DSE Biology Diagnostic: Biodiversity and Conservation

Unit Test 1: Species Richness, Species Evenness, and Simpson's Diversity Index

Question

Two nature reserves, A and B, were surveyed for the number and abundance of butterfly species.

Species	Reserve A (number of individuals)	Reserve B (number of individuals)
Species 1	90	20
Species 2	5	20
Species 3	3	20
Species 4	1	20
Species 5	1	20
Total	100	100

(a) Define the terms species richness and species evenness. [2 marks]

(b) Calculate Simpson's Diversity Index (D) for Reserve A and Reserve B using the formula:

$D = 1 - \sum \left(\frac{n}{N}\right)^{2}$

where $n$ = number of individuals of a species, and $N$ = total number of individuals. [4 marks]

(c) Explain which reserve is more biodiverse and what this means for the stability of the ecosystem. [3 marks]

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Worked Solution

(a) Species richness: The number of different species present in a particular area or community. In this case, both reserves have a species richness of 5.

Species evenness: A measure of how evenly distributed the individuals are among the different species. A community where all species have roughly equal abundances has high evenness; a community dominated by one or a few species has low evenness.

(b) Reserve A ($N = 100$):

$D = 1 - \left[\left(\frac{90}{100}\right)^{2} + \left(\frac{5}{100}\right)^{2} + \left(\frac{3}{100}\right)^{2} + \left(\frac{1}{100}\right)^{2} + \left(\frac{1}{100}\right)^{2}\right]$

$D = 1 - [0.81 + 0.0025 + 0.0009 + 0.0001 + 0.0001]$

$D = 1 - 0.8136 = 0.1864$

Reserve B ($N = 100$):

$D = 1 - 5 \times \left(\frac{20}{100}\right)^{2}$

$D = 1 - 5 \times 0.04$

$D = 1 - 0.20 = 0.80$

(c) Reserve B is more biodiverse (D = 0.80 vs D = 0.19). Both have the same species richness (5 species), but Reserve B has much higher species evenness (all species equally abundant), while Reserve A is dominated by Species 1 (90% of individuals).

A higher Simpson's Diversity Index indicates greater biodiversity. A more biodiverse ecosystem is generally more stable and more resilient to environmental changes (e.g. disease, climate change, habitat disturbance). If one species is lost in Reserve B, the impact on the ecosystem is smaller because many other species can fill its ecological role. In Reserve A, if Species 1 were lost, the ecosystem would be severely affected because Species 1 dominates the community.

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Unit Test 2: In Situ vs Ex Situ Conservation

Question

(a) Distinguish between in situ conservation and ex situ conservation, giving one example of each. [4 marks]

(b) Explain two advantages of in situ conservation over ex situ conservation. [2 marks]

(c) Describe the role of CITES (Convention on International Trade in Endangered Species) in conservation. [2 marks]

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Worked Solution

(a) In situ conservation: Conservation of species within their natural habitat. The species remains in its original ecosystem, interacting with other species and the environment. Example: establishing a national park or nature reserve to protect a natural habitat and the species within it.

Ex situ conservation: Conservation of species outside their natural habitat. Individuals are removed from their natural environment and cared for in a controlled setting. Examples: zoos, botanical gardens, seed banks, and captive breeding programmes.

(b) Two advantages of in situ conservation:

1. Preserves the entire ecosystem: In situ conservation protects not just the target species but the entire ecological community, including interacting species, food webs, and ecological processes (e.g. nutrient cycling, pollination). Ex situ conservation only protects individual species.

2. Species continue to evolve naturally: In their natural habitat, species continue to undergo natural selection and evolution in response to their environment, maintaining their genetic diversity and adaptability. In ex situ conservation, species are removed from their natural selection pressures.

(Alternative: more cost-effective for large areas; maintains natural behaviour of animals.)

(c) CITES is an international agreement that aims to ensure that international trade in specimens of wild animals and plants does not threaten their survival. CITES classifies species into different appendices:

• Appendix I: Species threatened with extinction -- international trade is generally prohibited (except in exceptional circumstances).
• Appendix II: Species not necessarily threatened with extinction but could become so if trade is not controlled -- trade is regulated with export permits.
• Appendix III: Species protected in at least one country -- trade is regulated at the request of that country.

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Unit Test 3: Edge Effects and Habitat Fragmentation

Question

(a) Explain what is meant by habitat fragmentation and describe how it can threaten biodiversity. [3 marks]

(b) Explain what edge effects are and why they can be detrimental to species living in the interior of a habitat fragment. [3 marks]

(c) A large forest of 1000 hectares is divided into two fragments: one of 800 hectares and one of 200 hectares. Explain why the 200-hectare fragment is likely to support fewer species than a single, continuous 200-hectare forest that has never been part of a larger habitat. [4 marks]

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Worked Solution

(a) Habitat fragmentation is the process by which a large, continuous area of habitat is broken up into smaller, isolated patches (fragments), usually by human activities such as road construction, agriculture, or urban development.

Fragmentation threatens biodiversity because:

• Isolation: Fragments are separated by inhospitable habitat (e.g. farmland, roads), preventing migration and gene flow between populations. This reduces genetic diversity and increases the risk of inbreeding depression.
• Reduced area: Smaller fragments support smaller populations, which are more vulnerable to extinction from random events (e.g. disease, natural disasters).
• Edge effects: Smaller fragments have a higher edge-to-interior ratio, exposing more of the habitat to edge effects (see part b).

(b) Edge effects refer to the changes in environmental conditions that occur at the boundary (edge) between a habitat fragment and the surrounding modified landscape. At the edge:

• There is more exposure to wind, light, and temperature extremes.
• There is greater disturbance from human activity, invasive species, and predators that prefer edge habitats.
• The microclimate at the edge is drier and more variable than in the interior.

These edge conditions can be detrimental to interior species -- species that require the stable, sheltered conditions found deep within the habitat. As the habitat fragment shrinks, the proportion of interior habitat decreases and the edge effects penetrate deeper into the fragment, reducing the area suitable for interior species.

(c) The 200-hectare fragment from a previously larger forest is likely to support fewer species than a naturally occurring 200-hectare forest because of:

1. Edge effects: The isolated 200-hectare fragment has a much larger edge-to-interior ratio than it would if it were a continuous, naturally bounded forest. Edge effects penetrate further into the smaller fragment relative to its area, reducing the amount of interior habitat.

2. Species-area relationship: Larger habitats support more species. When a large habitat is fragmented, the total number of species supported by all fragments combined is typically less than the number supported by the original continuous habitat of the same total area. Some species are lost during the fragmentation process because they cannot survive in the smaller fragments.

3. Isolation: The 200-hectare fragment is isolated from the remaining 800-hectare fragment. Species that require larger territories or that cannot cross the intervening habitat may be lost from the smaller fragment. There is no rescue effect (immigration from nearby populations) to recolonise extinct populations.

4. Time since fragmentation: Extinction debt -- some species may still be present but are "committed to extinction" and will gradually die out because the fragment is too small to support viable populations in the long term.

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Integration Test 1: Conservation Methods and Sustainability

Question

A tropical rainforest is being cleared for palm oil plantations. Several endangered species, including a species of orangutan, live in this forest.

(a) Evaluate the following three conservation strategies for the endangered orangutan population: (i) Establishing a captive breeding programme in a zoo. (ii) Creating a protected wildlife reserve within the forest. (iii) Promoting sustainable palm oil production. [6 marks]

(b) Explain why maintaining genetic diversity within the orangutan population is important for its long-term survival. [3 marks]

(c) Describe how DNA profiling can be used in the management of a captive breeding programme to maintain genetic diversity. [3 marks]

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Worked Solution

(a) (i) Captive breeding programme: This is an ex situ conservation method. It directly protects individual orangutans from habitat loss and can increase their numbers through controlled breeding. However, it removes them from their natural habitat, so they may lose natural behaviours. It is also expensive and reintroduction to the wild is difficult if the original habitat has been destroyed. It does not address the root cause (habitat loss).

(ii) Protected wildlife reserve: This is an in situ conservation method. It protects the orangutan's natural habitat, allowing them to live and reproduce naturally while maintaining ecological interactions. It preserves the entire ecosystem. However, it requires enforcement against illegal logging and poaching, and the reserve size may be insufficient if the surrounding habitat is degraded (edge effects). It is generally the most effective long-term strategy if adequately protected.

(iii) Sustainable palm oil production: This addresses the root cause of the problem by promoting farming practices that do not destroy the rainforest. The Roundtable on Sustainable Palm Oil (RSPO) certifies palm oil produced without deforestation. This allows economic development while maintaining biodiversity. However, it requires widespread industry adoption and effective monitoring. It is a long-term solution but difficult to enforce globally.

(b) Maintaining genetic diversity is important because:

1. A genetically diverse population has a wider range of alleles, making it more likely that some individuals possess traits that can survive environmental changes (e.g. new diseases, climate change). This increases the population's adaptability and resilience.

2. Low genetic diversity (due to inbreeding in a small population) leads to inbreeding depression -- an increased frequency of harmful recessive alleles being expressed, resulting in reduced fitness, lower fertility, higher infant mortality, and increased susceptibility to disease. This can push the population towards extinction.

(c) DNA profiling in captive breeding:

1. DNA samples are taken from each individual orangutan in the captive population.
2. DNA profiling reveals the genetic relatedness between individuals -- which individuals are closely related and which are more genetically different.
3. Breeders use this information to select mating pairs that are least genetically related to each other. This maximises genetic diversity in the offspring and minimises inbreeding.
4. DNA profiling can also identify the presence of rare or valuable alleles that should be preserved in the population.
5. Over generations, DNA profiling helps maintain a healthy, genetically diverse captive population that has the best chance of long-term survival and potential reintroduction to the wild.

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Integration Test 2: Human Impact and Sustainability

Question

The human population has grown exponentially over the past 200 years, placing increasing pressure on natural resources.

(a) Explain how deforestation contributes to (i) an increase in atmospheric $CO_{2}$ concentration, and (ii) a reduction in biodiversity. [4 marks]

(b) Describe the concept of sustainable development and give one example of a sustainable practice in resource management. [3 marks]

(c) A country decides to replace 50% of its fossil fuel electricity generation with wind power. Evaluate the environmental benefits and limitations of this decision. [4 marks]

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Worked Solution

(a) (i) Increase in atmospheric $CO_{2}$:

• Trees absorb $CO_{2}$ from the atmosphere during photosynthesis. Deforestation removes these trees, reducing the rate at which $CO_{2}$ is removed from the atmosphere.
• When trees are cut down, they are often burned (slash-and-burn agriculture) or left to decompose. Both burning and decomposition release the stored carbon in the trees as $CO_{2}$ back into the atmosphere.
• Deforestation also reduces the number of trees available for future $CO_{2}$ absorption, compounding the problem.

(ii) Reduction in biodiversity:

• Forests are highly biodiverse ecosystems, containing a vast number of species of plants, animals, fungi, and microorganisms. Deforestation destroys habitats, directly killing many species and displacing others.
• Habitat fragmentation isolates populations, reducing gene flow and making populations more vulnerable to extinction.
• Many species have specialised niches and cannot survive outside the forest ecosystem. Removing the forest removes their food sources, shelter, and breeding sites.
• The loss of keystone species can trigger cascade effects, causing further species loss throughout the food web.

(b) Sustainable development is development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs. It balances economic growth, social well-being, and environmental protection.

Example of sustainable practice: Selective logging (instead of clear-cutting) -- only mature, commercially valuable trees are harvested, leaving the forest structure largely intact. This allows the forest to regenerate naturally while still providing timber for economic use. Young trees are left to grow, and the habitat is preserved for wildlife.

(Alternative: rotational grazing; using renewable resources such as solar/wind power; sustainable fishing quotas.)

(c) Environmental benefits:

• Wind power generates electricity without burning fossil fuels, so it produces no $CO_{2}$ emissions during operation, reducing the country's contribution to the greenhouse effect and climate change.
• Wind power produces no air pollution (no sulphur dioxide, nitrogen oxides, or particulate matter), reducing acid rain and respiratory health problems.
• Wind is a renewable resource that will not be depleted.

Limitations:

• Wind power is intermittent -- it only generates electricity when the wind is blowing at sufficient speed. This requires energy storage systems or backup power sources (which may still be fossil fuels).
• Wind turbines can have negative impacts on wildlife, particularly birds and bats (collision risk).
• Wind farms require large areas of land (or offshore space), which may cause visual pollution, noise, and conflict with other land uses.
• Manufacturing and installing wind turbines has an environmental cost (mining for materials, energy for construction).
• The initial setup cost is high, although operational costs are low.