Body size, colony size, and range size in ants (Hymenoptera: Formicidae): are patterns along elevational and latitudinal gradients consistent with Bergmann's Rule?

Body size of organisms often increases with latitude and elevation, a pattern commonly called Bergmann's Rule. Though this pattern has been documented in many endothermic taxa, relatively few insect taxa have been examined, with some taxa showing strong support and other taxa showing little or no support for the rule. For colonial organisms (social insects, corals, bryozoans) size can also be estimated as the number of sub-units. Consequently, for ants the number of workers per colony should also increase with latitude or elevation. Here, we test whether body size or colony size is related to latitude and elevation for ants in eastern North America. We found no positive relationship between body size or colony size and elevation or latitude. However, species with large latitudinal ranges also had large elevational ranges, suggesting that species that are able to tolerate broad climatic conditions have the largest ranges. In addition, species with high latitudinal maxima also had high elevational maxima. Taken together, our results do not support Bergmann's Rule in ants, in contrast to other studies on ants. But climate imposes limits on ant distributions in similar ways along both elevational and latitudinal gradients.