Ontogenetic Variation In Diet Research Articles

Ontogenetic shift in diet of a large elapid snake is facilitated by allometric change in skull morphology

As snakes are limbless, gape-limited predators, their skull is the main feeding structure involved in prey handling, manipulation and feeding. Ontogenetic changes in prey type and size are likely to be associated with distinct morphological changes in the skull during growth. We investigated ontogenetic variation in diet from stomach contents of 161 Dugite specimens (Pseudonaja affinis, Elapidae) representing the full range of body size for the species, and skull morphology of 46 specimens (range 0.25–1.64 m snout-vent-length; SVL). We hypothesised that changes in prey type throughout postnatal ontogeny would coincide with distinct changes in skull shape. Dugites demonstrate a distinct size-related shift in diet: the smallest individuals ate autotomised reptile tails and reptiles, medium-sized individuals predominantly ate mammals, and the largest individuals had the most diverse diet, including large reptiles. Morphometric analysis revealed that ~40% of the variation in skull shape was associated with body size (SVL). Through ontogeny, skulls changed from a smooth, bulbous cranium with relatively small trophic bones (upper and lower jaws and their attachments), to more rugose bones (as a likely reflection of muscle attachment) and relatively longer trophic bones that would extend gape. Individual shape variation in trophic bone dimensions was greater in larger adults and this likely reflects natural plasticity of individuals feeding on different prey sizes/types. Rather than a distinct morphological shift with diet, the ontogenetic changes were gradual, but positive allometry of individual trophic bones resulted in disproportionate growth of the skull, reflected in increased gape size and mobility of jaw bones in adults to aid the ingestion of larger prey and improve manipulation and processing ability. These results indicate that allometric scaling is an important mechanism by which snakes can change their dietary niche.

First record of predation on <i>Rhinella diptycha</i> (Anura, Bufonidae) by <i>Caiman latirostris</i> (Crocodylia, Alligatoridae)

Caimans of the species Caiman latirostris, which are widely distributed in South America, are opportunistic predators. They show ontogenetic variation in diet, with young individuals initially feeding on invertebrates and then gradually adding vertebrates in their diets as they grow up. However, due to inexperience, young individuals may end up eating dangerous prey, such as poisonous amphibians. The intoxication caused by eating an individual of Rhinella diptycha may produce local irritation to the caiman, and even lead it to death shortly after ingestion. To avoid this threat, some animals use particular feeding strategies, such as starting to eat the prey’s posterior part, or eating only its viscera. In this note, we report the first case of a predation event of an adult individual of the poisonous toad R. diptycha by a young individual of C. latirostris that we observed in a pond of the Southeast of Brazil. The caiman waited until the toad was dead before starting swallowing slowly, from the anterior part of the body. We did not observe any sign that the caiman was affected by the prey ingestion, even some hours later after ingestion. Our register suggests that the caiman may be tolerant or adapted to eat this poisonous prey and encourage research on the causes and mechanisms of this tolerance.

Insights on diet dynamics of Indian mackerel Rastrelliger kanagurta (Cuvier, 1816)

The diet of Indian mackerel Rastrelliger kanagurta (Cuvier, 1816) is reported based on the gut content analysis of specimens collected along the central Kerala coast, India. The study indicated ontogenetic variations in diet with diet breadth being highest in the largest size class of >231 mm total length (TL). Copepods followed by diatoms were the preferred food items. Detritus was an important diet component, especially during the pre-monsoon season and in the larger (>231 mm TL) size groups. The Preponderal Index (Ip) indicated seasonal differences in proportions of the various prey consumed. Spearman Rank Correlation Coefficient indicated similar diet quality during monsoon (June-September) and post-monsoon (October-January) seasons; but significant differences as compared to pre-monsoon season (February-May). Based on the results of the study, Indian mackerel was classified as an opportunistic feeder with a diet component that broadly reflects its seasonal-spatial habitats and local food availability.

Ontogenetic variation in diet and habitat of Irrawaddy dolphins (Orcaella brevirostris) in the Gulf of Thailand and the Andaman Sea

AbstractIrrawaddy dolphins (Orcaella brevirostris) are threatened, little‐known cetaceans primarily jeopardized by fishing gear entanglement. Information regarding life history, foraging ecology, and movement are crucial to determine management units and conservation regions. This is the first analysis of the ontogenetic changes in diet and habitat of Irrawaddy dolphins from the Gulf of Thailand and the Andaman Sea using stable isotopes from skin and teeth. Results suggest limited age and sex structure indicated by weak ontogenetic and sexual variability in δ15N and δ13C in teeth. Significant variation in δ13C and δ15N values were observed between three Gulf regions and the Andaman Sea, indicating distinct regional groups. Isotope mixing models run on soft tissues from the eastern Gulf revealed a diet based primarily on fishes and secondarily on crustaceans, suggesting overlap with fishery targets. Conservation strategies that focus on reducing regional competition with humans and bycatch mortality are proposed. Fishing gear improvements and monitoring of fishing operations are a potential immediate response to reduce anthropogenic impact.

Patterns in micronekton diversity across the North Pacific Subtropical Gyre observed from the diet of longnose lancetfish (Alepisaurus ferox)

We examined the diet of a common midwater predator, the longnose lancetfish (Alepisaurus ferox, n=1371), with respect to fork length, season, and capture location within the North Pacific Subtropical Gyre (NPSG). While A. ferox fed diversely across 97 prey families, approximately 70% of its diet by wet weight consisted of seven prey families (fishes: Sternoptychidae, Anoplogastridae, Omosudidae, Alepisauridae; hyperiid amphipods: Phrosinidae; octopods: Amphitretidae; polychaetes: Alciopidae). Altogether, these micronekton prey families constitute a poorly known forage community distinct from those exploited by other pelagic predators and poorly sampled by conventional methods. We demonstrate ontogenetic variation in diet between two size classes of A. ferox (<97cm fork length=“small”, ≥97cm fork length=“large”). Large A. ferox consumed more fish and octopods, fewer crustaceans, and were more cannibalistic than small A. ferox. Ontogenetic shifts in vertical foraging habitat were observed as the consumption of larger and more mesopelagic prey with increasing fork length. Spatial and seasonal variation in the diet of A. ferox is consistent with expected patterns of variation in prey distribution with respect to oceanographic features of the NPSG. Within both size classes, the diets of specimens collected from the oligotrophic core of the NPSG were more diverse than those collected near the boundaries of the gyre and appeared to track seasonal variation in the position of the northern boundary of the gyre. Our data suggest seasonal and spatial variability in the composition of midwater forage communities exploited by A. ferox across the NPSG, and demonstrate that sustained monitoring of diet could provide valuable insights into long-term changes in these understudied communities.

Diets of deepwater oreos (Oreosomatidae) and orange roughy Hoplostethus atlanticus.

The diets of black oreo Allocyttus niger, smooth oreo Pseudocyttus maculatus, spiky oreo Neocyttus rhomboidalis and orange roughy Hoplostethus atlanticus were determined from examination of contents of 240, 311, 76 and 415 non-empty stomachs, from fishes sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand. Hoplostethus atlanticus had an opportunistic predatory strategy with a broad diet dominated by prawns and mesopelagic teleosts, but with substantial components of mysids and cephalopods. Pseudocyttus maculatus was strongly specialized on gelatinous zooplankton (jellyfish and salps). Allocyttus niger consumed mainly salps and hyperiid amphipods, and to a lesser extent fishes, prawns, mysids and copepods. Neocyttus rhomboidalis primarily consumed salps, along with mysids, euphausiids and fishes. Only P. maculatus did not exhibit significant ontogenetic variation in diet. The diets were also influenced by year and bottom depth. Differences in the distributions and diets of the four species probably reduce conflicts in resource use.

Ontogenetic variations in the diet of two invasive gobies, Neogobius melanostomus (Pallas, 1814) and Ponticola kessleri (Günther, 1861), from the middle Danube (Slovakia) with notice on their potential impact on benthic invertebrate communities

In this study, ontogenetic variations in diet of invasive bighead goby Ponticola kessleri and round goby Neogobius melanostomus from the middle Danube were analysed. Index of stomach fullness, Fulton's condition factor, index of food importance, frequency of occurrence, biomass, electivity, and proportions of invasive organisms in their diet were examined. Changes in the diet during ontogeny of both species emphasise the differences in their trophic niches. Our results combined with literary data suggest that bighead goby may threaten small native benthic fish species as a predator (especially in the invasion front), whereas round goby can potentially impact native fish species of all ontogenetic phases by competing for food. Round goby appear to have strong impact on bivalves, especially in the invasion front. High consumption of invasive organisms by bighead goby may help the native macroinvertebrate community. Thus, in contrast to round goby, bighead goby does not seem to be a hot candidate for being a nuisance invader.

Exploring trophic strategies of exotic caprellids (Crustacea: Amphipoda): Comparison between habitat types and native vs introduced distribution ranges

The trophic ecology of non-native species is a key aspect to understand their invasion success and the community effects. Despite the important role of caprellid amphipods as trophic intermediates between primary producers and higher levels of marine food webs, there is very little information on their feeding habits. This is the first comprehensive study on the trophic strategies of two co-occurring introduced caprellids in the Spanish coasts: Caprella scaura and Paracaprella pusilla. The diet of 446 specimens of C. scaura and 230 of P. pusilla was analyzed to investigate whether there were differences in the feeding habits in relation to habitat characteristics (natural vs artificial hard substrata), type of host substrata (bryozoans and hydroids) and native vs introduced distribution ranges (Brazil vs Spain). Results revealed differences in diet preferences of the two species that have important implications for their trophic behaviour and showed a limited food overlap, which may favour their coexistence in introduced areas. In general terms, P. pusilla is a predator species, showing preference by crustacean prey in all of its life stages, while C. scaura feeds mainly on detritus. Although no sex-related diet shifts were observed in either of the species, evidence of ontogenetic variation in diet of C. scaura was found, with juveniles feeding on more amount of prey than adults. No diet differences were found between native and introduced populations within the same habitat type. However, P. pusilla exhibited a shift in its diet when different habitats were compared in the same distribution area, and C. scaura showed a flexible feeding behaviour between different host substrata in the same habitat type. This study shows that habitat characteristics at different scales can have greater influence on the feeding ecology of exotic species than different distribution ranges, and support the hypothesis that a switch between feeding strategies depending on habitat characteristics could favour invasion success.

Functional implications of ontogenetic and sexual dimorphic dentition in the eastern shovelnose ray Aptychotrema rostrata (Shaw &amp; Nodder, 1794)

Unlike other elasmobranchs, batoids exhibit sexually dimorphic dentition. The functional implications of such dentition, however, remain understudied. For the present study, ontogenetic and sexual dimorphism in tooth and jaw structure, together with the functional implications of this dimorphism, were determined in the eastern shovelnose ray, Aptychotrema rostrata. Sexually dimorphic dentition and jaw structure was first observed in sub-adult age classes, with males developing a pronounced lower jaw at the symphysis. Monognathic heterodonty was prominent in mature males, with teeth in the symphyseal region developing significantly greater heights and sharpness ratios in comparison to females. Ex vivo mechanical grip strength tests were used to determine simulated bite-grip tenacity. The mean peak pull-out forces required to withdraw a section of a dissected pectoral fin from between jaws closed with a constant occlusal force was highest for mature males, intermediate for mature females and lowest for immature females and males. Although the species exhibits ontogenetic variations in diet, these were unrelated to sex. Rather, the larger and highly cuspidate teeth of mature males increased the bite-grip tenacity, which likely aids in copulation.

Feeding habits and predator-prey size relationships of mandarin fishSiniperca chuatsi(Basilewsky) in a shallow lake, central China

The diet and predator-prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.

Feeding habits and ontogenetic diet shifts of hairtail, Trichiurus margarites, in the Beibu Gulf of the South China Sea

The monthly and ontogenetic variations in diet of hairtail Trichiurus margarites Li (1992) [20] (Perciformes, Trichiuridae) were examined in the Beibu Gulf of the South China Sea from October 2008 to September 2009. Stomachs of 666 hairtail ranging in size from 121 mm to 561 mm pre-anal length (PL) were sampled monthly from commercial fish catches. Fish were the primary prey, with Decapterus maruadsi (Perciformes, Carangidae) averaging 23% by number, 34% by weight, and 49% by Index of Relative Importance (IRI). Other important prey in the diet included the small benthic fish, Bregmaceros rarisquamosus and Bregmaceros nectabanus (Gadiformes, Bregmaceroridae) and the decapod shrimp, Acetes chinensis, with IRI percentages of 8%, 4%, and 3%, respectively. Low rates of cannibalism and predation on 30 additional species of prey were observed. Trophic diversity (Brillouin Index, H z ) was moderate throughout the year. Mean feeding intensity (Repletion Index, RI) varied considerably by month and increased with the gonad maturity stages of hairtail; conversely, the proportion of empty stomachs decreased with maturity stages, from 60.9% empty at Stage I to 41.6% empty at Stage VI. Prey weight and numbers differed significantly among the 14 PL size classes and increased with body size. Cluster analysis of prey IRI values also indicated differences in the feeding habits of hairtail by size class. Understanding the monthly and ontogenetic changes in hairtail diet may assist in the development and improvement of marine ecosystem modeling for the Beibu Gulf, South China Sea.

Trophic Niche Variation and Individual Specialization inHypsiboas pulchellus(Duméril and Bibron, 1841) (Anura, Hylidae) from Uruguay

6 Corresponding author. ABSTRACT. Intrapopulation variation includes age and sexual variation, but also individual niche specialization. Individual specialization has important effects on dynamics at population or community levels. Environmental variation and intraspecific interactions are factors that can promote or enhance this kind of variation. Despite its relevance, knowledge about individual specialization in amphibians is still scarce, especially in species from temperate regions. In this study we analyzed the intrapopulational variation of the trophic niche in Hypsiboas pulchellus from a population in southern Uruguay. Particularly, we analyzed ontogenetic and sexual variation and individual specialization of the diet. We found ontogenetic variation in diet as a result of a shift from flies to beetles with increasing body size of frogs, but there were no differences in diet between males and females. We also found evidence of individual specialization, which varied seasonally together with population trophic niche width; during the warm season (October-March), individual specialization and population TNW both increased.

Spatial, temporal and ontogenetic variation in diet of anchovy ( Engraulis encrasicolus) on the Algerian coast (SW Mediterranean)

The diet of anchovy Engraulis encrasicolus was studied in three regions (Béjaia, Bénisaf and Ghazaouet) along the Algerian coast. Ontogenetic, spatial and seasonal variations in anchovy diet were investigated using multivariate analyses and analysed in relation with sea surface temperature and chlorophyll- a. 46 prey taxa of varying size between 0.57 mm ( Euterpina acutifrons) and 6.8 mm (fish larvae) were recorded. Whatever the season, the region or the fish size, anchovy is exclusively zooplanktivorous and copepods were the most present prey, constituting 87% by number of the prey taken and found in 98% of the anchovy stomachs examined. However, their occurrence and number varied according to the different areas, seasons and fish size. During its first year of life, anchovy feeds almost exclusively on copepods (mainly small and medium size prey). As anchovy grows, copepods are gradually substituted by large crustaceans such as decapods and amphipods. Hierarchical cluster analysis, analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated a distinct diet of anchovy of the bay of Bejaia from those of the bays of Bénisaf and Ghazaouet probably due to differences in hydrologic conditions. Diet differences also occurred between seasons. Summer and spring have distinct prey assemblages each and showed low diet similarities with the two other seasons. More prey species were found in the diet during winter (36) and autumn (30) and the vacuity index was lower in winter. Temporal variability in satellite-derived chlorophyll- a matched the seasonal variability in the diversity of the anchovy prey and feeding intensity as reflected by the vacuity index, suggesting further investigation of the potential use of satellite-derived chlorophyll- a data as a proxy for anchovy feeding intensity.

How does diet influence the reproductive seasonality of tropical freshwater fish?: A case study of a characin in a tropical mountain river

Seasonal breeding of tropical freshwater fish may be synchronized with periods of high food consumption. We explored this hypothesis by studying the relationship between diet and reproductive activity of Creagrutus guanes (Teleostei, Characidae). Our results showed that C. guanes had a generalist and omnivorous diet dominated by aquatic insects (mainly Diptera larvae) and seeds. Creagrutus guanes did not show intersexual or ontogenetic variation in diet. Peaks of feeding activity during rainy months were not synchronized with breeding in dry months. Our results do not support the hypothesis that the reproductive season has to be synchronized with high food consumption. We discussed the hypothesis fat reserves may be an important factor for the desynchronization of peaks of feeding and reproduction as explanation of seasonal breeding of this species.

Seasonal Variation in Guild Structure of the Puget Sound Demersal Fish Community

Identification of food web linkages is a major aim in ecology because it provides basic information on trophic flows and the potential for interspecific interactions. In addition, policy and restoration measures mandated to conform to ecosystem-based management principals can benefit from information on temporal and spatial variability in community-level interactions. Here, we analyzed guild structure of the demersal fish assemblage in Puget Sound, WA, a temperate estuarine system on the US west coast. Using diet information from 2,401 stomachs collected across three seasons (fall, winter, and summer), we identified guild membership for 21 fish species, examined seasonal guild switching, and tested for seasonal shifts in predation and for differences in the degree of diet overlap at the assemblage level. We accounted for ontogenetic variation in diet by dividing species into large (L) and small (S) size classes when appropriate. Using cluster analysis and a permutation approach, we identified seven significant guilds that were typified by predation on benthic invertebrates, pelagic invertebrates, and piscivory. Of the 18 species with more than one season of diet information, six switched guilds (Pacific sanddab L, sturgeon poacher, Pacific tomcod S, speckled sanddab, rex sole, and rock sole S). At the assemblage level, we tested for seasonal differences in prey use between seasons by performing an analysis of similarities based on Bray–Curtis diet similarities and found no significant difference. However, diet overlap was significantly higher in the summer than the fall and winter (with summer > fall > winter) indicating that diets within the assemblage converged in the summer. These results indicate that analyses of guild structure and diet overlap can reveal seasonal variation in community trophic structure and highlight intra-annual food web variation in the Puget Sound demersal fish community.

Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria)

The Rhynchocephalia are a group of small diapsid reptiles that were globally distributed during the early Mesozoic. By contrast, the only extant representatives, Sphenodon punctatus and S. guntheri (Tuatara), are restricted to New Zealand off-shore islands. The Rhynchocephalia are widely considered to be morphologically uniform but research over the past 30 years has revealed unexpected phenotypic and taxonomic diversity. Phylogenetically "basal taxa" generally possess relatively simple conical or columnar teeth whereas more derived taxa possessed stouter flanged teeth and sophisticated shearing mechanisms: orthal in some (e.g., Clevosaurus hudsoni) and propalinal in others (e.g., S. punctatus). This variation in feeding apparatus suggests a wide range of feeding niches were exploited by rhynchocephalians. The relationship of skull shape to skull length, phylogenetic grouping, habit, and characters relating to the feeding apparatus are explored here with geometric morphometric analysis on two-dimensional landmarks. Principle components analysis demonstrates that there are significant differences between phylogenetic groups. In particular, Sphenodon differs significantly from all well known fossil taxa including the most phylogenetically basal forms. Therefore, it is not justifiable to use Sphenodon as a solitary outgroup when studying skull shape and feeding strategy in squamates; rhynchocephalian fossil taxa also need to be considered. There are also significant differences between the skull shapes of aquatic taxa and those of terrestrial taxa. Of the observed variation in skull shape, most variation is subsumed by variation in dentary tooth base shape, the type of jaw movement employed (e.g., orthal vs. propalinal) and the number of palatal tooth rows. By comparison, the presence or absence of flanges, dentary tooth number and palatal tooth row orientation subsume much less. Skull length was also found to be a poor descriptor of overall skull shape. Compared to basal rhynchocephalians members of more derived terrestrial radiations possess an enlarged postorbital area, a high parietal, and a jaw joint positioned ventral to the tooth row. Modification of these features is closely associated with increased biting performance and thus access to novel food items. Some of these same trends are apparent during Sphenodon ontogeny where skull growth is allometric and there is evidence for ontogenetic variation in diet.

Trophic interrelationships amongst cichlid fishes in a tropical African reservoir (Lake Chivero, Zimbabwe)

The diet of seven cichlid species of Lake Chivero, Zimbabwe, was investigated from October 2004 to April 2005 to determine the degree of dietary overlap and interspecific competition. These fish could be separated into four groups. Two microphages, Oreochromis niloticus and O. macrochir, fed mostly on blue-green algae and their diets, in all size classes, overlapped almost completely. This suggested a high degree of competition between the two species and may account for the fact that O. niloticus, introduced into the lake in the 1980s is now the dominant species. There was also a significant dietary overlap between the two macrophages Tilapia sparrmanii and T. rendalli, which were macrophages with macrophytes as a significant component of their diet. Interspecific competition between these two species may account for the increase in the abundance of T. sparrmanii and a decrease in the numbers of T. rendalli over the last two decades. The diet of two small omnivores Pharyngochromis acuticeps and Pseudocrenilabrus philander consisted of algae, zooplankton, plant material, fish and detritus and also overlapped extensively, but these species probably avoid competition by living in different habitats; P. philander is usually associated with vegetation while P. acuticeps tends to live in more open waters. The last species, Serranochromis robustus, was largely piscivorous. There were no ontogenetic variations in diet, apart from P. acuticeps where small fish fed mainly on zooplankton becoming omnivorous in larger ones, and S. robustus where the diet shifted from zooplankton in specimens <50 mm SL to fish in larger size classes. Data available from the 1960s and 1970s indicate that the diets of some species have changed with invertebrates such as chironomid larvae being previously more important in all diets, while most species now take a higher proportion of algae. This reflects changes in the lake, which is eutrophic and has experienced severe algal blooms since 1960.

Diet and dental development of three species of Roeboides (Characiformes: Characidae)

Lepidophagy has been recorded in various species of Roeboides. In this study we analyzed ontogenetic variation in diet and dental development of three Roeboides species (R. paranensis, R. prognathus and R. microlepis). Roeboides paranensis consumed mainly insects, scales and microcrustaceans, and the smaller individuals (&lt;3.4 cm - SL) consumed mostly insects. Scale were only consumed by individuals greater than 3.4 cm. Scales were the dominant item in the diet in all sizes of R. prognathus. The diet of R. microlepis was composed primarily of whole fishes, however, the smaller individuals (&lt;5.4 cm) consumed only insects. During ontogeny, exterior migration of teeth in the mouth started at 3.7 cm in R. paranensis and 6.5 cm in R. microlepis. As body length increased more teeth migrated exteriorly. This leads to greater consumption of scales by three species. Roeboides prognathus appeared to be most specialized on scales, since they composed 80% of the diet, and was the species with the highest number of external teeth and the most developed.

Interspecific and intraspecific variation of δC and δN in deposit‐ and suspension‐feeding bivalves (Macoma balthica and Cerastoderma edule): Evidence of ontogenetic changes in feeding mode of Macoma balthica

Deposit and suspension feeders can switch feeding behavior and show variations in feeding mode as individuals pass through life‐cycle stages. Stable carbon and nitrogen isotopes were used to trace changes in diet of the tellinid bivalves M. balthica (facultative deposit feeder) and C. edule (obligatory suspension feeder), according to their size class. Analyses of variance showed differences in the d13C between the species. C. edule showed a diet composed of microphytoplankton, whereas M. balthica could feed on a mixed diet of microalgae from benthos and plankton. Values of Δ13C depended significantly on body size in M. balthica, providing evidence of ontogenetic variation in diet with small juveniles feeding entirely on microphytobenthos, while there was a gradual tendency for larger sizes to feed more on microphytoplankton. Therefore, although these species rely on different sources of food, large animals of M. balthica can overlap the trophic niche of C. edule. Population dynamics of the animals should be considered in food‐web studies.

Spatial, seasonal and ontogenetic variation in diet of Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides )

This paper describes spatial, temporal and biotic patterns in the diet of Greenland halibut ( Reinhardtius hippoglossoides , Walbaum) sampled from three different areas of the Barents Sea, namely the Hopen Deep (nursery area), the Bear Island Channel and the continental slope (spawning ground), during April 1996 to January 1998. Percentage of empty stomachs was based on 3294 specimens, and the relative importance of prey groups was assessed using stomach contents from 486 specimens. Multivariate analyses (i.e. Correspondence Analysis and Canonical Correspondence Analysis) were applied to examine which variables could best account for dietary variation. Spatial (horizontal and vertical) and temporal components appeared to be most influential on the variation in diet composition, whereas biotic variables (i.e. predator size, sex and maturity stage) appeared to be of less importance. It is proposed that regional and seasonal differences in diet composition are caused by spatial and temporal variations in abundance and distribution of some of the major prey species, i.e. Atlantic herring ( Clupea harengus ) and capelin ( Mallotus villosus ). On the slope there were also clear ontogenetic changes in diet; in smaller Greenland halibut (<50 cm) crustaceans and the cephalopod Gonatus fabricii were the prevailing prey, whereas for larger specimens teleosts and fish offal were the dominating components of the diet. Smaller Greenland halibut appeared to have been foraging at greater depths (>700 m) than the larger ones.