Differences In Gut Contents Research Articles

The trophic blockage hypothesis is not supported by the diets of fishes on Seine Seamount

AbstractSeveral hypotheses exist about the trophic mechanisms that support fish stocks at seamounts. This study investigated the diets of benthopelagic fish species on the summit plateau of Seine Seamount (NE Atlantic), testing the sound‐scattering layer interception hypothesis. A combined approach of gut content, stable isotopes and fatty‐acid biomarker analyses was employed. Fish species included zooplanktivores, benthivores, piscivores and species with mixed crustacean/cephalopod/fish diets. Trophic coupling between pelagic food sources and benthopelagic fish consumers was apparent based on three main lines of evidence: (i) dominance of pelagic prey in the guts of zooplanktivores, (ii) stable isotope enrichment of consumers indicative of a pelagic prey source, and (iii) high proportions of fatty acids that are typical of phytoplankton and zooplankton in the storage lipids of fishes and their similarity with fatty acid signatures of pelagic prey. Elevated levels of arachidonic acid in a benthivorous species suggested a minor dietary contribution of rhodophytes. The lack of larger taxa that undergo diel vertical migrations in the fish guts suggests that it is horizontal fluxes of non‐, or weakly migrating zooplankton that are the main food supply to the resident fish consumers. Overall, there was no unambiguous support for the trophic blockage hypothesis. Differences in gut contents, trophic position and storage lipid fatty acid signatures of zooplanktivorous fishes indicate some degree of resource partitioning with respect to feeding habitats, prey selection and ontogenetic diet shifts. Irrespective of body size and feeding mode, the benthopelagic fishes occupied intermediate trophic positions between the 3rd and 4th trophic level in a food web composed mainly of omnivorous species.

Trophic positions of omnivores are not always flexible: Evidence from four species of freshwater crayfish

Omnivores are generally believed to be flexible in their diet and trophic position: seasonal, ontogenetic and site-based differences in trophic position have been observed. We compared consumed and assimilated diet among four species within a group of omnivorous freshwater crayfish, to determine whether species that occur together at a site occupy different trophic positions. Diets of Geocharax falcata, Gramastacus insolitus, Cherax destructor and Euastacus bispinosus (Decapoda: Parastacidae) were compared using stable isotopes (δ13C and δ15N) and gut content analysis across nine sites that varied in their species composition. Gramastacus insolitus consumed mainly plant material across all sites. Geocharax falcata consumed either plants or animals or both at different sites. Its trophic level was consistently similar to G. insolitus, despite differences in gut contents and source for dietary carbon. Cherax destructor consumed animals and had a relatively stable trophic position among sites. Relative trophic position of these three species was consistent across sites and regardless of food consumed, they were positioned as omnivores at a lower trophic level than predators but higher than primary producers and herbivores. Euastacus bispinosus occupied a higher trophic level than other invertebrate species but δ13C levels did not differ among sites. Cherax destructor and G. falcata may show flexibility in food sources and in the assimilation of food that determines their trophic position relative to other crayfish species. In contrast, G. insolitus and E. bispinosus are likely to show both a more fixed diet and less flexible trophic position. Therefore, not all omnivores show the flexible diet and trophic position generally reported in the literature. Some species of omnivorous crayfish may maintain a relatively constant trophic position across sites, seasons or changes in food availability regardless of whether their consumed diet alters or not.

Diet of four species of deep-sea isopods (Crustacea: Malacostraca: Peracarida) in the South Atlantic and the Southern Ocean

The food of four species of asellote isopods (Crustacea, Malacostraca), Haploniscusrostratus, Haploniscus unicornis, Acanthocope galatheae and Betamorpha fusiformis, was evaluated by analysis of their gut contents. The isopods were sampled at several stations on the abyssal plains of Guinea Basin, Angola Basin and Cape Basin (southeast Atlantic), the Weddell Sea abyssal plain and the Antarctic continental slope during the DIVA and ANDEEP expeditions in 2000, 2001 and 2005. While all species had mineral particles in their guts and mucus material was the most frequent food item, the remaining gut contents differed among species. Betamorpha fusiformis fed mostly on phytodetritus, especially in the Southern Ocean basins and ingested along with it whole calcareous foraminifers. Acanthocope galatheae showed some differences in gut contents between basins, but in the Guinea Basin, the contents were to a large extent stercomata, i.e., waste pellets of soft-walled foraminifers, i.e., the Komokiaceae. Indications were that the haploniscids were feeding on detritus and agglutinating foraminifers (stercomata). This indicates spatial differences in food availability for this diverse group of deep-sea isopods and the importance of poorly known foraminiferal groups, like the Komokiaceae, as a food source in the deep sea.

Non‐interactive effects of habitat complexity and adult crayfish on survival and growth of juvenile crayfish (Pacifastacus leniusculus)

Summary1. In a 1‐month outdoor stream channel experiment, we investigated the relative importance of habitat complexity (i.e. cobbled area) and the presence of adult signal crayfish (Pacifastacus leniusculus) males on the survival and growth of juveniles.2. In treatments with high habitat complexity, more juveniles survived, more were newly moulted and they had a higher specific growth rate (SGR) at the end of the experiment than juveniles in treatments with low habitat complexity. The presence of adult males did not affect survival, moulting stage or growth of the juveniles.3. The presence of adult males decreased juvenile activity during night. Juveniles in treatments with low habitat complexity were more active than juveniles in high habitat complexity during both day and night.4. There was no difference in total invertebrate biomass between treatments. However, some invertebrate taxa, such as Chironomidae larvae, were affected by habitat complexity or the presence of adult crayfish. Juvenile crayfish in all channels had consumed detritus, algae and Chironomidae larvae and there were no differences in gut contents or stable isotope signals (carbon and nitrogen) between treatments, indicating a similar diet among the juveniles across treatments. However, the biomass of chironomids was significantly higher in channels with adult crayfish present, indicating a decreased consumption of chironomids by juveniles in the presence of adults.5. Our results suggest that the recruitment of juvenile crayfish is mostly affected by habitat complexity. The competition for food and shelter and aggressive interactions between the juveniles were most pronounced in low habitat complexity, indicating that habitats with a good access to shelter will enhance recruitment of juvenile crayfish in streams.

Arctic sea ice as feeding ground for amphipods - food sources and strategies

The amphipod species Gammarus wilkitzkii, Apherusa glacialis, Onisimus nanseni and O. glacialis live permanently associated with the Arctic sea ice. Qualitative and semi-quantitative investigations of gut contents and faeces showed that all four species use detritus as the main food source. Detrital lumps from the underside of sea ice had the same item composition as amphipod gut contents and faeces. Crustacean remains and ice algae were additional food items, but overall they were quantitatively less important. All species are omnivorous; however, differences in gut contents, behavioural observations and functional–morphological studies of the mandibles suggest a differentiation within this feeding strategy. G. wilkitzkii is a detritivorous-carnivorous-necrophagous-suspension-feeding species and shows the most complex feeding strategy. O. nanseni and O. glacialis are predominantly detritivorous-necrophagous, whereas A. glacialis is characterised as a more herbivorous-detritivorous species. By using a variety of the available food sources under Arctic sea ice, the amphipods are well adapted to the under-ice habitat and are less influenced by temporal and spatial variations. Furthermore, the wide food spectrum of all four species reduces the intra- and interspecific competition in a habitat where certain food sources are limited or only seasonally available.

Gut content analysis of mosquito larvae (Diptera: Culicidae) using DAPI stain and epifluorescence microscopy.

A method using 4'6-diamidino-2-phenylindole (DAPI) stain and epifluorescence microscopy for analyzing the food ingested by mosquito larvae is described. When stained with DAPI, food items (organic detritus, bacteria, algae, and protozoans) can be identified by fluorescence, color, and shape. Bacteria appear blue and protozoans light blue with a distinct nucleus, organic detritus autofluoresces dull yellow, chlorophyll in algae appears dull red, and algal nuclei are blue. This method revealed qualitative and quantitative differences in gut contents among fourth instars of Aedes triseriatus (Say), Anopheles quadrimaculatus Say, and Coquillettidia perturbans (Walker). The method is applicable to gut content analysis of other filter-feeding arthropods.

Utilization of alkali-treated grain. 1. Alkali-treated grain in complete diets for steers and lambs

In one experiment, 32 lambs were offered (ad libitum) diets based on whole or NaOH-treated barley, or whole or NaOH-treated oats. The live-weight gains from 17 to 35 kg live weight were 371, 290, 258 and 229 g/day, respectively, while the calculated carcass weight gains were 190, 161, 86 and 118 g/day, respectively. There were large differences in the gut contents at slaughter which were 5.0, 3.3, 9.2 and 3.0 kg for the four diets, respectively. Forty-eight, Hereford-cross steers were allocated to six dietary treatments which consisted of unrestricted access to one of the following diets: NaOH-treated barley; rolled barley; NaOH-treated oats; rolled oats; NaOH-treated wheat; or NaOH-treated maize. The steers were fattened from 325 to 425 kg live weight. The average live weight gains were 1.56, 1.91, 1.37, 1.38, 1.49 and 1.42 kg/day, respectively. The steers receiving rolled barley achieved the greatest live weight gains ( P < 0.05). The rumen contents at slaughter were 19.8, 32.2, 24.2, 46.0, 20.8 and 18.4 kg, respectively. Because of differences in gut contents, the only significant differences in carcass weight gain were found for the steers receiving rolled oats, for which carcass gain was lower than that for any other treatment ( P < 0.001). Sixteen, Hereford-cross steers were allowed free access to diets containing either NaOH-treated barley alone, or NaOH-treated barley mixed with 10% of chopped straw. The live weight gains from 325 to 425 kg live weight were 1.55 and 1.07 kg/day, and food conversion was 5.7 and 8.4 kg feed/kg gain respectively.

Food sources and foraging tactics in tropical rain pools

Pools on exposed rocks are common over much of Africa. Based on dimensions and position, those examined are of three types. Each type is inhabited by larvae of virtually a single dipteran species at high densities (over two million larvae m−2). Location of the pools suggests that food might be a limiting factor. However, events, including defecation in pools by civets and genets, fruit fall and wind-bornepollen, apparentlyensure that this is not the case. In this environment of superabundance animals are presumably free to choose favoured items of food. Each aninial species does, indeed, take a characteristic assemblage of food items. However, each species is shown to eat whatever it can swallow, differences in gut contents being due to differences in tlic clratactctisric food iterns available in each type of pool. Most algae are excluded because they are too largc or inaccessible, which means that the pool food chains are based largely on allochthonous detritus. There is no reason to believe that food type, perse, has any influence in determining which of the three dipteran species is present.

Selective Deposit Feeding by the Deep-Sea Archaeogastropod Bathybembix aeola

Analyses of paired sedlment and gut samples from specimens of the bathyal trochid gastropod Bathybemblx aeola (Watson) reveal selective ingestion of fine particles from a mixed mud and sand substrate. The radula is the selecting organ. Results contradict the prevalent notion that sediment-ingesting gastropods are lndiscnminant. The standard concept of the unselective deposit feeder as a primitive, generalist vacuum cleaner of the sea floor is difficult to accept from a morpholog~cal viewpoint because it requires perfecting a feeding apparatus capable of taking an unbiased sample. Results are con~patible wlth the hypothesis that se lec t~ve ingestion of fine particles with greater surface area of organic coating is energetically efficient. Selective feeding is a theoreticdlly appealing adaptive solution to dividing and efficiently using limited resources among the diversity of benthic invertebrates known to coexlst in the deep sea (Sanders, 1968; Grassle and Sanders, 1973). In deposit-feeding organisms, however, selectivity may not be so much an ecological problem related to conlpetition and resource partitioning as it is a problem relatlng the sizes and qualities of particles in the substrate to the sizes of organisms and the biomechanics and morphology of their feeding apparatus. From the point of view of the organism living in an environment in which organic matter is relatively scarce (Filatova, 1969; Sanders and Hessler, 1969), plasticity of feedlng behavior may be advantageous (Gage, 1978), and the ingestion of mud may be viewed as a problem in maximizing net energy gain (Taghon et al., 1978). Instances of selective feeding in the deep sea have been difficult to establish. Inferences in the literature are based on particle-size ranges and types in gut contents (Menzies, 1962; Carey, 1972). However, dramatic differences in gut contents of organisms coexisting in the same environment may reflect microhabitat selection (as in surface vs. subsurface feeding) rather than a morphologically based system of particle selection and rejection. Dredge hauls and grab O Inter-Research/Printed in F. R Germany samples mix sediments and separate organisms from feeding microhabitats. The difficulty of sampling an organism together with the substrate upon which it is feeding (particularly on and in thinly-stratified sediments) strictly limits inferences of selectivity. Fortuitous mini substrate samples from the vicinity of the mouth, taken by 2 llving specimens of the large (shells > 30 mm high) sediment-ingesting trochid gastropod Bathybernbix aeola (Watson) at the t ~ m e of their collection (R/V Soyo Maru sta. T 2 3 , 3504.6'N, 13929.0'E, 700 m) provide nearly ideal data for comparison with gut contents. When disturbed, a gastropod crawling on a soft substrate may retract into its shell carrying sediment that is trapped behind the tight-fitting operculum. An individual is thus occasionally capable of providing 2 samples of its feeding substrate: one taken by the retracting foot and the other by the feeding organ or radula. Paired, snail-collected sediment and gut samples from the two individuals were analyzed separately (4 runs) with a zone-sensing particle-size analyzer, revealing replicate distributions of particle size strongly skewed toward fine sand in the 2 substrate samples, with differential accun~ulation of the fine fraction in the gut samples. Fig. 1 shows a distinctly~ bimodal distribution of particles in the gut, with the largest mode in the clayand silt-size range. The virtual identity of grain-size distributions from the 2 specimens is remarkable. Inferences of selectivity are strengthened by examination of the radula as a morphological basis of particle selection. Bathybembix and a n allied group of deep-water deposit-feeding genera (Calliotropis, Cidarina, Ginebis, Convexia) have a distinctive radula (Fig. 2a, b, c) with several features that represent good design for ingesting fine particles from a mixed sediment (Hickman, 1980). The radula is of the rhipidoglossate type, with a longitudinal band of robust central 340 Mar. Ecol. Prog. Ser 6: 339-342, 1981

Cereal processing and food utilization by sheep. 3. The effect of replacing whole barley by whole oats on food utilization and firmness and composition of subcutaneous fat

SUMMARY1. Forty-eight early-weaned lambs were used in an experiment in which whole barley was gradually replaced by whole oats in order to produce different types of rumen fermentation.2. The type of rumen fermentation promoted by whole barley did not give rise to excessively soft fat in female lambs; in males, however, some carcasses were unacceptable. An increase in the proportion of propionic acid in the rumen liquor was associated with an increased proportion of odd- and branched-chain fatty acids and a decreased proportion of stearic acid in carcass fat. When the molar proportion of propionic acid in the rumen liquor was above 30%, three out of every five carcasses from the entire male lambs had excessively soft fat.3. Assessment of food utilization was complicated by lower daily intakes of digestible organic matter (DOM) when more than about 15% of barley was replaced by oats and also influenced by changes in gut contents. With 100% whole barley the mean gut fill was 4·7 kg while with 100% oats it was 9·4 kg.Assuming a maintenance requirement of 100 kcal metabolizable energy/kg0·75, it was calculated that the digestible organic matter of oats was utilized more efficiently than that of barley to produce empty-body gain. Most of the differences in utilization disappeared if an adjustment was made for differences in gut contents. The results indicate that the maintenance requirement/kg0·75 decreases with increasing gut content.

Seasonal and Inter-Specific Variation in Major Components of the Gut Contents of Some Woodland Collembola

The biotic relationships of organisms living in the soil have a great influence on the twin environmental processes of nutrient cycling and energy flow and have been subject to considerable study. Despite this fact many aspects of soil biology, especially the trophic interrelationships of the several hundred species of arthropods which may be found in a square metre of soil are little understood. In particular, little is known of the feeding biology of the Collembola (Insecta: Apterygota) which maintain populations of many thousands of individuals/M2 in nearly all soils. Although their total biomass is low (Hale 1966; Healey 1970) these large populations must play some part in soil processes, although perhaps a peripheral one (Macfadyen 1963). Several studies suggest that the gut contents of Collembola species living together in a habitat may have a very similar appearance (e.g. Poole 1959; McMillan & Healey 1971) and that differences in gut contents between the same species in different habitats may be greater than that between different species within one habitat (Gilmore & Raffensperger 1970; Bodvarsson 1970). This, together with the presence in the guts of many species of obviously indigestible material, such as large mineral particles (Poole 1959; B6dvarsson 1970) has suggested that the Collembola are unspecialized and indiscriminate feeders. However, this apparent ability of large numbers of detritivore species to coexist in a habitat while utilizing identical or very similar food resources is in conflict both with general ecological theory (de Bach 1966; Slobodkin, Smith & Hairston 1967) and with experience with other animal communities (e.g. Reynoldson & Davies 1970) which suggests that groups of related species sharing habitats usually evolve food differentiation. This paper describes a technique intended to provide a quantitative basis for the analysis and interpretation of collembolan gut contents and is part of a programme of work designed to investigate the basis of coexistence of detritivore species.

Habitat Specificity in Three Sympatric Species of Ameiva (Reptilia: Teiidae)

Three sympatric species of Ameiva in Costa Rica (A. quadrilineata, A. festiva, and A. leptophrys) were found in distinct habitats with respect to vegetation cover, a ground isolation, environmental temperatures, surface litter, and activity periods. Ameiva quadrilineata commonly forages in an area of open, low vegetation cover adjacent to bare soil. Its habitat is sunnier and warmer than those occupied by the other two Ameiva. A. festiva usually forages in the open edge of forests are lower where somewhat lower percentages of ground are exposed to direct sunlight and there are lower environmental temperatures than in the habitat of A. quadrilineata. Its peak of foraging activity is later in the morning than is that of A. leptophrys. Adult a. leptophrys forage even deeper into the forest than the other two species where even less of the ground surface is insolated, the ground substrate temperatures are lower, and there is a higher percentage of ground litter. However, this species basks in the same area in which A. festiva forages, but earlier in the morning. Newly hatched A. leptophrys are found in an ecological habitat distinct from that of the adults, but very similar to that of adult A. festiva. There appeared to be no differences in gut contents among the three species with respect to type of food items. However, A quadrilineata contained slightly smaller sized food items than did the other two species. Body temperatures while foraging were very similar in all three species, but were maintained under very different sunlight conditions and microclimatic temperatures.