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Measuring biodiversityAQA A-Level Biology: Flashcards

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What is biodiversity?

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What is biodiversity?
The variety of living organisms in an area, from a small local habitat to the whole Earth.
What is species richness?
The number of different species in a community.
Why is species richness alone a limited measure?
It ignores the number of individuals in each species, so it cannot show how evenly they are spread.
What does an index of diversity describe?
The relationship between the number of species in a community and the number of individuals in each species.
State the equation for the index of diversity.
d=N(N−1)∑n(n−1)d = \frac{N(N-1)}{\sum n(n-1)}
In the index of diversity equation, what does N stand for?
The total number of organisms of all species.
In the index of diversity equation, what does n stand for?
The total number of organisms of each species.
What does a high value of d suggest?
A diverse community with many species and/or individuals evenly spread, which is likely to be stable.
What does a low value of d suggest?
A community dominated by one or a few species, which is more vulnerable to environmental change.
What is the lowest possible value of d?
1, for a community containing a single species.
A species has only 1 individual in a sample. What is n(n-1) for it?
0 (1 × 0 = 0).
Why is a value of d most useful when compared?
On its own it has little meaning; comparing habitats or the same habitat over time shows differences in diversity.
Why does random sampling improve a diversity estimate?
It avoids bias, so the sample is more likely to represent the whole habitat.

Exam questions on Measuring biodiversity

  1. Two ponds were each surveyed with the same sampling effort. Each pond contained four species and 100 individuals in total. In pond A the individuals were shared equally between the four species. In pond B, one species made up 97 of the individuals and each of the other three species was represented by a single individual.
    Explain why species richness alone is not a sufficient measure of the biodiversity of the two ponds.2 marks
  2. An ecologist calculated the index of diversity (d) for ground beetles in two habitats. The value for a hedgerow was 1.8 and the value for an area of ancient woodland was 14.5.
    Suggest why the community in the woodland is likely to be more stable than the community in the hedgerow when the environment changes.2 marks
  3. A survey of ground beetles in a woodland used randomly placed pitfall traps and recorded five species, with 12, 8, 5, 3 and 2 individuals of each. A sample collected in the same way in a neighbouring conifer plantation contained three species, with 25, 4 and 1 individuals of each.
    Calculate the index of diversity (d) for the woodland sample, using d=N(N−1)∑n(n−1)d = \frac{N(N-1)}{\sum n(n-1)}. Show your working.3 marks
See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).