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• Omnivory is a key consumer parameter that should be quantified in soil food webs. • Soil food web connections to aboveground and aquatic networks need more attention. • Cross-ecosystem fluxes via soil-borne insects and to vertebrates are understudied. • New methods facilitate understanding of soil food webs as an open ecosystem pool. Soil food webs were long considered an ecosystem sink for primary production and a black box of reticulated interactions. Quantification of multiple and changing interactions among consumers and resources within and beyond soil food webs stands up as a major challenge. In this mini-review/opinion paper, I present development of ideas on soil food-web structure focusing on resource omnivory – a central characteristic that is linked to food-web structure and stability. There is plenty of empirical evidence for trophic differentiation among soil invertebrates along different food-web dimensions (food resources, trophic levels, microhabitats, time). This comes along with the pervasive idea of widespread omnivory in soil food webs. I argue that we need to quantitatively assess multiple-resource feeding by soil consumers and related drivers across various taxa and different ecosystem types to come closer to predictions of soil food-web structure and dynamics. At the meta-ecosystem level, cross-ecosystem omnivory (i.e. feeding across energy fluxes from different ecosystems) plays an important role in connecting soil with aboveground and aquatic food webs. Aboveground-belowground studies have been focusing on the interfaces such as the rhizosphere and litter surface. Broader cascading impacts of the energy and organismic fluxes across these interfaces within the recipient ecosystem are, however, less understood. Of particular interest here are connections of vertebrate communities to soil food webs and the central role of soil-borne insects in cross-ecosystem energy exchange. Interactions between soil and aquatic food webs span for dozens to hundreds of meters from the terrestrial-aquatic interface, transferring significant amount of energy and matter between these ecosystems. Consequent changes of the structure and functioning in the recipient ecosystem requires more attention, especially how biodiversity-ecosystem functioning relationships manifest across ecosystems. Continuously developing methods, such as compound-specific isotopic analyses, can facilitate quantification of cross-ecosystem omnivory, helping to understand effects of food-web changes across the ecosystem borders. Overall, I present soil food webs as an open and dynamic pool with multiple cross-ecosystem connections and call for quantitative studies in this direction. [ABSTRACT FROM AUTHOR]

In temperate ecosystems, resource availability fluctuates seasonally due to changes in environmental conditions and productivity. Intra‐ and inter‐specific trophic niche overlap under resource limitation is a measure of competitive interactions and influences species coexistence and community dynamics, but patterns of this overlap are influenced by anthropogenic activities. To investigate seasonal trophic niche dynamics of coexisting fish species in a flow‐altered river, we analysed prey resources, stomach content samples and stable isotope signatures of mottled sculpin Cottus bairdii and juvenile brown trout Salmo trutta in the Blue River, Colorado, USA, a high‐elevation oligotrophic river. Prey biomass (i.e. benthic macroinvertebrates) peaked in spring and declined through summer and autumn. Stomach content and stable isotope analysis results showed that diet composition of mottled sculpin and brown trout varied seasonally in response to changes in prey availability. Stomach content analysis results revealed that in autumn, both species exhibited the highest frequency of empty stomachs and expanded population trophic niches due to increased inter‐individual diet variation despite decreased individual trophic niche breadth. Inter‐specific trophic niche overlap was relatively high across all seasons, but the lowest degree of overlap occurred in autumn of both years when prey availability was lowest. Isotopic analysis revealed similar trends to stomach content analysis, of wider isotopic niches and reduced overlap in autumn compared to spring. Our data indicated that seasonal variation affected individual‐ and population‐level trophic niche dynamics and inter‐specific niche overlap between mottled sculpin and brown trout. This trophic segregation under resource limitation may serve as a mechanism that facilitates species coexistence in a flow‐regulated, oligotrophic river. [ABSTRACT FROM AUTHOR]

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ13C and δ15N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ13C and δ15N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem. [ABSTRACT FROM AUTHOR]

Cold‐water lakes situated in high latitudes and altitudes have pivotal socio‐ecological importance both globally and locally. However, they are increasingly threatened by multiple anthropogenic stressors, such as climate change, hydropower and invasive species. The development of efficient management strategies is therefore urgently needed and requires a comprehensive understanding of the factors influencing the biodiversity and ecological processes of these ecosystems. We provide a holistic knowledge base for informed future research and management by addressing the interplay between local and global environmental drivers of food webs in Arctic charr (Salvelinus alpinus, Salmonidae) and brown trout (Salmo trutta, Salmonidae) dominated cold‐water lakes in Fennoscandia. The trophic niche and population dynamics of these generalist top consumers provide extensive insights into the effects of natural and anthropogenic drivers on food webs in intensively studied Fennoscandian cold‐water lakes, covering marked biogeographical gradients in abiotic and biotic conditions. Drawing on a synthesis of existing literature, our focus is on three pivotal drivers: (1) lake location and connectivity, (2) lake area and morphometry and (3) fish community composition. These drivers significantly influence the complexity and the origin and flow of energy in lake food webs, and ultimately the size structure of the charr and trout populations. Furthermore, we highlight ongoing environmental changes in Fennoscandian cold‐water lakes caused by hydropower and invasive species. Finally, we identify crucial knowledge gaps and propose management actions for improving the future state of Fennoscandian cold‐water lake ecosystems and their charr and trout populations. [ABSTRACT FROM AUTHOR]

Soil food webs were long considered an ecosystem sink for primary production and a black box of reticulated interactions. Quantification of multiple and changing interactions among consumers and resources within and beyond soil food webs stands up as a major challenge. In this mini-review/opinion paper, I present development of ideas on soil food-web structure focusing on resource omnivory – a central characteristic that is linked to food-web structure and stability. There is plenty of empirical evidence for trophic differentiation among soil invertebrates along different food-web dimensions (food resources, trophic levels, microhabitats, time). This comes along with the pervasive idea of widespread omnivory in soil food webs. I argue that we need to quantitatively assess multiple-resource feeding by soil consumers and related drivers across various taxa and different ecosystem types to come closer to predictions of soil food-web structure and dynamics. At the meta-ecosystem level, cross-ecosystem omnivory (i.e. feeding across energy fluxes from different ecosystems) plays an important role in connecting soil with aboveground and aquatic food webs. Aboveground-belowground studies have been focusing on the interfaces such as the rhizosphere and litter surface. Broader cascading impacts of the energy and organismic fluxes across these interfaces within the recipient ecosystem are, however, less understood. Of particular interest here are connections of vertebrate communities to soil food webs and the central role of soil-borne insects in cross-ecosystem energy exchange. Interactions between soil and aquatic food webs span for dozens to hundreds of meters from the terrestrial-aquatic interface, transferring significant amount of energy and matter between these ecosystems. Consequent changes of the structure and functioning in the recipient ecosystem requires more attention, especially how biodiversity-ecosystem functioning relationships manifest across ecosystems. Continuously developing methods, such as compound-specific isotopic analyses, can facilitate quantification of cross-ecosystem omnivory, helping to understand effects of food-web changes across the ecosystem borders. Overall, I present soil food webs as an open and dynamic pool with multiple cross-ecosystem connections and call for quantitative studies in this direction.

Abstract Knowing what the highest-level mammalian carnivores and intermediate levels eat throughout the geography and how human activities may affect their community dynamics is relevant information to focusing and deciding on conservation efforts within a territory. In this review, we characterize geographically the accumulated knowledge about the trophic niche of terrestrial mammalian carnivore species and evaluate the spatial relationship between the species richness distribution and the geographical distribution of their trophic knowledge in Chile. We found 88 peer-reviewed papers that include trophic studies per se, theses, and short notes carried out in Chile, where at least one trophic element was reported for terrestrial mammalian carnivore species. We found a positive relationship between the species richness distribution pattern and the spatial distribution of accumulated trophic knowledge, i.e., most of the papers have been conducted in Central-southern Chile (Central Chile and Temperate Forest ecoregions) responding to the highest co-occurrence of carnivore species within the limits of the biodiversity hotspot, the most threatened area in the country. Despite this general relationship, we recognize gaps in knowledge regarding regions of the country that require more research effort, such as O’Higgins, Maule, and Ñuble regions, as well as focus efforts on certain species with no or almost no knowledge of their trophic ecology, such as Leopardus colocola, Lyncodon patagonicus and Conepatus chinga. Except for the northern Chilean ecosystems, there is a generalized report of high consumption of exotic mammals in the diet of carnivores in the center and south of the country. However, of the 98 localities recognized in the 88 papers, 20.4% correspond to an anthropized environment, while most (79.6%) correspond to a “non-anthropized” environment or protected area. We hope this review allows researchers and decision-makers to consider the knowledge and lack thereof of carnivore trophic interactions as an opportunity to conserve entire natural communities throughout the Chilean territory.

In the Atlantic Arctic, bowhead whales (Balaena mysticetus) were nearly exterminated by European whalers between the seventeenth and nineteenth centuries. The collapse of the East Greenland–Svalbard–Barents Sea population, from an estimated 50 000 to a few hundred individuals, drastically reduced predation on mesozooplankton. Here, we tested the hypothesis that this event strongly favoured the demography of the little auk (Alle alle), a zooplanktivorous feeder competitor of bowhead whales and the most abundant seabird in the Arctic. To estimate the effect of bowhead whaling on little auk abundance, we modelled the trophic niche overlap between the two species using deterministic simulations of mesozooplankton spatial distribution. We estimated that bowhead whaling could have led to a 70% increase in northeast Atlantic Arctic little auk populations, from 2.8 to 4.8 million breeding pairs. While corresponding to a major population increase, this is far less than predicted by previous studies. Our study illustrates how a trophic shift can result from the near extirpation of a marine megafauna species, and the methodological framework we developed opens up new opportunities for marine trophic modelling. [ABSTRACT FROM AUTHOR]

Knowing what the highest-level mammalian carnivores and intermediate levels eat throughout the geography and how human activities may affect their community dynamics is relevant information to focusing and deciding on conservation efforts within a territory. In this review, we characterize geographically the accumulated knowledge about the trophic niche of terrestrial mammalian carnivore species and evaluate the spatial relationship between the species richness distribution and the geographical distribution of their trophic knowledge in Chile. We found 88 peer-reviewed papers that include trophic studies per se, theses, and short notes carried out in Chile, where at least one trophic element was reported for terrestrial mammalian carnivore species. We found a positive relationship between the species richness distribution pattern and the spatial distribution of accumulated trophic knowledge, i.e., most of the papers have been conducted in Central-southern Chile (Central Chile and Temperate Forest ecoregions) responding to the highest co-occurrence of carnivore species within the limits of the biodiversity hotspot, the most threatened area in the country. Despite this general relationship, we recognize gaps in knowledge regarding regions of the country that require more research effort, such as O'Higgins, Maule, and Ñuble regions, as well as focus efforts on certain species with no or almost no knowledge of their trophic ecology, such as Leopardus colocola, Lyncodon patagonicus and Conepatus chinga. Except for the northern Chilean ecosystems, there is a generalized report of high consumption of exotic mammals in the diet of carnivores in the center and south of the country. However, of the 98 localities recognized in the 88 papers, 20.4% correspond to an anthropized environment, while most (79.6%) correspond to a "non-anthropized" environment or protected area. We hope this review allows researchers and decision-makers to consider the knowledge and lack thereof of carnivore trophic interactions as an opportunity to conserve entire natural communities throughout the Chilean territory. [ABSTRACT FROM AUTHOR]

Simple Summary: Investigating the dietary preferences and ecological niche characteristics of mammals can reveal their adaptive strategies under environmental changes, as well as the interrelationships and coexistence mechanisms among coexisting sympatric species. In this study, we analyzed the stomach contents of three coexisting rodents commonly found in the Meili Snow Mountain, Yunnan Province, China, using DNA metabarcoding technology to elucidate their food composition and diversity. The results revealed that, despite the presence of ecotope overlap, the three species were clearly separated in terms of their main food sources, suggesting that they may coexist in the same habitat by using different proportions and types of food to minimize interspecific food competition. Understanding the dietary preferences and ecological niche characteristics of mammals not only reveals their adaptive strategies under environmental changes but also reveals the interspecific relationships and coexistence mechanisms among sympatric species. Nevertheless, such data are scarce for rodents inhabiting areas spanning a wide altitude range. This study employed DNA metabarcoding technology to analyze the stomach contents of Apodemus ilex, Apodemus chevrieri, and Niviventer confucianus, aiming to investigate their dietary compositions and diversity in the Meili Snow Mountain in Yunnan Province, China. Levins's and Pianka's indices were used to compare the interspecific niche breadth and niche overlaps. The results revealed the following: (1) Insecta (relative abundance: 59.4–78.4%) and Clitellata (relative abundance: 5.2–25.5%) were the primary animal food sources for the three species, while Magnoliopsida (relative abundance: 90.3–99.9%) constitutes their main plant food source. Considerable interspecific differences were detected in the relative abundance of primary animal and plant foods among the three species; (2) There was partial overlap in the genus-level animal food between A. ilex and N. confucianus (Ojk = 0.4648), and partial overlap in plant food between A. ilex and A. chevrieri (Ojk = 0.3418). However, no overlap exists between A. chevrieri and N. confucianus, either in animal or plant food; (3) There were no significant interspecific differences in the α-diversity of animal and plant foods among the three species. The feeding strategies and ecological niche variations of these rodents support the niche differentiation hypothesis, indicating that they have diversified in their primary food sources. This diversification may be a strategy to reduce competition and achieve long-term coexistence by adjusting the types and proportions of primary foods consumed. [ABSTRACT FROM AUTHOR]

Yellow-phase Japanese eel Anguilla japonica (Temminck & Schlegel, 1846) utilize a variety of anthropogenically impacted habitats. An extensive understanding of the trophic ecology and habitat use is necessary for the conservation of this endangered species. In this study, we analysed the trophic ecology and feeding habitat of Japanese eels in two small rivers, the Akugawa River and Takase River in Wakayama Prefecture, Japan, dominated by an urban landscape and agricultural land use, respectively. The main goals were to assess the dietary diversity and trophic niche width for eels of two size classes (small eels: ≤ 240 mm total length, large eels: > 240 mm total length) in both habitats. The suitability of both rivers as a feeding habitat for eels was also evaluated. The trophic ecology of eels was inferred based on analysis of carbon and nitrogen stable isotopes, as well as stomach contents. Our results indicated that both rivers are suitable habitats to accommodate this eel, but to varying degrees. The dietary diversity of small eels and trophic niche width differed between rivers, indicating limiting factors, such as insufficient food sources and unfavourable abiotic habitat requirements for small eels in urban rivers. Also, the body condition of eels was found to be lower in the urban Akugawa River than in the Takase River. [ABSTRACT FROM AUTHOR]

Understanding the strength, direction and consequences of the trophic impacts of invasive fish on functionally analogous native fishes is important in invasion impact assessment and for informing management programmes. As functionally analogous native and invasive fishes can share prey resources, there is high potential for competitive interactions, which could affect trophic niche sizes and positions.The highly invasive mrigal carp Cirrhinus mrigala and native mud carp Cirrhinus molitorella now co‐exist in many freshwaters in southern China, raising concern on the consequences for mud carp. The trophic interactions of the two species and their consequences (for growth rates and trophic niche sizes as the isotopic niche, calculated using δ13C and δ15N) were tested in a pond enclosure experiment based on additive and substitutive treatments using fish in allopatric and sympatric contexts, with results compared with invaded wild communities.In the experiment, specific growth rates decreased significantly as fish abundance in treatments increased. These density‐dependent effects were observed in both species and were independent of whether the treatment was allopatric or sympatric. In allopatric treatments, isotopic niches of mud carp increased in size with fish number. Conversely, in sympatric treatments, mud carp isotopic niche size decreased with increased mrigal carp number. For mrigal carp, isotopic niche sizes decreased as fish number increased in both allopatric and sympatric treatments.In sympatric experiment treatments, the isotopic niches of mud carp and mrigal carp were always divergent. This was, however, in contrast to four invaded wild communities, where the isotopic niches of the two fishes always had some overlap.Experimental and field data suggest that although native mud carp could be impacted by mrigal carp, these impacts might only manifest when the species are at very high abundances and inter‐specific competitive interactions could be intense. These results also suggest the two species have mechanisms that reduce their inter‐specific interactions to minimise their competitive interactions, thus any ecological impacts from mrigal carp might manifest more from indirect than direct processes. [ABSTRACT FROM AUTHOR]

In order to have a deep understanding of the role of ocean squid in Northwest Pacific Ocean food web, samples were collected during the comprehensive scientific survey launched by the Ministry of Agriculture and Rural Affairs in 2021 and 2022. Carbon and nitrogen stable isotope technology was used to analyze the muscle stable isotopes and nutritional niches of two cephalopod species, Ommastrephes bartramii and Onychoteuthis borealijaponicus, in Northwest Pacific Ocean. The results show that O. bartramii δ13C and δ15N values between sites were significantly different. O. borealijaponicus δ13C values between the two sites showed significant differences, while the δ15N values were not significant. Muscle δ13C and δ15N values between O. bartramii and O. borealijaponicus showed significant differences. During ontogeny, the δ13C and δ15N values of O. bartramii and O. borealijaponicus were not significantly associated with carcass length. The nutrient niche width of O. bartramii (SEAc=0.35‰²) is greater than that of O. borealijaponicus (SEAc= 0.20‰²), with a moderate overlap between the two squids (0.314) . The high niche overlap between males and females is 0.988 and 0.76, respectively. The analysis shows that the δ13C values of O. bartramii and O. borealijaponicus are influenced by SST and feeding effects, while the δ15N values are influenced by feeding effects. The utilization of food and habitat resources was highly similar in both female and male cephalopod groups. [ABSTRACT FROM AUTHOR]

Niche partitioning is a common strategy species use to avoid competition for limited resources, allowing them to coexist. Rodent species often reduce competition by spatial segregation and trophic differentiation, but behavioural differences, particularly related to foraging, can also be important. Therefore, temporal segregation can also be an important mechanism for species coexistence, as it helps them avoid sub‐optimal habitats. We found three rodent species (the native Octodon degus and O. lunatus, and the exotic Rattus rattus) foraging on endemic palm Jubaea chilensis seeds, a highly valuable but limited resource. We hypothesized that these rodent species could coexist by segregating foraging in time, showing behavioural differences. To test this, we used camera traps to monitor the fate of J. chilensis seeds and rodent activity at 25 feeding stations. From 596 photographic records, we identified 128 as O. degus, 232 as O. lunatus and 236 as R. rattus. Octodon degus had a diurnal activity, while O. lunatus and R. rattus were nocturnal, showing significant temporal segregation. However, we found no spatial association among these rodents. We found significant behavioural differences in decision and handling times and seed removal rates, with O. degus having the greatest seed removal rate. Nevertheless, we found some nocturnal O. degus records in which the three rodent species were co‐foraging, which may suggest that the resource is limited but valuable enough to shift from exploitation to interference competition. Our results suggest that temporal and behavioural differentiation are more important than spatial segregation and trophic differentiation. Thus, niche partition over multiple dimensions might allow for species coexistence. [ABSTRACT FROM AUTHOR]

Feeding habits of herbivorous fishes play an important role in shaping the form and function of coastal marine ecosystems. Rabbitfishes (Siganidae) are important consumers of macroalgae on Indo‐West Pacific coral reefs. However, it is unclear how their diet varies among and within species at biogeographical scales, casting doubt on their precise functional roles across different regions. The present study assessed the inter‐ and intra‐specific diet variation of four rabbitfishes (Siganus trispilos, Siganus corallinus, Siganus virgatus and Siganus doliatus) factored by morphological relatedness among populations from Ningaloo Reef (western Australia), the Great Barrier Reef (GBR, eastern Australia) and the Yaeyama Islands (Okinawa Prefecture, Japan). Results showed that the region had a strong effect on diet, effectively reducing the expected effect of morphologic similitude. While intra‐specific differences were only significant when populations inhabited different regions; interspecific differences were not as predicted, with different morphotypes having similar diets when populations inhabited the same regions. Rabbitfishes consumed more corticated and filamentous macroalgae on the GBR, more foliose and membranous macroalgae at the Yaeyama Islands, and more leathery macroalgae at Ningaloo Reef. The findings indicate that rabbitfishes have high diet plasticity, and hence their functional role as mediators of competition between macroalgae and corals can change across biogeographic regions. Local context is therefore important when assessing the diet and functional role of herbivorous fishes. As climate change unfolds, shifts in the distribution, trophic behaviour and function of species are expected, making the study of trophic plasticity more important. [ABSTRACT FROM AUTHOR]

Understanding consumer–resource interactions is essential for understanding the trophic dynamics of species-rich fish communities. Woodland et al. (Oikos 125:556–565, 2016) assumed that trophic position (TP) distributions of primary consumers and tertiary species are restricted versus intermediate consumers tending to be omnivores with broader TP distribution, where these omnivores often dominate the overall biomass. With rare evidence supporting this hypothesis in a river, we tested it in the species-rich Pearl River fish assemblage, China. Using bulk stable isotope (SI) approach (δ13C, δ15N), the TPs, SI distribution parameters, isotopic niche sizes (as standard ellipse areas, SEA) and interspecific niche overlap were calculated for the abundant fish species. Fishes of intermediate TPs (i.e. omnivores) had larger δ13C variance/ range, broader isotopic niches and higher niche overlap compared to fishes at low TPs and high TPs, indicating a higher degree of trophic redundancy among the omnivores, whereas high TP fish had narrower niche and lower niche overlap, indicating trophic partitioning among tertiary species. These omnivores at intermediate TPs between 2.4 and 2.8 dominated fish biomass. The results not only support the Woodland et al. (Oikos 125:556–565, 2016) hypothesis in the river, but also provide a novel explaining in how niche sizes and overlap vary by TP. [ABSTRACT FROM AUTHOR]

The feeding behavior and trophic niche overlap between Stone Marten (Martes foina Erxleben, 1777) and Red Fox (Vulpes vulpes Linnaeus, 1758) in two regions of Bulgaria with different human influence were determined. A total of 1,440 fecal samples were collected from agricultural area in the Upper Thracian Plain and from near-natural habitat in Central Stara Planina Mts. In agricultural area, both predators preferred fruits in all seasons, while rodents dominated in winter diets in the mountain area. Our results showed that the Stone Marten and the Red Fox had high trophic niche overlap in both habitats. [ABSTRACT FROM AUTHOR]

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Species diversity depends on the capacity of species to coexist, and when these share similar ecological requirements some degree of partitioning of the ecological niche is expected. Within the order Carnivora, direct and indirect interspecific interactions shape community structure and composition. Although strong negative interactions (e.g., interspecific killing) are expected between large carnivores and subordinate species, mesocarnivores that dominate most human disturbed landscapes can still strongly compete for resources given their similar body size and energy requirements. To identify the mechanisms of coexistence between mesocarnivore species in a Mediterranean landscape we assessed the ecological niche overlap between five species (Vulpes vulpes, Meles meles, Martes foina, Herpestes ichneumon, Genetta genetta), by simultaneously measuring the space, time, and trophic resource use. The multi-species occupancy model fit to camera-trapping data revealed spatial co-occurrence between most species’ pairs and an avoidance pattern between only stone marten and Eurasian badger (78 % probability of a negative effect). Using genetically identified scats, we assessed trophic niche breadth and overlap. Niche breadth was narrow for red fox, Eurasian badger, and stone marten, given these species consumed almost exclusively fruits and arthropods, and so trophic niche overlap was high. For the genet and the mongoose, the consumption of different food resources (e.g., mammals, birds, and reptiles) increased niche breadth and decreased the niche overlap with the other sympatric species. Finally, niche segregation was more significant along the temporal axis, since the mongoose has a diurnal activity pattern and the remaining carnivore species, although mostly nocturnal, had small asynchronies in the activity peaks which could decrease the chance of direct encounters. Therefore, our results suggest that similar habitat preferences and ecological requirements rather than interspecific competition shape the mesocarnivores’ resource use in this landscape. Nonetheless, fine-scale temporal segregation seems the main mechanism to facilitate coexistence, together with small differences in trophic resource use, especially for species with high spatial and temporal overlap.

Ceratoscopelus warmingii, a common mesopelagic fish in cold seep ecosystems, plays a crucial role in transferring energy and materials between different water layers, thereby influencing deep-sea carbon cycling and storage. In August 2023, we collected samples from four depths (75 m, 400 m, 500 m, and 600 m) in cold seep waters to analyze the trophic niche characteristics of C. warmingii using stable isotope techniques. The results indicated significant differences in δ13C and δ15N values among the water layers, with mean δ13C and δ15N values of −19.85 ‰±0.33 ‰ and 8.41 ‰±0.62 ‰, respectively. Indicators of trophic structure showed distinct vertical differentiation, with the width of the trophic niche decreasing as depth increased. At 75 m and 400 m, the consistency of CR and NR indicators and high trophic niche overlap indicated similar food sources, confirming vertical migration behavior. In contrast, at 500 m, the MNND and SDNND values suggested a more stable trophic structure, while at 600 m, changes in feeding sources pointed to a distinct population. The Standard Ellipse Area of Overlap (SEAc) was highest between 75 m and 400 m, while the divergence of trophic ecological niches at 600 m, with different food sources, suggests that cold seep ecosystems at this depth provide a relatively stable trophic structure for C. warmingii and support the formation of an independent population. In cold seep ecosystems, C. warmingii employs adaptive trophic strategies to optimize survival under varying habitat conditions at different depths. This vertical trophic differentiation reduces intraspecific competition and enhances population stability in deep-sea habitats. This study enhances our understanding of the trophic niche and vertical migration of C. warmingii in cold seep ecosystems, significantly contributing to our knowledge of biodiversity, energy flow, and material cycling in these unique environments.

1. Individual niche specialization is widespread in natural populations and has key implications for higher levels of biological organization. This phenomenon, however, has been primarily quantified in resource niche axes, overlooking individual variation in environmental associations (i.e. abiotic conditions organisms experience).2. Here, we explore what we can learn from a multidimensional perspective of individual niche specialization that integrates resource use and environmental associations into a common framework.3. By combining predictions from theory and simple simulations, we illustrate how (i) multidimensional intraspecific niche variation and (ii) the spatiotemporal context of interactions between conspecifics scale up to shape emergent patterns of the population niche.4. Contemplating individual specialization as a multidimensional, unifying concept across biotic and abiotic niche axes is a fundamental step towards bringing this concept closer to the n‐dimensional niche envisioned by Hutchinson. [ABSTRACT FROM AUTHOR]

The number of individuals to be sampled is a key element in the sampling design of any study as it directly affects the estimations and inferences made. Additionally, in cases where several replicates per individual can be taken, it is important to define how the sampling effort will be distributed between the intraindividual and interindividual components (within and between individuals, respectively). Determining how samples should be distributed among these components can help optimize the available resources and reduce bias in the estimations. To study population trophic diversity, the total niche width (TNW) is usually estimated, which is an approximation of resource diversity at the population level. TNW is the sum of the resource diversity consumed at the intraindividual (replicates) and interindividual (individuals) level. In this study, the effect of prioritizing the number of individuals or the number of replicates on the accuracy and precision of TNW estimations was tested. Multiple isotopic (δ13C and δ15N) values per individual in populations with different degree of individual specialization were simulated. Then, isotopic data from natural populations within the same species (available published studies) were used to assess the results obtained with simulated data. It was found that TNW estimations were more accurate and precise when prioritizing the number of individuals over the replicates, along the entire individual gradient of trophic specialization. Therefore, it is advisable to prioritizing the number of individuals. This methodological contribution should be considered in future studies that use repeated measures of isotopic data to estimate TNW. [ABSTRACT FROM AUTHOR]

Simple Summary: Trophic niches, as one of the important dimensions of niche theory, show the nutritional requirements of species; they can reflect their position in the ecosystem trophic level, and functional status, as well as the nutritional relationships between species. Similarities in body structure and ecological needs may lead to interspecific nutritional competition, and species may undergo niche differentiation through different foraging strategies. The body tissues of consumers contain stable isotope signatures that reflect their dietary information, and stable isotope analysis has been widely used in animal diet research. In this study, stable isotope techniques were used to assess the dietary information and nutritional niches of Sitta yunnanensis and Sitta nagaensis coexisting in Yunnan Province. S. yunnanensis and S. nagaensis mainly preyed on six orders, including Orthoptera, with overlapping food resources but different dietary ratios. Their two niches were differentiated, with S. yunnanensis having wider trophic niches. This study provides new insights into the food resources and trophic niches of S. yunnanensis and S. nagaensis, and the mechanisms behind their coexistence were consistent with the niche hypothesis. Sympatric closely related species may experience interspecific trophic competition due to ecological similarity; they may isolate in terms of diet or habitat use as a strategy to avoid competition. The body tissues of consumers contain stable isotope signatures information that can be applied to infer their dietary information. In this study, δ13C and δ15N stable isotopes were analyzed to determine the dietary information and trophic niches of sympatric coexisting Sitta yunnanensis and Sitta nagaensis. The results showed that the food sources of S. yunnanensis and S. nagaensis were from six orders, including Orthoptera, and the cumulative contribution rate was 99.97%, with the two species eating similar diets but at different rates. The larger δ13C of S. yunnanensis indicates that it had a wider range of habitats for feeding, while the difference in δ15N values was not significant (p > 0.05), indicating that both species feed on similar nutrient levels. As determined by Bayesian ellipses, the isotopic niches of S. yunnanensis and S. nagaensis were differentiated; the isotopic niche width of S. yunnanensis is 2.69‰2, which was larger than that of S. nagaensis (0.73‰2), indicates that differentiation between the two species in diet or habitat use reduced competition. Trophic niche differentiation and differences in foraging proportions may be the principal resource allocation mechanisms behind S. yunnanensis and S. nagaensis coexistence. [ABSTRACT FROM AUTHOR]

We investigated the trophic dynamics between neustonic copepod communities and particulate organic matter (POM) sourced from contrasting water masses, i.e., high- and low-salinity areas, within the northeastern East China Sea. The sampling of neustonic copepod communities occurred three times in the summer (June, August, and September) of 2021, and considered the influx of the Yangtze River Diluted Water (YRDW) and the extension of the Tsushima Warm Current (TWC). To examine the relationship between the neustonic copepods and surface POM, we employed stable isotope techniques. Surprisingly, the neustonic copepod community exhibited a reluctance to feed on surface POM. The neustonic copepod community in the YRDW-dominated area in August showed higher δ13C values than those in the TWC-dominated area. The trophic groups within the neustonic copepod population appeared to consume selectively depending on the individual preferred prey sizes and composition. Using the POM from the water masses that affected the food sources consumed by neustonic copepods, we found a strong dependence on prey items originating from the TWC. This result suggests that the marine neustonic copepod community does not rely significantly on food sources derived from riverine freshwater. [ABSTRACT FROM AUTHOR]

The rupture of the Fundão dam is considered the largest mining failure in history, which had a particularly detrimental impact on fish populations, as the mud from the ore tailings significantly altered the water quality and habitat of Doce River basin. This study aimed to assess the trophic structure of fish communities in areas impacted and not impacted by the dam rupture in the Doce River basin. To evaluate the food web structure, community-wide trophic niche, and trophic positions of fish, stable isotopes of carbon (δ13C) and nitrogen (δ15N) were utilized across ten sites (seven impacted and three control). In general, fish appeared to assimilate resources such as invertebrates, algae, and periphyton, although the importance of each resource varied among sites. The site closest to the dam rupture exhibited a more simplified trophic structure compared to the control sites and those nearer the river mouth. In this site, most fish species occupied a similar trophic position. Trophic niches also exhibited the greatest dissimilarity between the site closest to the dam failure and those farther away from it, with an expansion of trophic niche breadth observed with an increase in the distance from the dam rupture. Our study provided valuable insights into the trophic structure of fish communities within the Doce River basin, shedding light on the trophic ecology of the 59 fish species investigated. We also emphasize the importance of our study for future assessments of ore tailings dam failure disasters and evaluating the effectiveness of mitigation measures for Doce River basin recovery. [ABSTRACT FROM AUTHOR]

Abstract Feeding habits of herbivorous fishes play an important role in shaping the form and function of coastal marine ecosystems. Rabbitfishes (Siganidae) are important consumers of macroalgae on Indo‐West Pacific coral reefs. However, it is unclear how their diet varies among and within species at biogeographical scales, casting doubt on their precise functional roles across different regions. The present study assessed the inter‐ and intra‐specific diet variation of four rabbitfishes (Siganus trispilos, Siganus corallinus, Siganus virgatus and Siganus doliatus) factored by morphological relatedness among populations from Ningaloo Reef (western Australia), the Great Barrier Reef (GBR, eastern Australia) and the Yaeyama Islands (Okinawa Prefecture, Japan). Results showed that the region had a strong effect on diet, effectively reducing the expected effect of morphologic similitude. While intra‐specific differences were only significant when populations inhabited different regions; interspecific differences were not as predicted, with different morphotypes having similar diets when populations inhabited the same regions. Rabbitfishes consumed more corticated and filamentous macroalgae on the GBR, more foliose and membranous macroalgae at the Yaeyama Islands, and more leathery macroalgae at Ningaloo Reef. The findings indicate that rabbitfishes have high diet plasticity, and hence their functional role as mediators of competition between macroalgae and corals can change across biogeographic regions. Local context is therefore important when assessing the diet and functional role of herbivorous fishes. As climate change unfolds, shifts in the distribution, trophic behaviour and function of species are expected, making the study of trophic plasticity more important.

Urbanization dramatically alters the ecological landscape, posing strong and novel challenge to wild animals. Although the behavioural adaptations of wildlife to urbanization have been well documented, the activity time budget and feeding habits of tree squirrels in Afro-tropical cities have received considerably limited investigations. Here, we studied the activity budget, feeding habits and habitat use by the Gambian sun squirrel (Heliosciurus gambianus) on the University of Ghana, Legon main campus in Accra, Ghana. Data was collected from December 2021 to July 2022 using focal sampling. We found that the activity pattern of H. gambianus was bimodal, with peaks in the mornings and evenings. Their activity budget composed largely of feeding (43.8%), foraging (23.1%) and observing (12.5%). Although the squirrels' activities were higher in the dry season, there was no significant difference between their activity budget in the dry and wet seasons. The Gambian sun squirrels consumed flowers, fruits/seeds and young leaves from 11 (six local and five exotic) tree species, but their diet composition varied seasonally. The squirrels used areas with high density or linear strip of tall trees (≥ 3.5 m) with overlapping canopies that enabled arboreal movement as they rarely used the ground. They nested in tree hollows and attic of buildings. Our study provides the first systematic data on the activity budget, feeding habits and habitat use of H. gambianus in a West African city and University campus. Our data can inform urban land-use planning and effective conservation of urban habitats and tree squirrels in Afro-tropical cities. [ABSTRACT FROM AUTHOR]

The spread of non-native species is one of the outcomes of global change, threatening many native communities through predation and competition. Freshwater ecosystems are particularly affected by species turnover with non-native species. One species that has been established in Central Europe for many decades - or even a few centuries - is the amphipod crustacean Gammarus roeselii. Although G. roeselii is nowadays widespread in major river systems, there have been recent reports of its spread into smaller streams that are typically inhabited by the native species Gammarus fossarum. Due to their leaf shredding ability, G. fossarum takes up a key position in headwater streams. This raises the important question, to what extent G. roeselii can equivalently take over this function. To answer this question, we collected both species from nine different sites in a mid-mountain river system (Kinzig catchment, Hesse, Germany) and investigated their functional similarity using a combination of stable isotope analysis, gut content and functional morphology. The species hardly differed in morphological characteristics, only females showed differences in some traits. Gut content analysis indicated a broad dietary overlap, while stable isotopes showed a higher trophic position of G. roeselii. The observed functional overlap could intensify interspecific competition and allow the larger and more predaceous G. roeselii to replace G. fossarum in the future as a headwater keystone species. However, the differentiation in the stable isotopes also shows that co-existence can occur by occupying different trophic niches. Moreover, the wide range of inhabited sites and exploited resources demonstrate the omnivorous lifestyle of G. roeselii, which is likely to help the species succeed in rapidly changing environments. [ABSTRACT FROM AUTHOR]

The trophic niche of aquatic generalist predators is influenced by ontogeny, habitat characteristics, availability and type of prey, and competitive interactions. Many interrelated lake characteristics influence the availability of prey and may thereby impact foraging niches and the trajectory of ontogenetic niche shifts. Our work uses Eurasian perch (Perca fluviatilis) as a model species to examine the correlation of multiple lake and fish community characteristics with the size‐dependency of perch populations' realised trophic niche. We used carbon and nitrogen stable isotopes to correlate the changes in perch trophic position across a gradient of total lengths in seven gravel pit lakes that differed in lake morphology, habitat heterogeneity, productivity, structural complexity, and fish community composition. Perch populations in lakes with more shallow‐water habitat reached a higher trophic position at smaller sizes than perch in deeper lakes. However, the changes in trophic position with increasing size were less pronounced compared to perch from deeper lakes. Large individuals from the latter perch populations ultimately achieved higher mean trophic positions compared to fish from shallow lakes. Perch in lakes with more shallow‐water habitat may, therefore, achieve lower rates of piscivory because of higher relative availability of macroinvertebrates or greater competition with zooplanktivores. Our results suggest that large, piscivorous perch are more likely to develop in deeper lakes, and that these changes in perch trophic position across ontogeny are more strongly related to the depth of lakes than to the type of structured habitat in the littoral zone. [ABSTRACT FROM AUTHOR]

Arsenic (As) is a toxic environmental contaminant with global public health concern. In aquatic ecosystems, the quantification of total As is restricted chiefly to the individual organisms. The present study has quantified the total As in different trophic layers (sediment–water-phytoplankton-periphyton-zooplankton-fish-gastropod-hydrophytes) of lentic freshwater ecosystems. As transfer pathways quantifying the transmission rate across trophic-level compartmental route were delineated using a novel model-based approach along with its potential contamination risk to humans. Lentic water bodies from Indo-Gangetic region, a core area of groundwater As, were selected for the present investigation. The study revealed that among the lower biota, zooplankton were the highest accumulator of total As (5554–11,564 µg kg−1) with magnification (rate = 1.129) of the metalloid, followed by phytoplankton (2579–6865 µg kg−1) and periphytic biofilm (1075 to 4382 µg kg −1). Muscle tissue of zooplanktivore Labeo catla is found to store higher As (80–115 µg kg−1 w.w.) compared to bottom-dwelling omnivore Cirrhinus mrigala (58–92 µg kg−1 w.w.). Whereas, Amblypharyngodon mola has accumulated higher As (203–319 µg kg−1 w.w.) than Puntius sophore (30–98 µg kg−1 w.w.) that raised further concern. The hepatic concentration indicated arsenic-mediated stress based on As stress index (threshold value = 1). Mrigal and Mola showed significant biomagnification among fishes while biodiminution was observed in Catla, Bata, Rohu and Punti. All the studied fishes were under the arsenic mediated stress. In the 'sediment–water-periphytic biofilm-gastropod' compartment, the direct grazing accumulation was higher (rate = 0.618) than the indirect path (rate = 0.587). Stems of edible freshwater macrophytes accumulated lesser As (32–190 µg kg−1 d.w.) than roots (292–946 µg kg−1 d.w.) and leaves (62–231 µg kg−1 d.w.). The target cancer risk (TCR) revealed a greater concern for adults consuming edible macrophyte regularly. Similarly, the varied level of target hazard quotient and TCR for adults consuming fishes from these waterbodies further speculated significant health concerns. The trophic transfer rate of environmental As in soil–water-biota level at an increasing trophic guild and consumer risk analysis have been unravelled for the first time in the Indo-Gangetic plains, which will be helpful for the strategic mitigation of As contamination. [ABSTRACT FROM AUTHOR]

Competition arises when species share a limited resource, but this can be avoided through niche partitioning. Despite the large body of literature on diadromous fishes, very few studies have focused on niche partitioning when competing for resources. Diadromous fishes are suffering a global decline throughout their range in part due to their peculiar life history traits as they migrate from the sea to freshwater to spawn or the reverse. They are particularly sensitive to river fragmentation induced by barriers. Dams for instance are expected to alter the spatial distribution and resource exploitation of diadromous fishes as well as other organisms. Here, we studied the ecological niche of six taxa of diadromous fishes, temporally co-occurring in the same land-sea continuum obstructed by two river dams. We used Bayesian mixing models run on C and N isotopes to infer the various habitats used and the origin of the trophic carbon in muscle and scale tissues of diadromous fishes. Results showed that the sub-adults of Anguilla anguilla, juveniles of Petromyzon marinus, and Salmo trutta exploit mainly the freshwater, or marine part for adults of Lampetra fluviatilis, whereas juveniles of Platichthys flesus and Mugilidae use all the habitats of the land-sea continuum. In the freshwater habitat, the microphytobenthos and biofilm are the main sources of carbon used, while in the marine habitat, the basal carbon sources are more diverse. The analyses of niche overlaps between diadromous fishes demonstrate that the widest isotopic niches, observed for A. anguilla and P. flesus, also have more impact within the community. Results are discussed in terms of intra- and interspecific competition between these diadromous fishes and their generalist/specialist strategies in an obstructed catchment. [ABSTRACT FROM AUTHOR]

We here present the first study on the consumed prey by an epigean population of the Italian cave salamander (Speleomantes italicus) from the Republic of San Marino. Using the harmless technique of stomach flushing, we aimed to provide the first data on the diet and on the degree of individual specialization that characterizes the studied population. We performed two-night surveys (one in autumn 2022 and one in spring 2023) in which we opportunistically searched for salamanders in forested areas and dry walls. Captured salamanders were sexed, weighed, photographed, measured and stomach flushed. Overall, we inspected the stomach contents of 67 individuals, recognizing 1,018 prey items belonging to 28 different prey categories. The examined population was mainly composed by generalist individuals, and no differences in number and diversity of prey consumed were observed among salamanders. Contrarily to what has been observed in other Speleomantes species, flying prey provided a minor contribution to the diet of the investigated population. Our study produced the first information on the diet of Speleomantes italicus from the Republic of San Marino, representing the starting point for future assessments on the dietary habits of this specific population. [ABSTRACT FROM AUTHOR]

Diet is one of the most important dimensions of the trophic niche, contributing to understanding intra- and interspecific interactions in food webs. Amazophrynella teko was described in 2018, and given the scarcity of information about its feeding ecology, we describe here the diet of this species in a population from eastern Amazonia based on stomach flushing. We analyzed the stomach contents of 68 A. teko (18 juveniles, 13 females, and 37 males). We found 360 prey items from 23 prey categories from males (Shannon-Wiener index: H’ = 2.36, N = 29), 17 for females (H’ = 1.53, N = 12), and 14 for juveniles (H’ = 2.35, N = 11). Formicidae were the most abundant prey items (284 prey items), Myrmicinae were the most abundant subfamily, and Crematogaster was the most abundant genus in all age/sex groups. Females had a narrower niche amplitude (BA = 0.08) than juveniles (BA = 0.58) and males (BA = 0.21). Trophic niche overlap between males and females (Ojk = 0.92), and between males and juveniles (Ojk = 0.77), higher than the overlap between females and juveniles (Ojk = 0.55). The prey category accumulation curve, in relation to the number of stomachs flushed, did not reach an asymptote. The relationship between the SVL and JW of the toads with the volume of prey was not significant for males, females, and juveniles. The larger jaw width of females observed in our study may be related to the greater volume of prey they consumed. There were no significant differences among the diets for males, females, and juveniles based on the volumetric composition of prey. Amazophrynella teko feeds largely on ants but opportunistically will forage on other invertebrates such as spiders, beetles, and mites. The present study provides relevant information about the feeding ecology of A. teko, a poorly known species from north Brazil, eastern Brazilian Amazonia. [ABSTRACT FROM AUTHOR]

The Wanshan Archipelago, situated in the Pearl River Estuary, stood as a key fishing ground in China, boasting abundant fishery resources. To investigate variations in trophic niches and food sources among different islands within the Wanshan Archipelago, and to advance research on fish food webs and energy flow in the Pearl River Estuary, this study conducted a survey of fish communities in nearshore islands (Guishan Island, Dongao Island) and offshore islands (Wailingding Island, Wanshan Island) using triple gill nets during the autumn of 2021. The trophic niche characteristics of fishery organisms in these islands were analyzed utilizing carbon and nitrogen stable isotope technology. The results indicated that trophic niche width and biodiversity of fish communities in the nearshore islands surpassed those in the offshore islands, and the food chain length exhibited a trend of Guishan Island (4.04) > Dongao Island (3.98) > Wanshan Island (3.91) > Wailingding Island (3.86). The trophic niche indexes (CR, NR, CD, and SEAc) of fish communities in nearshore islands were higher compared to those on offshore islands, while MNND and SDNND suggested that fish communities in offshore islands were at a lower trophic level. Zooplankton emerged as the primary food source for fishery organisms in the Wanshan Archipelago. Feeding rates on zooplankton were 68.8 % and 70.4 % in Guishan Island and Dongao Island, and 53.7 % and 58.0 % in Wailingding Island and Wanshan Island, respectively. The proportion of benthic organisms fed near offshore islands was higher than nearshore islands. This study speculated that the fish in nearshore islands may shift from zooplankton food chain to benthic food chain. In addition, this study compared the trophic niche differences among the four islands in the Pearl River Estuary, clarified the diversity of feeding sources and trophic structure within fish communities, and revealed significant distinctions in fish food webs between the islands inside and outside the Pearl River Estuary. It will provide new information on the trophic interactions of fish in the Pearl River Estuary, and help to promote the ecological development and sustainable use of fishery resources.

Abstract Freshwater fishery resources in Chinese rivers have been markedly impaired as the results of overfishing, damming, and watershed development. However, little is known about trophic ecology of fish assemblages in the rivers of China. In this study, fishes were collected from an upstream, midstream, and downstream site of the Moyangjiang River, Southern China, to investigate trophic niche structure using stable isotope analysis. We calculated several trophic niche metrics using δ13C and δ15N ratios of the fish assemblages at each study site. Results showed no significant differences in the δ13C ratios between the pelagic and benthic fish assemblages at each study site. This suggests a homogenous dietary base shared by all fish at each site, likely as the result of continuous water column mixing in this shallow and fast‐moving river. The upstream fish assemblage had the greatest species abundance and trophic diversity. The fish assemblage at the midstream site displayed the smallest trophic niche space (total area of the δ13C and δ15N bi‐plot space) and trophic diversity. The midstream site also showed the most depleted 13C, suggesting a more degraded habitat compared with the other two study sites. The fish assemblages at the downstream site displayed the greatest basal resource diversity, largest CR, and trophic niche space and trophic diversity. However, the fish assemblage at the downstream site also displayed the lowest species abundance, redundancy, and evenness of trophic spacing. These findings suggest that the trophic niche of the fish assemblage at the downstream site, which received resources from upstream flow, experienced greater watershed development and greater in situ production, demonstrating positive and negative impacts by anthropogenic activities. Future studies should also gather information on fish production, watershed development, and water quality, to aid in the interpretation of the stable isotope analysis of fish trophic niches.

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.

Documenting long‐term changes in the trophic structure of food webs and how species respond to these changes is essential to forecast their vulnerability and resilience to environmental stressors. Over the past decades, the St. Lawrence marine ecosystem (Canada) has experienced major changes in its physical, chemical, and biological conditions from overfishing, acoustic and chemical pollution, climate change, and the increased abundance of some top predators. These changes have likely affected the trophodynamics of the ecosystem, and are suspected to have deleterious effects on endangered species of mammals and other components of the ecosystem, such as blue whales (Balaenoptera musculus), fin whales (B. physalus), and beluga (Delphinapterus leucas). This study examined the trophic structure of the St. Lawrence marine ecosystem, including the isotopic niche of various species, over two periods of contrasting pressures from anthropogenic and climatic stressors (1995–2003 vs. 2019–2021). Stable isotope ratios were measured in 1240 samples of 21 species of marine invertebrates, fishes, and mammals sampled during both periods. A significant change in the isotopic value and niche position between periods is observed in most of the sampled species. While the direction of change and effect size were not uniform among species, these changes confirmed that substantial modifications in community structure have occurred over time. Niche overlap decreased considerably among some of the pelagic and demersal fishes, and among whale species during the most recent period. Combined with a concomitant reduction in niche breadth in several species, these observations suggested that resource sharing was limited among these species. This study highlighted some degree of dietary plasticity in several species, and a long‐term change in the trophic structure of the St. Lawrence marine ecosystem, with likely effects on diet composition and energetics of several populations, including endangered species. [ABSTRACT FROM AUTHOR]

Forest canopies maintain a high proportion of arthropod diversity. The drivers that structure these communities, however, are poorly understood. Therefore, integrative research connecting tree species identity and environmental stand properties with taxonomic and functional community composition of canopy arthropods is required. In this study, we investigated how the taxonomic, functional and trophic composition of arboreal spider communities is affected by tree species composition and associated differences in canopy structure and prey availability in temperate forests. We sampled canopy spiders as well as their potential prey using insecticidal fogging in monospecific and mixed stands of native European beech, native Norway spruce and non-native Douglas fir. Trophic metrics were obtained from stable isotope analysis and structural canopy properties were assessed with mobile laser scanning. Monospecific native spruce stands promoted local canopy spider abundance and diversity, but native beech and beech–conifer mixtures had the highest diversity at landscape scale. Spider community composition differed between monospecific stands, with broadleaf–conifer mixtures mitigating these differences. Irrespective of tree species identity, spider abundance, taxonomic diversity, functional richness and isotopic richness increased in structurally heterogeneous canopies with high prey abundances, but functional evenness and trophic divergence decreased. Our study shows that canopy spiders are differentially affected by tree species identity, canopy structure and prey availability. Broadleaf–conifer mixtures mitigated negative effects of (non-native) conifers, but positive mixture effects were only evident at the landscape scale. Structurally heterogeneous canopies promoted the dominance of only specific trait clusters. This indicates that intermediate heterogeneity might result in high stability of ecological communities. [ABSTRACT FROM AUTHOR]

Species‐rich communities exhibit higher levels of ecosystem functioning compared with species‐poor ones, and this positive relationship strengthens over time. One proposed explanation for this phenomenon is the reduction of niche overlap among plants or animals, which corresponds to increased complementarity and reduced competition.In order to examine the potential of increased complementarity among plants or animals to strengthen the relationship between diversity and ecosystem functions, we integrated models of bio‐energetic population dynamics and food‐web assembly. Through the simulation of various scenarios of plant and animal complementarity change, we sought to elucidate the mechanisms underlying the observed increases in (1) primary productivity, (2) control of herbivores by predators and (3) reduction of herbivore pressure on plants in species‐rich communities.Our findings reveal that increased niche complementarity of plants can steepen the diversity–function relationships if it does not increase their intraspecific competition, while increasing complementarity among animals during community assembly can also have a positive effect but with considerable variability.The study highlights the importance of trait variation both among and within species and the interplay between intra‐ and interspecific competition strength in shaping the functioning of ecosystems over time. These results offer insights into the mechanisms underpinning the diversity–functioning relationship and have practical implications for ecosystem management and conservation efforts. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Sympatric closely related species may experience interspecific trophic competition due to ecological similarity; they may isolate in terms of diet or habitat use as a strategy to avoid competition. The body tissues of consumers contain stable isotope signatures information that can be applied to infer their dietary information. In this study, δ13C and δ15N stable isotopes were analyzed to determine the dietary information and trophic niches of sympatric coexisting Sitta yunnanensis and Sitta nagaensis. The results showed that the food sources of S. yunnanensis and S. nagaensis were from six orders, including Orthoptera, and the cumulative contribution rate was 99.97%, with the two species eating similar diets but at different rates. The larger δ13C of S. yunnanensis indicates that it had a wider range of habitats for feeding, while the difference in δ15N values was not significant (p > 0.05), indicating that both species feed on similar nutrient levels. As determined by Bayesian ellipses, the isotopic niches of S. yunnanensis and S. nagaensis were differentiated; the isotopic niche width of S. yunnanensis is 2.69‰2, which was larger than that of S. nagaensis (0.73‰2), indicates that differentiation between the two species in diet or habitat use reduced competition. Trophic niche differentiation and differences in foraging proportions may be the principal resource allocation mechanisms behind S. yunnanensis and S. nagaensis coexistence.

Competition arises when species share a limited resource, but this can be avoided through niche partitioning. Despite the large body of literature on diadromous fishes, very few studies have focused on niche partitioning when competing for resources. Diadromous fishes are suffering a global decline throughout their range in part due to their peculiar life history traits as they migrate from the sea to freshwater to spawn or the reverse. They are particularly sensitive to river fragmentation induced by barriers. Dams for instance are expected to alter the spatial distribution and resource exploitation of diadromous fishes as well as other organisms. Here, we studied the ecological niche of six taxa of diadromous fishes, temporally co-occurring in the same land–sea continuum obstructed by two river dams. We used Bayesian mixing models run on C and N isotopes to infer the various habitats used and the origin of the trophic carbon in muscle and scale tissues of diadromous fishes. Results showed that the sub-adults of Anguilla anguilla, juveniles of Petromyzon marinus, and Salmo trutta exploit mainly the freshwater, or marine part for adults of Lampetra fluviatilis, whereas juveniles of Platichthys flesus and Mugilidae use all the habitats of the land–sea continuum. In the freshwater habitat, the microphytobenthos and biofilm are the main sources of carbon used, while in the marine habitat, the basal carbon sources are more diverse. The analyses of niche overlaps between diadromous fishes demonstrate that the widest isotopic niches, observed for A. anguilla and P. flesus, also have more impact within the community. Results are discussed in terms of intra- and interspecific competition between these diadromous fishes and their generalist/specialist strategies in an obstructed catchment.

Abstract Documenting long‐term changes in the trophic structure of food webs and how species respond to these changes is essential to forecast their vulnerability and resilience to environmental stressors. Over the past decades, the St. Lawrence marine ecosystem (Canada) has experienced major changes in its physical, chemical, and biological conditions from overfishing, acoustic and chemical pollution, climate change, and the increased abundance of some top predators. These changes have likely affected the trophodynamics of the ecosystem, and are suspected to have deleterious effects on endangered species of mammals and other components of the ecosystem, such as blue whales (Balaenoptera musculus), fin whales (B. physalus), and beluga (Delphinapterus leucas). This study examined the trophic structure of the St. Lawrence marine ecosystem, including the isotopic niche of various species, over two periods of contrasting pressures from anthropogenic and climatic stressors (1995–2003 vs. 2019–2021). Stable isotope ratios were measured in 1240 samples of 21 species of marine invertebrates, fishes, and mammals sampled during both periods. A significant change in the isotopic value and niche position between periods is observed in most of the sampled species. While the direction of change and effect size were not uniform among species, these changes confirmed that substantial modifications in community structure have occurred over time. Niche overlap decreased considerably among some of the pelagic and demersal fishes, and among whale species during the most recent period. Combined with a concomitant reduction in niche breadth in several species, these observations suggested that resource sharing was limited among these species. This study highlighted some degree of dietary plasticity in several species, and a long‐term change in the trophic structure of the St. Lawrence marine ecosystem, with likely effects on diet composition and energetics of several populations, including endangered species.

Species in sympatry can coexist due to some degree of niche partitioning. Four cetacean species, Guiana (Sotalia guianensis), franciscana (Pontoporia blainvillei), Atlantic spotted (Stenella frontalis), and rough-toothed dolphins (Steno bredanensis), frequently occur in Ilha Grande Bay (RJ), with three of them presenting residence pattern. This tropical bay is considered a biodiversity hotspot and preserved by marine protected areas, though located in a highly developed region of the Southwestern Atlantic Ocean. To verify niche partitioning and segregation in these species and to explore the trophic structure of this cetacean community, their isotopic niches were investigated through carbon (δ13C) and nitrogen (δ15N) stable isotopes in the muscle of specimens stranded in the region between 2012 and 2022. The rough-toothed dolphin had the largest niche area and high segregation. On the other hand, there was a high niche overlap between the species that have site fidelity patterns in the bay. The Atlantic spotted dolphin had the highest values for almost all the Layman metrics, a large niche area, and trophic diversity; the Guiana dolphin explored a diverse variety of resources, and the franciscana dolphin presented the narrowest and most overlapped niche and the lowest niche diversification. This is the first study to access the trophic ecology of this cetacean community. Our results indicate that the region is an important foraging area for three of the studied species, with a high diversity and availability of resources that might enable the high niche overlap observed for resident species. The findings for the threatened and small franciscana population in this recently discovered habitat bring concern. Therefore, the area deserves conservation attention to prevent anthropogenic stressors from interfering in the relationship balance between these sympatric predators.

Quantitative and qualitative characteristics of nutrition of some cohabiting rodent species in the High-Mountain Zone of the Republic of Dagestan have been studied. The diet of S. uralensis consisted of 23, C. gud, of 22, M. arvalis, of 27, C. migtatorius, of 26, and D. nitedula, of 19 plant species. The most diverse diet was found in the common vole and gray hamster. In spring, sedges dominated in the diets of rodents, in the summer, rations consisted mainly of cereals, and autumn, predominantly from the species of the forbs and legume groups. In all, except for the forest dormouse, the conjugation of diets with the structure of herbaceous vegetation was revealed. The maximum values of the degree of similarity of the diets of rodents were found in pairs of wood mouse – Gudaur vole, Gudaur vole – gray hamster, and common vole – gray hamster. As a result, a sufficient level of food supply, a wide range of microstations, and intrapopulation adaptation mechanisms make it possible for the considered rodent species to live together in the study area. [ABSTRACT FROM AUTHOR]

In order to elucidate the effects of fishing ban strategies in different lakes on population dynamics and niche overlap of three cultrinae fishes, Xiliang Lake, a complete fishing ban strategy lake, and Futou Lake, a seasonal fishing ban strategy lake, were selected as the study sites. Three cultrinae fishes Culter alburnus, Culter dabryi and Cultrichthys erythropterus were studied. The dynamic parameters offish population such as quantity per unit effort, biomass per unit effort, total length, body weight and relative fatness were analyzed. The food sources and contribution rates of three cultrinae fishes were analyzed using stable isotope technique, and the spatio-temporal niche breadth, trophic niche breadth and overlap indices of three cultrinae fishes in lakes with different fishing ban strategies were compared. The results showed as follows: The biomass per unit effort of three cultrinae fishes in the complete fishing ban strategy lake was significantly higher than that of the seasonal fishing ban strategy lake, and their total length distribution range was wider than that of the seasonal fishing ban strategy lake;In the seasonal fishing ban strategy lake, the temporal-spatial niche of three cultrinae fishes overlapped significantly; In the lake that complete fishing ban strategy, three species of cultrinae had wider trophic niche breadth. The results provide scientific basis for the improvement of the fishing ban strategies and the sustainable utilization of fishery resources in the key waters of the Yangtze River basin. [ABSTRACT FROM AUTHOR]

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Trophic niche partitioning is a mechanism that facilitates the coexistence of ecologically similar species by sharing their resource use. However, detailed information of the trophic niche in insectivorous birds is usually limited by the lack of accurate identification of consumed food resources. The use of DNA metabarcoding has proved useful for molecular identification of the taxa present in bird faecal samples. Here, we used this molecular technique to study the diets of six steppe passerine species distributed in two Special Protection Areas in central Spain, and to characterize the dietary niche overlap and the prey composition differences between bird species. In total, we distinguished 112 diet items, covering 39 arthropod families of 13 orders. Although significant dietary differences existed in prey species composition, our results indicated a 74% overlap in steppe bird dietary niche, mostly due to high consumption of abundant arthropod prey such as beetles, grasshoppers and spiders in the breeding season by all bird species. The lowest overlap was found for the dietary niches of the Greater Short‐toed Lark Calandrella brachydactyla and Dupont's Lark Chersophilus duponti, a scarce and threatened species, which appeared to be the species with the most distinct dietary niche within the community. Our results make a significant contribution to the knowledge of shrub‐steppe bird diets and their trophic interactions, indicating that some extent of interspecific resource partitioning occurs in the study area, notably between Dupont's Lark and the Greater Short‐toed Lark. Our study demonstrates the value of DNA metabarcoding in the assessment of passerine diets and provides useful ecological results for the design of biodiversity conservation programmes in the increasingly scarce and threatened steppe habitats. [ABSTRACT FROM AUTHOR]

Pacific Northwest Indigenous communities historically managed terrestrial and marine environments to increase the productivity and access of traditional foods. Sea gardens, also called clam gardens, were an Indigenous aquaculture method that increased traditional food habitat for targeted food species such as bivalves. This study utilized fatty acid biomarker analysis alongside stable isotopic analysis with bivalve condition indices of traditionally harvested littleneck clams (Leukoma staminea) to investigate dietary and trophic differences between sea gardens and non-walled beaches in Kanish Bay, Quadra Island, British Columbia. We utilized non-metric multidimensional scaling, distance-based redundancy analysis (db-RDA), and Bayesian three-source isotopic mixing models to examine impacts of environmental drivers on bivalve dietary composition and condition at four sea garden sites and four non-walled sites. Bivalve tissue saturated fatty acids (sum SFAs) showed statistical significance (Mann-Whitney U-Test, W = 3447, P = 0.01), indicating that sea garden clams (x2 = 34.96; SD = 7.56) had higher mean relative percent areas of SFAs compared to nonwalled sites (x2 = 31.76; 7.71). Bivalve monounsaturated fatty acids (MUFAs) showed statistical significance (Mann-Whitney U-Test, W = 1202, P = 0.01, a = 0.05), indicating sea garden clams (x2 = 3.48; SD = 3.78) had lower mean relative percent areas of MUFAs compared to those in non-walled sites (x2 = 6.97; SD = 5.90). Sea garden bivalves were found to feed at a higher trophic level, with a slimmer dietary range, compared to non-walled clams. Both dietary marker differences and differentiated trophic positioning suggest decreased physiological stressors impacting feeding of bivalves, differences in dietary particulate intake, or a combination of both occurring at sea garden sites compared to non-walled sites. Correlations within a db-RDA indicate that bivalves with high body condition indices at sea garden sites were benefiting from decreased stress related to favorable salinity and oxygen parameters, which positively impacted bivalve feeding and respiration. Observed trophic niche differences and fatty acid differences would also be explained by this suggested mechanism. We conclude that partial trophic shifts and fatty acid changes of sea garden L. staminea bivalves are consistent with stress-alleviated bivalve responses, and match correlated variables in our db-RDA. Trophic niche differences and fatty acid shifts between sea gardens and non-walled sites should be further explored by using a quantitative method to identify sea gardens from nonwalled sites in addition to established field verification methods. [ABSTRACT FROM AUTHOR]

Despite the current increase in studies on the diet of neotropical anurans, few of them take a comparative approach between syntopic species. The objective of this study was to compare the diet of four syntopic species of the genus Physalaemus. The collections occurred between November 2014 and January 2016 in a preserved area of the subtropical Atlantic Forest in southern Brazil. We compared the gastrointestinal content of 109 individuals distributed in the species Physalaemus biligonigerus, P. cuvieri, P. gracilis and P. henselii. We measured the Index of Relative Importance of each prey category and calculated trophic niche breadth using the Levins’ index (Bsta) and trophic niche overlap using the Pianka’s index (Ojk). We also applied compositional analysis to evaluate feeding specializations. Formicidae was the most important prey category for P. biligonigerus (IRI = 88.5%) and P. gracilis (IRI = 39.1%). For P. henselii and P. cuvieri, the most important category was Isopoda (IRI = 51.7% and 57.9%, respectively), followed by Formicidae (IRI = 34.9% and 24.8%). Isopoda was also important in the diet of P. gracilis (IIR = 28.6%), followed by Araneae (IIR = 22.6%). The trophic niche breadth of the four species was narrow, all smaller than 0.32, and the lowest was recorded for P. biligonigerus (0.04). The trophic niche overlap was higher between P. biligonigerus and P. cuvieri (96%), and between P. gracilis and P. henselii (95%). Only P. gracilis presented a significant level of feeding specialization. The differences in their diets suggest different uses of the resources, which could relate to different ways of exploring the microhabitat. [ABSTRACT FROM AUTHOR]