Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

We used a factorial experiment to examine interacting effects of male density, female density, and sunfish (predation risk) on mating dynamics of the stream water strider (Aquarius remigis). Many of our results corroborated earlier studies on the isolated effects of each factor on mating behavior. The effect of each factor, however, depended on the other factors. For example, in low density pools, predation risk decreased male general activity, male/female harassment rates, mating activity, and mating duration and increased the large male mating advantage. At higher densities, however, water striders apparently enjoyed "safety in numbers" and did not alter their mating dynamics in response to the presence of predators. Female activity showed a particularly complex response to male density and fish. When males were scarce, fish caused females to reduce their activity. However, when males were abundant, fish increased female activity, probably because fish decreased male activity thus releasing females from harassment by males. The three treatment factors also had interacting effects on male mating success. In the absence of fish, when females were scarce, increased male density resulted in a decrease in mean male mating success; however, when females were abundant, increased male density enhanced mean male mating success. In contrast, in the presence of fish, male density had little effect on male mating success. Many of the observed mating patterns can be explained by the effects of ecological and social factors on male/female conflicts; that is, on male harassment of females and female reluctance to mate.