4.2.5 Simpson's Index

• 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:

• •  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

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

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.