IB Biology · Theme A: Unity and diversity · SL and HL
A4.2 Conservation of biodiversity
A one-page summary of A4.2 Conservation of biodiversity, the key terms to know, and sample exam questions with answers. For the full lesson, open the illustrated revision slides or practise in the app.
Guiding questions
What factors are causing the sixth mass extinction of species?
How can conservationists minimize the loss of biodiversity?
What A4.2 covers
What biodiversity is, and how fast it's changing
- A4.2.1Biodiversity has three levels, not one
- A4.2.2More species alive today than ever recorded
Why biodiversity is being lost
- A4.2.3Five ways humans drive extinction
- A4.2.3Terrestrial megafauna: the moa, gone in 150 years
- A4.2.3A marine loss: the Caribbean monk seal
- A4.2.3A third case: the dodo of Mauritius
- A4.2.4An ecosystem can vanish intact
- A4.2.4A second case, closer to home: the tallgrass prairie
- A4.2.5The evidence isn't one number
- A4.2.6One overarching cause
Responding: conservation in practice
- A4.2.7Protect it where it lives
- A4.2.7Putting nature back: rewilding & reclamation
- A4.2.7When the habitat is already gone
- A4.2.7The last resort: seed & tissue banks
- A4.2.8Not every endangered species is equal
A4.2 Conservation of biodiversity: summary
What is biodiversity
- Three levels: ecosystem, species, genetic.
- Richness = species count; evenness = how evenly spread.
Species & extinction scale
- ~1.8M species described; ~8.7M estimated total.
- Five past mass extinctions; possibly a sixth underway now.
Direct causes
- Habitat loss, overexploitation, invasive species, pollution, climate change.
- Case studies: North Island giant moa, Caribbean monk seal.
Ecosystem loss
- Land-use change, fragmentation, freshwater & marine degradation.
- Case study: mixed dipterocarp forest, Southeast Asia.
Evidence & drivers
- IUCN Red List; Living Planet Index (73% decline since 1970).
- Overarching cause: population growth + rising consumption.
Conservation
- In situ (reserves, corridors, rewilding) vs ex situ (zoos, seed banks).
- EDGE prioritises evolutionarily distinct, endangered species.
Key terms
- Biodiversity
- The total variety of life at every level — ecosystem, species and genetic.
- Species richness
- The number of different species present in a community.
- Species evenness
- How evenly individuals are distributed among those species.
- Genetic diversity
- The range of alleles within a species' own gene pool.
- Anthropogenic
- Caused by human activity, not a natural event.
- In situ conservation
- Protecting a species inside its own natural habitat.
- Ex situ conservation
- Protecting a species outside its natural habitat (zoos, seed banks).
- IUCN Red List
- The global assessment of a species' extinction risk.
- EDGE score
- A ranking combining evolutionary distinctiveness with endangerment.
Sample exam questions
Three of the 32 multiple-choice questions for A4.2. Try each one before opening the answer.
Question 1. Which definition best describes biodiversity?
- The total number of individual organisms present
- The variety of ecosystems, species and genes
- The mass of all living organisms present
- The number of trophic levels in a food web
Show the answer
Answer: B. Biodiversity is measured at three levels: the variety of ecosystems, the variety of species, and the genetic variety within species.
Question 2. Two communities each contain four species. Community A has individuals shared roughly equally between the species; community B is dominated by one species. Which statement is correct?
- Community A has greater richness than community B
- Community B has greater evenness than A
- Community A has greater evenness than community B
- The two communities have identical diversity
Show the answer
Answer: C. Both have the same richness (four species), but A shares individuals more equally, so A has higher evenness and therefore higher overall diversity.
Question 3. 'Splitters' recognize more species within a taxonomic group than 'lumpers' do, even when looking at the same specimens. This is best explained by the nature-of-science idea that:
- splitters and lumpers are studying genuinely different sets of organisms
- the same observations can be classified in different ways, since classification involves subjective judgement as well as data
- one of the two groups must always be using incorrect data
- classification decisions have no effect on estimated species counts
Show the answer
Answer: B. Classification is an example of pattern recognition, but the same observed variation can be classified differently depending on where a scientist draws the line between one species and a distinct but similar one, which is why splitters and lumpers can disagree on the same specimens.
Linking questions
Questions that connect A4.2 to other parts of the course, the kind that come up in Paper 2.
- How do the interactions and stability of an ecosystem depend on its biodiversity? (see C4.1, D4.2)
- How could climate change alter species distributions and add to the current biodiversity crisis? (see D4.3)
- How does natural selection depend on the genetic diversity within a species? (see D4.1, A4.1)
- How does the classification of species help conservationists identify and prioritise biodiversity? (see A3.1, A3.2)
Practise A4.2
Study notes, every question and full markschemes for A4.2 are in the app with Pro. Two lessons are completely free to try: A1.1 Water and B1.1 Carbohydrates and lipids.