OCR AS Biology

Revision Notes

4.2.5 Simpson's Index

Simpson's 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 (species richness) but also the evenness of abundance across the different species in that area (species evenness)
  • Simpson’s index of diversity (D) can be used to quantify the biodiversity of an area

Simpson’s index

  • The formula is:

Simpson's Index equation

    •  Where:
      • n = total no. of organisms for a single species
      • N = total no. of organisms for all species
  • To calculate Simpson’s Index:
    • Step 1: First calculate n / N for each species
    • Step 2: Square each of these values
    • Step 3: Add them together and subtract the total from 1
  • To understand what the value of D means you need to know the following:
      • The value of D can fall between 0 and 1
      • Values near 1 indicate high levels of biodiversity
      • Values near 0 indicate low levels of biodiversity

Worked Example

Samples of different insect species in a back garden were collected using sweep nets and identification keys. Use the data to calculate Simpson’s Index.

The results and working out are seen in the table below. The figures have been rounded to three decimal places for columns 3 and 4

Worked example of Simspon’s Index Table, downloadable AS & A Level Biology revision notes

D = 1 – 0.172 = 0.828

As the value of D is much closer to 1 than 0, it can be said that this is a relatively high value for biodiversity.

Exam Tip

Remember, you will be provided with the formula for Simpson’s Index in the exam so you do not need to recall this.

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