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).
[2] It has therefore been proposed that the definition of gamma diversity does not need to be tied to a specific spatial scale, but gamma diversity can be measured for an existing dataset at any scale of interest.
[3] If results are extrapolated beyond the actual observations, it needs to be taken into account that the species diversity in the dataset generally gives an underestimation of the species diversity in a larger area.
This measure allows weighting rare and abundant species in different ways, just as the diversity indices collectively do, but its meaning is intuitively easier to understand.
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.