Feeding biology of sunfishes: patterns of variation in the feeding mechanism

Fishes are generally believed to differ in their ability to alter (modulate) their feeding behaviour in response to different prey. We investigated modulation quantitatively in four species of sunfishes (Centrarchidae) by evaluating the variation in 11 electromyographic variables measured from recordings of electrical activity in head muscles during feeding on three prey types. The experimental design used allowed us to partition variation between species, among individuals within species, among prey types, and among feedings. Duration of activity of the sternohyoideus muscle was the only variable significantly different among the four species. All variables showed significant differences among individuals within species. The overall range of activity of each muscle activity variable was about the same for all four sunfishes. However, three species showed a significant ability to modulate most muscle variables while a fourth did not change its feeding response with respect to prey type. The results indicate that: (1) intraspecific variation is an important source of variability in functional attributes that should be accounted for in comparisons between species; (2) the ability of some species to modulate appears to be independent of the potential variability in muscle activity possessed by each species; (3) closely related species can differ considerably in their ability to alter muscle electrical activity patterns during feeding; and (4) a quantitative assessment of variation in electromyographic patterns is a powerful approach for asking questions about differences in feeding behaviour.     

Functional consequences of trophic specialization in pufferfishes

1. Trophic breadth may be correlated with behavioural and functional versatility or flexibility (Liem 1984), such that species with limited diets would be predicted to be less versatile or flexible in their feeding capabilities than would trophic generalists. The relationship was examined between the trophic breadth of a species and the degree to which muscle activity is influenced by prey type in two species of pufferfishes: Chilomycterus schoepfi, a specialist on hard-shelled prey, and Sphoeroides nephalus, a generalist predator. It was predicted that the specialist would show a decreased ability to alter its motor pattern in response to prey type and an increased amount of motor-pattern variability when feeding on different prey.
2. Electromyographic recordings of five feeding muscles were made from five individuals per species feeding on four prey types that differed in their hardness and escape abilities. Muscle-activity duration, relative onset and integrated rectified area were analysed for prey capture and manipulation behaviours for each prey type.
3. Prey-type effects on mean motor-pattern variables for capture were limited to one of 14 variables in each species. Prey effects on buccal manipulation were not significant for any of the 14 variables for C. schoepfi, but S. nephalus exhibited prey effects for seven out of 14 variables. No differences in motor-pattern variation were found for the strike, but species differed significantly in overall motor-pattern variability during buccal manipulation; C. schoepfi, the dietary specialist, exhibited greater motor variability than S. nephalus, the dietary generalist.
4. The results therefore support a direct relationship between the trophic breadth of a species and its functional versatility for buccal manipulation. In contrast, prey capture was a relatively stereotyped behaviour for both species, as few prey-type effects were found.     

PATTERNS OF VARIATION IN AQUATIC AMBYSTOMATID SALAMANDERS: KINEMATICS OF THE FEEDING MECHANISM

Patterns of variation in the feeding mechanism of three species of ambystomatid salamanders (Ambystoma dumerilii, A. mexicanum, and A. ordinarium) were studied to provide insight into the nature of variation in kinematic parameters of the jaw mechanism associated with prey capture. A nested analysis of variance design provided an assessment of the amount of variation in six kinematic variables (measured from 200 frames/sec films of feeding behavior) both among species and among individuals within species. For all six variables, a highly significant proportion of the variance was explained at the intraspecific level. Among species, the most robust discriminators were variables associated with movement of the hyoid. The variables reflecting gape and lifting of the head provided no significant discrimination among species and had large error variances. The hyoid apparatus is the most phylogenetically conservative component of the feeding mechanism in lower vertebrates and was the most stereotyped component of feeding behavior within the salamander species studied here.     

The ontogeny of functional design: metamorphosis of feeding behaviour in the tiger salamander (Ambystoma tigrinum)

The ontogeny of feeding behaviour was studied quantitatively in the tiger salamander, Ambystoma tigrinum , to elucidate the relative importance of morphological and environmental changes on form and function. High-speed films of prey capture provided data for a frame-by-frame analysis of seven kinematic parameters of feeding behaviour. By comparing underwater feeding of larval and metamorphosed individuals, the effect of morphological changes occurring at metamorphosis on the feeding kinematic pattern was determined. By comparing metamorphosed animals feeding in the water and on land, changes in feeding kinematics associated with the environmental transition (and thus the differing physical properties of water and air) were determined. Both univariate and multivariate analyses failed to demonstrate any differences between larval and metamorphosed aquatic feedings for seven kinematic variables. However, when individuals feed on land, a radical shift in hyoid kinematics was observed. In addition, multivariate analysis showed that terrestrial feedings differed from aquatic feedings in having longer duration head movements. The lack of a kinematic difference between larval and metamorphosed individuals feeding in the water indicates that the morphological changes occurring at metamorphosis do not impose any obligatory kinematic consequences. Rather, metamorphosed Ambystoma tigrinum acquire the ability to modulate their kinematic pattern depending on the environment.     

Evolution of asynchronous motor activity in paired muscles: effects of ecology, morphology, and phylogeny

Many studies of feeding behavior have implanted electrodes unilaterally(in muscles on only one side of the head) to determine the basicmotor patterns of muscles controlling the jaws. However, bilateralimplantation has the potential to achieve a more comprehensiveunderstanding of modification of the motor activity that maybe occurring between the left and right sides of the head. Inparticular, complex processing of prey is often characterizedby bilaterally asynchronous and even unilateral activation ofthe jaw musculature. In this study, we bilaterally implant feedingmuscles in species from four orders of elasmobranchs (Squaliformes,Orectolobiformes, Carcharhiniformes, Rajoidea) in order to characterizethe effects of type of prey, feeding behavior, and phylogenyon the degree of asynchronous muscle activation. Electrodeswere implanted in three of the jaw adductors, two divisionsof the quadratomandibularis and the preorbitalis, as well asin a cranial elevator in sharks, the epaxialis. The asynchronyof feeding events (measured as the degree to which activityof members of a muscle pair is out of phase) was compared acrossspecies for capture versus processing and simple versus complexprey, then interpreted in the contexts of phylogeny, morphology,and ecology to clarify determinants of asynchronous activity.Whereas capture and processing of prey were characterized bystatistically similar degrees of asynchrony for data pooledacross species, events involving complex prey were more asynchronousthan were those involving simple prey. The two trophic generalists,Squalus acanthias and Leucoraja erinacea, modulated the degreeof asynchrony according to type of prey, whereas the two behavioralspecialists, Chiloscyllium plagiosum and Mustelus canis, activatedthe cranial muscles synchronously regardless of type of prey.These differences in jaw muscle activity would not have beendetected with unilateral implantation. Therefore, we advocatebilateral implantation in studies of cranial muscle functionin fishes, particularly when investigating behaviors associatedwith processing complex prey. Incorporating this methodologywill provide a more detailed understanding of the coordinationand evolution of paired-muscle function in the feeding apparatusrelative to behavioral and ecological performance.     

Ecomorphological relationships among Caribbean tetraodontiform fishes

The anatomy of the oral jaw apparatus, lever-arm mechanics and the diet of six species of Caribbean fishes in the order Tetraodontiformes were investigated to explore the relationships between trophic morphology and feeding habit in these fishes. Tetraodontiforms use their oral jaw apparatus to capture and reduce a broad range of prey types such as plankton, polychaete worms, holothuroids, sea urchins, crabs, molluscs, gorgonians and algae. The different feeding habits of tetraodontiforms are reflected by differences in the morphological and biomechanical features of their oral jaw apparatus that appear to enhance their abilities to feed on hard prey organisms. Species that bite and crush hard, benthic prey organisms had more massive bones and muscles, longer jaw-opening in-levers, and higher jaw-closing lever ratios than the planktivorous, suction-feeding species. Masses of the jaw and suspensorium bones and lower jaw adductor muscles as well as the jaw-opening in-levers and jaw-closing lever ratios of crushers were greater than those of biters. In contrast, the mass of the adductor muscle of the upper jaw did not vary among species with different diets, indicating that this muscle may not be central to the factors that determine patterns of prey use in these fishes. The diversity of feeding behaviours and the wide range of feeding habits among fishes in the order Tetraodontiformes illustrate the versatility of the oral jaw apparatus as a single functional feeding system in fishes.     

Modulation in Feeding Kinematics and Motor Pattern of the Nurse Shark <Emphasis Type="Italic">Ginglymostoma cirratum</Emphasis>

Synopsis Studies of feeding in bony fishes have almost universally demonstrated the ability of individuals to modulate their method of capture in response to differing stimuli. Preliminary evidence indicates that morphologically specialized inertial suction feeding sharks are the most likely fishes to lack inherent modulatory ability. We examined the ability of the nurse shark, Ginglymostoma cirratum, to modulate its feeding behavior based on different food types and sizes. G. cirratum is an inertial suction feeding fish that is apparently stereotyped in its food capture behavior. Electromyography showed no statistical difference between feeding motor patterns based on food type (squid or fish) or size (gape width or twice gape width), although there were slight inter-individual differences in the onset of muscle firing for some muscles. Kinematic analysis showed a statistical difference in variables associated with durations for different food types, with the durations for all variables being faster for squid bites than fish bites, but no difference based on the size of the food item. This apparent lack of modulation may be associated with specialization of the morphology and behavior of G. cirratum for obligate suction prey capture. This functional specialization constrains the method in which G. cirratum captures prey but does not appear to result in dietary specialization. An unusual post capture spit-suck manipulation allows this shark to handle and ingest large prey.     

Vulnerability of marine forage fishes to piscivory: effects of prey behavior on susceptibility to attack and capture

We conducted a series of size-structured laboratory experiments to quantify and compare the susceptibility of several estuarine and marine forage fishes to attack and capture by piscivorous predators. Size-dependent estimates of capture success, handling time, and prey profitability were generated from single-species experiments offering bay anchovy, Atlantic menhaden, Atlantic silverside, and age-0 striped bass to piscivores. Bay anchovy and Atlantic menhaden were most susceptible to capture and yielded high profitability compared to Atlantic silverside and age-0 striped bass prey. Variation in capture success among forage species was particularly influential in generating disparate profitability functions. Although morphological differences among forage species contributed to variation in susceptibility to predation, behavioral analyses indicated that variable reaction distances to approaching predators and activity levels of prey may explain a large fraction of the observed differences in susceptibility. When several forage species were offered to predators simultaneously in larger enclosures, mortality was highest and occurred earlier for bay anchovy and Atlantic menhaden compared to other prey, which points to the strong influence of predator capture success on overall forage fish vulnerability. Our results demonstrate species-specific differences among forage fishes in the ability to avoid attack and capture by piscivores, and we conclude that the expression of antipredator behaviors contributes significantly to variation in forage species vulnerability.     

Cranial movements during suction feeding in teleost fishes: Are they modified to enhance suction production?

Suction is produced during prey capture by most teleost fishes. Here, we ask two questions about the functional basis of suction feeding. First, is there variation in the kinematic pattern produced by different species while suction feeding? Second, do species termed 'suction specialists' demonstrate similar modifications to their feeding behavior? We used 10 kinematic variables in a principal component analysis to identify axes of variation among 14 suction feeding teleost species (representing nine families and five orders within the Euteleostei) that demonstrate different feeding habits and habitats. MANOVA and Tukey post hoc tests were used to assess differences among species. Most species clustered together on the principal component axes, suggesting a generalized mechanism that facilitates unidirectional flow. Typically, only one species stood out as 'extreme' on each functional axis, and a species that stood out on one axis did not stand out on others. Only one species, the flatfish Pleuronichthys verticalis, an obligate benthic feeder, demonstrated modifications consistent with enhanced suction production. This species displayed a suite of changes that should enhance suction production, including large hyoid depression, large cranial rotation, and small gape. We suggest that suction performance may be greatest in such obligate benthic feeders because cranial morphology is highly modified and prey are captured from the substrate.     

A forceful upper jaw facilitates picking-based prey capture: biomechanics of feeding in a butterflyfish,Chaetodon trichrous

Biomechanical models of feeding mechanisms elucidate how animals capture food in the wild, which, in turn, expands our understanding of their fundamental trophic niche. However, little attention has been given to modeling the protrusible upper jaw apparatus that characterizes many teleost species. We expanded existing biomechanical models to include upper jaw forces using a generalist butterflyfish, Chaetodon trichrous (Chaetodontidae) that produces substantial upper jaw protrusion when feeding on midwater and benthic prey. Laboratory feeding trials for C. trichrous were recorded using high-speed digital imaging; from these sequences we quantified feeding performance parameters to use as inputs for the biomechanical model. According to the model outputs, the upper jaw makes a substantial contribution to the overall forces produced during mouth closing in C. trichrous. Thus, biomechanical models that only consider lower jaw closing forces will underestimate total bite force for this and likely other teleost species. We also quantified and subsequently modeled feeding events for C. trichrous consuming prey from the water column versus picking attached prey from the substrate to investigate whether there is a functional trade-off between prey capture modes. We found that individuals of C. trichrous alter their feeding behavior when consuming different prey types by changing the timing and magnitude of upper and lower jaw movements and that this behavioral modification will affect the forces produced by the jaws during prey capture by dynamically altering the lever mechanics of the jaws. In fact, the slower, lower magnitude movements produced during picking-based prey capture should produce a more forceful bite, which will facilitate feeding on benthic attached prey items, such as corals. Similarities between butterflyfishes and other teleost lineages that also employ picking-based prey capture suggest that a suite of key behavioral and morphological innovations enhances feeding success for benthic attached prey items.     

Prey capture in long-jawed butterflyfishes (Chaetodontidae): the functional basis of novel feeding habits

Several species of butterflyfishes (Chaetodontidae) possess extremely elongate jaws, and feed mostly by probing the benthos and biting off pieces of attached invertebrates. In contrast, Forcipiger longirostris, the longest-jawed chaetodontid, exhibits a novel pattern of prey use, feeding almost exclusively on small caridean shrimp, a mobile and highly elusive prey type that lives within the structure of coral reefs. We explored the functional basis of this novel pattern of prey use by comparing prey capture kinematics in this and four other butterflyfish species, including two other species that possess elongate jaws. High speed video recordings of feeding events on live adult brine shrimp were analyzed from individuals of five species: Forcipiger longirostris, F. flavissimus, Chelmon rostratus, Heniochus acuminatus, and Chaetodon xanthurus. We focused on a comparison among species of the relative contribution of "suction", measured as the amount of movement of the prey toward the predator's mouth, and "ram", measured as the distance moved by the predator toward the prey during the strike. All five species utilized a combination of suction and ram while feeding on brine shrimp. The contribution of suction did not differ significantly among species. However, F. longirostris exhibited a ram contribution to the strike that was more than twice that seen in any of the other species, permitting this species to initiate strikes from the greatest initial predator-prey distance. F. longirostris is known to possess a major structural novelty in the feeding mechanism that permits anterior movement of the entire jaw apparatus. The ability of this species to feed successfully on elusive prey appears to be related to exceptional jaw protrusion, resulting in greater use of ram during prey capture. This ability to protrude long, slender jaws toward the prey may allow it to move the jaws without detection within close enough proximity of the prey to then permit the effective use of suction. The use of extensive ram in this manner by small-mouthed fishes may be more widespread than previously thought.     

Motor pattern control for increasing crushing force in the striped burrfish (Chilomycterus schoepfi)

The relationship between muscular force modulation and the underlying nervous system control signals has been difficult to quantify for in vivo animal systems. Our goal was to understand how animals alter muscle activation patterns to increase bite forces and to evaluate how accurate these patterns are in predicting crushing forces. We examined the relationship between commonly used measures of cranial muscle activity and force production during feeding events of the striped burrfish (Chilomycterus schoepfi), a mollusc crushing specialist. We quantified the force required to crush a common gastropod prey item (Littorina irrorata) of burrfish using a materials testing device. Burrfish were fed these calibrated prey items while we recorded electromyograms (EMGs) from the main jaw closing muscles (adductor mandibulae A1beta, A2alpha, and A2beta). We quantified EMG activity by measuring the burst duration, rectified integrated area, and then calculated the intensity of activity from these two variables. Least squares regressions relating force to crush (Fcrush) and all EMG variables were calculated for each fish. Multiple regression analyses were used to determine how much of the variation in Fcrush could be explained by muscle activation patterns. We found that 20 cm burrfish are capable of generating extremely high crushing forces (380 N peak force) primarily by increasing the duration of muscle activity. EMG variables explained 71% of the total variation in force production. After accounting for the inherent variation in Fcrush of snails, EMGs do a very good job of predicting bite forces for these fish.     

Effects of prey type on motor pattern variance in tetraodontiform fishes

It is unclear whether the high variance of electromyographic parameters measured in feeding teleost fishes reflects functionally significant motor variation that is under control of the fish, or functionally insignificant variation characteristic of EMG data. We addressed this issue by examining the effect of three prey, differing in physical characteristics, on the feeding motor pattern in three fishes of the Order Tetraodontiformes: the filefish, Monacanthus hispidus; the triggerfish, Balistes capriscus; and the puffer, Sphoeroides nephelus. EMG recordings were made from subdivisions of the mouth closing adductor mandibulae muscle and the mouth opening levator operculi muscle in four fish from each species feeding on live fiddler crabs, live shrimp, and pieces of cut squid mantle. Analysis of variance was used to test for effects of prey type on the standard deviation of muscle burst duration, burst onset time, and average burst amplitude in the adductor muscles. The filefish exhibited a doubling of standard deviation of burst duration in all muscles when feeding on fiddler crabs; triggerfish showed increased standard deviations in onset times and duration of two muscles when feeding on squid mantle; and the puffer showed no effects of prey on motor variability. The observation that prey type can elicit more than a doubling in the standard deviation of some EMG traits indicates that a large portion of the within-prey type variance is under direct control of the individual fish, suggesting an even greater level of fine motor control in teleost feeding mechanisms than previously recognized.     

The functional morphology of lingual prey capture in a scincid lizard,Tiliqua scincoides (Reptilia: Squamata)

We investigated the functional morphology of lingual prey capture in the blue‐tongued skink, Tiliqua scincoides, a lingual‐feeding lizard nested deep within the family Scincidae, which is presumed to be dominated by jaw‐feeding. We used kinematic analysis of high‐speed video to characterize jaw and tongue movements during prey capture. Phylogenetically informed principal components analysis of tongue morphology showed that, compared to jaw‐feeding scincids and lacertids, T. scincoides and another tongue‐feeding scincid, Corucia zebrata, are distinct in ways suggesting an enhanced ability for hydrostatic shape change. Lingual feeding kinematics show substantial quantitative and qualitative variation among T. scincoides individuals. High‐speed video analysis showed that T. scincoides uses significant hydrostatic elongation and deformation during protrusion, tongue‐prey contact, and retraction. A key feature of lingual prey capture in T. scincoides is extensive hydrostatic deformation to increase the area of tongue‐prey contact, presumably to maximize wet adhesion of the prey item. Adhesion is mechanically reinforced during tongue retraction through formation of a distinctive “saddle” in the foretongue that supports the prey item, reducing the risk of prey loss during retraction.     

Morphology and function of the feeding apparatus of the lungfish, Lepidosiren paradoxa (Dipnoi)

The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics. In particular, the process of initial prey capture shares four salient functional features with other primitive vertebrates: 1) prey capture by suction feeding, 2) cranial elevation at the cranio-vertebral joint during the mouth opening phase of the strike, 3) the hyoid apparatus plays a major role in mediating expansion of the oral cavity and is one biomechanical pathway involved in depressing the mandible, and 4) peak hyoid excursion occurs after maximum gape is achieved. Lepidosiren also possesses four key morphological and functional specializations of the feeding mechanism: 1) tooth plates, 2) an enlarged cranial rib serving as a site for the origin of muscles depressing the hyoid apparatus, 3) a depressor mandibulae muscle, apparently not homologous to that of amphibians, and 4) a complex sequence of manipulation and chewing of prey in the oral cavity prior to swallowing. The depressor mandibulae is always active during mouth opening, in contrast to some previous suggestions. Chewing cycles include alternating adduction and transport phases. Between each adduction, food may be transported in or out of the buccal cavity to position it between the tooth plates. The depressor mandibulae muscle is active in a double-burst pattern during chewing, with the larger second burst serving to open the mouth during prey transport. Swallowing is characterized by prolonged activity in the hyoid constrictor musculature and the geniothoracicus. Lepidosiren uses hydraulic transport achieved by movements of the hyoid apparatus to position prey within the oral cavity. This function is analogous to that of the tongue in many tetrapods.     

Prey-handling Behaviour of Newly Hatched Snakes in Two Species of the Genus Elaphe with Comparison to Adult Behaviour

The prey-handling behaviour of two species of Asian ratsnakes was studied in the laboratory. In experiment 1, effects of prey size and type (mouse, lizard and frog) on capture position, direction of ingestion, condition of prey at ingestion, and prey-handling method were investigated using newly hatched Elaphe quadrivirgata. Prey size did not affect these variables except prey-handling method in frog trials: large frogs were more frequently constricted after a delay of more than 1 s than small frogs, and small frogs were usually simply seized. On the other hand, prey type affected prey-handling method: mice and lizards were more frequently constricted or pinioned than frogs. When hatchlings of E. quadrivirgata tried to coil around a prey animal immediately after striking, they frequently failed or released their coils within 10 s after striking. In experiment 2, prey-handling behaviour of adult E. climacophora was examined with mice of various sizes. Adult E. climacophora tended to constrict large mice immediately after striking, whereas they simply seized small mice. Only one out of 38 mice which were constricted immediately after striking was released from the coils within the subsequent 10 s. Large mice were killed prior to ingestion, whereas small mice were swallowed alive. Large mice tended to be swallowed head first. Experiment 3 was conducted to investigate effects of mouse size on prey-handling behaviour of newly hatched E. climacophora. Mouse size affected condition of prey at ingestion and prey-handling method but not capture position and direction of ingestion. Possible relationships between feeding ecology and the differences of prey-handling behaviour among Elaphe are discussed.     

Importance of consumptive and non-consumptive prey mortality in a coupled predator–prey system

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina , imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three – nine densities of small or large individuals of each prey species.
2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non-consumptive elements. Non-consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested.
3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non-consumptive mortality (death not followed by ingestion).
4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non-consumptive mortality increased with prey density, although the relationships differed with prey species and size. The non-consumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non-consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes ) or accelerating (small Daphnia ) rate.
5. These results suggest that the importance of consumptive and non-consumptive mortality to total prey mortality needs to be considered when modelling predator–prey dynamics.     

Functional morphology of the feeding mechanism in aquatic ambystomatid salamanders

This study addresses four questions in vertebrate functional morphology through a study of aquatic prey capture in ambystomatid salamanders: (1) How does the feeding mechanism of aquatic salamanders function as a biomechanical system? (2) How similar are the biomechanics of suction feeding in aquatic salamanders and ray-finned fishes? (3) What quantitative relationship does information extracted from electromyograms of striated muscles bear to kinematic patterns and animal performance? and (4) What are the major structural and functional patterns in the evolution of the lower vertebrate skull? During prey capture, larval ambystomatid salamanders display a kinematic pattern similar to that of other lower vertebrates, with peak gape occurring prior to both peak hyoid depression and peak cranial elevation. The depressor mandibulae, rectus cervicis, epaxialis, hypaxialis, and branchiohyoideus muscles are all active for 40–60 msec during the strike and overlap considerably in activity. The two divisions of the adductor mandibulae are active in a continuous burst for 110–130 msec, and the intermandibularis posterior and coracomandibularis are active in a double burst pattern. The antagonistic depressor mandibulae and adductor mandibulae internus become active within 0.2 msec of each other, but the two muscles show very different spike and amplitude patterns during their respective activity periods. Coefficients of variation for kinematic and most electromyographic recordings reach a minimum within a 10 msec time period, just after the mouth starts to open. Pressure within the buccal cavity during the strike reaches a minimum of ?25 mmHg, and minimum pressure occurs synchronously with maximum gill bar adduction. The gill bars (bearing gill rakers that interlock with rakers of adjacent arches) clearly function as a resistance within the oral cavity and restrict posterior water influx during mouth opening, creating a unidirectional flow during feeding. Durations of electromyographic activity alone are poor predictors of kinematic patterns. Analyses of spike amplitude explain an additional fraction of the variance in jaw kinematics, whereas the product of spike number and amplitude is the best statistical predictor of kinematic response variables. Larval ambystomatid salamanders retain the two primitive biomechanical systems for opening and closing the mouth present in nontetrapod vertebrates: elevation of the head by the epaxialis and depression of the mandible by the hyoid apparatus.     

Functional groups in piscivorous fishes

Piscivory is a key ecological function in aquatic ecosystems, mediating energy flow within trophic networks. However, our understanding of the nature of piscivory is limited; we currently lack an empirical assessment of the dynamics of prey capture and how this differs between piscivores. We therefore conducted aquarium‐based performance experiments, to test the feeding abilities of 19 piscivorous fish species. We quantified their feeding morphology, striking, capturing, and processing behavior. We identify two major functional groups: grabbers and engulfers. Grabbers are characterized by horizontal, long‐distance strikes, capturing their prey tailfirst and subsequently processing their prey using their oral jaw teeth. Engulfers strike from short distances, from high angles above or below their prey, engulfing their prey and swallowing their prey whole. Based on a meta‐analysis of 2,209 published in situ predator–prey relationships in marine and freshwater aquatic environments, we show resource partitioning between grabbers and engulfers. Our results provide a functional classification for piscivorous fishes delineating patterns, which transcend habitats, that may help explain size structures in fish communities.     

The feeding ecology of the pit-making ant lion larva,Myrmeleon bore: Feeding rate and species composition of prey in a habitat

The prey species composition and feeding rate of the pit-making ant lion larva,Myrmeleon bore Tjeder, which inhabits open sandy areas, were examined. Not less than 30 prey species, most of which were ants, were collected during a research period of 1.5 years. First instar larvae most often (81.1%) captured ants. Although 3rd instar larvae captured larger-sized prey than individuals of any other instar, they also captured small prey. The feeding rate of 3rd instar larvae was estimated by using the frequency of observed predation (FOP; (no. of ant lions handling a prey)/(total no. of pits observed)), the prey-handling time and the rhythm of daily foraging activity. FOP ofM. bore larvae was constant on the whole from spring to autumn. It was estimated that each captured 1.25 prey per day on average during this period. This estimate, however, was the feeding rate for days on which there was no rain. Assuming that the larvae cannot capture prey due to pit destruction when there is more than 10 mm of rainfall per day, the figure was reduced to 1.03 prey/day. The estimated feeding rate was evaluated with reference to larval foraging behavior.