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PubMed2006

Identifying and quantifying prey consumption using stomach temperature change in pinnipeds.

For many marine predators knowledge of foraging behavior is limited to inferences based on changes in diving or movement patterns at sea. This results in an incomplete and potentially inaccurate view of the foraging ecology of a species. This study examined the use of stomach temperature telemetry to identify and quantify prey consumed in both a phocid (northern elephant seal Mirounga angustirostris) and an otariid (California sea lion Zalophus californianus) species. In addition, we used opportunistic water consumption by northern elephant seals to test a method to distinguish between prey and water ingestion. Over 96% of feedings could be identified based on a decline in stomach temperature, even when meals were separated by as little as 70 min. Water consumption was distinguishable from prey consumption, as the rate of recovery in stomach temperature was significantly faster for water (F(1,142) = 79.2, P < 0.01). However, using this method, the overlap in recovery rates between prey and water resulted in 30.6% of water ingestion events being misclassified as prey ingestion. For both species, the integral calculated from the decline in stomach temperature over time (area above the curve) could be used to estimate mass consumed, when adjusted for the temperature difference between the prey and core body temperature. For California sea lions, there was a significant effect of individual on the ability to quantify prey consumed, which was not related to their mass or sex. Although many factors may influence the ability to use stomach temperature change to identify and quantify prey consumed, this study has shown measures of stomach temperature can accurately identify prey consumption and provide an estimate of meal mass, allowing for a greater understanding of the feeding behavior of marine mammals.

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PubMed1990

Prey capture in the praying mantis Tenodera aridifolia sinensis: coordination of the capture sequence and strike movements.

Coordination of the complete capture sequence of the praying mantis has been studied in detail using several specially developed photographic techniques. The mantis was able to attack prey throughout a large three-dimensional capture zone by changing body orientation relative to its perch. This orientation centred prey on the median plane and brought it within an attack zone relative to the prothorax. Alignment with the median plane simplifies the attack since the prey can then be localized using only two dimensions. The attack comprised several stereotyped components which together formed a single movement sequence of all six legs. Although too rapid for visual feedback, a simple mechanism permits steering of these movements to capture prey at particular locations within the attack zone. These findings are contrasted with those from studies of mantis visual behaviour and a simple mechanism is suggested for how prey location is encoded to produce steering of the attack.

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PubMed2000

Role of prey-capture experience in the development of the escape response in the squid Loligo opalescens: a physiological correlate in an identified neuron.

Although extensively used for biophysical studies, the squid giant axon system remains largely unexplored in regard to in vivo function and modulation in any biologically relevant context. Here we show that successful establishment of the recruitment pattern for the giant axon in the escape response elicited by a brief electrical stimulus depends on prey-capture experience early in life. Juvenile squid fed only slow-moving, easy-to-capture prey items (Artemia salina) develop deficits in coordinating activity in the giant axon system with that of a parallel set of non-giant motor axons during escape responses. These deficits are absent in cohorts fed fast-moving, challenging prey items (copepods). These results suggest that the acquisition of inhibitory control over the giant axon system is experience-dependent and that both prey-capture and escape behavior depend on this control.

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PubMed2001

The effects of the light environment on prey choice by zebra finches.

Recent research has highlighted the extent to which birds utilise ultraviolet vision in mate choice and foraging. However, neither the importance of the ultraviolet compared with other regions of the visual spectrum nor the use of wavelength cues in other visual tasks have been explored. We assessed the individual choices of zebra finches (Taeniopygia guttata) for different-coloured seeds (red and white millet) under lighting conditions in which filters selectively removed blocks of the avian-visible spectrum corresponding to the spectral sensitivity of the four retinal cone types that subserve colour vision in this species. The effects corresponded to those predicted from the calculated distances between seed types, and between each seed type and the background, in a simple model of tetrachromatic colour space. As predicted for this foraging task, the removal of long-wavelength information had a greater influence than the removal of shorter wavelengths, including ultraviolet wavelengths. These results have important implications for predator-prey interactions and suggest that future studies of natural foraging should consider variations in the light environment.

Animals↗
PubMed2002

Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae).

The kinematics of feeding on fish have been studied in the aquatic feeding specialist Chelus fimbriatus, the fringed turtle, to provide a basic description of complete feeding cycles. Anatomical findings supplement the kinematic results. High-speed video (500 frames x s(-1)) recordings and X-ray film (150 frames x s(-1)) are used to analyse the kinematic variables characterizing head, hyoid, oesophageal and prey movements. The high velocities, especially of mouth opening, the forward thrust of the head and suction of the prey, are unique among turtles and comparable with those of aquatic salamanders and certain fishes (unidirectional feeders, in contrast to Chelus fimbriatus). The expandability of the pharynx and the anterior half of the oesophagus enables a specific type of unidirectional flow, at least during the early stages of the feeding cycle. This considerably improves the feeding performance compared with that of other aquatic turtles. The streamlined shape of the skull, the large hyoid apparatus, the highly reduced tongue and the extremely distensible oesophagus support the kinematics to a great extent, making C. fimbriatus a specialized suction feeder that can be regarded as one endpoint in the feeding evolution of aquatic reptiles.

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PubMed2002

High feeding costs limit dive time in the largest whales.

Large body size usually extends dive duration in air-breathing vertebrates. However, the two largest predators on earth, the blue whale (Balaenoptera musculus) and the fin whale (B. physalus), perform short dives for their size. Here, we test the hypothesis that the foraging behavior of these two species (lunge-feeding) is energetically expensive and limits their dive duration. We estimated the cost of lunge-feeding in both species using an approach that combined attaching time/depth recorders to seven blue whales and eight fin whales and comparing the collected dive information with predictions made by optimality models of dive behavior. We show that the rate at which whales recovered from a foraging dive was twice that of a non-foraging dive and that the cost of foraging relative to the cost of travel to and from the prey patch was 3.15 in blue whales (95 % CI 2.58-3.72) and 3.60 in fin whales (95 % CI 2.35-4.85). Whales foraged in small areas (<1 km(2)) and foraging bouts lasted more than one dive, indicating that prey did not disperse and thus that prey dispersal could not account for the limited dive durations of the whales. Despite the enormous size of blue whales and fin whales, the high energetic costs of lunge-feeding confine them to short durations of submergence and to areas with dense prey aggregations. As a corollary, because of their limited foraging time under water, these whales may be particularly vulnerable to perturbations in prey abundance.

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PubMed2002

Intensity control during target approach in echolocating bats; stereotypical sensori-motor behaviour in Daubenton's bats, Myotis daubentonii.

When approaching a prey target, bats have been found to decrease the intensity of their emitted echolocation pulses, called intensity compensation. In this paper we examine whether intensity compensation in the echolocation of bats is flexible or stereotyped. We recorded the echolocation calls of Daubenton's bats (Myotis daubentonii) while the animals attacked targets of different dimensions. Myotis daubentonii reduced the peak sound pressure level emitted by about 4dB for each halving of distance, irrespective of the target presented (mealworms and two different sizes of spheres). The absolute sound pressure level emitted by the bat is not or only a little affected by target strength. Furthermore, the decrease in emitted intensity over distance shows less scatter than the same intensity over time for the last 20 cm of target approach. The bats matched the emitted intensity to target distance equally well for the spheres (aspect-invariant target strength) as for the mealworms (aspect-dependent echo strength). We therefore conclude that intensity compensation does not rely on feedback information from received intensity, but instead follows a stereotyped pattern.

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PubMed2001

Possible competitive displacement of planorbids by Melanoides tuberculata in Minas Gerais, Brazil.

Several species of snails, including Pomacea haustrum, Marisa cornuarietis and Helisoma duryi, have been identified as probable competitors and/or predators of planorbid intermediate hosts of Schistosoma. During the last few years, studies carried out in the Caribbean region have shown reductions and even disappearances of populations of Biomphalaria glabrata and B. straminea in breeding places where the snail Melanoides tuberculata was introduced. Observations made over a period of 10 years in two lakes close to Belo Horizonte, MG, showed that there were marked reductions in autochthonous populations of B. glabrata and B. straminea after the arrival of M. tuberculata, both Biomphalaria species disappearing completely after eight years.

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PubMed2006

Diverse trait-mediated interactions in a multi-predator, multi-prey community.

Trait-mediated interactions (TMII) can alter the outcome or magnitude of species interactions. We examined how the interaction between a guild of ground and rove beetles and their fly egg prey was altered by a larger predator, the ground beetle Pterostichus melanarius, and an additional prey, aphids. In field and laboratory experiments, we manipulated the presence or absence of P. melanarius and aphids and recorded the impact of these manipulations on beetle activity and fly egg predation. Individually, aphids, by serving as preferred prey, and P. melanarius, by reducing focal beetle activity, weakened egg predation. However, egg predation was restored when both aphids and P. melanarius were present together, because aphids triggered greater foraging activity, and thus increased incidental predation of fly eggs, by P. melanarius. Thus, TMII among subsets of the community that were disruptive to predation on fly eggs could not be summed to predict the dominant, positive TMII within a more diverse community. Future TMII studies should include more realistic representations of species diversity, and should not ignore the influence of prey on predator behavior.

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PubMed2006

Jellyfish aggregations and leatherback turtle foraging patterns in a temperate coastal environment.

Leatherback turtles (Dermochelys coriacea) are obligate predators of gelatinous zooplankton. However, the spatial relationship between predator and prey remains poorly understood beyond sporadic and localized reports. To examine how jellyfish (Phylum Cnidaria: Orders Semaeostomeae and Rhizostomeae) might drive the broad-scale distribution of this wide ranging species, we employed aerial surveys to map jellyfish throughout a temperate coastal shelf area bordering the northeast Atlantic. Previously unknown, consistent aggregations of Rhizostoma octopus extending over tens of square kilometers were identified in distinct coastal "hotspots" during consecutive years (2003-2005). Examination of retrospective sightings data (>50 yr) suggested that 22.5% of leatherback distribution could be explained by these hotspots, with the inference that these coastal features may be sufficiently consistent in space and time to drive long-term foraging associations.

Animals↗
PubMed1988

Changes in feeding and foraging patterns as an antipredator defensive strategy: a laboratory simulation using aversive stimulation in a closed economy.

The effects of the risk of electric shock on the meal patterns of rats living in an operant chamber were investigated. Rats could obtain food by working on a response lever that provided reinforcement according to chained fixed-ratio continuous reinforcement schedules that allowed the animals control over meal size. Using a two-compartment operant chamber with a safe nesting area and manipulanda area with a grid floor, shock could be correlated with responding on the schedule. Shocks (less than or equal to 1.25 per hour) were scheduled to occur randomly throughout the day, independent of the rat's behavior. Shock caused a reorganization of meal patterns such that the animals took less frequent but larger meals. This pattern reduced the time the animals spent at risk without compromising caloric balance. Similar changes in feeding pattern were obtained in both hooded and albino rats. Exposure to shock in a separate chamber did not produce these behavioral modifications. The magnitude of shock-induced alterations of meal patterns was greater with chained fixed-ratio 90 continuous reinforcement than with chained fixed-ratio 10 continuous reinforcement. Additionally, the rats seemed to be able to reduce food intake but increase caloric efficiency, such that the reduced food intake did not have deleterious effects on maintenance of body weight. These behavioral modifications reduced the number of shocks received from that which would have been expected if meal pattern changes had not occurred. We suggest that this technique may provide a useful laboratory simulation of the impact that the risk of predation has on foraging behavior.

Animals↗
PubMed2000

A spatial model of antipredator vigilance.

Many species of animals have to perform two contradictory tasks: feeding, and avoiding becoming food for others. A large number of theoretical and empirical studies have investigated the trade-off between feeding and antipredator vigilance, especially in birds. An important factor which has been neglected in these studies is that of the area occupied by the flock. If individuals feed close together, competition increases and feeding rates decrease. However, if individuals space themselves widely, then vigilance efficiency goes down and there is an increased predation risk. We develop a vigilance model which allows birds to control the area the flock occupies as well as their vigilance rate. The optimal strategy is found for the birds under a variety of environmental conditions. In particular the effect of each environmental parameter on this optimum is considered in turn. How the model can be adapted for different bird species is also investigated.

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