Trophic Feeding Research Articles

Intraspecific variation in trophic feeding levels and organochlorine concentrations in glaucous gulls (Larus hyperboreus) from Bjørnøya, the Barents Sea.

Biomagnification contributes to high concentrations of persistent organochlorines (OC) in some Arctic vertebrates. Glaucous gulls (Larus hyperboreus) on Bjørnøya in the western Barents Sea were studied to compare the intraspecific variation in OC concentration with variation in trophic feeding levels, estimated from ratios of nitrogen isotopes. Liver tissue samples from 40 adult glaucous gulls were analysed for hexachlorobenzene (HCB), oxychlordane, p,p'-dichlorodiphenyltrichloroethane (DDT) and its metabolite p,p'-DDE, Mirex, and nine congeners of polychlorinated biphenyl (PCB). The ratios of the heavier to lighter isotope of carbon (13C/12C) and nitrogen (15N/14N), expressed as delta13C and delta15N, were measured in liver and muscle. Hepatic concentrations of the nine PCB congeners (Sigma 9 PCB) ranged from 16 microg/g lipid weight to 292 microg/g lipid weight. The delta15N ranged from 14.0/1000 to 15.3/1000 in muscle. Seven of the 14 OC measured, sigma DDT, and sigma 9 PCB were positively correlated to delta15N from muscle tissue. No correlations were found between OC and delta13C. The present results indicate that OC concentrations are partly dependent on the foraging strategy of the gull. The r2 of the linear regressions suggests that up to 18% of the variation in the OC concentrations could be explained by variation in food preference.

Trophic feeding of the preterm infant.

Trophic feeding is the practice of feeding minute volumes of enteral feeds in order to stimulate the development of the immature gastrointestinal tract of the preterm infant This paper reviews the randomized controlled studies that have examined the physiological and clinical responses to trophic feeding of the preterm infant. Trophic feeding alters gastrointestinal disaccharidase activity, hormone release, blood flow, motility and microbial flora. Clinical benefits appear to include improved milk tolerance, greater postnatal growth, reduced systemic sepsis and shorter hospital stay. There is currently no evidence of any adverse effects following trophic feeding.

Trophic feeding of the preterm infant

Trophic feeding is the practice of feeding minute volumes of enteral feeds in order to stimulate the development of the immature gastrointestinal tract of the preterm infant This paper reviews the randomized controlled studies that have examined the physiological and clinical responses to trophic feeding of the preterm infant. Trophic feeding alters gastrointestinal disaccharidase activity, hormone release, blood flow, motility and microbial flora. Clinical benefits appear to include improved milk tolerance, greater postnatal growth, reduced systemic sepsis and shorter hospital stay. There is currently no evidence of any adverse effects following trophic feeding.

Use of stable-carbon and -nitrogen isotopes to assess weaning and fasting in female polar bears and their cubs

In some species, stable-isotope techniques can provide insights into dietary regimens where there are temporal shifts in trophic level or feeding frequency. We determined stable carbon (δ13C) and nitrogen (δ15N) isotope values for plasma and milk proteins and δ13C values for milk lipids from female polar bears (Ursus maritimus) and cubs to (i) ascertain whether cubs are at a higher trophic level than their mothers as a result of nursing and whether we can determine when weaning occurs, and (ii) determine the impact of seasonal fasting on δ13C and δ15N values. The plasma δ13C values for mothers and cubs were similar to milk-protein δ13C values and were significantly enriched in 13C compared with those for milk lipid. Plasma from cubs of the year (COYs) in spring, when milk was their only diet, was isotopically enriched in 15N by 1.0‰ over that of their mothers (δ15N = 21.5 ± 0.8‰ (mean ± SD) for cubs and 20.5 ± 0.5‰ for mothers) and depleted in 13C by 0.8 ‰ (δ13C = –19.6 ± 0.5‰ for cubs and –18.8 ± 0.8‰ for mothers). For bears who fasted between summer and fall (3–4 months), plasma became depleted in 13C by 0.5‰ and in 15N by 1‰. Plasma from females, who had fasted from summer to spring (7–8 months) and given birth to cubs, became enriched in 13C by 0.7‰ and in 15N by 2‰. By using stable-isotope analyses we were able to show that (i) young cubs were at a higher trophic level than their mother when milk was their only food source, and (ii) seasonal fasting influenced δ13C and δ15N values. However, we were not able to use stable-isotope analyses to determine the exact time of weaning.

Temporal trophic shifts and feeding diversity in two sympatric, neotropical, omnivorous fishes: Astyanax bimaculatus and Pimelodus maculatus in Rio Tibagi (Paraná, Southern Brazil)

In this study, we explored whether the two dominant, morphologically divergent, omnivores, Astyanax bimaculatus (Characidae) and Pimelodus maculatus (Pimelodidae) in the high diversity (>100 species) fish assemblage of the Neotropical Rio Tibagi (southern Brazil) exhibited full overlap in the use of feeding resources similar to those reported for closely related species in Rio Amazonas. Monthly feeding patterns were assessed in two years of contrasting hydrological conditions and were compared with those reported for other, allopatric populations within their distributional range. Astyanax and Pimelodus fed at all trophic levels and exhibited an acute ability to shift prey as a response to environmental variations or food shortage. Although aquatic and terrestrial insects and seeds of native and introduced plants were the major food items, spatial separation across the water column and ecomorphological constrains seem to prevent a simultaneous use of the same food items by the two species. Except when cultivated seeds (i.e. maize) were most abundant after harvest, overlap in the use of feeding resources was negligible, if any. We suggest that the assessment of trophic relationships in Neotropical fish assemblages require more detailed studies than those actually available.

ENTERAL FEEDING OF THE MICROPREMIE

Clinical practice demands knowledge of gastrointestinal ontogeny and the factors that affect our ability to use enteral feeding in the micropremie. The decisions regarding milk type (when and how it should be given) are considered in the light of current physiologic and clinical evidence. Special considerations apply in the micropremie who is also small for gestational age and NEC must be avoided. Trophic feeding now has an established role, allowing the infant to benefit from enteral feeds even when full nutritive milk feeding is not possible.

WHAT CAN STABLE ISOTOPES (δ15N AND δ13C) TELL ABOUT THE FOOD WEB OF SOIL MACRO-INVERTEBRATES?

Animals reflect the stable isotope ratios (δ15N and δ13C) of their diet, with a slight enrichment in 15N that allows the use of δ15N as a trophic-level indicator. Stable isotope contents were measured for the litter, soil, and macro-invertebrates of three temperate deciduous forest sites, in spring, summer, and autumn, to study the trophic structure of this community. No distinct trophic structure could be derived from measurements of δ13C. In contrast, when the δ15N values of all animal species were grouped together, the hypothesis of an isotopically similar diet was rejected. Therefore, the community spreads over more than one trophic level and was subdivided into detritivores and predators. The potential detritivore food sources in the forest litter and soil showed a variety of isotopic ratios. Despite this fact, the variance of the isotopic ratios of the detritivorous species was not larger than what could be expected from interspecific variability of trophic isotopic enrichment alone. This was also the case for the predators in most of the sample sets. However, in some cases this variance was significantly larger, due to a small number of species with high δ15N values. The δ15N values of the detritivores indicated that the mean δ15N value of their food was close to that measured for the superficial litter layers. The difference in δ15N between detritivores and predators was highly significant and never significantly different from the value expected for one trophic transfer (3.4‰), although often slightly higher. Most of the litter macro-invertebrate community we studied can therefore be described as belonging to two trophic levels, one feeding on the superficial litter layers (or on soil fractions that have a similar δ15N value), and a second trophic level feeding on the first, with some indication of intraguild predation among the predators. Between-site differences of up to 7‰ were found for δ15N in the litter, and the δ15N values of the whole animal community were shifted in accordance with the local value of the litter δ15N. Therefore, the trophic structure must be studied in relation to the local isotopic content of the litter. Seasonal differences in isotopic ratios of the litter or animal samples were neither large nor consistent. These findings indicate similar trophic structure of the communities at the three sites and during the three sampling periods.

Randomised controlled study of clinical outcome following trophic feeding

AIMSTo determine the effect of trophic feeding on clinical outcome in ill preterm infants.METHODSA randomised, controlled, prospective study of 100 preterm infants, weighing less than 1750 g at birth and...

An Index of Biotic Integrity: A Test with Limnological and Fish Data from Sixty Florida Lakes

An index of biotic integrity (IBI) that used eight fish assemblage metrics was examined for effectiveness in estimating anthropogenic impacts to 60 Florida lakes ranging in size from 2 ha to more than 12,400 ha. The lakes ranged in trophic status from oligotrophic to hypereutrophic and had aquatic macrophyte abundances (percent lake volume infested) ranging from less than 1% to 100%. Fish species were classified by trophic feeding guild and tolerance to increases in turbidity or warming and decreases in dissolved oxygen concentration. Fish assemblage metrics tested were as follows: Number of fish species, number of native fish species, number of Lepomis species, number of piscivorous species, number of generalist species, number of invertivore species, number of species intolerant of increased turbidity or warming and decreased dissolved oxygen concentration, and number of species tolerant of increased turbidity or warming and decreased dissolved oxygen concentration. The total IBI scores and the data used to calculate individual metrics were unable to accurately predict the degree of anthropogenic impact to 60 Florida lakes, as estimated by personal observations of local limnologists, lake chloride concentrations, and road densities in the watersheds. Lake surface area and lake trophic status have a dominant influence on the fish assemblage metrics tested in this study. Thus, the IBI approach may be of limited usefulness for predicting anthropogenic impact in lake data sets that have wide ranges of surface areas and trophic status classifications.

Trophic Feedings and High Density Lipoprotein (HDL) Heterogeneity in Premature Infants

Trophic Feedings and High Density Lipoprotein (HDL) Heterogeneity in Premature Infants

Trophic position and individual feeding histories of fish from Lake Okeechobee, Florida

We used C and N stable isotope measurements to identify trophic position and feeding histories of fish from Lake Okeechobee, one of the largest lakes in North America. When δ15N values were used to estimate trophic levels, analyses of about 500 individual fish collected in two seasons at five sites showed that trophic level varied from 2 (herbivore) to 4.3 (second-level carnivore) among the 29 fish species examined. Lower trophic levels predominated among small fish caught at a littoral marsh site, and highest trophic levels were found among larger offshore fish. Marsh fish showed about three times the C isotope variation than did offshore fish, consistent with the wider array of foods in the marsh versus offshore food web. In addition to these community-level results, there were often unexpected large isotopic differences between individuals in almost all fish species examined, suggesting large differences in individual feeding behavior. Isotopic analyses indicate long-term differences in feeding among individuals, in addition to the short-term differences often observed in stomach content studies. Long-term individual variation in fish foraging may be important in understanding variation in other biochemical parameters measured in fish, such as Hg or PCB contents.

Randomised controlled trial of trophic feeding and gut motility

OBJECTIVESTo determine the effect of trophic feeding on gastric emptying and whole gut transit time in sick preterm infants.METHODSA randomised, controlled, prospective study of 70 infants weighing less than 1750...

THE ROLE OF OMNIVORY IN A NEOTROPICAL STREAM: SEPARATING DIURNAL AND NOCTURNAL EFFECTS

The role of omnivory in structuring communities is potentially great in lowland neotropical streams that are characterized by an abundance of macroconsumers that consume both insects and algae. Here, we separate effects of natural densities of diurnal fishes and nocturnal shrimps in structuring the benthic community of a stream draining Costa Rica’s Atlantic slope. We experimentally manipulated the spatial and temporal access of fishes and shrimps to benthic resources, in situ, using electric “fences” powered by solar-powered fence chargers. Both fishes and shrimps significantly reduced inorganic sediment mass, organic ash-free dry mass (AFDM), densities of larval Chironomidae, and total insects: their combined effects were greater than effects of either group alone, and there was no significant interaction. Fishes shifted algal community composition from diatoms to green and blue-green algae and benthic insect communities towards chironomids, while shrimps had no significant effect on community composition. Effects of fishes were generally greater than those of shrimps, and this is due, in part, to higher natural densities and foraging pressures of fishes. Furthermore, shrimps foraged for significantly longer periods of time in the treatment where fishes were excluded than in the combined fish and shrimp access treatment, suggesting that diurnally feeding fishes are strong “interactors,” mediating resource availability to nocturnally feeding shrimps. Natural erosion and sediment-mediated effects of macroconsumers (both direct and indirect) also affected algal communities: a manual sediment removal experiment resulted in significant reductions of diatom biovolume and increases in the filament length of green and blue-green algae. Our results show the importance of: (1) assessing macroconsumer effects in a relatively natural depositional environment subject to background erosion and sloughing (i.e., in this case by using electric exclosures); (2) evaluating effects of natural densities of both diurnal and nocturnal macroconsumers through time in the context of these abiotic effects; and (3) distinguishing between the response of different types of algal resources (e.g., diatoms vs. green and blue-green algae), which are differentially affected by sedimentation and erosion. Cage experiments, short-term observations, or one-time sampling of undifferentiated “algae” may artificially overestimate trophic effects and underestimate abiotic effects. We found no evidence of a trophic cascade. Our findings are in agreement with the theoretical prediction that large-sized omnivores have strong direct trophic (feeding) effects, both on smaller primary consumers (insects) and basal resources (algae).

Minimal enteral nutrition for promoting feeding tolerance and preventing morbidity in parenterally fed infants.

Because of concern that feedings may increase the risk of necrotizing enterocolitis, some high-risk infants have received prolonged periods of parenteral nutrition without enteral feedings. Providing minimal enteral feedings during this period of parenteral nutrition was developed as a strategy to enhance feeding tolerance and decrease time to reach full feedings. For high-risk neonates receiving parenteral feedings, to assess the effect of minimal enteral nutrition (MEN) compared to no enteral nutrient intake on measures of feeding tolerance and neonatal outcome. Searches were performed of the Oxford Database of Perinatal Trials, MEDLINE, abstracts and conference proceedings, references from relevant publications in the English language, and studies identified by personal communication. Only randomized or quasi-randomized clinical trials were considered. Trials were included if they enrolled high-risk infants randomly assigned to receive minimal enteral feedings (defined as dilute or full strength feedings providing <= 25 kcal/kg/d for >= 5d) or no enteral nutrient intake (no feedings or water only). The two reviewers reached consensus for inclusion of trials. Data regarding clinical outcomes were extracted and evaluated by the two reviewers independently of each other. Authors were contacted as needed and feasible to clarify or provide missing data. The specific data that were needed were requested in writing. Among infants given minimal enteral nutrition (MEN), there was an overall reduction in days to full enteral feeding, total days that feedings were held, and total hospital stay. There was no discernible effect on necrotizing enterocolitis. The evidence of benefit from MEN in these analyses is not convincing for a variety of reasons--the inherent difficulty of assessing enteral feedings in high-risk infants, the small size and methodologic limitations of the studies to date, unexplained heterogeneity with respect to some of the apparent benefits, the potential for bias to affect the findings in unblinded studies, and the unexcluded possibility that MEN might increase necrotizing enterocolitis. For these reasons, it is unclear whether MEN should be used in lieu of an equal period of time without enteral feedings.

Variations in Nutrition Personnel and Practice Among 7 Neonatal Intensive Care Units

LEARNING OUTCOME: To understand the variations in nutrition personnel and practice in 7 neonatal intensive care units previously found to have significantly different growth rates in very low birth weight infants. A prospective study of over 1600 very low birth weight (VLBW) infants found significantly different growth rates among 7 neonatal intensive care units (NICUs), even after controlling for birth weight and severity of illness. We hypothesized that variations in nutrition personnel and practice may contribute to these outcomes. In a survey of these NICUs, we found 2 of 7 units had no RD, and the remaining 5 units ranged from 41-110 patients per RD full-time equivalent. The majority of the RDs in these 5 units had graduate degrees, but three of 5 NICUs employed one or more RDs with less than 5 years experience. Nutrition documentation by RDs was included in patient records for 4 of 5 NICUs. Only 1 NICU typically started parenteral nutrition and lipids within the first 48 hours of life. Three NICUs provided trophic feedings, although techniques varied. The general goal for calories was greater than or equal to 150 calories per kilogram for VLBW infants for 2 of the units; only 2 NICUs used protein supplements. All units monitored weights daily, but only 3 followed head circumference and length measurements weekly. Our survey confirmed variations in general nutrition policies among units, but found no obvious relationships among these practices and growth patterns in the VLBW infants. Identification and replication of optimal nutrition strategies may improve growth and healing in this highly vulnerable population, and shorten NICU stays, with concomitant cost benefits. Therefore, further research into specific nutrition practices and optimal growth is warranted.

Determination of digestive enzyme kinetics: a new method to define trophic niches in freshwater snails.

Fluorogenic substrate analogues (MUF substrates) are very sensitive in detecting hydrolytic enzymes. This method was adapted for the quantitative analysis of extracellular enzymes in snails and other animals. It was then used to determine cellobiase, chitobiase, protease, esterase, phosphatase and lipase in the digestive tract of Radix peregra and Bithynia tentaculata. The method was sensitive enough to determine the complete enzyme kinetics (K m, V max values) in the esophagus, stomach, digestive gland and intestine of single animals adapted to various natural foods. With the exception of lipase and phosphatase, K m values were between 15 and 30 mmol l-1, independent of prefeeding. Enzyme activities, in contrast, changed with food conditions: cellobiase-activities ranged from 80 to 8000 picokatal, esterase from 500 to 3000 pKat, chitobiase from 150 to 750 pKat and protease from 100 to 1100 pKat per animal. R. peregra had cellobiase activities 10 times higher than B. tentaculata. For chitobiase, esterase and protease the enzyme activities were in the same order of magnitude in both species. All enzymes differed significantly in activity between prefeeding regimes. This variability with prefeeding was much higher in Bithynia than in Radix. These results help to better define the trophic niches and feeding specializations of the two species studied.

Influence of Trophic Position and Feeding Location on Contaminant Levels in the Gulf of the Farallones Food Web Revealed by Stable Isotope Analysis

In this study, we present the levels of organochlorine (∑DDT, ∑HCH, ∑chlordane, HCB, and ∑PCBs) and metal (Pb, Hg, and Se) contaminants and their relationship to stable carbon and nitrogen isotope values in the Gulf of the Farallones marine food web. This food web consisted of two species of euphausiids (Euphausia pacifica and Thysanoessa spinifera), two fish species [short-bellied rockfish (Sebastes jordani) and anchovy (Engraulis mordax)], four bird species [common murre (Uria aalge), Brandt's cormorant (Phalacrocorax penicillatus), rhinoceros auklet (Cerorhinca monocerata), and pigeon guillemot (Cepphus columba)], and the northern sea lion (Eumetopias jubatus). We used a novel method of using egg albumen to determine stable isotope values. The values of δ13C ranged from −20.1‰ in the euphausiids to −15.0‰ in the northern sea lion and were consistant with a pelagic/offshore vs benthic/inshore results found in other studies. Values of δ15N in the Gulf of the Farallones food web ranged from 11.2‰ in the e...

Feeding, Function, and Phylogeny: Analysis of Historical Biomechanics in Labrid Fishes Using Comparative Methods

Recently developed methods in phylogenetic systematics enable the discovery of as? sociations among diverse characters of organisms such as morphology, biomechanics, and ecology among clades. In this study, the results of multiple character correlation techniques were compared using a data set on the functional morphology and ecology of feeding in the Cheilinini and outgroups (Perciformes: Labridae). The following two questions were addressed: What are the patterns of evolutionary change in structure and function of the feeding mechanisms of labrid fishes? Are evolutionary changes in trophic structure, feeding biomechanics, and feeding ecology congruent at different levels of labrid phylogeny? This study integrated previous work on the phylogenetic relationships of labrid fishes, quantitative modeling of jaw protrusion and hyoid depression mechanisms, analysis of morphometric variation in the trophic apparatus, and descrip? tion of the natural diet of labrids. Analysis of phylogenetic association between dietary and bio- mechanical characters within the phylogeny was performed using character optimization to map characters onto the phylogeny. Statistical tests of association between pairs of discrete characters involved contingent states tests and concentrated changes tests. Phylogenetic correlations between continuous quantitative characters were determined using the methods of squared-change parsi? mony, independent contrasts, and phylogenetic autocorrelation. A diversity of techniques yielded similar answers in this case study, suggesting that evolution of dietary habits and feeding behavior is tightly linked to the biomechanics of the feeding apparatus. (Functional morphology; system? atics; ecology; character correlation; comparative methods; phylogeny; Labridae.)

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.

Lindeman's Contradiction and the Trophic Structure of Ecosystems

R. L. Lindeman's empirically based generalizations that both progressive efficiencies and percent of energy lost due to respiration increase with trophic level appeared contradictory, because he linked trophic levels in series to form a simple trophic chain. This model equates the energy not respired by the populations aggregated to form a trophic level to the productivity of the populations assigned to the next trophic level. This is clearly not the case for Cedar Bog Lake and ecosystems generally, because of nonpredatory losses and energy gains from other than the previous step in the trophic chain, e.g., bacterivory, detritivory, and feeding on organisms at more than one trophic level. Network analyses of energy—flow models make possible an objective and unambiguous definition of trophic level that does not suffer this contradiction. Trophic guild is proposed as an alternative to trophic level when is meant is an aggregation of species with similar trophic resources.