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The strategies that allow invasive alien species to perpetuate themselves in the long term are still poorly understood in invasion science. Considering top predators, a key issue is how they overcome the prey decline which they have caused during the invasion process. We investigate factors related to the persistence, impacts and long‐term success of the emerging peacock bass (Cichlidae: Cichla) invasion, a fish native to the Amazon biome that has been introduced globally.We analysed a robust temporal database that includes comparisons (1994–2002 vs. 2015–2017) on the diet of Cichla ocellaris, the abundance of this invader, its prey and competitors in a human‐modified ecosystem. In addition, we compare the frequency of cannibalism (presence or absence) between native versus non‐native populations, and between natural versus human‐modified ecosystems in the American continent. Four hypotheses were tested: (i) prey and competitor populations decrease through time as a result of predation impacts; (ii) cannibalism is size‐ and density‐dependent, and increases after native prey decline; (iii) cannibalism is more frequent in non‐native populations; and (iv) the abundance of invader decreases over time because of reduced resources and increased cannibalism.Our results revealed that the impacts of introducing this predator into communities are temporally cumulative and continue to evolve even after 70 years since its introduction. These impacts have led to dramatic reductions in prey availability, resulting in widespread cannibalism. Adult individuals preying on juveniles in areas with higher abundances of peacock bass indicated that cannibalism is size‐ and density‐dependent. Cannibalism was more frequent in non‐native populations and in human‐modified ecosystems. A complex feedback process (reproduce and cannibalise frequently) may be responsible for overcoming long‐term resource scarcity, and the cannibalism may not be a regulatory force strong enough to surpass the reproductive success of the population.Our findings at the local and continental scale converge to confirm the cannibalism as an adaptive invasiveness strategy that facilitates the invasion process and makes populations self‐sustainable in the long term, which may jeopardise the efficacy of management actions for these top predators introduced globally. [ABSTRACT FROM AUTHOR]

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

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub‐adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub‐adult stages. The results revealed that both δ13C and δ15N values varied greatly across populations and between ontogenetic groups, and complex spatio‐ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub‐adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial‐ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems. [ABSTRACT FROM AUTHOR]

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

In fast-flowing streams, caddisfly larvae are responsible for processes that collectively determine the efficiency with which the detritivore community is able to decompose autochthonous and allochthonous detritus. This ecosystem function ensures high water quality and represents a precious service for resident rural communities. The analysis of δ13C and δ15N in eight caddisfly taxa from a mid-mountain stream evidenced a remarkable complementarity in their feeding preferences. An aquatic moth mimicking the caddis mode of life was also included in the survey and its feeding niche appeared to be in between the one of caddis taxa. Moderate niche overlap was interpreted in terms of low functional redundancy, implying that in case of a reduction in diversity, no taxon could be a perfect substitute for another, with a loss of functional efficiency. Low redundancy could be caused by niche segregation due to avoidance of competition/interference between taxa. The broad range of δ13C and δ15N described in this study warns against attributing single δ13C and δ15N to Trichoptera as a group, or even to single families. These results contribute to the still poorly known distribution of East African caddisflies and to the characterisation of feeding preferences of Afrotropical trichopteran larvae. [ABSTRACT FROM AUTHOR]

Back‐to‐back marine heatwaves in 2016 and 2017 resulted in severe coral bleaching and mortality across the Great Barrier Reef (GBR). Encouragingly, some corals that survived these events exhibit increased bleaching resistance and may represent thermally tolerant populations that can better cope with ocean warming. Using the GBR as a natural laboratory, we investigated whether a history of minimal (Heron Island) or severe (Lizard Island) coral bleaching in 2016 and 2017 equates to stress tolerance in a successive heatwave (2020). We examined the genetic diversity, physiological performance, and trophic plasticity of juvenile (<10 cm) and adult (>25 cm) corals of two common genera (Pocillopora and Stylophora). Despite enduring greater cumulative heat stress (6.3°C week−1 vs. 5.6°C week−1), corals that experienced the third marine heatwave in 5 years (Lizard) exhibited twice as high survival and visual bleaching thresholds compared to corals that had not experienced significant bleaching in >10 years (Heron). Surprisingly, only one shared host–Symbiodiniaceae association was uncovered between locations (Stylophora pistillata–Cladocopium "C8 group") and there was no genetic overlap in Pocillopora–Cladocopium partnerships, suggesting turnover in species composition from recent marine heatwaves. Corals within the species complex Pocillopora that survived the 2016 and 2017 marine heatwaves at Lizard Island were the most resilient, exhibiting three times greater calcification rates than conspecifics at Heron Island. Further, surviving corals (Lizard) had distinct isotopic niches, lower host carbon, and greater host protein, while conspecifics that had not experienced recent bleaching (Heron) had two times greater symbiont carbon content, suggesting divergent trophic strategies that influenced survival (i.e., greater reliance on heterotrophy vs. symbiont autotrophy, respectively). Ultimately, while corals may experience less bleaching and survive repeated thermal stress events, species‐specific trade‐offs do occur, leaving open many questions related to the long‐term health and recovery of coral reef ecosystems in the face of intensifying marine heatwaves. [ABSTRACT FROM AUTHOR]

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.

Coral communities can survive in stressful environments; however, the mechanisms corals employ to endure challenging conditions are poorly understood. This study assessed how the heterotrophy of three coral genera (Acropora spp., Porites spp. and Platygyra spp.) varies among sites in the Dampier Archipelago, Western Australia, exposed to different levels of turbidity. Stable isotope δ13C and δ15N analysis of coral host and endosymbionts were combined with modern Bayesian isotopic niche analysis to demonstrate that heterotrophy in all three coral genera increased in highly turbid environments. While all coral genera were found to be more heterotrophic in highly turbid waters, Porites spp. favoured heterotrophy across all levels of turbidity, whereas Platygyra spp. and Acropora spp. were less heterotrophic at sites with lower turbidity. Thus, some scleractinian corals can alter their feeding strategies in response to turbidity levels. As nearshore coral reefs experience increased and prolonged turbidity with intensifying climate change and anthropogenic development, the knowledge gained from this study will allow for improved environmental impact assessment and predictive modelling for future coral reef conservation. [ABSTRACT FROM AUTHOR]

The diet of widely distributed species is influenced by the availability of food resources, which can vary according to local conditions. Thus, heterogeneity in diet patterns can help understand population structure and illustrate biogeographic boundaries. In this study, published and unpublished datasets of regurgitated material and stable isotopes of carbon (δ13C) and nitrogen (δ15N) from whole blood of brown boobies (Sula leucogaster) in the southwestern Atlantic Ocean (27°51′S to 0°55′N) were used to assess dietary spatial patterns. The variations in prey composition and isotopic niche breadth were associated with colony location (coastal/oceanic), genetic population structure, and marine biogeographic zonings—Large Marine Ecosystems, Longhurst's Biogeochemical Provinces, and Spalding's Provinces and Ecoregions. Boobies from coastal and southern colonies showed higher diversity in their diet compared with boobies from oceanic and northern colonies, given the presence of demersal taxa associated with bottom trawling discards. The variation in prey composition from regurgitates and stable isotopes was well framed with genetic structure and biogeographic boundaries, although less fitting with Spalding's zoning. The brown booby showed trophic plasticity throughout the study area, suggesting that their diet is shaped by food resources available around the colonies, including those from fishery discards. These results demonstrate that highly mobile vertebrates are potentially useful samplers of the marine environment, able to indicate the diversity of prey organisms available in the foraging area through diet, and support biogeographic zonings. Furthermore, diet composition associated with population structure sheds light on local adaptation as a potential mechanism for promoting/disrupting gene flow in seabirds. [ABSTRACT FROM AUTHOR]

Many traits including trophic niche parameters are attributed to species. However, generalist species may vary in trophic niches with environments, making species‐based knowledge hard to extrapolate beyond local food webs. Here we tested trophic consistency in oribatid mite species (Acari), one of the most abundant arthropods that occupy all trophic levels in soil food webs. We used stable isotope analysis to compare trophic niches of 40 Oribatida species that co‐occur in litter (OL) and soil (0–5 cm, mainly OF/H, AH) of five forest types (native European beech, non‐native Douglas fir, range‐expanding Norway spruce, two beech–conifer mixed forests). Although stable isotope signatures of bulk material differed between litter and soil, 13C and 15 N values of Oribatida species were remarkably stable irrespective of soil depth. Furthermore, Oribatida were more enriched in 13C in European beech than in coniferous forests, but forest type little affected 15 N values of Oribatida across a range of site conditions. We conclude that Oribatida species occupy virtually identical trophic niches (δ13C and δ15N values) irrespective of the soil depth they colonize and that forest management including non‐native tree species little affects trophic position (δ15N values) of oribatid mites. Our findings suggest that the trophic position can be used as a trait in community analysis of Oribatida across forest ecosystems. Our results further indicate that trophic niches of generalist species can be highly consistent irrespective of environment. [ABSTRACT FROM AUTHOR]

The contribution of non-indigenous species to the transfer of contaminants in invaded food webs represents an active research area. Here we measured trace metals and CN stable isotopes in five populations of the invasive Atlantic blue crab Callinectes sapidus and in baseline bivalve species from Spain, Italy and Greece. They were used to estimate trophic transfer effects and the trophic position and isotopic niche of C. sapidus. Maximum trophic transfer effects occurred where the crab showed the largest isotopic niches and highest trophic positions; furthermore, the consistency of trace metal profiles between bivalves and crabs co-varied with the trophic position of the latters. Omnivory may influence the success of an invasive species, but also limit its effectiveness for biomonitoring. However, our results indicated that stable isotopes analysis provides a clarifying background where to cast patterns of contamination of the blue crab as well as of other omnivorous biomonitor species. [Display omitted] • Callinectes sapidus is invasive in the Mediterranean Sea. • Metals content was analyzed in five populations from Italy, Greece, and Spain. • Variations in trophic position reflected on metals trophic transfer. • Omnivory may hamper the use of a species for biomonitoring. • Stable isotope analysis may provide clarifying information. [ABSTRACT FROM AUTHOR]

Simple Summary: The population of the pipefish Syngnathus acus inhabiting Cíes Archipelago (NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. The population consisted almost exclusively of large adults, whose abundances decreased significantly from mid-autumn after the breeding season. S. acus is a secondary consumer that prefers amphipods, but mature specimens were less selective than immature fish. The present study highlights the outstanding size of the fish and the exceptional occurrence of breeders on the studied area. The great pipefish Syngnathus acus is one of the most representative European syngnathids, being highly associated with seagrass and macroalgal beds. Surprisingly, the ecology of this large ovoviviparous marine fish has received scanty attention. The population inhabiting three sites on Cíes Archipelago (Atlantic Islands National Park, NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. Abundances were highly variable across seasons and sites, decreasing significantly from mid-autumn. The population consisted almost exclusively of large adults that migrate by the end of the breeding season, which extended from mid-spring to summer. Operational sex ratios suggest that the species is sex-role reversed. S. acus is a secondary consumer (Trophic position = 3.36 ± 0.05), preferring amphipods but displaying annual and seasonal dietary plasticity. Mature fish were less selective than immatures (especially females), with a higher preference for amphipods (36–68%) in the former. The second most-preferred prey were carideans, copepods, or isopods, depending on the year and the reproduction state. Overall, the wider trophic niches in females and immature specimens compared to males and mature fish would indicate a higher variability in both the use of prey resources and/or their origin. The present study highlights the trophic plasticity and unique features of S. acus population in the Cíes Archipelago, especially regarding the outstanding size of the fish and the exceptional occurrence of breeders. [ABSTRACT FROM AUTHOR]

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

As the environment is getting warmer and species are redistributed, consumers can be forced to adjust their interactions with available prey, and this could have cascading effects within food webs. To better understand the capacity for foraging flexibility, our study aimed to determine the diet variability of an ectotherm omnivore inhabiting kelp forests, the sea urchin Echinus esculentus, along its entire latitudinal distribution in the northeast Atlantic. Using a combination of gut content and stable isotope analyses, we determined the diet and trophic position of sea urchins at sites in Portugal (42° N), France (49° N), southern Norway (63° N), and northern Norway (70° N), and related these results to the local abundance and distribution of putative food items. With mean estimated trophic levels ranging from 2.4 to 4.6, omnivory and diet varied substantially within and between sites but not across latitudes. Diet composition generally reflected prey availability within epiphyte or understorey assemblages, with local affinities demonstrating that the sea urchin adjusts its foraging to match the small-scale distribution of food items. A net "preference" for epiphytic food sources was found in northern Norway, where understorey food was limited compared to other regions. We conclude that diet change may occur in response to food source redistribution at multiple spatial scales (microhabitats, sites, regions). Across these scales, the way that key consumers alter their foraging in response to food availability can have important implication for food web dynamics and ecosystem functions along current and future environmental gradients. [ABSTRACT FROM AUTHOR]

The great pipefish Syngnathus acus is one of the most representative European syngnathids, being highly associated with seagrass and macroalgal beds. Surprisingly, the ecology of this large ovoviviparous marine fish has received scanty attention. The population inhabiting three sites on Cíes Archipelago (Atlantic Islands National Park, NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. Abundances were highly variable across seasons and sites, decreasing significantly from mid-autumn. The population consisted almost exclusively of large adults that migrate by the end of the breeding season, which extended from mid-spring to summer. Operational sex ratios suggest that the species is sex-role reversed. S. acus is a secondary consumer (Trophic position = 3.36 ± 0.05), preferring amphipods but displaying annual and seasonal dietary plasticity. Mature fish were less selective than immatures (especially females), with a higher preference for amphipods (36–68%) in the former. The second most-preferred prey were carideans, copepods, or isopods, depending on the year and the reproduction state. Overall, the wider trophic niches in females and immature specimens compared to males and mature fish would indicate a higher variability in both the use of prey resources and/or their origin. The present study highlights the trophic plasticity and unique features of S. acus population in the Cíes Archipelago, especially regarding the outstanding size of the fish and the exceptional occurrence of breeders.

• Trophic flexibility of corals with different symbionts (PdC or PdD) was assessed. • PdC had a higher autotrophic capacity than PdD, despite lower symbiont density. • Trophic strategy of PdC was more flexible than that of PdD across seasons. • Corals relied more on autotrophy in summer, but heterotrophy in winter. • Symbiont genus can determine the nutritional strategy and adaptability of corals. 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. [ABSTRACT FROM AUTHOR]

The colonization of novel reservoirs tends to support opportunistic species that undergo mass proliferation after the reservoir is formed. It is common that in this process, a species will change its diet based on resource availability. This is the case in the Salto Caxias reservoir, Iguaçu River, where five Astyanax species presented changes in their diets after damming. The present study aimed to evaluate possible changes in the feeding activity and condition factor of five sympatric species of Astyanax in the Salto Caxias reservoir in different areas impacted by damming. Sampling was carried out before and after damming the Salto Caxias reservoir. The fish feeding activity and nutritional status were inferred by the mean stomach repletion index and the mean condition factor, respectively. Most of the studied species showed a general decrease in feeding activity and condition factor. Both studied regions, the upstream region and the dam region, presented changes in the analyzed factors. These observations suggest that regardless of diet changes, nutritional status is negatively impacted in altered environments. The nutritional deficit occurs (i) if the diet is altered due to adaptive limitations on the use of the available resources and (ii) if the diet remains unaltered due to the scarcity of the preferred feeding resource. Such decreases might lead to reductions in the population size due to limitations on growth and reproduction until the environment feeding resources can sustain those populations. [ABSTRACT FROM AUTHOR]

The invasion of non-native fishes is a leading cause of extinction and imperilment of native freshwater fishes. Evidence suggests that introduced species with generalist diets have the potential for greatest impacts through competition and predation even though populations are often comprised of specialist individuals. The northern pike (Esox lucius), a predatory fish, has been widely introduced outside its native range for recreational fishing purposes, especially in western North America, and it has been implicated in declines and extirpations of native fishes. We synthesized over 2900 individual northern pike diet records across 31 waterbodies from the native and introduced ranges in Alaska to quantify the extent of diet specialization and generalization relative to freshwater prey communities. To control for effects of ontogenetic diet shifts, we separately analyzed major size classes of northern pike and inferred and visualized trophic plasticity from prey-specific abundance indices and ordination. Diet generalization was common in northern pike among waterbodies and usually consisted of individuals consuming macroinvertebrates. However, when available, individual northern pike diets showed specialization on fishes, amphibians, small mammals, and dragonflies. The reliance on macroinvertebrate prey by northern pike from small, isolated lakes in the native and invasive ranges suggests that dietary plasticity facilitates persistence of these predators in the absence of preferred fish prey. Broadly, this synthesis supports the hypothesis that trophic plasticity and diet generalization widely occur among invasive and native populations of northern pike which is likely to enhance the probability of introduction success, exacerbate their environmental impacts, and complicate management of this potentially invasive freshwater predator. [ABSTRACT FROM AUTHOR]

Abiotic change can alter species interactions by modifying species' trophic roles, but this has not been well studied. Until now, bromeliad-dwelling tipulid larvae were thought to positively affect other macroinvertebrates via a facilitative processing chain. However, under drought, we found the opposite. We performed two microcosm experiments in which we factorially manipulated water level and predation by tipulids, and measured the effects on mosquito and chironomid larvae. The experiments differed in whether high water was contrasted with low or no water, allowing us to distinguish between the effects of desiccation stress (no water) and increased encounter rates due to compression of habitat or reductions in prey mobility (low and no water). We also included a caged tipulid treatment to measure any non-consumptive effects. As well as directly reducing prey survival, reductions in water level indirectly decreased chironomid and mosquito survival by altering the trophic role of tipulids. Our results suggest that increased encounter rates with prey led to tipulids becoming predatory under simulated drought, as tipulids consumed prey under both low and no water. When water level was high, tipulids exerted negative non-consumptive effects on prey survival. Because opportunistic predators are common throughout aquatic ecosystems, the effects of drought on the trophic roles of species may be widespread. Such restructuring of food webs should be considered when attempting to predict the ecological effects of environmental change. [ABSTRACT FROM AUTHOR]

Competition and predation alter individual traits of organisms, and these effects can scale-up to have consequences on community structure and dynamics. The relative importance of competition and predation will depend largely on the local assemblage of species, the type of predators, or the degree of niche segregation. We experimentally investigated the interplay of competition and predation on the structure and trophic level (measured via stable isotope analysis) of a seven-species Neotropical freshwater guild using a mesocosm approach in central Panama. We tested the effect of two types of predators (dragonfly nymphs or adult water bugs) in combination with the presence/absence of a common competitor, the red-eyed treefrog (Agalychnis callidryas), on four core species of tadpoles. We also distinguished between consumptive and non-consumptive effects of each type of predator by presenting them to tadpoles caged or freely roaming. Dragonfly larvae were more efficient predators than water bugs, but these effects were not uniform for all tadpole species. All amphibian species grew bigger when raised in the presence of an uncaged dragonfly nymph, presumably due to reduced competition through thinning, but tadpoles were smaller when exposed to caged dragonfly nymphs indicating the existence of non-consumptive predator effects as well. Predator presence also altered the relative trophic position of the different amphibian species, causing some tadpole species to increase and others to decrease their trophic status. Despite the presumed ecological similarity of tadpole species in the guild, the interplay of competition and predation had varying effects on the trophic status of nearly every species. Our results indicate that community composition can greatly affect the trophic level of larval amphibians, and that predation may have a greater role than competition in structuring Neotropical larval amphibian guilds.

The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding., (© 2023 American Association for Anatomy.)

Predicting how alterations in sea ice-mediated primary production will impact Arctic food webs remains a challenge in forecasting ecological responses to climate change. One top-down approach to this challenge is to elucidate trophic roles of consumers as either specialists (i.e., consumers of predominantly one food resource) or generalists (i.e., consumers of multiple food resources) to categorize the dependence of consumers on each primary producer. At Hanna Shoal in the Chukchi Sea, Alaska, we used stable carbon and nitrogen isotope data to quantify trophic redundancy with standard ellipse areas at both the species and trophic guild levels. We also investigated species-level trophic plasticity by analyzing the varying extents that three end-members were assimilated by the food web using the mixing model simmr (Stable Isotope Mixing Model in R). Our results showed that ice algae, a combined phytoplankton and sediment organic matter composite (PSOM), and a hypothesized microphytobenthos (MPB) component were incorporated by consumers in the benthic food web, but their importance varied by species. Some primary consumers relied heavily on PSOM (e.g, the amphipods Ampelisca sp. and Byblis sp.; the copepod Calanus sp.), while others exhibited generalist feeding and obtained nutrition from multiple sources (e.g., the holothuroidean Ocnus glacialis , the gastropod Tachyrhynchus sp., the sipunculid Golfingia margaritacea , and the bivalves Ennucula tenuis , Nuculana pernula , Macoma sp., and Yoldia hyperborea ). Most higher trophic level benthic predators, including the gastropods Buccinum sp., Cryptonatica affinis, and Neptunea sp, the seastar Leptasterias groenlandica , and the amphipod Anonyx sp. also exhibited trophic plasticity by coupling energy pathways from multiple primary producers including PSOM, ice algae, and MPB. Our stable isotope data indicate that consumers in the Hanna Shoal food web exhibit considerable trophic redundancy, while few species were specialists and assimilated only one end-member. Although most consumers were capable of obtaining nutrition from multiple food sources, the timing, quantity, and quality of ice-mediated primary production may still have pronounced effects on food web structure. [ABSTRACT FROM AUTHOR]

Running waters are among the most threatened ecosystems globally, having altered hydrological regimes, homogenized habitat, and impaired water quality. These multiple stressors impact aquatic biodiversity and ecosystem function across space and time, although a clear mechanistic understanding is still lacking. Here, we examined the trophic response of macroinvertebrates among streams in a Swiss lowland catchment encompassing a gradient of land uses. Clear compositional changes were observed as anthropogenic impacts increased from least-impacted to agricultural and urbanized sites. Taxonomic diversity was lowest at sites with morphological and water quality impairment (agricultural sites), whereas taxonomic identity (susceptible vs. generalist species) mainly changed due to water quality degradation (agricultural and urban sites) based on the SPEAR (pesticides) index. Using stable isotopes (δC, δN), a simplification in macroinvertebrate trophic structure was evident along the land use gradient. At a site receiving wastewater treatment effluent, stable isotopes also revealed trophic shifts in primary consumers that corresponded to changes in available food resources. Results further showed that some taxa losses, e.g., the mayfly Ecdyonurus, to land- use effects may be due to low trophic plasticity. The combination of analyses, including stable isotopes, provided an improved mechanistic understanding of community and population responses to land-use changes along river networks. [ABSTRACT FROM AUTHOR]

Se analizó y comparó el espectro trófico de 2 poblaciones de Physalaemus albonotatus que habitan en ecosistemas diferentes: a) un terreno baldío urbano y b) un área protegida del valle aluvial del río Paraná Medio. La dieta de Physalaemus albonotatus está compuesta fundamentalmente de hormigas, coleópteros, colémbolos e isópodos, pero con numerosas presas secundarias. Al comparar 3 grupos etarios de los individuos en cada población (adultos, subadultos y jóvenes) se encontró una variación ontogenética relacionada con el volumen, cantidad y tipo de presa ingerida. Los anfibios adultos consumieron mayor cantidad de presas y más voluminosas, pero el nicho trófico de los jóvenes fue más amplio. Entre los adultos, la similitud de la dieta entre sexos fue muy elevada, aunque las hembras consumieron más hormigas que los machos. Si bien el solapamiento trófico entre las poblaciones fue elevado, la amplitud trófica resultó mayor en la población del humedal fluvial. Las diferencias en la alimentación encontradas entre las 2 poblaciones y lo registrado en otros trabajos realizados en diferentes ambientes reflejan la plasticidad trófica de este anuro, característica que le permite prosperar en hábitats diversos, incluso en los muy antropizados.We analyzed and compared the feeding of 2 populations of Physalaemus albonotatus inhabiting different ecosystems: a) an urban vacant lot, and b) a protected area of Middle Paraná River floodplain. The diet of Physalaemus albonotatus is mainly composed by ants, beetles, springtails and woodlouses, but also included several secondary preys. While comparing adults, subadults and juveniles diet on each population, we found an ontogenetic diet variation related to changes in prey type and volume as well as in number of prey items per gut. Bigger frogs consumed a greater amount of prey and more voluminous arthropods, while juveniles had a larger trophic niche breadth. Despite the great similarity in diet between sexes, adult females consumed a larger amount of ants than males did. Although trophic niche overlap between both populations was high, trophic niche breadth was wider for Paraná River floodplain population. Feeding differences found between studied populations and populations inhabiting other environments as described on literature reflects the trophic plasticity of this species and its capacity to thrive at different habitats, including markedly anthropogenically impacted environments.

By bone remodeling and changing of muscle volume, fish can adapt to changes in mechanical loads they are confronted with, including dietary changes such as prey hardness. This capability of a genotype to develop different phenotypes in response to varying environment is known as phenotypic plasticity. Differences in prey type being consumed might trigger such a phenotypic plasticity in fish. In European eel, two morphotypes exist: broadheads and narrowheads. Studies based on gut content have shown that broadheads consume larger and harder prey, such as fish, whereas narrowheads feed on smaller prey, such as benthic invertebrates. These studies, however, are performed on yellow eels with a minimum length of 30 cm, and only provide indirect evidence that head shape is affected by diet differences. Here, we performed a feeding experiment on glass eels that just swam up the European rivers to start feeding. These glass eels were captured and separated in three groups: one group was given hard feed requiring biting, the second group got soft feed that could be sucked in and the final group, which acted as a control group, was given a mixture of both. We found that hard feeders developed a broader general head width and postorbital region than soft feeders. This region is associated with the location of the jaw muscles, indicating that hard feeders develop larger muscles to cope with the harder prey. Hard feeders, however, also grew more slowly than soft feeders, suggesting that net energy uptake of hard feeders was lower as prey handling required more energy and time. Specimens of the control group, finally, developed intermediate head widths, implying that they are not fully adapted to feed on either hard or soft prey. In conclusion, this study provides the first direct evidence that diet influences the head shape of European eel.

Endophytic fungi inhabit the living tissues of every terrestrial plant species thus far examined. In at least some cases they significantly improve stress tolerance of their hosts. We asked whether endophytic fungi play other ecological roles, specifically whether the leaf endophytes of Quercus gambelii persist during the course of leaf decomposition, requiring a transition from a biotrophic to a saprotrophic mode of nutrition. Using automated ribosomal intergenic spacer analysis (ARISA), we found that endophyte fungal OTU diversity declined as decomposition commenced, but some endophytes persisted for months during which leaves were decomposing. In contrast, saprotroph fungi OTU diversity increased as decomposition progressed. These results are consistent with the hypothesis that some biotrophic endophytes persist in leaves during decomposition by becoming saprotrophic, and that the niche occupied by them is broader than expected. [ABSTRACT FROM AUTHOR]

In some environments, species may exhibit trophic plasticity, which allows them to extend beyond their assigned functional group. For Gammarus minus, a freshwater amphipod classified as a shredder or detritivore, cave populations have been observed consuming heterotrophs as well as shredding leaves, and therefore may be exhibiting trophic plasticity. To test this possibility, we examined the C and N stable isotope and C/N ratios for cave and spring populations of G. minus. A 15-day feeding experiment using leaves and G. minus from a spring population established that the diet-tissue discrimination factor was 3.2 ‰ for δN. Cave G. minus were 8 ‰ higher in δN relative to cave leaves, indicating they did not derive nitrogen from leaves, whereas field collected spring populations were 2-3 ‰ higher than spring leaves, indicating that they did. Cave G. minus were 2.6 ‰ higher in δN than the cave isopod, Caecidotea holsingeri. Relative to spring populations, Organ Cave G. minus were N enriched by 6 ‰, suggesting they occupied a different trophic level, or incorporated an isotopically distinct N source. While stable isotopes cannot tell what the cave G. minus are eating, the isotopes certainly show that G. minus are not eating leaves and are trophically distinct form the surface populations. Differences in C/N ratios were observed, but reflect the size of the G. minus examined and not feeding group or habitat. The isotope data strongly support the hypothesis that cave populations of G. minus have become generalist or omnivorous by including animal protein in their diet. [ABSTRACT FROM AUTHOR]

Two phenotypes are present within the European eel population: broad-heads and narrow-heads. The expression of these phenotypes has been linked to several factors, such as diet and differential growth. The exact factors causing this dimorphism, however, are still unknown. In this study, we performed a feeding experiment on glass eels from the moment they start to feed. Eels were either fed a hard diet, which required biting and spinning behavior, or a soft diet, which required suction feeding. We found that the hard feeders develop a broader head and a larger adductor mandibulae region than eels that were fed a soft diet, implying that the hard feeders are capable of larger bite forces. Next to this, soft feeders develop a sharper and narrower head, which could reduce hydrodynamic drag, allowing more rapid strikes towards their prey. Both phenotypes were found in a control group, which were given a combination of both diets. These phenotypes were, however, not as extreme as the hard or the soft feeding group, indicating that some specimens are more likely to consume hard prey and others soft prey, but that they do not selectively eat one of both diets. In conclusion, we found that diet is a major factor influencing head shape in European eel and this ability to specialize in feeding on hard or soft prey could decrease intra-specific competition in European eel populations. [ABSTRACT FROM AUTHOR]

In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations. [ABSTRACT FROM AUTHOR]

We examined trophic relationships in a newly established community 1.5 years after the Hebei Spirit oil spill on the west coast of Korea. Carbon and nitrogen stable isotope ratios in consumers and their potential food sources were compared between the oil-spill site and reference site, located 13.5 km from the oil-spill spot. The isotopic mixing model and a novel circular statistics rejected the influx of petrogenic carbon into the community and identified spatial consistencies such as the high contributions of microphytobenthos, food-chain length, and the isotopic niche of each feeding guild between sites. We suggested that high level of trophic plasticity and the prevalence of omnivory of consumers may promote the robustness of food web against the oil contamination. Furthermore, we highlighted the need of holistic approaches including different functional groups to quantify changes in the food web structure and assess the influence of different perturbations including oil spill. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that the highly flexible feeding repertoire of juvenile Chaetodipterus faber reflects their trophic adaptability by quantifying the feeding behaviour of juveniles in situ, for the first time, in a northeastern Brazilian estuary. The fishes presented a preference for alga-rich habitats, irrespective of the substrate type chosen during feeding bouts. The analysis of stomach contents revealed omnivorous feeding habits, indicating that the ingestion of plant material occurs incidentally during foraging for benthic prey hidden under the alga. Particulate feeding in the water column was often as important as bottom feeding on alga-rich substrates. The results of this study are consistent with those of other ephippid species in different coastal environments, which typically exploit an ample diversity of food items from different substrates. Therefore, the flexibility observed in the feeding behavior of the most ephippid species may be a fundamental determinant of the ecological success of this group. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted in Bocas del Toro, Almirante bay, which is a reef environment strongly influenced from terrestrial and river run off, sedimentation from dredging and port activities, and eutrophication from waste water and agricultural effluences. The two most abundant coral species, Porites furcata and Agaricia tenuifolia were used to investigate differences in feeding strategies. An ex situ isotope 13C and 15N pulse chase labeling experiment with phytoplankton and zooplankton was developed to be able to determine differences in the corals competence to use them for their heterotrophic nutrition. These tracers were furthermore used to follow exchange rates between the coral hosts and symbionts. By conducting labeling experiments with phyto- and zooplankton, natural plankton cultures and corals, this study developed an optimized labeling technique to follow a coral food chain. Feeding experiments under low light conditions could furthermore elucidate qualitative differences in the heterotrophy. P. furcata was found to have a stronger heterotrophic competence than A. tenuifolia, which was more dependent on photosynthetic nutrition, seen in the lower δ13C and δ15N ratios of A. tenuifolia. Furthermore, P. furcata demonstrated the ability to regulate their symbiotic interaction, to a strong exchange between host and symbiont and at the same time suppressing the autotrophic activity, seen in a strong overlap of δ13C and δ15N ratios. Also, P. furcata was able to decouple their symbiosis, seen in host and symbiont isotope values with distances of a whole trophic step. A. tenuifolia was found to increase its photosynthesis, using the host's waste products. This was seen in the accumulation of heavy isotopes within the zooxanthellae during the feeding experiments. Zooxanthellae of A. tenuifolia reached values significantly higher than those of P. furcata, due to their increased effort to maintain photosynthesis. Host waste products were incorporated into the symbiotic metabolism, thus a heavy isotope fractioning took place within the endodermic zooxanthellae metabolism. The methodological approach using 13C as a food chain tracer was not successful when passing three food chain steps (phytoplankton-zooplankton-coral), whereby 15N can be considered as a reliable tracer which could elucidate heterotrophic pathways up to the coral host and symbiont. Phytoplankton incorporated most heavy isotopes under constant light conditions after 24h, zooplankton after 48h feeding and corals after 4days feeding. These findings will help to optimize experimental approaches to assess heterotrophic competences and thus to quantitatively valuate coral reefs as a natural filter system. [Copyright &y& Elsevier]

Following up on previous investigations on the stress resistance of corals, this study assessed the trophic plasticity of the coral Stylophora subseriata in the Spermonde Archipelago (Indonesia) along an eutrophication gradient. Trophic plasticity was assessed in terms of lipid content and fatty acid composition in the holobiont relative to its plankton (50-300 μm) food as well as the zooxanthellae density, lipid, FA and chlorophyll a content. A cross-transplantation experiment was carried out for 1.5 months in order to assess the trophic potential of corals. Corals, which live in the eutrophied nearshore area showed higher zooxanthellae and chlorophyll a values and higher amounts of the dinoflagellate biomarker FA 18:4n-3. Their lipid contents were maintained at similar to levels from specimens further away from the anthropogenic impact source going up to 14.9 ± 0.9 %. A similarity percentage analysis of the groups holobiont, zooxanthellae and plankton >55 μm found that differences between the FA composition of the holobiont and zooxanthellae symbionts were more distinct in the site closer to the shore, thus heterotrophic feeding became more important. Transplanted corals attained very similar zooxanthellae, chlorophyll a and lipid values at all sites as the specimens originating from those sites, which indicates a high potential for trophic plasticity in the case of a change in food sources, which makes this species competitive and resistant to eutrophication. [ABSTRACT FROM AUTHOR]

1. Rainbow ( Oncorhynchus mykiss) and brown trout ( Salmo trutta) are widespread and invasive salmonids with important lethal effects as predators, although indirect effects are also possible. We used stable isotope analyses (δ15N, δ13C) to explore how the density of invasive trout in 25 Patagonian lakes alters the trophic niche (TN) of a widespread native fish, Galaxias platei (Galaxiidae). We also explored how the density of the galaxiid influences the TN of invasive trout. 2. We quantified two aspects of the TN: (i) the proportion of littoral carbon (PL) and (ii) trophic height (TH) (i.e. the 'height' at which the fish feeds in the food web). We related these measures of TN in a given species to the density of other species (as estimated by catch-per-unit-effort). 3. As G. platei body size increased, their PL increased (increasing littoral feeding) in several lakes. However, none of the fish species investigated showed changes in PL with increasing density of the other fish species. TH increased with body size in all three species. In addition, the TH of large G. platei declined with increasing trout density and, reciprocally, the TH of large S. trutta decreased with decreasing G. platei density. 4. The reciprocal effects of native and the invasive fish on TH were as large as a shift of one trophic level. This pattern is consistent with an exhaustion of galaxiid prey for both piscivorous G. platei and S. trutta in lakes with high trout density. 5. These finding support the suggested management strategy of culling trout from overpopulated lakes, which should simultaneously protect native fish and enhance a lucrative sport fishery for large trout. [ABSTRACT FROM AUTHOR]

The fish community of Lake Victoria, East Africa, has continued to exhibit an intriguing degree of resiliency despite stress from anthropogenic activities. Frequent environmental perturbations include wild fluctuations in fishing pressure, limnological conditions, and lake levels. Surprisingly, many of the endemic and other indigenous fishes have survived, and some have even increased in numbers in recent years. While a positive development, this resiliency is a red flag to scientists because we do not understand it, or know whether it can be expected to continue. Furthermore, besides issues of immediate human well-being, there remain grave concerns about long term resource sustainability. This paper explores possible reasons for ecological resilience in the Lake Victoria fish community, with a focus on omnivory and functional redundancy as possible explanations. The analysis used published data based on both traditional gut content analysis (GCA) and stable isotope analysis (SIA). Trophic plasticity is ubiquitous among the surviving fishes of Lake Victoria. This, combined with an overall simplification of the food web, contributed to the lake community's current resilience. [ABSTRACT FROM AUTHOR]

Host plants of the stenodemine mirid Teratocoris saundersi Douglas & Scott, 1869 in Iceland include the grasses Agrostis capillaris, Deschampsia cespitosa, Elymus repens, and Leymus arenarius (Poaceae), and sedges, Carex spp. (Cyperaceae). Specific host associations for T. saundersi in Iceland previously were unknown. Larvae and adults fed mainly on leaves and stems of their graminoid hosts; during cloudy weather, the bugs were observed in thatch beneath host plants. An adult fed on nectar from a flower of arctic sea rocket, Cakile arctica (Brassicaceae). Larvae and adults fed occasionally as predators or scavengers on small Diptera and pierced human skin. Observations on zoophagy further document the use of animal matter by species of Teratocoris Fieber, 1858, whereas adventitious biting by T. saundersi is reported for the first time. The zoophagous tendencies of T. saundersi might contrast with the feeding habits of stenodemines that are regarded as strict phytophages, for example, most species of Stenodema Laporte, 1833 and Trigonotylus Fieber, 1858. [ABSTRACT FROM AUTHOR]

This study describes experimental herbivory and detritivory of three common native aquatic macrophyte species by the introduced Mozambique tilapia Oreochromis mossambicus (Peters) (Pisces: Cichlidae), and its physiological response to their consumption. There was a highly significant effect of fish herbivory on plant weight for each of the macrophyte species, but this effect was not influenced by any preference for periphyton. Despite the herbivory, there was a highly significant loss of fish body weight across all plant species and weight could only be maintained by supplementary feeding of a high protein fish flake. These results suggest that despite eating these plants, an alternative food resource may be needed for survival and may trigger trophic plasticity in O. mossambicus. [ABSTRACT FROM AUTHOR]

Abstract: The study investigated the trophic ecology of the gastropod Hydrobia ulvae in different habitat types within an intertidal bay. The results point out two major trophic pathways involving H. ulvae in this bay. On the one hand, in sandy/muddy sediments Hydrobia derives most of its energy from allochtonous detritus derived from Enteromorpha sp and the total SOM pool. In addition, in these sediments, the phototrophic purple bacteria mats played a substantial trophic role in the diet of Hydrobia. On the other hand, in a Spartina maritima marsh, the gastropod appears firstly dependent of autochtonous detritus derived from this plant. The minor contribution of microphytobenthos to the diet of Hydrobia is consistent with a relatively low presence of epipelic diatoms at the sampling sites. These results provide evidence that the trophic ecology of H. ulvae inhabiting intertidal sediments is quite plastic and does not necessarily rely primarly on microphytobenthos. Consequently, in a single bay, the small spatial scale variability in the origin and availability of detritus have direct implications on the food incorporation by H. ulvae. [Copyright &y& Elsevier]

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the world's most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator–prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed ( n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments. [ABSTRACT FROM AUTHOR]

Coastal lagoons are characterized by high habitat heterogeneity where natural habitats coexist with artificial ones, historically set up to support human activities. Increasing anthropogenic pressure may lead to progressive degradation of the most vulnerable lagoonal habitats and the associated biological communities. One of the strictly estuarine-dependent fish species that may be affected by the degradation of lagoon habitats is the South European toothcarp Aphanius fasciatus , archetype of Mediterranean lagoon residents. Carbon and nitrogen stable isotopes were used to disentangle the influence of habitat types (natural vs artificial) and fish community (multi-trophic context) on the trophic niche features of A. fasciatus. Fish communities and organic matter sources were sampled in two Mediterranean lagoons located at the northernmost (Lagoon of Venice) and at the mid-latitude (Stagnone di Marsala, Trapani) of A. fasciatus distribution. Results showed evidence of high trophic adaptability of A. fasciatus , whose omnivorous feeding habit resulted in seasonal changes in isotopic niche width and niche partitioning with co-occurring species, constituting an advantage in habitats characterized by high seasonal variation of resources availability. Furthermore, while macrophytes drove the main trophic pathways leading to A. fasciatus in natural habitats, artificial habitats were mainly based on sedimentary organic matter routes. These outcomes broaden our knowledge on how natural and artificial habitats trophically support A. fasciatus populations and results are discussed in light of the ecological implications for environmental management of coastal lagoons. • Aphanius fasciatus may be affected by the degradation of coastal lagoon habitats. • Trophic niche of the species was assessed across lagoon habitats. • A. fasciatus showed high trophic adaptability across habitat types. • Trophic pathways differed between natural and artificial habitats. • Both natural and artificial habitats are crucial for A. fasciatus conservation. [ABSTRACT FROM AUTHOR]

• Yellow-legged gull's diet has changed over the last decades. • Yellow-legged gulls adapt their diet to anthropogenic food subsidies availability. • Anthropogenic food subsidies availability may be key in adjusting population size. For centuries, human activities have altered the population dynamics of wildlife. New anthropogenic food sources provide a predictable and abundant food supply that often induces very significant changes in the size, distribution, and behaviour of many populations, with ultimate consequences on the structure and functioning of natural ecosystems. Here, we combine historical and contemporary feather samples of a population of a superabundant, opportunistic predator, the yellow-legged gull Larus michahellis , to assess its trophic ecology and relate it to human activities in the long term. Dietary assessments were based on stable isotope analysis of carbon, nitrogen, and sulphur (δ 13C, δ 15N and δ 34S), and were conducted through three end-point (marine prey, waste from landfills-slaughterhouses, and terrestrial invertebrates) Bayesian mixing models. Our results suggest that gulls' diet showed a progressive decrease in the consumption of marine prey throughout the most recent period (late 20th century onwards), linked to an increase in the consumption of meat waste and small terrestrial invertebrates. Reported dietary changes over the sampling period correlated positively with the availability of marine resources around the breeding area. We provide evidence suggesting that the ability of gulls to exploit efficiently diverse anthropogenic food subsidies likely resulted in the exponential demographic increase of this population throughout the 20th century. In addition, current regulations affecting the availability of these food resources (e.g., fishing discards and landfill waste) likely reversed this trend over the last decade. Long-term evidence of population trophic plasticity, like the one we present here, is essential to implement and support management and conservation actions that limit the availability of anthropogenic resources, especially when it comes to superabundant, problematic species. [ABSTRACT FROM AUTHOR]

Aquatic pollution is known to reduce biodiversity and disrupt wildlife populations. Mercury (Hg) pollution is pervasive worldwide, contributing to the degradation of ecosystems, and causing deleterious effects to exposed organisms and populations. Batoids have a life history linked to the benthic substrate of coastal areas and occupy upper trophic levels. These combined with large bodies, long lifespan, and slow growth rates contributes to increased uptake and accumulation of Hg. However, mechanisms governing these associations are not well understood. Using multiple biogeochemical tracers (δ13C, δ15N and total Hg), we describe trophic interactions of three sympatric batoid species inhabiting an urbanized estuary and identify diet sources that contribute to Hg accumulation and trophic position among these mesopredators. We also use the Bat-ray (Myliobatis californica) as a model species, to compare diet composition, trophic position, and isotopic niche between two populations in two Californian bays. Trophic plasticity in M. californica was characterized by isotopic niche, diet proportions, and trophic position estimates using Bayesian statistics. We found diet and local contamination background strongly associated with Hg accumulation, and Hg levels that exceed EPA water quality criterion (<0.3 μg.g−1 w.w.) in all studied species. • Sympatric batoids occupy similar trophic positions but distinct foraging niches. • Batoids with overlapping isotopic niche present distinct contamination levels. • Hg levels were associated to differences in species-specific diets. • Plasticity in diet and isotopic niche of Myliobatis californica are described. [ABSTRACT FROM AUTHOR]

• Gammarids often colonise sinking-cave stream. • Cave-dwelling individuals reached sexual maturity later compared to surface conspecifics. • Subterranean females produced significantly larger, but fewer, eggs compared to surface population. • Trophic position and omnivory are higher for cave-dwelling adults. • Subterranean populations may be faced with phosphorous shortage, nut not nitrogen. Freshwater gammarids are known to colonise occasionally sinking-cave streams, providing contrasting morphological, life-history and ecophysiological adaptations compared to their surface conspecifics. In this study, a subterranean and a surface population of the species Gammarus balcanicus was surveyed for one year in a sinking-cave stream from the Western Carpathians (Romania). The results showed that the cave-dwelling population comprised individuals that were significantly larger compared to their surface conspecifics, had larger body-size at sexual maturity and that the females produced fewer, but larger eggs, compared to the population situated outside the cave. The trophic position and the omnivory were significantly higher for the cave-dwelling compared to surface population and the elemental imbalance for C:P molar ratios lower, but similar for C:N. However, the subterranean population did not present troglomorphic characters or longer lifespan as known for other cave-surface paired crustaceans. This, together with the rather extensive hydrological connection of the habitats, suggests active gene-flow between populations and similar response to seasonality for body-size distributions, indicating that the observed ecophysiological and life-history differences are rather the consequence of phenotypic plasticity than the result of genetic adaptation. [ABSTRACT FROM AUTHOR]