Size Distributions of Butterfly Species and the Effect of Latitude on Species Sizes

For butterfly species (Papilionoidea) of the Australian and Afrotropical regions, average wingspan decreases with increasing latitude. Species size distributions are approximately lognormal, and for species greater than the modal size the relationship between log number of species and log size is characterised not by a negative slope of 2, as previously suggested from the Hutchinson/MacArthur model, but by a clearly discontinuous association with an initial negative slope of 1.4 increasing to 4 for the largest species, suggesting a possible upper limit to species sizes. A similar relationship exists for May's tentative species number/size distribution for all organisms. Possible reasons are discussed for the effect of latitude on butterfly species sizes, and for skewed species number/size distributions.