Conservation of biodiversity — IB Diploma Biology SL
IB Biology A4.2: biodiversity, causes of the sixth mass extinction and ecosystem loss, evidence for a biodiversity crisis, and conservation approaches.
Revision notes
4 short notes, in the order of the specification. Each one in short:
Biodiversity is the variety of life in all its forms, levels and combinations, including ecosystem diversity, species diversity and genetic diversity. Millions of species have been discovered, named and described, but many more remain to be discovered. Evidence from fossils suggests that more species are alive on Earth today than at any time in the past.
Anthropogenic extinction is caused by human activity and drives the current sixth mass extinction. The North Island giant moa was hunted to extinction soon after human settlement of New Zealand, and the Caribbean monk seal was killed for oil and lost its food. Mixed dipterocarp forest in Southeast Asia is lost through logging, clearance for plantations and fire.
Evidence for a biodiversity crisis comes from reliable surveys of biodiversity repeated over time in many habitats, summarised in IPBES reports. Repeated surveys show change in species richness and evenness. The overarching cause is human population growth, together with over-exploitation, urbanization, deforestation and land clearance, pollution, and the spread of pests, diseases and invasive alien species by global transport.
Conservation of biodiversity needs several approaches, because no single approach is sufficient and different species need different measures. These include in situ conservation and nature reserves, rewilding and reclamation of degraded ecosystems, ex situ conservation in zoos and botanic gardens, and seed or tissue banks. The EDGE of Existence programme prioritises species that are evolutionarily distinct and globally endangered.
Exam questions
8 exam-style questions (23 marks), each with its mark scheme.
Answer the questionsFlashcards
16 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecosystems (unity and diversity) on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
Name the three levels of biodiversity.
Show answer
Ecosystem diversity, species diversity and genetic diversity.
What does fossil evidence suggest about the number of species alive today?
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There are more species alive today than at any time in the past.
Why must biodiversity surveys be repeated?
Show answer
To provide evidence of change in species richness and evenness over time.
What is the overarching cause of the current biodiversity crisis?
Show answer
Human population growth.
What does EDGE stand for?
Show answer
Evolutionarily distinct and globally endangered.
Frequently asked questions
What are the three levels of biodiversity?
Biodiversity is the variety of life in all its forms, levels and combinations. Ecosystem diversity is the variety of habitats in an area. Species diversity is the number of species and how evenly individuals are spread between them. Genetic diversity is the variety of alleles within a species, which helps populations adapt to change.
What is causing the sixth mass extinction?
The sixth mass extinction is caused by human activity. Human population growth is the overarching cause, acting through hunting and other over-exploitation, urbanization, deforestation and land clearance for agriculture, pollution, and the spread of pests, diseases and invasive alien species by global transport. Case studies such as the moa and Caribbean monk seal show these causes.
Why did the North Island giant moa go extinct?
The North Island giant moa was hunted to extinction within about two centuries of human settlement of New Zealand. People hunted the birds and took eggs, and burned forest habitat. Moa bred slowly and had no evolved fear of land predators, so their populations could not recover from hunting pressure.
What is the difference between in situ and ex situ conservation?
In situ conservation protects species in their natural habitats, for example in managed nature reserves, so they keep interacting with their community. Ex situ conservation keeps species away from their habitat, in zoos, botanic gardens, or seed and tissue banks. Several approaches are needed because no single approach is sufficient for every species.
Why does the EDGE programme focus on evolutionarily distinct species?
Evolutionarily distinct species have few or no close relatives, so each represents a large amount of unique evolutionary history. If such a species is also globally endangered and becomes extinct, unique genes and features are lost that no other species carries. With limited funds, the EDGE programme prioritises these species.
Written and checked against the IB Biology SL specification · Updated October 2026