Proboscis Length and the Coexistence of Bumblebee Species

Proboscis length spacings were studied among species in local and regional communities of bumblebees in Europe and North America. A simple numerical method has been developed which takes into account abundances of the species. Species in local and regional communities were arranged by descending abundance, and observed spacings in proboscis lengths were then calculated for increasing number (k) of species ranked by abundance. Observed spacings are compared with those obtained by making all possible k species combinations of the species pool of S species. Observed and expected spacings are compared by dividing their difference by the standard deviation of the expected spacing. In most of the studied communities the proboscis lengths of the most abundant species are more similar than expected on the basis of competition theory. The observed clustering of proboscis length of the 2 to 5 most abundant species in the communities is most likely the result of uneven availability of flower resources, classified by depth of corolla tubes of individual flowers.