Simpson index

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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 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.

1 Overview
2 See also
3 References
4 External links

[edit] Overview

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:

$D=\frac{\sum_{i=1}^S n_i(n_i-1)}{N(N-1)}$

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.

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.

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