Reduced Prey Capture Research Articles

Condition-dependent spider web architecture in the western black widow, Latrodectus hesperus

Animals use behavioural plasticity to cope with conflicting selective pressures. We investigated how prey availability affects the spinning of cobwebs, whose architecture influences both prey capture and defence. Fed western black widows spun cobwebs containing more silk than did fasted spiders. However, fed spiders invested relatively less silk in the sheets and sticky gumfooted threads of webs and relatively more silk in supporting threads than did fasted spiders. The material properties of silk spun by fed and fasted spiders were relatively similar, but silk threads spun by fed spiders were twice as thick as those of fasted spiders, increasing web strength by 225%. Finally, spiders fed late in the experiment did not reproduce, even though they received the same amount of food as spiders fed earlier, 43% of which reproduced. The reallocation of silk in cobwebs away from sheets and sticky gumfooted threads, which function in prey capture, to supporting threads, which surround spiders with defensive clouds of silk, is consistent with reduced foraging effort and increased predation risk avoidance by fed spiders. Furthermore, this behavioural shift occurs as spiders are reproducing, when spiders can most afford the costs of reduced prey capture and would most benefit from enhanced protection. Our results contrast with those of previous studies on orb-weaving spiders, which found reductions in the sizes of webs as spiders caught more food. Thus, the architectures of spider webs reflect many selective pressures, the effects of which may vary with physiological state.

Differences in prey capture in grass shrimp, Palaemonetes pugio, collected along an environmental impact gradient.

The waterways and associated salt marshes along the western border of Staten Island, New York (Arthur Kill) have long been under environmental duress. Environmental threats include industrial and municipal discharges, oil spills, and possible leachate from landfills. These impacts are compounded due to the low flushing of this body of water. Grass shrimp, Palaemonetes pugio, inhabiting the Arthur Kill are, therefore, potentially at risk of exposure to metal and organic pollutants. Successful prey capture (of live brine shrimp, Artemia franciscana) was used to compare the relative health of shrimp collected from three sites along an environmental impact gradient. Study sites included a relatively unimpacted harbor (Great Kills Harbor, GK) and two creeks adjoining the Arthur Kill (Nassau Creek, NC, and Richmond Creek, RC). Shrimp originating from GK exhibited a rate of prey capture (6.3 prey h(-1)) that was about two times greater (p < 0.05) than that of shrimp originating from a creek behind a series of landfills (RC, 3.2 prey h(-1)). The rate of prey capture for shrimp collected from a creek impacted by historic smelting activities (NC) was intermediate (5.4 prey h(-1)). Laboratory studies with shrimp from a pristine site (Tuckerton, NJ) exposed to RC conditions (i.e., sediment and water) for eight weeks indicate that reduced prey capture can be induced in healthy shrimp. Finally, video analysis suggests that reduced prey capture in RC shrimp may not be the result of less effort, but rather the combination of (1) 80% fewer (p < 0.05) prey being captured with a lunge type of attack and (2) a greater reliance (p < 0.05) on a less efficient grab type of foraging behavior (64% success rate for RC versus 87% success rate for GK; p = 0.058). These results indicate that sublethal toxicity in environmentally impacted populations can occur and that prey capture may be used to assay the relative health of field specimens. Additionally, impaired prey capture may have important implications for the energy flow within impacted environments.

Direct and indirect effects of sediment pulse duration on stream invertebrate assemblages and rainbow trout (Oncorhynchus mykiss) growth and survival

Elevated concentrations of inorganic sediment supply in streams may impair many biological functions. However, the contribution of exposure duration to the observed impacts has not been previously considered. We evaluated the effects of sediment pulse duration using 14 streamside flow-through experimental channels, each of which contained a naturally colonised invertebrate assemblage and 10 rainbow trout (Oncorhynchus mykiss) fry. Channels were exposed to fine sediment pulses of constant concentration but varied pulse duration (ranging from 0 to 6 h) every second day over 19 days. Total abundance of benthic invertebrate and family richness declined as sediment pulse duration increased. Invertebrate drift total abundance increased as pulse duration increased; however, family richness of drift decreased. Trout length and mass gain over the 19-day period was negatively correlated with pulse duration. Path analysis suggests that the direct effects of fine sediment on trout (impaired vision leading to reduced prey capture success and (or) increased metabolic costs from physiological stress) are more important to trout growth than indirect effects (decreased drift and benthic invertebrate richness and drift abundance).

Behavioral effects in mummichog larvae ( Fundulus heteroclitus) following embryonic exposure to methylmercury

Embryos of the mummichog, Fundulus heteroclitus, were exposed to concentrations of methylmercury (meHg) below those that can cause morphological abnormalities. After hatching, larvae were kept in clean water and tested periodically for ability to capture prey ( Artemia salina) or for their swimming performance and predator avoidance. Embryonic exposure to 10 μg/liter meHg resulted in reduced prey capture ability by early larvae, measured as total Artemia caught in 1 and 5 min. However, older larvae recovered from the behavioral deficits, perhaps owing to a compensation for early CNS insult. Fish from a chronically polluted environment (Piles Creek (PC), a tributary of the Arthur Kill), previously shown to have high tolerance to the teratogenic effects of higher concentrations of meHg, proved to be less susceptible to these behavioral effects than fish from a relatively uncontaminated site (EH). Also, the PC control larvae captured prey far more effectively than the EH larvae, although they made more miscues. When tested for swimming performance after embryonic exposure to 10 μg/liter, EH larvae had increased performance when compared to controls. This effect was also transitory. The improved swimming performance did not correspond to improved ability to avoid predation by grass shrimp ( Palaemonetes pugio). The increased swimming performance may correspond to greater total activity, making them more likely to attract the predator's attention and resulting in increased capture. Thus, negative, though temporary, effects were observed in both prey capture and predator avoidance after embryonic exposure to meHg.

Effects of stream acidity on non‐breeding dippers cinclus cinclus in the south‐central highlands of Scotland

Abstract Macroinvertebrate and Dipper Cinclus cinclus abundances and pH were assessed on four rivers in the south‐central highlands of Scotland in early winter 1990 to examine the general applicability of Dipper/acidity relationships established during the breeding season (Ormerod et al., 1985; Vickery, 1991). The most acid waters had the lowest invertebrate biomasses and Dipper densities. Birds on these rivers spent significantly more of the morning foraging and less time at rest, apparently reflecting reduced prey capture rates and hence the greater time required to replace overnight mass losses. Analysis of published data on seasonal changes in Dipper population densities and individual energetic demands suggests that even accounting for the higher numbers of Dippers in all habitats during autumn and winter, energetic requirements both of individuals and populations are greatest during breeding, when the costs of self maintenance are coupled with the additional demands of chick rearing. However, from the patterns found here and elsewhere during autumn it appears that the effects of acidity on Dipper populations are important generally during both the breeding and non‐breeding seasons.

Notes: Reduction in Prey Capture Ability and Condition of Mummichogs from a Polluted Habitat

Previous studies have shown that mummichogs Fundulus heteroclitus inhabiting Piles Creek, a polluted tributary of the Arthur Kill in Linden, New Jersey, do not grow as well as conspecifics from more pristine habitats. Our study was designed to investigate whether or not reduced prey capture ability contributes to the impaired growth in the pollution-stressed population. When presented with juvenile guppies Poecilia reticulata as food, the mummichogs from Piles Creek did not capture them as effectively as did fish from a reference site in Southampton, New York. Furthermore, field-collected specimens from the reference site showed both greater body weight for a given length and fuller stomachs than Piles Creek specimens. Gut contents of Piles Creek fish consisted primarily of detritus and sediments, whereas those of the reference fish were largely crustacean remains. Thus, the reduced growth in the Piles Creek population may be due in part to reduced feeding rate.

Factors affecting zooplankton feeding by the sea anemoneAiptasia pallida

Effects of various treatments on prey capture, prey ingestion and ingestion time of individualArtemia salina nauplii by the sea anemoneAiptasia pallida Verrill were studied in the laboratory. Exposure to crudeArtemia homogenate, 5 × 10−4 M reduced glutathione or 5 × 10−4 M proline significantly decreased the number ofArtemia that were captured and ingested but had no significant effect on the ingestion time of individualArtemia. Multiple captures increased the total ingestion time but decreased ingestion time per prey item. Results suggest that, under these conditions, the prey capture phase of zooplankton feeding was somewhat distinct from the ingestion phase since chemical stimuli that significantly reduced prey capture had no significant effect on ingestion time.