Age-related changes in foraging strategies and energetic constraints in the fishing spider, Dolomedes triton

Based on movement patterns during the search for prey, predators can generally be placed into one of two categories: active or passive searchers. Some predators may switch between search modes as prey densities, prey types, or metabolic needs change. An age-related switch in foraging strategies in the female fishing spider Dolomedes triton (Araneae: Pisauridae) was discovered, and experiments were conducted to examine the adaptive significance of this change in behavior. Initially, individual spiders were marked and followed during two consecutive seasons on two ponds. Adult females consistently traveled significantly greater distances per day than did juveniles. Repeated observations on individual spiders indicated that females switch to a more active search mode upon maturation. This behavioral change occurs in synchrony with increased energy demands due to the accumulation of yolk in the eggs.; A food-supplementation field experiment tested the hypothesis that the observed changes in activity following maturation represent a switch from passive to active foraging in response to the increased need for energy. Adult females were systematically assigned to either a food-supplemented group that received crickets added to their diet or to a control group that received no additional prey. Fed females moved less than control females but similar distances per day as juveniles. Control spiders moved greater distances than juveniles. Fed females also gained weight at a faster rate and hatched more than twice as many spiderlings as the control females. Laboratory experiments tested the hypothesis that this behavioral shift is associated with increased responsiveness to prey when female D. triton become mature. Crickets were introduced to the water surface at three distances (5 cm, 15 cm, and 30 cm) from adult or juvenile female fishing spiders. At 30 cm, adults were more likely to attack and exhibit shorter latencies than juveniles. Juveniles were equally likely as adults to attack at shorter distances.; The results of these studies are consistent with the hypothesis that foraging strategies of female fishing spiders change with maturity in response to increased energy requirements associated with reproduction. Successful reproduction may require increased food levels as the spiders struggle to acquire sufficient energy to provision their eggs with yolk. A change in foraging behavior that includes heightened responsiveness to prey may result in greater energy acquisition.