# Conservation of biodiversity

> IB Biology SL · IB Biology SL (2025 syllabus)
> Source: https://www.owlsprep.com/study/ib-biology-sl-u3-conservation-of-biodiversity/

This sub-topic explores the value of global biodiversity, major human-caused threats to species and ecosystems, and evidence-based conservation strategies used to prevent extinction and restore degraded natural habitats.

**Prerequisites:** [Community ecology and species interactions](https://www.owlsprep.com/study/ib-biology-sl-u2-community-ecology/); [Population dynamics and carrying capacity](https://www.owlsprep.com/study/ib-biology-sl-u2-population-dynamics/)

## Learning objectives

- Distinguish biodiversity at genetic, species and ecosystem levels
- Explain the main human-caused threats to biodiversity
- Compare and evaluate in situ and ex situ conservation strategies
- Apply island biogeography and indicator species concepts to conservation

## Levels of Biodiversity

**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.

**Worked example:** 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.

1. 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.
2. 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.
3. 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.
4. 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.

## Threats to Biodiversity

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.

> **HIPPO Mnemonic for Major Threats**
>
> **H**abitat loss and fragmentation, **I**nvasive alien species, **P**ollution, **P**opulation (human) growth, **O**verexploitation

**Worked example:** 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.

1. Step 1: Habitat fragmentation reduces the total population size of the lizard, which lowers genetic diversity and increases the risk of inbreeding depression.
2. 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.
3. 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.
4. Conclusion: The fragmented habitat will almost certainly lead to local extinction of the endemic lizard.

**Check your understanding**

Test your understanding of the main threat to global biodiversity:

1. 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

   *Answer:* Habitat loss and fragmentation

   *Why:* Correct. Habitat loss from deforestation, agriculture, and urbanization is the leading cause of species extinction globally.

## Indicator Species and Island Biogeography

**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.

**Worked example:** 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.

1. Step 1: Treat the fragments as 'islands' in a human-modified landscape, and apply the island biogeography model.
2. 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.
3. 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.
4. Conclusion: Patch A will have higher native bee species richness because it is larger and closer to the source population.

## Conservation Strategies: In Situ vs Ex Situ

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.

**Worked example:** Evaluate the use of ex situ conservation for a critically endangered large mammal whose natural habitat has been almost completely destroyed by human activity.

1. Step 1: Identify the advantages of ex situ conservation in this scenario:
2. - It prevents immediate extinction of the species when no intact habitat remains for in situ conservation.
3. - It allows for captive breeding programs to increase the population size from the few remaining individuals.
4. Step 2: Identify the disadvantages of ex situ conservation:
5. - It is very expensive to maintain large mammals in captivity long-term.
6. - Captive-bred individuals often lose natural behaviors required for survival in the wild, making reintroduction difficult.
7. - It does not conserve the original ecosystem or other interacting species that depend on the mammal.
8. 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.

**Comparing methods**

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
  - 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
  - Cons: Very high long-term cost; Does not conserve native ecosystem; Limited genetic diversity in captive populations

## Common pitfalls

- **Wrong:** Confusing species diversity with the full definition of biodiversity
  - Why it fails: 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: Always mention genetic, species, and ecosystem diversity when asked to define or describe biodiversity.
- **Wrong:** Claiming ex situ conservation is always better than in situ conservation
  - Why it fails: Candidates often overemphasize captive breeding, but in situ is the preferred long-term strategy for most conservation goals.
  - Correct: Frame ex situ conservation as an emergency backup measure, and in situ as the preferred long-term approach.
- **Wrong:** Mixing up indicator species and keystone species
  - Why it fails: These two terms are often confused but have completely different definitions. Examiners frequently test this distinction.
  - Correct: Remember: indicator species reflect environmental conditions; keystone species have a disproportionate effect on ecosystem structure.
- **Wrong:** Ignoring genetic diversity when discussing habitat fragmentation
  - Why it fails: Candidates often only mention loss of habitat area, but the key impact on small populations is reduced genetic diversity.
  - Correct: Always link habitat fragmentation to smaller population size, lower genetic diversity, and higher extinction risk.

## 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 |

## 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.

- [Population dynamics](https://www.owlsprep.com/study/ib-biology-sl-u3-population-dynamics/)
- [Nitrogen and nutrient cycling](https://www.owlsprep.com/study/ib-biology-sl-u3-nitrogen-and-nutrient-cycling/)
- [Theme D: Continuity and Change](https://www.owlsprep.com/study/ib-biology-sl-u4-overview/)

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