Seasonal Dietary Shifts Research Articles

Seasonal niche segregation of two sympatric xenocyprinid fishes

Xenocypris microlepis (Bleeker, 1871) and Xenocypris davidi (Bleeker, 1871) are two closely related xenocyprinid species potentially subject to exploitative competition. They often coexist in many freshwater ecosystems, which offers an opportunity to analyze their relationships. The present study describes the seasonal feeding habits of age‐3 X. microlepis and X. davidi in Xin'anjiang Reservoir, located in Zhejiang, China, as determined by stable isotope analysis. Particulate organic matter (POM; 50%) and periphyton (50%) were the major items observed in the X. microlepis diet, whereas periphyton (>60%) was prevalent in the X. davidi diet. Seasonal variations were observed in the diet compositions of both xenocyprinid species. Whereas X. microlepis tended to ingest more sediment organic matter (SOM) in autumn than in spring and summer, SOM was the secondary food item for X. davidi over the three seasons. The seasonal diet shift observed in this work indicates niche segregation of the sympatric pair. The results of this study contribute to the current knowledge of seasonal trophic interactions in predator–prey systems where sympatric xenocyprinids are present.

Pastoralists and mobility in the Oglakhty cemetery of southern Siberia: new evidence from stable isotopes

Abstract

Dietary Shifts May Trigger Dysbiosis and Mucous Stools in Giant Pandas (Ailuropoda melanoleuca).

Dietary shifts can result in changes to the gastrointestinal tract (GIT) microbiota, leading to negative outcomes for the host, including inflammation. Giant pandas (Ailuropoda melanoleuca) are physiologically classified as carnivores; however, they consume an herbivorous diet with dramatic seasonal dietary shifts and episodes of chronic GIT distress with symptoms including abdominal pain, loss of appetite and the excretion of mucous stools (mucoids). These episodes adversely affect the overall nutritional and health status of giant pandas. Here, we examined the fecal microbiota of two giant pandas’ non-mucoid and mucoid stools and compared these to samples from a previous winter season that had historically few mucoid episodes. To identify the microbiota present, we isolated and sequenced the 16S rRNA using next-generation sequencing. Mucoids occurred following a seasonal feeding switch from predominately bamboo culm (stalk) to leaves. All fecal samples displayed low diversity and were dominated by bacteria in the phyla Firmicutes and to a lesser extent, Proteobacteria. Fecal samples immediately prior to mucoid episodes had lower microbial diversity as compared to mucoids. Mucoids were mostly comprised of common mucosal-associated taxa including Streptococcus and Leuconostoc species, and exhibited increased abundance for bacteria in the family Pasteurellaceae. Taken together, these findings indicate that mucoids may represent an expulsion of the mucosal lining that is driven by changes in diet. We suggest that these occurrences serve to reset their GIT microbiota following changes in bamboo part preference, as giant pandas have retained a carnivorous GIT anatomy while shifting to an herbivorous diet.

Seasonal dietary shift to zooplankton influences stable isotope ratios and total mercury concentrations in Arctic charr (Salvelinus alpinus (L.))

Seasonal dietary shifts by Arctic charr (Salvelinus alpinus (L.)) are common in subarctic lakes, but less is known about how the shift to pelagic zooplankton feeding during the growing season affects stable isotope ratios and mercury concentrations. We sampled Arctic charr, zooplankton and benthic macroinvertebrates from oligotrophic Lake Galggojavri, northern Norway, in June, August and September. Stomach content, age, total length, weight, condition and sex were recorded for all individuals, and liver and muscle tissues were sampled for stable isotope (δ13C, δ15N) and total mercury analyses. We predicted that a dietary shift to zooplankton would lead to depleted 13C and increased mercury levels in charr. Arctic charr consumed benthic prey in June, but shifted to zooplankton feeding in August–September. Stable isotope mixing models revealed increased pelagic reliance towards September. Mercury content in liver increased from June to September, whereas muscle showed opposite trend. In stepwise multiple regression analyses, mercury content in muscle was explained by fish length, month and δ13C (R 2 = 0.46), whereas in liver month, δ13C and δ15N were the main explaining factors (R 2 = 0.69). Seasonal dietary shifts appeared to have an effect on total mercury content in charr, and thus sampling month should be considered when designing future monitoring programmes.

Stable isotope characterization of Rainy River, Ontario, lake sturgeon diet and trophic position

Abstract Lake sturgeon ( Acipenser fulvescens ) are considered threatened and many populations have declined since the early 1890s. Limited food web studies have been conducted with lacustrine lake sturgeon populations while similar studies do not exist for riverine populations. We use stable isotope analysis to study the diet composition of lake sturgeon captured in the Rainy River, Ontario. Historical reports of lake sturgeon consumption of fish and fish eggs exist, but both prey have largely been considered as a minor contribution to the overall diet of lake sturgeon. More recent dietary studies have focused on juvenile sturgeon and report low or no incidence of fish or fish eggs in lake sturgeon diets. The results of the stable isotope studies of Rainy River lake sturgeon suggest they obtain a large portion of their energy from organic material derived directly or indirectly from fish. Results parallel those recently reported for adult sturgeon in Lake Winnebago, Wisconsin, and are important in the context of contributing modern technical verification to earlier historical reports of fish and fish eggs in lake sturgeon diets. The results of this study provide evidence of potential seasonal or temporal shifts in lake sturgeon diet and further evidence to the potential shift in resource use based on life stage. Estimates of isotopic niches for the Rainy River sturgeon establish an important baseline for future changes in food web structure that might accompany the introduction of invasive species or the addition of anthropogenic stressors that could have implications for lake sturgeon conservation.

Evidence of nutrient partitioning in coexisting deep-sea echinoids, and seasonal dietary shifts in seasonal breeders: Perspectives from stable isotope analyses

The role of nutrition in echinoid growth and reproduction, as well as the mechanisms utilized to cope with food limitations in the deep sea remains under studied. We investigate echinoid feeding mechanisms within deep-sea submarine canyons in the NE Atlantic using a stable-isotope approach. Ten echinoid species were collected with a remotely operated vehicle. δ13C and δ15N stable isotope analyses (SIA) were conducted on echinoid tissues in order to investigate food sources assimilated with respect to nutrient partitioning between coexisting taxa, and seasonal dietary changes in food supply. Gut content analysis was conducted in conjunction with SIA.Echinoid taxa spanned three benthic trophic levels. This large trophic range might suggest an expansion of the trophic niches of echinoid taxa possibly to reduce interspecific competition for limited food resources. Evidence of nutrient partitioning among coexisting taxa was also found in the carbon data. Significant interspecific differences were found in the δ13C signatures of the somatic and reproductive tissues suggesting that different sources of carbon are assimilated into all tissues after the deposition of phytodetritus has taken place on the deep sea floor. However, this pattern differed for the data obtained before the deposition of phytodetritus; similar sources of carbon were assimilated into somatic tissues of different taxa, while some of these different taxa utilized significantly different sources of carbon to manufacture their reproductive tissues.While specific food sources could not be resolved from the carbon data of the present study, enriched δ15N values suggest that echinoids incorporate foods with distinctly higher δ15N values than that of POM and sediment, which could result from opportunistic feeding as well as bioerosion of the live coral framework and consequent grazing of fauna attached to the dead coral infrastructure.Seasonally deposited phytodetritus was incorporated into the reproductive tissues of the seasonal breeder, Gracilechinus alexandri, but not those of continuous breeders, Cidaroida and Echinothurioida. The material however was also found to support somatic tissue growth in cidaroids. These results suggest that seasonal breeders might utilize surface-derived phytodetritus to manufacture reproductive tissues, while continuous breeders might only utilize it for somatic tissue growth or not at all. Results for seasonal dietary shifts were compromised by poor spatial repeatability and thus require further investigation to understand better the role of phytodetritus in fuelling the growth and reproduction of deep-sea echinoids.

Seasonal Shifts in Diet and Gut Microbiota of the American Bison (Bison bison).

North American bison (Bison bison) are becoming increasingly important to both grassland management and commercial ranching. However, a lack of quantitative data on their diet constrains conservation efforts and the ability to predict bison effects on grasslands. In particular, we know little about the seasonality of the bison diet, the degree to which bison supplement their diet with eudicots, and how changes in diet influence gut microbial communities, all of which play important roles in ungulate performance. To address these knowledge gaps, we quantified seasonal patterns in bison diet and gut microbial community composition for a bison herd in Kansas using DNA sequencing-based analyses of both chloroplast and microbial DNA contained in fecal matter. Across the 11 sampling dates that spanned 166 days, we found that diet shifted continuously over the growing season, allowing bison to take advantage of the seasonal availability of high-protein plant species. Bison consumed more woody shrubs in spring and fall than in summer, when forb and grass intake predominated. In examining gut microbiota, the bacterial phylum Tenericutes shifted significantly in relative abundance over the growing season. This work suggests that North American bison can continuously adjust their diet with a high reliance on non-grasses throughout the year. In addition, we find evidence for seasonal patterns in gut community composition that are likely driven by the observed dietary changes.

Endoparasites of the Eastern Rock Sengi (Elephantulus myurus) from South Africa.

The endoparasite fauna of the eastern rock sengi ( Elephantulus myurus Thomas and Schwann) was studied for the first time for any sengi species from September 2007 until August 2008 in the Limpopo Province of South Africa. From the 121 sengis examined, we recovered 11 endoparasite taxa, including 9 nematodes, 1 cestode family (Hymenolepididae), and 1 pentastomid species (Armillifer armillatus (Wyman, 1834)). The overall endoparasite prevalence was high, at 100%, and largely attributable to the nematode Maupasina weissi Seurat, 1913 , with only a single individual being parasite free. Despite the high diversity, species richness was low (1.58 ± 0.06) and only M. weissi and spiruroid larvae occurred at a prevalence exceeding 8%. The abundance of M. weissi varied significantly between seasons and was lowest in summer and autumn. In contrast, the abundance of spiruroid larvae remained relatively constant across seasons in males, but was significantly higher in spring and summer compared to winter in females. These patterns may be generated by an accumulation of M. weissi with age as well as sex-specific seasonal shifts in diet. An updated list on the hosts and geographic range of parasites of sengis is provided.

Niche plasticity in invasive fishes in the Great Lakes

The geographic range of an invasive species is a key determinant of relative impact in the invaded region. Comparison of invasive species that are widespread or rare in invaded ranges can highlight mechanistic traits that determine the risk of impact from invasion. Round Goby (Neogobius melanostomus) is more geographically widespread and abundant than Tubenose Goby (Proterorhinus semilunaris) across invaded ranges of the Laurentian Great Lakes. We used stable isotopes of carbon (δ13C) and nitrogen (δ15N) in liver and muscle to contrast the isotopic niche breadth and niche plasticity of Round Goby and Tubenose Goby near the inflow and outflow of Lake St. Clair and in western Lake Superior. At all sites, Round Goby and Tubenose Goby that matched in size (21–53 mm standard length) had distinct isotopic niches with no overlap, driven by higher δ15N in Round Goby. The variation in isotopic niche, and the mean difference in δ13C and δ15N between muscle and liver, was greater for Round Goby, suggesting both greater seasonal shifts in diet and niche plasticity in this more widely established invader. Round Goby that were significantly larger than Tubenose Goby had broader isotopic niches and greater niche plasticity in the majority of cases and this was associated with isotopic niche overlap with smaller Round Goby and Tubenose Goby. Our findings suggest that a broad and plastic isotopic niche provides scope for wider establishment range in invasive fish species.

Seasonal dietary shifts and food resource exploitation by the hog badger (Arctonyx collaris) in a Chinese subtropical forest

Spatial and temporal fluctuations in the availability of food resources can affect adaptive foraging strategies substantially, with the potential to promote temporal dietary switching and specialisation among generalist carnivores. To understand this relationship better at the causal level, we examined spatial and temporal variation in diet composition and diversity in the hitherto little-known hog badger (Arctonyx collaris), in comparison to the environmental abundance of principal food resources, in a subtropical forest of central China. Here, hog badgers fed predominantly on earthworms and fruits, complemented with arthropod imagoes and invertebrate larvae, whereas vertebrate prey categories (mammals, birds and reptiles) were consumed infrequently. We observed strong seasonal variation in the consumption of different food categories. Earthworms predominated during spring, fruits in autumn, and earthworms, complemented by arthropods, in summer, with hog badgers apparently hibernating in winter. Fluctuation in dietary preferences between seasons and habitats correlated only partially with environmental food abundance; in autumn, when fruit abundance peaked, and despite a concomitant peak in earthworm abundance, hog badgers exhibited a dietary shift, indicating a preference for fruit, over earthworms. This resulted in autumnal minima in seasonal food niche breadth and evenness values. We conclude that, in this region, hog badgers exhibited a generalist diet but switched between food categories in response to changes in environmental seasonal abundance.

Trace elements and ingested plastic debris in wintering dovekies (Alle alle)

We provide the first report on winter concentrations of 32 trace metals from dovekies (Alle alle), a small, Arctic seabird that has a seasonal shift in diet from small zooplankton in the breeding season to larger zooplankton and small fish in the non-breeding season. Concentrations of selected trace elements, as well as stable carbon (δ13C) and nitrogen (δ15N) isotope concentrations for a sample of 25 dovekies, were similar between adult males and females, and there was evidence that dovekies feeding at higher trophic levels had higher hepatic Hg. We also found plastic debris in nine of 65 (14%) gizzards examined. Our study helps provide a more complete picture of the foraging ecology and contaminant profile of dovekies, an important species in Arctic marine food webs.

Trophic niche and habitat shifts of sympatric Gerreidae.

The diet and mouth growth rates of three Gerreidae species (Eugerres brasilianus, Eucinostomus melanopterus and Diapterus rhombeus) were assessed at different ontogenetic phases (juveniles, sub-adults and adults) in order to detect allometric growth, and whether they are related to habitat and seasonal changes in the Goiana Estuary, north-east Brazil. The importance of each prey for each ontogenetic phase was described using the index of relative importance. The three species showed seasonal ontogenetic shifts in diet and allometric growth of mouth morphology. They also had an exclusively zoobenthic diet, comprising mainly Polychaeta, Copepoda, Ostracoda, Gastropoda and Bivalvia. Mouth development showed a possible influence on diet changes for E. melanopterus. Significant interactions (P < 0·01) were detected among seasons, areas and ontogenetic phases for the most important prey for E. brasilianus and E. melanopterus. Diet overlaps are evidence of intra and interspecific competition among gerreids for specific prey. A conceptual model of the competition and seasonal diet shifts among ontogenetic phases of gerreids is given. The sediment ingested due to the feeding mechanisms of Gerreidae species could also partially explain the ingestion of synthetic items observed for all ontogenetic phases, which indicates one of a myriad effects of human activities (e.g. artisanal fishery) in this estuary.

Effects of dietary fracture toughness and dental wear on chewing efficiency in geladas (Theropithecus gelada).

Chewing efficiency has been associated with fitness in mammals, yet little is known about the behavioral, ecological, and morphological factors that influence chewing efficiency in wild animals. Although research has established that dental wear and food material properties independently affect chewing efficiency, few studies have addressed the interaction among these factors. We examined chewing efficiency, measured as mean fecal particle size, as a function of seasonal shifts in diet (and corresponding changes in food fracture toughness) in a single breeding population of a grazing primate, the gelada monkey, at Guassa, Ethiopia. We also measured dental topographic traits (slope, angularity, and relief index) and relative two- and three-dimensional shearing crest lengths in a cross-sectional wear series of gelada molars. Chewing efficiency decreased during the dry season, a pattern corresponding to the consumption of foods with higher fracture toughness. Older individuals experienced the most pronounced decreases in chewing efficiency between seasons, implicating dental wear as a causal factor. This pattern is consistent with our finding that dental topographic metrics and three-dimensional relative shearing crest lengths were lowest at the last stage of wear. Integrating these lines of behavioral, ecological, and morphological evidence provides some of the first empirical support for the hypothesis that food fracture toughness and dental wear together contribute to chewing efficiency. Geladas have the highest chewing efficiencies measured thus far in primates, and may be analogous to equids in their emphasis on dental design as a means of particle size reduction in the absence of highly specialized digestive physiology.

Low concentrations of contaminants in an invasive cyprinid, the rudd, in a Great Lakes Area of Concern.

The invasive, omnivorous rudd Scardinius erythrophthalmus is abundant in the upper Niagara River, a Great Lakes Area of Concern. Invasive species can alter trophic and contaminant pathways, but complex ontogenetic and seasonal diet shifts by rudds make it difficult to predict their chemical burdens relative to other fishes. We quantified concentrations of chemical residues in rudds and compared them to six fish species from various trophic levels. Rudds contained low concentrations of total dichlorodiphenyltrichloroethane (mean=0.02μg/g), Hg (mean=0.03μg/g), and polychlorinated biphenyls (mean=0.06μg/g); these concentrations were among the lowest for all species examined. Concentrations of aldrin, heptachlor, hexachlorobenzene, total hexachlorocyclohexanes, mirex, and total chlordanes were less than the method detection limit for all rudds examined. If reducing rudd biomass is determined to be beneficial, resource managers could consider targeted harvest, given the low concentrations of contaminant in rudds and their susceptibility to capture.

Flight muscle carnitine palmitoyl transferase activity varies with substrate chain length and unsaturation in the hoary bat (Lasiurus cinereus)

Fat is an important fuel for bats to support high metabolic rates in extended periods of flight. The fatty acid composition of adipose stores could affect whole animal exercise performance, as fatty acids vary in rates of mobilization and oxidation. A key step in the fatty acid oxidation pathway is transporting fatty acids from the cytosol into mitochondria, mediated by the enzyme carnitine palmitoyl transferase (CPT). Therefore, understanding the substrate preference patterns of CPT in bats is important for interpreting the consequences of adipose fatty acid profiles. We measured CPT activity with eight different fatty acyl CoA substrates (16:0, 16:1ω7, 18:0, 18:1ω9, 18:2ω6, 18:3ω3, 20:4ω6, and 22:6ω3) in the pectoralis muscle of migrating and nonmigrating hoary bats (Lasiurus cinereus (Beauvois, 1796)). The pattern of substrate preference was similar to the patterns previously reported for birds and rats and was not affected by migration. Generally, activity increased with the number of double bonds and was higher with 16 carbon fatty acids compared with 18 carbon fatty acids. Given the observed substrate variation in CPT activity, there is no evidence to suggest that recently reported seasonal changes in the adipose fatty acid composition of migrating hoary bats would lead to increased lipid oxidation rate, and may instead be a consequence of seasonal shifts in diet.

Seasonal dietary shifts and selection of Iberian wild goat Capra pyrenaica Schinz, 1838 in Peneda-Gerês National Park (Portugal)

Seasonal dietary shifts and selection of Iberian wild goat Capra pyrenaica Schinz, 1838 in Peneda-Gerês National Park (Portugal)

Seasonal dietary shifts and selection of Iberian wild goat Capra pyrenaica Schinz, 1838 in Peneda-Gerês National Park (Portugal)

This study intended to know Iberian wild goat Capra pyrenaica Schinz, 1838 feeding strategy in two proximate mountains it recently recolonized, Gerês and Amarela (Peneda-Gerês National Park, PGNP, Portugal). For that purpose we studied species dietary composition using faecal diet microhistological determinations and also its diet selection. Albeit wild goat exhibited an intermediate browse - graze behaviour in the two areas, grazing was more pronounced in Gerês while browsing in Amarela. Both areas presented a dietary shift in spring consisting in an increase on the consumption and preference for graminoids. This feeding strategy extended through summer only in Amarela. Results obtained are congruent with wild goat generalist feeding behaviour in other regions of the Iberian Peninsula and suggest that species feeding strategy in PGNP respond to spatial patterns of resources, specifically of graminoids, and to livestock stocking rates and management.

Responses to River Inundation Pressures Control Prey Selection of Riparian Beetles

BackgroundRiparian habitats are subjected to frequent inundation (flooding) and are characterised by food webs that exhibit variability in aquatic/terrestrial subsidies across the ecotone. The strength of this subsidy in active riparian floodplains is thought to underpin local biodiversity. Terrestrial invertebrates dominate the fauna, exhibiting traits that allow exploitation of variable aquatic subsidies while reducing inundation pressures, leading to inter-species micro-spatial positioning. The effect these strategies have on prey selection is not known. This study hypothesised that plasticity in prey choice from either aquatic or terrestrial sources is an important trait linked to inundation tolerance and avoidance.Method/Principal FindingsWe used hydrological, isotopic and habitat analyses to investigate the diet of riparian Coleoptera in relation to inundation risk and relative spatial positioning in the floodplain. The study examined patch scale and longitudinal changes in utilisation of the aquatic subsidy according to species traits. Prey sourced from terrestrial or emerging/stranded aquatic invertebrates varied in relation to traits for inundation avoidance or tolerance strategies. Traits that favoured rapid dispersal corresponded with highest proportions of aquatic prey, with behavioural traits further predicting uptake. Less able dispersers showed minimal use of aquatic subsidy and switched to a terrestrial diet under moderate inundation pressures. All trait groups showed a seasonal shift in diet towards terrestrial prey in the early spring. Prey selection became exaggerated towards aquatic prey in downstream samples.Conclusions/SignificanceOur results suggest that partitioning of resources and habitat creates overlapping niches that increase the processing of external subsidies in riparian habitats. By demonstrating functional complexity, this work advances understanding of floodplain ecosystem processes and highlights the importance of hydrological variability. With an increasing interest in reconnecting rivers to their floodplains, these invertebrates represent a key functional element in ensuring that such reconnections have demonstrable ecological value.

Trophic ecology of black scabbardfish, Aphanopus carbo in the NE Atlantic—Assessment through stomach content and stable isotope analyses

The black scabbardfish is a deep water species of high commercial interest in the NE Atlantic. Specimens were collected from commercial trawls to the west of the British Isles and from longliners operating near Madeira between September 2008 and May 2010. Stomach content analysis was confined to samples from the northern area, because of a high number of empty stomachs from Madeira. Stable isotope analyses identified that black scabbardfish feeds on species with epipelagic and benthopelagic affinities. For the west of British Isles, the δN values were significantly different between seasons suggesting a change in the diet throughout the year. Black scabbardfish have higher δN and δC values compared with other co-occurring benthopelagic feeders and lower nitrogen values than the true benthic predators and/or scavengers. Comparison with stable isotope analysis in samples from Madeira indicated that black scabbardfish feed at a similar trophic level and has the same trophic niche width in both areas, assuming similar baseline isotope compositions. The diet in the northern area comprised fish (68% N), crustaceans (22% N) and cephalopods (15% N) with blue whiting (Micromesistius poutassou) constituting 40% of the prey. Seasonal shift in diet was observed, with a predominance of blue whiting (70%) in the first quarter of the year, shifting to a more diverse diet in the remainder of the year. These results indicate that the diet of black scabbardfish is closely linked with the seasonal migration of blue whiting and that they likely select prey in proportion to availability. This study demonstrates that the combined used of both methods can elucidate the trophic ecology of black scabbardfish, in situations where conventional methods alone provide insufficient data.

Fifty years later: trophic ecology and niche overlap of a native and non-indigenous fish species in the western basin of Lake Erie

Since the introduction of white perch (Morone americana) into Lake Erie over 50 years ago, the population size of native yellow perch (Perca flavescens) has decreased up to 79 % and significant changes to the ecosystem have occurred. We examined long-term population estimates and used stable isotopes of carbon (δ 13C) and nitrogen (δ 15N) paired with stomach content analysis to quantify the trophic ecology and niche overlap of adult yellow perch and white perch in the western basin of Lake Erie. We found that changes in yellow perch abundance since 1979 appeared to be better correlated with changes in fishery exploitation rates than with food competition effects from white perch. At the time of this study, yellow perch were found to have higher δ 13C values, indicating greater utilization of benthic food resources than white perch, and white perch occupied higher trophic positions based on δ 15N. The diets of both species varied spatially and seasonally based on stable isotopes and stomach contents, likely driven by changes in prey abundance. Comparison of niche widths using stable isotope population metrics and Schoener diet similarity index suggested a low to moderate degree of niche overlap between species. Isotopic niches of white perch were generally larger than those of yellow perch demonstrating broader resource utilization by this non-indigenous species. We submit that isotopic niche overlap comparisons are more appropriate for studies seeking to understand interactions among populations over course temporal scales, while diet overlap indices, such as the Schoener index provide a means to study fine-scale interactions such as ontogenetic and seasonal diet shifts.