Trophic Ecology Research Articles

Temporal and Spatial Comparison of Mercury Bioaccumulation in the Lower Trophic Levels of a Post-glacial Lake Food Web.

Total mercury (Hg) concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotopes were quantified among aquatic invertebrate and sediment samples collected from Keuka Lake in New York's Finger Lakes region to evaluate temporal and spatial variability in Hg bioaccumulation and trophic ecology among these lower trophic levels. Hg concentrations ranged from 6.3 to 158.8ng/g (dry wt) across dreissenid mussel, zooplankton, and juvenile (< 10mm) and adult (≥ 10mm) mysid shrimp (Mysis diluviana) samples. Hg concentrations were higher in samples collected from the western basin in 2015 relative to those for samples collected from this basin in 2022 (p < 0.001). While no specific mechanisms could be identified to explain this difference, higher δ15N values for zooplankton collected in 2015 support conclusions regarding the role of zooplankton trophic status on Hg concentrations in these populations. Spatial patterns in Hg concentrations were of generally low variability among samples collected from the lake's east, west and south basins in 2022. Trophic positions as inferred by δ15N were represented by adult mysids > juvenile mysids > large zooplankton (≥ 500µm) > dreissenid mussels ≥ small zooplankton (64-500µm). Differences were evident among the regression slopes describing the relationships between sample Hg concentrations and δ15N values across the lake's three basins (p = 0.028). However, this was primarily attributed to high δ15N values measured in dreissenid mussels collected from the south basin in 2022. Biota sediment accumulation factors ranged from 0.2 to 2.3 and were highest for adult M. diluviana but mysid δ13C values generally supported a pelagic pathway of Hg exposure relative to benthic sediments. Overall, these results provide additional support regarding the contributions of lower trophic levels to Hg biomagnification in aquatic food-webs.

Larval trophic ecology of small pelagic fishes: a review of recent advances and pathways to fill remaining knowledge gaps

Early life stages constitute a bottleneck for most fish populations, particularly for small pelagic fish (SPF), for which the interannual variability in recruitment strength is very high, and recruits frequently constitute the bulk of the population biomass. Finding the right prey (in terms of size and quality) during these early stages is critical for recruitment success. In this work, we synthesize the available literature on the trophic ecology of the early life stages of SPF, particularly clupeiforms. Works published during the last decade (2013-2022, 37 papers) were compared to those published previously (1920-2012, 107 papers). Gut content analysis of field-caught larvae is still the most commonly used technique (44%), while the use of biomarkers (e.g. stable isotopes and fatty acid composition), molecular tools (e.g. metabarcoding) and multitrophic approaches has increased in the last decade. Significant new knowledge was gained recently, such as that on larval feeding rates and behavior through laboratory experiments for species kept in culture (e.g. Atlantic herring, Pacific and Atlantic sardines), but some old challenges remain, such as the high vacuity rates of field-caught larvae. Lastly, we provide recommendations for future studies, such as the use of complementary techniques, the importance of studying ontogenetic shifts, the use of metabarcoding for analyzing the diet of early larvae that depend on microplankton, and the identification of prey with high taxonomic resolution. Such studies are essential to better understand larval growth and survival at sea, and thus to better understand and predict SPF population dynamics.

A metabarcoding assessment of the diet of the insectivorous bats of Madeira Island, Macaronesia

Abstract Understanding the trophic structure of species assemblages is crucial in order to comprehend how syntropic species coexist in space and time. Bats are the second most taxonomically diverse group of mammals and display a wide range of dietary strategies. Due to their ability to disperse over water, ca. 60% of all extant bat species occur on islands and for the most part their interspecific ecological interactions are poorly known. Using DNA metabarcoding, this study offers the first insights into the diet of Macaronesian bats by providing a holistic overview of prey consumed by all 3 bat species found on Madeira Island (Pipistrellus maderensis, Nyctalus leisleri verrucosus, and Plecotus austriacus) and investigating both interspecific (between P. maderensis and N. l. verrucosus) and intraspecific (between female and male N. l. verrucosus) dietary differences. We identified a total of 110 species of arthropod prey in the diet of the 3 bat species, including multiple agriculture and forestry pest species, a human disease-relevant species, and numerous taxa not previously recorded on the island. Lepidoptera was the primary prey order for all 3 bat species. The diet composition of P. maderensis and N. l. verrucosus differed significantly, with P. maderensis consuming more Diptera and multiple prey taxa not found in the diet of N. l. verucosus. Moreover, male N. l. verrucosus exhibited a broader niche breadth than females. This study is among the first to use DNA metabarcoding to evaluate the diet of insular bats and thus greatly advances knowledge regarding the trophic ecology and pest suppression services of these poorly-known mammals.

Trophic ecology and small‐scale differentiation of ecological groups of franciscana dolphin, Pontoporia blainvillei, in southeastern Brazil, revealed by carbon and nitrogen stable isotopes

AbstractThe franciscana, Pontoporia blainvillei, is an endemic dolphin off the east coast of South America and is considered the most endangered cetacean in the western South Atlantic. In the present study, we analyzed the muscle tissue of 24 franciscana dolphins found on the coast of Espírito Santo (ES) between 2010 and 2019 to investigate trophic ecology using carbon and nitrogen stable isotope analysis. In addition, 127 prey were analyzed to identify the preferred prey. The most important prey species in the diet of the franciscana dolphins were Trichiurus lepturus, Chirocentrodon bleekerianus, and Pellona harroweri. The franciscana dolphins were grouped into three subareas according to where they were collected throughout the distribution: 1 (North), 2 (Center), and 3 (South). In subarea 1, the preferred prey were Stellifer spp., Isopisthus parvipinnis, and P. harroweri, while in subareas 2 and 3, the prey were similar, changing the order of preference among them (Stellifer spp., T. lepturus, and C. bleekerianus). Finally, we identify two possible ecological groups of franciscana dolphins on the coast of ES, influenced by different carbon sources. Our results improve our understanding of the franciscana dolphin's trophic ecology and habitat use, providing new information and guidelines for species conservation in the region.

Camera-traps detect the maned wolf preying on broad-snouted caiman eggs

The maned wolf (Chrysocyon brachyurus) is a South-American canid of which conservation guidelines have been implemented due to its population vulnerability. Its trophic ecology demonstrates an omnivorous and opportunistic diet, and even flexibility in response to anthropogenic disturbances. Among the food items identified, the consumption of reptiles is scarce, and includes snakes and lizards. We monitored broad-snouted caiman (Caiman latirostris) nests during four nesting seasons through camera trapping, in savannas and grasslands areas, and recorded maned wolves feeding on caiman eggs during periods of drought. The consumption of an uncommon item, even at low frequency, suggests that camera trapping could become a complementary tool for studying the dietary habits of the maned wolf. Caimans have been a priority for conservation, while maned wolves are currently being released and reintroduced in order to reverse their vulnerable population status. This trophic interaction must be monitored in the long term, to project integral conservation strategies that include both emblematic species.

Assessment of trophic segregation amongst gentoo penguin (Pygoscelis papua) individuals in Antarctica using a non-invasive methodology

Abstract Individual trophic specialization (ITS) refers to the trophic diversification amongst individuals within a population. The gentoo penguin (Pygoscelis papua) is considered a trophic generalist at the population level, but little is known about its individual trophic differentiation. We assessed the degree of ITS at one of its main breeding colonies: Ardley Island, South Shetland Islands. We used skin from 19 dead individuals to determine species and sex by molecular methods and a nail for stable isotope analysis of δ15N and δ13C. Isotopic niche metrics and ITS were estimated for the population and for each sex. We found a moderately high degree of ITS associated with the trophic position of the resources consumed (δ15N) for the population and both sexes, as well as a moderate degree of ITS in the foraging habitat (δ13C) for the population and females. Females showed a higher exclusive niche area, suggesting that they use resources and foraging areas that males do not, probably related to reproductive energy demands. Given the high population density of this species, ITS could function as a mechanism to decrease intraspecific competition. This combination of genetic and isotopic tools allowed us to provide relevant information on the trophic ecology of the gentoo penguin without manipulating animals or using invasive methods.

Trophic niche overlap of deep-sea fish species revealed by the combined approach of stomach contents and stable isotopes analysis in the Central Tyrrhenian Sea

Understanding the trophic ecology of marine ecosystems is a key challenge given that they are subject to anthropogenic pressures that can alter the integrity of the food web. The bathyal zone of the Central Tyrrhenian Sea is characterized by an high level of community biodiversity, heavy anthropogenic pressure and thus represents a fundamental environment for the study of trophic relationships between demersal fish species which live in sympatry, but this basin still remains data deficient. To fill this information gap, we investigated the trophic niche overlap of four deep-sea fish species, Galeus melastomus, Helicolenus dactylopterus, Lepidorhombus boscii, and Trisopterus capelanus, in the Central Tyrrhenian Sea using an integrated approach of stomach content and stable isotopes analysis (δ13C and δ15N). Our analysis revealed that the blackmouth catshark G. melastomus displays a wide trophic niche with considerable overlap with other fish species, as it consumed diverse prey including fish, crustaceans, and cephalopods, thus proving a generalist and opportunistic feeding behavior. The blackbelly rosefish H. dactylopterus exhibits a narrower isotopic trophic niche comprising mainly benthic crustaceans and so suggesting a marked specialism in feeding strategy. The diet of the four-spotted megrim L. boscii showed a marked overlap with that H. dactylopterus, as these species shared a similar benthic habit and relied upon a similar pool of resource. The poor cod T. capelanus showed a diverse diet comprising both prey captured close to the bottom, especially decapod and mysid crustaceans, and bathypelagic prey, mainly Osteichthyes, Myctophidae, and amphipod Hyperiidae, with an intermediate partially segregated isotopic niche width. The combination of stomach content analysis and stable isotopes analysis provided the first characterization of the trophic relationships, shedding light on the trophic niche overlap of these four ecologically important deep sea fish species. The diets of the four investigated species showed similarities in the composition of prey, but also differences which allows them to partially reduce competition. This information may be of crucial relevance for the development of effective management and conservation strategies for the bathyal Mediterranean environment.

Total mercury in three small tunas from southeastern Brazil: Stable isotope relations and human risk assessment

Mercury (Hg) bioaccumulation can be highly variable in marine species. Its concentration is influenced by several physico-chemical and biotic processes, including size, age, diet composition and foraging habitats. Herein, we addressed total mercury (THg) concentrations in three small tuna species in Brazil: the frigate tuna Auxis thazard, the little tunny Euthynnus alletteratus and the skipjack tuna Katsuwonus pelamis. Samples were collected from commercial landings in the SE Brazilian coast from 2017 to 2019. The influence of trophic ecology and habitat preference on Hg accumulation was assessed through stable isotope [carbon (δ13C) and nitrogen (δ15N)] measurements. Additionally, the human health risk regarding the species consumption was assessed by the estimated weekly intake (EWI) and the provisional tolerable weekly intake (PTWI) for total consumers, adult men and adult women. Variables such as size and age were positively correlated to Hg, due to the bioaccumulation process. Trophic position appears to positively influence the mercury concentrations for A. thazard and K. pelamis, since relationship between δ15N and THg was significant. For E. alletteratus, the lack of relationship suggests that δ15N values do not vary much among adult fish (> 300 mm). Muscle THg concentrations in the three species did not exceed the established tolerable limit for mercury by Brazilian and international organs, as indicated by the %PTWI. This finding suggests that the consumption of those species caught off southeast Brazil at the considered amounts does not present a risk for healthy adults.

Vertical trophic structure and niche partitioning of gelatinous predators in a pelagic food web: Insights from stable isotopes of siphonophores

AbstractGelatinous zooplankton are increasingly recognized as key components of pelagic ecosystems, and there have been many recent insights into their ecology and roles in food webs. To examine the trophic ecology of siphonophores (Cnidaria, Hydrozoa), we used bulk (carbon and nitrogen) and compound‐specific (nitrogen) isotope analysis of individual amino acids (CSIA‐AA). We collected samples of 15 siphonophore genera using blue‐water diving, midwater trawls, and remotely operated vehicles in the California Current Ecosystem, from 0 to 3000 m. We examined the basal resources supporting siphonophore nutrition by comparing their isotope values to those of contemporaneously collected sinking and suspended particles (0–500 m). Stable isotope values provided novel insights into siphonophore trophic ecology, indicating considerable niche overlap between calycophoran and physonect siphonophores. However, there were clear relationships between siphonophore trophic positions and phylogeny, and the highest siphonophore trophic positions were restricted to physonects. Bulk and source amino acid nitrogen isotope (δ15N) values of siphonophores and suspended particles all increased significantly with increasing collection depth. In contrast, siphonophore trophic positions did not increase with increasing collection depth. This suggests that microbially reworked, deep, suspended particles with higher δ15N values than surface particles, likely indirectly support deep‐pelagic siphonophores. Siphonophores feed upon a range of prey, from small crustaceans to fishes, and we show that their measured trophic positions reflect this trophic diversity, spanning 1.5 trophic levels (range 2.4–4.0). Further, we demonstrate that CSIA‐AA can elucidate the feeding ecology of gelatinous zooplankton and distinguish between nutritional resources across vertical habitats. These findings improve our understanding of the functional roles of gelatinous zooplankton and energy flow through pelagic food webs.

Quantifying the δ15N trophic offset in a cold-water scleractinian coral (CWC): implications for the CWC diet and coral δ15N as a marine N cycle proxy

Abstract. The nitrogen (N) isotope composition (δ15N) of cold-water corals is a promising proxy for reconstructing past ocean N cycling, as a strong correlation was found between the δ15N of the organic nitrogen preserved in coral skeletons and the δ15N of particulate organic matter exported from the surface ocean. However, a large offset of 8 ‰–9 ‰ between the δ15N recorded by the coral and that of exported particulate organic matter remains unexplained. The 8 ‰–9 ‰ offset may signal a higher trophic level of coral dietary sources, an unusually large trophic isotope effect or a biosynthetic δ15N offset between the coral's soft tissue and skeletal organic matter, or some combinations of these factors. To understand the origin of the offset and further validate the proxy, we investigated the trophic ecology of the asymbiotic scleractinian cold-water coral Balanophyllia elegans, both in a laboratory setting and in its natural habitat. A long-term incubation experiment of B. elegans fed on an isotopically controlled diet yielded a canonical trophic isotope effect of 3.0 ± 0.1 ‰ between coral soft tissue and the Artemia prey. The trophic isotope effect was not detectably influenced by sustained food limitation. A long N turnover of coral soft tissue, expressed as an e-folding time, of 291 ± 15 d in the well-fed incubations indicates that coral skeleton δ15N is not likely to track subannual (e.g., seasonal) variability in diet δ15N. Specimens of B. elegans from the subtidal zone near San Juan Channel (WA, USA) revealed a modest difference of 1.2 ± 0.6 ‰ between soft tissue and skeletal δ15N. The δ15N of the coral soft tissue was 12.0 ± 0.6 ‰, which was ∼6 ‰ higher than that of suspended organic material that was comprised dominantly of phytoplankton – suggesting that phytoplankton is not the primary component of B. elegans' diet. An analysis of size-fractionated net tow material suggests that B. elegans fed predominantly on a size class of zooplankton ≥500 µm, implicating a two-level trophic transfer between phytoplankton material and coral tissue. These results point to a feeding strategy that may result in an influence of the regional food web structure on the cold-water coral δ15N. This factor should be taken into consideration when applying the proxy to paleo-oceanographic studies of ocean N cycling.

Stable isotopes delineate regional pelagic food web structure in British Columbia’s coastal ocean

The pelagic food webs of British Columbia’s (BC) coastal oceans have never had a comprehensive review of their trophic structure. In this study, we analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of pelagic food web components collected from four regions in southern BC: Juan de Fuca Strait, the Strait of Georgia, Queen Charlotte Strait, and Queen Charlotte Sound during an August 2019 survey. In addition, conductivity, temperature, and depth (CTD), chlorophyll, and nutrient data were collected to assess the oceanographic basis for regionalization. Between regions, we observed differences in the isotopic baseline driven by regional oceanography. Likewise, we also observed oceanography-driven differences in regional food chain length, carbon range, and isotopic overlap. Species-specific trophic level and isotopic niche were determined. For common pelagic species, we described how trophic level varied regionally, was not always in line with previously published dietary data, and instead largely tracked regional changes in food chain length. We conclude that variable food web properties and trophic ecology can manifest across the small spatial scales of the BC coast’s discrete regions.

Trophic niche partitioning of golden cuttlefish (Sepia esculenta) during ontogeny revealed by stable isotope analysis and DNA metabarcoding

Cephalopods are becoming more important in global fishery. Understanding the trophic ecology partitioning during their ontogeny is critical to the stock assessment and fishery management. The golden cuttlefish (Sepia esculenta), one of commercially important cephalopod species has been found at different life-history stages that co-inhibit in the coastal waters of Qingdao, China. In the present study, the trophic ecology of S. esculenta was assessed by using stable isotope analysis (SIA: based δ13C and δ15N from muscle and liver tissue) and DNA metabarcoding of the stomach contents through high-throughput sequencing (HTS). SIA uncovered the variation in isotope niche and trophic position of S. esculenta during ontogeny. DNA metabarcoding showed a higher resolution of prey identification than before. The combined analysis of SIA and DNA metabarcoding indicated that diet shifts occurred in the ontogeny of S. esculenta. Paralaval and juvenile prefer zooplankton, while sub-adult and adult prefer demersal fishes. The standard ellipse area (SEAc) indicated that low isotope niche overlaps among paralaval, juvenile and sub-adult of S. esculenta, which reflect the squid foraging strategy during ontogeny. The study confirmed that S. esculenta resources can be partitioned into different life stages, suggesting a survival strategy to maintain population dynamics.

Food web structure of fish communities of Doce River, 5years after the Fundão dam failure.

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.

Distribution and stable isotope ratio characteristics of Japanese eel leptocephali in relation to hydrographic structure of their Pacific Ocean spawning area

AbstractTo understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early‐stage larvae were distributed south of or near the salinity front, confirming that the salinity front is an important oceanic feature to understand spawning locations of the Japanese eel. Larger size larvae tended to distribute into higher latitudes. Transport to northern latitudes with their growth would facilitate transport into the Kuroshio region, but retention in the Subtropical Countercurrent (STCC) might be detrimental. Preleptocephalus isotope ratios reflected maternal ratios, but feeding‐stage leptocephali (8–56 mm) tended to have higher ∂15N values at lower latitudes typically in areas south of a salinity front. Feeding larvae quickly assimilate isotope ratios from the NEC after spawning and early growth. Large differences of ∂13C values of larvae between the NEC and STCC might vary with spatial baselines in the two currents. However, diel vertical migrations should be considered, because the isotope ratios in particulate organic matter distinctly depend on the depth. Comparisons among Japanese eel larvae and other taxa of leptocephali in the NEC illustrate the need for further studies on the trophic ecology of leptocephali.

Diet Diversity of the Fluviatile Masu Salmon, Oncorhynchus masou (Brevoort 1856) Revealed via Gastrointestinal Environmental DNA Metabarcoding and Morphological Identification of Contents.

Masu salmon, Oncorhynchus masou (Brevoort 1856), a commercially important fish species endemic to the North Pacific Ocean, attained national second-level protected animal status in China in 2021. Despite this recognition, knowledge about the trophic ecology of this fish remains limited. This study investigated the diet diversity of fluviatile Masu salmon in the Mijiang River, China, utilizing the gastrointestinal tract environmental DNA (GITeDNA) metabarcoding and morphological identification. The results revealed a diverse prey composition, ranging from terrestrial and aquatic invertebrates to small fishes. The fluviatile Masu salmon in general consumed noteworthily more aquatic prey than terrestrial prey. There were much more prey taxa and a higher diet diversity detected by GITeDNA metabarcoding than by morphological identification. GITeDNA metabarcoding showed that larger and older Masu salmon consumed significantly more terrestrial insects than aquatic prey species did, with 7366 verses 5012 sequences in the group of ≥20 cm, 9098 verses 4743 sequences in the group of ≥100 g and 11,540 verses 729 sequences in the group of age 3+. GITeDNA metabarcoding also showed size- and age-related diet diversity, indicating that the dietary niche breadth and trophic diversity of larger and older Masu salmon increased with food resources expanding to more terrestrial prey. Terrestrial invertebrates of riparian habitats play a vital role in the diet of fluviatile Masu salmon, especially larger individuals, highlighting their importance in connecting aquatic and terrestrial food webs. Conservation plans should prioritize the protection and restoration of riparian habitats. This study advocates the combined use of GITeDNA metabarcoding and morphological observation for a comprehensive understanding of fish diet diversity.

Understanding the feeding ecology of the broadnose sevengill shark (Notorynchus cepedianus) in Patagonia, Argentina

The broadnose sevengill shark (Notorynchus cepedianus) is classified as Vulnerable by the IUCN, and its population in the Southwest Atlantic is declining. Despite some progress in understanding the ecological requirements of the sevengill shark, there are still several information gaps. Essential aspects of its trophic ecology, such as main prey items or key feeding grounds, remain uncertain and this information is essential for developing effective conservation strategies. Stable isotopes and spontaneous regurgitations were analyzed to describe the trophic ecology of sevengill sharks within a marine protected area (MPA) of Península Valdés in Patagonia, Argentina. Analysis of spontaneous regurgitations revealed that the southern elephant seal (Mirounga leonina) was the primary prey item (70%) for the sevengill shark, during abundance peaks of both species in the MPA. However, the stable isotope analysis indicated that the teleosts were the main prey item, and the overall contribution of the elephant seal to the diet of the sevengill shark was around 30%. In addition, the contribution of each prey group varied with the size of the individuals. The estimated trophic position was 4.43, placing the species among the apex predators of the region. This study confirmed the use of the MPA as an essential foraging ground and contributed to identifying its main prey items. Also, it reflects the need to expand conservation tools beyond this particular coastal protection.

Trophic ecology of sympatric sea turtles in the tropical Atlantic coast of Brazil

The Tropical Atlantic coast of Brazil is a hotspot area for multiple sea turtle species at all life stages. The multiple nearshore reefs and beaches, oceanic islands, and the only atoll in the south Atlantic Ocean, are suitable for year-round foraging, migration corridors, and nesting activities of five sea turtle species. Still, relatively few studies have assessed trophic niche among sympatric sea turtles which can provide a better understanding of how closely related species compete/partition the available resources. Using multiple biogeochemical tracers (i.e., nitrogen (δ15N) and carbon (δ13C) stable isotopes, and mercury (Hg)), we disentangled the trophic niches of four sea turtle species – the green turtle (Chelonia mydas), the loggerhead turtle (Caretta), the hawksbill turtle (Eretmochelys imbricata), and the olive ridley turtle (Lepidochelys olivacea) – co-occurring in nesting and foraging habitats along the northeastern coast of Brazil. We found interspecific differences in isotopic and contamination niches, as well as intraspecific niche variation associated with life stage. Differences in the estimation niche models associated to life-stage in C. caretta support the notion of ontogenetic shift in habitat and diet composition previously reported for this species. Oceanic habitat signatures were observed in juvenile green turtles and adult olive turtles, while nearshore habitat signatures were observed in adult hawksbill turtles.

Niche overlap across landscape variability in summer between two large herbivores using eDNA metabarcoding.

Understanding the relationship between a species feeding strategy and its environment (trophic ecology) is critical to assess environmental requirements and improve management policies. However, measuring trophic interactions remains challenging. Among the available methods, quantifying the plant composition of a species' diet indicates how species use their environment and their associated niche overlap. Nevertheless, most studies focusing on herbivore trophic ecology ignore the influence that landscape variability may have. Here, we explored how landscape variability influences diet composition through niche overlap. We used eDNA metabarcoding to quantify the diet composition of two large herbivores of the Bialowieza Forest, red deer (Cervus elaphus) and European bison (Bison bonasus) to investigate how increasing habitat quality (i.e. higher abundance of deciduous forage species) and predation risk (i.e. density of wolf in the area) influence their diet composition and niche partitioning. Our findings indicate diet composition is non-homogeneous across the landscape, both within and between species. Red deer showed greater diet variability and lower niche overlap within species compared to bison. We detected a reduction of niche overlap for red deer with increasing predation risk, leading to more dissimilar diets, suggesting their feeding behaviour is affected by wolf presence. This correlation was not found for bison, which are rarely predated by wolf. Higher habitat quality was associated with higher niche overlap only within bison, probably due to their suboptimal feeding strategy as browsers. These results show the importance of integrating environment-induced diet variation in studies aimed at determining the landscape usage or niche overlap of a species.

Trophic niche patterns of endangered Sandelia bainsii and Amatolacypris trevelyani in the Eastern Cape, South Africa: Insights from stable isotope analysis

Abstract Despite supporting a disproportionately large fraction of the global biodiversity, freshwater ecosystems are ranked as the most highly threatened habitats ahead of both terrestrial and marine ecosystems. Furthermore, many regions are still characterized by limited knowledge on taxonomy and ecology of freshwater fishes. The need for ecological information in understudied regions is important particularly where there are recent discoveries of new species and unique lineages and for threatened and endangered taxa that require conservation management. This study evaluated the trophic ecology of two freshwater fish species Sandelia bainsii and Amatolacypris trevelyani that are both classified as endangered in the International Union for Conservation of Nature (IUCN) Red List. These two species, which are narrow‐range endemics in the Eastern Cape, South Africa, comprise allopatric lineages whose ecology is poorly known. This study used stable isotope analysis to evaluate the food web patterns, explore the trophic niche dynamics and estimate the prey source contributions for the two species in different headwater habitats. The fishes isotopic niche sizes were spatially variable, suggesting the likely importance of stochastic variation in resource availability and probable interspecific interactions. The three lineages within S. bainsii exhibited low isotopic niche overlap onto those of sympatric fishes in most habitats. Isotopic mixing model revealed that these lineages' diets were mostly dominated by gatherers/collectors. In comparison, the two lineages within A. trevelyani exhibited high niche overlap with other species and generally had variable diets. Despite the low and high niche overlap patterns of S. bainsii and A. trevelyani, respectively, the isotopic niche overlap patterns of co‐occurring species onto those of the former suggest the likely lack of competitive hierarchies. The trophic niche patterns of these two endangered species helped to shed some light on the potential invasion risks by non‐piscivorous fishes with opportunistic feeding habits, which could exert competitive interspecific interactions.

Does urbanisation have an impact on the trophic ecology of the Algerian hedgehog Atelerixalgirus in northern Algeria?

The Algerian hedgehog, which is an endemic Mediterranean species, is a nocturnal and terrestrial insectivorous mammal. Atelerixalgirus' populations are widespread in various habitats comprising human agglomeration, such as rural, suburban or natural ecosystems. However, the impact of the habitat's characteristics on its diet remains unknown in Algeria. To contribute to a better understanding of this question, we have analysed 158 faeces samples of the Algerian hedgehog in three different areas: urban, suburban and natural area. The findings show that the Algerian hedgehog is an opportunistic species. It feeds on several classes of Arthropoda, but the harvester ant Messorbarbarus dominates largely its menu with AR = 74.81% in the diverse habitats. Furthermore, the HAC and FCA analyses confirm the positive impact of the level of urbanisation and the anthropogenic activity on the Algerian hedgehog prey richness in the north of Algeria (79 prey species and 5574 individuals ingested in the urban area, compared to 64 prey species and 3188 individuals ingested in the natural zone).