AQA A Level Biology

Revision Notes

4.6.3 Index of Diversity

The Index of Diversity

  • Once the abundance of different species in an area has been recorded the results can be used to calculate the species diversity or biodiversity for that area
  • Species diversity looks at the number of different species in an area but also the evenness of abundance across the different species
  • An index of diversity is a measurement that describes the relationship between the number of species present and how each species contributes to the total number of organisms that are present in that community
  • It is a much more informative measurement than species richness
    • For example, habitat A has 10 different plant species and habitat B has 7 different plant species
    • Habitat A would have a greater species richness score than habitat B
    • However, in habitat A there is only one individual of each plant species present (10 individuals present) while in habitat B there are over 20 individuals of each species present (over 140 individuals present)
    • Habitat B would have a greater index of diversity than habitat A

The index of diversity formula

  • The formula is:

Index of diversity equation_1, downloadable AS & A Level Biology revision notes

  • Where:
    • n = total no. of organisms for a single species in the community
    • N = total no. of organisms in the community
    • Σ = sum of
  •  The larger the number obtained, the higher the level of diversity

Maths Skill: Calculating the Index of Diversity

Index of diversity equation_1, downloadable AS & A Level Biology revision notes

  • To calculate:
    • Step 1: Calculate N(N-1) to find value A
    • Step 2: Calculate n(n-1) for each species
    • Step 3: Add these numbers together to find value B
    • Step 4: Divide value A by value B
  • The possible values of index diversity are significant:
    • The larger the number obtained, the higher the levels of diversity

Worked Example

Samples of different insect species in a back garden were collected using sweep nets and identification keys. Use the data recorded to calculate the index of diversity.

Index of diversity question table, downloadable AS & A Level Biology revision notesThe formula is:Index of diversity equation_1, downloadable AS & A Level Biology revision notes

       Step one:       Calculate N(N-1) to find value A

N(N-1) = 202(202-1) = 202(201) = 40602

       Step two:       Calculate n(n-1) for each species

       Step three:     Add these numbers together to find value B

Index of diversity working table, downloadable AS & A Level Biology revision notes

      Step four:      Divide value A by value B

40602÷ 6884 = 5.898

Index of Diversity,d = 5.90

Exam Tip

Remember, you will be provided with the formula in the exam.

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.
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