Non-native ants are smaller than related native ants

I compare the sizes of non-native and native ants to evaluate how worker si ze may be related to the ability of a species to invade new habitats. I com pare the size of 78 non-native ant species belonging to 26 genera with the size of native congeneric species; native ants are larger than non-native a nts in 22 of 26 genera. Ants were sorted by genera into fighting and nonfig hting groups, based on observations of interspecific interactions with othe r ant species. In all of the genera with monomorphic worker castes that fig ht during competition, the non-native species were smaller than the native species. The genera that engage in combat had a higher frequency of signifi cantly smaller size in non-native ants. I selected Wasmannia auropunctata f or Further studies, to compare native and non-native populations. Specimens of W. auropunctata from nonnative populations were smaller than conspecifi c counterparts from its native habitat. I consider hypotheses to explain wh y non-native ants are smaller in size than native ants, including the role of colony size in interspecific fights, changes in life history, the releas e from intraspecific fighting, and climate. The discovery that fighting non -natives are smaller than their closest native relatives may provide insigh t into the mechanisms for success of non-native species, as well as the rol e of worker size and colony size during interspecific competition.