Factors affecting the outcome of aggressive territorial interactions in dark wing damselflies (Calopteryx maculata).

Abstract

Based on the field observations of dark wing damselflies in Northern Michigan it was hypothesized that the outcome of aggressive territorial interactions may be affected by properties of the site, the intruder, or the interaction. Specifically, that a high quality site, many females present, low residence time, the intruder being a previous resident, high interaction time, and/or small resident size would decrese resident wins. To test this, field data on these parameters was collected during interactions and correlated with resident wins or losses. Three qualitatively different territorial sites were used and the individuals were marked for identification. Observations were made of both unassisted behavior and field experiments that entailed the removal of a resident male who was released immediately upon re-occupation of the site. Most of the short-time resident data came from these experiments. Out of 46 interactions the resident lost 22% of the time, those losses occurring in the highest quality territories 100% of the time. Chi-square and t-test analysis did not show statistical significance for any of the parameters tested except interaction time and size of participants. The limited number of trials regarding size makes its significance questionable. The results indicate that the residence effect may be less important that previously reported. If so, the number of resident losses in the high quality territories coupled with lengthy interaction times may indicate that it is not uncommon for intruders to find that the reproductive benefits outweigh the energetic costs of conflict.