Foraging Behavior In Response Research Articles

Increased Parasitization of Aphids on Trap Plants Alongside Vials Releasing Synthetic Aphid Sex Pheromone and Effective Range of the Pheromone

Aphid-infested cereal trap plants were used to detect the effects of aphid sex pheromone components on aphid parasitoid activity in arable field margins. The presence of aphid sex pheromones significantly increased parasitization levels by aphid parasitoids on the plants. By placing plants alongside and at varying distances away from a pheromone-releasing vial, the technique was used to measure the distance over which a point source of aphid sex pheromone could increase parasitization levels. Pheromone-releasing vials significantly increased parasitization by the generalist parasitoid Praon volucre on plants adjacent to vials and on plants placed 20 cm away. When the distance between pheromone-releasing vials and aphid-infested plants was increased to 1 m, parasitization by P. volucre was increased only on the plant adjacent to the vial, whereas parasitization by the specialist parasitoid Aphidius rhopalosiphi was also increased on plants placed 1 m away. This indicates a possible difference between the parasitoids in their foraging behaviour in response to semiochemical cues during host selection. When the experiment was repeated with some trap plants placed 3 m away from the pheromone-releasing vial, parasitization was again concentrated on plants directly alongside the vial, but only P. volucre appeared to be active in the field at the time of this experiment, so the effect on A. rhopalosiphi could not be assessed. The results are encouraging for the prospects of using aphid sex pheromones to manipulate parasitoids in order to improve aphid population control.

Growth Hormone Increases Risk‐Taking in Foraging Rainbow Trout

Animals can adjust their foraging behavior in response to variable predation risks.1,2 The energetic state of an animal strongly influences decisions that balance feeding against the risk of being preyed upon.2 Growth hormone (GH) stimulates growth in fish, and should therefore increase the metabolic demands and the feeding motivation.3 This, in turn, may increase the willingness to risk exposure to predators during feeding.1,2 The aim of this study was to test the hypothesis that GH reduces antipredator responses by increasing feeding motivation.

Behaviorally Mediated Trophic Cascades: Effects of Predation Risk on Food Web Interactions

Trophic cascades are regarded as important signals for top-down control of food web dynamics. Although there is clear evidence supporting the existence of trophic cascades, the mechanisms driving this important dynamic are less clear. Trophic cascades could arise through direct population-level effects, in which predators prey on herbivores, thereby decreasing the abundance of herbivores that impact plant trophic levels. Trophic cascades could also arise through indirect behavioral-level effects, in which herbivore prey shift their foraging behavior in response to predation risk. Such behavioral shifts can result in reduced feeding time and increased starvation risk, again lowering the impact of herbivores on plants. We evaluated the relative importance of these two mechanisms, using field experiments in an old-field system composed of herbaceous plants, grasshopper herbivores, and spider predators. We created two treatments, Risk spiders that had their chelicerae glued, and Predation spiders that remained unmanipulated. We then systematically evaluated the impacts of these predator manipulations at behavioral, population, and food web scales in experimental mesocosms. At the behavioral level, grasshoppers did not distinguish between Risk spiders and Predation spiders. Grasshoppers exhibited significant shifts in feeding-time budget in the presence of spiders vs. when alone. At the grasshopper population level, Risk spider and Predation spider treatments caused the same level of grasshopper mortality, which was significantly higher than mortality in a control without spiders, indicating that the predation effects were compensatory to risk effects. At the food web level, Risk spider and Predation spider treatments decreased the impact grasshoppers had on grass biomass, supporting the existence of a trophic cascade. Moreover, Risk spider and Predation spider treatments produced statistically similar effects, again indicating that predation effects on trophic dynamics were compensatory to risk effects. We conclude that indirect effects resulting from antipredator behavior can produce trophic-level effects that are similar in form and strength to those generated by direct predation events.

BEHAVIORALLY MEDIATED TROPHIC CASCADES: EFFECTS OF PREDATION RISK ON FOOD WEB INTERACTIONS

Trophic cascades are regarded as important signals for top-down control of food web dynamics. Although there is clear evidence supporting the existence of trophic cascades, the mechanisms driving this important dynamic are less clear. Trophic cascades could arise through direct population-level effects, in which predators prey on herbivores, thereby decreasing the abundance of herbivores that impact plant trophic levels. Trophic cascades could also arise through indirect behavioral-level effects, in which herbivore prey shift their foraging behavior in response to predation risk. Such behavioral shifts can result in reduced feeding time and increased starvation risk, again lowering the impact of herbivores on plants. We evaluated the relative importance of these two mechanisms, using field experiments in an old-field system composed of herbaceous plants, grasshopper herbivores, and spider predators. We created two treatments, Risk spiders that had their chelicerae glued, and Predation spiders that remained unmanipulated. We then systematically evaluated the impacts of these predator manipulations at behavioral, population, and food web scales in experimental mesocosms. At the behavioral level, grasshoppers did not distinguish between Risk spiders and Predation spiders. Grasshoppers exhibited significant shifts in feeding-time budget in the presence of spiders vs. when alone. At the grasshopper population level, Risk spider and Predation spider treatments caused the same level of grasshopper mortality, which was significantly higher than mortality in a control without spiders, indicating that the predation effects were compensatory to risk effects. At the food web level, Risk spider and Predation spider treatments decreased the impact grasshoppers had on grass biomass, supporting the existence of a trophic cascade. Moreover, Risk spider and Predation spider treatments produced statistically similar effects, again indicating that predation effects on trophic dynamics were compensatory to risk effects. We conclude that indirect effects resulting from antipredator behavior can produce trophic-level effects that are similar in form and strength to those generated by direct predation events.

Diurnal, Intraseasonal, and Intersexual Variation in Foraging Behavior of the Common Yellowthroat

Foraging characteristics of breeding Common Yellowthroats (Geothlypis tichas sinuosa) on the central California coast varied between early morning and midday periods, among periods within the nesting season, and between sexes. From early morning to midday, yellowthroats increased their use of vegetation at heights below 1 m and above 3 m, but reduced their use of vegetation at heights of 2-3 m. A midseason increase in the use of vegetation at heights above 3 m occurred after 3 May. Male yellowthroats foraged at significantly greater heights, on average, were more likely to choose flycatching over other maneuvers, and were possibly better adapted, morphologically and behaviorally, to exploit spatiotemporal changes in prey abundance than were females. Singing males occurred at greater heights, on average, than either foraging males or females, but did not differ from foraging birds in their use of substrates or plant species. We evaluated the use of plant species for foraging in comparison with availability within 10 m of foraging individuals and over the entire study area, and found significant diurnal and intraseasonal patterns of selection. Common Yellowthroats actively selected arroyo willow (Salix lasiolepis) at both spatial scales of availability during all diurnal and seasonal periods. Use of foraging maneuvers varied intraseasonally but was independent of diurnal period. We found no significant interaction between diurnal and intraseasonal patterns of foraging. Our results suggested that Common Yellowthroats alter their foraging behavior in response to changes in foraging conditions associated with diurnal and intraseasonal dynamics of freshwater marsh ecosystems. Pooling of foraging data over diurnal or intraseasonal periods, or between sexes, may mask significant differences that are important in understanding foraging characteristics.

Natural selection in the laboratory for a change in resistance byDrosophila melanogaster to the parasitoid waspAsobara tabida

The selection response of the polymorphic hostD. melanogaster (Meigen) to the braconid waspA. tabida (Nees) is addressed. Cages of flies with and without wasps were initiated with a population ofD. melanogaster that exhibited variation both in larval foraging behavior and in encapsulation ability. Encapsulation ability was measured as the proportion of parasitized larvae that produce a hardened capsule which encapsulates the wasp egg and ultimately kills the wasp larva. We determined whether the host population changed its encapsulation ability and/or its foraging behavior in response to the wasp. Both species were collected from a local orchard whereA. tabida is the only wasp known to parasitizeD. melanogaster larvae. The naturally occurring genetic polymorphism for rover and sitter larval foraging behavior inD. melanogaster is also found in this field population.A. tabida's vibrotactic search behavior enables it to detect rover more frequently than sitter larvae. Rover larvae move significantly more while feeding than do sitter larvae. In this field population, rover larvae also show higher encapsulation abilities than do sitter larvae. Six cage populations, three without wasps and three with wasps, each containing an equal mixture of rover and sitter flies, were established in the laboratory and maintained for 19 fly generations. Selection pressure in the laboratory was similar to that found in the field population from which the flies and wasps were derived. We found that larvae from cages with wasps developed a significantly higher frequency of encapsulation than those reared without wasps. We were, however, unable to detect a change in larval movement (rover or sitter behavior) in larvae from cages subject to selection from wasps compared to larvae from cages containing no wasps. This may have resulted from a balance between two selective forces, selection against rovers by the wasps' use of vibrotaxis, and selection for rovers resulting from their increased encapsulation abilities

Effects of Substrate on Foraging Decisions by a Namib Desert Gerbil

We investigated the role of foraging and escape substrates on foraging decisions of a Namib Desert gerbil, Gerbillurus tytonis (Rodentia), in the field. We used the giving-up density technique, which uses artificial seed trays to assess foraging decisions. We tested whether the foraging decisions made in the trays were an artifact of prior knowledge of a food source by comparing giving-up densities in trays that were randomly placed in different parts each night with that in trays that remained in fixed position throughout the experiment. There was no significant difference in giving-up densities between these two treatments, which suggests that prior knowledge of food location does not affect foraging decisions. We examined the preferences of gerbils for the different substrates using seed trays. The gerbils showed significant differences among habitats in the amount of seed taken and between new-moon and full-moon nights. They removed more seeds where the difference between the size of the seeds and the size of the sand substrate was large. This finding is congruent with the hypothesis that tactile discriminatory ability affects the foraging behavior of these rodents. Although these rodents alter their foraging behavior in response to predation risk, there was no significant difference in the amount of seeds taken in habitats differing only in the degree of compaction of escape substrates.

Foraging in yellow perch,Perca flavescens: biological and physical factors affecting diel periodicity in feeding, consumption, and movement

We examined the diel chronology in food consumption and dietary composition, and in the local distribution of yellow perch,Perca flavescens, at 3 h intervals over two 24 h periods during the summer at Baptiste Lake, Alberta. Feeding intensity, as indicated by changes in stomach fullness, increased throughout the day, peaked in late evening, and almost ceased after sunset. Changes in perch densities at the sampling site reflected the pattern of feeding intensity, indicating that movements into the littoral zone are correlated with foraging. Perch diet composition, analyzed as percent occurrence, relative numerical abundance, and percent contribution by weight, differed significantly between times of day, particularly between day and night, and between sampling periods. These differences could be related both to prey behavior and distribution, and to changes in perch foraging behavior in response to light intensity. In terms of biomass, forage fish, amphipods, chironomids, and trichoptera were the most important food items on both sampling dates.

The role of learning in fish behaviour

The behavioural patterns of fish are the result of innate (‘built-in’) patterns of maturation (developmental changes) and of learning processes (imprinting and trial-and-error learning). Innate behavioural patterns are considered to be ‘hard-wired’ and inflexible. However, through learning, fish can adapt to environmental change. For instance, the homing behaviour of fish may be partly the result of the development of specific parts of the brain and partly because of changes in behaviour with experience. Similarly, one can assume that the feeding mode of fish involving snap-responses is innate, but learning enables fish to modify their foraging behaviour in response to a fluctuating environment. By reviewing these and other examples, such as the role of recognition learning and socially transmitted behaviour, one can illustrate the importance of learning in the everyday life of fishes. Although learning plays a large role in the behaviour of fishes, the learning capacity of fishes may also be useful to fisheries research and hatchery operations.

Auditory adaptations for prey capture in echolocating bats

Auditory adaptations for prey capture in echolocating bats

Ptilochronology: Feather Growth Bars as Indicators of Nutritional Status

Ptilochronology: Feather Growth Bars as Indicators of Nutritional Status

The swimming behavior of the freshwater calanoid copepods Limnocalanus macrurus Sars, Senecella calanoides Juday and Epischura lacustris Forbes

The swimming behavior of the freshwater calanoid copepods Epischura lacustris , Senecella calanoides , and Limnocalanus macrurus was examined using a videotape analysis technique. E. lacustris and S. calanoides alternate between periods of slow gliding and passive sinking. L. macrurus does not exhibit sinking behavior; its swimming activity consists of slow and steady gliding interrupted occasionally by jumps. All three copepods exhibit behavioral responses when exposed to prey organisms, as expressed by an increase in the duration of sinking for E. lacustris and S. calanoides , a decrease in sinking speed for S. calanoides , and a less circuitous swimming path for L. macrurus . These behavioral changes may allow the copepods to allocate more time for prey detection, to be less detectable by potential prey and to reduce the frequency of path re-crossing. The results demonstrate the relationship between the swimming and feeding behavior of calanoid copepods and are consistent with previous findings that copepods have the ability to modify their foraging behavior in response to changes in food conditions.

Habitat Quality and the Foraging Behaviour of Coccinellid Larvae

SUMMARY (1) The aim of this study was to determine whether an invertebrate predator with limited sensory abilities could modify its foraging behaviour in response to changes in habitat quality, and so maximize its feeding rate. (2) The effects of hunger, rate of prey encounter and rate of food intake on the foraging behaviour of fourth instar Coccinella septempunctata L. larvae were investigated. (3) The duration of area-restricted searching behaviour following prey encounter increased with increasing hunger. This increased the probability of encountering a subsequent prey item and ultimately the time spent in a patch and the degree to which each patch was exploited. (4) Handling time increased as hunger increased. (5) Changes in the duration of the area-restricted searching behaviour and handling time were dependent on hunger level and not average encounter rate or average rate of food intake. (6) Extensive searching behaviour did not change with hunger level. (7) Hunger-induced changes in foraging behaviour enabled larvae to forage in a manner consistent with optimal foraging theory.