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The separation of macro-level and microbial food webs is typical but has important limits. A multilayered food web conceptual model is needed because microbial food webs are nested within macro-organisms. These multilayered microbial food webs likely influence the network dynamics of macro-level food webs. A multilayered food webs model opens new avenues for empirical investigations into the complexity of ecological networks. The model can provide a new lens through which to view a network's response to ecosystem changes. Food webs are typically defined as being macro-organism-based (e.g., plants, mammals, birds) or microbial (e.g., bacteria, fungi, viruses). However, these characterizations have limits. We propose a multilayered food web conceptual model where microbial food webs are nested within food webs composed of macro-organisms. Nesting occurs through host–microbe interactions, which influence the health and behavior of host macro-organisms, such that host microbiomes likely alter population dynamics of interacting macro-organisms and vice versa. Here, we explore the theoretical underpinnings of multilayered food webs and the implications of this new conceptual model on food web ecology. Our framework opens avenues for new empirical investigations into complex ecological networks and provides a new lens through which to view a network's response to ecosystem changes. [ABSTRACT FROM AUTHOR]

The composition of fatty acids in the muscle tissue of the unique Central Asian carp-like fish, Potanin Altai osman Oreoleuciscus potanini, was studied for the first time. The populations of these fish in the reservoirs of the semiarid zone (Durgun and Taishir) during the period of their formation are considered. It was shown that the content of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in O. potanini corresponds to the median of this value in the order Cypriniformes. It was established that the basis of the food web of the herbivorous form of this species consists of microalgae (diatoms, Euglena and, possibly, chrysophytes), as well as bacteria. At the same time, the levels of bacterial biomarkers, 15-17BCFA and 17:0 were significantly higher in fish in the Durgun reservoir, whereas the level of EPA (diatom biomarker) in O. potanini was higher in the Taishir reservoir. The established higher values of the heavy nitrogen isotope content in the muscles of O. potanini from the Taishir reservoir are most likely associated with the yet unformed benthic communities and with the incomplete diversification of the riverine form of the Potanin Altai osman into lacustrine forms. [ABSTRACT FROM AUTHOR]

Understanding biotic interactions and how they vary across habitats is important for assessing the vulnerability of communities to climate change. Receding glaciers in high mountain areas can lead to the hydrologic homogenization of streams and reduce habitat heterogeneity, which are predicted to drive declines in regional diversity and imperil endemic species. However, little is known about food web structure in alpine stream habitats, particularly among streams fed by different hydrologic sources (e.g., glaciers or snowfields). We used gut content and stable isotope analyses to characterize food web structure of alpine macroinvertebrate communities in streams fed by glaciers, subterranean ice, and seasonal snowpack in the Teton Range, Wyoming, USA. Specifically, we sought to (1) assess community resource use among streams fed by different hydrologic sources, (2) explore how variability in resource use relates to feeding strategies, and (3) identify which environmental variables influenced resource use within communities. Average taxa diet differed among all hydrologic sources, and food webs in subterranean ice‐fed streams were largely supported by the gold alga Hydrurus. This finding bolsters a hypothesis that streams fed by subterranean ice may provide key habitat for cold‐water species under climate change by maintaining a longer growing season for this high‐quality food resource. While a range of environmental variables associated with hydrologic source (e.g., stream temperature) were related to diet composition, hydrologic source categories explained the most variation in diet composition models. Less variable diets within versus among streams suggest high trophic flexibility, which was further supported by high levels of omnivory. This inherent trophic flexibility may bolster alpine stream communities against future changes in resource availability as the mountain cryosphere fades. Ultimately, our results expand understanding of the habitat requirements for imperiled alpine taxa while empowering predictions of their vulnerability under climate change. [ABSTRACT FROM AUTHOR]

Freshwater macroinvertebrates can connect tropical forests and stream food webs by consuming both terrestrially and aquatically produced foods, but direct observations of nocturnal feeding behavior in these natural ecosystems are rare. Observational data on decapods feeding behavior are limited partly because they are cryptic and often forage at night to avoid predators and competitors. We hypothesized that freshwater decapods forage on riparian fruit fall based on its relatively high energy and nutrient content. We used underwater cameras to video record night-time foraging under dim red light. Palm fruits (Acrocomia aculeata (Jacq.) Lodd. ex Mart.) were added to determine rates of feeding responses among crabs (Silviocarcinus australis Magalhães and Turkay, 1996) and shrimp (Macrobrachium amazonicum Heller, 1862) in a spring-fed, clear-water stream in the state of Mato Grosso do Sul, Brazil. Within 30 min, shrimp located the fruit, and within 60 min, crabs began shredding the pulp of the palm fruit. Crabs fed on the palm fruits, on average five times longer than shrimp and produced pieces of palm fruit pulp that some shrimp consumed without aggressively interacting with the crab. Small fish also consumed some palm pulp particles. This interaction network is an example of fruit-fall processing based on indirect facilitation among different types of consumers. [ABSTRACT FROM AUTHOR]

Knowledge about how ecological networks vary across global scales is currently limited given the complexity of acquiring repeated spatial data for species interactions. Yet, recent developments in metawebs highlight efficient ways to first document possible interactions within regional species pools. Downscaling metawebs towards local network predictions is a promising approach to using the current data to investigate the variation of networks across space. However, issues remain in how to represent the spatial variability and uncertainty of species interactions, especially for large-scale food webs. Here, we present a probabilistic framework to downscale a metaweb based on the Canadian mammal metaweb and species occurrences from global databases. We investigated how our approach can be used to represent the variability of networks and communities between ecoregions in Canada. Species richness and interactions followed a similar latitudinal gradient across ecoregions but simultaneously identified contrasting diversity hotspots. Network motifs revealed additional areas of variation in network structure compared with species richness and number of links. Our method offers the potential to bring global predictions down to a more actionable local scale, and increases the diversity of ecological networks that can be projected in space. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'. [ABSTRACT FROM AUTHOR]

Global declines in animal populations suggest global causes. Herbivores are uniquely vulnerable to declines in the nutrient density of the plants they consume. CO 2 pollution is a global agent of nutrient dilution: the impoverishment of plant tissue, bite for bite, of the elements essential for herbivore survival. As plants assimilate higher levels of CO 2 , nutrient dilution can create flammable 'green deserts' of low-quality food for herbivores already limited by elements from nitrogen to sodium to zinc. We posit that nutrient dilution is a key driver – rich in testable predictions – of global declines in herbivore abundance. Its impact should be highest in productive and/or nutrient-poor ecosystems like tropical forests and the open oceans. It is reversed by fertilization. It acts regardless of habitat size or pesticide use. It thus complements these and other agents of herbivore decline. Nutrient dilution (ND) – the decrease in the concentration of nutritional elements in plant tissue – arises from an increase in the mass of carbohydrates and/or a decrease in the 20+ essential elements. Increasing CO 2 levels and its promotion of biomass are linked to nutrient dilution. We build a case for nutrient dilution as a key driver in global declines in herbivore abundance. Herbivores must build element-rich animal tissue from nutrient-poor plant tissue, and their abundance commonly increases with fertilization of both macro- and micronutrients. We predict the global impacts of nutrient dilution will be magnified in some of Earth's most biodiverse, highly productive, and/or nutrient-poor ecosystems and should favor specific traits of herbivores, including sap-feeding and ruminant microbiomes. [ABSTRACT FROM AUTHOR]

Objective: The Redeye Bass Micropterus coosae is a piscivore introduced into California, which has become a threat to the state's endemic freshwater fishes. It has eliminated native fishes from the middle reaches of the Cosumnes River, our study stream, which is the largest stream without a major dam on its main stem in the Sacramento–San Joaquin River drainage, central California, USA. We thoroughly documented its novel life history and ecology in California to shed light on why it has been such a successful invader despite its relatively small native range. Methods: Over 4000 stable carbon and nitrogen isotope samples were utilized to refine our understanding of fish trophic position within the river food web, along with a stable isotope mixing model that accounts for uncertainty in trophic enrichment data. Result: Growth was slow, with an adult size range of 9–25 cm standard length (SL), although few were larger than 15‐cm SL (5–6 years old). Stable isotope analyses showed that Redeye Bass dominate the river ecosystem to the exclusion of most native fishes, occupying multiple trophic levels and microhabitats. Adults largely consumed non‐native crayfish and large aquatic insects, while juveniles consumed aquatic insects, the size of prey increasing with Redeye Bass length. There was no evidence of cannibalism. Redeye Bass have effectively occupied the diverse trophic positions of at least four native fish species and have altered the trophic position of Rainbow Trout Oncorhynchus mykiss in sites where they co‐occur with bass. Conclusion: The introduction of Redeye Bass poses a continuing threat to native stream fishes in California and elsewhere. Impact statementThe Redeye Bass is a predatory fish that is endemic to the Coosa River system, spanning Georgia and Alabama, in the southeastern United States, but introduced into California. It now dominates a California river ecosystem, eliminating native fishes and simplifying the food web. Its success demonstrates the unintended consequences of introducing even fish with a small native range into a region with an already stressed native fish fauna. [ABSTRACT FROM AUTHOR]

Periphyton is an important basal food source for many aquatic consumers by directly or indirectly providing long-chain polyunsaturated fatty acids (LC-PUFA). Although periphyton LC-PUFA content is highly sensitive to aqueous nutrients, the majority of prior studies have been conducted in low-nutrient aquatic environments. Less is known about how periphyton LC-PUFA content may change in response to higher nutrient concentrations in rivers. We conducted a periphyton culturing experiment by manipulating a gradient of aqueous nutrient concentrations from 0.002 to 0.18 mg P/L to investigate how aqueous nutrients affected periphyton FA from oligotrophic to eutrophic waters. Our results showed a significant curvilinear relationship between aqueous water nutrients and periphyton FA. In oligotrophic conditions, periphyton LC-PUFA increased as aqueous nutrients increased, whereas in eutrophic waters, periphyton LC-PUFA decreased as aqueous nutrients increased. The change of taxonomic composition, especially the increase of diatom density, was a significant factor influencing periphyton LC-PUFA content. Additionally, periphyton biomass experienced a significant increase with elevated aqueous nutrients, which differed from periphyton LC-PUFA. Our study detected the response of periphyton FA to aqueous nutrients from oligotrophic to eutrophic conditions, and provided a reference for the protection of river ecosystems. [ABSTRACT FROM AUTHOR]

Understanding the factors that determine the occurrence and strength of ecological interactions under specific abiotic and biotic conditions is fundamental since many aspects of ecological community stability and ecosystem functioning depend on patterns of interactions among species. Current approaches to mapping food webs are mostly based on traits, expert knowledge, experiments, and/or statistical inference. However, they do not offer clear mechanisms explaining how trophic interactions are affected by the interplay between organism characteristics and aspects of the physical environment, such as temperature, light intensity or viscosity. Hence, they cannot yet predict accurately how local food webs will respond to anthropogenic pressures, notably to climate change and species invasions. Herein, we propose a framework that synthesises recent developments in food‐web theory, integrating body size and metabolism with the physical properties of ecosystems. We advocate for combination of the movement paradigm with a modular definition of the predation sequence, because movement is central to predator–prey interactions, and a generic, modular model is needed to describe all the possible variation in predator–prey interactions. Pending sufficient empirical and theoretical knowledge, our framework will help predict the food‐web impacts of well‐studied physical factors, such as temperature and oxygen availability, as well as less commonly considered variables such as wind, turbidity or electrical conductivity. An improved predictive capability will facilitate a better understanding of ecosystem responses to a changing world. [ABSTRACT FROM AUTHOR]

Abstract Global change drives multiple facets of biodiversity including interaction diversity, which is fundamental for ecosystem functioning. However, studying trophic interactions is challenging in meta‐ecosystems, that is ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. While analytical methods based on abundances of polyunsaturated fatty acids (PUFAs) and stable isotopes of amino acids (AAs) are being increasingly used, it has never been explored if both approaches could be: (i) combined in mixing models to enhance precision in dietary inference (ii) compared to disentangle transfers of various PUFAs and proteins in food webs in the wild. We explore the utility of analytical approaches based on PUFA abundances and AA isotopes to resolve resource transfers in a natural riparian food web. We focus on spiders and their potential prey from blue, green and brown sources to address three important and persisting methodological issues in food‐web ecology, namely whether (i) essential AA carbon isotopes can resolve protein origin from blue, green and brown resources, (ii) PUFA relative abundance and AA isotopes can be combined in a mixing model to provide higher precision estimates (i.e. narrower intervals) and (iii) combining the two approaches can unveil the coupling of protein and PUFA transfers in food webs. Our research demonstrates the power of AA isotopes and PUFAs to distinguish blue, green, and brown sources and their transfer up to consumers. We show that combining PUFA relative abundance and AA isotopes in a mixing model provides overall estimates similar to the individual estimates but significantly increases precision. In addition, we showcase how combining approaches unveil the coupling of protein and PUFA transfers. For instance, we show that most PUFAs are less concentrated from prey to predators, relative to proteins, highlighting uncoupling of PUFAs and protein transfer along food chains. We show for the first time the effectiveness of combining AA isotopes and PUFA abundances, particularly relevant for complex trophic interactions in a meta‐ecosystem context. Our study illustrates the trophic uncoupling of proteins and PUFAs, highlighting the necessity in combining both approaches.

Estuaries are essential habitats for recreational and commercial fish that are shaped by both natural and anthropogenic processes. In Louisiana a combination of climate change and planned coastal restoration actions is predicted to increase freshwater introduction to coastal estuaries. As such there is a need to quantify the relationships between estuarine fish ecology and salinity to aid in predicting how species will respond to shifts in salinity. We investigated the relative abundance and dietary niches of adult (24.5 ± 5.4 cm standard length) spotted seatrout Cynoscion nebulosus across varying salinity regimes (oligohaline, mesohaline, and polyhaline) within Barataria Bay, Louisiana, using a combination of net sampling and gut content and stable isotopes analysis. We found that the relative abundance of C. nebulosus was lowest at the oligohaline site, translating to approximately five fewer fish captured for every single psu decrease in a site's average annual salinity. In contrast, we found that diets and, to a lesser extent, isotopic niches had a high degree of overlap across sites with differing salinity regimes. Fish and penaeid shrimp were the most common and important prey taxa recovered from guts at all sites. The small isotopic differences found among sites were likely due to spatial variation in hydrogeochemical baselines, and the observed isotopic overlap provides support for the idea that C. nebulosus move between adjacent salinity regimes and forage throughout Barataria Bay. Our results contribute to a greater understanding of the salinity preference and trophic ecology of C. nebulosus that can aid in predicting their responses to future salinity and habitat changes within Barataria Bay associated with predicted climate change and planned coastal restoration actions. [ABSTRACT FROM AUTHOR]

Zooplankton are the key intermediary between primary production and the fish community and a cornerstone of marine food webs, but they are often poorly represented in models that tend to focus on fish, charismatic top predators, or ocean biogeochemistry. In this study, we use an intermediate complexity end‐to‐end food web model of the North Sea with explicit two‐way coupling of zooplankton to phytoplankton and higher trophic levels to ask whether this matters. We vary the metabolic rate of omnivorous zooplankton (OZ) as a proxy for uncertainties in our understanding and modeling of zooplankton form and function, and moving beyond previous studies we look at the impacts on the food web in concert with climate warming and fishing. We consider impacts on food web state and time to recover the relevant unfished state after fishing ceases. We also consider potential impacts on pelagic and demersal fishing fleets if we assume that they are constrained by the requirement to allow recovery to an unfished state within a certain period of time as a way of ensuring consistency with Good Environmental Status as required by EU and UK legislation. We find that all three aspects considered are highly sensitive to changes in the treatment of zooplankton, with impacts being larger than for warming of 2 or 4°C across most food web functional groups, particularly for apex predators. We call for a programme of research aimed at improving our understanding of zooplankton ecology and its relationship to the wider food web, and we recommend that improved representations of zooplankton are incorporated in future modeling studies as a priority. [ABSTRACT FROM AUTHOR]

Nutrients can shape ecological interactions but remain poorly integrated into ecological networks. Concepts such as nutrient‐specific foraging nevertheless have the potential to expose the mechanisms structuring complex ecological systems. Nutrients also present an opportunity to predict dynamic processes, such as interaction rewiring and extinction cascades, and increase the accuracy of network analyses.Here, we propose the concept of nutritional networks. By integrating nutritional data into ecological networks, we envisage significant advances to our understanding of ecological processes from individual to ecosystem scales.We show that networks can be constructed with nutritional data to illuminate how nutrients structure ecological interactions in natural systems through an empirical example. Throughout, we identify fundamental ecological hypotheses that can be explored in a nutritional network context, alongside methods for resolving those networks.Nutrients influence the structure and complexity of ecological networks through mechanistic processes and concepts including nutritional niche differentiation, functional responses, landscape diversity, ecological invasions and ecosystem robustness. Future research on ecological networks should consider nutrients when investigating the drivers of network structure and function. [ABSTRACT FROM AUTHOR]

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems.Here, we first characterised a tropical stream meta‐food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population‐level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka–Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability.The model resulted in a stable meta‐food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta‐food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non‐specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale.Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size‐dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human‐impacted landscapes. [ABSTRACT FROM AUTHOR]

Increasing human pressures threaten fish diversity, with potentially severe but unknown consequences for the functioning of riverine food webs.Using a 17‐year dataset from multi‐trophic fish communities, we investigated the long‐term effects of human pressure on the diversity and food web functioning. Combining metabolic scaling and ecological network principles, we calculate the annual energy fluxes through trophic compartments (top‐carnivore, mesocarnivore, detritivore and omnivore). Energy fluxes link trophic compartments, and thus represents food web functions such as carnivory, omnivory, herbivory and detritivory.Species richness across all trophic compartments was positively associated with energy flux. However, species richness decreased over time, as did the energy flux at the whole‐network level, which was reduced by 75%. Human pressure negatively affected both species richness and energy flux. Moreover, the negative impacts of human pressure on energy flux have intensified over time.Our results illustrate how human pressure can reduce diversity and erode the energy flux through food webs, with negative implications for the ecosystem functioning. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Global change drives multiple facets of biodiversity including interaction diversity, which is fundamental for ecosystem functioning. However, studying trophic interactions is challenging in meta‐ecosystems, that is ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. While analytical methods based on abundances of polyunsaturated fatty acids (PUFAs) and stable isotopes of amino acids (AAs) are being increasingly used, it has never been explored if both approaches could be: (i) combined in mixing models to enhance precision in dietary inference (ii) compared to disentangle transfers of various PUFAs and proteins in food webs in the wild.We explore the utility of analytical approaches based on PUFA abundances and AA isotopes to resolve resource transfers in a natural riparian food web. We focus on spiders and their potential prey from blue, green and brown sources to address three important and persisting methodological issues in food‐web ecology, namely whether (i) essential AA carbon isotopes can resolve protein origin from blue, green and brown resources, (ii) PUFA relative abundance and AA isotopes can be combined in a mixing model to provide higher precision estimates (i.e. narrower intervals) and (iii) combining the two approaches can unveil the coupling of protein and PUFA transfers in food webs.Our research demonstrates the power of AA isotopes and PUFAs to distinguish blue, green, and brown sources and their transfer up to consumers. We show that combining PUFA relative abundance and AA isotopes in a mixing model provides overall estimates similar to the individual estimates but significantly increases precision. In addition, we showcase how combining approaches unveil the coupling of protein and PUFA transfers. For instance, we show that most PUFAs are less concentrated from prey to predators, relative to proteins, highlighting uncoupling of PUFAs and protein transfer along food chains.We show for the first time the effectiveness of combining AA isotopes and PUFA abundances, particularly relevant for complex trophic interactions in a meta‐ecosystem context. Our study illustrates the trophic uncoupling of proteins and PUFAs, highlighting the necessity in combining both approaches. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) pose a significant and increasing threat globally, with plastics accounting for around 60–80% of marine trash. Plastic particles with a size of 5000 µm or less are referred to as microplastics (MPs). These MPs can enter the marine organisms either through their diet or by trophic transfer. This can potentially expose people to these particles. According to the literature, around 21.9% of fish, 18.4% of seabirds, 11.7% of arthropods, and 7.8% of molluscs in marine systems are at risk from plastic pollution. The LATAM region experiences significant MP contamination that primarily originates from wastewater treatment plants, industrial effluents, maritime sources, and the decomposition of macro–mesoplastics. The majority of research conducted in the LATAM region focuses on MPs in natural habitats, specifically examining the presence of MPs in biota (such as fish, mussels, squids, turtles, and even insects) and sediments. In order to conduct a thorough analysis of the sources and spread of microplastics (MPs) in marine organisms, we conducted a comprehensive assessment of the available literature on microplastic research in Latin American countries. The objective was to evaluate the origin, destinations, and pathways via which MPs are transferred. An assessment of the prevalence of microplastics (MPs) in marine organisms would yield significant insights into the potential health hazards posed by plastic pollution to humans. [ABSTRACT FROM AUTHOR]

Aim Location Time Period Major Taxa Studied Methods Results Main Conclusions The relationship between body size and trophic position (BS–TP) typically exhibits a positive correlation in aquatic foodwebs, but the strength of this relationship is contingent on ecosystem type and climate. Different hypotheses have been proposed to elucidate climate and ecosystem type effects on the BS–TP relationship for ray‐finned fish. However, our understanding of whether such a relationship evolved in a correlated fashion, spanning various climates and ecosystem types, remains limited.Temperate and tropical marine and freshwater ecosystems.Present to millions of years ago.Ray‐finned fish.We used a phylogenetic tree and TP and BS data of more than a thousand freshwater and marine ray‐finned fishes, from distinct climates and ecosystems, to investigate patterns on macroevolutionary time scales of the evolutionary correlation of BS and TP. As part of our investigation, we also ran analyses excluding herbivores and detritivores from the dataset, then further focusing solely on carnivores.We found distinct patterns of the BS–TP evolutionary correlation for different climates and ecosystems. The evolutionary correlation between BS and TP was significant for all ecosystem type–climate combinations, except for tropical freshwater ecosystems. The results remained consistent even after accounting for phylogenetic uncertainty and when excluding herbivores and detritivores from the analysis.We found a weaker evolutionary correlation between BS and TP in tropical freshwater ecosystems. These findings are consistent with the stronger BS–TP relationship between extant taxa in temperate climates compared to the tropics, illustrating how evolutionary dynamics might have influenced the trophic structure of fish and contributed to shaping macroecological patterns of the BS–TP relationship. Our findings suggest that limitations that hinder evolutionary integration between BS and TP might be primarily attributed to energetic constraints imposed by temperature and the availability of C‐rich food resources at the base of the foodweb. [ABSTRACT FROM AUTHOR]

Assessments of ecosystem functioning are a fundamental ecological challenge and an essential foundation for ecosystem‐based management. Species trophic position (TP) is essential to characterize food web architecture. However, despite the intuitive nature of the concept, empirically estimating TP is a challenging task due to the complexity of trophic interaction networks. Various methods are proposed to assess TPs, including using different sources of organic matter at the base of the food web (the 'baseline'). However, it is often not clear which methodological approach and which baseline choices are the most reliable. Using an ecosystem‐wide assessment of a tropical reef (Marquesas Islands, with available data for 70 coral reef invertebrate and fish species), we tested whether different commonly used TP estimation methods yield similar results and, if not, whether it is possible to identify the most reliable method. We found significant differences in TP estimates of up to 1.7 TPs for the same species, depending on the method and the baseline used. When using bulk stable isotope data, the choice of the baseline significantly impacted TP values. Indeed, while nitrogen stable isotope (δ15N) values of macroalgae led to consistent TP estimates, those using phytoplankton generated unrealistically low TP estimates. The use of a conventional enrichment factor (i.e. 3.4‰) or a 'variable' enrichment factor (i.e. according to feeding guilds) also produced clear discrepancies between TP estimates. TPs obtained with δ15N values of source amino acids (compound‐specific isotope analysis) were close to those assessed with macroalgae. An opposite seasonal pattern was found, with significantly lower TPs in winter than in summer for most species, with particularly pronounced differences for lower TP species. We use the observed differences to discuss possible drivers of the diverging TP estimates and the potential ecological implications. Based on a case study from a remote coral reef ecosystem in the Pacific Ocean, this work analyses how several potential sources of organic matter (i.e. 'baselines') and calculation methods strongly affect assessments of trophic positions. We also demonstrated that seasonal temporality and feeding guild are important parameters to be considered. [ABSTRACT FROM AUTHOR]

We used an extensive multispecies dataset to examine how C and N stable isotope ratios (δ13C and δ15N) of aquatic consumers varied with body size in populations of northern lakes. Ontogenetic variation in tissue δ13C and δ15N was evident in a diversity of aquatic consumers. Relationships with body size tended to be stronger and more consistently positive for δ15N, and more variable in nature for δ13C. Among-population variation in ontogenetic slopes was greater for δ13C than for δ15N for most biota examined. Relationships between δ13C and δ15N and body size were still significant even after accounting for variation owing to tissue C:N and body condition. Ontogenetic variation was more strongly linked to age than body size in some fishes, particularly for δ15N, but age effects, inferred from growth rate, also accounted for variation in δ13C and δ15N beyond body size effects; δ13C tended to be positively related and δ15N tended to be negatively related to growth rate. There was only limited evidence of concordance in ontogenetic slopes between co-habiting pairs of species, suggesting that the factors driving ontogenetic variation in stable isotope ratios may be largely species- or population-specific. However, ontogenetic slopes of individual taxa were related to various lake habitat features representing climate, ecosystem size, and water clarity. The proportion of isotopic niche space attributable to ontogenetic variation can be substantial and this has implications for applying and interpreting isotopic niche metrics. Our study provides the broadest and most comprehensive analysis of ontogenetic variation in isotopic compositions of freshwater consumers to date and our results underscore the need to account for this variation in the analysis of freshwater food webs. [ABSTRACT FROM AUTHOR]

Biological invasions can threaten biodiversity by outcompeting native species and disrupting food webs. Invasive species are now a leading driver of biodiversity and imperiled species declines worldwide. In temperate forests of eastern North America, understory plant communities are frequently dominated by invasive woody shrubs and trees. For many species of insectivorous birds and mammals, these invasive plants may threaten populations by providing less and/or lower quality food. Conservation practitioners expend significant resources to remove invasive plants, but evidence that such practices improve food abundance or quality to wildlife is surprisingly limited. Using a bird exclusion experiment, we compared arthropod abundance, biomass, and quality (protein content), and bird foraging intensity among four invasive and six native woody plant species in a Connecticut, USA forest. Analysis revealed instances where native trees were actually poorer foraging resources for songbirds than certain species of invasive shrubs. Some invasive species, such as honeysuckle (Lonicera morrowii), supported higher arthropod biomass and protein content than the native plants. Conversely, Japanese barberry (Berberis thunbergii) had fewer arthropods overall and arthropods of lower protein content compared to native shrubs. Contrary to predictions from other food web experiments, bird predation effects were of similar magnitude on native and invasive plants, demonstrating that insectivorous songbirds foraged as intensively on the invasive plants as they did on the native plants. We recommend a regionally tailored and species-specific approach to invasive plant management that targets species that provide low-quality foraging opportunities relative to the quality of the local native plant community. [ABSTRACT FROM AUTHOR]

Conservation and restoration of wetlands have become a global priority as awareness of their importance increases. At present, efforts to restore wetlands have primarily focused on enhancing water quality and biodiversity, with little attention paid to analyzing the recovery of the food web. We investigated the differences in food web attributes between natural and restored wetlands in Qingtongxia wetlands on the upper reaches of the Yellow River, China. Our results showed that there were no significant differences in the community structure of aquatic organism (fish, macroinvertebrates, zooplankton, phytoplankton and macrophytes) and water parameters (TP, TN, DO, et al.) between natural and restored wetlands. Restored wetlands had higher total system throughput and primary productivity compared to natural wetlands, which increased the proportion of the detritus food chain in the energy supply. However, energy transfer at the system level was less efficient than in natural wetlands. Indices of cycling, path length and network analysis showed that the restored wetland was less mature but more stable than the natural wetland. Given the inconsistency of food web recovery with water variables and aquatic assemblages, integrating community and food web approaches in future wetland restoration will be critical to refining restoration goals and enhancing conservation efforts. [ABSTRACT FROM AUTHOR]

Protist plankton can be divided into three main groups: phytoplankton, zooplankton, and mixoplankton. In situ methods for studying phytoplankton and zooplankton are relatively straightforward since they generally target chlorophyll/photosynthesis or grazing activity, while the integration of both processes within a single cell makes mixoplankton inherently challenging to study. As a result, we understand less about mixoplankton physiology and their role in food webs, biogeochemical cycling, and ecosystems compared to phytoplankton and zooplankton. In this paper, we posit that by merging conventional techniques, such as microscopy and physiological data, with innovative methods like in situ single-cell sorting and omics datasets, in conjunction with a diverse array of modeling approaches ranging from singlecell modeling to comprehensive Earth system models, we can propel mixoplankton research into the forefront of aquatic ecology. We present eight crucial research questions pertaining to mixoplankton and mixotrophy, and briefly outline a combination of existing methods and models that can be used to address each question. Our intent is to encourage more interdisciplinary research on mixoplankton, thereby expanding the scope of data acquisition and knowledge accumulation for this understudied yet critical component of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Linking the species interactions occurring at the scale of local communities to their potential impact at evolutionary timescales is challenging. Here, we used the high‐resolution fossil record of mammals from the Iberian Peninsula to reconstruct a timeseries of trophic networks spanning more than 20 million years and asked whether predator–prey interactions affected regional extinction patterns. We found that, despite small changes in species richness, trophic networks showed long‐term trends, gradually losing interactions and becoming sparser towards the present. This restructuring of the ecological networks was driven by the loss of medium‐sized herbivores, which reduced prey availability for predators. The decrease in prey availability was associated with predator longevity, such that predators with less available prey had greater extinction risk. These results not only reveal long‐term trends in network structure but suggest that prey species richness in ecological communities may shape large scale patterns of extinction and persistence among predators. [ABSTRACT FROM AUTHOR]

In North America, white‐nose syndrome (WNS) has caused precipitous declines in hibernating bat populations, raising the question of whether the rapid loss of arthropodivorous bats may affect the abundance of their prey. During the summers of 2015–2018 (1 year after the arrival of WNS in Wisconsin, USA), we performed intensive arthropod black‐light trapping, ultrasonic acoustic monitoring, and emergence counts at 10 little brown (Myotis lucifugus) and big brown (Eptesicus fuscus) bat maternity roosts with paired control sites. For little brown bats, which are severely affected by WNS, roost counts declined by 95% over the four‐year period, compared to a 38% decline in big brown bat roost counts. Total arthropod abundance decreased by 49%, although decreases among common little brown bat prey were less severe. Our natural predator exclusion experiment supports existing evidence that bats can have measurable trophic impacts on arthropod communities, primarily via top‐down effects on common prey. [ABSTRACT FROM AUTHOR]

Warming temperatures are altering communities and trophic networks across Earth's ecosystems. While the overall influence of warming on food webs is often context‐dependent, increasing temperatures are predicted to change communities in two fundamental ways: (1) by reducing average body size and (2) by increasing individual metabolic rates. These warming‐induced changes have the potential to influence the distribution of food web fluxes, food web stability, and the relative importance of deterministic and stochastic ecological processes shaping community assembly. Here, we quantified patterns and the relative distribution of organic matter fluxes through stream food webs spanning a broad natural temperature gradient (5–27°C). We then related these patterns to species and community trait distributions of mean body size and population biomass turnover (P:B) within and across streams. We predicted that (1) communities in warmer streams would exhibit smaller body size and higher P:B and (2) organic matter fluxes within warmer communities would increasingly skew toward smaller, higher P:B populations. Across the temperature gradient, warmer communities were characterized by smaller body size (~9% per °C) and higher P:B (~7% faster turnover per °C) populations on average. Additionally, organic matter fluxes within warmer streams were increasingly skewed toward higher P:B populations, demonstrating that warming can restructure organic matter fluxes in both an absolute and relative sense. With warming, the relative distribution of organic matter fluxes was decreasingly likely to arise through the random sorting of species, suggesting stronger selection for traits driving high turnover with increasing temperature. Our study suggests that a warming world will favor energy fluxes through "smaller and faster" populations, and that these changes may be more predictable than previously thought. [ABSTRACT FROM AUTHOR]

Carbon (δ13C) and nitrogen (δ15N) isotopes were used to evaluate spatial, temporal, and interspecific differences in trophic relationships of four fish species (Paralichthys dentatus, Anchoa mitchilli, Leiostomus xanthurus, and Bairdiella chrysoura) in Maryland's coastal bays. The δ13C values for all species were more enriched in 2017 than in 2018, a year of higher-than-average rainfall that likely caused higher amounts of terrestrial carbon to enter the estuary. There were significant differences among species in the δ13C values, with L. xanthurus being the least depleted (−17.2‰ in 2017; −18.8‰ in 2018). Spatially, the δ13C values of the species, particularly P. dentatus and B. chrysoura, were more depleted in the northern bays, which have a higher nutrient content and receive more freshwater inflow directly from tributaries, than the southern bays. The observed δ13C values (−19.5 ± 0.2‰ to –17.2 ± 0.3‰), however, indicate that marine phytoplankton was the primary carbon source of the fishes. Overall, A. mitchilli was the most enriched in δ15N (13.0‰), and L. xanthurus was the most depleted (10.2‰). δ15N was more enriched in fish from the more human-impacted northern bays than in fish from the southern bays, though this might also have stemmed from the differences in the diet composition of the species in the northern and southern bays. A. mitchilli had the highest trophic level, while L. xanthurus and P. dentatus had the lowest trophic levels. Niche breadth was widest in L. xanthurus compared to the other fish species, suggesting a higher variability in diets among L. xanthurus individuals, leading to specialized diets. There was a high niche overlap between B. chrysoura, A. mitchilli, and L. xanthurus, which indicates they fed on similar prey resources. [ABSTRACT FROM AUTHOR]

The Structure of Scientific Revolutions by Thomas Kuhn has influenced scientists for decades. It focuses on a progression of science involving periodic, fundamental shifts-revolutions-from one existing paradigm to another. Embedded in this theory is the concept of normal science, that is, scientists work within the confines of established theory, a process often compared to a type of puzzle-solving. This Kuhnian aspect of scientific research has received little attention relative to the much-scrutinized concepts of revolutions and paradigms. We use Kuhn's normal science framework to reflect on the way ecologists practice science. This involves a discussion of how theory dependence influences each step of the scientific method, specifically, how past experiences and existing research frameworks guide the way ecologists acquire knowledge. We illustrate these concepts with ecological examples, including food web structure and the biodiversity crisis, emphasizing that the way one views the world influences how that person engages in scientific research. We conclude with a discussion of how Kuhnian ideas inform ecological research at practical levels, such as influences on grant funding allocation, and we make a renewed call for the inclusion of philosophical foundations of ecological principles in pedagogy. By studying the processes and traditions of how science is carried out, ecologists can better direct scientific insight to address the world's most pressing environmental problems.

Abstract Understanding biotic interactions and how they vary across habitats is important for assessing the vulnerability of communities to climate change. Receding glaciers in high mountain areas can lead to the hydrologic homogenization of streams and reduce habitat heterogeneity, which are predicted to drive declines in regional diversity and imperil endemic species. However, little is known about food web structure in alpine stream habitats, particularly among streams fed by different hydrologic sources (e.g., glaciers or snowfields). We used gut content and stable isotope analyses to characterize food web structure of alpine macroinvertebrate communities in streams fed by glaciers, subterranean ice, and seasonal snowpack in the Teton Range, Wyoming, USA. Specifically, we sought to (1) assess community resource use among streams fed by different hydrologic sources, (2) explore how variability in resource use relates to feeding strategies, and (3) identify which environmental variables influenced resource use within communities. Average taxa diet differed among all hydrologic sources, and food webs in subterranean ice‐fed streams were largely supported by the gold alga Hydrurus. This finding bolsters a hypothesis that streams fed by subterranean ice may provide key habitat for cold‐water species under climate change by maintaining a longer growing season for this high‐quality food resource. While a range of environmental variables associated with hydrologic source (e.g., stream temperature) were related to diet composition, hydrologic source categories explained the most variation in diet composition models. Less variable diets within versus among streams suggest high trophic flexibility, which was further supported by high levels of omnivory. This inherent trophic flexibility may bolster alpine stream communities against future changes in resource availability as the mountain cryosphere fades. Ultimately, our results expand understanding of the habitat requirements for imperiled alpine taxa while empowering predictions of their vulnerability under climate change.

We examined the feeding ecology of planktonic crustaceans at three waterbodies situated across a latitudinal gradient in Europe (Croatia, Poland, Lithuania) using stable isotope measurements (δ13C, δ15N) in animal tissues. Relative, lake-specific values of δ15N showed that in all lakes, calanoid copepods occupied the highest trophic position, while Daphnia sp. and Diaphanosoma sp. were located closer to primary producers with Cyclopoid copepods located between these groups. We found a negative correlation between C:N ratio (proxy for lipid content) and δ15N, which indicates lipid content declined with the trophic level of the animals. Employment of stable isotope-based approach allows better recognition of trophic linkages than could be inferred from classical methods, and therefore our results contribute improvement of management strategies developed for aquatic ecosystems.

In spring (April 28‒May16, 2022) plankton of the shallow-water zone of the Rybinsk Reservoir, the biomass of large, predatory ciliates with symbiotic algae was 5‒8 times lower than that in the periods of late April‒May of 1971 and 1977, and their share in the total biomass of ciliates (Bcil) decreased from 46.5−47.1% to 8.9%. At the same time, the biomass of algophagous ciliates in the plankton increased by 1.8−2.0 times and their proportion in Bcil – from 15.7−24.5% to 44.6%. In April‒May 2022, ciliates were the main component of the planktonic community of heterotrophic organisms and viruses. In the planktonic food web of the reservoir shallow zone, they played a key role in the transformation of organic carbon of primary producers and detritus to a higher trophic level.

Temporal variation in food web structure is widespread among highly seasonal environments, such as the Arctic, and is driven by changes in resource availability. Variation in resource availability can lead to species differences in diet composition, isotopic niche width, and trophic position (TP) across seasons. Here, we used tissue samples that represent two distinct turnover rates for diet (liver = shorter term, muscle = longer term) from 18 fish and three marine mammal species to investigate seasonal (i) variation in TPs within the Southampton Island marine ecosystem of Hudson Bay, (ii) variation in consumer isotopic niche width within this part of the food web, and (iii) variation in community niche dynamics among a fish and marine mammal community using stable carbon (δ13C) and nitrogen (δ15N) isotope analyses. Many zooplanktivores and piscivores increased in TP in summer (i.e., shorter-term turnover period), whereas benthic feeders dependent on ice-obligate prey decreased in TP. Most isotopic niche widths and community metrics (δ15N range, total ellipse area, mean centroid distance) were higher in liver than muscle. Our findings demonstrate seasonal changes in TPs, which suggests that Arctic communities may be differentially affected by longer ice-free periods and earlier onset of primary production due to accelerated climate change.

Quantifying trophic relationships of marine species is fundamental to the construction and performance of ecosystem models, development of effective ecosystem-based fisheries management strategies, and support of trait-based approaches to ecological risk assessment. Accounting for food web dynamics in taxonomically diverse ecosystems, such as the California Current Large Marine Ecosystem (CCLME), is especially challenging because of the sheer number of trophic linkages and their inherent variability. Consequently, analyses that can inform the most appropriate means of aggregating species or other taxonomic groups into assemblages or guilds are critical to reducing system complexity for modeling and management, particularly when data are limited. To provide a methodological approach that is globally applicable in such cases, we define trophic guilds within biogeographic regions of the CCLME, compare results among these regions, and discuss ecological and management implications. Within each biogeographic region, predator guilds were clearly demarcated by foraging habitat (benthic, nearshore pelagic, offshore pelagic), scale of foraging movements, and trophic position. Furthermore, trophic guilds were distinctive for each region, with species composition and the noted ecological characteristics largely driving guild structure. Predator species that are reliant on continental slope and offshore foraging habitat, such as adult Pacific Hake, have diets that are representative of these areas and are similar throughout the CCLME. Generally, larger, more mobile predators that typically feed in deeper offshore waters, including swordfish, sea lions, and sharks clustered together in multiple bioregions along the coast; all reliant primarily on fishes and squids. Throughout bioregions, groundfishes preyed on benthic invertebrates (e.g., decapods, amphipods, polychaetes), while shelf-oriented pelagic predators, including smaller salmon, preyed on pelagic invertebrates (e.g., euphausiids, copepods, gelatinous zooplankton). A large number of forage taxa that are well represented in this study have dynamics largely dependent on oceanographic conditions at a regional scale (e.g., decapods), basin scale (e.g., copepods), or a combination of both (e.g., euphausiids, Northern Anchovy). Such distinctions indicate that spatial and temporal scales of coherence of predators and prey also must be considered in development of ecosystem models and evaluation of management strategies. Our study quantifies the spatial coherence of predator guilds integrated over decades within and across bioregions of the CCLME, providing an improved understanding of regional ecosystem functioning. The analytical approach we developed may be easily extended to address similar ecological and ecosystem based fisheries management priorities in other marine regions.

Abstract: Aim: Theory predicts fish community biomass to decline with increasing temperature due to higher metabolic losses resulting in less efficient energy transfer in warm‐water food webs. However, whether these metabolic predictions explain observed macroecological patterns in fish community biomass is virtually unknown. Here, we test these predictions by examining the variation in demersal fish biomass across productive shelf regions. Location: Twenty one continental shelf regions in the North Atlantic and Northeast Pacific. Time Period: 1980–2015. Major Taxa Studied: Marine teleost fish and elasmobranchs. Methods: We compiled high‐resolution bottom trawl survey data of fish biomass containing 166,000 unique tows and corrected biomass for differences in sampling area and trawl gear catchability. We examined whether relationships between net primary production and demersal fish community biomass are mediated by temperature, food‐web structure and the level of fishing exploitation, as well as the choice of spatial scale of the analysis. Subsequently, we examined if temperature explains regional changes in fish biomass over time under recent warming. Results: We find that biomass per km2 varies 40‐fold across regions and is highest in cold waters and areas with low fishing exploitation. We find no evidence that temperature change has impacted biomass within marine regions over the time period considered. The biomass variation is best explained by an elementary trophodynamic model that accounts for temperature‐dependent trophic efficiency. Main Conclusions: Our study supports the hypothesis that temperature is a main driver of large‐scale cross‐regional variation in fish community biomass. The cross‐regional pattern suggests that long‐term impacts of warming will be negative on biomass. These results provide an empirical basis for predicting future changes in fish community biomass and its associated services for human wellbeing that is food provisioning, under global climate change.

Substantial increases in non-native aquatic vegetation have occurred in the upper San Francisco Estuary over the last 2 decades, largely from the explosive growth of a few submerged and floating aquatic plant species. Some of these species act as ecosystem engineers by creating conditions that favor their further growth and expansion as well as by modifying habitat for other organisms. Over the last decade, numerous studies have investigated patterns of expansion and turn-over of aquatic vegetation species; effects of vegetation on ecosystem health, water quality, and habitat; and effects of particular species or communities on physical processes such as carbon and sediment dynamics. Taking a synthetic approach to evaluate what has been learned over the last few years has shed light on just how significant aquatic plant species and communities are to ecosystems in the Sacramento-San Joaquin Delta. Aquatic vegetation affects every aspect of the physical and biotic environment, acting as ecosystem engineers on the landscape. Furthermore, their effects are constantly changing across space and time, leaving many unanswered questions about the full effects of aquatic vegetation on Delta ecosystems and what future effects may result, as species shift in distribution and new species are introduced. Remaining knowledge gaps underlie our understanding of aquatic macrophyte effects on Delta ecosystems, including their roles and relationships with respect to nutrients and nutrient cycling, evapotranspiration and water budgets, carbon and sediment, and emerging effects on fish species and their habitats. This paper explores our current understanding of submerged and floating aquatic vegetation (SAV and FAV) ecology with respect to major aquatic plant communities, observed patterns of change, interactions between aquatic vegetation and the physical environment, and how these factors affect ecosystem services and disservices within the upper San Francisco Estuary.

Background: Together with the intensification of dry seasons in Neotropical regions, increasing deforestation is expected to exacerbate species extinctions, something that could lead to dramatic shifts in multitrophic communities and ecosystem functions. Recent studies suggest that the effects of habitat loss are greater where precipitation has decreased. Yet, experimental studies of the pure and interactive effects of drought and deforestation at ecosystem level remain scarce. Methods: Here, we used rainshelters and transplantation from rainforest to open areas of natural microcosms (the aquatic ecosystem and microbial-faunal food web found within the rainwater-filled leaves of tank bromeliads) to emulate drought and deforestation in a full factorial experimental design. We analysed the pure and interactive effects of our treatments on functional community structure (including microorganisms, detritivore and predatory invertebrates), and on leaf litter decomposition in tank bromeliad ecosystems. Results: Drought or deforestation alone had a moderate impact on biomass at the various trophic level, but did not eliminate species. However, their interaction synergistically reduced the biomass of all invertebrate functional groups and bacteria. Predators were the most impacted trophic group as they were totally eliminated, while detritivore biomass was reduced by about 95%. Fungal biomass was either unaffected or boosted by our treatments. Decomposition was essentially driven by microbial activity, and did not change across treatments involving deforestation and/or drought. Conclusions: Our results suggest that highly resistant microorganisms such as fungi (plus a few detritivores) maintain key ecosystem functions in the face of drought and habitat change. We conclude that habitat destruction compounds the problems of climate change, that the impacts of the two phenomena on food webs are mutually reinforcing, and that the stability of ecosystem functions depends on the resistance of a core group of organisms. Assuming that taking global action is more challenging than taking local-regional actions, policy-makers should be encouraged to implement environmental action plans that will halt habitat destruction, to dampen any detrimental interactive effect with the impacts of global climate change. [ABSTRACT FROM AUTHOR]

Identification of the key biotic and abiotic drivers within food webs is important for understanding species abundance changes in ecosystems, particularly across ecotones where there may be strong variation in interaction strengths. Using structural equation models (SEMs) and four decades of integrated data from the San Francisco Estuary, we investigated the relative effects of top‐down, bottom‐up, and environmental drivers on multiple trophic levels of the pelagic food web along an estuarine salinity gradient and at both annual and monthly temporal resolutions. We found that interactions varied across the estuarine gradient and that the detectability of different interactions depended on timescale. For example, for zooplankton and estuarine fishes, bottom‐up effects appeared to be stronger in the freshwater upstream regions, while top‐down effects were stronger in the brackish downstream regions. Some relationships (e.g., bottom‐up effects of phytoplankton on zooplankton) were seen primarily at annual timescales, whereas others (e.g., temperature effects) were only observed at monthly timescales. We also found that the net effect of environmental drivers was similar to or greater than bottom‐up and top‐down effects for all food web components. These findings can help identify which trophic levels or environmental factors could be targeted by management actions to have the greatest impact on estuarine forage fishes and the spatial and temporal scale at which responses might be observed. More broadly, this study highlights how environmental gradients can structure community interactions and how long‐term data sets can be leveraged to generate insights across multiple scales. [ABSTRACT FROM AUTHOR]

Low-order streams and riparian wetlands are important contributors to the drainage network in the landscape. However, there has been little research into the nature of these ecosystems in Brazil. Our estimates show that riparian wetlands of low-order streams and other small associated wetlands cover at least 25% of the forested part of the Amazon basin and about 10% of the Cerrado region. Information on the semi-arid Caatinga is lacking, but ~ 3% of the area may be occupied by riparian wetlands and other small wetland types, many of which are periodically dry. Riparian vegetation includes a very large richness in tree species. The amount and species richness of herbaceous plants depend on light availability. In-streams of the semi-arid region of Brazil, hydrophytes are restricted by unpredictable flash floods and periodic drought. Aquatic food webs are largely based on the organic matter produced by the riparian vegetation. Large-scale agriculture and cattle ranching pose a serious threat to riparian wetlands, their biodiversity, and their function as a buffer in the hydrological cycle of the landscape. A nation-wide screening program would provide a more detailed picture and allow the elaboration of a national conservation and restoration program for the Brazilian riparia. [ABSTRACT FROM AUTHOR]

The overall assumption that scorpions are generalist predators is often based on conspicuous information from the literature. Here, we compiled a list of prey consumption by scorpions from different environments in Brazil to produce a documentation of predations by this taxon. This list is based on observations made under natural conditions in Atlantic Forest, Caatinga, and Cerrado formations. We compiled 135 predation instances including 11 scorpion species from field work through 14 years. The observed diet composition of the scorpions was mainly based on cockroaches, crickets, grasshoppers, spiders, and other scorpions. Such data highlights the generalist diet and cannibalism of scorpions with many cannibalistic events among the records of intraguild predation. Overall, this study broadens the knowledge of the diet composition of Brazilian scorpions under natural conditions. [ABSTRACT FROM AUTHOR]

Functional responses describe foraging rates across prey densities and underlie many fundamental ecological processes. Most functional response knowledge comes from simplified lab experiments, but we do not know whether these experiments accurately represent foraging in nature. In addition, the difficulty of conducting multispecies functional response experiments means that it is unclear whether interaction strengths are weakened in the presence of multiple prey types. We developed a novel method to estimate wild predators' foraging rates from metabarcoding data and use this method to present functional responses for wild wolf spiders foraging on 27 prey families. These field functional responses were considerably reduced compared to lab functional responses. We further find that foraging is sometimes increased in the presence of other prey types, contrary to expectations. Our novel method for estimating field foraging rates will allow researchers to determine functional responses for wild predators and address long‐standing questions about foraging in nature. [ABSTRACT FROM AUTHOR]

How diverse species coexist in nature remains a challenging issue that is not yet resolved in ecology. The traditional approach to tackling this problem uses an ecological community network comprising various biological interaction links between species, such as predator-prey, mutualism, and competition. However, in nature, the interaction between any species pair is not limited to a singular interaction; instead, various interactions occur mostly in two ways, such as competition/facilitation in plants, mutualism/antagonism in consumer-resource mutualisms, and reciprocal predation. Here, using an ecological community model, I show that such so-called dual interactions play a key role in stabilizing ecological communities. Theory predicts that dual interactions can stabilize ecological communities through the balance of positive and negative effects, which behave as if the interactions disappear. Communities with dual interactions are inherently more stable than a classical random community with multiple types of singular interactions, suggesting that dual interactions are more widespread than expected in nature and help to maintain ecological communities. [ABSTRACT FROM AUTHOR]

Quantifying trophic relationships within and between species in terms of trophic position, ontogeny and trophic diversity provides information on community-level structure and function. Little attention has been focused on examining the trophic structure and temporal changes of communities in freshwater-marine coupled systems in the subarctic and associated impacts of anthropogenic activity on trophic interactions. Therefore, the objective of this study was to quantify the trophic position of mobile consumers (15 species in total) within the lower Churchill River area (Churchill, Manitoba, Canada), examine trophic position variation in relation to ontogeny, and measure the trophic diversity of a fish assemblage before (1993–1995) and after (2019–2020) the installation of the Churchill River weir in the late 1990s. We used stable isotopes (δ13C and δ15N) to quantify individual and group-level variation in trophic position of thirteen fish species and two seal species and also assessed six community-level metrics of a three fish species assemblage between time periods. Overall, species that mainly foraged on freshwater resources occupied lower trophic positions than species that mainly consumed marine resources. Trophic position increased with fish age only in cisco, fourhorn sculpin, Greenland cod and northern pike. A temporal shift from a trophically diverse to a more trophically redundant fish assemblage occurred between 1993–1995 and 2019–2020. As a result, these predator species now play similar trophic roles. Information on the long-term change in trophic structure of this sub-Arctic estuarine system may help with understanding how anthropogenic activity and climate change have influenced the trophic diversity of a fish assemblage inhabiting this system. [ABSTRACT FROM AUTHOR]

Abstract Assessments of ecosystem functioning are a fundamental ecological challenge and an essential foundation for ecosystem‐based management. Species trophic position (TP) is essential to characterize food web architecture. However, despite the intuitive nature of the concept, empirically estimating TP is a challenging task due to the complexity of trophic interaction networks. Various methods are proposed to assess TPs, including using different sources of organic matter at the base of the food web (the ‘baseline’). However, it is often not clear which methodological approach and which baseline choices are the most reliable. Using an ecosystem‐wide assessment of a tropical reef (Marquesas Islands, with available data for 70 coral reef invertebrate and fish species), we tested whether different commonly used TP estimation methods yield similar results and, if not, whether it is possible to identify the most reliable method. We found significant differences in TP estimates of up to 1.7 TPs for the same species, depending on the method and the baseline used. When using bulk stable isotope data, the choice of the baseline significantly impacted TP values. Indeed, while nitrogen stable isotope (δ15N) values of macroalgae led to consistent TP estimates, those using phytoplankton generated unrealistically low TP estimates. The use of a conventional enrichment factor (i.e. 3.4‰) or a ‘variable’ enrichment factor (i.e. according to feeding guilds) also produced clear discrepancies between TP estimates. TPs obtained with δ15N values of source amino acids (compound‐specific isotope analysis) were close to those assessed with macroalgae. An opposite seasonal pattern was found, with significantly lower TPs in winter than in summer for most species, with particularly pronounced differences for lower TP species. We use the observed differences to discuss possible drivers of the diverging TP estimates and the potential ecological implications.

The potential for forecasting the dynamics of ecological systems is currently unclear, with contrasting opinions regarding its feasibility due to ecological complexity. To investigate forecast skill within and across systems, we monitored a microbial system exposed to either constant or fluctuating temperatures in a 5-month-long laboratory experiment. We tested how forecasting of species abundances depends on the number and strength of interactions and on model size (number of predictors). We also tested how greater system complexity (i.e. the fluctuating temperatures) impacted these relations. We found that the more interactions a species had, the weaker these interactions were and the better its abundance was predicted. Forecast skill increased with model size. Greater system complexity decreased forecast skill for three out of eight species. These insights into how abundance prediction depends on the connectedness of the species within the system and on overall system complexity could improve species forecasting and monitoring.

The content of total mercury in organs and tissues (brain, muscles, kidneys, and liver) has been studied in common shrew and in common vole, living in different geomorphological regions of the Vologda Oblast. Mercury content is statistically significantly higher (2–5 times) in common shrew than in common vole. In common shrew, average mercury content (μg/g dry weight) decreases in the series: kidneys (0.158 ± 0.016) > liver (0.086 ± 0.01) > muscles (0.084 ± 0.011) > brain (0.059 ± 0.006); in common vole, kidneys (0.026 ± 0.003) > brain (0.024 ±0.004) > muscles (0.016 ±0.003) > liver (0.013 ± 0.002). Mercury content in organs of common shrew and of common vole, caught in the western geomorphological region with high swampiness and a large number of lakes, is statistically significantly higher (2–3 times) comparing to those captured in the eastern geomorphological region with a developed river network.

In the global ocean, more than 380 species are known to ingest microplastics (plastic particles less than 5 mm in size), including mid-trophic forage fishes central to pelagic food webs. Trophic pathways that bioaccumulate microplastics in marine food webs remain unclear. We assess the potential for the trophic transfer of microplastics through forage fishes, which are prey for diverse predators including commercial and protected species. Here, we quantify Northern Anchovy (Engraulis mordax) exposure to microplastics relative to their natural zooplankton prey, across their vertical habitat. Microplastic and zooplankton samples were collected from the California Current Ecosystem in 2006 and 2007. We estimated the abundance of microplastics beyond the sampled size range but within anchovy feeding size ranges using global microplastic size distributions. Depth-integrated microplastics (0-30 m depth) were estimated using a depth decay model, accounting for the effects of wind-driven vertical mixing on buoyant microplastics. In this coastal upwelling biome, the median relative exposure for an anchovy that consumed prey 0.287-5 mm in size was 1 microplastic particle for every 3399 zooplankton individuals. Microplastic exposure varied, peaking within offshore habitats, during the winter, and during the day. Maximum exposure to microplastic particles relative to zooplankton prey was higher for juvenile (1:23) than adult (1:33) anchovy due to growth-associated differences in anchovy feeding. Overall, microplastic particles constituted fewer than 5% of prey-sized items available to anchovy. Microplastic exposure is likely to increase for forage fishes in the global ocean alongside declines in primary productivity, and with increased water column stratification and microplastic pollution.

We compared three sets of highly resolved food webs with and without parasites for a subarctic lake system corresponding to its pelagic and benthic compartments and the whole-lake food web. Key topological food-web metrics were calculated for each set of compartments to explore the role parasites play in food-web topology in these highly contrasting webs. After controlling for effects from differences in web size, we observed similar responses to the addition of parasites in both the pelagic and benthic compartments demonstrated by increases in trophic levels, linkage density, connectance, generality, and vulnerability despite the contrasting composition of free-living and parasitic species between the two compartments. Similar effects on food-web topology can be expected with the inclusion of parasites, regardless of the physical characteristics and taxonomic community compositions of contrasting environments. Additionally, similar increases in key topological metrics were found in the whole-lake food web that combines the pelagic and benthic webs, effects that are comparable to parasite food-web analyses from other systems. These changes in topological metrics are a result of the unique properties of parasites as infectious agents and the links they participate in. Trematodes were key contributors to these results, as these parasites have distinct characteristics in aquatic systems that introduce new link types and increase the food web’s generality and vulnerability disproportionate to other parasites. Our analysis highlights the importance of incorporating parasites, especially trophically transmitted parasites, into food webs as they significantly alter key topological metrics and are thus essential for understanding an ecosystem’s structure and functioning. [ABSTRACT FROM AUTHOR]