LIFTING THE VEIL ON ABUNDANCE PATTERNS

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.