Lifting the veil on abundance patterns

Abstract

The distribution of species abundances in samples from large species assemblages appears to follow a lognormal distribution truncated on the left at what Preston called the `veil line'. MacArthur suggested that if we could see the entire, unveiled distribution of abundances in the assemblage, we would discover that the distribution is left-skewed. This suggestion takes on a particular interest because, as we will show, Sugihara's so-far successful model of abundance patterns predicts that abundance distributions are more likely to be left- than right-skewed. Recently published estimates of the population sizes of British bird species allow us to observe the completely unveiled distribution of a natural assemblage. This data set is, perhaps, uniquely informative because of the accuracy of the population size estimates of rare British bird species. The distribution is indeed left-skewed and the degree of left-skewness is quantitatively compatible with Sugihara's model.