Variation In Diet Composition Research Articles

Properties of vertebrate predator-prey networks in the high Arctic.

Predation is an important ecological process that can significantly impact the maintenance of ecosystem services. In arctic environments, the relative ecological importance of predation is thought to be increasing due to climate change, partly because of increased productivity with rising temperatures. Therefore, understanding predator-prey interactions in arctic ecosystems is vital for the sustainable management of these northern regions. Network theory provides a framework for quantifying the structures of ecological interactions. In this study, we use dietary observations on mammalian and avian predators in a high arctic region, including isolated peninsulas on Ellesmere Island and north Greenland, to construct bipartite trophic networks. We quantify the complexity, specialization, and nested as well as modular structures of these networks and also determine if these properties varied among the peninsulas. Mammal prey remains were the dominant diet item for all predators, but there was spatial variation in diet composition among peninsulas. The predator-prey networks were less complex, had more specialized interactions, and were more nested and more modular than random expectations. However, the networks displayed only moderate levels of modularity. Predator species had less specialized interactions with prey than prey had with predators. All network properties differed among the peninsulas, which highlights that ecosystems often show complex responses to environmental characteristics. We suggest that gaining knowledge about spatial variation in the characteristics of predator-prey interactions can enhance our ability to manage ecosystems exposed to environmental perturbations, particularly in high arctic environments subject to rapid environmental change.

Variation in dietary composition of the Banna fanged frog (Limnonectes bannaensis Ye, Fei, Xie & Jiang, 2007) from Vietnam

Abstract The Banna fanged frog (Limnonectes bannaensis) is known from China, Laos, and Vietnam; however knowledge about the natural history and dietary requirements of this species is virtually lacking. In this study, we provide data on the variation in dietary composition of L. bannaensis based on stomach-flushing of 117 individuals (41 males and 76 females) captured and subsequently released during our recent field work in Son La Province, northwestern Vietnam. A total of 19 prey categories with 513 items, comprising 502 items of invertebrates, seven items of vertebrates, and four unidentified items were found in the stomachs of L. bannaensis. The most important groups among the prey of L. bannaensis were Coleoptera (38.04%), followed by Hymenoptera (9.31%), Araneae (7.93%), Polydesmida (7.07%), Orthoptera (6.37%), Hemiptera (5.23%), and Lepidoptera (5.01%). Adult males (16 prey categories) consumed preys with slightly lower diversity than adult females (17 prey categories). There was 88.25% overlap in the diet between males and females and in both sexes the trophic spectrum was similar, predominantly consisting of Coleoptera, Polydesmida, Araneae, Hymenoptera, Orthoptera, Lepidoptera, and Hemiptera.

Diet of the Invasive Atlantic Blue Crab Callinectes sapidus Rathbun, 1896 (Decapoda, Portunidae) in the Guadalquivir Estuary (Spain)

The Atlantic blue crab Callinectes sapidus (Decapoda, Portunidae) Rathbun, 1896 is native to the east coasts of North and South America and has recently expanded its distribution in the non-native range into the Gulf of Cadiz (SW Iberian Peninsula, Europe). Considering the impacts caused by this invasive species in numerous estuarine ecosystems and its generalist feeding behavior, this study aims to provide the first account of the Atlantic blue crab diet on the East Atlantic coast. We studied the species’ feeding habits using stomach content analyses to predict food web interactions and putative impacts. Samples were obtained in the Guadalquivir estuary (SW Spain, Europe), which was colonized in 2017. The main food items identified on their stomach were, fish (49.9%), mollusks (44.4%) and crabs (32.3%). They also consumed plant material (27.2%), and the sediment (32.3%) in their digestive tract was likely the result of secondary ingestion. The Atlantic blue crab exhibited the same omnivorous behavior as in the native area. There was no sexual variation in diet composition or feeding activity in general, but there was a seasonal variation in the diet composition of females. The decrease of the caramote prawn Penaeus kerathurus (Forskål 1775) observed in the Guadalquivir estuary since 2021 is likely not due to the Atlantic blue crab because they seldomly eat this prey. Overall, our study provides clear baseline information to expand the knowledge about the ecological roles of the Atlantic blue crab in non-native ecosystems.

Variation of the Montezuma Quail's Diet in Arizona, New Mexico, and Texas

The Montezuma quail (Cyrtonyx montezumae) is a game bird that inhabits oak-juniper-pine savannas of Arizona, New Mexico, and Texas, extending its range south into montane grasslands of Mexico. The species occurs within a complex matrix of public and private rangeland in which land management regimes and habitat quality are disparate. Given that food limitation can be a driver of wildlife populations, studies of the Montezuma quail diet can inform the management of its habitat. Our objective was to determine the composition and variation of the Montezuma quail's diet in Arizona, New Mexico, and Texas by macrohistological analysis of crops (n = 175) collected in 2016−2020 during winter in all three states and during spring in Texas. We used Dirichlet regression to determine the effects of ecological factors on diet composition. Winter diet in Arizona was mainly represented by woodsorrel bulbs (Oxalis spp.; 35.22% of dry weight), sedge rhizomes and bulbs (Cyperus spp.; 30.92%), and acorns (Quercus spp.; 7.17%). Winter diet in New Mexico consisted mainly of sedge bulbs (64.13%), bushbean seeds (Macroptilium sp.; 15.82%), and Hall's panicum seeds (Panicum hallii; 10.11%). Winter diet in Texas was composed of sedge rhizomes and bulbs (28.17%), Texas snoutbeans (Rhynchosia senna; 22.49), Hall's panicum seeds (19.54%), and wild onions (Allium spp.; 8.58%). Spring diet in Texas included sedge rhizomes and bulbs (67.90%), woodsorrel bulbs (19.49%), and Texas snoutbeans (5.55%). Geographic variation in diet composition was related to climatic, ecological, and intrinsic factors. For instance, in addition to being consumed by males at a higher rate, woodsorrel bulbs were also consumed at a greater rate in hotter and wetter locations. Along with novel information about the Montezuma quail diet in Texas, our investigation will stimulate questions relevant to rangeland and wildlife management, including determinants of habitat quality and the effects of climate change on wildlife populations.

Long-term effects of 3-nitrooxypropanol on methane emission and milk production characteristics in Holstein Friesian dairy cows

The objective was to determine the long-term effect of 3-nitrooxypropanol (3-NOP) on CH4 emission and milk production characteristics from dairy cows receiving 3-NOP in their diet for a full year, covering all lactation stages of the dairy cows. Sixty-four late-lactation Holstein Friesian cows (34% primiparous) were blocked in pairs, based on expected calving date, parity, and daily milk yield. The experiment started with an adaptation period of 1 week followed by a covariate period of 3 weeks in which all cows received the same basal diet and baseline measurements were performed. Directly after, cows within a block were randomly allocated to 1 of 2 dietary treatments: a diet containing on average 69.8 mg 3-NOP/kg DM (total ration level, corrected for intake of non-supplemented GreenFeed bait) and a diet containing a placebo. Forage composition as well as forage to concentrate ratio altered with lactation stage (i.e., dry period and early, mid, and late lactation). Diets were provided as a total mixed ration and additional bait was fed in GreenFeed units which were used for emission measurements. Supplementation of 3-NOP did not affect total dry matter intake (DMI), body weight or body condition score, but resulted in a 6.5% increase in the yields of energy-corrected milk and fat- and protein-corrected milk (FPCM). Furthermore, milk fat and protein as well as feed efficiency were increased upon 3-NOP supplementation. Overall, a reduction of 21%, 20%, and 27% was achieved for CH4 production (g/d), yield (g/kg DMI), and intensity (g/kg FPCM), respectively, upon 3-NOP supplementation. The CH4 mitigation potential of 3-NOP was affected by the lactation stage dependent diet to which 3-NOP was supplemented. On average, a 16%, 20%, 16%, and 26% reduction in CH4 yield (g/kg DMI) was achieved upon 3-NOP supplementation for the dry period, and early, mid, and late lactation diet, respectively. The CH4 mitigation potential of 3-NOP was affected by the length of 3-NOP supplementation within a lactation stage dependent diet and by variation in diet composition within a lactation stage dependent diet as a result of changes in grass and corn silage silos. In conclusion, 3-NOP reduced CH4 emission from cows receiving 3-NOP for a year, with a positive impact on production characteristics. The CH4 mitigation potential of 3-NOP was influenced by diet type, diet composition, and nutrition value, and the efficacy of 3-NOP appeared to decline over time but not continuously. Associated with changes in diet composition, increased efficacy of 3-NOP was observed at the start of the trial, at the start of a new lactation, and, importantly, at the end of the trial. These results suggests that diet composition has a large effect on the efficacy of 3-NOP, perhaps even larger than the week of supplementation after first introduction of 3-NOP. Further studies are needed to clarify the long-term effect of 3-NOP on CH4 emission and to further investigate the effect that variation in diet composition may have on the mitigation potential of 3-NOP.

Biology of Length-weight and Feeding in Juveniles and Adults of Air-breathing Perch <i>Anabas testudineus</i> (BLOCH)

The biology of feeding and growth pertaining to seasonal variations in diet composition, length-weight relationship and condition factor of Anabas testudineus was studied for a period of one year in two size group fishes (Group I: juveniles of <100 mm and Group II: adults of >100 mm). The length-weight relationship of the fish for Group I was W=0.00849 L3.2168 and for Group II was W=0.00877 L3.1502. The relative condition factor fluctuated from 1.032 to 1.372 indicating a significant variation (p < 0.05) in two size groups. The feeding intensity was maximum during October to December. Diet composition indicated the highest occurrence of insects followed by crustaceans and decayed organic matter. It also showed variations in different size group of fishes.

Spatiotemporal variability in diet composition of Greenland halibut (Reinhardtius hippoglossoides) from the eastern Canadian Arctic.

Greenland halibut (Reinhardtius hippoglossoides) sustain one of the most lucrative fisheries in the eastern Canadian Arctic and Labrador Sea. This species also plays an important role in food web connectivity and benthic-pelagic coupling. Despite the relatively rich knowledge of this species, R. hippoglossoides ecology in these specific areas remains poorly understood. The main aim of this study was to characterize the diet of this deepwater fish in the Labrador Sea and Davis and Hudson Straits and characterize the predator-prey relationship with northern shrimp (Pandalus borealis), another commercially important species in the region. Stomach contents analyses were conducted on 1199 fish captured from 2018 to 2020. Small specimens (<20 cm) fed on invertebrates, whereas larger individuals (>60 cm) fed primarily on fish, indicative of size-related changes in diet composition. The relative abundance of Pandalus shrimp species in the environment was reflected in the diet. Location appeared to be the most influential variable on feeding patterns. Distinct oceanographic conditions among areas, resulting in differences in prey availability, could explain these results. Arctic cod (Boreogadus saida) and redfish (Sebastes sp.) were selected in locations where fish prey were the most abundant. These results shed light on the opportunistic nature of R. hippoglossoides and its preference for fish at large size. With the rapidly changing oceanographic conditions of Arctic waters, a distributional change in the biomass of shrimp is expected. Results suggest that an increase in abundance of predatory groundfish species in the system (e.g., Sebastes sp.) could lead to acute predation on shrimp and competition with R. hippoglossoides. By revealing key trophic links within the demersal ecosystem, this work provides valuable information on the development of ecosystem approaches to fisheries management for the region.

DNA metabarcoding reveals seasonal changes in diet composition across four arthropod-eating lizard species (Phrynosomatidae: Sceloporus).

Diet composition and its ecological drivers are rarely investigated in coexisting closely related species. We used a molecular approach to characterize the seasonal variation in diet composition in four spiny lizard species inhabiting a mountainous ecosystem. DNA metabarcoding revealed that the lizards Sceloporus aeneus, S. bicanthalis, S. grammicus, and S. spinosus mostly consumed arthropods of the orders Hemiptera, Araneae, Hymenoptera, and Coleoptera. The terrestrial lizards S. aeneus and S. bicanthalis mostly predated ants and spiders, whereas the arboreal-saxicolous S. grammicus and saxicolous S. spinosus largely consumed grasshoppers and leafhoppers. The taxonomic and phylogenetic diversity of the prey was higher during the dry season than the rainy season, likely because reduced prey availability in the dry season forced lizards to diversify their diets to meet their nutritional demands. Dietary and phylogenetic composition varied seasonally depending on the species, but only dietary composition varied with altitude. Seasonal dietary turnover was greater in S. spinosus than in S. bicanthalis, suggesting site-specific seasonal variability in prey availability; no other differences among species were observed. S. bicanthalis, which lives at the highest altitude in our study site, displayed interseasonal variation in diet breadth. Dietary differences were correlated with the species' feeding strategies and elevational distribution, which likely contributed to the coexistence of these lizard species in the studied geographic area and beyond.

Seasonal and spatial variations in the diet of the Egyptian mongoose in its north-eastern Iberian range edge

The Egyptian mongoose (Herpestes ichneumon) is considered a generalist and opportunistic predator whose European distribution is restricted to Iberia. However, all the previous studies on the Egyptian mongoose’s diet in the Iberian Peninsula have been performed in Portugal and Doñana National Park (southwestern Spain), covering a small region of the species’ current distribution. To improve the knowledge on the trophic ecology of the species, we estimated the feeding habits of the Egyptian mongoose in central Spain, its north-eastern range edge. Our study was based on the analysis of (1) scats (n = 251) and (2) stomach contents (n = 32); samples were collected between 2018 and 2022. We calculated the relative frequency of occurrence (%RFO) and the percentage consumed biomass (%CB) for 12 food groups across central Spain and we assessed site-seasonal variations in diet composition in three study areas. We also estimated rabbit densities in the three study areas to assess the effect of rabbit abundance on mongoose diets. Overall, our results showed that European rabbits were the group with highest %CB (30.7%) in the diet of the Egyptian mongoose, followed by reptiles (19.9%) and small mammals (19.9%). In the intensively studied areas, the %CB of rabbits was the highest in the area with the highest abundance of this prey, whereas reptiles had the highest %CB in the area with the lowest availability of rabbits. Diet diversity (Shannon index) varied between 1.73 and 2.47 in those areas and was inversely related to the availability of rabbits. Our results confirm the dietary flexibility of this predator that adapts its diet to the relative availability of different prey species in different habitats.

Length–weight relationship and seasonal variations in diet composition of whiting (Merlangius merlangus) in the South-eastern Black Sea

ABSTRACT The sex ratio, length–weight relationship (LWR) and diets based on stomach contents of whiting (Merlangius merlangus) were investigated in the south-eastern Black Sea, Turkey. A total of 3507 females (7.5–24.0 cm), 1602 males (9.4–20.0 cm), and 78 unidentified sex (5.5–16.5 cm) whiting were caught during monthly sampling from February to December 2017. The sex ratio was dominated by females, and their ratio (♀:♂, 1:0.46) significantly deviated from 1:1. The LWR indicated a negative allometric growth for males, while females had a positive allometric growth pattern. The stomach content analysis based on the relative importance index (IRI%) indicated exclusively piscivorous diets dominant by Sprattus sprattus and Engraulis encrasicolus made up more than 91 IRI% of the total diets of M. merlangus. The modified Costello-Amundsen’s graphical analyses evinced the specialized feeding strategy of M. merlangus throughout this study. The contribution of these two preys to the diets of M. merlangus showed considerable seasonal variations that were totally dependent on their abundance. Sprattus sprattus contributed to more than 98% of the total diets during June, July and August, while in the following months, E. encrasicolus appeared to take its position. Based on fish size, a general trend of a rise in prey diversity was found with increasing fish size. Also, the contribution of S. sprattus tended to decrease with increasing predator size, which is replaced by a rise in E. encrasicolus contribution. Hence, larger M. merlangus predominantly fed on E. encrasicolus while smaller size predators preferred to feed on S. sprattus.

Does variation in plant diversity and abundance influence browsing intensity in black rhinos?

AbstractVariations in forage availability, selection and preferences can lead to intense foraging competition and depletion of food consequently lowering diet quality and population performance of black rhino species. This study investigated seasonal variations in rhino diet, foraging, preference and browsing intensity and how this is influenced by plant diversity and availability in Mkomazi National Park (MKONAPA). Fifty‐eight square grids were randomly selected in each season, and plots were laid for vegetation assessment during wet and dry seasons in the sanctuary. Browsed species by rhinos were compared with rhino feeding data from fourteen rhino range areas within Africa. More than 85% of species edible in MKONAPA were similar to those in rhino range areas. Acalypha ornata, Grewia similis and Commiphora africana were highly utilised specie in both seasons. Diversity and abundance of consumed browses decreased towards the dry season while browsing intensity increased with forage preference in both seasons and was prominent when browse availability was low in dry seasons. Our study established seasonal variation in dietary composition, browsing intensity and preferences for black rhinos. We suggest establishing nutritional composition of preferred forages, assessing density of competitor browsers, translocating excess rhinos or expanding the sanctuary to meet the recommended ecological carrying capacity.

Intraguild predation is increased in areas of low prey diversity in a generalist predator community.

Niche differentiation and intraguild predation (IGP) can allow ecologically similar species to coexist, although it is unclear which coexistence mechanism predominates in consumer communities. Until now, a limited ability to quantify diets from metabarcoding data has precluded the use of sequencing data to determine the relative importance of these mechanisms. Here, we pair a recent metabarcoding quantification approach with stable isotope analysis to examine diet composition in a wolf spider community. We compare the prevalence of resource partitioning and IGP in these spiders and test whether factors that influence foraging performance, including individual identity, morphology, prey community and environmental conditions, can explain variation in diet composition and IGP. Extensive IGP is likely the primary coexistence mechanism in this community, and other factors to which foraging variation is often attributed do not explain diet composition and IGP here. Rather, IGP increases as prey diversity decreases. Foragers are driven to IGP where resource niches are limited. We highlight the need to examine how drivers of predator-prey interaction strengths translate into foraging in natural systems.

Relationships among total mixed ration nutritional components and reproductive performance in high-producing dairy herds

The main objective of the present study was to determine whether composition of total mixed ration influences reproductive performance in high-producing commercial dairy farms. Dairy producers and nutritional consultants from 48 dairy farms located in Wisconsin agreed to provide reproductive data and dietary information on high milk production pens during the main breeding period for the previous 12 mo. Dietary components (percentage of dry matter) were crude protein (CP), rumen degradable (RDP) and undegradable (RUP) protein, neutral detergent fiber (NDF), nonfiber carbohydrates (NFC), starch, and fat. Reproductive data were service rate (SR), overall pregnancy per artificial insemination (P/AI) and P/AI at the first service, 21-d pregnancy rate (PR), days open, and percentage of cows pregnant by 150 d in milk (PREG150). Participating herds had lactating Holstein cows (range = 143 to 2,717) housed in freestall facilities. Statistical analyses were performed with CORR and GLIMMIX of SAS (SAS Institute Inc.). Daily average milk production of herds was 38.9 ± 0.60 kg/d (30.0 to 50.4 kg/d). Overall SR was 58.5% (39–73) and P/AI was 36.1% (22–49). Overall 21-d PR was 20.3% (10–42%). Correlation between SR and PR was 0.59, whereas correlation of overall P/AI and P/AI at first service with PR were both 0.72. Similarly, for PREG150, correlation with overall P/AI (0.63) and P/AI at first service (0.66) were greater than with SR (0.48). There was large variation in diet composition, with CP varying from 16.0 to 18.7%, NDF from 24.9 to 35.1%, NFC from 31.7 to 46.6%, starch from 20.1 to 30.8%, and fat from 3.1 to 6.7%. Overall, there were no detectable associations of CP, RDP, and RUP with reproductive measures. The strongest relationship was a decrease in reproductive performance with increasing dietary NFC including overall P/AI (−0.48), P/AI at first service (−0.51), and PREG150 (−0.33). Starch also had a negative relationship with P/AI at first service (−0.35). Conversely, greater NDF was positively associated with P/AI at first service (0.34). Fat content was also positively associated with P/AI at first service (0.34). When NFC was divided in tertiles (<40, 40 to 42.2, and >42.2% NFC), the highest tertile had lower overall P/AI (39 vs. 36 vs. 31%), P/AI at first service (43 vs. 40 vs. 33%), and PREG150 (54 vs. 53 vs. 47%). In conclusion, farms with greater dietary NFC may have compromised reproductive performance. Correspondingly, herds with greater NDF content may achieve high milk production with potentially positive associations with reproduction. Other relationships of dietary components on reproduction were not as obvious in this herd-level analysis.

Immune Responses of the Black Soldier Fly Hermetia illucens (L.) (Diptera: Stratiomyidae) Reared on Catering Waste.

The black soldier fly (BSF), Hermetia illucens L. (Diptera: Stratiomyidae), has a great bioconversion potential and ability to develop on diverse substrates. Although the use of catering waste and food by-products containing meat and fish would reduce the footprint of the insect sector, to date, in Europe, their use is still facing legal obstacles for insects as food and feed. Since a major request from the EU insect sector is to diversify the spectrum of allowed substrates, and considering that variations in diet composition could influence insect immune responses, we evaluated the impact of different catering wastes on BSF prepupae immunity. Insects were reared on five diets: one based on feed for laying hens and four based on catering waste containing (i) fruits and vegetables; (ii) fruits, vegetables and bread; (iii) fruit, vegetables, bread and dairy products; (iv) fruits, vegetables, bread, meat and fish. The gene expression of two antimicrobial peptides (AMPs), one defensin and one cecropin, was assessed. Moreover, the hemolymph inhibitory activity against Escherichia coli DH5α and Micrococcus yunnanensis HI55 was evaluated using diffusion assays in solid media. The up-regulation of both AMPs' encoding genes was observed in insects fed a bread-added and dairy product-added diet. All hemolymph samples showed inhibitory activity against both bacteria, affecting the colony size and number. The obtained results show how catering waste positively influences the H. illucens immune system. The possibility of modulating AMP expression levels through the diet opens up new perspectives in the management of insect health in mass rearings.

Sphingosine 1-phosphate mediates adiponectin receptor signaling essential for lipid homeostasis and embryogenesis

Cells and organisms require proper membrane composition to function and develop. Phospholipids are the major component of membranes and are primarily acquired through the diet. Given great variability in diet composition, cells must be able to deploy mechanisms that correct deviations from optimal membrane composition and properties. Here, using lipidomics and unbiased proteomics, we found that the embryonic lethality in mice lacking the fluidity regulators Adiponectin Receptors 1 and 2 (AdipoR1/2) is associated with aberrant high saturation of the membrane phospholipids. Using mouse embryonic fibroblasts (MEFs) derived from AdipoR1/2-KO embryos, human cell lines and the model organism C. elegans we found that, mechanistically, AdipoR1/2-derived sphingosine 1-phosphate (S1P) signals in parallel through S1PR3-SREBP1 and PPARγ to sustain the expression of the fatty acid desaturase SCD and maintain membrane properties. Thus, our work identifies an evolutionary conserved pathway by which cells and organisms achieve membrane homeostasis and adapt to a variable environment.

Patterns of variation in dietary composition among four populations of Alpine salamanders (Salamandra atra prenjensis)

Abstract In this paper we studied the diet in four allopatric populations of alpine salamanders in the Dinarides (Salamandra atra prenjensis). Food consumption was assessed by stomach flushing while food availability by pitfall traps and netting. We aimed to: (i) assess the realized dietary niche, (ii) investigate prey preferences, (ii) explore individual specialization, clustering and nestedness. All populations have an equally wide dietary span that is among the largest reported for terrestrial salamanders. On the other hand, the amount of ingested prey is rather low compared to other salamander species; the quantity of consumed prey did not differ among populations but younger individuals fed more than adults. Food composition somewhat differed among populations but not among sex/age classes. In all four populations, the bulk of diet consisted of beetles, spiders, snails and millipedes; except for beetles, such prey was also preffered together with centipedes and isopods. For most of the prey categories, the direction of the electivity indices was the same across populations. In none of the populations a nested pattern in the interindividual subdivision of dietary resources was registered. However, indications for individual specialization and modularity were observed disclosing that the broad niche of populations is composed of smaller individual niches that cluster along the dietary axis. Overall, the four populations have very similar structural characteristics of the dietary niche and there is little evidence for local dietary differentiation probably due to the absence of drivers for change.

Life in the Fast Lane: Feeding and Growth of Juvenile Steelhead and Chinook Salmon in Main‐Stem Habitats of the Columbia River Estuary

AbstractVery little is known about the ecology of juvenile Pacific salmon Oncorhynchus spp. that rapidly traverse estuaries. For these species and life history types, main‐stem habitats are thought to largely function as migratory corridors rather than as productive habitats that support feeding or growth, although little research has focused on this issue. This is especially true in the highly modified Columbia River estuary, where it is unclear whether fast‐migrating salmon benefit from extensive tidal marsh restoration. To address this deficit, we sampled migratory juvenile steelhead O. mykiss and Chinook Salmon O. tshawytscha at locations spread across nearly 200 km of the Columbia River estuary. Our results demonstrated that these juvenile salmon were actively feeding and growing as they moved downstream; dominant prey included chironomids, other insects, and corophiid and gammarid amphipods. We also observed variation in diet composition and quantity between years, which was likely associated with the highly contrasting river conditions. Insulin‐like growth factor 1 hormone levels and the size of juvenile salmon increased as the fish moved downstream, suggesting that prey quality and quantity were sufficient to fuel rapid growth, which may increase survival in marine waters. Our results have direct management implications for habitat restoration and suggest the potential for competition between hatchery and wild salmon. Overall, our results support a fundamental shift in the view of main‐channel estuarine habitats from serving primarily as a migration corridor to serving as productive habitat where rapidly moving salmon actively feed and grow.

Time-Scale Analysis of Prey Preferences and Ontogenetic Shift in the Diet of European Hake Merluccius merluccius (Linnaeus, 1758) in Southern and Central Tyrrhenian Sea

Merluccius merluccius is one of the most important Mediterranean benthopelagic predators. It represents a key species for the ecosystem’s functioning due to its fundamental role in the energy transferal between different domains and depth strata. The aim of this study was to explore the feeding habits of European hakes in the southern and central Mediterranean Sea, and also to analyze timescale variations and ontogenetic shift in five size length classes. A total of 411 stomachs collected from 2018 to 2020 were analyzed to assess diet and feeding habits. Results confirmed hakes’ role as a generalist benthopelagic predator, preying both in the suprabenthic layer and in the entire water column. Concerning the ontogenetic diet shift, juvenile hakes prefer zooplanktonic prey, while larger hakes have a diet mainly based on teleosts and decapods. The variations in diet composition between years, characterized by a fluctuation of cephalopods, bioluminescent teleost species and mesopelagic crustaceans, have highlighted the ability of European hake to model its diet to the geographical and prey availability. These features make analysis of the diet of M. merluccius essential to understanding the trophic dynamic existing in bentho-meso-pelagic environments, to improve ecosystem conservation in accordance with ecosystem-based fishery management.

Variation in diet composition and its relation to gut microbiota in a passerine bird

Quality and quantity of food items consumed has a crucial effect on phenotypes. In addition to direct effects mediated by nutrient resources, an individual’s diet can also affect the phenotype indirectly by altering its gut microbiota, a potent modulator of physiological, immunity and cognitive functions. However, most of our knowledge of diet-microbiota interactions is based on mammalian species, whereas little is still known about these effects in other vertebrates. We developed a metabarcoding procedure based on cytochrome c oxidase I high-throughput amplicon sequencing and applied it to describe diet composition in breeding colonies of an insectivorous bird, the barn swallow (Hirundo rustica). To identify putative diet-microbiota associations, we integrated the resulting diet profiles with an existing dataset for faecal microbiota in the same individual. Consistent with previous studies based on macroscopic analysis of diet composition, we found that Diptera, Hemiptera, Coleoptera and Hymenoptera were the dominant dietary components in our population. We revealed pronounced variation in diet consumed during the breeding season, along with significant differences between nearby breeding colonies. In addition, we found no difference in diet composition between adults and juveniles. Finally, our data revealed a correlation between diet and faecal microbiota composition, even after statistical control for environmental factors affecting both diet and microbiota variation. Our study suggests that variation in diet induce slight but significant microbiota changes in a non-mammalian host relying on a narrow spectrum of items consumed.

Seasonal variations in the plant diet of the Chinese Monal revealed by fecal DNA metabarcoding analysis

The Chinese Monal (Lophophorus lhuysii) is an alpine-obligate galliform species of global conservation priority. It has been listed as a first class protected wildlife species in China, requiring conservation actions during the 14th Five-Year Plan period. However, the diet composition of Chinese Monal and its seasonal variations have rarely been studied, constraining the effective conservation of the species. Here, we investigated the plant diet composition of the Chinese Monal and its seasonal variations using a DNA metabarcoding approach on fecal samples. We collected 190 fecal samples of the Chinese Monals from the central Qionglai Mountains located in China, and analyzed the plant diet of this species using a DNA metabarcoding approach. Taxonomic profiling of higher plants in the fecal samples was performed using the second internal transcribed spacer (ITS2) amplicon. Downstream analyses, including rarefaction curves, nonmetric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA), were used to explore the seasonal variations in diet composition. The Chinese Monal foraged a wide range of plant recipes composed of 35 families and 83 genera throughout the year, with Brassicaceae, Apiaceae, and Poaceae as the dominant families, and Cardamine as the dominant genus. The species consumed plants from 62 genera from 28 families during the breeding season (n ​= ​81) and 66 genera from 31 families during the non-breeding season (n ​= ​109). Further, the plant diet composition significantly varied between the breeding and non-breeding seasons, especially for the frequency of occurrence and relative read abundances at genus level. Our study analyzed the plant diet of the Chinese Monal at a high resolution for the first time, and the results revealed that the seasonal variations in its plant diet composition was adapted to plant phenology and foraging strategy. Fritillaria species, a previously confirmed important food resource for the Chinese Monal, were not detected in any fecal samples, potentially due to overharvesting of Fritillaria bulbs for Traditional Chinese Medicine. Therefore, we highly recommend further restriction of herb gathering in Chinese Monal habitats to facilitate the conservation of this endangered species. Altogether, our study enriches essential ecological information for the Chinese Monal and also provides insights into conservation management for this endangered species.