Trophic Niche Differentiation Research Articles

Isotopic diversity and niche patterns reveal contrasting resource use among co-occurring non-native fishes within a flow-altered African river system

AbstractClassic and contemporary trophic ecology-based studies have shown that most non-native freshwater fish species (NNS) that integrate into novel environments have the potential to influence the recipient ecosystems’ structure and function. However, the interspecific trophic interactions amongst co-occurring NNS within invaded systems remain poorly studied. Here, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyses to examine general fish trophic diversity patterns (native and non-native fishes) and to explore trophic niche patterns amongst co-occurring NNS within a flow-modified river system, the Great Fish River (South Africa). The system was characterised by isotopic variation, which revealed spatial differences in trophic complexity from uninvaded headwater tributaries to invaded mainstem and downstream sections. Two of the invaded sections, the upper mainstem of the Great Fish River (UGFR) and the Koonap River, had low isotopic overlaps between NNS and the native fish assemblages. Furthermore, co-occurring NNS in these two invaded sections had variable isotopic niche sizes and low interspecific isotopic niche overlaps, suggesting the potential for trophic differentiation. By comparison, there was evidence of high resource use patterns among NNS within the lower mainstem section of the Great Fish River (LGFR), which likely reflected trophic plasticity. Overall, results of this study provided evidence of both trophic niche differentiation (UGFR and Koonap River) and niche overlap (LGFR) as probable mechanisms of co-occurrences of the non-native fishes within different invaded sections of the Great Fish River system, and underscores the difficulties associated with predicting their trophic impacts.

Trophic Niche Differentiation in Two Sympatric Nuthatch Species (Sitta yunnanensis and Sitta nagaensis).

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.

The Sympatric Coexistence Mechanism: A Case Study of Two Penahia Species in the Beibu Gulf, South China Sea.

The study of trophic relationships among closely related species plays an important role in deepening our understanding of the resource utilization characteristics, differentiation patterns, and population dynamics of co-occurring species in the same habitat. This research uses two congeneric fish species, Pennahia pawak and Pennahia anea, as examples. Based on a stomach content analysis and a carbon-nitrogen stable isotope analysis, a comparative analysis of their feeding habits and trophic niches is conducted. Additionally, a spatial niche analysis is employed to explore the coexistence and competitive mechanisms between these two closely related fish species. The results show that specialized feeding habits mitigate intraspecific competition as the population densities increase. The carbon and nitrogen stable isotope analysis reveals variations in the feeding habits and trophic levels with body length, indicating adaptive shifts in prey selection. Despite similar food resources, niche differentiation arises due to differences in dominant prey, facilitating coexistence. Differences in spatial niche further contribute to niche separation and coexistence. In resource-limited environments, species such as Pennahia utilize trophic and spatial niche differentiation to collectively exploit resources and achieve coexistence, with implications for fishery management favoring Pennahia resource occupancy capabilities.

Symbiont genus determines the trophic strategy of corals: Implications for intraspecific competition for energy sources in coral reefs

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.

Water level fluctuations associated with hydrological connectivity consolidate the food web stability of the largest Chinese freshwater lake via mediating trophodynamics and trophic structure

Variation in hydrological connectivity (HC) between rivers and lakes gives rise to periodic large water level fluctuation (WLF) in river-connected lakes (RCL). However, how WLF shapes the material cycling and concomitant trophodynamics of RCL remain unclear. Here we evaluated the resource availability, relative contributions of autochthonous and allochthonous carbon sources (by Bayesian mixing models) and trophic structure (using δ13C and δ15N) of Lake Poyang, the largest freshwater lake in China, during different hydrological periods. Terrestrial C3 plants in the aquatic/terrestrial transition zones (ATTZ) were the main supporter of aquatic consumers all year round. Compared with historical data, the contributions of autochthonous production to aquatic food webs were low. This is primarily ascribed to the influences of hydrological regimes in that the operation of Three Gorges Dam and HC changed the rhythm of WLF in Lake Poyang, restricting the production of aquatic vegetation and epiphytic algae. Most common fish species indicated higher trophic positions (TPs) during the dry than wet season, but only eleven of thirty-six common species showed a statistically significant increase (p < 0.05). Our study reveals a relatively consistent trophic diversity of consumer communities (fish and aquatic invertebrates) during dry and wet seasons, but each trophic guild showed specific trophic response to WLF, as they flexibly adjusted feeding strategies and the degree of trophic niche differentiation. Although WLF triggered fluctuations in the resource availability and species composition of lake food webs, and the TPs and trophic niches of aquatic consumers during different hydrological periods, the resource diversity and habitat complexity driven by HC and WLF reduced the strength of trophic interactions, and thus resulted in overall stability of food web trophodynamics and trophic structure of Lake Poyang. Our findings highlighted the importance of HC and natural WLFs in maintaining the ecosystem stability of large floodplain lakes, and that seasonal WLF patterns should be maintained in future floodplain lake management to conserve biodiversity and the resilience of ecological functions.

Diet composition, niche overlap and partitioning of five sympatric rhinolophid bats in Southwestern China during summer

Understanding trophic niche differentiation is critical for exploring interspecific competition and stable coexistence among morphologically similar sympatric species. Bats are an ideal model for studying trophic niche differentiation among species because of their high taxonomic and ecological diversities, as well as their special life history traits. Although many factors can affect bat trophic niches, few studies have combined multiple factors to investigate the influences on bat trophic niches. In this study, we analyzed the summer diet and potential influencing factors of five sympatric rhinolophid bats in southwestern China: Rhinolophus macrotis, Rhinolophus osgoodi, Rhinolophus ferrumequinum, Rhinolophus affinis, and Rhinolophus pusillus. All five species mainly fed on Lepidopteran and Dipteran insects, with a large trophic niche breadth for each species and a low degree of dietary overlap. With the exception of R. affinis and R. pusillus, significant differences in diet composition were detected among species, which indicated relatively low interspecific competition. Canonical correspondence analysis showed that both echolocation calls and body size significantly affected interspecific diet differentiation, while wing morphology and bite force had relatively weak effects. This study suggests that the combined effects of multiple factors may drive trophic niche differentiation among five rhinolophid bat species in the study area.

New perspectives on soil animal trophic ecology through the lens of C and N stable isotope ratios of oribatid mites

Knowledge of the trophic ecology of soil animals is important for understanding their high alpha diversity as well as their functional role in soil food webs and systems. In the last 20 years, the analysis of natural variations in stable isotope ratios (15N/14N, 13C/12C) has revolutionized our view on soil animal trophic ecology. Here, we review the state of the art of the trophic ecology of a highly abundant and diverse soil animal taxon, oribatid mites (Oribatida), investigated by stable isotope analyses. The review is based on 25 papers reporting stable isotope data of 292 oribatid mite taxa from 30 different sites. Four main findings emerged. (1) Oribatid mites cluster into six trophic groups, i.e. moss feeders, lichen feeders, primary decomposers, fungal feeders/secondary decomposers, predators/scavengers and marine algal feeders, plus one additional group, which incorporates CaCO3 in their cuticle for defence but still belongs to the fungal feeders/secondary decomposers group. (2) Of the 292 species studied 43.7% were classified as fungal feeders/secondary decomposers, 27.0% as primary decomposers and 15.7% as predators/scavengers, only few species include CaCO3 into their skeleton (6.1%), feed on lichens (4.9%), mosses (2.1%) or marine algae (0.7%). (3) In about one-third of the species studied the trophic niche was constant or varied little between sites or habitats, but in two-thirds of the species their trophic niche varied between habitats, with some species even shifting trophic levels, indicating trophic plasticity. (4) When aggregated at higher taxonomic level oribatid mite species clustered in only three instead of six trophic groups. This indicates that species within the same high level taxon often belong to different trophic groups, for example because feeding habits evolved convergently. Therefore, to accurately reflect the trophic ecology of oribatid mites their stable isotope signatures need to be analysed at species level. However, stable isotope analyses also have limitations, e.g. feeding on bacteria and fungi cannot be separated, and the same is true for feeding on ectomycorrhizal and arbuscular mycorrhizal fungi. Other methods such as fatty acid, amino acid and molecular gut content analyses as well as microbiome analyses may complement stable isotope studies and resolve oribatid mite trophic niche differentiation at a higher resolution. This will contribute to a better understanding of the local coexistence of large numbers of species in soil. Finally, we provide perspectives on how to integrate microarthropods into soil food webs using stable isotope and other methods allowing deeper insight into their trophic structure.

Trophic niche differentiation between invasive and native frog species in urban wetlands of Kunming, China

Non-native species often proliferate and become invasive in urban ecosystems. Knowing the interactions between the overlapping trophic niches of invasive and native species is imperative, and answering this question of how they succeed in these ecosystems is an area of active research. Here, frogs were collected from eight sites in the suburbs of Kunming, including 74 non-native American bullfrogs (Lithobates catesbeianus), 115 native Yunnan pond frogs (Nidirana pleuraden, YPF) and 26 non-native black-spotted pond frogs (Pelophylax nigromaculatus, BPF). The diversity indices and niche widths of the sampled frogs’ stomach contents were determined, and δ13C and δ15N isotopes in their muscle tissue measured for a subset of samples. At sites where multiple species occurred, the prey Shannon-Wiener diversity index and niche width of the bullfrog were higher than those of BPF yet lower than those of YPF. The prey diversity and niche width of YPF decreased significantly at the level of individual populations. The overlap between the trophic niches of bullfrog and sympatric frogs ranged from 0.3 to 0.37 based on their stomach contents, while that between the YPF and BPF was 0.68. These results demonstrate that bullfrog and YPF eat some items in common, for which competition is likely, but this is not as pronounced as between YPF and BPF. Plotting values of δ13C (x-axis) against δ15N (y-axis) isotopes, the standard ellipse areas at the LaoY site, where all three species co-occurred, were 23.75, 12.9, and 11.95 for bullfrog, YPF, and BPF, respectively. The maximal standard ellipse area of YPF across the sites without bullfrog invasion was 4.74. These results showed that bullfrog’s prey diversity did not exceed that of YPF in the co-distributed environments, yet its isotopic niche was nonetheless larger. Stomach contents can only convey short-term dietary composition whereas carbon isotopes can reveal relatively long-term nutritional trends, so we conclude the trophic niche width is larger for Bullfrog than YPF. Their degree of overlap is large, which suggests both species have similar ecological functions and experience intense interspecific competition.

Diet composition and trophic niche differentiation of Neogobius melanostomus along an invasion gradient in a large lowland river

The Ponto-Caspian goby Neogobius melanostomus (Pallas 1814) is a widespread non-native fish species in European rivers. It occurs in high abundance and can potentially alter the food webs of invaded water bodies profoundly. However, the invasion process usually goes unnoticed, and changes in food webs during the early stages of invasions are rarely described. Here, we studied populations of N. melanostomus along an invasion gradient in the Elbe River (Germany) and tested the effects of time since invasion on the diets and the associated trophic dynamics in two dominant habitats, i.e., rip rap and sand. Results showed that the abundance and biomass of N. melanostomus was lowest at the most recently invaded sites. The trophic niche space quantified by stable isotopes (δ ¹³ C and δ ¹⁵ N) showed that populations at earlier invaded sites exhibited a wider trophic niche than those at the most recently invaded sites. Diptera and Crustacea were the most abundant taxa in N. melanostomus guts at both habitat structures. At rip rap habitats, N. melanostomus showed a significant increasing preference for Crustacea and a decreasing one for Gastropoda along the invasion gradient. At sand habitats no significant relationships between the invasion gradient and electivity index for N. melanostomus were detected. We demonstrated that the invasion stage and habitat in which N. melanostomus occurs affect the feeding preference of this invasive fish and that these factors are therefore important for tracing changes in the macroinvertebrate communities of affected river systems.

Feeding habits and multifunctional classification of soil‐associated consumers from protists to vertebrates

ABSTRACTSoil organisms drive major ecosystem functions by mineralising carbon and releasing nutrients during decomposition processes, which supports plant growth, aboveground biodiversity and, ultimately, human nutrition. Soil ecologists often operate with functional groups to infer the effects of individual taxa on ecosystem functions and services. Simultaneous assessment of the functional roles of multiple taxa is possible using food‐web reconstructions, but our knowledge of the feeding habits of many taxa is insufficient and often based on limited evidence. Over the last two decades, molecular, biochemical and isotopic tools have improved our understanding of the feeding habits of various soil organisms, yet this knowledge is still to be synthesised into a common functional framework. Here, we provide a comprehensive review of the feeding habits of consumers in soil, including protists, micro‐, meso‐ and macrofauna (invertebrates), and soil‐associated vertebrates. We have integrated existing functional group classifications with findings gained with novel methods and compiled an overarching classification across taxa focusing on key universal traits such as food resource preferences, body masses, microhabitat specialisation, protection and hunting mechanisms. Our summary highlights various strands of evidence that many functional groups commonly used in soil ecology and food‐web models are feeding on multiple types of food resources. In many cases, omnivory is observed down to the species level of taxonomic resolution, challenging realism of traditional soil food‐web models based on distinct resource‐based energy channels. Novel methods, such as stable isotope, fatty acid and DNA gut content analyses, have revealed previously hidden facets of trophic relationships of soil consumers, such as food assimilation, multichannel feeding across trophic levels, hidden trophic niche differentiation and the importance of alternative food/prey, as well as energy transfers across ecosystem compartments. Wider adoption of such tools and the development of open interoperable platforms that assemble morphological, ecological and trophic data as traits of soil taxa will enable the refinement and expansion of the multifunctional classification of consumers in soil. The compiled multifunctional classification of soil‐associated consumers will serve as a reference for ecologists working with biodiversity changes and biodiversity–ecosystem functioning relationships, making soil food‐web research more accessible and reproducible.

Trophic plasticity of mixotrophic corals under contrasting environments

Abstract Mixotrophic organisms can derive nutrition from both auto‐ and heterotrophy, which allows them to use a variety of trophic pathways to sustain their metabolic demands under variable conditions. Therefore, when facing environmental change, these organisms are expected to demonstrate an intrinsic ability to acclimatize through trophic plasticity. Scleractinian corals are ecologically important mixotrophs, but understanding their trophic plasticity has been impaired by an oversimplification towards inconsistent proxies of coral diet and overlooking intraspecific variability. Here, we applied a Bayesian analysis of carbon and nitrogen stable isotope data to determine the trophic niches of six common species of scleractinian corals and their associated endosymbionts, and combined it with an unsupervised machine learning algorithm to identify trophic behaviours and strategies. We found a variable amount of nutritional plasticity identified by different trophic behaviours within and between mixotrophic corals living under the same environmental conditions. Furthermore, we observed changes in trophic plasticity across environmental conditions. Corals from variable environments had larger host and endosymbiont niches than corals from stable environments. In addition, deeper corals had niches indicating a greater degree of heterotrophy than shallow corals. Collectively, corals exhibited distinct trophic strategies by promoting trophic niche differentiation along the mixotrophic continuum and conspecific individual colonies displayed high trophic variation. Our results provide a foundation to understand how mixotrophic organisms may adjust their nutrition in response to ongoing global environmental change and the consequential modification of benthic assemblages.

Coexistence strategies of invaded gobies in the Dianchi Lake, Yunnan, China

Gobiids are widespread invasive species, with many species from this group usually invade into the same ecosystem simultaneously. Understanding the mechanisms underlying the coexi-stence of different gobiid species in the sympatric habitats is a key issue in fish invasion ecology. Incorporating morphological analyses, spatial distribution survey, and trophic analyses, we examined the coexistence strategy of Mugilogobius myxodermus and related species (the earlier invaders) in Dianchi Lake, Yunnan, China. Our results showed significant differences in morphology and spatial distribution among the four invasive gobies species (i.e., M. myxodermus, Micropercops swinhonis, Rhinogobius giurinus and Rhinogobius cliffordpopei). The spatial niche index of M. myxodermus was the highest. Food composition between M. myxodermus and other gobies was significantly different, with the former mainly feeding on Chydorus ovalis and Cypris sp. The trophic diversity index of M. myxodermus was the highest. Overall, we found that morphological differences, spatial niche diffe-rentiation, and trophic niche differentiation contributed to the coexistence of the gobies in Dianchi Lake, which could help M. myxodermus reduce interspecific competition. Importantly, the feeding strategy is the key factor determining population size and habitas of M. myxodermus during their competition with the other gobies, and finally contributing to the dominant position in the study area.

Multidimensional trophic niche revealed by complementary approaches: Gut content, digestive enzymes, fatty acids and stable isotopes in Collembola.

Trophic niche differentiation may explain coexistence and shape functional roles of species. In complex natural food webs, however, trophic niche parameters depicted by single and isolated methods may simplify the multidimensional nature of consumer trophic niches, which includes feeding processes such as food choice, ingestion, digestion, assimilation and retention.Here we explore the correlation and complementarity of trophic niche parameters tackled by four complementary methodological approaches, that is, visual gut content, digestive enzyme, fatty acid and stable isotope analyses—each assessing one or few feeding processes, and demonstrate the power of method combination.Focusing on soil ecosystems, where many omnivore species with cryptic feeding habits coexist, we chose Collembola as an example. We compiled 15 key trophic niche parameters for 125 species from 40 studies. We assessed correlations among trophic niche parameters and described variation of these parameters in different Collembola species, families and across life‐forms, which represent microhabitat specialisation.Correlation between trophic niche parameters was weak in 45 out of 64 pairwise comparisons, pointing at complementarity of the four methods. Jointly, the results indicated that fungal‐ and plant‐feeding Collembola assimilate storage, rather than structural polysaccharides, and suggested bacterial feeding as a potential alternative feeding strategy. Gut content and fatty acid analyses suggested alignment between ingestion and assimilation/retention processes in fungal‐ and plant‐feeding Collembola. From the 15 trophic niche parameters, six were related to Collembola family identity, suggesting that not all trophic niche dimensions are phylogenetically structured. Only three parameters were related to the life‐forms, suggesting that species use various feeding strategies when living in the same microenvironments.Consumers can meet their nutritional needs by varying their food choices, ingestion and digestion strategies, with the connection among different feeding processes being dependent on the consumed resource and consumer adaptations. Multiple methods reveal different dimensions, together drawing a comprehensive picture of the trophic niche. Future studies applying the multidimensional trophic niche approach will allow us to trace trophic complexity and reveal niche partitioning of omnivorous species and their functional roles, especially in cryptic environments such as soils, caves, deep ocean or benthic ecosystems.

Trophic niche differentiation and utilisation of food resources in Collembola is altered by rainforest conversion to plantation systems.

Intensively managed monoculture plantations are increasingly replacing natural forests across the tropics resulting in changes in ecological niches of species and communities, and in ecosystem functioning. Collembola are among the most abundant arthropods inhabiting the belowground system sensitively responding to changes in vegetation and soil conditions. However, most studies on the response of Collembola to land-use change were conducted in temperate ecosystems and focused on shifts in community composition or morphological traits, while parameters more closely linked to ecosystem functioning, such as trophic niches, received little attention. Here, we used stable isotope analysis (13C and 15N) to investigate changes in the trophic structure and use of food resources by Collembola in Jambi province (Sumatra, Indonesia), a region that experienced strong deforestation in the last decades. Isotopic values of Collembola from 32 sites representing four land-use systems were analyzed (rainforest, rubber agroforest, rubber (Hevea brasiliansis) and oil palm (Elaeis guineensis) monoculture plantations). Across Collembola species Δ13C values were highest in rainforest suggesting more pronounced processing of litter resources by microorganisms and consumption of these microorganisms by Collembola in this system. Lower Δ13C values, but high Δ13C variation in Collembola in oil palm plantations indicated that Collembola shifted towards herbivory and used more variable resources in this system. Small range in Δ15N values in Collembola species in monoculture plantations in comparison to rainforest indicated that conversion of rainforest into plantations is associated with simplification in the trophic structure of Collembola communities. This was further confirmed by generally lower isotopic niche differentiation among species in plantations. Across the studied ecosystems, atmobiotic species (Symphypleona and Paronellidae) occupied the lowest, whereas euedaphic Collembola species occupied the highest trophic position, resembling patterns in temperate forests. Some species of Paronellidae in rainforest and jungle rubber had Δ15N values below those of leaf litter suggesting algivory (Salina sp.1, Callyntrura sp.1 and Lepidonella sp.1), while a dominant species, Pseudosinella sp.1, had the highest Δ15N values in most of the land-use systems suggesting that this species at least in part lives as predator or scavenger. Overall, the results suggest that rainforest conversion into plantation systems is associated with marked shifts in the structure of trophic niches in soil and litter Collembola with potential consequences for ecosystem functioning and food-web stability.

Dinner with the roommates: trophic niche differentiation and competition in a mutualistic ant‐ant association

1. The potential for competition is highest among species in close association. Despite net benefits for both parties, mutualisms can involve costs, including food competition. This might be true for the two neotropical ants Camponotus femoratus and Crematogaster levior, which share the same nest in a presumably mutualistic association (parabiosis).2. While each nest involves one Crematogaster and one Camponotus partner, both taxa were recently found to comprise two cryptic species that show no partner preferences and seem ecologically similar. Since these cryptic species often occur in close sympatry, they might need to partition their niches to avoid competitive exclusion.3. Here, we investigated first, is there interference competition between parabiotic Camponotus and Crematogaster, and do they prefer different food sources under competition? And second, is there trophic niche partitioning between the cryptic species of either genus?4. Using cafeteria experiments, neutral lipid fatty acid and stable isotope analyses, we found evidence for interference competition, but also trophic niche partitioning between Camponotus and Crematogaster. Both preferred protein‐ and carbohydrate‐rich baits, but at protein‐rich baits Ca. femoratus displaced Cr. levior over time, suggesting a potential discovery‐dominance trade‐off between parabiotic partners. Only limited evidence was found for trophic differentiation between the cryptic species of each genus.5. Although we cannot exclude differentiation in other niche dimensions, we argue that neutral dynamics might mediate the coexistence of cryptic species. This model system is highly suitable for further studies of the maintenance of species diversity and the role of mutualisms in promoting species coexistence.

Dietary niche differentiation in a mesopredatory dasyatid assemblage

Most batoids are mesopredators and are often hypothesised to play important ecological roles. However, a comprehensive understanding into these roles remains limited given the paucity of information of their trophic habits. St. Joseph Atoll ( $$5.43^{\circ }\hbox { S}$$ , $$53.35^{\circ }\hbox { E}$$ ) is a remote ecosystem that hosts a resident assemblage of dasyatids (Pastinachus ater, Urogymnus granulatus, and U. asperrimus). Both stomach contents (SC) and stable isotope samples (SI) ( $$\delta ^{15}\hbox {N}$$ and $$\delta ^{13}\hbox {C}$$ ) were collected in 2015 and used to investigate the trophic niches of this dasyatid assemblage and whether these niches differed inter- and intra-specifically. Dasyatid muscle samples as well as baseline samples of potential prey species and primary producers were collected for SI analyses. SC data highlighted significant inter-specific differences in diet, U. granulatus juveniles mostly consumed decapod crustaceans (Callianassidae and Portunidae) and P. ater juveniles mostly consumed bivalve molluscs. The mean species trophic positions for juveniles of all three species ranged from 2.9 to 3.6 when calculated using $$\delta ^{15}\hbox {N}$$ and from 3.4 to 3.6 when calculated using stomach content data. Analysis of $$\delta ^{13}\hbox {C}$$ showed that all juveniles were reliant upon the same carbon resources (primarily derived from seagrass beds) at the base of the food web. Diet appeared to change with size as larger individuals displayed lower $$\delta ^{13}\hbox {C}$$ and higher $$\delta ^{15}\hbox {N}$$ compared to smaller juveniles. Additionally, isotope values of the smallest individuals were similar to the largest individuals, suggesting maternal meddling. The identified patterns of inter- and intra-specific trophic niche differentiation may be indicative of competitive effects and contributes to the understanding of mesopredators in community trophic dynamics.

Comparing Trophic Niches of Sympatric Raptors in Agricultural Landscape in Central Poland

According to basic ecological principle, species that share the same niche do not occupy the same environment for a long time, and sympatry of two or more such species provides an interesting field for the analysis of their trophic niche differentiation. To examine the potential differences in the dimensions of the trophic niche we studied the diet of three sympatric avian predators that prey on colonial Microtus rodents. The study area in central Poland is located in an agricultural landscape, composed of crop fields, as well as meadows and pastures located within a small river valley. The pellets of long-eared owl (Asio otus), barn owl (Tyto alba) and kestrel (Falco tinnunculus) were collected from the 750 m2 study site including church building and its surrounding in the spring of 2016 and 2017. The analysis of pellets provided data on a total of 4128 vertebrate prey individuals (1914 from barn owl, 1749 from long-eared owl, and 465 from kestrel). The most important prey group of all three predators were small mammals (90%, 14 species) and the most frequently preyed species was Microtus arvalis (making up 72% of vertebrate prey of long-eared owl, 59% of kestrel and 53% of barn owl). Despite the general similarity in the diet composition, there were differences in the contribution of several prey species (e.g. Soricomorpha, M. arvalis, Mus musculus, Rattus norvegicus, and Apodemus spp.) and the diversity of the diet between the predators. We conclude that the trophic niches of the studied sympatric species differ in several dimensions, including diel activity, prey size and taxon-specific feeding preferences.

Temporal shifts in intraspecific and interspecific diet variation among 3 stream predators

Intraspecific variation is increasingly recognized as an important factor in ecological interactions that can exceed the role of interspecific variation. Few studies, however, have examined how variation in intra- and interspecific resource use affect trophic interactions over time within a seasonally-dynamic food web. We compared diets with respect to predator body size and predator species identity over 3 seasons by collecting stomach contents from 2028 Reticulate Sculpin (Cottus perplexus), 479 Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii), and 107 Pacific Giant Salamanders (Dicamptodon tenebrosus) in western Oregon streams. In each season, predator body size was strongly associated with dietary composition and positively related to taxonomic breadth and the size of individual prey. Intra- and interspecific diet variation changed substantially across seasons, with much greater interspecific variation in spring than in summer and autumn. Interspecific differences in foraging mode (e.g., benthic vs drift feeding) were associated with predator-specific responses to a seasonal pulse in the availability of terrestrial thrip larvae (Thysanoptera) and contributed to temporal variation in trophic niche differentiation. These findings show that the relative magnitudes of intra- and interspecific diet differentiation can change over time in systems that receive seasonal resource pulses. Our results highlight the dynamic nature of food webs and the need to incorporate sampling over relevant temporal scales to understand species interactions.

Spider webs, stable isotopes and molecular gut content analysis: Multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders

Abstract Adaptive radiations are typically characterized by niche partitioning among their constituent species. Trophic niche partitioning is particularly important in predatory animals, which rely on limited food resources for survival. We test for trophic niche partitioning in an adaptive radiation of Hawaiian Tetragnatha spiders, which have diversified in situ on the Hawaiian Islands. We focus on a community of nine species belonging to two different clades, one web‐building and the other actively hunting, which co‐occur in wet forest on East Maui. We hypothesize that trophic niches differ significantly both: (a) among species within a clade, indicating food resource partitioning, and (b) between the two clades, corresponding to their differences in foraging strategy. To assess niches of the spider species, we measure: (a) web architecture, the structure of the hunting tool, and (b) site choice, the physical placement of the web in the habitat. We then test whether differences in these parameters translate into meaningful differences in trophic niche by measuring (c) stable isotope signatures of carbon and nitrogen in the spiders’ tissues, and (d) gut content of spiders based on metabarcoding data. We find significant interspecific differences in web architecture and site choice. Importantly, these differences are reflected in stable isotope signatures among the five web‐building species, as well as significant isotopic differences between web‐builders and active hunters. Gut content data also show interspecific and inter‐clade differences. Pairwise overlaps of web architecture between species are positively correlated with overlaps of isotopic signature. Our results reveal trophic niche partitioning among species within each clade, as well as between the web‐building and actively hunting clades. Based on the correlation between web architecture and stable isotopes, it appears that the isotopic signatures of spiders’ tissues are influenced by architectural differences among their webs. Our findings indicate an important link between web structure, microhabitat preference and diet in the Hawaiian Tetragnatha. A free Plain Language Summary can be found within the Supporting Information of this article.

Large Dietary Niche Overlap of Sympatric Open-space Foraging Bats Revealed by Carbon and Nitrogen Stable Isotopes

Sympatric bats engage in various strategies for dietary niche partitioning such as different microhabitat use; however, no previous study has yet looked at potential dietary niche partitioning in mammals foraging in a space void of any physical structure. Here, we used stable isotope ratios of carbon and nitrogen to investigate if three insectivorous bats of central Thailand, Chaerephon plicatus, Taphozous melanopogon and T. theobaldi, partition food resources when foraging in the open space of the lower boundaries of the troposphere. We quantified the isotopic dietary niches of these species and compared niche dimensions within the guild of openspace foraging bats and between this guild and the edge-foraging bat Hipposideros larvatus. Our results showed that stable isotope ratios of bats differed between wet and dry seasons. Consistently, open-space foraging bat species shared a similar isotopic composition in both seasons, which contrasted that of the edge-space foraging H. larvatus. Isotopic niche dimensions of open-space foraging bats were smaller than those of the edge-space foraging bat. Based on isotopic data, we inferred that open-space foraging bats foraged mostly on dipterans which may fly or drift to higher altitudes where these bats hunt. In contrast, H. larvatus included mostly beetles from C4food webs in their diet, highlighting that this species is an important predator of pest insects of C4crops, namely cane sugar and corn. Our study emphasizes that the unstructured aerosphere in which open-space foraging bats hunt insects may promote a large overlap in the diet of these species. We conclude that mechanisms other than trophic niche differentiation, such as the motion capacity of bat species, both in terms of covered distances and accessed altitudes may facilitate the coexistence of high-altitude foraging bats.