Food Capture Research Articles

Using physiology and behaviour to understand the responses of fish early life stages to toxicants

The use of early life stages of fishes (embryos and larvae) in toxicity testing has been in existence for a long time, generally utilizing endpoints such as morphological defects and mortality. Behavioural endpoints, however, may represent a more insightful evaluation of the ecological effects of toxicants. Indeed, recent years have seen a considerable increase in the use of behavioural measurements in early life stages reflecting a substantial rise in zebrafish Danio rerio early life-stage toxicity testing and the development of automated behavioural monitoring systems. Current behavioural endpoints identified for early life stages in response to toxicant exposure include spontaneous activity, predator avoidance, capture of live food, shoaling ability and interaction with other individuals. Less frequently used endpoints include measurement of anxiogenic behaviours and cognitive ability, both of which are suggested here as future indicators of toxicant disruption. For many simple behavioural endpoints, there is still a need to link behavioural effects with ecological relevance; currently, only a limited number of studies have addressed this issue. Understanding the physiological mechanisms that underlie toxicant effects on behaviour so early in life has received far less attention, perhaps because physiological measurements can be difficult to carry out on individuals of this size. The most commonly established physiological links with behavioural disruption in early life stages are similar to those seen in juveniles and adults including sensory deprivation (olfaction, lateral line and vision), altered neurogenesis and neurotransmitter concentrations. This review highlights the importance of understanding the integrated behavioural and physiological response of early life stages to toxicants and identifies knowledge gaps which present exciting areas for future research.

Prey–predator dynamics in rotifers: density‐dependent consequences of spatial heterogeneity due to surface attachment

Classical models of prey-predator interactions assume that per capita prey consumption is dependent on prey density alone and that prey consumption (functional response) and consumer proliferation (numerical response) operate on the same timescales and without time lags. Several modifications have been proposed for resolving this timescale discrepancy, including variants where the functional response depends on both prey and predator densities. A microcosm system with the rotifer Brachionus 'Nevada' feeding on the prasinophyte Tetraselmis sp. showed significant (P < 0.0005) increases in steady-state biomasses of both prey and predators with increasing carrying capacity (represented by total phosphorus of the growth medium), which is inconsistent with predictions based on the traditional prey-only-dependent functional response. We provide data indicating that surfaces where the predator can attach provide a high-quality habitat for rotifers, which can result in a predator-dependent functional response. We also show that partitioning between the attached and free-swimming habitats was fast compared to the timescale of the numerical response. When attached to surfaces, rotifers maximized net energy gain by avoiding the high cost of swimming and by increased food capture due to reduced viscous drag. A mathematical model with prey-dependent functional response and wall-attached and free-swimming fractions of the population describes our data adequately. We discuss the implications of this finding for extrapolating microcosm experiments to systems with other surface-to-volume ratios, and to what extent our findings may apply to other popular model organisms for prey-predator interaction.

Reflection of induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of the “hunger center” in the lateral hypothalamus in rabbits

We studied reflection of artificially induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of "hunger center" of the lateral hypothalamus in the absence and presence of food. The threshold stimulation of the lateral hypothalamus in hungry and satiated animals in the absence of food induced incessant food-procuring behavior paralleled by regular generation of spike bursts in masticatory muscles with biomodal distributions of intervals between pulses. This reaction of masticatory muscles during stimulation of the lateral hypothalamus in the absence of food was an example of the anticipatory reaction reflecting characteristics of the action result acceptor. Higher level of hunger motivation during threshold stimulation of the lateral hypothalamus in hungry and satiated rabbits in the course of effective food-procuring behavior increased the incidence of spike burst generation during the food capture phase, but did not modify this parameter during the chewing phase. Impulse activity of the masticatory muscles reflected convergent interactions of food motivation and support excitation on neurons of the central generator of chewing pattern.

Use of shelters and marking sites by Lontra longicaudis (Olfers, 1818) in lotic and semilotic environments

The Neotropical otter Lontra longicaudis (Olfers, 1818) (Carnivora: Mustelidae) is a semi-aquatic species spread throughout Central and South America, except Chile. It uses cavities on the river banks or spaces amidst dense vegetation as shelter and defecates in conspicuous places as a means of territorial marking. The study was conducted between April 2008 and March 2009, aiming to compare and correlate the frequency of shelter use and marking by the otters, considering vertical vegetation cover, height, distance, disturbance degree and type of structure/substrate factors, in a lotic environment (Sapé stream, São Paulo state, Brazil) and a semi-lotic environment (Canoas I hydroelectric reservoir, Paranapanema Valley, São Paulo and Paraná states, also in Brazil). The aim was to compare and correlate the frequency of shelter use and marking by the otters, considering factors like vertical vegetation cover, height, distance, degree of disturbance and type of structure/substrate in two areas. It was evidenced that the otter's shelters show visual protection differences in each environment. Around the reservoir, the otters make greater use of areas with higher degrees of disturbance and are selective about the type of shelter structure. Along the stream, the otters favor areas with greater vegetation cover to demarcate. Our results warrant emphasis that other abiotic, biotic or density dependent factors (population number and intra or interspecific competition, for example) may be responsible for the otters' different choice of sites used for shelters and markings in the two environments but they were not identified in this study. Moreover, the different number of samples obtained in each location may have harmed the statistical analyses. However, based on the results, we were able to conclude that the species is able to adapt to the altered environment of the reservoir, using shelters and depositing markings according to the imposed environmental conditions and, whenever possible, it takes advantage of the facilitated food capture offered by environment. Nevertheless, the otters still present some dependence on areas with preserved vegetation, where they find sites with better shelter and marking conditions.

It pays to have a big mouth: mushroom corals ingesting salps at northwest Borneo

During daytime dives in July 2011 on the reefs of Kota Kinabalu (Sabah, Malaysia), large quantities of slow-moving salps (Tunicata: Thaliacea: Salpida) were observed. Some of these were seen to be caught and ingested by various mushroom corals (Fungiidae) and an anchor coral (Euphylliidae). The predators had complete salps (2–6 cm long) or partly digested salp remnants stuck inside their wide-open mouths. Salps that were observed landing on top of mushroom corals did not escape. They became captured by tentacles and were transported towards the opening coral mouths. To our knowledge, the present in situ observation is the first record of numerous salps being consumed by corals. All the observed predating coral species, either belonging to monostomatous or polystomatous species, possessed large mouths. The presence of multiple mouths enables mushroom corals to become larger than those with single mouths. Because a large polyp size facilitates the capture of food, it is advantageous for them to be polystomatous, especially when they possess a large mouth.

Evolutionary Simplification of Velar Ciliation in the Nonfeeding Larvae of Periwinkles (Littorina spp.)

The evolutionary loss of larval feeding has occurred multiple times in gastropods (e.g., 1, 2), with variable consequences for larval structures used to capture partic ulate food: in some cases, derived nonfeeding larvae retain structures used for food capture, but in others these are reduced or lost (2, 3). The fate of these structures in non feeding larvae has implications for the potential re-evolu tion of larval feeding (4, 5). Larval feeding has been lost at least once in the genus Littorina, but nonfeeding larvae of some species in the genus retain the velum, using its mar ginal cells for endocytotic uptake of capsular albumen (3). Retention of the velum, one of whose main ancestral func tions is particle capture, suggests that re-evolution of larval feeding might be possible in this group (5). We show that nonfeeding larvae of four Littorina spp. have lost the ciliary bands presumably used by their ancestors to concentrate planktonic food particles from suspension. Re-evolution of feeding in these larvae thus would require regaining op posed ciliary bands or other feeding structures. Acquisition of similar comparative data from other gastropod clades may help elucidate the conditions favoring loss of ancestral feeding structures in derived nonfeeding larvae. The larvae of marine invertebrates are diverse in form

Effects of ocean-acidification-induced morphological changes on larval swimming and feeding

Reduction in global ocean pH due to the uptake of increased atmospheric CO(2) is expected to negatively affect calcifying organisms, including the planktonic larval stages of many marine invertebrates. Planktonic larvae play crucial roles in the benthic-pelagic life cycle of marine organisms by connecting and sustaining existing populations and colonizing new habitats. Calcified larvae are typically denser than seawater and rely on swimming to navigate vertically structured water columns. Larval sand dollars Dendraster excentricus have calcified skeletal rods supporting their bodies, and propel themselves with ciliated bands looped around projections called arms. Ciliated bands are also used in food capture, and filtration rate is correlated with band length. As a result, swimming and feeding performance are highly sensitive to morphological changes. When reared at an elevated P(CO2) level (1000 ppm), larval sand dollars developed significantly narrower bodies at four and six-arm stages. Morphological changes also varied between four observed maternal lineages, suggesting within-population variation in sensitivity to changes in P(CO2) level. Despite these morphological changes, P(CO2) concentration alone had no significant effect on swimming speeds. However, acidified larvae had significantly smaller larval stomachs and bodies, suggesting reduced feeding performance. Adjustments to larval morphologies in response to ocean acidification may prioritize swimming over feeding, implying that negative consequences of ocean acidification are carried over to later developmental stages.

The Method for Estimating the Amount of Catalyst of Artificial Hail Suppression by Rocket

based on the theory of “food capture”, adopted BL-1 rainfall rocket with various resources, choose three typical cases to estimate catalyst dosage. Describe the practical bomb number might much more than theory. Different scale and development means different lunched bomb. At the same time, save bomb cost under the circumstance of hail suppression.

Bio‐inspired Design of Submerged Hydrogel‐Actuated Polymer Microstructures Operating in Response to pH

IO N Responsive and reversibly actuating surfaces have attracted signifi cant attention recently due to their promising applications as dynamic materials [ 1 ] that may enable microfl uidic mixing, [ 2 ] particle propulsion and fl uid transport, [ 3 ] capture and release systems, [ 4 ] and antifouling. [ 5 ] Analogs in nature serve as inspiration for the design of such advanced adaptive materials systems—microorganisms use fl agella for propulsion, [ 6 ] cilia line the human respiratory tract to sweep mucus from the lungs and prevent bacterial accumulation, [ 7 ] and echinoderms use pedicellariae for body cleaning and food capture. [ 8 ] Signifi cant characteristics of these biological systems include functionality in a fl uidic environment, controllable actuation direction or pattern, and the ability to translate chemical signals or stimulus into mechanical motion. Researchers have taken various approaches to fabricating biomimetic actuators, among which are biomorph actuators made using microelectromechanical systems (MEMS) technology, [ 9 ] magnetically actuated polydimethylsiloxane (PDMS) structures, [ 10 ] and artifi cial cilia or actuators made from responsive gel. [ 11 , 12 ] However, most fabricated actuators, such as MEMS or magnetically actuated PDMS posts, must be driven by an external force or fi eld and are not responsive to chemical stimuli. Actuating structures that have been made from responsive hydrogel are either low aspect ratio and their motion is not patternable, [ 11 ] or the movement is irreversible. [ 12 ] Microscale actuation systems which exhibit reversible chemo-mechanical response and control of actuation direction or pattern have proven diffi cult to achieve. Inspired by biological actuators, which can be broadly interpreted as composites consisting of an active “muscle” component coupled with a passive “bone” structure, we recently developed a hybrid actuation system in which a crosslinked polyacrylamide-based hydrogel, acting as an analog to muscle, drives the movement of embedded silicon [ 13 , 14 ] or polymer [ 15 ]

The influence of flow velocity and food concentration on Lophelia pertusa (Scleractinia) zooplankton capture rates

Lophelia pertusa is the most significant framework building scleractinian coral in European seas, yet the reproductive strategy, longevity, growth and food capture rates for the species remain poorly understood. In this study an experimental investigation into the ability of L. pertusa to capture zooplankton from suspension was conducted. By direct ROV sampling approximately 350 L. pertusa polyps were collected from the Tisler reef, Norway and maintained under temperature controlled conditions in recirculating flumes. These polyps were subdivided into three replicate groups of ~ 120 polyps and maintained in waters with flow velocities of 2.5 cm s − 1 or 5.0 cm s − 1 . Suspended Artemia salina nauplii food concentrations of between 345 and 1035 A. salina l − 1 were introduced. L. pertusa net capture rates were assessed by monitoring the reduction in suspended A. salina concentration in each flume over 24 h. Maximum net capture rates were higher in flumes with a 2.5 cm s − 1 flow regime, at 73.3 ± 2.0 A. salina polyp − 1 h − 1 (mean ± SD) than those with 5 cm s − 1 flow (19.8 ± 11.8 A. salina polyp − 1 h − 1 ). Maximum net capture rates were lower in flumes with A. salina densities of < 690 A. salina l − 1 than in flumes with higher food densities under comparable flow velocities. The maximum net capture rates observed represent maximum carbon capture rates of 66.4 ± 2.0 μg C polyp − 1 h − 1 and 17.9 ± 10.7 μg C polyp − 1 h − 1 under 2.5 and 5 cm − 1 s − 1 flow speeds respectively. The results of this study indicate that L. pertusa captures zooplankton more efficiently under slower flow velocities.

Stable isotopes reveal limitations in C and N assimilation in the Caribbean reef corals Madracis auretenra, M. carmabi and M. formosa

We used tissue δ 15 N and δ 13 C to elucidate nitrogen and carbon utilization in 3 branching coral species of the genus Madracis. Coral branches were sampled between 5 and 47 m water depth, and tissue was sub-sampled from the tips and sides of branches. Photosynthetically active radiation (PAR) ranged between 1 and 71% of surface PAR. There was a good correlation between δ 15 N and δ 13 C, and these had similar ranges of 5.6 and 5.2‰, respectively, suggesting that light-driven photo- synthesis is a strong factor in isotope fractionation. However, at shallow depths, δ 13 C decreased more strongly while δ 15 N remained constant, while at deeper depths δ 15 N decreased while δ 13 C remained constant. Comparisons of δ 13 C in polyps and zooxanthellae revealed that prey capture at the tips of branches was more pronounced than at the corresponding sideward-facing positions and that corals at deeper depths did not increase their food uptake to compensate for a decrease in photosynthetic carbon assimilation. This indicates that foraging in branching Madracis depends on current regimes and prey encounter rather than selective food capture. The systematic analysis of tissue δ 15 N along a steep depth gradient revealed that the shallow-water coral M. auretenra was nitrogen limited throughout its entire depth range.

The Spatial Variation of Extreme Tooth Breakage in an Herbivore and Potential Age Structure Effects

Teeth are essential in mammals for the capture, handling and processing of food and self-defense. The rate of deterioration may affect longevity and indicate certain environmental conditions. The goal of this study was to characterize tooth conditions of moose (Alces alces) from multiple regions and to make inferences of possible causes of variation. An assessment of > 5500 moose incisors, found that the frequency of breakage and rate of decline in incisor integrity, with age, was much higher in Cape Breton and Newfoundland (breakage from 6% to 47%) than in New Brunswick, Ontario, New Hampshire, Vermont, and Yukon (breakage from 1% to 6%). Incisai degradation, among jurisdictions, differed significantly though population age structures did not appear different. The two jurisdictions most affected by incisai deterioration, Cape Breton and Newfoundland, are inhabited by genetically distinct subspecies, at higher densities than other regions; therefore, breakage may be linked to local environmental conditions.

Caribbean reef squid, Sepioteuthis sepioidea, use ink as a defense a gainst predatory French grunts, Haemulon flavolineatum

Many animals release secretions in defense against predators. Some marine molluscs, including cephalopods (squid, octopus, cuttlefish) and gastropods (sea hares), release a colored ink secretion. Observational evidence supports the idea that inking is a defensive behavior that protects cephalopods from predators by forming a visual smokescreen or visual mimic (pseudomorph). Another possible function of cephalopod ink is to act against the chemical senses of predators either as a deterrent or distracting food mimic (phagomimic). Experimental tests of both hypotheses are lacking for cephalopods. In our study, we tested the hypothesis that squid use ink as a defense against attacks by predatory fish by performing three sets of experiments to examine the behavior of juvenile French grunts, Haemulon flavolineatum, toward ink from Caribbean reef squid, Sepioteuthis sepioidea. In the first set of experiments, a pseudomorph assay, in which ink was presented between a fish and a piece of food, assessed effects of ink on the approach and capture phase of a predator's attack. This showed that a pseudomorph of squid ink hindered the attack by significantly delaying food capture as well as evoking significantly more avoidance of or biting at the pseudomorph compared to a control pseudomorph of carboxymethylcellulose. A pseudomorph of carboxymethylcellulose plus food color to simulate the color of squid ink had a similar effect to the squid ink pseudomorph. In a second set of experiments, a disc assay, in which ink was added to meat-flavored paper discs, examined ink's effect on the consumption of food, simulating ink's protective effect if a squid and its ink are taken into a predator's mouth. This showed that squid ink added to meat-flavored discs significantly changed handling of the discs and increased, though non-significantly, their rejection. The same food color as used in the pseudomorph assay, when added to meat-flavored discs, significantly affected handling and rejection of the discs, showing that the food color itself, intended as a control, is unpalatable. In the third set of experiments, the disc assay was used to show that ink did not increase the acceptance of unflavored (i.e. without meat) discs, a result suggesting that ink is not a phagomimic. Our study presents the first experimental results supporting the hypothesis that inking protects squid against predatory fish, and that it acts during both the capture and consummatory phases of attacks: during the capture phase through visual and/or chemical effects against predators, and during the consummatory phase through unpalatable chemicals.

Capture of Particles by Direct Interception by Cilia During Feeding of a Gastropod Veliger

Ciliary feeders vary in the arrangement of ciliary bands and mechanisms of capture of food. Some larvae use opposed parallel bands of preoral (prototroch) and postoral (metatroch) cilia. Hypotheses for the mechanism of particle capture include filtration by adhesion to a cilium that overtakes a particle (direct interception), but until now unequivocal evidence for this mechanism has been lacking. Here, high-speed video recordings of veliger larvae of the gastropod Lacuna vincta demonstrated direct interception of particles by prototrochal cilia. Adhesion between cilium and particle was seen when a prototrochal cilium tugged a diatom chain into the food groove while in contact with one part of the chain. In several recorded events, a prototochal cilium overtook a particle during its effective stroke and subsequently pulled the particle inward with its recovery stroke; thereupon, the particle was deposited onto the food groove and transported to the mouth. Captures varied, however. In some cases the particle was intercepted multiple times in one capture event; in others, several cilia passed a particle without interception. Particles occasionally remained in the area of recovery strokes, indicating retention without continuing adhesion to a cilium. In three events, a particle lost from prototrochal cilia was intercepted and moved into the food groove by metatrochal cilia. Particles as wide as or wider than the food groove were also captured and transported but were not ingested.

Ink secretion protects sea hares by acting on the olfactory and nonolfactory chemical senses of a predatory fish

Ink secretion of sea hares, Aplysia californica, is a mixture of ink from the ink gland and opaline from the opaline gland. Its defensive mechanisms against predatory spiny lobsters include deterrent compounds that are unpalatable and amino acids that stimulate appetitive responses (phagomimicry) or interfere with chemoreception (sensory disruption) by predators. The current study aimed to identify mechanisms whereby sea hares use ink secretion to defend against a fish predator, in this case the bluehead wrasse, Thalassoma bifasciatum. We show that inking by live sea hares decreased the probability that wrasses strike sea hares. Ink protected sea hares by affecting two phases of feeding. First, an ink cloud between a wrasse and food decreased the probability that the wrasse captured the food. Second, if the wrasse captured food treated with ink, then that food was less likely to be accepted. In neither assay did opaline have a significant effect. Inactivating the olfactory sense of fish through nares occlusion eliminated the deterrent effect of ink on food capture but not the effect of ink on food acceptance, thus showing that olfaction mediates responses to deterrents during the capture phase of feeding and that nonolfactory chemical senses mediate responses to deterrents during the acceptance phase. These nonolfactory chemical senses may be intraoral senses, as fish did not reject pellets until after they were captured. Ink did not protect through phagomimicry, since neither ink nor opaline was accepted, despite the fact that mixtures containing the amino acid components of ink and opaline were accepted.

Mechanisms of temporary adhesion in benthic animals

Adhesive systems are ubiquitous in benthic animals and play a key role in diverse functions such as locomotion, food capture, mating, burrow building, and defence. For benthic animals that release adhesives, surface and material properties and external morphology have received little attention compared to the biochemical content of the adhesives. We address temporary adhesion of benthic animals from the following three structural levels: (a) the biochemical content of the adhesive secretions, (b) the micro- and mesoscopic surface geometry and material properties of the adhesive organs, and (c) the macroscopic external morphology of the adhesive organs. We show that temporary adhesion of benthic animals is affected by three structural levels: the adhesive secretions provide binding to the substratum at a molecular scale, whereas surface geometry and external morphology increase the contact area with the irregular and unpredictable profile of the substratum from micro- to macroscales. The biochemical content of the adhesive secretions differs between abiotic and biotic substrata. The biochemistry of the adhesives suitable for biotic substrata differentiates further according to whether adhesion must be activated quickly (e.g. as a defensive mechanism) or more slowly (e.g. during adhesion of parasites). De-adhesion is controlled by additional secretions, enzymes, or mechanically. Due to deformability, the adhesive organs achieve intimate contact by adapting their surface profile to the roughness of the substratum. Surface projections, namely cilia, cuticular villi, papillae, and papulae increase the contact area or penetrate through the secreted adhesive to provide direct contact with the substratum. We expect that the same three structural levels investigated here will also affect the performance of artificial adhesive systems.

Ultrastructure and Molecular Phylogenetic Position of a Novel Phagotrophic Stramenopile from Low Oxygen Environments: Rictus lutensis gen. et sp. nov. (Bicosoecida, incertae sedis)

A novel free free-living phagotrophic flagellate, Rictus lutensis gen. et sp. nov., with two heterodynamic flagella, a permanent cytostome and a cytopharynx was isolated from muddy, low oxygen coastal sediments in Cape Cod, MA, USA. We cultivated and characterized this flagellate with transmission electron microscopy, scanning electron microscopy and molecular phylogenetic analyses inferred from small subunit (SSU) rDNA sequences. These data demonstrated that this organism has the key ultrastructural characters of the Bicosoecida, including similar transitional zones and a similar overall flagellar apparatus consisting of an x fiber and an L-shape microtubular root 2 involved in food capture. Although the molecular phylogenetic analyses were concordant with the ultrastructural data in placing R. lutensis with the bicosoecid clade, the internal position of this relatively divergent sequence within the clade was not resolved. Therefore, we interpret R. lutensis gen. et sp. nov. as a novel bicosoecid incertae sedis.

Animal tool use: current definitions and an updated comprehensive catalog

AbstractDespite numerous attempts to define animal tool use over the past four decades, the definition remains elusive and the behaviour classification somewhat subjective. Here, we provide a brief review of the definitions of animal tool use and show how those definitions have been modified over time. While some aspects have remained constant (i.e., the distinction between 'true' and 'borderline' tool use), others have been added (i.e., the distinction between 'dynamic' and 'static' behaviours). We present an updated, comprehensive catalog of documented animal tool use that indicates whether the behaviours observed included any 'true' tool use, whether the observations were limited to captive animals, whether tool manufacture has been observed, and whether the observed tool use was limited to only one individual and, thus, 'anecdotal' (i.e., N = 1). Such a catalog has not been attempted since Beck (1980). In addition to being a useful reference for behaviourists, this catalog demonstrates broad tool use and manufacture trends that may be of interest to phylogenists, evolutionary ecologists, and cognitive evolutionists. Tool use and tool manufacture are shown to be widespread across three phyla and seven classes of the animal kingdom. Moreover, there is complete overlap between the Aves and Mammalia orders in terms of the tool use categories (e.g., food extraction, food capture, agonism) arguing against any special abilities of mammals. The majority of tool users, almost 85% of the entries, use tools in only one of the tool use categories. Only members of the Passeriformes and Primates orders have been observed to use tools in four or more of the ten categories. Thus, observed tool use by some members of these two orders (e.g., Corvus, Papio) is qualitatively different from that of all other animal taxa. Finally, although there are similarities between Aves and Mammalia, and Primates and Passeriformes, primate tool use is qualitatively different. Approximately 35% of the entries for this order demonstrate a breadth of tool use (i.e., three or more categories by any one species) compared to other mammals (0%), Aves (2.4%), and the Passeriformes (3.1%). This greater breadth in tool use by some organisms may involve phylogenetic or cognitive differences — or may simply reflect differences in length and intensity of observations. The impact that tool usage may have had on groups' respective ecological niches and, through niche-construction, on their respective evolutionary trajectories remains a subject for future study.

Estimation of Bioenergetics Parameters for a Stunted Northern Pikeminnow Population of South Central British Columbia

We estimate bioenergetics parameters using length-age and mark-recapture data for a stunted population of Northern pikeminnow on the Bonaparte plateau, British Columbia using a seasonal reproduction, skeletal allocation model. We show that using field data alone it was possible to estimate food consumption rates, standard metabolic rate and metabolic Q10 parameters, the proportional increase in feeding rate per 10 o C increase (Qc), but that prior parameter ranges must be specified. Using the estimated parameter set, we predict body sizes using warmer water temperatures from Cultis Lake, British Columbia and the John Day Reservoir, Columbia River. We show that surface temperature differ- ences between the Bonaparte plateau, John Day reservoir and Cultus Lake alone are insufficient to explain very large un- der-predictions of body size for these areas. In addition to diet differences, fish are likely choosing between fine-scale temperature and food-density environments to optimize capture and metabolism of food.

Assessment of movement patterns in Folsomia candida (Hexapoda: Collembola) in the presence of food

We showed that Folsomia candida (a blind soil-dwelling Collembola) was able to shift from non-directional (random or search strategy) to directional (target-oriented) movements at short distance of food. We measured departure from linearity and access (or not) to food by the springtail according to distance to the target position. Video-records and image analysis were used to obtain numerical data at 0.2 s interval. The probability of food capture within 10 min (maximum duration of the experiment) was negatively related to distance. Two patterns can be observed along successful trajectories in our experimental conditions (22 °C, ambient light, still air), non-directional movement being followed by directional movement when the animals approach food at 25 mm.