Prey Capture Success Research Articles

Foraging advantages of mixed-species association between solitary and colonial orb-weaving spiders.

This study investigated association between solitary orb-weaving spiders and a colonial orb-weaving spider, Metepeira incrassata (Araneae: Araneidae). Spiders were sampled along transects and an index of species association showed that two of the species were associated more frequently than expected based on a null hipothesis of random co-occurrence. The potential advantages of mixed-species association were investigated by comparing prey-capture success of one of these associates, Nephila clavipes (Araneae: Tetragnathidae), when it occurs alone, in single-species groups, and when associated with M. incrassata colonies. Field observations of prey-capture success by all three of these categories of N. clavipes revealed that individuals in M. incrassata colonies captured significantly more prey than solitaries or individuals in single-species groups. The increase in prey capture by N. clavipes in M. incrassata colonies may result from utilization of a foraging niche which intercepts a diffirent spectrum of prey than that available to single-species groups or solitaries. Related to this enhanced prey consumption is greater fecundity of spiders in association with M. incrassata as compared to solitaries or individuals in single-species groups.

Visual acuity and feeding in larval Premnas biaculeatus

Ontogenetic change in the visual acuity of Premnas biaculeatus larvae was determined both behaviourally and anatomically. Visual acuity improved substantially between early feeding (day 3 post‐hatch) and the pre‐settlement (day 10 post‐hatch) larvae but, at both ages, the anatomically‐measured visual acuity was greater than that determined behaviourally. It appears that estimated anatomical visual acuity values substantially over‐estimate the functional visual acuity realized under normal conditions. The distribution of the reactive angles indicated that most frequently prey within 0 to 9° of the longitudinal larval axis elicited a feeding response at both larval ages. This suggests that stereoscopic vision is used extensively during feeding in this species. The prey capture success with rotifers ranged from 96% at 3 days post‐hatch to 100% at 10 days post‐hatch. These values differ markedly from previous studies on temperate species and highlight the well developed abilities of larval P. biaculeatus at a given

How feeding performance and energy intake change with a small increase in the body size of the three‐spined stickleback

Changes in the foraging behaviour due to variation in the body size of the three‐spined stickleback Gasterosteus aculeatus were investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predation.

How feeding performance and energy intake change with a small increase in the body size of the three-spined stickleback

Changes in the foraging behaviour due to variation in the body size of the three-spined stickleback Gasterosteus aculeatus were investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predation.

Encounter rates and swimming behavior of pause‐travel and cruise larval fish predators in calm and turbulent laboratory environments

We observed the feeding and swimming behavior of freely swimming cod (Gadus morhua) and herring (Clupea harengus) larvae in calm and turbulent (ɛ = ~7.4 × 10 ‒8 m2 s‒3) laboratory environments at limiting and satiating abundances of Acartia tonsa prey. Attack position rates (a measure of prey encounter rate in unsatiated larvae) were significantly higher in turbulent than in calm water at low food abundances for two size groups of cod. The difference in cod attack position rate between calm and turbulent water was much less when prey was more abundant. Attack position rates of herring larvae were higher in turbulent water than in calm water, but the difference was not significant. Interspecific differences in swimming and pausing behavior were related to differences in prey search strategy used by the two species (cod: pause‐travel; herring: cruise). We used a newly developed search model for pause‐travel predators in calm and turbulent environments to compare encounter rates for predators using cruise and pause‐travel search strategies. Encounter rates for cod and herring larvae, estimated with respective search models, were similar in calm and low turbulence water; at high turbulence levels, the pause‐travel model predicts higher encounter rates than does the cruise model. In terms of prey encounter rate, cod larvae benefit more from turbulent motion than do herring larvae. However, aspects of larval behavior other than prey search strategy (e.g. prey capture success) need to be examined experimentally before the overall effects of turbulence on larval fish feeding rates can be fully evaluated.

Prey capture success, feeding frequency and daily food intake rates in rohu, Labeo rohita (Ham.) and singhi, Heteropneustes fossilis (Bloch) larvae

Using the rotifer Brachionus calyciflorus and the cladocerans Ceriodaphnia rigaudi, Moina macrocopa and Daphnia carinata as prey (food) species, the capture success (CS), frequency of feeding and total daily food intake of rohu (Labeo rohita) and singhi (Heteropneustes fossilis) larvae were determined. The CS in both rohu and singhi was a direct function of their age as well as hunger level, but at any given age it was inversely related to prey size. The larvae fed more or less continuously, even during the night hours. Gut evacuation rates were slower in singhi than in rohu. The daily food consumption rates in rohu and singhi larvae were 13.3% and 17.7% at age 6 days, and 8.0 and 10.1% of the dry body weight at age 12 days, respectively. Although as adults rohu and singhi have distinct food niches, they did not differ significantly in the larval stages in the parameters studied. The implications of these findings for larval rearing in the aquaculture of rohu and singhi are discussed.

Rear Leg Amputation and Subsequent Adaptive Behavior During Reintroduction of A Green Tree Frog, Hyla cinerea

The left rear leg of a green tree frog, Hyla cinerea was amputated following a severe femoral fracture. After convalescence, the frog was reintroduced into the display area where volunteers monitored its locomotive abilities, successful capture of prey, and interaction with other frogs for one week. The frog adapted well and continues to be a popular and valuable feature of the exhibit.

The effects of temperature on feeding in zooplanktivorous walleye,Stizostedion vitreum, larvae

We examined the prey capture process in walleye larvae (9.8–18.0 mm mean length) feeding on zooplankton (density 1501−1) in laboratory aquaria at 15,18.5 and 22°C. Larvae were starved for ≥8 h prior to the experiment and only allowed to feed for ≤10 min during the experiment in order to minimize the influence of gut processing or satiation on feeding behaviour. Prey consumption (μg min−1) increased exponentially and prey capture success (%) increased logarithmically with mean walleye length. Prey consumption and attack rate (strikes min−1) increased significantly with increasing temperature. The effect of temperature on capture success was slight (2% increase from 15 to 22°C) and not significant. Walleye showed positive electivity for medium-sized prey (0.3–0.6 mm body width, mostlyCeriodaphnia quadrangula), negative electivity for small prey (≥0.3 mm, mostly cyclopoid copepods) and neutral electivity for large prey (≥0.6 mm, mostlyDaphnia sp.). Neither prey species electivity nor prey size electivity were significantly affected by temperature. However, prey size electivity did show a fairly large effect size with respect to temperature and we suggest that this relationship should be examined further. These results indicate that temperature affects prey capture in walleye larvae primarily by influencing attack rate.

An Energetic Model of Microhabitat Use for Rainbow Trout and Rosyside Dace

We constructed an energetic model to determine the optimal focal point current velocity (i.e. microhabitat) for rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus funduloides) in Coweeta Creek, a fifth—order stream in North Carolina, USA. Energetic costs were evaluated by quantifying the metabolic expenditure associated with swimming at a given velocity. We estimated bebefits by measuring potential energetic gains of feeding at a given velocity. This included estimates of the ability of the fish to capture prey at different current velocities as well as etimates of the frequency and the energy content of drifting prey at various velocities. We derived separate models for small (53—70 mm SL [standard length]) and medium (71—125 mm SL) trout, and medium (47—52 mm SL) and large (53—70 mm SL) dace for all seasons, deriving net energy gain as a function of current velocity. We predicted fishes would occupy velocities at which net energy gain was maximized. Predicted velocities were compared with those utilized by fishes inhabiting Coweeta Creek. Optimal velocities predicted by energetic models ranged from 7.7 to 22.1 cm/s, and closely matched actual velocity use (average deviation = 2.6 cm/s). Prey capture success appeared to be the most important component in the models. Consequently, we constructed models based solely upon aspects of capture success; the average deviation from veolocity use with these models was only 1.8 cm/s. Thus, the ability of dace and trout to capture prey at varying velocities appears to be the dominant factor affecting microhabitat selection in these species.

Factors affecting the reproductive success of the crab spider Misumenoides formosipes: the covariance between juvenile and adult traits

To examine the importance of covariance between stages in traits related to foraging, we quantified the relationships between reproductive success and sizerelated variability in weight gain in juvenile and adult instars of the crab spider Misumenoides formosipes (Araneae: Thomisidae). Prereproductive weight and fecundity are both highly correlated with carapace width, a linear measure of size which does not change within an instar. In field populations, adult females with larger carapaces gain more weight and are more likely to reproduce than females with smaller carapaces. The growth rate of spiders fed ad libitum in the laboratory is unrelated to size, suggesting that size-related differences in the field are due to variation in prey-capture success. Adult females with a carapace width less than 3.4 mm comprised 22% of the population, but were never found to reproduce. Of the individuals that did reproduce, a 17% increase in carapace width resulted in a 100% increase in fecundity. Juvenile stages must be examined to understand adult foraging and reproductive success, because the net weight gained by juvenile instars determines adult size. The final weight gained by spiders in the antepenultimate and penultimate instars explained nearly all the variation in carapace width in the penultimate and adult instars, respectively. We found that constraints on foraging in late juvenile stages are different from the adult stage. Penultimate foraging behavior differs from that of adults, because of constraints on foraging in the period preceding ecdysis. Additionally, in both late juvenile instars, carapace width had little or no effect on the final weight gained within the instar suggesting that factors that affect foraging are different between the juvenile and adult stages. These analyses stress the fact that to fully understand the effects of foraging on reproductive success, we must examine stage-specific constraints throughout an organism's life history.

Asymmetric interactions in semiaquatic insects.

Interspecific interactions were studied in three coexisting species of predatory semiaquatic insects: Gyrinus substriatus Steph. (Coleoptera), Gerris lacustris (L.) and Gerris argentatus Schumm. (Hemiptera). Prey capture success was observed in trials with individuals of two different species. Two prey sizes were used: fruit flies Drosophila melanogaster and Mediterranean flour moths Ephetia kuehniella (Zeller). When the two species were starved for the same period of time, G. substriatus was generally more successful at catching prey than either Gerris species, independent of prey size. However, when individuals from the formerly dominant species of the pair were less hungry (i.e. fed shortly before trials), their prey capture success decreased. Prey sharing and prey stealing were observed in trials with large prey and occurred both intra- and interspecifically. The shift in dominance with differing hunger levels and the existence of prey sharing and prey stealing may make the interspecific competition more symmetric allowing these species to coexist.

Predator shoaling moderates the confusion effect in blue-green chromis, Chromis viridis

In experiments, blue-green chromis [Chromis viridis (Cuvier 1830)] were fed on either scattered or aggregated swarms of brine shrimp (Artemia sp.). Ten runs with each prey dispersion treatment were performed with shoals of one, two, five and ten chromis. The mean lag in reaching peak feeding rate for fish fed on aggregated prey was significantly shorter in the larger chromis shoals. In contrast, with the scattered treatment all such lags were similar and very short. As foraging proceeded, higher feeding rates were observed in the larger feeding shoals, regardless of prey dispersion. Prey capture success (i.e. the rate of retention of intercepted prey) declined with time, but was significantly higher in groups of ten fish. Two main conclusions emerge. Firstly, grouping facilitated initiation of feeding by individuals preying on concentrated swarms and reduced the delay in reaching a maximum feeding level. This may have been due to a suppression of the confusion effect through reduced reliance upon vigilance. Secondly, reduced vigilance allowed larger shoals of chromis to feed effectively over more extended periods. Trends of increasing shoal cohesion and decreasing prey retention rate with time were consistent with a postulated increase in antipredator vigilance with declining feeding motivation.

Capture of submerged prey by little egrets, Egretta garzetta garzetta: strike depth, strike angle and the problem of light refraction

How little egrets eatch submerged prey was observed in the field. The proportion of successful strikes was measured relative to the angle and depth of the strike and the water level in the pond. Prey capture success was significantly related to strike angle, being highest at the most acute angles. Strike depth had no effect on capture success. Strikes were more successful in shallow streams than in full or partly drained ponds. Adult breeding birds were as successful as non-breeders and uveniles, but performed deeper strikes more often. There was also significant variation between individuals in capture success. Light refraction had no apparent effect on the egrets' capture success.

The Role of Sensory Receptors in the Predatory Behavior of the Brown Tree Snake, Boiga irregularis (Squamata: Colubridae)

The brown tree snake (Boiga irregularis) is indigenous to parts of costal Australia, New Guinea, and the Solomon Islands (McCoy, 1980; Cogger, 1983). It can be found in a variety of habitats (Fritts, 1988), but it is arboreal and most common in primary and secondary growth forests (Savidge, 1986, 1987; Fritts et al., 1987). Its dentition is usually referred to as rear fanged, in which one or two posterior maxillary teeth are enlarged and bear on their labial faces an open groove associated with a connecting duct from Duvernoy's gland. The snakes appear to feed opportunistically: stomach and intestinal content analyses reveal a diet of birds and their eggs, lizards and their eggs, and small mammals (Savidge, 1988). The diets of males and females are the same, but medium to large snakes (over 120 cm SVL) tend to consume a larger proportion of birds, bird eggs, and mammals (Savidge, 1988). They are considered nocturnal in their natural habitat (Fritts, 1988; Chiszar, 1990), an activity continued in captivity (Chiszar et al., 1985). The eyes of the brown tree snake are large and the pupils are slit-like. A vomeronasal organ is present, but like other colubrid snakes, the brown tree snake lacks anatomically distinct thermosensitive facial pits. Eyes, chemosensory receptors (olfactory epithelium, vomeronasal organ), and thermosensitive pits are known to be important in the predatory behavior of certain venomous snakes (de Cock Buning, 1983). When denied visual information, pit vipers can still uccessfully strike prey, presumably by compensating with thermosensitive receptors (Noble and Schmidt, 1937; Dullemeijer, 1961). However, without such alternative sensory receptors the brown tree snake would seem to require alternative sensory input to compensate for loss of visual information during nocturnal forays for food. To assess feeding performance in the absence of visual information, prey capture success of brown tree snakes with and without blindfolds was compared. The purposes of this experiment were to describe the changes in predatory behavior (normal and blindfolded), and to produce hypotheses about how the sensory versatility of the nervous system might modulate the strike based upon alternative routes of sensory input. All brown tree snakes used were collected on Guam.

Mechanisms of intra-and interspecific interference between larval stoneflies.

Behavior of focal individuals of two potentially competing sympatric stonefly species, Megarcys signata and Kogotus modestus (Perlodidae), was videotaped in flow-through plexiglass arenas placed in the East River, Gunnison County, Colorado. Focal individuals were observed alone and in pairs with conspecifics and allospecifics at four prey (Baetis bicaudatus, Baetidae, Ephemeroptera) densities to determine whether competitors and prey resource levels affected prey capture rates. Presence of conspecific or allospecific competitors reduced stonefly prey capture rates, especially for Kogotus, the smaller of the two species, due to a significant decline in predator-prey encounter rates with competitors present. This competitive effect was not observed at the lowest and highest prey densities due to very low or very high predator-prey encounter rates, respectively. Thus, interference affected feeding rates only at intermediate prey densities. Competitors had no effect on the probability of attacks per prey encounter or capture success per attack. Within each stonefly species the effects of intra-and interspecific interference on feeding rates were similar, even though behavioral responses by both stoneflies to interspecific encounters were more frequent than to encounters with conspecifics. Kogotus showed the highest levels of response to encounters with other stoneflies, maintaining those high levels of response to Megarcys over all prey densities. Further, male Kogotus, which are the smaller sex, responded more frequently to competitive interactions than did females. These data are consistent with the hypothesis that interspecific interference was asymmetrical with Megarcys, the larger species, being the superior competitor.

The Relative Importance of Visual and Chemical Cues for Foraging in Newborn Blue-Striped Garter Snakes (Thamnophis Sirtalis Similis)

Although vision is known to be important for natricine snakes that specialize in aquatic predation, its relative importance for those species having more general diets is not clear. In this study, I experimentally manipulated exposure of newborn blue-striped garter snakes (Thamnophis sirtalis similis) to a) different combination of visual and chemical cues and b) aquatic prey that differed in their visibility to snakes. Visual cues, in the absence of chemical cues, were insufficient to elicit foraging although were important in successful capture of prey. These results support earlier observations that visual cues are not involved in eliciting attacks but may serve to orient attacks elicited by chemical cues.

Analysis of six foraging behaviors as toxicity indicators, using juvenile smallmouth bass exposed to low environmental pH.

Six foraging behaviors were evaluated for use in toxicity bioassays with fishes. Response time and strike frequency were used to measure fish activity, average and longest fixation distance, to measure visual acuity, while prey capture frequency and strike success were used to measure fish coordination and agility. In this study, the feeding behaviors were used to evaluate the effects of chronic exposure to acidic water on juvenile smallmouth bass (Micropterus dolomieui). Feeding responses to two types of live prey, tubificids and Daphnia magna, were recorded for bass exposed to pH 4.7 and 4.2. Fish held at the lower pH level had significantly lower fixation distances, prey capture success and capture frequencies with both prey types, indicating that high levels of acidity may impair visual acuity, coordination, and agility. The foraging behaviors evaluated herein appear to be useful in toxicity testing because they are easily quantified and indicate changes that may affect growth and survival in long-term exposures.

Social foraging in cliff swallows: local enhancement, risk sensitivity, competition and the avoidance of predators

Colonically nesting cliff swallows, Hirundo pyrrhonota, in southwestern Nebraska, U.S.A., often forage socially, in groups of two to more than 1000 individuals, on ephemeral concentrations of insects. Social foraging was promoted through information transfer among individuals at fixed colony sites, and through local enhancement in which foraging activities of some individuals attracted others to a food source. Cliff swallows feeding in groups had greater average foraging success (prey capture attempts per min) than birds feeding solitarily. Variance in prey capture success, and thus foraging risk, declined with group size and was greatest for solitary foragers. Solitary cliff swallows whose foraging success equalled or exceeded that expected from social foraging remained solitary during a given foraging bout. Solitary foragers whose success fell below that expected from social foraging joined foraging groups. For individuals foraging socially there was no consistent relationship between foraging success and group size, indicating little competition among group members for food and little resource depression. Social foraging in cliff swallows is probably not an adaptation mainly to decrease individuals' risk of predation because foraging success did not differ for birds foraging on the edges versus in the centres of groups, and individuals foraging on the edges did not try to move toward the centre. These data are consistent with risk-sensitive foraging models and provide the first empirical demonstration with free-living animals that social foraging is associated with decreased individual variance in foraging success.

Competition for perches between larval damselflies: the influence of perch use on feeding efficiency, growth rate and predator avoidance

SUMMARY. 1. In an investigation of perch use by two species of larval damselfies, Coenagrion puella (Linn.) and Ischnura elegans (van der Linden), larvae spaced out on a grid of vertical cocktail sticks, in the absence of food, to a greater extent than expected from a random model. Spacing was the result of direct interaction between larvae, and was not related to the level of hunger of the larvae over a 10 day starvation period.2. Prior ownership of a perch was not a predictor of success in conflicts between larvae of the same instar. In contests between different instars larger larvae were more likely to win conflicts. Some small larvae appear to remain undetected in the presence of larger conspecifies.3. At one level of food availability, perch ownership did not influence growth rate or mortality of C. puella or I. etegans. However, it did allow greater prey capture success rate.4. Coenagrion puella larvae showed more movement in the absence of perches both in terms of actual distance moved and amount of swimming activity. The amount of swimming activity was reduced by addition of a predator (sticklebacks. Gasterosteus aculeatus or Pungitius pungitius) to the tank both in the absence and presence of an alternative food supply for the fish. Duration of individual swimming bouts was unaffected.5. Sticklebacks attacked C. puella larvae significantly more often in the absence of perches, with a strong bias towards swimming larvae.6. It is proposed that the major advantage of perch possession to C. puella larvae is in the reduction of predation as a consequence of the reduction in larval movement.

Methods for studying the energetics of freely diving animals

Advances in instrumentation and labeled water methodologies are providing new insights into at-sea behavior and energetics of freely diving animals. Used concurrently, these approaches can add significantly to our understanding of the physiological ecology of diving animals. In this paper I review existing information on at-sea behavior and free-ranging metabolism of diving mammals and birds, and discuss the methods available to assess at-sea diving food consumption, energy expenditure, and behavior. Finally, using the limited available data for northern fur seals, I present approaches for the analysis of concurrently collected data on at-sea metabolism and diving behavior. These include estimation of prey capture success per dive, rate of energy acquisition per dive, time–energy budget analysis, and diving metabolic rate derived from regression analysis. I hope that this discussion will stimulate interest in a potentially powerful method of understanding the physiology and ecology of freely diving animals in nature.