0.6 to 1.2. For example, frugivorous birds and mammals in tropical forests show a Z value of 1.15. Students were asked to interpret what these different Z values imply for conservation planning.

Question 1: Write the equation representing species-area relationship and identify each variable.

The equation is: log S = log C + Z log A, where S = species richness, A = area, Z = slope of the line (regression coefficient), and C = Y-intercept.
On a non-logarithmic scale, the relationship is a rectangular hyperbola.

Question 2: What is the significance of the Z value (slope of regression) in the species-area relationship? How does it differ for small versus large areas?

The Z value (regression coefficient) indicates the rate at which species richness increases with area. For smaller regions, Z lies in the range of 0.1 to 0.2, meaning species richness increases relatively slowly with area.
For very large areas like entire continents, Z values range from 0.6 to 1.2, indicating a much steeper increase in species richness with area, suggesting that larger geographical units contain far more unique species.

Question 3: Based on the species-area relationship, explain how this concept is important for biodiversity conservation, particularly for designing protected areas and predicting species loss due to habitat destruction.

The species-area relationship helps conservationists predict how many species will be lost if a certain fraction of habitat is destroyed. Since species richness is directly tied to area, reducing habitat area leads to predictable declines in species numbers.
Larger protected areas preserve more species because a steeper Z value on continental scales means each unit of area lost at large scales causes disproportionately greater species loss. Therefore, protecting large contiguous tracts of habitat is more effective than protecting many small fragments.
The relationship also guides the design of wildlife reserves — larger and more connected reserves support greater biodiversity and reduce extinction rates, informing decisions on minimum area requirements for viable populations of endangered species.

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Case Set 4

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Ritu, a biology teacher, was explaining to her class why tropical regions have far greater species diversity than temperate or polar regions. She described three major hypotheses: first, tropical regions have been relatively undisturbed for millions of years, providing a long evolutionary time for species diversification. Second, tropical environments are less seasonal and more constant and predictable, promoting niche specialisation and greater species diversity. Third, more solar energy is available in the tropics, contributing to higher productivity and indirectly supporting greater diversity. As an example, she cited the Amazonian rainforest, which is home to more than 40,000 plant species, 1,300 bird species, and over 1,25,000 invertebrates, illustrating the extraordinary richness of tropical biodiversity.

Question 1: What is the latitudinal gradient in biodiversity? Give one example with data to support it.

Latitudinal gradient in biodiversity refers to the pattern where species diversity generally decreases as we move from the equator towards the poles.
Example: Colombia (near the equator) has nearly 1,400 species of birds, while New York (41°N) has only 105 species and Greenland (71°N) has only 56 species.

Question 2: How does the stability of tropical environments contribute to greater species diversity?

Tropical environments are less seasonal, relatively more constant and predictable compared to temperate regions.
Such constant and stable environments promote niche specialisation — species can evolve to exploit very specific ecological niches without facing the stress of extreme seasonal changes, leading to a greater number of coexisting species and higher overall species diversity.

Question 3: Discuss all three hypotheses that explain why tropical regions harbour greater biodiversity than temperate or polar regions.

First hypothesis (Evolutionary time): Unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years, providing a long evolutionary time for species diversification and accumulation.
Second hypothesis (Environmental stability): Tropical environments are less seasonal, more constant and predictable. Such stable conditions promote niche specialisation, allowing more species to coexist by occupying distinct ecological roles, thus increasing overall species diversity.
Third hypothesis (Solar energy and productivity): There is more solar energy available in the tropics, which contributes to higher productivity. Higher productivity provides more resources (food, habitat) for a greater number of species, indirectly supporting greater diversity.

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Case Set 5

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In a seminar on conservation biology, a speaker discussed the alarming rate of species extinction. He mentioned that the IUCN Red List (2004) documents the extinction of 784 species in the last 500 years, including 338 vertebrates, 359 invertebrates, and 87 plants. He noted that current extinction rates are 100 to 1,000 times faster than pre-human rates. Presently, 12% of all bird species, 23% of all mammal species, 32% of all amphibian species, and 31% of all gymnosperm species face extinction threats. He also introduced Paul Ehrlich's 'rivet popper hypothesis' to explain why even the loss of seemingly unimportant species can be devastating to ecosystem stability, comparing an ecosystem to an airplane held together by rivets (species).

Question 1: What does the IUCN Red List (2004) reveal about species extinction in recent times?

The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates, and 87 plants) in the last 500 years.
Currently, more than 15,500 species worldwide face the threat of extinction, and current extinction rates are estimated to be 100 to 1,000 times faster than pre-human rates.

Question 2: Explain the 'rivet popper hypothesis' given by Paul Ehrlich. How does it relate to biodiversity loss?

Paul Ehrlich's rivet popper hypothesis compares an ecosystem to an airplane held together by thousands of rivets (species). When passengers remove rivets (cause species to go extinct), it may not affect flight safety initially, but as more rivets are removed, the plane becomes dangerously weak.
This illustrates that the loss of even seemingly unimportant species can weaken an ecosystem over time; the loss of keystone species (like rivets on the wings) that drive major ecosystem functions is an especially serious threat to ecosystem stability.

Question 3: Distinguish between the current 'Sixth Extinction' and the five previous mass extinctions in Earth's history. What consequences might the current extinction rates have on ecosystems?

The five previous mass extinctions occurred over billions of years due to natural causes (geological events, meteorite impacts, volcanic activity), and species extinction rates were much lower compared to today.
The Sixth Extinction currently in progress is driven primarily by human activities (habitat destruction, overexploitation, invasive species, pollution). The current extinction rates are 100 to 1,000 times faster than in pre-human times.
Consequences include: (a) decline in plant production, (b) lowered resistance to environmental perturbations such as droughts, and (c) increased variability in ecosystem processes such as plant productivity, water use, and pest/disease cycles. If trends continue, nearly half of all species on Earth might be wiped out within 100 years.

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Chapter sections

Chapter 13: Biodiversity and Conservation | Case Study Questions

Passage

Question 1: What is a biodiversity hotspot? Name any two biodiversity hotspots found in India.

Question 2: Why is the Western Ghats region considered a biodiversity hotspot? Mention any two features that qualify it.

Question 3: Explain the significance of protecting biodiversity hotspots for global conservation. How does in situ conservation help in protecting these regions?

Passage

Question 1: What is co-extinction? Give one example from the passage or your chapter.

Question 2: How does habitat fragmentation contribute to biodiversity loss? Give two specific effects.

Question 3: Describe the 'Evil Quartet' of biodiversity loss. Why is habitat destruction considered the most important cause?

Passage

Question 1: Write the equation representing species-area relationship and identify each variable.

Question 2: What is the significance of the Z value (slope of regression) in the species-area relationship? How does it differ for small versus large areas?

Question 3: Based on the species-area relationship, explain how this concept is important for biodiversity conservation, particularly for designing protected areas and predicting species loss due to habitat destruction.

Passage

Question 1: What is the latitudinal gradient in biodiversity? Give one example with data to support it.

Question 2: How does the stability of tropical environments contribute to greater species diversity?

Question 3: Discuss all three hypotheses that explain why tropical regions harbour greater biodiversity than temperate or polar regions.

Passage

Question 1: What does the IUCN Red List (2004) reveal about species extinction in recent times?

Question 2: Explain the 'rivet popper hypothesis' given by Paul Ehrlich. How does it relate to biodiversity loss?

Question 3: Distinguish between the current 'Sixth Extinction' and the five previous mass extinctions in Earth's history. What consequences might the current extinction rates have on ecosystems?

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