Gamma diversity

In ecology, gamma diversity (γ-diversity) is the total species diversity in a landscape. The term was introduced by R. H. Whittaker^[1] together with the terms alpha diversity (α-diversity) and beta diversity (β-diversity). Whittaker's idea was that the total species diversity in a landscape (γ) is determined by two different things, the mean species diversity in sites at a more local scale (α) and the differentiation among those sites (β). According to this reasoning, alpha diversity and beta diversity constitute independent components of gamma diversity:

γ = α × β

Scale considerations

The area or landscape of interest may be of very different sizes in different situations, and no consensus has been reached on what spatial scales are appropriate to quantify gamma diversity.

Different concepts

Researchers have used different ways to define

Calculation

Suppose species diversity is equated with the effective number of species in a dataset. Then gamma diversity can be calculated by first taking the weighted mean of species proportional abundances in the dataset, and then taking the inverse of this mean. The equation is

${\displaystyle {}^{q}\!D_{\gamma }={\frac {1}{\sqrt[{q-1}]{\sum _{i=1}^{S}p_{i}p_{i}^{q-1}}}}.}$

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 ${\displaystyle p_{i}}$.

Large values of q lead to smaller gamma diversity than small values of q, because increasing q increases the weight given to those species with the highest proportional abundance, and fewer equally abundant species are hence needed to obtain this proportional abundance.[3]^[11]

See also

• Alpha diversity
• Beta diversity
• Zeta diversity
• Diversity index
• Global biodiversity
• Measurement of biodiversity
• Species richness

References