The residency effect in territorial males in the species Calopteryx maculata.

Abstract

Male damselflies of the species Calopteryx maculata are territorial. They defend territories which are high in quality and will increase their reproductive success. It is believed that in aggressive encounters, the territorial or resident male, will show a ""residency effect."" Residency effect is defined as a pattern in which a resident of a territory has an advantage in aggressive encounters because he has more recently assessed the territory quality and its resources. I designed my study to test if in fact the Calopteryx maculata are illustrating the residency effect. I conducted my study on the Maple River during the reproductively active period in August 1993. I identified two sites of high territory quality. I captured and contained damselflies for fifteen minutes. New territorial males subsequently took over the unoccupied territories. I released the experimental damselflies and recorded the number of male-male interactions, who initiated the interaction, time of the interactions, type of interaction, and the winner. The winner is defined as the damselfly who remains in the territory after the aggressive encounters. In analyzing the data I found that there was no capturing effect on the damselfly (p<.001). The controls were able to reestablish their territory when there were no competitors. The experimental were unable to return to their original territory. Therefore I can conclude that the present condition on the territory (occupied or not occupied) was the determining factor. Next I found that the residential damselfly significantly won more aggressive encounters and tended to remain in his territory (.005<p<.001). The non-territorial male tended was often forced to leave. I also found that the residential damselfly significantly initiated more aggressive acts than the non-territorial male (p<.001). The fact that the residential male initiates the aggressive interactions and tends to win them, supports my hypothesis that the residential male shows a residency effect.