Dietary Switching Research Articles

Toxicity and Starvation Induce Major Trophic Isotope Variation in Daphnia Individuals: A Diet Switch Experiment Using Eight Phytoplankton Species of Differing Nutritional Quality.

Stable isotope values can express resource usage by organisms, but their precise interpretation is predicated using a controlled experiment-based validation process. Here, we develop a stable isotope tracking approach towards exploring resource shifts in a key primary consumer species Daphnia magna. We used a diet switch experiment and model fitting to quantify the stable carbon (δ13C) and nitrogen (δ15N) isotope turnover rates and discrimination factors for eight dietary sources of the plankton species that differ in their cellular organization (unicellular or filamentous), pigment and nutrient compositions (sterols and polyunsaturated fatty acids), and secondary metabolite production rates. We also conduct a starvation experiment. We evaluate nine tissue turnover models using Akaike's information criterion and estimate the repetitive trophic discrimination factors. Using the parameter estimates, we calculate the hourly stable isotope turnover rates. We report an exceedingly faster turnover value following dietary switching (72 to 96 h) and a measurable variation in trophic discrimination factors. The results show that toxic stress and the dietary quantity and quality induce trophic isotope variation in Daphnia individuals. This study provides insight into the physiological processes that underpin stable isotope patterns. We explicitly test multiple alternative dietary sources and fasting and discuss the parameters that are fundamental for field- and laboratory-based stable isotope studies.

Effects of Diet Induced Weight Reduction on Cartilage Pathology and Inflammatory Mediators in the Joint Tissues.

Obesogenic diets contribute to the pathology of osteoarthritis (OA) by altering systemic and local metabolic inflammation. Yet, it remains unclear how quickly and reproducibly the body responds to weight loss strategies and improve OA. In this study we tested whether switching obese diet to a normal chow diet can mitigate the detrimental effects of inflammatory pathways that contribute to OA pathology. Male C57BL/6 mice were first fed with obesogenic diet (high fat diet) and switched to normal chow diet (obese diet → normal diet) or continued obese diet or normal diet throughout the experiment. A mouse model of OA was induced by surgical destabilization of the medial meniscus (DMM) model into the knee joint. Outcome measures included changes in metabolic factors such as glucose, insulin, lipid, and serum cytokines levels. Inflammation in synovial biopsies was scored and inflammation was determined using FACs sorted macrophages. Cartilage degeneration was monitored using histopathology. Our results indicate, dietary switching (obese diet → normal diet) reduced body weight and restored metabolic parameters and showed less synovial tissue inflammation. Systemic blood concentrations of pro-inflammatory cytokines IL-1α, IL-6, IL-12p40, and IL-17 were decreased, and anti-inflammatory cytokines IL-4 and IL-13 were increased in dietary switch group compared to mice that were fed with obesogenic diet continuously. Although obese diet worsens the cartilage degeneration in DMM OA model, weight loss induced by dietary switch does not promote the histopathological changes of OA during this study period. Collectively, these data demonstrate that switching obesogenic diet to normal improved metabolic syndrome symptoms and can modulate both systemic and synovium inflammation levels.

Timing of dietary switching by savannah elephants in relation to crop consumption

Tree and grass quality on the African savannah shows seasonal variation, driving mixed-feeding herbivores to switch between browsing and grazing. During this switch, crop consumption could be an attractive alternative to browsing. We analysed elephant diet variability in the Okavango Delta, Botswana, using faecal stable isotope ratios of carbon (δ^13C) and frequencies of elephant crop consumption, to determine the extent to which crop consumption relates to this potential switch. Although elephants did increase their relative grass consumption in the wet season, browse dominated the annual diet. After February, the proportion of grass in the diet dropped considerably, and continued decreasing through April when farmers reported most crop consumption. Generalized Linear Models revealed that the occurrence of elephant crop consumption increased with the proportion of grass consumed and with decreasing grass quality. The proportion of grass in elephant faeces increased with increasing crop consumption intensity. As crop consumption could also be related to nutrient deficiencies in elephant diet, we calculated the total dietary input of nutrients to reveal potential deficiencies. Elephant diet contained insufficient levels of sodium year-round, and insufficient phosphorus from February to July. As the latter coincides with the timing of crop consumption, we consider our results an indication that phosphorus –and potentially sodium - deficiencies, could play a role in elephant dietary choices, including crop consuming behaviour. Further experimental research is required to show whether supplying elephants with supplementary phosphorus and sodium sources could reduce this micro-nutrient deficiency, and could play a role in reducing elephant crop consumption.

It's the fiber, not the fat: significant effects of dietary challenge on the gut microbiome

BackgroundDietary effects on the gut microbiome play key roles in the pathophysiology of inflammatory disorders, metabolic syndrome, obesity, and behavioral dysregulation. Often overlooked in such studies is the consideration that experimental diets vary significantly in the proportion and source of their dietary fiber. Commonly, treatment comparisons are made between animals fed a purchased refined diet that lacks soluble fiber and animals fed a standard vivarium-provided chow diet that contains a rich source of soluble fiber. Despite the well-established critical role of soluble fiber as the source of short chain fatty acid production via the gut microbiome, the extent to which measured outcomes are driven by differences in dietary fiber is unclear. Further, the interaction between sex and age in response to dietary transition is likely important and should also be considered.ResultsWe compared the impact of transitioning young adult and 1-year aged male and female mice from their standard chow diet to a refined low soluble fiber diet on gut microbiota community composition. Then, to determine the contribution of dietary fat, we also examined the impact of transitioning a subset of animals from refined low-fat to refined high-fat diet. We used a serial sampling strategy coupled with 16S rRNA marker gene sequencing to examine consequences of recurrent dietary switching on gut microbiota community dynamics. Analysis revealed that the transition from a chow diet to a refined diet that lacks soluble fiber accounted for most of the variance in community structure, diversity, and composition across all groups. This dietary transition was characterized by a loss of taxa within the phylum Bacteroidetes and expansion of Clostridia and Proteobacteria in a sex- and age-specific manner. Most notably, no changes to gut microbiota community structure and composition were observed between mice consuming either refined low- or high-fat diet, suggesting that transition to the refined diet that lacks soluble fiber is the primary driver of gut microbiota alterations, with limited additional impact of dietary fat on gut microbiota.ConclusionCollectively, our results show that the choice of control diet has a significant impact on outcomes and interpretation related to diet effects on gut microbiota. As the reduction of soluble fiber may influence synthesis of microbial metabolites that are important for regulating metabolic, immune, behavioral, and neurobiological outcomes, additional studies are now needed to fully delineate the contribution of fat and fiber on the gut microbiome.5A_gngDrGFKiXbsBX4nexEVideo Abtract.

Angiosperm to Gymnosperm host-plant switch entails shifts in microbiota of the Welwitschia bug, Probergrothius angolensis (Distant, 1902).

The adaptation of herbivorous insects to new host plants is key to their evolutionary success in diverse environments. Many insects are associated with mutualistic gut bacteria that contribute to the host's nutrition and can thereby facilitate dietary switching in polyphagous insects. However, how gut microbial communities differ between populations of the same species that feed on different host plants remains poorly understood. Most species of Pyrrhocoridae (Hemiptera: Heteroptera) are specialist seed-feeders on plants in the family Malvaceae, although populations of one species, Probergrothius angolensis, have switched to the very distantly related Welwitschia mirabilis plant in the Namib Desert. We first compared the development and survival of laboratory populations of Pr.angolensis with two other pyrrhocorids on seeds of Welwitschia and found only Pr.angolensis was capable of successfully completing its development. We then collected Pr.angolensis in Namibia from Malvaceae and Welwitschia host plants, respectively, to assess their bacterial and fungal community profiles using high-throughput amplicon sequencing. Comparison with long-term laboratory-reared insects indicated stable associations of Pr.angolensis with core bacteria (Commensalibacter, Enterococcus, Bartonella and Klebsiella), but not with fungi or yeasts. Phylogenetic analyses of core bacteria revealed relationships to other insect-associated bacteria, but also found new taxa indicating potential host-specialized nutritional roles. Importantly, the microbial community profiles of bugs feeding on Welwitschia versus Malvaceae revealed stark and consistent differences in the relative abundance of core bacterial taxa that correlate with the host-plant switch; we were able to reproduce this result through feeding experiments. Thus, a dynamic gut microbiota may provide a means for insect adaptation to new host plants in new environments when food plants are extremely divergent.

The importance of functional responses among competing predators for avian nesting success

AbstractThe relationship between the rate of predation and prey abundance is an important component of predator–prey dynamics. However, functional responses are less straightforward when multiple predators compete for shared prey. Interactions among competing predators can reduce or enhance effects of predation on prey populations. Because many avian populations experience high rates of nest predation, understanding the role of specific predators on nest mortality will lead to more informed conservation and management strategies which attempt to increase productivity by removing certain predators or managing habitat to limit their impact.Our goal was to evaluate effects of specific predators and the influence of nest abundance on nest mortality.We monitored snowy ploverCharadrius nivosusnests across 7 years at two study areas in Utah, USA, with remote cameras. We modelled predator‐specific hazard rates for nest mortality in a Bayesian framework to assess relationships between competing predators and the role of nest abundance on predator‐specific hazard rates.We found that hazard rates for nest mortality by gullsLarusspp. decreased with increasing nest abundance, whereas nest mortality by foxesVulpesspp. and ravensCorvus coraxinitially increased, indicating that dietary switching may occur when nests become more abundant. Nest mortalities of specific predators were often not independent and ranged between compensatory (e.g. mammalian mesopredators) and superadditive (e.g. avian predators) across the breeding season.The non‐independence between nest mortalities suggests that reductions in some predators may not translate to additive increases in overall nest success. Analyses of cause‐specific mortality are rarely applied to avian nests, but examination of interacting impacts among competing predators on nest survival may provide insight into specific drivers of avian population dynamics.A freePlain Language Summarycan be found within the Supporting Information of this article.

Feeding responses of the golden jackal after reduction of anthropogenic food subsidies

Little is known of the resources that limit or promote the rapidly expanding golden jackal (Canis aureus) population in Europe. We hypothesised that in an area of intensive big game hunting, a reduction of the main food resource (human subsidised big game viscera) would result in dietary switching. We used multivariate analyses to test whether the dietary composition of 200 jackal stomachs varied between two 2-yearly survey occasions, the first without big game viscera removal (availability of 68 kg viscera/year/km2) followed by a period with viscera removal (minimum of 50 kg of viscera/year/km2 removed). The proportion of empty stomachs and the stomach wet content weight did not differ between the two periods. Even after the reduction of food subsidies, the primary food of jackals was viscera and carrion from wild ungulates (frequency of occurrence: 45% vs. 30%; wet weight: 55% vs. 29%, respectively), and scavenging was not affected by season or sex. Log-linear analysis of frequency data revealed no significant differences between survey occasions in consumption of either food type. MANCOVA of wet weight data revealed that in the first period with food subsidies jackals consumed a higher proportion of adult wild boar (11.6% vs. 1.3%; from predation or scavenging), while juvenile wild boar (0 vs. 11.8%; from predation or scavenging), domestic animals (0.8% vs. 6.2%; mostly from scavenging) and invertebrates (2.6% vs. 4.1%) increased in the second period. The stomachs in the second survey occasion contained more varied food items, but the trophic niche was not significantly wider. The feeding responses of this mesopredator to the reduction of food subsidies were less pronounced than expected. Because in high big game density areas, wild ungulate carrion from different mortality causes are available in high quantities throughout the year, predator populations can be maintained despite the high amount of viscera removal.

Dietary divergence is associated with increased intra-specific competition in a marine predator

Optimal foraging theory predicts that when food is plentiful all individuals should take a small range of preferred prey types, but as competition increases less preferred prey will be included in the diet. This dietary switching may not be uniform among individuals, which produces discrete dietary clusters. We tested this hypothesis for gentoo penguins at Bird Island, South Georgia, using stable isotope analysis and biologging. Competition, in the form of the density of foraging dives, increased markedly from incubation to chick-rearing owing to increased foraging effort. Birds responded behaviourally by exploiting a greater portion of the available foraging radius and increasing dive depths. Dietary niche width doubled and two discrete dietary clusters appeared; one comprising birds that consumed mostly krill and another that ate a greater proportion of demersal fish. There were no differences in morphology between the dietary classes, but birds in the fish class had a tendency to dive deeper, which suggests a behavioural basis for specialization. Our findings are consistent with the hypothesis that intra-specific competition expands the population’s dietary niche width and drives divergence in diets among individuals.

Interannual Variation in Diet, Dietary Diversity, and Dietary Overlap in Three Sympatric Strepsirrhine Species in Southeastern Madagascar

Dietary data are used to categorize species diets, but these categorizations do not take into account the mutability of food resources in time or space, the level of interspecific competition in various communities as these resources change, nor the dietary flexibility of species. In this study, we assess the diets of three sympatric species, Eulemur rufifrons, Propithecus edwardsi, and Varecia variegata, in the Vatoharanana site in Ranomafana National Park, Madagascar. We determine dietary diversity, overlap, and interannual variation with data collected from 2001 to 2003. We then compare results on food preference and time feeding with data collected on each species in the late 1980s and early 1990s to determine whether these findings are consistent over the long term. We found little interannual variation in the proportion of time spent eating particular plant parts for each of the lemur species during the three study years (2001–2003), and between the earlier and current study. Food items were not always consumed based solely on availability. Dietary diversity was lower in the two frugivorous species (V. variegata and E. rufifrons) compared with the folivorous species (P. edwardsi), and V. variegata and E. rufifrons were more likely to focus their feeding time on one particular genus and plant part in each year. The study species used different strategies to deal with food, particularly fruit, shortages such as a plastic social structure (V. variegata), habitat shifting (E. rufifrons), and dietary switching (P. edwardsi). Although there was low dietary overlap between the study species, they depended on a small number of shared fruits in each of the study years (Chrysophyllum, Syzygium, Ocotea, Plagioscyphus), which may indicate some potential for interspecific competition. Because these lemur species, like all primates, lead relatively long lives (avg. >30 years) and have slow rates of aging, longitudinal studies are needed to test hypotheses reliant on basic dietary information.

Aestivation dynamics of bogong moths (Agrotis infusa) in the Australian Alps and predation by wild pigs (Sus scrofa)

We document predation of aestivating bogong moths (Agrotis infusa) by wild pigs (Sus scrofa) at a location in the Australian Alps. This is the first known record of pigs preying on bogong moths. Wild pigs are recent colonisers of the region, though already the population appears seasonally habituated to foraging on aestivating moths. This is indicative of adaptation of a feral animal undertaking dietary resource switching within what is now a modified ecosystem and food web. The significance of this predation on moth abundance is unclear. Long-term monitoring to compare numbers of moths with historical surveys undertaken before the colonisation by wild pigs will require that they are excluded from aestivation sites. Our surveys in 2014–15 observed bogong moths to arrive about one month earlier compared with a similar survey in 1951–52, though to also depart earlier.

Estimating tissue-specific discrimination factors and turnover rates of stable isotopes of nitrogen and carbon in the smallnose fanskate Sympterygia bonapartii (Rajidae).

This study aimed to estimate trophic discrimination factors (TDFs) and metabolic turnover rates of nitrogen and carbon stable isotopes in blood and muscle of the smallnose fanskate Sympterygia bonapartii by feeding six adult individuals, maintained in captivity, with a constant diet for 365 days. TDFs were estimated as the difference between δ(13) C or δ(15) N values of the food and the tissues of S. bonapartii after they had reached equilibrium with their diet. The duration of the experiment was enough to reach the equilibrium condition in blood for both elements (estimated time to reach 95% of turnover: C t95%blood = 150 days, N t95%blood = 290 days), whilst turnover rates could not be estimated for muscle because of variation among samples. Estimates of Δ(13) C and Δ(15) N values in blood and muscle using all individuals were Δ(13) Cblood = 1·7‰, Δ(13) Cmuscle = 1·3‰, Δ(15) Nblood = 2·5‰ and Δ(15) Nmuscle = 1·5‰, but there was evidence of differences of c.0·4‰ in the Δ(13) C values between sexes. The present values for TDFs and turnover rates constitute the first evidence for dietary switching in batoids based on long-term controlled feeding experiments. Overall, the results showed that S. bonapartii has relatively low turnover rates and isotopic measurements would not track seasonal movements adequately. The estimated Δ(13) C values in S. bonapartii blood and muscle were similar to previous estimations for elasmobranchs and to generally accepted values in bony fishes (Δ(13) C = 1·5‰). For Δ(15) N, the results were similar to published reports for blood but smaller than reports for muscle and notably smaller than the typical values used to estimate trophic position (Δ(15) N c. 3·4‰). Thus, trophic position estimations for elasmobranchs based on typical Δ(15) N values could lead to underestimates of actual trophic positions. Finally, the evidence of differences in TDFs between sexes reveals a need for more targeted research.

Land or sea? Foraging area choice during breeding by an omnivorous gull.

BackgroundGeneralist predators may vary their diet and use of habitat according to both internal state (e.g. breeding stage) and external (e.g. weather) factors. Lesser black-backed gulls Larus fuscus (Linnaeus 1758) are dietary generalists, foraging in both terrestrial and marine habitats during breeding. We investigate what affects the gulls’ propensity to forage at sea or on land. We assess the importance of terrestrial foraging to gulls in the Baltic Sea (sub. sp. L. f. fuscus), looking especially at their use of agricultural fields.ResultsThrough the GPS tracking of 19 individuals across 3 years we tracked 1038 foraging trips and found that 21.2 % of foraging trips were predominantly terrestrial, 9.0 % were a mix of terrestrial and marine, and 68.5 % were exclusively marine. Terrestrial trips were (1) more frequent when departing around sunrise, whereas marine trips occurred throughout the day. Additionally, trips with mostly land-based foraging decreased as the breeding season progressed, suggesting dietary switching coincident with the onset of chick provisioning. (2) During cloudy and cold conditions terrestrial foraging trips were more likely. (3) We found no differences between sexes in their land-based foraging strategy. (4) Gull individuals showed great variation in foraging strategy. Using observations of agricultural fields, carried out for one year, we found that (5) gulls preferentially foraged on fields with short vegetation, and there was a positive association with occurrence of waders and other species of gulls. (6) The availability and use of these preferred fields decreased through the breeding period.ConclusionsThis study found high prevalence of terrestrial foraging during early breeding as well as support for dietary switching early in the breeding season. The overall tendency for marine or terrestrial foraging was consistent within individuals, with gull identity accounting for much of the variation observed in foraging trips. Our results suggest that anthropogenic terrestrial food sources may play a role in the low breeding success of these gulls through either variation in quantity and/or quality. Finally, our study demonstrates the potential of combining data from GPS-tracking of individual animals with the ‘ground-truthing’ of habitat visited to elucidate the otherwise nebulous behavior of a generalist predator.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-016-0078-5) contains supplementary material, which is available to authorized users.

Dietary Flexibility and Feeding Strategies of Eulemur: A Comparison with Propithecus

Despite the great variety of habitats in Madagascar, Eulemur has successfully populated most forested habitats on the island. Although the high dietary flexibility of Eulemur is often credited as one of the drivers of its evolutionary success, other behavioral evidence suggests a limited capacity for dietary switching. To shed light on the feeding strategies of Eulemur, we compared the dietary flexibility between populations of this genus with that of another widespread lemur taxon, Propithecus. We hypothesized that Eulemur would show greater dietary flexibility than Propithecus, which has a digestive system specialized for folivory, and that Eulemur living in dry forests would switch its diet from fruit to other food seasonally. To examine these hypotheses, we performed a phylogenetic least-squares analysis on 10 populations of Eulemur and 7 of Propithecus to assess the contribution of environmental variables and body mass on their dietary flexibility while controlling for phylogenetic relatedness. Eulemur relied heavily on fruit and did not show large variations in primary food over the year. Propithecus consumed leaves and fruits equally and exhibited considerable flexibility across seasons. Therefore, in contrast to our predictions, the anatomical specialization for fiber digestion heightens dietary flexibility in Propithecus. At the intrageneric level, we found similar ecogeographic variation; populations of both genera with heavier body mass consumed more fruit. As we predicted, Eulemur in drier habitats switched the diet from fruit to alternative food more frequently. To compensate for low dietary flexibility, Eulemur mostly adopts a power-feeding strategy by which it increases energy expenditure to acquire patchily distributed fruit resources.

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.

Habitat shifting by the common brown lemur (Eulemur fulvus fulvus): a response to food scarcity

During periods of food scarcity, most primates display behavioral responses, such as dietary switching or adjustment of traveling and foraging efforts, within home ranges. In rare cases, several primate species leave their home ranges for other remote habitats to seek alternative resources; this migration-like behavior is termed "habitat shifting." Reports of habitat shifting have concentrated on platyrrhines, but this behavior has rarely been observed among prosimians. During 1 year of observation of a troop of common brown lemurs (Eulemur fulvus fulvus) in Ankarafantsika National Park, northwestern Madagascar, habitat shifting occurred twice. To understand the causes of this behavior, I examined the seasonal availability of fruit resources in the range continuously used by the troop during the year (defined as the annual range) and compared feeding activities and vegetation types between the annual range and new areas. The troop usually stayed within a 38.7-ha annual range, defined by a 95 % fixed kernel analysis based on GPS location data collected at 5-min intervals. In April 2007, the lemurs suddenly moved to a habitat 1.0-1.5 km south of their annual range and concentrated on the consumption of Grewia triflora fruits for 2 weeks. In November 2007, they visited a habitat 0.8-1.7 km southeast of the annual range and exploited fruits of Landolphia myrtifolia. These new areas were open habitats with high densities of the respective fruit species. The density of fruiting trees was low in the annual range during these periods; thus, habitat shifting to areas with different phenological productivity appeared to be an effective response to fruit scarcity. Brown lemurs are generally categorized as a nonterritorial species, and the lemurs observed here showed no agonistic behavior in intergroup encounters during range shifting. Such nonterritoriality may allow brown lemurs to shift habitats, a behavior resulting in long-term absence from their annual range.

Diet of an opportunistically frugivorous carnivore,Martes flavigula, in subtropical forest

In response to foraging for foods that fluctuate in availability, generalists often exhibit the ability to switch between different food sources. Many of the Carnivora on an omnivorous–frugivorous diet display temporal dietary switching and specialism, but the mechanisms underlying this are incompletely understood. Here we studied the diet of the opportunistically frugivorous yellow-throated marten (Martes flavigula) with regard to food-resource exploitation in a subtropical forest of central China. Diet was determined through scat analyses combined with surveys to estimate local food abundance. Peak fruit consumption and the lowest utilization of small mammals occurred when fruit abundance reached its temporal maximum in the environment in synchrony with a concomitant peak in small mammal abundance. When both fruits and small mammals were least abundant in the environment, the marten's diet shifted to the maximum utilization of small mammals with no fruit consumption. This dietary switching could not be explained by the fluctuation in the abundance of principal prey in the environment, that is, small mammals, but by the ease of procurement of fruit at peak fruiting season. The marten's diet thus does not simply reflect primary resource abundance but is a function of the relative abundance and inferred availability of alternative food types. This case study of the yellow-throated marten provides insight into foraging strategies that depend on the relative, temporal availability of food types, a phenomenon observed for other generalist omnivores (including several Carnivora).

Effects of rice husk diluted dietary switching on the phenotypic change of gastrointestinal tract in adult ganders

1. An experiment was conducted to test the directionality, scaling and reversibility of phenotypic responses of the gastrointestinal tract (GIT) of adult ganders to rice husk (RH) diluted dietary switching. 2. A total of 96 140-d-old ganders were acclimatised to a basal diet for 2 weeks. The birds were randomly assigned to 4 treatments. On d 1, diets in the experimental groups were switched from the basal diet to diets which contained 200, 400 or 600 g/kg RH by mass, with no RH in the basal diet. After 21 d, the diet of all the experimental birds was switched back to the basal diet until d 42. 3. Increasing RH content significantly increased feed intake, and a decreased trend appeared after diet-switching. The weights of geese fed on the 600 g/kg RH diet for 21 d reduced, and were significantly less than those of the other three groups, while body weights (BW) of the geese in all groups increased after diet-switching back to the basal diet. At d 21, significantly heavier relative weights of proventriculus, gizzard and all gut components, except duodenum, were observed in birds fed on a 600 g/kg RH diet, and significantly heavier relative weights of gizzard were observed in birds given a 400 g/kg RH diet. Thickness of the two gastric walls, gizzard length and all gut components lengths increased significantly in birds given a 600 g/kg RH diet compared with the other three groups. At d 42, no significant differences were noted in the relative weights or lengths of GIT, except for the caeca, which were significantly heavier in birds fed on 600 g/kg RH diet. 4. The results of the experiment were in accordance with the predictions of the hypothesis that there is matching between loads and capacities. The observed phenotypic responses were directional and scaled to the demands.

Foraging and ranging behavior during a fallback episode: Hylobates albibarbis and Pongo pygmaeus wurmbii compared

Periodic episodes of food scarcity may highlight the adaptive value of certain anatomical traits, particularly those that facilitate the acquisition and digestion of exigent fallback foods. To better understand the selective pressures that favored the distinctive dental and locomotor morphologies of gibbons and orangutans, we examined the foraging and ranging behavior of sympatric Hylobates albibarbis and Pongo pygmaeus wurmbii during an episode of low fruit availability at Tuanan, Kalimantan Tengah, Indonesia. We found that Hylobates ranged 0.5 km day(-1) or 33% farther than did Pongo, but the overall daily ranging of both species did not vary as fruit availability decreased by as much as 50%. Among gibbons, we observed dietary switching to fallback foods; in particular, there was a progressively greater reliance on figs, liana products, and unripe fruit. Orangutans relied heavily on unripe fruit and fracture-resistant bark and pith tissues. Despite these divergent fallback patterns, the stiffness of fruit mesocarp consumed by Hylobates and Pongo did not differ. We discuss canine and molar functional morphology with respect to dietary mechanics. Next, to contextualize these results, we discuss our findings with respect to forest structure. The rain forests of Southeast Asia have been described as having open, discontinuous canopies. Such a structure may inform our understanding of the ranging behavior and distinctive locomotion of apes in the region, namely richochetal brachiation and quadrumanous clambering. Our approach of integrating behavioral ecology with physical measures of food may be a powerful tool for understanding the functional adaptations of primates.

Do Ruminants Alter Their Preference for Pasture Species in Response to the Synchronization of Delivery and Release of Nutrients?

When offered a free choice between different forage species presented in a pasture association, ruminants will choose a mixed diet, even when one dietary component could meet all of their nutritional needs. Thus, preference and selection cannot be explained simply by the common measures of species nutritive or feeding value. The question then arises, what is the nutritional basis of the dietary choices that animals make? The objective of this paper is to review the role of synchronization of forage composition factors and nutrient release patterns on the processes controlling preference in grazing ruminants. The satiety theory is used as a model system to explore outcomes of changing the physico-chemical attributes of forages on grazing behavior of sheep and cattle. The review will examine further the biological basis for the alteration in meal pattern, duration and extent in ruminants offered clover only (relatively high rumen degradable protein content) compared to animals eating only grass (with relatively low rumen degradable protein content), or a mixture of grass and clover. One theory that has been proposed to explain the induction of satiety in grazing ruminants is the rate of release of ammonia from the soluble protein fraction of the forage, and subsequent uptake in the blood. By mixing grass with the clover, the animal is able to increase the duration of the meal potentially reflecting a “better” dietary balance of energy to soluble protein that controls the rate of accumulation of ammonia in rumen fluid. This concept is evaluated in light of recent data from in vitro studies examining digestive efficiency. From this analysis, it is clear that direct, real-time information on the relationships between forage physico-chemical factors, rumen condition, meal initiation and cessation, and dietary switching is needed to further develop propositions about the control of dietary choices of grazing ruminants.

Dietary switching of collembola in grassland soil food webs

Soil food webs are characterised by complex direct and indirect effects among the organisms. Consumption of microorganisms by soil animals is considered as an important factor that contributes to the stability of communities, though cascading effects within the food web can be difficult to detect. In a greenhouse experiment, an addition of a high number the fungal feeding collembola Folsomia quadrioculata was applied to grassland soil food webs in monocultures of three plant species: Plantago lanceolata (forb), Lotus corniculatus (legume) and Holcus lanatus (grass). The abundance of microorganisms, determined as the abundances of phospholipid fatty acids (PLFAs) and the abundances of resident invertebrates, nematodes and collembolans, did not change due to the addition of F. quadrioculata. Trophic positions of collembolans were determined by analyses of natural abundances of 15N stable isotopes. The use of food resources by microorganisms and collembolans was determined by 13C analysis of microbial PLFAs and solid samples of collembolans. δ 13C values of the resident collembola Folsomia fimetaria were lower in the presence of F. quadrioculata than in the control food webs indicating a use of more depleted 13C food resources by F. fimetaria. The δ 15N values of F. fimetaria did not change at the addition of F. quadrioculata thus no change of trophic levels was detected. The switch of F. fimetaria to a different food resource could be due to indirect interactions in the food web as the two collembolan species were positioned on different trophic positions, according to different δ 15N values.