Conservation of biodiversity
IB Biology SLΒ· Theme C: Interactions and InterdependenciesΒ· 15 min read
1. Levels of Biodiversityβ β ββββ± 4 min
Biodiversity
The variety of life on Earth, measured at three interconnected, nested levels: genetic diversity, species diversity, and ecosystem diversity.
Example:
A tropical rainforest has higher biodiversity across all three levels than a single-crop agricultural field.
Biodiversity is not just a count of different species. Genetic diversity within populations supports resilience to environmental change, while ecosystem diversity maintains overall global ecosystem function that supports human life.
A small island population of 12 endangered birds has no observed genetic variation. A large mainland population of the same species has high genetic variation. Explain which population is at greater long-term risk of extinction.
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Step 1: Recall that genetic diversity is variation in heritable traits within a population. This variation allows populations to adapt to new threats like disease or climate change.
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Step 2: If a new disease arrives at the island population, all individuals are genetically identical, so none will carry a resistance allele. All individuals will get sick and die, wiping out the entire population.
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Step 3: In the mainland population, genetic variation means some individuals will likely carry a resistance allele. These individuals will survive the disease and reproduce, so the population will persist.
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Conclusion: The small island population with no genetic diversity is at far greater risk of extinction.
Exam tip:
Always specify which level of biodiversity you are referring to in exam answers. Marks are awarded for correctly classifying biodiversity at the three levels.
2. Threats to Biodiversityβ β β βββ± 5 min
Current rates of species extinction are 100-1000 times higher than the natural background extinction rate, driven almost entirely by human activity. The main threats can be easily remembered with a common mnemonic.
A new housing development clears 70% of a native woodland that is home to an endemic lizard species, leaving only two small isolated fragments. Explain why the remaining fragments are unlikely to support the lizard long-term.
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Step 1: Habitat fragmentation reduces the total population size of the lizard, which lowers genetic diversity and increases the risk of inbreeding depression.
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Step 2: Small isolated patches cannot support the minimum viable population size required for long-term survival. Random events like a single wildfire or disease outbreak can wipe out the entire local population.
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Step 3: This lizard is endemic, meaning it is only found in this woodland. There is no external source of new lizards to recolonize the fragments if the local population dies out.
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Conclusion: The fragmented habitat will almost certainly lead to local extinction of the endemic lizard.
Test your understanding of the main threat to global biodiversity:
Which of the following is the greatest current threat to global biodiversity?
Overexploitation of fisheries and game
Habitat loss and fragmentation
Industrial pollution
Invasive alien species
Reveal answer
1 βCorrect. Habitat loss from deforestation, agriculture, and urbanization is the leading cause of species extinction globally.
3. Indicator Species and Island Biogeographyβ β β βββ± 5 min
Indicator Species
A species whose presence, absence, or abundance reflects a specific environmental condition or the overall health of a habitat.
Example:
High lichen abundance indicates low levels of sulfur dioxide air pollution.
The theory of island biogeography describes how the size of a habitat patch and its distance from a large source population affects species richness. These principles apply to any fragmented habitat, not just true islands.
Two native bee habitat fragments separated by a highway are surveyed. Patch A is 100 ha and 1 km from a large intact reserve. Patch B is 50 ha and 10 km from the same reserve. Predict which patch will have higher native bee species richness and explain why.
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Step 1: Treat the fragments as 'islands' in a human-modified landscape, and apply the island biogeography model.
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Step 2: Larger habitat patches support larger population sizes, lower extinction rates, and a wider range of niches than smaller patches. 100 ha Patch A is larger than 50 ha Patch B.
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Step 3: Patches closer to a source population (the intact reserve) have higher colonization rates, meaning new species from the reserve can more easily reach and establish in the patch. Patch A is much closer than Patch B.
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Conclusion: Patch A will have higher native bee species richness because it is larger and closer to the source population.
4. Conservation Strategies: In Situ vs Ex Situβ β β βββ± 6 min
Conservation strategies are divided into two main categories: in situ (on-site) and ex situ (off-site) conservation. Both are valuable, and most effective conservation programs use a combination of the two approaches.
In situ conservation
Conservation of species in their natural habitat, through creation of protected areas, habitat restoration, and sustainable management of land.
Example:
A national park protecting an intact native grassland ecosystem.
Evaluate the use of ex situ conservation for a critically endangered large mammal whose natural habitat has been almost completely destroyed by human activity.
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Step 1: Identify the advantages of ex situ conservation in this scenario:
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- It prevents immediate extinction of the species when no intact habitat remains for in situ conservation.
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- It allows for captive breeding programs to increase the population size from the few remaining individuals.
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Step 2: Identify the disadvantages of ex situ conservation:
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- It is very expensive to maintain large mammals in captivity long-term.
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- Captive-bred individuals often lose natural behaviors required for survival in the wild, making reintroduction difficult.
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- It does not conserve the original ecosystem or other interacting species that depend on the mammal.
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Conclusion: Ex situ conservation is a necessary emergency measure for this species, but long-term survival requires habitat restoration to allow reintroduction and permanent in situ conservation.
Key trade-offs between the two main conservation approaches:
In situ conservation
Protects species in natural habitat
+ Pros: Conserves entire ecosystem and all interacting species; Allows natural evolutionary adaptation; Lower long-term cost
β Cons: Cannot protect against immediate threats like poaching; Requires large intact areas of habitat
Ex situ conservation
Protects species outside natural habitat
+ Pros: Prevents immediate extinction when in situ is not possible; Allows research and captive breeding; Can support reintroduction programs
β Cons: Very high long-term cost; Does not conserve native ecosystem; Limited genetic diversity in captive populations
5. Common Pitfalls
Wrong move:
Confusing species diversity with the full definition of biodiversity
Why:
Many candidates only describe species diversity when asked for biodiversity, but the IB definition includes three levels. You will lose marks for missing the other two levels.
Correct move:
Always mention genetic, species, and ecosystem diversity when asked to define or describe biodiversity.
Wrong move:
Claiming ex situ conservation is always better than in situ conservation
Why:
Candidates often overemphasize captive breeding, but in situ is the preferred long-term strategy for most conservation goals.
Correct move:
Frame ex situ conservation as an emergency backup measure, and in situ as the preferred long-term approach.
Wrong move:
Mixing up indicator species and keystone species
Why:
These two terms are often confused but have completely different definitions. Examiners frequently test this distinction.
Correct move:
Remember: indicator species reflect environmental conditions; keystone species have a disproportionate effect on ecosystem structure.
Wrong move:
Ignoring genetic diversity when discussing habitat fragmentation
Why:
Candidates often only mention loss of habitat area, but the key impact on small populations is reduced genetic diversity.
Correct move:
Always link habitat fragmentation to smaller population size, lower genetic diversity, and higher extinction risk.
6. Quick Reference Cheatsheet
Concept | Key Summary | Exam Key Point |
|---|---|---|
Biodiversity levels | Genetic: variation within population; Species: variation of species; Ecosystem: variation of habitats | Name all three for full marks |
HIPPO Threats | Habitat loss, Invasive species, Pollution, Human population growth, Overexploitation | Habitat loss is the #1 threat |
Island Biogeography | Larger + closer patches = higher species richness | Applies to all fragmented habitats |
Indicator Species | Reflects specific environmental conditions | Used to assess habitat health |
In situ | Conservation in natural habitat | Preferred long-term strategy |
Ex situ | Conservation outside natural habitat | Emergency measure only |
7. Frequently Asked
What is the difference between in situ and ex situ conservation?
In situ protects species in their natural habitat, preserving the entire ecosystem. Ex situ removes species to controlled settings (zoos, seed banks) as an emergency measure when in situ conservation is not possible. Most effective conservation uses a combination of both.
Why is genetic biodiversity important for conservation?
Genetic diversity allows populations to adapt to changing conditions like disease, climate change, or new invasive species. Small populations with low genetic diversity are at much higher risk of extinction.
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2025 Β· Paper 1
Multiple choice on threats to biodiversity
- 2024 Β· Paper 2
8 mark evaluation of in situ vs ex situ
- 2023 Β· Paper 1
Question on indicator species role
Going deeper
What's Next
Conservation of biodiversity is a core applied ecology topic that connects to all themes of IB Biology SL, from the impact of human activity on global systems to the role of genetic diversity in evolution. This sub-topic builds on your prior knowledge of community interactions and population dynamics, and provides the framework for evaluating the effectiveness of different sustainability strategies, a common extended response question in exams. Understanding the trade-offs between different conservation approaches also helps you structure balanced evaluation answers, which are key to achieving high marks. Next, you can explore how climate change amplifies existing threats to biodiversity, and how human activity drives global biodiversity loss.