Prey Feeding Research Articles

Habitat complexity alters lethal and non-lethal olfactory interactions between predators and prey

Habitat complexity often modifies rates of prey capture by visual predators, but little is known about how structural features affect non-visual olfactory consumers. Laboratory studies indi- cate that turbulent water flow over complex bedforms mixes chemical information in ways that con- fuse some olfactory foragers but improve the odor-tracking abilities of burrowing gastropods (whelks Busycon spp.). We augmented bottom roughness in a soft-sediment estuary to test the hypothesis that turbulent mixing of chemical attractants in the field increases whelk predation on hard clams Merce- naria mercenaria. Thin flat layers of shell fragments around the perimeter of experimental clam plots increased turbulent mixing of prey odors relative to those emanating from control plots. Assessment of prey mortality after 4 wk of exposure revealed that whelk predation on clams surrounded by shells was significantly higher than on clams surrounded by natural sediment. A second set of experiments showed that open prey plots containing a centrally caged (non-lethal) whelk experienced lower mor- tality due to avoidance responses of prey, but surrounding those plots with shells counteracted the non-lethal predator effect and led to significantly greater consumption by naturally foraging whelks. Shell treatments did not increase prey feeding or reduce predator interference. Results suggest that whelks hunt more successfully when bottom roughness increases turbulent mixing of prey chemicals or disrupts prey abilities to detect and respond to predator odors. When integrated over time, habitat- related differences in chemical transfer and olfactory behavior could have important implications for populations of both predators and prey.

Krill-feeding behaviour of gentoo penguins as shown by animal-borne camera loggers

Animal-borne camera loggers were used to examine the patterns of prey encounter and feeding behaviour of gentoo penguins at King George Island, Antarctica. The still images from the camera loggers showed that the penguins encountered the swarms of krill for 25.5% (range: 8–38%) of their dives (>5 m) on average, during their foraging trips (mean duration of 5.4 h, n = 7 trips). They encountered krill swarms during the dives to 10–70 m depth, in pelagic as well as benthic habitats. In the benthic habitat, the penguins swam just above the sea floor and headed downward over a krill swarm, probably using the sea floor to assist them to feed on mobile swarms. The shallow coastal waters would be the important foraging habitat of gentoo penguins breeding in King George Island.

Omnivory and stability of food webs

The role and prevalence of omnivory, defined as feeding on more than one trophic level, are critical to understand food web structure and dynamics. Whether omnivory stabilizes or destabilizes food webs depends on the assumptions of theoretical models. Recently, Tanabe and Namba [Tanabe, K., Namba, T., 2005. Omivory creates chaos in simple food web models. Ecology 86, 3411–3414] found that omnivory can create chaos in a simple food web model with linear functional responses and 12 model parameters. In this paper, first we numerically examined bifurcation diagrams with all the parameters as bifurcation parameters, including self-limitation of the intermediate consumer and predator. Chaos spontaneously appears when the intraguild predator’s consumption rates are low for nutrient-rich intraguild prey and high for nutrient-poor basal resource and the intraguild prey reproduces efficiently feeding on the basal resource. Second, we investigated effects of the addition of a species into the basic model food web which exhibits chaos. The additional species is assumed to consume only one of the basal resource, intermediate consumer, or omnivorous predator. Consequences of the addition greatly depend on the trophic level on which the additional species feeds. While the increased diversity of predators feeding on the intermediate consumer stabilizes the web, the increased diversity of prey feeding on the basal resource induces collapse of the food web through exploitative competition for the basal resource. The food chain with the top predator feeding on the omnivorous predator is highly unstable unless the mortality of the top predator is extremely low. We discuss the possibility of real-world chaos and the reason why stability of food webs strongly depends on the topological structure of the webs. Finally, we consider the implications of our results for food web theory and resource management.

Mesoscale exploitation of a major tuna concentration in the Indian Ocean

The paper analyzes the daily catch, fishing effort and fish size data of the purse seine fleet fishing in the western Indian Ocean in February 2005, when a major concentration of tuna occurred and was heavily exploited by this surface fishery. This tuna concentration event occurred over a period of just 12 days, in an area of about 3500 square nautical miles located to the west of the Seychelles. This small stratum produced a total catch of 22 000 t, corresponding to 6.5% of the total fishing mortality of all adult yellowfin (Thunnus albacares) in the entire Indian Ocean in 2005. Sets were made mainly on free schools and the catch mainly composed of large yellowfin tuna. The average CPUE and the average catch per set were very large, 65 t and 85 t per fishing day, respectively. This “event” took place in a precise area where a high concentration of chlorophyll had been localized 18 days before. The subsequent concentration of tuna schools probably arose due to the high densities of their prey feeding on this large phytoplankton biomass. This phytoplankton bloom was observed at the edge of an anticyclonic eddy, but its origin and its high density cannot be fully explained by available environmental data. The adult yellowfin were probably at a reproductive stage and actively feeding on the local food chain generated by the phytoplankton bloom. Such an event is extreme, but typical of tuna purse seine fisheries where fleets often search for such tuna patches. These events play an important role in tuna fisheries due to the increase in fishing effort and fishing efficiency of purses seiners, both of which increase their impact on the resource. The fine scale study of such events and their improved integration into tuna stock assessments is recommended.

More sharing when there is less: insights on spider sociality from an orb-weaver's perspective

I examined the potential genetic and environmental determinants of population differences in the foraging behaviour of the colonial spider Parawixia bistriata by using reciprocal transplant and prey manipulation experiments. The population differences noted from a previous study are primarily associated with the degree to which this spider captures prey as a group: P. bistriata show a higher frequency of group capture of prey in dry habitats with lower prey levels than in wet habitats where prey levels are higher. I recorded data on the tendency to capture and feed in groups and the number of individuals feeding on that prey. The transplant experiments revealed population differences in the tendency to capture prey as a group. Individuals from dry habitat showed a greater tendency to participate in group capture and feeding of prey in their native habitat than did individuals from wet habitat or than individuals that were transplanted to dry and wet habitats. In addition, the size of capture and feeding groups showed a significant habitat effect. Individuals from wet habitat did not differ in their tendency to attack prey when transplanted to dry habitat, suggesting that P. bistriata from wet habitat represents an ecotype that lacks behavioural plasticity. In contrast, individuals from dry habitat showed a plastic response. Potential causes of the behavioural plasticity shown by spiders from dry habitat are discussed. Group-foraging behaviour can have a significant effect on the fitness of these spiders, as suggested by their success under low prey conditions.

Non-lethal predator effects on the feeding rate and prey selection of the exotic zebra mussel Dreissena polymorpha

Predators may induce changes in prey feeding that indirectly influence both the impact of prey on resource abundances and their interactions with other species in their community. We evaluated whet ...

Non‐lethal predator effects on the feeding rate and prey selection of the exotic zebra mussel Dreissena polymorpha

Predators may induce changes in prey feeding that indirectly influence both the impact of prey on resource abundances and their interactions with other species in their community. We evaluated whether clearance and excretion (faeces plus pseudofaeces) of phytoplankton by zebra mussels were affected by the presence of predatory cues from roach, Rutilus rutilus, and signal crayfish, Pasifastacus leniusculus. We found that non‐lethal effects of predators can alter zebra mussel clearance rate and thus the impact of zebra mussels on phytoplankton. Risk cues released by both predators had similar negative effects on clearance rate of zebra mussels and cascading positive indirect effects on phytoplankton resources. Predation risk had a stronger effect on zebra mussels’ clearance rate of cyanobacteria and diatoms than cryptophytes and chrysophytes. The presence of predators did not significantly affect the rate at which zebra mussels expelled and excreted phytoplankton, although there was a tendency for more chlorophyll to be expelled and excreted in the presence of predators. Our results contribute to the growing evidence that predators indirectly affect resource dynamics and food web structure through their non‐lethal effects on consumers. Our results suggest that exotic species such as zebra mussels can show behavioural responses to both native (e.g. roach) and exotic (e.g. crayfish) predators.

Effect of dietary phospholipid level on the development of gilthead sea bream (Sparus aurata) larvae fed a compound diet

The aim of the study was to determine the influence of dietary phospholipid (PL) levels on survival and development of first feeding gilthead sea bream (Sparus aurata) larvae. Larvae were fed from day 4 to 23 posthatching with an isoproteic and isolipidic formulated diet with graded levels of PL from 90-150 g kg(-1) dry matter (DM). A dietary PL content of more than 90 g kg(-1) DM seems to be necessary for sustaining growth of first feeding sea bream larvae. The survival rates of larvae fed the formulated diets (31-40% at day 23) were similar to those generally observed in marine aquaculture hatcheries with live prey feeding sequence. However, this high survival rate was not associated with high growth and the larvae showed, at the end of the study, a high proportion of individuals with abnormal liver and calculi in the urinary bladder. It is concluded that although the diets used here cannot be used in total replacement of live preys, they constitute a solid starting point for further nutritional studies with first feeding gilthead sea bream larvae.

Diet estimation based on an integrated mixed prey feeding experiment using Arctocephalus seals

Food web models depend on identifying which taxa are eaten and in what proportion they are consumed. Arctocephalus seals are generalist foragers and are an ongoing focus of Southern Hemisphere marine ecosystem research. This is the first feeding experiment to use Arctocephalus spp. to assess the utility of hard part scat analysis for diet estimation, based on mixed prey diets integrated over several days. Recovery rates of otoliths were extremely low for all taxa (0–9%). Although we could not collect scats produced during a 90 min period each day, during which the seals had access to a large pool, this result could not be attributed to otolith robustness, pinniped species or class, activity level, meal size or frequency, or fat content of the diet. We conclude that the unusually low recovery rates in this study may be due to unaccounted scats produced during 90 min of each day, if they contained otolith numbers an order of magnitude greater than all otoliths retrieved from scats produced during the other 22.5 h of each day, and/or may be related to the digestive processing of a mixed prey diet. Our study demonstrates the inadequacy of using otoliths in field collected scats for diet estimation due to the high level of unexplained variability of otolith occurrence in scats. We also identify two new potential sources of this variability. These are variability in numbers of otoliths per scat depending on activity level when a scat is excreted, and variability in recovery rates of otoliths as a function of the complexity of the diet.

Ladybird mothers mitigate offspring starvation risk by laying trophic eggs

A large proportion of ladybird beetle (Coleoptera: Coccinellidae) eggs are apparently infertile—they do not develop an embryo and are consumed by larvae hatching within the egg batch. The predicted benefits of egg consumption for larvae are empirically well supported. An important question, however, remains: are these eggs a maternal strategy to feed offspring (i.e., trophic eggs) or did egg eating evolve to exploit unavoidably infertile eggs? We investigated the adaptive value of infertile eggs in laboratory experiments with multicoloured Asian ladybirds (Harmonia axyridis). Female H. axyridis were assigned to low and high resource environments for brief intervals; we predicted that tactics to facilitate egg cannibalism, such as infertile egg production and hatching asynchrony, would be adopted in low food environments in which starvation risk for offspring is greater. We conducted two experiments in this manner that provided females with information about resource levels through prey feeding or scent. We also observed female oviposition patterns and tested for infertile egg distributions that departed from random. Females produced 56% more infertile eggs in the low vs. the high food treatment; however, hatching synchrony did not change. We consider a potential confound between information and nutrition state unlikely because ladybirds are well able to tolerate low food for 24 h, the duration of trials, and because females were in good condition when trials began. Results suggest that ladybirds use information from prey encounter to manipulate the proportion of trophic eggs in a manner consistent with the adaptive hypothesis, the first evidence of trophic egg plasticity in a non-eusocial insect.

Do lizards and snakes really differ in their ability to take large prey? A study of relative prey mass and feeding tactics in lizards

Adaptations of snakes to overpower and ingest relatively large prey have attracted considerable research, whereas lizards generally are regarded as unable to subdue or ingest such large prey items. Our data challenge this assumption. On morphological grounds, most lizards lack the highly kinetic skulls that facilitate prey ingestion in macrostomate snakes, but (1) are capable of reducing large items into ingestible-sized pieces, and (2) have much larger heads relative to body length than do snakes. Thus, maximum ingestible prey size might be as high in some lizards as in snakes. Also, the willingness of lizards to tackle very large prey items may have been underestimated. Captive hatchling scincid lizards (Bassiana duperreyi) offered crickets of a range of relative prey masses (RPMs) attacked (and sometimes consumed parts of) crickets as large as or larger than their own body mass. RPM affected foraging responses: larger crickets were less likely to be attacked (especially on the abdomen), more likely to be avoided, and less likely to provide significant nutritional benefit to the predator. Nonetheless, lizards successfully attacked and consumed most crickets < or =35% of the predator's own body mass, representing RPM as high as for most prey taken by snakes. Thus, although lizards lack the impressive cranial kinesis or prey-subduction adaptations of snakes, at least some lizards are capable of overpowering and ingesting prey items as large as those consumed by snakes of similar body sizes.

Activities of selected digestive enzymes during larval development of large yellow croaker ( Pseudosciaena crocea)

Large yellow croaker is an important marine fish species for aquaculture in China. Larval rearing of this species is still based on live prey feeding. The aim of this study was to describe the onset and development of the main digestive enzymes during larval development of this species, in order to obtain essential data for the formulation of a compound diet adapted to larvae. Enzymatic assays were conducted from day 1 post hatching to day 40 in larvae fed the following live prey sequence: rotifers, Artemia nauplii, copepods, and then frozen copepods. Assays were done on whole larvae until day 19, then on dissected larvae and on purified brush border membranes of intestine. Pancreatic enzymes, amylase, and trypsin, showed high activities from early stages, even before mouth opening. Mechanisms of pancreatic secretion were achieved from day 19. Enzymes of brush border membranes, alkaline phosphatase, and aminopeptidase N, increased abruptly between day 23 and 25, showing maturation of the intestinal digestive process. These data, together with data describing mouth enlargement during development, suggest that large yellow croaker larvae could be fed successfully with a compound diet from early stages, at least from day 23.

Which role do lacewings and ants play as predators of the citrus leafminer in Spain?

In a study about the impact of natural enemies of Phyllocnistis citrella Stainton conducted in Spain, predation appeared as the most important mortality factor. Predators responded to changes in flushing, and this was attributed to continuous availability of preferential prey feeding on tender flushes. In this paper the role of aphid-mutualists and generalist predators feeding on aphids as well as on P. citrella (ants and lacewings, respectively), has been investigated. In the laboratory, Chrysoperla carnea Stephens could complete its development when fed on P. citrella third instars only. In the field, highly statistically significant regressions were obtained between prey indicators (aphid density and flush) and C. carnea densities. Nevertheless, using P. citrella density resulted in a negative relationship. In another field trial, predation rates did not change when ants were excluded from P. citrella-infested trees. Therefore, neither ants, nor lacewings could be identified as key-predators of P. citrella. Although we could not prove the efficiency of these predators, these studies have given us the chance to become aware of the existence of an important guild of unidentified generalist natural enemies.

SPACE-USE PATTERNS OF BOBCATS RELATIVE TO SUPPLEMENTAL FEEDING OF NORTHERN BOBWHITES

Abstract In the southeastern United States, supplemental feeding of northern bobwhites (Colinus virginianus) is a common management practice. To determine whether bobcats (Lynx rufus) are attracted to supplemental food provided to northern bobwhites and whether this food affects bobcat home-range size, we radiomarked bobcats and assessed space use relative to supplemental feeding. We found little evidence to suggest that bobcat home-range sizes were affected by the supplemental food, but we observed bobcats to be approximately 10 times closer to supplemental food than expected under a null model. Our data suggest that supplemental feeding of prey can result in a spatial response by predators. Further research is needed to determine whether supplemental feeding of prey attracts other top predators and whether supplemental feeding results in decreased prey survival by attracting predators.

Prey feeding increases water stress in the omnivorous predator Dicyphus hesperus

AbstractThe effects of water stress (produced by water deprivation and prey feeding) on plant feeding were investigated in the omnivorous predator Dicyphus hesperus Knight (Hemiptera: Miridae). The objective was to determine if prey feeding aggravated water deficits and thus increased plant feeding. We measured plant feeding in a factorial experiment where female D. hesperus were prepared for experiments by providing or withholding water and/or prey for 24 h. We then evaluated the amount of plant feeding on Nicotiana tabacum seedlings by the direct observation of insects at three different densities of the prey, Ephestia kuehniella eggs. The amount of plant feeding, as measured by frequency of plant feeding bouts and time spent plant feeding during observation, was significantly greater for water‐deprived individuals than for those that had been provided with water. Individuals that had been provided with prey fed on plants at a significantly higher frequency than prey‐deprived individuals at two of the prey densities used in the experiment. These results support the hypothesis that plant feeding in zoophytophagous Hemiptera facilitates prey feeding by providing water that is essential for predation.

Predation by red-jointed fiddler crabs on congeners: interaction between body size and positive allometry of the sexually selected claw

The enlarged (major) claw of male fiddler crabs is used in contests over breeding burrows and is waved to attract females. We recently discovered that males of the red-jointed fiddler crab, Uca minax, also use the claw to kill smaller-sized fiddler crabs, U. pugnax and U. pugilator, with which they co-occur in Atlantic coast salt marshes. Large U. minax males use walking legs or the enlarged claw to capture prey feeding on moist sand flats. On sand flats, small U. minax males and females are much less common than large males, suggesting that large males move onto sand flats to seek prey. Males of prey species use the major claw against attacking predators and, consequently, are more likely than females to escape. In laboratory experiments, large U. minax males were more likely to attack and kill small-clawed males and females than large-clawed males, consistent with a preference for more vulnerable, less threatening prey. The size of the major claw is a positive allometric function of body size. The allometric function varies little among species. Also, the mechanical advantage and indices of closing speed and closing force of the major claw, when corrected for body size, are not consistently greater in U. minax relative to prey species. Thus, predation by U. minax males may reflect the opportunity afforded by larger body size and positive allometric growth, which result in a major claw that is more massive than the prey it is directed against. Copyright 2003.

Early weaning of winter flounder (Pseudopleuronectes americanus Walbaum) larvae on a commercial microencapsulated diet

Like most small marine fish larvae, the stomachs of winter flounder Pseudopleuronectes americanus are undeveloped at first feeding and have relatively reduced digestive capacity. This work was undertaken to test whether larvae at the onset of stomach differentiation (larval size about 5.5 mm) could be early weaned onto a commercial microencapsulated diet. We assessed the effect of early weaning by first comparing growth performance (standard length, total protein content and age at metamorphosis) of larvae fed enriched live prey from first feeding to a size of 5.5 mm and then reared on three different feeding regimes until metamorphosis: (1) live prey (LP) as a control group; (2) mixed feeding of live prey and microencapsulated diet (LP-ME); (3) exclusively microencapsulated diet (ME) after fast weaning over 4 days (to a larval size of 6.2 mm). No differences were observed between larval development in the two first groups, which began metamorphosis at 40 days old. The larvae of the third group showed significantly slower growth that resulted in a delay of 4 days in the onset of metamorphosis. Differences in live prey availability between the treatments and the short transition period to allow the larvae to adapt to the new diet were identified as possible contributing factors to the slower growth and to the delay in metamorphosis of early weaned larvae. In a second experiment, the transitional weaning period was increased until the larvae were 6.6 mm in length. Weaning at that size resulted in no slowing of growth or delay in metamorphosis, suggesting that the feeding schedule was adequate.

Infochemical-mediated niche use by the predatory mites Typhlodromalus manihoti and T. aripo (Acari: Phytoseiidae)

In Africa, Typhlodromalus manihoti and T. aripo, two introduced predators of the cassava green mite Mononychellus tanajoa, occupy different parts of cassava foliage. In the present study, niche use by these two predators, as mediated by prey-induced infochemicals, was investigated. In response to prey feeding damage, cassava plant parts emit volatile blends, that attract phytoseiidae predators. When given a choice between old cassava leaves infested with M. tanajoa and either apices or young cassava leaves infested with M. tanajoa, T. aripo displayed a marked preference for odors emitted from either infested apices or infested young leaves over infested old leaves but showed no preference for odors from apices versus young leaves, all infested with M. tanajoa. Typhlodromalus manihoti did not discriminate between volatiles from the three infested cassava plant parts. Our data show that T. aripo uses differences in volatile blends released by infested cassava plant parts and restricts its fundamental niche to a realized niche, which enables coexistence with its competitor T. manihoti.

Mechanisms of benthic prey capture in wrasses (Labridae)

Teleost fishes capture prey using ram, suction, and biting behaviors. The relative use of these behaviors in feeding on midwater prey is well studied, but few attempts have been made to determine how benthic prey are captured. This issue was addressed in the wrasses (Labridae), a trophically diverse lineage of marine reef fishes that feed extensively on prey that take refuge in the benthos. Most species possess strong jaws with stout conical teeth that appear well-suited to gripping prey. Mechanisms of prey capture were evaluated in five species encompassing a diversity of feeding ecologies: Choerodon anchorago (Bloch, 1791), Coris gaimard (Quoy and Gaimard, 1824), Hologymnosus doliatus (Lacepede, 1801), Novaculichthys taeniourus (Lacepede, 1801) and Oxycheilinus digrammus (Lacepede, 1801). Prey capture sequences were filmed with high-speed video at the Lizard Island Field Station (14°40′S, 145°28′E) during April and May 1998. Recordings were made of feeding on pieces of prawn suspended in the midwater and similar pieces of prawn held in a clip that was fixed to the substratum. Variation was quantified among species and between prey types for kinematic variables describing the magnitude and timing of jaw, hyoid, and head motion. Species differed in prey capture kinematics with mean values of most variables ranging between two and four-fold among species and angular velocity of the opening jaw differing seven-fold. The kinematics of attached prey feeding could be differentiated from that of midwater captures on the basis of faster angular velocities of the jaws and smaller movements of cranial structures which were of shorter duration. All five species used ram and suction in combination during the capture of midwater prey. Surprisingly, ram and suction also dominated feedings on attached prey, with only one species making greater use of biting than suction to remove attached prey. These data suggest an important role for suction in the capture of benthic prey by wrasses. Trade-offs in skull design associated with suction and biting may be particularly relevant to understanding the evolution of feeding mechanisms in this group.

Advancement of rotifer culture and manipulation techniques in Europe

Since no artificial feed formulation for first feeding of marine larval fish has been developed yet, live prey feeding remains essential in commercial marine hatchery operations. Because cultured rotifers are relatively poor in eicosapentaenoic acid (EPA: 20:5n-3) and docosahexaenoic acid (DHA: 22:6n-3), it is essential and therefore common practice to enrich these live prey with emulsions of marine oils. The short-term exposure to oil emulsions results in lipid-encapsulated rotifers with high EPA and DHA levels. However, these rotifers are prone to fast losses of their gut content and show a distortion in their protein/lipid balance. Rather than submerging rotifers in oil emulsions, it is often preferred to use formulated culture diets when medium to low enrichment values are needed in live prey. The use of these diets contributes not only to the filling of the gut of the rotifers with nutrients, it generally creates a more stable entire body composition which is important especially when rotifers are not consumed immediately by the larvae. New culture techniques for rotifers, such as closed recirculation systems, are offering new possibilities for continuous supplies of high quality rotifers at 10 times higher densities than in batch cultures. The production increase in these systems is explained by the better water quality obtained by the introduction of protein skimmers, ozone treatment, and biological filtration. Although disinfection of rotifers remains a bottleneck, it has been observed that rotifer populations cultured at high densities are not prone to higher bacterial infestation. Also, the problem of unexplained mortalities in batch cultures seems to be partly solved by the introduction of recirculation systems or by bacterial management (introduction of probionts), which allow more reliable rotifer production.