This index is determined by both the number of species and the even distribution of individuals among those species (relative dominance). It indicates the degree of uncertainty of predicting the species of a given individual picked at random from a community. In other words, if the diversity is high, you have a poor chance of correctly predicting the species of the next individual picked at random. The formula is:

H= -sum(Pi ln[Pi])

Where:

Pi (relative abundance) = ni/N

Where:

ni = number of individuals in species i

N= total number of individuals in all species

H (the uncertainty of predicting the species) will range from 0 for a community with a single species, to over 7 for a very diverse community.

Species Evenness (E)

Using species riches (R) and the Shannon Wiener index (H), you can also compute a measure of evenness. The formula is:

E= H/ln (R)

Evenness (E) is a measure of how similar the abundance of different species are. When there are similar proportions of all species then evenness is one, but when the abundance are very dissimilar (some rare and some common species) then the value increases.

1. Use all three indices to determine which of the follow three communities of 100 individuals is most diverse.

Community 1 contained 10 species with 91 individuals in the first species, and one individual in each of the remaining species.

Community 2 also contains 10 species, but there are 10 individuals in each species.

Community 3 only contains 5 species with 20 individuals in each species.