What does biodiversity actually measure, and why does it matter at the genetic, species and habitat levels?
The meaning of biodiversity at the genetic, species and habitat levels, how species and habitat diversity are measured and estimated, and the value of biodiversity to humans and ecosystems.
A focused answer to AQA A-Level Environmental Science 3.1.2, covering the three levels of biodiversity, the index of diversity, sampling and estimation, and the ecological and economic value of biodiversity.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
AQA wants you to define biodiversity at three levels (genetic, species and habitat), explain how species diversity is measured using an index of diversity, describe how diversity is estimated by sampling, and explain why biodiversity is valuable. Command words are Define, Explain and Calculate, so you must be ready to compute an index of diversity.
The three levels of biodiversity
Measuring species diversity
Species diversity depends on both how many species are present (richness) and how evenly individuals are spread among them (evenness). A community where one species dominates has lower diversity than one where individuals are spread evenly, even if both contain the same number of species.
Estimating biodiversity by sampling
It is impossible to count every organism, so diversity is estimated from samples. Plants and slow-moving organisms are sampled with quadrats placed at random along transects; mobile animals are sampled by pitfall traps, nets or mark-release-recapture. Random sampling reduces bias, and a larger number of replicate samples gives a more reliable estimate from which the index is calculated.
The value of biodiversity
- Ecological value. Greater biodiversity tends to make ecosystems more stable and resilient to disturbance, because more species can fill key roles, and it underpins services such as pollination and nutrient cycling.
- Economic value. Biodiversity provides food, timber, medicines, and genetic resources for crop and livestock breeding; wild relatives of crops are a reservoir of useful alleles.
- Aesthetic and ethical value. Wild species and habitats have recreational, cultural and intrinsic worth.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20195 marksCalculate the index of diversity for a community of three species with 9, 3 and 3 individuals, using the formula given, and explain what the value indicates.Show worked answer →
A full worked calculation is expected using Simpson's index of diversity, .
Total individuals , so .
For each species, : , , , summing to .
So .
Interpretation: the value combines richness and evenness; a higher value means greater diversity. Here one species dominates, so is modest. Award the correct , the sum of , the final value, and a comment that dominance lowers diversity.
AQA 20214 marksExplain why an index of diversity is a better measure of biodiversity than a simple count of the number of species present.Show worked answer →
Markers reward the richness-plus-evenness reasoning.
A simple species count records only richness (how many species) and treats a community where one species dominates the same as one where individuals are spread evenly. An index of diversity combines richness with evenness (the relative abundance of each species), so it distinguishes these cases.
A community dominated by a single species is ecologically less diverse and less resilient than an even one, even with the same species count, so the index gives a more meaningful picture of community structure. Full marks need both the evenness point and a reason it matters ecologically.
Related dot points
- The conditions that allowed life to develop on Earth, the role of liquid water and an oxygen atmosphere, the changing of conditions by living organisms, and the Gaia hypothesis of self-regulation.
A focused answer to AQA A-Level Environmental Science 3.1.1, covering the physical conditions that allow life on Earth, the role of liquid water and the oxygen atmosphere, how organisms changed the planet, and the Gaia hypothesis.
- The reasons biodiversity should be conserved, the causes of biodiversity loss, and the range of in-situ and ex-situ conservation methods used to protect species and habitats.
A focused answer to AQA A-Level Environmental Science 3.1.4, covering reasons to conserve biodiversity, the causes of species loss, and in-situ and ex-situ conservation methods including reserves, captive breeding, seed banks and legislation.
- The processes that move carbon and nitrogen through the biosphere, atmosphere, hydrosphere and lithosphere, including photosynthesis, respiration, nitrogen fixation, nitrification, denitrification and decomposition.
A focused answer to AQA A-Level Environmental Science 3.1.3, covering the carbon cycle and nitrogen cycle, the key biological and physical processes that drive them, and how human activity disrupts each cycle.
- Methods of sampling populations and habitats including quadrats, transects and capture techniques, the importance of random sampling and replication, and the abiotic and biotic factors that are monitored.
A focused answer to AQA A-Level Environmental Science 3.6 research methods, covering sampling techniques such as quadrats, transects and mark-release-recapture, the importance of random sampling and replication, and the abiotic and biotic factors monitored.
- The flow of energy through ecosystems via food chains and trophic levels, the inefficiency of energy transfer, productivity, and the cycling of matter that supports life in the biosphere.
A focused answer to AQA A-Level Environmental Science 3.1.5, covering energy flow through food chains, trophic levels, the inefficiency of transfer, productivity, and how matter cycles through the biosphere.