Diversity Index: Shannon Index/Shannon-Weaver Index (H)
A diversity index is the measure of species diversity in a given community. It is different from species richness in that unlike richness it also shows community composition and takes into account the relative abundance of species that are present in the community.
Shannon Index is a commonly used diversity index that takes into account both abundance and evenness of species present in the community. It is explained by the formula:
H = -∑ (Pi * ln Pi)
H = the Shannon diversity index
Pi = fraction of the entire population madeup of species i (proportion of a species i relative to TOTAL number of species present, not encountered)
S = numbers of species encountered
Here, a high value of H would be a representative of a diverse and equally distributed community and lower values represent less diverse community. A value of 0 would represent a community with just one species.
Shannon’s equitability (EH) measures the evenness of a community and can be easily calculated by diving the value of H with H_max, which equals to lnS(S=number of species encountered). Its value ranges between 0 and 1, with being complete evenness.