INTERACTING EFFECTS OF PREDATION RISK AND MALE AND FEMALE DENSITY ON MALE-FEMALE CONFLICTS AND MATING DYNAMICS OF STREAM WATER STRIDERS

used a factorial experiment to examine interacting effects of male den sity, female density, and sunfish (predation risk) on mating dynamics of the stream water strider (Aquarius remigis), Many of our results co rroborated earlier studies on the isolated effects of each factor on m ating behavior. The effect of each factor, however, depended on the ot her factors. For example, in low density pools, predation risk decreas ed male general activity, male/female harassment rates, mating activit y and mating duration and increased the large male mating advantage. A t higher densities, however, water striders apparently enjoyed ''safet y in numbers'' and did not alter their mating dynamics in response to the presence of predators. Female activity showed a particularly compl ex response to male density and fish. When males were scarce, fish cau sed females to reduce their activity. However, when males were abundan t, fish increased female activity, probably because fish decreased mal e 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 dens ity resulted in a decrease in mean male mating success; however, when females were abundant, increased male density enhanced mean male matin g success. In contrast, in the presence of fish, male density had litt le effect on male mating success. Many of the observed mating patterns can be explained by the effects of ecological and social factors on m ale/female conflicts; that is, on male harassment of females and femal e reluctance to mate.