MALE AMPHIPODS (COROPHIUM VOLUTATOR [PALLAS]) SHOW FLEXIBLE BEHAVIOR IN RELATION TO RISK OF PREDATION BY SANDPIPERS

Based on theory, we predicted that males, but not females, of the intertidal amphipod, Corophium volutator (Pallas), would show variation in crawling activity in relation to risk of sandpiper predation. We chose two mudflats in the upper Bay of Fundy for study. One mudflat was visited by thousands of semipalmated sandpipers (Calidris pusilla L.) in the late summers; the other mudflat was not visited by sandpipers. As predicted, we found that only males showed reductions in their crawling activity and only at the mudflat visited by sandpipers. Moreover, temporal and experimentally-produced spatial variation in feeding activity of sandpipers at that mudflat was closely associated with temporal and spatial variation in male crawling activity. Direct predation by sandpipers could not account for the drastic reductions in crawling activity of males. That flexible behaviour exists in this species and is restricted to one sex is intriguing. Although our results support the theory on evolution of flexible behaviour, we are still uncertain of the extent to which flexible behaviour influences known demographical differences between subpopulations of C. volutator.