Shannon-Wiener Index

Choose this diversity calculation from the Alpha Diversity tab.

This presents the Shannon-Wiener (also incorrectly known as Shannon-Weaver) diversity index for each sample. A simple plot of the way the index changes between samples is displayed by clicking on the Graph tab on the output window.

The function was originally devised to determine the amount of information in a code or signal, and is defined as:

where pi = the proportion of individuals in the ith species. Species Diversity & Richness calculates the index using the natural logarithm.

In terms of species abundance:

where ni = the number of species with i individuals. The information measure is nits for base e and bits per individual for base 2 logarithms.

This ever-popular index is really not as good as its popularity would imply. However, it appears pleasantly sophisticated! To quote Southwood and Henderson (2000) "..it is an insensitive measure of the character of the S:N relationship and is dominated by the abundant species". The value of the Shannon-Wiener Index usually lies between 1.5 and 3.5 for ecological data and rarely exceeds 4.0. May (1975) notes that if species follow a log normal abundance distribution the sample must hold 100,000 species for H to be greater than 5.0. By itself, this index often gives little more insight than Species number.

To compare two indices see Testing for significant differences between indices.