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The use of marine subsidies by terrestrial predators can facilitate substantial transfer of nutrients between marine and terrestrial ecosystems. Marine resource subsidies may have profound effects on predator ecology, influencing population and niche dynamics. Expanding niches of top consumers can impact ecosystem resilience and interspecific interactions, affecting predator-prey dynamics and competition. We investigate the occurrence, importance, and impact of marine resources on trophic ecology and niche dynamics in a highly generalist predator, the caracal (Caracal caracal), on the Cape Peninsula, South Africa. Caracals have flexible diets, feeding across a wide range of terrestrial and aquatic prey. We use carbon and nitrogen stable isotope analysis of fur samples (n = 75) to understand trophic position and niche shifts in coastal and inland foragers, as well as the implications of a diet rich in marine resources. We found significant differences in isotope signatures between these groups, with higher δ 13 C (P < 0.05) and δ 15 N values (P < 0.01) in coastal foragers. Isotope mixing models reveal that these elevated signatures were due to non-terrestrial food subsidies, where approximately a third of coastal foraging caracal diet comprised marine prey. The addition of marine prey species to diet increased both the trophic level and isotope niche size of coastal foraging caracals, with potential impacts on prey populations and competition. Our results suggest that marine prey are an important dietary resource for coastal foraging caracals, where seabirds, including two endangered species, are a major component of their diet. However, there are likely risks associated with these resource benefits, as routine consumption of seabirds is linked with higher pollutant burdens, particularly metals. Increased encounters between this terrestrial predator and seabirds may be a result of increased mainland colonies due to changes in habitat availability and the highly opportunistic and generalist foraging behaviour of a native predator., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Abstract Habitat loss and degradation are key drivers of the current biodiversity crisis. Most research focuses on the question of which traits allow species to persist in degraded habitats. We asked whether a species' trophic position or niche width influences the resilience of species in degraded habitats and to what extent habitat degradation affects trophic interactions between species. We used nitrogen isotope ratios (15N:14N, expressed as δ15N value) to quantify and compare trophic positions and niche widths of understory birds inhabiting old‐growth and young secondary forests in the Pacific lowlands of Costa Rica. We found that a species' trophic position rather than its trophic niche width determined its persistence in secondary forests. Species feeding at lower trophic levels in old‐growth forests were less likely to persist in secondary forests than those occupying a higher trophic position in old‐growth forests. This pattern is likely induced by the occurrence of relatively large‐bodied habitat specialists with a flexible and high‐trophic level diet in secondary forests. These habitat specialists likely caused generalist bird species to lower their trophic position relative to conspecifics in old‐growth forests. Regarding trophic niche widths, species in secondary forests tend to have larger niche widths than old‐growth forest species. However, as old‐growth forest specialists and generalists did not differ in their niche widths, no systematic effect of trophic niche width on species persistence after forest disturbance was found. This is the first study that shows a systematic effect of trophic position on the persistence of a wide range of bird species in a disturbed forest ecosystem. It therefore provides important insights into species' responses to habitat degradation and the conservation value of secondary forests. To improve habitat quality for old‐growth forest birds and facilitate avian seed dispersal, the creation of large contiguous forest patches should be prioritised when implementing reforestation measures.

Abstract Animals that co‐occur in a region (sympatry) may share the same environment (syntopy), and niche differentiation is expected among closely related species competing for resources. The masked booby (Sula dactylatra) and smaller congeneric red‐footed booby (Sula sula) share breeding grounds. In addition to the inter‐specific size difference, females of both species are also larger than the respective males (reversed sexual size dimorphism). Although both boobies consume similar prey, sometimes in mixed‐species flocks, each species and sex may specialize in terms of their diet or foraging habitats. We examined inter‐ and intra‐specific differences in isotopic values (δ13C and δ15N) in these pelagically feeding booby species during the incubation period at Clarion Island, Mexico, to quantify the degrees of inter‐ and intra‐specific niche partitioning throughout the annual cycle. During incubation, both species preyed mainly on flyingfish and squid, but masked boobies had heavier food loads than red‐footed boobies. There was no overlap in isotopic niches between masked and red‐footed boobies during breeding (determined from whole blood), but there was slight overlap during the non‐breeding period (determined from body feathers). Female masked boobies had a higher trophic position than conspecific males during breeding; however, no such pattern was detected in red‐footed boobies. These results provide evidence of inter‐ and intra‐specific niche partitioning in these tropical seabird species, particularly during the breeding period and in the more‐dimorphic species. Our results suggest that these closely related species use different strategies to cope with the same tropical marine environment.

The contribution of two basal energy sources – detrital organic matter and primary producers – as part of aquatic food webs varies typically along river continua. A host of barriers to river flow increase the water residence time and sediment and nutrient retention in reservoirs worldwide, and potentially alter the balance between detritus-based and algae-based energy pathways in the downstream food webs. We explored this issue on the Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high sediment runoff. Seasonal measurements of the following parameters were compared upstream and downstream of the reservoirs of two large dams (16 m and 36 m high): sediment fluxes, nutrient and chlorophyll a concentrations, algal communities in the epilithic biofilm (taxonomic composition, biomass and growth), and benthic invertebrate communities (abundance and trophic guild structure). As anticipated, annual sediment fluxes were much lower downstream of the reservoirs, where significant decreases in water turbidity, phosphate and silicate concentrations were recorded. A higher chlorophyll a concentration in water and a higher contribution of pelagic algae taxa to the photosynthetic biofilm suggested drifting and deposition of reservoir-borne phytoplankton downriver. Photosynthetic biofilm growth was higher downstream of the reservoirs in spring and fall, and so was the abundance of herbivores in the invertebrate community, notably scrapers and algae eaters. Energy pathways within riverine food webs were traced using stable isotope analyses of carbon (C) and nitrogen in the tissues of aquatic consumers (invertebrates and fish). Mixing models revealed a discontinuity in the origin of the C entering the food webs along the river continuum, confirming a greater contribution of algal C to aquatic consumers downstream of the reservoirs. These results illustrate mechanisms whereby large reservoirs can modulate C flow in food webs along a small coastal river with high sediment loads, and make it possible to anticipate the effects of dam removal on the future river ecosystem.

Coral reefs are typically found in nutrient-limited waters, which may restrict the growth and expansion of corals. Nevertheless, corals are mixotrophs that may adjust to the variation in the availability of energy sources by switching their major nutritional mode between autotrophy (i.e., synthesizing their own food by symbionts) and heterotrophy (i.e., consuming external food sources). Such trophic plasticity may, however, be subject to symbiont genus and environmental conditions. Using a widespread coral species (Pocillopora damicornis), we examine how symbiont genus (Cladocopium vs. Durusdinium) affects the physiological traits (biomass, symbiont density, C:N ratio and chlorophyll content) of corals and their trophic strategy across seasons (summer and winter) based on stable isotope markers (δ13C and δ15N). We found that corals dominated by Cladocopium (PdC) had a lower symbiont density, but higher autotrophic capacity (higher cellular chlorophyll content and higher δ13C) than those by Durusdinium (PdD). Across seasons, the trophic strategy of PdC was flexible that the autotrophic capacity was reduced by 37.1 % from summer to winter, whereas the trophic strategy of PdD remained relatively unchanged. PdC had a greater heterotrophic capacity in winter, while PdD in summer. Our findings suggest that symbiont genus can determine the trophic flexibility of corals and drive trophic niche differentiation between conspecific corals. By adaptively changing trophic strategy, intraspecific competition of corals for energy sources can be reduced, possibly allowing them to persist in oligotrophic waters and adapt to the future oceanic climate.

Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and habitat use of the extant franciscana dolphin (Pontoporia blainvillei) prior to human influence. Here, we subject 19 fossil and 21 contemporary specimens to stable carbon and oxygen isotope analysis (after first ruling out diagenesis via Fourier transform infrared spectroscopy). The two groups differ in their isotopic composition (PERMANOVA, p < .01), with fossils yielding more disparate d13C values and recent samples more disparate d18O values. Their isotopic niches show an overlap of -20%, with that of the fossils being slightly wider (SEAc = 2.25-2 versus 1.84-2). We attribute these differences to impoverished modern fish communities and temporal changes in freshwater influx. [ABSTRACT FROM AUTHOR]

The notion that closely related species resemble each other in ecological niche space (i.e., phylogenetic dependence) has been a long-standing, contentious paradigm in evolutionary biology, the incidence of which is important for predicting the ecosystem-level effects of species loss. Despite being examined across a multitude of terrestrial taxa, many aspects of niche conservatism have yet to be explored in marine species, especially for characteristics related to resource use and trophic behavior (Eltonian niche characteristics, ENCs). We combined ENCs derived from stable isotope ratios at assemblage- and species-levels with phylogenetic comparative methods, to test the hypotheses that benthic marine fishes (1) exhibit similar assemblage-wide ENCs regardless of geographic location and (2) display phylogenetically dependent ENCs at the species level. We used a 12-species sub-set of the monophyletic group Rajidae sampled from three independent assemblages (Central California, Gulf of Alaska, and Northwest Atlantic), which span two ocean basins. Assemblage-level ENCs implied low trophic diversity and high evenness, suggesting that Rajidae assemblages may exhibit a well-defined trophic role, a trend consistent regardless of geographic location. At the species level, we found evidence for phylogenetic dependence of ENCs relating to trophic diversity (i.e., isotopic niche width; SEAc). Whether individuals can be considered functional equivalents across assemblages is hard to ascertain because we did not detect a significant phylogenetic signal for ENCs relating to trophic function (e.g., trophic position). Thus, additional, complimentary approaches are required to further examine the phylogenetic dependence of species functionality. Our approach illustrates the potential of stable isotope-derived niche characteristics to provide insight on macroecological processes occurring across evolutionary time, which could help predict how assemblages may respond to the effects of species loss.

Over the last hundred years, many large carnivore species have suffered range contractions, population losses, and habitat alterations that may be influencing their dietary preferences. To identify shifting isotopic niches and reconstruct past and present diets from species of high conservation concern, stable isotope analysis (SIA) of δ13C and δ15N values of tissue from museum collections and ongoing non-invasive monitoring programs offers an effective approach. Here, we assessed the long-term alterations in the trophic structure of a generalist large carnivore over a time of population loss and recovery. Wolverine stable carbon (δ13C) and nitrogen (δ15N) isotopes were measured in hair samples collected from 44 individuals in Finland for the period 1905–2020, and potential dietary were quantified using isotopic niche metrics shifts in two study areas. We provide evidence of a long-term diet shift in Finnish wolverines, with a temporal depletion of hair’s δ13C (β = −0.016‰, R² = 0.46, p < 0.001). Correspondingly, there was a shift in the isotopic niches of the Historical population (before the year 2000) and Recent population (after 2000), with the niche overlap between the Historical and Recent periods being only 33% throughout Finland, and even lower in the two study areas (22% to 24%). The breadth of the isotopic niche, however, did not significantly differ between the two periods, suggesting that despite a change in diet composition, wolverines did not specialize more. The trophic level of wolverines in Finland was stable throughout the study period, with no significant change in δ15N with time (β = 0.0055‰, R² = 0.043, p = 0.17). In summary: A) the strong trophic resilience of this top predator was shown by the stability of its niche breadth and trophic level feeding regime during periods of population decline and recovery as well as during a period of major anthropogenic alterations in their environment; B) the use of SIA methods on historical and recent hairs provided a unique tool to unravel long-term changes in wolverine feeding strategies.

Remnant oyster reefs support diverse communities of invertebrates and fish, and there is growing interest in restoring this important habitat. Whether the construction of new oyster reefs will enhance or simply redistribute existing fisheries' productivity depends on their trophic role–which, to date, is unknown for Australian estuaries. In this study, conducted in Port Stephens, Australia, stable isotope analysis was used to determine trophic linkages among remnant oyster reefs and their resident and transient species. Specifically, this study elucidated whether the potential trophic linkages could be arising through the direct consumption of reef-forming bivalves or from the uptake of oyster-generated organic matter found in the sediment and consumption of reef-dwelling organisms. A total of six primary producers and 35 consumers of distinct feeding guilds were sampled. Results indicated oyster reefs are contributing to the trophic ecology of both resident and transient species, both through direct predation on the reef bivalves but also indirectly through consumption of the reef benthic organic matter and consumption of other reef-dwelling organisms. Oysters and mussels were an important prey group (> 40% contribution) for three resident and five transient species, including polychaetes, blue swimmer crabs, toadfish, luderick, leatherjackets, oyster gobies, and stingarees. Benthic organic matter from the oyster reef was found to be a primary resource for 12 residents and four transient species, including crabs, shrimps, gastropods, and fish. Oyster reefs are key foraging grounds in the estuarine seascape, and their restoration will enhance fisheries productivity by broadening the trophic resource base and contribute to the estuarine energy transfer to higher trophic levels. [ABSTRACT FROM AUTHOR]

We utilized natural experiment opportunities presented by differential conditions (presence/absence of seabirds and invasive species) on cays in the Bahamas to study whether interisland variations in food resources contributed to gigantism in Allen Cays Rock Iguanas (Cyclura cychlura inornata). We analyzed the stable carbon (δ13C) and nitrogen (δ15N) isotope values from iguana tissues and resources from each island food web to test the predictions that (1) food webs on islands with seabirds exhibit the influence of marine subsidies from seabird guano, whereas those from non-seabird islands do not, and (2) size differences in iguanas among cays were due to either (a) supplemental food availability from mice and/or seabird carcasses killed by barn owls (Tyto alba) and/or (b) access to more nutrient-rich vegetation fertilized by seabird guano. Food web components from the seabird island (Allen Cay) had 5-9‰ higher δ15N values than those on the other cays and Allen Cay plants contained nearly two times more nitrogen. Bayesian stable isotope mixing models indicated that C3 plants dominated iguana diets on all islands and showed no evidence for consumption of mice or shearwaters. The iguanas on Allen Cay were ~ 2 times longer (48.3 ± 11.6 cm) and ~ 6 times heavier (5499 ± 2847 g) than iguanas on other cays and this was likely from marine-derived subsidies from seabird guano which caused an increase in nitrogen concentration in the plants and a resultant increase in the δ15N values across the entire food web relative to non-seabird islands.

We used compound‐specific isotope analysis of carbon isotopes in amino acids (AAs) to determine the biosynthetic source of AAs in fish from major tributaries to California's Sacramento‐San Joaquin river delta (i.e., the Sacramento, Cosumnes and Mokelumne rivers). Using samples collected in winter and spring between 2016 and 2019, we confirmed that algae are a critical component of floodplain food webs in California's Central Valley. Results from bulk stable isotope analysis of carbon and nitrogen in producers and consumers were adequate to characterize a general trophic structure and identify potential upstream and downstream migration into our study site by American shad Alosa sapidissima and rainbow trout Oncorhynchus mykiss, respectively. However, owing to overlap and variability in source isotope compositions, our bulk data were unsuitable for conventional bulk isotope mixing models. Our results from compound‐specific carbon isotope analysis of AAs clearly indicate that algae are important sources of organic matter to fish of conservation concern, such as Chinook salmon Oncorhynchus tshawytscha in California's Central Valley. However, algae were not the exclusive source of energy to metazoan food webs. We also revealed that other sources of AAs, such as bacteria, fungi and higher plants, contributed to fish as well. While consistent with the well‐supported notion that algae are critical to aquatic food webs, our results highlight the possibility that detrital subsidies might intermittently support metazoan food webs. [ABSTRACT FROM AUTHOR]

Simple Summary: Gonatus fabricii is the most abundant cephalopod in the Arctic and northern part of the North Atlantic, which are areas of rapid environmental change. It is very important as a predator of many species of fish and invertebrates and as a prey for larger fish, seabirds, and marine mammals. The life cycle of G. fabricii, in particular ontogenetic changes in diet and habitat, is little known. Ecological modelling is an important method to forecast ecosystems' dynamics in relation to a changing climate, and it is crucial to assess their present structure and functioning for a viable forecast. Here, the ontogenetic changes in the diet and habitat of large G. fabricii from West Greenland are studied using stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) along trajectories in chitin beaks, which function as archival structures. Using this approach, four stages with clearly distinct ecologies were revealed in the species' life cycle. This novel ecological periodization is a crucial baseline tool in Arctic marine ecosystem studies and cephalopod biology, and should be used in models to correctly reflect the ecological roles of G. fabricii in marine ecosystems. Cephalopods are important in Arctic marine ecosystems as predators and prey, but knowledge of their life cycles is poor. Consequently, they are under-represented in the Arctic ecosystems assessment models. One important parameter is the change in ecological role (habitat and diet) associated with individual ontogenies. Here, the life history of Gonatus fabricii, the most abundant Arctic cephalopod, is reconstructed by the analysis of individual ontogenetic trajectories of stable isotopes (δ13C and δ15N) in archival hard body structures. This approach allows the prediction of the exact mantle length (ML) and mass when the species changes its ecological role. Our results show that the life history of G. fabricii is divided into four stages, each having a distinct ecology: (1) epipelagic squid (ML < 20 mm), preying mostly on copepods; (2) epi- and occasionally mesopelagic squid (ML 20–50 mm), preying on larger crustaceans, fish, and cephalopods; (3) meso- and bathypelagic squid (ML > 50 mm), preying mainly on fish and cephalopods; and (4) non-feeding bathypelagic gelatinous females (ML > 200 mm). Existing Arctic ecosystem models do not reflect the different ecological roles of G. fabricii correctly, and the novel data provided here are a necessary baseline for Arctic ecosystem modelling and forecasting. [ABSTRACT FROM AUTHOR]

The Rio Grande cooter (Pseudemys gorzugi) is an imperiled freshwater turtle native to the southwestern United States and northeastern Mexico. Previous studies investigating P. gorzugi diet have focused on the population occupying the Black River drainage in southeastern New Mexico, while Texas populations have remained unexamined. During the summer and fall of 2020, we studied the dietary habits of P. gorzugi and the syntopic red-eared slider (Trachemys scripta elegans) at San Felipe Creek, Texas, USA using fecal content and stable isotope analyses. We also compared the isotopic niches of these 2 co-occurring turtle species. Filamentous algae were, volumetrically, the most important food item for male, female, and juvenile P. gorzugi. Stable isotope mixing models indicated that lotic and lentic filamentous algae had the greatest proportional contribution to P. gorzugi and T. s. elegans diets, respectively. Stable isotope dietary mixing models also indicate T. s. elegans had a more carnivorous diet, composed mostly of red-rimmed melania (Melanoides tuberculata) and red swamp crayfish (Procambarus clarkii). Carnivory in this species was further supported by enriched δ15N values and higher trophic position estimates. Pseudemys gorzugi and T. s. elegans had δ13C and δ15N signatures that significantly differed, and the 2 species showed little overlap in isotopic niche space, suggesting a low likelihood of intense resource competition. Our results demonstrate that the diet of P. gorzugi, and the isotopic niche overlap between P. gorzugi and T. s. elegans at San Felipe Creek differ from that in the Black River drainage of New Mexico. The information provided here contributes toward a more complete understanding of P. gorzugi ecology, is useful for identifying suitable habitat worthy of conservation, and can help guide the development of feeding regimes for captive assurance colonies. La tortuga de Río Grande (Pseudemys gorzugi) es una tortuga de agua dulce en peligro nativa del suroeste de los Estados Unidos y el noreste de México. Estudios previos que han investigado la dieta de P. gorzugi se han enfocado en la población que ocupa el drenaje del Black River en el sureste de Nuevo México, sin embargo, las poblaciones de Texas no han sido examinadas. Durante el verano y el otoño de 2020, estudiamos los hábitos alimentarios de P. gorzugi y la tortuga de orejas rojas sintópica (Trachemys scripta elegans) en San Felipe Creek, Texas, EE. UU. mediante un análisis de contenidos fecales e isótopos estables. Incluso comparamos los nichos isotópicos de estas dos especies de tortugas en coexistencia. Las algas filamentosas fueron, volumétricamente, el alimento más importante para machos, hembras y juveniles de P. gorzugi. Los modelos de mezcla de isótopos estables indican que las algas filamentosas lóticas y lénticas contribuyen en mayor parte proporcionalmente a las dietas de P. gorzugi y T. s. elegans, respectivamente. Los modelos de mezcla dietética de isótopos estables también indican que T. s. elegans tiene una dieta más carnívora, compuesta en mayor parte de melania de borde rojo (Melanoides tuberculata) y cangrejo de río rojo (Procambarus clarkii). La característica carnívora en esta especie fue respaldada aún más por valores de δ15N enriquecidos y estimaciones de posición trófica más altas. Pseudemys gorzugi y T. s. elegans tuvieron valores de δ13C y δ15N que diferían significativamente y las dos especies mostraron poca superposición en el espacio del nicho isotópico, lo cual sugiere una baja probabilidad de competencia intensa por los recursos. Nuestros resultados demuestran que la dieta de P. gorzugi y la superposición del nicho isotópico entre P. gorzugi y T. s. elegans en San Felipe Creek difieren de aquellas del drenaje del Black River de Nuevo México. La información proporcionada aquí contribuye a un conocimiento más completo de la ecología de P. gorzugi, es útil para identificar un hábitat adecuado digno de conservación y puede ayudar a guiar el desarrollo de regímenes de alimentación para colonias de seguridad cautivas. [ABSTRACT FROM AUTHOR]

Abstract Information on resource use and trophic dynamics of marine predators is important for understanding their role in ecosystem functioning and predicting population‐level responses to environmental change. Where separate populations experience different local environmental conditions, geographic variability in their foraging ecology is often expected. Within populations, individuals also vary in morphology, physiology, and experience, resulting in specialization in resource use. In this context, isotopic compositions of incrementally grown tissues such as keratinous hairs offer a valuable opportunity to study long‐term variation in resource and habitat use. We investigated the trophic ecology of female Cape fur seals (Arctocephalus pusillus pusillus) using carbon and nitrogen isotopic compositions of serially sampled whiskers collected at four breeding sites along the coast of South Africa. Drawing on over 900 isotopic measurements, we assessed geographic variability in isotopic niche width between colonies and the degree of individual specialization. We found slight, but clear geographic differences in isotopic ratios and isotopic niche widths, seemingly related to ecological setting, with niche widths being proportional to the area of available shelf and shelf‐slope habitat surrounding the colony. We further identified periodic oscillations in isotopic ratios, which likely reflect temporal patterns in foraging distribution and prey type, linked to shifts in the availability of prey resources and their interaction with constraints on individual females throughout their breeding cycle. Finally, individual specialization indices revealed that each of the study populations contain specialist individuals that utilize only a small subset of the total population niche width. The degree of individual specialization was, however, not consistent across colonies and may reflect an interactive influence between density‐dependent effects and habitat heterogeneity. Overall, this study provides important information on the trophic ecology of Cape fur seals breeding in South Africa and highlights the need to consider geographic and individual variability when assessing the foraging ecology of marine predators.

Although the concept of trophic interactions has been used for a long time, there are still considerable gaps in our understanding of the effect of various environmental factors on trophic interactions within river fish assemblages. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of 20 species of fish belonging to both eurytopic and rheophilic ecological groups from a large temperate rivers were used to evaluate overall trophic niche use and trophic position of species, and to find out how environmental variability associated with nutrient loading affects individual and community-wide aspects of trophic structure. The study was carried out at 11 sites along the European rivers Vltava and Elbe, representing a continuous gradient of pollution and habitat degradation. Corrected Standard Ellipse Area (SEAc) was significantly larger for the group of eurytopic ecological species than for rheophilic species. Despite narrower isotopic niche space, rheophilic fish species occupied a higher trophic position, suggesting that these species use resources more enriched in 15N. Of the 11 environmental variables tested, nutrients had a significant effect on trophic niche area of species (SEAc), indicating that eutrophication is of critical importance for fish assemblages. Isotopic niche area of species was found to be positively influenced by total phosphorus, and negatively affected by concentrations of nitrate (N-NO3−) and ammonia (N-NH4+). A negative association between oxygen demand and a measure of trophic diversity - mean distance to centroid (CD)- and a measure of density and clustering of species - mean nearest neighbor distance (MNND)- were found, indicating that the oxygen demand is a key factor influencing community trophic structure. An observed pattern where nutrient loading influenced both individual species and trophic structure of the fish assemblage provides strong support for an anthropogenic influence on riverine food webs.

Abstract Ecosystems are interconnected by energy fluxes that provide resources for the inhabiting organisms along the transition zone. Especially where in situ resources are scarce, ecosystems can become highly dependent on external resources. The dependency on external input becomes less pronounced in systems with elevated in situ production, where only consumer species close to the site of external input remain subsidized, whereas species distant to the input site rely on the in situ production of the ecosystem. It is largely unclear though if this pattern is consistent over different consumer species and trophic levels in one ecosystem, and whether consumer species that occur both proximate to and at a distance from the input site differ in their dependency on external resource inputs between sites. Using stable isotope analysis, we investigated the dependency on external marine input for common ground‐associated consumer taxa on small tropical islands with high in situ production. We show that marine input is only relevant for strict beach‐dwelling taxa, while the terrestrial vegetation is the main carbon source for inland‐dwelling taxa. Consumer species that occurred both close (beach) and distant (inland) to the site of marine input showed similar proportions of marine input in their diets. This supports earlier findings that the relevance of external resources becomes limited to species close to the input site in systems with sufficient in situ production. However, it also indicates that the relevance of external input is also species‐dependent, as consumers occurring close and distant to the input site depended equally strong or weak on marine input.

Abstract Devil facial tumor disease (DFTD) is a transmissible cancer affecting Tasmanian devils Sarcophilus harrisii. The disease has caused severe population declines and is associated with demographic and behavioral changes, including earlier breeding, younger age structures, and reduced dispersal and social interactions. Devils are generally solitary, but social encounters are commonplace when feeding upon large carcasses. DFTD tumors can disfigure the jaw and mouth and so diseased individuals might alter their diets to enable ingestion of alternative foods, to avoid conspecific interactions, or to reduce competition. Using stable isotope analysis (δ13C and δ15N) of whiskers, we tested whether DFTD progression, measured as tumor volume, affected the isotope ratios and isotopic niches of 94 infected Tasmanian devils from six sites in Tasmania, comprising four eucalypt plantations, an area of smallholdings and a national park. Then, using tissue from 10 devils sampled before and after detection of tumors and 8 devils where no tumors were detected, we examined whether mean and standard deviation of δ13C and δ15N of the same individuals changed between healthy and diseased states. δ13C and δ15N values were generally not related to tumor volume in infected devils, though at one site, Freycinet National Park, δ15N values increased significantly as tumor volume increased. Infection with DFTD was not associated with significant changes in the mean or standard deviation of δ13C and δ15N values in individual devils sampled before and after detection of tumors. Our analysis suggests that devils tend to maintain their isotopic niche in the face of DFTD infection and progression, except where ecological conditions facilitate a shift in diets and feeding behaviors, demonstrating that ecological context, alongside disease severity, can modulate the behavioral responses of Tasmanian devils to DFTD.

Terrestrial organic matter (t-OM) has been recognized as an important cross-boundary subsidy to aquatic ecosystems. However, recent evidence has shown that t-OM contributes little to promote secondary production in lakes because it is a low-quality food for aquatic consumers. To resolve this conflict, we performed a field experiment using leaf litter as t-OM. In the experiment, we monitored zooplankton biomass in enclosures with and without addition of leaf litter under shaded and unshaded conditions and assessed food web changes with stable isotope analyses. We then examined whether or not leaf litter indeed stimulates lake secondary production and, if it does, which food chain, the detritus-originated food chain (“brown” food chain) or the algae-originated food chain (“green” food chain), contributes more to this increase. Analyses with stable isotopes showed the importance of t-OM in supporting secondary production under ambient lake conditions. However, the addition of the leaf litter increased the zooplankton biomass under unshaded conditions but not under shaded conditions. We found that phosphorus was leached from leaf litter at much faster rate than organic carbon and nitrogen despite its low content in the leaf litter. These results showed that leaf litter stimulated the increase in zooplankton biomass mainly through the green food chain rather than the brown food chain because the leaf litter supplied limiting nutrients (i.e., phosphorus) for primary producers.Our results indicate that the functional stoichiometry of the subsidized organic matter plays a crucial role in determining the relative importance of brown and green food chains in promoting production at higher trophic levels in recipient ecosystems.

Abstract Exploring the process of diet selection will contribute to improvement in our understanding of animal foraging strategies. The overwhelming majority of ecological research on animal learning and foraging concentrates on how social learning influences the feeding styles of animals living in groups. In solitary animals that live long after independence from their mothers, foraging experience after independence is expected to have a significant influence on diet selection, but few studies have addressed this point. We used brown bears (Ursus arctos), which spend 1–2 years with their mothers before foraging alone, as a model species and investigated how their diet changed later in life. We estimated the diets of bears at the individual level by using stable isotope analysis of guard hairs and examined the factors that drove dietary variation. We also quantified the extent to which the diets of bears shifted by comparing the diets of bears at the time of capture with the average diet in their natal habitat. Our results indicated that females retained the average diet of their natal habitat, whereas the diets of males significantly changed more than 6 years after becoming independent from their mothers, when they reached physical maturity. Males were dependent on energy‐rich marine animals at older ages regardless of their natal habitats, which we attribute to several factors, including habitat exploration, acquisition of foraging experience, and social dominance. Our results provide the first evidence, suggesting that foraging experience after independence influences diet selection later in life in solitary large mammals.

The emergence of novel human pathogens is frequently linked with zoonotic events and human-wildlife interactions that promote disease transmission. Consequently, surveillance of wildlife populations for candidate diseases that could spread to humans is beneficial, but requires widespread collections of numerous samples. A legitimate means to acquire large sample sizes of waterfowl is through cooperation between researchers and hunters, who also work in concert with natural resource managers, landowners, and agricultural entities -e.g., aquaculture facilities. In addition to understanding the occurrence and spread of parasites and pathogens by birds, these samples can be used to answer questions about the ecology of various waterbird species. Body mass and morphometric data on hunter-donated specimen are useful for understanding bird condition and other dynamics of birds; however, when breast meat is removed prior to the acquisition of specimen weight, samples might not be as desirable. Here, we evaluate the utility of data obtained from a bird species that might be targeted by hunters and subsequently used to learn about their disease dynamics. Lesser Scaup (Aythya affinis) collected at aquaculture facilities were assessed for their stable isotope concentrations and parasites communities to learn about the birds’ foraging ecology. Discriminant analyses designed to classify birds by the aquaculture pond type from which they were collected included isotope data, Principal Components derived from parasite community data of 7 types, and birds’ body mass. We compared these to Double-crested Cormorants (Nannopterum auritum) feeding on catfish and found the two waterbird species exhibited different infracommunities of parasites Furthermore, some scaup demonstrated fish aquaculture pond type fidelity. Bird body mass was an important metric to include in analytical models when all parasite datatypes were not available. However, the combination of stable isotope concentrations and parasite infracommunity data (that includes prevalence, abundance, volume, and energy use) in models resulted in host ecology differentiation equal or better than models where bird body mass was included. Hunter-derived samples should be encouraged as a means for sample acquisition and be considered as an approach for aquaculture-wildlife conflict management as the information that can be obtained through these samples is multifaceted.

African forest hogs (genus Hylochoerus) are extant Afro-tropical suids that inhabit a variety of forest environments and thick bushlands and are predominantly herbivores. Hylochoerus likely evolved from a Pleistocene Kolpochoerus majus-like ancestor, but its recent evolutionary history is virtually unknown. Here, we describe a partial right lower third molar from the Late Pleistocene Wasiriya Beds of Rusinga Island (~50-36 ka). The crowns are mesiodistally compressed in a bunolophodont fashion and arranged in columnar pillars that resemble those of extant Hylochoerus. We provide accurate data derived from computed tomography on the hypsodonty index (HI) of extant Hylochoerus and show that the Rusinga third molar crown was as tall as those of its modern counterpart (HI = 1.8–2.0). Stable carbon isotope analyses suggest that the diet of the Rusinga specimen (δ13C = −17.0 ‰) was also like that of extant forest hogs (δ13C average = −17.6 ‰). This extremely negative value contrasts strikingly with those of other fossil large herbivores at Rusinga (δ13C average = −0.7 ‰.). Among the potential explanations for this anomaly, the most likely is that the Late Pleistocene paleoenvironments were more heterogeneous than previously considered and may have included closed-canopy woodland in the highlands of Rusinga. [ABSTRACT FROM AUTHOR]

Abstract An ecological niche has been defined as an n‐dimensional hypervolume formed by conditions and resources that species need to survive, grow, and reproduce. In practice, such niche dimensions are measurable and describe how species share resources, which has been thought to be a crucial mechanism for coexistence and a major driver of broad biodiversity patterns. Here, we investigate resource partitioning and trophic interactions of three sympatric, phylogenetically related and morphologically similar species of thrushes (Turdus spp.). Based on one year of data collected in southern Brazil, we investigated niche partitioning using three approaches: diet and trophic niche assessed by fecal analysis, diet and niche estimated by stable isotopes in blood and mixing models, and bipartite network analysis derived from direct diet and mixing model outputs. Approaches revealed that the three sympatric thrushes are generalists that feed on similar diets, demonstrating high niche overlap. Fruits from C3 plants were one of the most important food items in their networks, with wide links connecting the three thrush species. Turdus amaurochalinus and T. albicollis had the greatest trophic and isotopic niche overlap, with 90% and 20% overlap, respectively. There was partitioning of key resources between these two species, with a shared preference for fig tree fruits—Ficus cestrifolia (T. amaurochalinus PSIRI% = 11.3 and T. albicollis = 11.5), which was not present in the diet of T. rufiventris. Results added a new approach to the network analysis based on values from the stable isotope mixing models, allowing comparisons between traditional dietary analysis and diet inferred by isotopic mixing models, which reflects food items effectively assimilated in consumer tissues. Both are visualized in bipartite networks and show food‐consumers link strengths. This approach could be useful to other studies using stable isotopes coupled to network analysis, particularly useful in sympatric species with similar niches.

Abstract Age‐related changes in diet have implications for competitive interactions and for predator–prey dynamics, affecting individuals and groups at different life stages. To quantify patterns of variation and ontogenetic change in the diets of Tasmanian devils Sarcophilus harrisii, a threatened marsupial carnivore, we analyzed variation in the stable isotope composition of whisker tissue samples taken from 91 individual devils from Wilmot, Tasmania from December 2014 to February 2017. Both δ13C and δ15N decreased with increasing age in weaned Tasmanian devils, indicating that as they age devils rely less on small mammals and birds, and more on large herbivores. Devils

Ecological (isotopic) niche refers to a surface in a two-dimensional space, where the axes correspond to environmental variables that reflect values of stable isotopes incorporated in an animal's tissues. Carbon and nitrogen stable isotope ratios (δ13C-δ15N) notably provide precious information about trophic ecology, resource and habitat use, and population dynamics. Various metrics allow for isotopic niche size and overlap assessment. In this paper, we advocate α-minimum convex polygons (MCP) - that have long been used for home range estimation – as a relevant tool for isotopic niche size, overlap, and characteristics. The method allows for outlier rejection while being suited to data that are not Gaussian in the bivariate isotopic (δ13C-δ15N) space. The proposed indicators are compared to other existing approaches and are shown to be complementary. Notably an indicator of divergence within the niche is introduced, and allows for comparisons at low (n > 6) and different sample sizes. The R code is made publicly available and will enable ecologists to perform isotopic niche comparison, contraction and expansion assessment, and overlap, based on various methods.

Over recent years, mounting pressure has been placed on countries to assess their role in the ivory trade, with a view to tackling the rapidly declining numbers of elephants, due to poaching. The United Kingdom has been identified as a large re-exporter of ivory. Despite much of this trade being reported as legal or antique ivory, such provision of ivory to meet demand is known to fuel illegal markets and provide trade routes for modern ivory sales. Aside from ivory species and age, further analysis to evaluate geographic provenance, can inform where an elephant had lived, and so identify a source region or population where poaching occurred. The purpose of this study was to determine the age and species of ivory objects surrendered or seized in the UK and assess their likely geographic provenance through comparison of results from mitochondrial DNA and stable isotope analysis to publicly accessible georeferenced African elephant databases. The results demonstrated that the objects tested from an airport seizure were modern and matched existing haplotypes allowing for regional geographic inferences (supported by both techniques) to be obtained for most of these objects. In contrast, antique and modern ivory was detected amongst the amnesty objects, and several new mtDNA haplotypes were identified. Regional geographic inferences were achieved for some but not all of the objects tested. Our findings show this combination of methods provides a wealth of information which, could provide insight into targeted elephant populations and assist in disrupting international wildlife trade networks.

Studies of animal movement and migration over large geospatial scales have long relied on natural continental-scale hydrogen isotope (δ2H) gradients in precipitation, yet the physiological processes that govern incorporation of δ2H from precipitation into plant and then herbivore tissues remain poorly understood, especially at the molecular level. Establishing a biochemical framework for the propagation of δ2H through food webs would enable us to resolve more complicated regional-scale animal movements and potentially unlock new applications for δ2H data in animal ecology and eco-physiology. Amino acid δ2H analysis offers a promising new avenue by which to establish this framework. We report bulk tissue δ2H, δ13C, and δ15N data as well as amino acid δ2H and δ13C data from three Pipevine swallowtail (Battus philenor) tissues—caterpillars, butterfly bodies, and wings—as well as their obligate plant source: pipevine leaves (Aristolochia macrophylla). Insects are often dominant herbivores in terrestrial food webs and a major food source for many higher-level consumers, so it is particularly important to understand the mechanisms that influence insect tissue δ2H values. Our data reveal extensive δ2H variation within and among individuals of a relatively simple plant-herbivore system that cannot be explained by temporal or geospatial gradients of precipitation δ2H or dietary differences. Variations in essential amino acid δ2H and δ13C indicate that B. philenor acquire these compounds from an additional source that is isotopically distinct from pipevine leaves, potentially gut microbes. We also found multiple isotopic carryover effects associated with metamorphosis. This study emphasizes the strong influence of physiology on consumer-diet δ2H discrimination in a local population of pipevines and swallowtails and provides a template that can be broadly applied to Lepidoptera—the second most diverse insect order—and other holometabolous insects. Understanding these physiological mechanisms is critical to interpreting the large degree of δ2H variation in consumer tissues often observed at a single collection site, which has implications for using δ2H isoscapes to study animal movement. Further investigation into amino acid δ2H holds promise to elucidate how subsets of amino acids may be best utilized to address specific ecological and physiological questions for which bulk tissue δ2H is insufficient.

For centuries, human activities have altered the population dynamics of wildlife. New anthropogenic food sources provide a predictable and abundant food supply that often induces very significant changes in the size, distribution, and behaviour of many populations, with ultimate consequences on the structure and functioning of natural ecosystems. Here, we combine historical and contemporary feather samples of a population of a superabundant, opportunistic predator, the yellow-legged gull Larus michahellis, to assess its trophic ecology and relate it to human activities in the long term. Dietary assessments were based on stable isotope analysis of carbon, nitrogen, and sulphur (δ13C, δ15N and δ34S), and were conducted through three end-point (marine prey, waste from landfills-slaughterhouses, and terrestrial invertebrates) Bayesian mixing models. Our results suggest that gulls’ diet showed a progressive decrease in the consumption of marine prey throughout the most recent period (late 20th century onwards), linked to an increase in the consumption of meat waste and small terrestrial invertebrates. Reported dietary changes over the sampling period correlated positively with the availability of marine resources around the breeding area. We provide evidence suggesting that the ability of gulls to exploit efficiently diverse anthropogenic food subsidies likely resulted in the exponential demographic increase of this population throughout the 20th century. In addition, current regulations affecting the availability of these food resources (e.g., fishing discards and landfill waste) likely reversed this trend over the last decade. Long-term evidence of population trophic plasticity, like the one we present here, is essential to implement and support management and conservation actions that limit the availability of anthropogenic resources, especially when it comes to superabundant, problematic species.

According to the niche variation hypothesis (NVH), the populations with wider niches are phenotypically more variable than those with narrow niches. Giller expanded the NVH, suggesting that the niche width, morphological variation, and genetic diversity are all positively correlated. However, the hypothesis has been a subject of debate and discussion. In the present study, the NVH was tested by analyzing the relationships among trophic niche width, morphological variation, and genetic diversity of Hemiculter leucisculus, a widespread cyprinid fish. The fish samples were collected from six sites across Haihe, the Yellow, and the Yangtze River basins in China. The relationships among trophic niche width, morphological variation, and genetic diversity were analyzed using Pearson correlation at the inter-population level. Our analysis indicated that trophic niche width is significantly positively correlated with morphological variation, which corroborates the NVH. Morphological variation was significantly correlated to genetic diversity. However, no relationship was observed between trophic niche width and genetic diversity. We inferred that the dietary niche of H. leucisculus might change due to the plastic response toward environmental changes rather than due to the genetic variation. We also suggest that the effects of environment and heredity on the niche of the freshwater fish should be quantified separately in further studies.

Stable carbon (13C/12C; δ13C) and nitrogen (15N/14N; δ15N) isotope ratios are best used to assess wild animal diets when the isotopic differences between consumers and diets are known. These differences are called discrimination factors (expressed with Δ notation). We report the 1st Δ13C and Δ15N values between diet and fur from captive individuals held on controlled diets for 7 months and representing 4 felid species: African lions (Panthera leo), bobcats (Lynx rufus), Canada lynx (Lynx canadensis), and mountain lions (Puma concolor). All animals were fed a mix of diet items (beef, beef rib, a commercial carnivore diet, chicken, mice, rats, turkey, and turkey wings) that was consistent throughout their molting period. Weekly diet composition was determined by the percentage of mass of each diet item and overall δ13C and δ15N values were calculated for each animal's diet. The mean Δ13C and Δ15N values (± SD) between felid fur and their non-lipid-extracted diets were 1.1‰ ± 0.2‰ and 3.5‰ ± 0.0‰, respectively (African lion, n = 1 animal sampled at 2 intervals); 5.5‰ ± 0.5‰ and 4.1‰ ± 0.1‰, respectively (bobcats, n = 3); 2.4‰ and 3.3‰, respectively (Canada lynx, n = 1); and 4.7‰ ± 0.6‰ and 4.5‰ ± 0.2‰, respectively (mountain lions, n = 2). Variations in Δ13C and Δ15N values among species were likely due to dietary differences and we recommend the use of the Δ13C (5.5 ± 0.5) and Δ15N (4.1 ± 0.1) values obtained from the bobcats for future determinations of wild felid foraging ecology as they were held on diets composed of 100% whole animals and animal parts, which best reflects diets of wild felids. © 2014 American Society of Mammalogists.

Abstract The role of niche partitioning in structuring species‐rich soil animal communities has been debated for decades and generated the “enigma of soil animal diversity.” More recently, resource‐based niche partitioning has been hypothesized to play a very limited role in the assembly of soil animal communities. To test this hypothesis, we applied a novel combination of stable isotopes and null models of species co‐occurrence to quantify the extent of resource niche partitioning on a diverse oribatid mite community sampled from mature oak woodland. We asked whether species aggregate or segregate spatially and how these patterns correlated with the abundance of estimated trophic guilds. We also estimated the effects of environmental variables on community structure. All measured environmental variables accounted for 12% of variance in community structure, including 8% of pure spatial structure unrelated to measured environmental factors and 2% of pure environmental variance unrelated to spatial variation. Co‐occurrence analysis revealed 10 pairs of species that aggregated and six pairs of species that were spatially segregated. Values of δ15N indicated that five out of the 10 pairs of aggregated species occupied the same trophic guild, while values of δ13C indicated that species in these five pairs consumed resources of different quality, supporting a significant role of resource‐based niche partitioning. Also, one of the five pairs of segregated species occupied the same trophic guild but had overlapping δ13C values suggesting that these species do not co‐occur locally and thus minimize competition for shared resources. Partitioning of resources plays an underestimated role in soil microarthropod communities and different local communities consisted of the same trophic guilds with species identity changing from place to place. The sum of resource partitioning, multi‐trophic interactions, and microscale environmental variability in the environment is a viable solution to the enigma of soil animal diversity.

Palaeoecological interpretations are based on our understanding of dietary and habitat preferences of fossil taxa. While morphology provides approximations of diets, stable isotope proxies provide insights into the realized diets of animals. We present a synthesis of the isotopic ecologies (δ13C from tooth enamel) of North American mammalian herbivores since approximately 7 Ma. We ask: (i) do morphological interpretations of dietary behaviour agree with stable isotope proxy data? (ii) are grazing taxa specialists, or is grazing a means to broaden the dietary niche? and (iii) how is dietary niche breadth attained in taxa at the local level? We demonstrate that while brachydont taxa are specialized as browsers, hypsodont taxa often have broader diets that included more browse consumption than previously anticipated. It has long been accepted that morphology imposes limits on the diet; this synthesis supports prior work that herbivores with 'grazing' adaptions, such as hypsodont teeth, have the ability to consume grass but are also able to eat other foods. Notably, localized dietary breadth of even generalist taxa can be narrow (approx. 30 to 60% of a taxon's overall breadth). This synthesis demonstrates that 'grazing-adapted' taxa are varied in their diets across space and time, and this flexibility may reduce competition among ancient herbivores. [ABSTRACT FROM AUTHOR]

Abstract The notion that closely related species resemble each other in ecological niche space (i.e., phylogenetic dependence) has been a long‐standing, contentious paradigm in evolutionary biology, the incidence of which is important for predicting the ecosystem‐level effects of species loss. Despite being examined across a multitude of terrestrial taxa, many aspects of niche conservatism have yet to be explored in marine species, especially for characteristics related to resource use and trophic behavior (Eltonian niche characteristics, ENCs). We combined ENCs derived from stable isotope ratios at assemblage‐ and species‐levels with phylogenetic comparative methods, to test the hypotheses that benthic marine fishes (1) exhibit similar assemblage‐wide ENCs regardless of geographic location and (2) display phylogenetically dependent ENCs at the species level. We used a 12‐species sub‐set of the monophyletic group Rajidae sampled from three independent assemblages (Central California, Gulf of Alaska, and Northwest Atlantic), which span two ocean basins. Assemblage‐level ENCs implied low trophic diversity and high evenness, suggesting that Rajidae assemblages may exhibit a well‐defined trophic role, a trend consistent regardless of geographic location. At the species level, we found evidence for phylogenetic dependence of ENCs relating to trophic diversity (i.e., isotopic niche width; SEAc). Whether individuals can be considered functional equivalents across assemblages is hard to ascertain because we did not detect a significant phylogenetic signal for ENCs relating to trophic function (e.g., trophic position). Thus, additional, complimentary approaches are required to further examine the phylogenetic dependence of species functionality. Our approach illustrates the potential of stable isotope‐derived niche characteristics to provide insight on macroecological processes occurring across evolutionary time, which could help predict how assemblages may respond to the effects of species loss.

Subsequent to their introduction in the 1950s, Arctic charr Salvelinus alpinus have been able to establish a self‐sustaining population that has adapted to the unique conditions of the sub‐Antarctic Kerguelen Islands. Here, 48 individuals (198–415 mm) were caught with gillnets and their basic biology and feeding ecology were examined using stable isotope analysis. The Lac des Fougères population split use of littoral and pelagic resources evenly, although larger fish relied more heavily on littoral production and appear to follow the size‐dependent life history habitat template seen in many Scandinavian lakes where smaller sized individuals occupy the pelagic zone and larger individuals dominate the littoral habitat. In Kerguelen, Arctic charr mature at the same ages (5.6 years) as Arctic charr in both sub‐Arctic and Arctic lakes. Although mortality was average in comparison to comparator sub‐Arctic lakes, it was high in comparison to Arctic lakes. Maximal age (>7+) was at the lower end of the range typically seen in sub‐Arctic lakes. Although they inhabit a resource‐poor environment, Kerguelen Arctic charr showed no evidence of cannibalism. Thus, while Arctic charr can survive and reproduce in the relatively unproductive Kerguelen lake environments, survival and growth nevertheless appear to be traded off against survival and longevity. The uniqueness of the population location and the recency of its introduction suggest that further monitoring of the population has the potential to yield valuable insights into both the adaptability of the species and its likely responses to ongoing large‐scale environmental change as represented by climate change. [ABSTRACT FROM AUTHOR]

The Gulf of Ambracia, in northwestern Greece, hosts a highly threatened community of about 150 common bottlenose dolphins (Tursiops truncatus). Until now, information on their feeding habits was derived exclusively from fish scale samples collected during surface‐feeding events targeting small schooling epipelagic fish. The aim of this study was to determine the diet of bottlenose dolphins living in the Gulf of Ambracia through the application of Bayesian isotopic mixing models. Skin biopsy samples of 16 dolphins were analyzed and no difference related to sex or age‐class was found in δ13C and δ15N values. Results suggested that the dolphin diet was mainly based on Trachurus trachurus, species belonging to the family Sparidae: Diplodus annularis, Lithognathus mormyrus, and Sepia officinalis, which represented together about 42% ± 15% of the biomass ingested, followed by species belonging to the order Clupeiformes (Engraulis encrasicolus, Sardinella aurita, and Sardina pilchardus) and the genus Gobius (37% ± 17%). A better understanding of the feeding habits of these dolphins sheds light on the feeding ecology of this highly threatened population by, for instance, evidencing interactions with artisanal fisheries sharing the same target species, and is key for identifying adequate management measures consistent with an ecosystem‐based approach. [ABSTRACT FROM AUTHOR]

Mandrills are large‐bodied terrestrial forest primates living in particularly large social groups of several hundred individuals. Following these groups in the wild to assess differences in diet over time as well as among individuals is demanding. We here use isotope analyses in blood and hair obtained during repeated captures of 43 identified free‐ranging mandrills (Mandrillus sphinx) from Southern Gabon, to test how dietary variation relates to the season as well as an individual's age and sex. We measured the stable carbon (δ13C‰) and nitrogen (δ15N‰) isotope ratios in 46 blood and 214 hair section samples as well as from a small selection of mandrill foods (n = 24). We found some seasonal isotopic effects, with lower δ13C values but higher δ15N values observed during the highly competitive long dry season compared to the fruit‐rich long rainy season. Variation in δ13C was further predicted by individual age, with higher δ13C values generally found in younger individuals suggesting that they may consume more high canopy fruit than older individuals, or that older individuals consume more low canopy foliage. The best predictor for δ15N values was the interaction between age and sex, with mature and reproductively active males revealing the highest δ15N values, despite the observation that males consume substantially less animal food items than females. We interpret high δ15N values in these mature male mandrill blood and hair sections to be the result of nutritional stress associated with intense male–male competition, particularly during mating season. This is the first study showing isotopic evidence for nutritional stress in a free‐ranging primate species and may spark further investigations into male mandrill diet and energy balance. [ABSTRACT FROM AUTHOR]

Partial migration, where migrant and resident organisms coexist within the same population, has been found in many fishes. Although it seems obvious that different life cycles exploit habitats and food webs differently, few assessments about the trophic consequences of partial migration are available. To unveil part of this complexity, we combined otolith chemistry with stable isotope analyses data for hind-casting Merluccius australis habitat use and diet composition at age. By providing detailed information about lifetime variability in diet, trophic position, and prey demand of four M. australis life-cycle types, we show that these groups feed differentially in estuarine and oceanic habitats throughout their ontogeny. Although trophic positions were similar between habitats for juvenile and subadults, substantial differences between life-cycle types were found regarding lifetime diet and trophic demand. Thus, the more abundant and heavily exploited oceanic stock of M. australis was heavily dependent of estuarine habitats within the Patagonian Fjords System, where it consumes large biomasses of Macruronus magellanicus , Pasiphaea , Sprattus fuegensis , and Euphausiidae at earlier stages. We show ignoring trophic consequences of partial migration and life-cycle diversity may produce highly biased results, both in terms of prey and habitat use, which appears critical for multispecies and ecosystem management approaches. [ABSTRACT FROM AUTHOR]

Conservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age‐0 fish in efforts to re‐establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age‐0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age‐0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age‐0 fingerlings. We investigated feeding by age‐0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ13C) and nitrogen (δ15N) isotopes using Bayesian mixing model approaches. Isotopic values for age‐0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella. Competitive interactions among Bluegill Lepomis macrochirus, White Bass Morone chrysops, White Crappie Pomoxis annularis, and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short‐lived due to the rapid growth of age‐0 gar after their transition to piscivory. Trophic position of age‐0 Alligator Gar, Longnose Gar Lepisosteus osseus, and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus. In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within‐family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment. [ABSTRACT FROM AUTHOR]

Carbon and nitrogen stable isotope analyses were used to infer relative trophic structure and examine regional variation in trophic dynamics of fishes in the Florida Big Bend, an approximately 300 km stretch of relatively pristine coastline in the eastern Gulf Of Mexico that contains over 250,000 ha of seagrass. The Florida Big Bend is home to a diverse assemblage of fauna; and the ecosystem is regionally important through its support of robust fishing (recreational and commercial) and eco-tourism industries. Stable isotope analyses suggest assemblages of fishes in the Florida Big Bend are trophically diverse, with considerable isotopic overlap across many taxa. Patterns of trophic structure corroborated the results of similar studies of these and related taxa and in other seagrass ecosystems, and there appear to be multiple channels of primary production. Large elasmobranch fishes were most enriched in δ 15N with values well above the teleost fishes sampled, while smaller and demersal elasmobranchs had δ 15N signatures comparable to several species of predatory teleosts. Results of stable isotope analyses suggested high trophic redundancy and overlap in resource use among both teleost and elasmobranch fishes. Comparisons of regional stable isotope values revealed some spatial variability and indicated the southern Big Bend is isotopically distinct, suggesting a distinct regional faunal zone in this region, potentially due to greatly reduced river influence in the southern portion of the system. [ABSTRACT FROM AUTHOR]

White sharks (Carcharodon carcharias) are described as generalist predators, with a demonstrated ontogenetic dietary shift which occurs between subadult and adult life stages. Trophic ecology studies on white shark have been focused mainly on large and mature individuals, necessitating studies of young white shark trophic ecology to better understand their resource use. This study provides new insights into young white shark diet in the North eastern Pacific Ocean using stable isotope analysis in muscle tissues. We analyzed δ13C and δ15N values of young white shark muscle (n = 21) from Sebastián Vizcaino Bay (SBV) during 2015–2018. We found changes in prey composition across early [neonates, young-of-the-years (YOYs), juveniles] white shark life stages, with significant changes in isotopic composition throughout early ontogeny. Mixing model results indicate a high use of coastal areas for foraging, mainly for juvenile stages and the substantial contribution of pelagic preys (e.g., S. japonicus, Prionotus spp., Cynoscion spp., S. sagax, etc.) in YOYs, white shark diet also indicates an important role of offshore foraging. This change in isotopic composition likely represents the shift from the embryo's typical maternally derived isotopic signature, incorporated in offshore foraging regions, to the postpartum isotopic composition incorporated by foraging neonates in inshore nursery habitats. This study provides relevant information regarding young white shark feeding preferences, reinforces the importance of coastal areas as critical habitat for the development and the successful foraging of this species, and also provides indirect insights on the feeding habits of the adult female of white sharks, which constitutes a baseline for further research. [ABSTRACT FROM AUTHOR]

Bycatch is one of the key threats to juvenile marine turtles in the Mediterranean Sea. As fishing methods are regional or habitat specific, the susceptibility of marine turtles may differ according to inter- and intra-population variations in foraging ecology. An understanding of these variations is necessary to assess bycatch susceptibility and to implement region-specific management. To determine if foraging ecology differs with region, sex, and size of juvenile loggerhead turtles (Caretta caretta), stable isotope analysis of carbon and nitrogen was performed on 171 juveniles from a range of foraging regions across the central and eastern Mediterranean Sea. Isotope ratios differed with geographical region, likely due to baseline variations in δ13C and δ15N values. The absence of sex-specific differences suggests that within an area, all comparably sized animals likely exploit similar foraging strategies, and therefore, their susceptibility to fisheries threats will likely be similar. The isotope ratios of juveniles occupying the North East Adriatic and North Levantine basin increased with size, potentially due to increased consumption of more prey items at higher trophic levels from a more neritic source. Isotope ratios of juveniles with access to both neritic and oceanic habitats did not differ with size which is consistent with them consuming prey items from both habitats interchangeably. With foraging habitats exploited differently among size classes in a population, the susceptibility to fisheries interactions will likely differ with size; therefore, region-specific management approaches will be needed. [ABSTRACT FROM AUTHOR]