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Simpson's diversity index (also known as species diversity index) is one of a number of diversity indices, used to measure diversity. In ecology, it is often used to quantify the biodiversity of a habitat. It takes into account the number of species present, as well as the relative abundance of each species. The Simpson index represents the probability that two randomly selected individuals in the habitat will not belong to the same species.

Overview

For plant species the percentage cover in a square is usually used; for animal species, for example in a river, the number of organisms of a species is used. The reason percentage cover is used is because it is usually very difficult to count all the individual plants.

The formula for the Simpson index is:

${\displaystyle D=1-{\frac {\sum _{i=1}^{S}n_{i}(n_{i}-1)}{N(N-1)}},}$

where S is the number of species, N is the total percentage cover or total number of organisms and n is the percentage cover of a species or number of organisms of a species. In this form, D ranges from 1 to 0, with 1 representing infinite diversity and 0 representing no diversity.

When using the Simpson Index for lower numbers, misleading results can be obtained, with obviously less diverse areas having a higher index than they should. One way around this when studying on land is to include bare earth as an extra species, which yields more realistic results. A low Simpson index value equates high diversity, whereas a high value correlates to a low diversity (thus the index is typically subtracted from 1, as in the above formula).

The Simpson index was first proposed by the British statistician Edward H. Simpson in a paper in Nature in 1949.

See also

• Biodiversity
• Species richness
• Shannon index

References

• Edward H. Simpson (1949) Measurement of diversity. Nature 163:688 see http://www.wku.edu/~smithch/biogeog/SIMP1949.htm

External links

• http://www.countrysideinfo.co.uk/simpsons.htm

• Measurement of biodiversity