According to competition theory, when a population lives sympatrically with competitor populations, the variation in morphological characteristics within each population should be reduced. In allopatric populations, the variation in these characteristics should increase. I examined morphological character displacement in Polistes fuscatus populations in a north-south latitudinal gradient across the United States. P. fuscatus is sympatric with at least five other congeneric species in U.S. Gulf Coastal areas. As latitude increases, the number of species is reduced, and only P. fuscatus is found in Minnesota. Therefore, body size variation of P. fuscatus in Minnesota was predicted to be broader than the body size variation of P. fuscatus occurring in the southern U.S. To compare relative body size, I measured each species' forewing length, mesothorax width, and head capsule width from population samples from each of the latitudinal transects.
I found initial indications of character displacement in P. fuscatus across latitude, although future studies are needed. In a supplemental study, I found preliminary evidence of character displacement in island and continental populations of P. exclamans. An allopatric population of P. exclamans from Hatteras Island, North Carolina, had larger ranges of character measurements than one population of P. exclamans from continental North Carolina, and another population of P. exclamans from Alabama and Texas, where the populations are sympatric with at least four other species of Polistes.
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Whiteman, Noah K., "A Study of Morphological Character Displacement in the Social Wasp, Polistes fuscatus" (1998). Honors Theses. 643.