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

Simpson's index

• The formula is:

• To calculate Simpson’s Index:
  • Step 1: The first step is to calculate (n ÷ N) for each species
  • Step 2: Square each of these values
  • Step 3: Add them together and subtract the total from 1

• The possible values of D are significant:
  • • 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 calculations are seen in the table below. The figures have been rounded to four decimal places for columns 3 and 4

D = 1 - 0.1737 = 0.826 (3dp)

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