Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

Detection and capture of inert particles by calanoid copepods: the role of the feeding current

Although there is a scarcity of supporting empirical evidence,it has long been suspected that calanoid copepods use mechanoreceptionto detect the presence and location of potential prey itemsentrained in the feeding current. In this study, we documentthe first observations showing a freely swimming calanoid copepod,Skistodiaptomus oregonensis, attacking prey-sized, non-motile,inert particles entrained in the feeding current before theparticles contact the copepod's sensory appendages. Feedingcurrent geometry, fluid velocities and associated behavioursthat characterize these interactions are described. The resultsof this study show how copepod swimming behaviour, coupled witha low-velocity feeding current, not only increases copepod encounterrates with inert prey by increasing direct contact rates, butalso increases the probability of detecting and capturing remotelylocated prey that have well-developed escape responses. In turbulentregimes, a far-reaching, low-velocity feeding current shouldincrease encounter rates, but only if coupled with behavioursthat quickly minimize separation distances once prey is detected.     

Modulation in the feeding prey capture of the ant-lion, Myrmeleon crudelis

Ant-lions are pit-building larvae (Neuroptera: Myrmeleontidae), which possess relatively large mandibles used for catching and consuming prey. Few studies involving terrestrial arthropod larva have investigated prey capture behavior and kinematics and no study has shown modulation of strike kinematics. We examined feeding kinematics of the ant-lion, Myrmeleon crudelis, using high-speed video to investigate whether larvae modulate strike behavior based on prey location relative to the mandible. Based on seven capture events from five M. crudelis, the strike took 17.60 ± 2.92?msec and was characterized by near-simultaneous contact of both mandibles with the prey. Modulation of the angular velocity of the mandibles based on prey location was clearly demonstrated. M. crudelis larvae attempted to simultaneously contact prey with both mandibles by increasing mean angular velocity of the far mandible (65 ± 21?rad?sec(-1) ) compared with the near mandible (35 ± 14?rad?sec(-1) ). Furthermore, kinematic results showed a significant difference for mean angular velocity between the two mandibles (P<0.005). Given the lengthy strike duration compared with other fast-striking arthropods, these data suggest that there is a tradeoff between the ability to modulate strike behavior for accurate simultaneous mandible contact and the overall velocity of the strike. The ability to modulate prey capture behavior may increase dietary breadth and capture success rate in these predatory larvae by allowing responsive adjustment to small-scale variations in prey size, presentation, and escape response.     

Pythons metabolize prey to fuel the response to feeding

We investigated the energy source fuelling the post-feeding metabolic upregulation (specific dynamic action, SDA) in pythons (Python regius). Our goal was to distinguish between two alternatives: (i) snakes fuel SDA by metabolizing energy depots from their tissues; or (ii) snakes fuel SDA by metabolizing their prey. To characterize the postprandial response of pythons we used transcutaneous ultrasonography to measure organ-size changes and respirometry to record oxygen consumption. To discriminate unequivocally between the two hypotheses, we enriched mice (= prey) with the stable isotope of carbon (13C). For two weeks after feeding we quantified the CO2 exhaled by pythons and determined its isotopic 13C/12C signature. Ultrasonography and respirometry showed typical postprandial responses in pythons. After feeding, the isotope ratio of the exhaled breath changed rapidly to values that characterized enriched mouse tissue, followed by a very slow change towards less enriched values over a period of two weeks after feeding. We conclude that pythons metabolize their prey to fuel SDA. The slowly declining delta13C values indicate that less enriched tissues (bone, cartilage and collagen) from the mouse become available after several days of digestion.     

Numerical study of the feeding current around a copepod

Three-dimensional, numerical simulations of the feeding current around a tethered copepod were performed using a finite-volume code. The copepod's body shape was modeled to resemble Euchaeta norvegica, and was represented by a curvilinear body-fitted coordinate system. In the simulations, the appendages that generate the feeding current were replaced by a distribution of forces acting on the water adjacent and ventrally to the body. First, the accuracy of the code was verified by simulating two viscous, zero-Reynolds-number flows for which analytical solutions are available. Then, simulations with realistic body shape and Reynolds numbers were carried out. The main features of the computed feeding current were compared with observations from Yen and Strickler (Invert. Biol., 115, 191-205, 1996), and good agreement was obtained. The entrainment region, as visualized by tracking particles in the feeding current and by plotting the resulting stream-tube, is quite large. The result can be used to quantify how the copepod takes advantage of the feeding current to trap the algal particles in its capture area. The configuration of the feeding current near to the body surface of the copepod is controlled by how the copepod forces the feeding current and by the copepod's morphology. These parameters were varied and their effects studied in a systematic manner. Specifically, by comparing various spatial distributions of the same amount of total force, it was shown that a distributed force dissipates less energy (and increases the entrainment rate) than a concentrated force, it is thus energetically more desirable. Variations of the copepod's body shape and of the distribution of forces showed little effect on the far field of the feeding current, and therefore do not appear to affect the detectability by other mechano-receptional organisms. The length scale of the influence field of the feeding current was shown to be anisotropic in three directions, extending 5-7 mm above or ventrally to the copepod, <1 mm dorsally to the copepod and >1 cm down from the abdomen. The results also suggest that the net reaction force on the copepod from the feeding current is of the same order of magnitude as the excess weight of the copepod, but is not sufficient to balance the excess weight completely.      

Behavior of the rhabdocoel flatworm Mesostoma ehrenbergii in prey capture and feeding

The prey-capture and feeding behavior of the rhabdocoel flatworm Mesostoma ehrenbergii (Focke, 1836) was analyzed using a variety of live and dead prey, including Daphnia, mosquito larvae, and tubifex annelids. Prey-capture behavior was broken down into its individual components. Mesostoma could accommodate to and change its behavior depending on the size and type of prey. Mechanical rather than chemical cues were effective in inducing prey-capture behavior. No evidence for a special chemical paralysis as suggested by other workers was found. The apparent paralysis observed in cladocera such as Daphnia and mosquito larvae was, in part a behavioral response of the prey in ‘playing possum’ and also in part due to immobilization of the prey by the flatworm with mucous threads. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of light, prey density, and prey type on the feeding rates of Hemimysis anomala

Hemimysis anomala is a near-shore mysid native to the Ponto-Caspian region that was discovered to have invaded Great Lakes ecosystems in 2006. We investigated feeding rates and prey preferences of adult and juvenile Hemimysis in laboratory experiments to gain insight on the potential for Hemimysis to disrupt food webs. For both age groups (AGs), we measured feeding rates as a function of prey abundance (Bosmina longirostris as prey), prey type (B. longirostris, Daphnia pulex, and Mesocyclops sp.), and light levels (no light and dim light). Mean feeding rates on Bosmina increased with prey density and reached 23 ind. (2 h)^?1 for adults and 17 ind. (2 h)^?1 for juveniles. Dim light had little effect on prey selection or feeding rate compared to complete darkness. When feeding rates on alternate prey were compared, both AGs fed at higher rates on Bosmina than Daphnia, but only juveniles fed at significantly higher rates on Bosmina relative to Mesocyclops. No significant differences were observed between feeding rates on Mesocyclops and on Daphnia. Hemimysis feeding rates were on the order of 30–60% of their body weight per day, similar to predatory cladocerans that have been implicated in zooplankton declines in Lakes Huron and Ontario.     

Two predators feeding on two prey species: a result on permanence

For biological populations the precise asymptotic behavior of the corresponding dynamic system is probably less important than the question of extinction and survival of species. An ecological differential equation is called permanent if there exists some level k greater than 0 such that if the number xi(0) of species i at time 0 is positive for i = 1,2, ..., n then xi(t) greater than k for all sufficiently large times t Characterizations for permanence in a four-species prey-predator system modeled by the Lotka-Volterra equation are presented. The method used is based on a combination of two well-known approaches to dealing with permanence. An interesting feature is the occurrence of heteroclinic cycles.     

Opportunistic feeding by lions: non-preferred prey comprise an important part of lion diets in a habitat where preferred prey are abundant

Optimal foraging theory predicts less diverse predator diets with a greater availability of preferred prey. This narrow diet niche should then be dominated by preferred prey, with implications for predator–prey dynamics and prey population ecology. We investigated lion (Panthera leo) diets in Hluhluwe–iMfolozi Park (HiP), South Africa, to assess whether lions in a site with a high density of preferred prey (prey species weighing 92–632 kg as estimated from a published meta-analysis) have a narrow diet, consisting primarily of preferred prey. HiP is a useful study site to investigate this prediction because it is a productive landscape (with a high density of prey) where lion-preferred prey constitutes up to 33% of the prey available to lions. Furthermore, to investigate whether lions in HiP exhibit sex-specific diets as documented in other southern African populations, we estimated male and female lion diets separately. We were specifically interested in testing whether traditional approaches of estimating lion diets at the population level mask sex-specific predation patterns, with possible implications for management of lions in small to medium-sized fenced reserves. Lions in HiP preferred larger prey species (63–684 kg) and had diets with a larger proportion of preferred prey than reported in an African-wide meta-analysis. However, despite the high density of preferred prey species, 36% of lion diets still consisted of typically non-preferred species such as nyala (Tragelaphus angasii). This finding suggests that lions in HiP maintain a degree of opportunism even when preferred prey are abundant. Therefore, abundant, non-preferred prey are likely to be an important resource for lion populations. Sex-specific differences in lion diets were evident in HiP, suggesting that estimation of lion resource use and carrying capacity should consider opportunistic hunting and sex-specific differences in lion diets.     

Interpopulation variation in prey use and feeding biomechanics in Caribbean triggerfishes

The relationships between prey utilization and jaw biomechanics were explored in two Caribbean populations (La Parguera and Mona Island) of four trigger-fishes. The volumetric contribution of major prey types and six biomechanical features of the jaws that characterize biting strength were contrasted between populations. At Mona, Xanthichthys ringens ate 45% benthic organisms, whereas conspecifics at La Parguera fed exclusively on plankton. Balistes vetula at Mona consumed 63% soft and nonelusive invertebrates, in contrast to their La Parguera conspecifics, which consumed 62% hard prey. Differences in diet between populations were associated with differences in jaw biomechanics. Xanthichthys at Mona had jaw muscles, bones, and closing-lever ratios larger than those of fish at La Parguera, indicating a stronger bite. Balistes at Mona had 50% smaller jaw bones, muscles, and closing-lever ratios than their La Parguera conspecifics, indicating a weaker but swifter bite. Melichthys niger and Cantherhines macrocerus ate similar prey at the two locations and showed little difference in trophic anatomy. We hypothesize that the interpopulation differences in morphology are induced by the activities of feeding on different prey and enhance the feeding ability of fishes for locally dominant prey. Plasticity of the feeding mechanism may be a widespread attribute of fish feeding systems that promotes the ability of species to occupy multiple habitat types successfully.     

Emergent Allee effects in top predators feeding on structured prey populations

Top predators that forage in a purely exploitative manner on smaller stages of a size-structured prey population have been shown to exhibit an Allee effect. This Allee effect emerges from the changes that predators induce in the prey-population size distribution and represents a feedback of predator density on its own performance, in which the feedback operates through and is modified by the life history of the prey. We demonstrate that these emergent Allee effects will occur only if the prey, in the absence of predators, is regulated by density dependence in development through one of its juvenile stages, as opposed to regulation through adult fecundity. In particular, for an emergent Allee effect to occur, over-compensation is required in the maturation rate out of the regulating juvenile stage, such that a decrease in juvenile density will increase the total maturation rate to larger/older stages. If this condition is satisfied, predators with negative size selection, which forage on small prey, exhibit an emergent Allee effect, as do predators with positive size selection, which forage on large adult prey. By contrast, predators that forage on juveniles in the regulating stage never exhibit emergent Allee effects. We conclude that the basic life-history characteristics of many species make them prone to exhibiting emergent Allee effects, resulting in an increased likelihood that communities possess alternative stable states or exhibit catastrophic shifts in structure and dynamics.     

Tooth reorientation affects tooth function during prey processing and tooth ontogeny in the lesser electric ray, Narcine brasiliensis

The dental anatomy of elasmobranch fishes (sharks, rays and relatives) creates a functional system that is more dynamic than that of mammalian dentition. Continuous dental replacement (where new teeth are moved rostrally to replace older ones) and indirect fibrous attachment of the dentition to the jaw allow teeth to reorient relative to the jaw over both long- and short-term scales, respectively. In this study, we examine the processing behavior and dental anatomy of the lesser electric ray Narcine brasiliensis (Olfers, 1831) to illustrate that the freedom of movement of elasmobranch dentition allows a functional flexibility that can be important for complex prey processing behaviors. From static manipulations of dissected jaws and observations of feeding events in live animals, we show that the teeth rotate during jaw protrusion, resulting in a secondary grasping mechanism that likely serves to hold prey while the buccal cavity is flushed free of sediment. The function of teeth is not always readily apparent from morphology; in addition to short-term reorientation, the long-term dental reorientation during replacement allows a given tooth to serve multiple functions during tooth ontogeny. Unlike teeth inside the mouth, the cusps of external teeth (on the portion of the tooth pad that extends past the occlusal plane) lay flat, such that the labial faces act as a functional battering surface, protecting the jaws during prey excavation.     

Effects of prey motility and concentration on feeding in Acartia tonsa and Temora longicornis: the importance of feeding modes

Feeding experiments were conducted with the ambush-feeding copepodAcartia tonsa and the feeding-current-generating copepod Temoralongicornis. The copepods were offered a mixed diet of the dinoflagellateHeterocapsa triquetra and the ciliate Balanion comatum of similarcell size. The dinoflagellate was offered at a constant concentrationof 10–15 cells mL^–1, whereas the ciliate was offeredat a variety of concentrations, ranging from 7 to 57 cells mL^–1.Copepods with different feeding modes possess different mechanismsfor prey detection, suggesting that the two copepods would responddifferently to the two prey types. Both copepods had significantlyhigher clearance rates on the highly motile ciliate than onthe less motile dinoflagellate. In encounters between A. tonsaand its prey, we argue that this is due to the higher hydromechanicalsignal generated by the ciliate. The advection feeding copepodT. longicornis fed on the two prey according to their relativeconcentrations; in this case, we suggest that although B. comatumis capable of detecting feeding-current-generating predators,the feeding current velocity generated by T. longicornis isgreater than the escape velocity of this ciliate.     

Wolf spider feeding strategies: optimality of prey consumption in Pardosa hortensis

Feeding behaviour of the wolf spider Pardosa hortensis Thorell (Araneae, Lycosidae) was studied in the laboratory. Characteristics of feeding were measured while prey availability was increased and the results were compared with the predictions of three models: the marginal value theorem (MVT), gut limitation theory (GLT) and the digestion rate limitation model (DRL). As a result of more frequent encounters with prey, the wolf spiders were able to modify their feeding behaviour so that their net energy intake rate increased substantially. Handling time decreased by 30%, and consumption rate increased by 40%. Partial consumption of prey did not occur until the spiders became nearly satiated. This indicated that spiders did not reach the optimum predicted by MVT. The most plausible mechanism for the increased efficiency was prey-stimulated digestive enzyme production as suggested in DRL. The predictions of GLT were not applicable for most of the feeding session, though gut satiation had an influence on the final stages of feeding. P. hortensis seemed to apply a responsive but cautious strategy: (i) spiders improved feeding efficiency on entering the higher quality habitat, but (ii) feeding times appeared to be sub-optimal and (iii) spiders were also willing to continue feeding when, as they approached satiation, the previously high efficiency could not be maintained. Such feeding behaviour optimizes long-term energy intake when food is scarce and unpredictable, which corresponds well with the known degree of natural food limitation of these animals.     

Diel feeding pattern and prey selection of mesozooplankton on microplankton community

Mesozooplankton play an important role in transporting energy from microphytoplankton and microzooplankton to higher trophic levels. However there were few studies on the diel feeding patterns and prey selectivity of mesozooplankton. We conducted feeding experiments of mesozooplankton in the East China Sea to determine their respective diel feeding patterns on diatoms, ciliates and dinoflagellates, and to assess the contribution of these prey items to mesozooplankton diet. The results showed higher mesozooplankton grazing rates on ciliates and dinoflagellates than on diatoms at the day time, and the opposite pattern at the night time. A significant prey selection was observed, in which mesozooplankton positively selected ciliates and dinoflagellates during day and diatoms at night. The different grazing reactions of mesozooplankton toward each prey item might be related to the mobility of the prey. In all, microzooplankton (ciliates and dinoflagellates) provided the majority of the mesozooplankton carbon ingestion, even at a station dominated by small pennate diatoms. In particular, dinoflagellates are an important prey of mesozooplankton in the East China Sea and their contribution to the diet of mesozooplankton is unproportionate to their abundance.     

Time and extent of ciliary response to particles in a non-filtering feeding mechanism

Mechanisms of suspension feeding are usually described by the physics of inanimate filters. High-speed videorecordings in this study demonstrated that sea urchin larvae concentrate particles without filtration. They actively captured individual particles. At most times and places, the effective strokes of the swimming/feeding ciliary band were away from the circumoral field. Cilia of this band responded to particles by a reversal of beat that redirected the particle toward the circumoral field. A change of beat occurred along approximately 80 micro m of ciliary band during particle capture. Cilia responded 0.02 to 0.06 s after the particle was within reach of effective strokes and reversed beat, usually for about 0.1 to 0.2 s. The whole event (disruption of forward beat) generally lasted between 0.13 and 0.5 s. These observations imply reversed movement of a parcel of water much larger than the included captured particle, but particles are nevertheless greatly concentrated because water is directed toward the circumoral field only when and where a particle is sensed. Thus most of the concentration of particles occurs by a temporarily and locally redirected current, without filtration, and size and quality of particles captured depends on sensory capabilities, not the mechanics of filtration.     

The feeding habits of wolves in relation to large prey availability in northern Italy

We investigated wolf feeding habits in relation to the abundance of wild and domestic ungulates to test the hypothesis that large prey are preferred and that their abundance affects the use of other food categories and diet breadth. We determined diet composition by scat analysis from December 1987 to December 1992. The research was carried out in three study areas located in northern Italy and characterised by marked differences in wild and domestic ungulate abundance. In study area A (low wild and domestic ungulate availability) fruits, livestock, other vertebrates and wild ungulates made up the bulk of the diet (71% in volume). In area B (high availability of livestock) wolf diet was mainly based on sheep and wild boars (80% in volume). In study area C (high availability of wild ungulates) wild ungulates were the main food of wolves (90% in volume). Significant differences were found among study areas in the mean percentage volume of all food categories and in particular for wild ungulates, livestock, other vertebrates and fruits (p < 0.0001 in all cases). Diet breadth decreased in areas with high availability of large wild and domestic herbivores. The use of livestock species was lower where there was high abundance, richness and diversity of the wild ungulate guild. Selection for wild ungulate species was partially affected by their abundance: however other factors as prey social behaviour, adaptability to the habitat (for introduced species), and body size could have an important role in species selection by wolves. In particular in area C wild boars were selected for, roe and red deers avoided, and fallow deers and mouflons used as available. Livestock species were used in relation to their abundance and accessibility, in particular sheep were selected for and cattle avoided; but if calves bom in the pastures were considered as the only available cattle, they were selected for and sheep were used as available. Large and in particular wild herbivores were found to be of great importance for the wolf population maintenance in northern Italy, one of the most important recovery areas of Mediterranean wolves.     

Mixotrophy in the newly described phototrophic dinoflagellate Woloszynskia cincta from western Korean waters: feeding mechanism, prey species and effect of prey concentration

Woloszynskia species are dinoflagellates in the order Suessiales inhabiting marine or freshwater environments; their ecophysiology has not been well investigated, in particular, their trophic modes have yet to be elucidated. Previous studies have reported that all Woloszynskia species are photosynthetic, although their mixotrophic abilities have not been explored. We isolated a dinoflagellate from coastal waters in western Korea and established clonal cultures of this dinoflagellate. On the basis of morphology and analyses of the small/large subunit rRNA gene (GenBank accession number=FR690459), we identified this dinoflagellate as Woloszynskia cincta. We further established that this dinoflagellate is a mixotrophic species. We found that W. cincta fed on algal prey using a peduncle. Among the diverse prey provided, W. cincta ingested those algal species that had equivalent spherical diameters (ESDs) ≤12.6 μm, exceptions being the diatom Skeletonema costatum and the dinoflagellate Prorocentrum minimum. However, W. cincta did not feed on larger algal species that had ESDs≥15 μm. The specific growth rates for W. cincta increased continuously with increasing mean prey concentration before saturating at a concentration of ca. 134 ng C/ml (1,340 cells/ml) when Heterosigma akashiwo was used as food. The maximum specific growth rate (i.e. mixotrophic growth) of W. cincta feeding on H. akashiwo was 0.499 d(-1) at 20 °C under illumination of 20 μE/m(2) /s on a 14:10 h light-dark cycle, whereas its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was 0.040 d(-1). The maximum ingestion and clearance rates of W. cincta feeding on H. akashiwo were 0.49 ng C/grazer/d (4.9 cells/grazer/d) and 1.9 μl/grazer/h, respectively. The calculated grazing coefficients for W. cincta on co-occurring H. akashiwo were up to 1.1 d(-1). The results of the present study suggest that grazing by W. cincta can have a potentially considerable impact on prey algal populations.