On-line statistics

What is diversity?

The simplest measure of species diversity often used by ecologists is species richness, the number of species per unit area or volume. However, consider a situation where three samples have the same number of species but their relative abundances are quite different:

Which sample has the greatest diversity? All four species have the same species richness but there is clearly a large difference in the community composition of samples A and C. Sample C is clearly less diverse than sample A since the greatest number of individuals in the sample are woodlice. Diversity can be quantified using Simpsons index, an index that takes both the number of species and their relative contribution to the community into account.

Simpsons Index

where n is the number of individuals of a particular species and N is the total number of individuals. The number of animals representing each species is divided by the total number of animals in the sample and this figure is then squared. D is the total sum of these figures for each species.

Worked example

For sample A the number of woodlice present (n) is 3 and the total number of individuals in the sample (N) is 12. The figure for this species is therefore:

since n = 3 for each of these species, D = 1 - (0.0625 x 4) = 0.75

Source : Bakus (1990)

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Descriptive Stats

Diversity Indices

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Regression