Prey availability limits fecundity and influences the movement pattern of female fishing spiders

We conducted a food supplementation field experiment to test two hypotheses : (1) fecundity of the fishing spider Dolomedes triton is limited by a shor tage of prey, and (2) the increased movement of adult female D. triton exhi bited upon maturation is a foraging adaptation to lessen the impact of food limitation on egg production. Free ranging, uniquely marked adult female f ishing spiders were assigned either to a food-supplemented group that recei ved crickets in addition to their natural diet, or to a control group. Juve nile female spiders were also marked and their movement patterns were recor ded, but juveniles were not offered supplemental food. Food-supplemented ad ult females gained weight at a faster rate and hatched more than twice as m any offspring as control females. Adult females in the control group moved greater distances per day than did juvenile females. Supplemented adult fem ales moved shorter distances per day than control females, and the movement pattern of fed adults did not differ from that of juveniles. These results support the hypotheses that adult female D. triton are food limited, and t hat the increased movement of adult females is a switch in foraging behavio r that occurs during the reproductive period. Our finding that natural prey shortages limit egg production contrasts with laboratory-based studies of food limitation in the genus Dolomedes, and contradicts a basic assumption of a recent hypothesis that sexual cannibalism in Dolomedes is non-adaptive . These discrepancies highlight the importance of insights gained from fiel d experiments with natural populations.