Evidence of Competition Between Two Canopy Ant Species: Is Aggressive Behavior Innate or Shaped by a Competitive Environment?

Abstract

Competition occurs in all ecological communities, although it has not always been experimentally tested as a structuring force in the distribution of species. We tested the hypothesis that the aggressiveness exhibited byCamponotus rufipeschanges according to the pressures of a competitive environment. This is a dominant species in the montane forest of the Itacolomi State Park, Brazil, whereCamponotus sericeiventrisdoes not occur. Using bait traps in a field site where both species occur, (“Juiz de Fora” site) we showed thatC. sericeiventriswas able to removeC. rufipesworkers at the same bait. In the laboratory, we used dyadic encounters to test workers from both species taken from colonies found in areas where both occur and where onlyC. rufipeswas found.Camponotus rufipesfrom Itacolomi fought significantly less and was killed during the first few minutes in 60% of the events. On the other hand, the workers that co-existed withC. sericeiventrisin the field were more aggressive, but less efficient fighters than the latter. This investigation demonstrated existence of competition betweenC. rufipesandC. sericeiventris, and also the lower aggressiveness ofC. rufipes'individuals that did not co-exist in the field withC. sericeiventris.