Definitions: S, observed species richness; \(p_{i}\), relative abundance
of species i; q , exponent that determines the sensitivity to rare
species (0 = very sensitive, 2 = not very sensitive); N, observed number
of individuals in the sample; \(X_{i}\) number of individuals of species
i; ENS, the effective number of species which is the number of equally
abundant species that results in the same value of diversity as the
sample. To calculate \(E_{n}\), equation 3 can be solved numerically for
given values of \(S_{n}\)and n.