Species diversity is the effective number of different species
that are represented in a collection of individuals (a dataset).
The effective number of species refers to the number of equally-
abundant species needed to obtain the same mean proportional
species abundance as that observed in the dataset of interest
(where all species may not be equally abundant). Species
diversity consists of two components, species richness and
species evenness. Species richness is a simple count of species,
whereas species evenness quantifies how equal the abundances of
the species are. Calculation of diversity The denominator equals
mean proportional species abundance in the dataset as calculated
with the weighted generalized mean with exponent q - 1. In the
equation, S is the total number of species (species richness) in
the dataset, and the proportional abundance of the ith species
is . The proportional abundances themselves are used as weights.
The equation is often written in the equivalent form: The value
of q defines w