Does sexual conflict increase juvenile survival by reducing cannibalism?

To test the hypothesis that male harassment of females reduces adult female time spent on the water foraging (water use), and thus cannibalism by adult females on juveniles, we manipulated heterospecific prey availability, and social context in adult water striders and measured their effects on: 1) cannibalism of juveniles, 2) activity of adults and 3) habitat use of adults and juveniles. Cannibalism rarely occurred with alternative prey present, but was common without alternative prey. Without alternative prey, females cannibalized much more than males, but contrary to predictions, male presence did not reduce cannibalism rates. Male presence decreased female water use; however, this was counteracted by the fact that the lack of alternative prey increased female water use and activity while on the water. Furthermore, in groups of 4 males with 4 females, lack of alternative prey reduced male activity while on the water. Thus the predicted negative effect of sexual conflict on cannibalism was reduced by female and male responses to low food availability. Juveniles increased time off the water when more females or males were more on the water and active. Overall, cannibalism rates depended on alternative prey, male-female social dynamics, female foraging and juvenile refuge use.