Index of Diversity (AQA A Level Biology)

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:

• 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

• 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

       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

      Step four:      Divide value A by value B

40602÷ 6884 = 5.898

Index of Diversity,d = 5.90