<Dd> lim q → 1 q D = exp ⁡ (− ∑ i = 1 S p i ln ⁡ p i) (\ displaystyle \ lim _ (q \ rightarrow 1) () ^ (q) \! D = \ exp \ left (- \ sum _ (i = 1) ^ (S) p_ (i) \ ln p_ (i) \ right)) </Dd> <P> q = 2 corresponds to the arithmetic mean . As q approaches infinity, the generalized mean approaches the maximum p i (\ displaystyle p_ (i)) value . In practice, q modifies species weighting, such that increasing q increases the weight given to the most abundant species, and fewer equally abundant species are hence needed to reach mean proportional abundance . Consequently, large values of q lead to smaller species diversity than small values of q for the same dataset . If all species are equally abundant in the dataset, changing the value of q has no effect, but species diversity at any value of q equals species richness . </P> <P> Negative values of q are not used, because then the effective number of species (diversity) would exceed the actual number of species (richness). As q approaches negative infinity, the generalized mean approaches the minimum p i (\ displaystyle p_ (i)) value . In many real datasets, the least abundant species is represented by a single individual, and then the effective number of species would equal the number of individuals in the dataset . </P> <P> The same equation can be used to calculate the diversity in relation to any classification, not only species . If the individuals are classified into genera or functional types, p i (\ displaystyle p_ (i)) represents the proportional abundance of the ith genus or functional type, and D equals genus diversity or functional type diversity, respectively . </P>

Species is the number of species present in an ecological community