Simpson's diversity index is a measure of 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 belong to the same species.

For plant species the percentage cover in a quadrat 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 grass plants.

The formula for the Simpson index is $D=\backslash frac\{N(N-1)\}\{\backslash sum\; n(n-1)\}$ where 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.

When using Simpson Index for low number misleading results can be obtained, with obviously less diverse areas having a higher index than they should. One way round this when studying on land is to include bare earth as an extra species, this gives more realistic results.

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

References

• E.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
• http://www.snr.missouri.edu/NR211/topics/simpsons.html
• http://members.cox.net/bennowak/environment/envla/simpdivindex.htm

biodiversity | Indice di Simpson