Size Variability in the Worker Caste of a Social Insect (Veromessor pergandei Mayr) as a Function of the Competitive Environment

Abstract

Worker size polymorphism in colonies of Veromessor pergandei, a granivorous desert ant, is inversely related to the intensity of interspecific competition in the habitat for seven ant communities in the deserts of southern California and southern Arizona. Seed size preferences are positively correlated with worker body sizes, and diet breadth relative to seed size is probably enhanced by colony polymorphism. Niche shifts within colonies of these social insects may permit unusually fine adaptation to the resource environment. In contrast to solitary organisms, for which generalization of the diet may imply significant trade-offs, these ants may expand their utilization of resources where competitors are absent while retaining an efficient size match to the distribution of available resources.