Resource acquisition and alternative mating strategies in water striders

Behavioral polymorphisms occur among male and female water striders, Gems remigis, when competing for food and mates. Individuals of both sexes vie for positions in the fastest flowing portions of streams. Here prey capture rates are highest, as are those of swimming and aggression. Only the largest females, and males with the largest first appendages, can regularly maintain positions in these areas. The remaining females are arranged along the flow gradient according to their size with the smallest holding positions in pools of slow moving water. For the remaining males neither overall size, nor the size of the first appendages, appears to determine which males swim near the edge of streams, or which males swim as satellites behind those occupying the fast flowing productive areas. Preliminary data show that mating success of edge and satellite males are about equal, but significantly less than that of the centrally positioned males with the largest first appendages. Thus although it appears that morphological phenotype influences male competitive behavior, when the absolute size of the critical trait is small males adopt behavior after assessing the actions of others. For these "subordinate" males, behavioral assessment appears to produce an "ideal free" spatial distribution.