ConservationCambridge IGCSE Biology: Revision notes
Section 1
What is a sustainable resource and why does it matter?
A sustainable resource is one that is produced by the environment at the same rate at which it is removed, meaning it does not run out. This concept is central to conservation because it allows humans to use natural resources indefinitely without depleting them.
Key principle: If removal rate = replacement rate, the resource remains available for future generations.
Common examples of resources that can be managed sustainably:
- Forest timber
- Fish stocks
- Freshwater
- Crops
Unsustainable use occurs when removal exceeds the rate of natural replacement, leading to depletion and potential extinction of species or loss of ecosystem services.
Think of a bank account: if you withdraw money at exactly the rate your salary deposits it, your balance stays the same indefinitely. If you withdraw faster than you earn, you go bankrupt.
Section 2
Why do organisms become endangered or extinct?
Organisms face extinction risk from multiple human-caused and environmental factors:
| Cause | How it endangers species |
|---|---|
| Climate change | Alters habitats, food availability, and breeding conditions; species cannot adapt quickly enough |
| Habitat destruction | Removes shelter, breeding sites, and food sources; fragments populations |
| Hunting/overharvesting | Direct removal of individuals faster than reproduction replaces them |
| Pollution | Contaminates air, water, and soil; causes disease and reproductive failure |
| Introduced species | Outcompete native species for resources; may prey on natives; disrupt ecosystem balance |
Extinction occurs when the last individual of a species dies and the species no longer exists anywhere in the world. Endangered species are at high risk of extinction if current trends continue.
Examiners want you to link the cause to the mechanism: don't just say 'climate change causes extinction', explain how (e.g. 'rising temperatures shift food availability, causing starvation').
Giant pandas are endangered due to habitat destruction (bamboo forests cleared for human development), reducing available food and breeding sites. Poaching further reduced wild populations. Conservation now involves protection of forest reserves and captive breeding.
Section 3
How can endangered species be conserved?
Four main conservation strategies protect endangered species:
1. Monitoring and protecting species and habitats
- Regular surveys track population size and health
- Legal protection prevents hunting and trade
- Habitat restoration ensures sufficient resources
- Reduces human disturbance in sensitive areas
2. Education and awareness
- Public campaigns increase support for conservation
- Schools and media reduce demand for endangered species products
- Local communities understand the value of biodiversity
3. Captive breeding programmes
- Endangered species bred in controlled environments (zoos, research centres)
- Artificial insemination used when natural breeding fails; sperm is collected and inserted into females artificially
- In vitro fertilisation (IVF) involves fertilising eggs outside the body in laboratory conditions, then implanting embryos
- Offspring can be reintroduced to the wild if populations recover
4. Seed banks
- Seeds from endangered plants stored at low temperature in seed banks
- Preserves genetic diversity for future replanting
- Protects against extinction if wild populations are destroyed
Benefits of these methods: They increase survival rates, preserve genetic diversity, and allow species recovery without requiring immediate habitat restoration.
When answering about captive breeding, specify which technique is being used (artificial insemination or IVF) and why it is needed. Examiners reward precise understanding of the difference.
Students often think captive breeding alone is sufficient. Remember: it is a short-term solution that must be combined with habitat protection and education, otherwise reintroduced animals will face the same threats that endangered them.
Section 4
How can forests and fish stocks be conserved sustainably?
Conservation of forests:
- Education: Communities and users learn sustainable forestry practices; understand the ecosystem value of forests
- Protected areas: Legal designation prevents logging in ecologically sensitive regions
- Quotas: Limit the volume of timber harvested per year to match growth rate
- Replanting: New trees planted to replace those removed, maintaining forest cover and regeneration
Conservation of fish stocks:
| Method | How it works |
|---|---|
| Education | Reduce demand for overfished species; promote sustainable fishing practices |
| Closed seasons | Prohibit fishing during breeding periods, allowing population recovery |
| Protected areas | Designated marine reserves where fishing is banned or restricted |
| Controlled net types and mesh size | Large mesh allows juvenile fish to escape; bans on destructive gear (e.g. explosives) |
| Quotas | Limit catch per boat/year to match sustainable yield |
| Monitoring | Regular surveys of fish populations guide quota adjustment; track effectiveness |
Key principle for both: The harvest rate must not exceed the natural replacement rate. These methods ensure resources regenerate and remain available.
A fish stock conservation strategy might combine: closed seasons (no fishing June–August during spawning), protected marine reserves (no fishing allowed), monitoring of stock numbers annually, and quotas set based on monitoring data (e.g. maximum 10,000 tonnes caught per year).
Section 5
Why are conservation programmes necessary?
Conservation programmes serve multiple interconnected purposes:
1. Maintaining or increasing biodiversity
- Protects the variety of species and ecosystems
- Ensures ecosystem resilience and stability
- Provides insurance against future environmental changes
2. Reducing extinction
- Prevents permanent loss of species
- Saves organisms from irreversible disappearance
- Protects evolutionary lineages
3. Protecting vulnerable ecosystems
- Maintains entire communities of species that depend on each other
- Preserves ecosystem services (e.g. pollination, water filtration, climate regulation)
- Protects habitats that cannot be easily restored
4. Maintaining nutrient cycling and resource provision
- Organisms drive nutrient cycles (carbon, nitrogen, phosphorus) essential for life
- Ecosystems provide:
- Food: Direct protein and energy sources
- Drugs: Many pharmaceuticals derived from plants and animals
- Fuel: Timber, biofuels from sustainable sources
- Genes: Genetic material for breeding disease-resistant crops and developing new medicines
Without conservation, loss of species disrupts these services, impacting human survival and quality of life.
When asked 'why conserve', always link the reason to human benefit or necessity—examiners want you to understand conservation is practical, not just emotional. For example: 'Forests cycle carbon, reducing climate change' or 'Wild plants provide genes for crop breeding.'
Section 6
What are the risks when species populations become small?
When a species population is reduced to a small size, it faces critical genetic and demographic risks:
Reduced genetic variation
- Small populations have fewer different alleles (versions of genes)
- Inbreeding becomes inevitable; individuals breed with relatives
- Homozygosity increases: more harmful recessive alleles are expressed
- Fitness decreases: reduced ability to survive disease, adapt to environmental change, or reproduce successfully
- Genetic drift causes random loss of alleles, further reducing variation
Consequences of low genetic variation:
- Increased susceptibility to disease (limited immune gene diversity)
- Reduced fertility and survival of offspring
- Inability to adapt if environment changes (e.g. new pathogen, climate shift)
- Increased extinction risk even if habitat is restored
Example scenario: A captive breeding programme that starts with only 10 individuals will have much lower genetic diversity than starting with 100, limiting long-term survival chances.
Why this matters for conservation: Genetic variation is essential for species survival. Even if a population is protected, it may still go extinct due to genetic deterioration. This is why programmes aim to:
- Maximize the number of founders in captive breeding
- Maintain detailed breeding records to minimize inbreeding
- Use genetic testing to guide which individuals breed together
Students often think that if you protect a small population's habitat, it will automatically recover. In reality, genetic problems from small population size can cause extinction even with habitat protection. You must address genetic diversity in conservation plans.
A small population is like a cookbook with only 5 recipes: you can make the same dishes over and over, but you cannot create anything new or adapt if ingredients change. A large population is like a cookbook with 1000 recipes—more options, more flexibility, better chance of finding a solution.
Must Know
- Sustainable resources are produced at the same rate they are removed, so they do not run out; forests and fish stocks can both be managed sustainably
- Organisms become endangered or extinct due to: climate change, habitat destruction, hunting/overharvesting, pollution, and introduced species
- Four ways to conserve endangered species: (1) monitoring and protecting species/habitats, (2) education, (3) captive breeding (using artificial insemination or IVF), and (4) seed banks
- Forests are conserved by education, protected areas, quotas, and replanting; fish stocks are conserved by education, closed seasons, protected areas, controlled nets/mesh size, quotas, and monitoring
- Reasons for conservation: maintain biodiversity, reduce extinction, protect vulnerable ecosystems, and preserve nutrient cycling and resource provision (food, drugs, fuel, genes)
- Small populations lose genetic variation, increasing homozygosity, reducing fitness, and raising extinction risk even if habitat is protected
That's the notes covered.
Carry on to the next subtopic.