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Food webs capture the trophic relationships and energy fluxes between species, which has fundamental impacts on ecosystem functioning and stability. Within a food web, the energy flux distribution between a predator and its prey species is shaped by food quantity-quality trade-offs and the contiguity of foraging. But the distribution of energy fluxes among prey species as well as its drivers and implications remain unclear. Here we used 157 aquatic food webs, which contain explicit energy flux information, to examine whether a predator's foraging is asymmetric and biased towards lower or higher trophic levels, and how these patterns may change with trophic level. We also evaluate how traditional topology-based approaches may over- or under-estimate a predator's trophic level and omnivory by ignoring the asymmetric foraging patterns. Our results demonstrated the prevalence of asymmetric foraging in natural aquatic food webs. Although predators prefer prey at higher trophic levels with potentially higher food quality, they obtain their energy mostly from lower trophic levels with a higher food quantity. Both tendencies, that is, stronger feeding preference for prey at higher trophic levels and stronger energetic reliance on prey at lower trophic levels are alleviated for predators at higher trophic levels. The asymmetric foraging lowers trophic levels and omnivory at both species and food web levels, compared to estimates from traditional topology-based approaches. Such overestimations by topology-based approaches are most pronounced for predators at lower trophic levels and communities with higher number of trophic species. Our study highlights the importance of energy flux information in understanding the foraging behaviour of predators as well as the structural complexity of natural food webs. The increasing availability of flux-based food web data will thus provide new opportunities to reconcile food web structure, functioning and stability.

1. Almost all organisms grow in size during their lifetime and switch diets, trophic positions, and interacting partners as they grow. Such ontogenetic development introduces life-history stages and flows of biomass between the stages through growth and reproduction. However, current research on complex food webs rarely considers life-history stages. The few previously proposed methods do not take full advantage of the existing food web structural models that can produce realistic food web topologies. 2. We extended the niche model by Williams & Martinez (2000) to generate food webs that included trophic species with a life-history stage structure. Our method aggregated trophic species based on niche overlap to form a life-history structured population; therefore, it largely preserved the topological structure of food webs generated by the niche model. We applied the theory of allometric predator-prey body mass ratio and parameterized an allometric bioenergetic model augmented with biomass flow between stages via growth and reproduction to study the effects of a stage structure on the stability of food webs. 3. When life-history stages were linked via growth and reproduction, fewer food webs persisted while persisting food webs tended to retain more trophic species. Topological differences between persisting linked and unlinked food webs were small to modest. Temporal variability of biomass dynamics and slopes of biomass spectra were lower in the linked food webs than the unlinked ones, suggesting that a life-history stage structure enhanced stability of complex food webs. 4. Our results suggest a positive relationship between the complexity and stability of complex food webs. A life-history stage structure in food webs may play important roles in dynamics of and diversity in food webs.

Author(s): Nobriga, Matthew L.; Smith, Wiliam E. | Abstract: Striped Bass, Morone saxatilis, has been an established member of the San Francisco Estuary’s (estuary’s) aquatic community for nearly a century and a half. As a predator, it has the potential to shape community composition through top-down control of lower trophic species, including the endangered Delta Smelt, Hypomesus transpacificus. Invasive predators can be particularly disruptive to native communities because they present novel dangers to naive populations, but, as a long-established member of the aquatic community, Striped Bass has not previously been considered to limit the Delta Smelt population. Here, we develop an argument that Striped Bass are important to controlling Delta Smelt. We support this argument by reviewing historical data which suggests that declines in Delta Smelt before the current-day monitoring program were driven by the invasion of Striped Bass into the estuary. We describe this phenomenon as the ‘phantom predator’ hypothesis in the context of an analog to the shifting baseline syndrome previously described for marine fisheries. A deeper understanding of how well studied (and rapidly changing) bottom-up drivers of the estuary food web interact with poorly understood (but also rapidly changing) controls at the top of the food web could prove very important to the conservation of other declining native fishes and possible future attempts to re-introduce captive-reared Delta Smelt to the estuary.

Over the past century, the Earth has experienced roughly 0.4–0.8°C rise in the average temperature and which is projected to increase between 1.4–5.8°C by the year 2100. The increase in the Earth’s temperature directly influences physiological traits of individual species in ecosystems. However, the effect of these changes in community dynamics, so far, remains relatively unknown. Here we show that the consequences of warming (i.e., increase in the global mean temperature) on the interacting species persistence or extinction are correlated with their trophic complexity and community structure. In particular, we investigate different nonlinear bioenergetic tri-trophic food web modules, commonly observed in nature, in the order of increasing trophic complexity; a food chain, a diamond food web and an omnivorous interaction. We find that at low temperatures, warming can destabilize the species dynamics in the food chain as well as the diamond food web, but it has no such effect on the trophic structure that involves omnivory. In the diamond food web, our results indicate that warming does not support top-down control induced co-existence of intermediate species. However, in all the trophic structures warming can destabilize species up to a threshold temperature. Beyond the threshold temperature, warming stabilizes species dynamics at the cost of the extinction of higher trophic species. We demonstrate the robustness of our results when a few system parameters are varied together with the temperature. Overall, our study suggests that variations in the trophic complexity of simple food web modules can influence the effects of climate warming on species dynamics.

A few studies on simple food chain suggest that competition has a strong dampening ability till some degrees and play a vital role to stabilize the food chain dynamics in the ecosystems. Still, much work is needed to understand the complex role played by competition in the food chains and food webs with higher trophic. We have studied the effect of competition on the (i) Combination of two food chain model and (ii) Combination of a food chain with a food web model, having individually various stability conditions (point stability and instability (or chaos)). In most of these cases, we have observed that low competition favors chaotic dynamics exhibited by one of the original models but as competition increases, system come into stability (limit cycles to point stability) and extinction of some species occurred as high competition is not favorable for the coexistence of species. Also from our various combinations of model dynamics, we have observed a negative effect of competition on the stable systems as high competition brings point stability to oscillations with higher trophic species extinction. The threshold values of the competition for each models may vary with original model's stability conditions. With competition in these models, a bigger parameter stability domain is observed which increases along with competition (below to upper threshold). Such bigger stability domain enhances the species coexistence and reduces the probability of extinction as system has high probability to have stable solutions and far away from the extinction. Based on our observations, we hypothesize that competition may sustain coexistence and support biodiveristy of the ecosystem.

As we are living through a transformative response to a viral pandemic, this think piece suggests a reimagining of the environmental humanities in the open-ended inventories of feminist posthumanities and the low trophic registers of the oceanic. Sea farming of low trophic species such as seaweeds and bivalves is still underexplored option for the mitigation of climate change and diminishing species diversity in the warming oceans of the world. The affordances of low trophic mariculture for coastal life and for contributing to society’s transition into climate aware practices of eating, socializing and thinking is here considered, and showcased as an example of the practical uses of feminist environmental posthumanities.

Studies of trophic networks and the evaluation of processes that occur along altitudinal gradients in river systems are of great importance because they allow an understanding of energy flow dynamics and provide scientific tools for the planning and management of river ecosystems. This research describes the trophic network of aquatic macroinvertebrates along an altitudinal gradient of the Gaira River, a mountain Neotropical watercourse located in the Sierra Nevada de Santa Marta in northern Colombia. The organisms were collected in the upper, middle and lower reaches of the river during the rainy and dry seasons (between 2010 and 2013). Trophic relationships were evaluated through gut content analysis. The contents were determined and quantified using photographs and expert review, and a binary consumption matrix was used to determine the characteristics of the trophic network. We characterized the diet composition at each site for each season using discriminant analysis. Trophic networks during the dry seasons showed higher trophic species richness and linkage density, and the predominance of coarse particulate organic matter (CPOM) and fine particulate organic matter (FPOM) in the high and medium sections of the river. During the dry seasons the diets had a lower number of basal species, but in the low river section there was a high percentage of fungi and microalgae. During the rainy seasons, no patterns were observed for the percentage of resources. Results indicated a direct relation between periods of hydrologic stability and an increase of CPOM during dry seasons and an increase of resource diversity consumed by macroinvertebrates at all sites during the rainy season, showing that changes in trophic networks of the Gaira River were more important during seasonal periods than along the altitudinal gradient. Keywords: Aquatic insects, Food chain length, Gaira River, Gut contents, Trophic relations

Trophic cascades have been assigned an exaggerated even mythic status by some ecologists, but they are only one type of pathway in a complicated food web. The human mind is drawn to patterns like the proverbial ‘moth to the flame’. The distinctive checkerboard pattern of alternating + − + − + changes in populations on adjacent trophic levels in a trophic cascade is no exception. Unfortunately, this pattern has been too frequently equated with unrealistic ecological significance. Loop analysis, a qualitative network methodology, analyses all pathways and feedbacks in a food web simultaneously and it identifies many aspects of food web structure and function like trophic cascades, distinguishes operating from non-operating pathways, and predicts changes in standing crops and their correlation patterns. In this paper, the trophic relationships of food chains are expanded systematically into food web models that help illustrate some of the earliest claims about trophic cascades and their role in food webs. Several current definitions are contrasted to the loop analysis results. A more precise definition for a ‘top-down’ trophic cascade is proposed as well as the term ‘trophic escalade’ for particular types of ‘bottom-up’ trophic pathways that are also consistent with loop analysis. Suggestions for identifying trophic cascades are provided. Loop analysis, as an observing lens, provides an improved perspective on the role of trophic cascades. As Hegel claimed, “The truth is the whole”, and it cannot be found in an isolated part, in fact, the process of isolation precludes this possibility.

Understanding the structure and function of a lake’s ecosystem is the premise and foundation to implementing ecosystem-based management. However, evaluating the status of the ecosystem of a lake as a whole is still difficult when it comes to selecting indicators, determining standards, and interpretating results. In order to quantify the ecosystem status of Lake Baiyangdian (BYD), a holistic food web model was built using Ecopath with Ecosim. Eleven Ecological Network Analysis indicators classified into three categories (ecological function, ecological maturity, and food web structure) were selected according to their representativeness and availability. Based on the published literature on similar freshwater lakes or reservoirs in the world, quantile-based classification criteria are obtained. Furthermore, the Analytic Hierarchy Process was employed to assign the weight of an indicator according to its importance, sensitivity, and adaptability. An integrated evaluation framework was formed after synthesizing the evaluation value using a fuzzy comprehensive evaluation method. It was concluded that the ecological state of Lake BYD in 2009–2010 could be graded “Bad”, featuring a low-quality mature ecosystem, low trophic transfer efficiency, and linear, simple, and fragile connections between trophic levels. More specifically, the “Medium” grade detritivory:herbivory ratio (D:H), mean trophic level of the catch (MTLC), and “Bad” grade of transfer efficiency (TE) indicate that the composition of trophic species is unbalanced and the material and energy transfer is inefficient. “Good” grades of total primary production over biomass (TPP/TB), biomass over total system throughput ratio (TB/TST), and relative ascendency (A/C), together with “Median” grade of total primary production over total respiration ratio (TPP/TR), show characteristics of a mature ecosystem due to a high biomass of macrophytes, although here is a “low quality” in terms of exergy. In terms of the performance of the food web structure, all indicators achieve a “Bad” grade, suggesting a linear, simple, and fragile network. According to our modeling results, controlling the excessive macrophyte biomass, restoring fish biodiversity, and mitigating the pressures of overexploitation are suggested for the ecosystem-based management of BYD. This paper provides an integrated method to evaluate the ecological state of a shallow lake when its own reference state is unavailable.

The loss of riparian forests can disrupt the structure and function of lotic ecosystems through increased habitat homogenization and decreased resource diversity. We conducted a field experiment and manipulated structural complexity and basal resource diversity to determine their effect on multiple aspects of community and food-web structure of degraded tropical streams. In-stream manipulations included the addition of woody debris (WD) and the addition of wood and leaf packs (WLP). The addition of structural complexity to degraded streams promoted detritus retention and had a positive effect on stream taxonomic richness, abundance and biomass. At the conclusion of the experiment, abundance and richness in the WD-treated reaches increased by over 110% and 80%, respectively, while abundance and richness in the WLP-treated reaches increased by over 280% and 170% respectively. Wood debris and leaves were consumed only by few taxa. Detritivorous taxa were the most abundant trophic guild at the beginning and at the end of the experiment. Food webs in treated reaches were relatively more complex in terms of links and species at the conclusion of the experiment, with highest maximum food chain length in the WD treatments and highest number of trophic species, links, link density, predators and prey at the WLP treatment. Despite differences observed in diet-based food webs, there was little variation in isotopic niche space, likely due to the high degree of omnivory and trophic redundancy, which was attributed to the importance of fine detritus that supported a broad range of consumers. Even in these degraded streams, aquatic taxa responded to the addition of increased complexity suggesting that these efforts may be an effective first step to restoring the structure and function of these food webs.

Community structures of benthic invertebrates in different alpine stream types have been well documented and modeled against environmental conditions and change. However, community structure cannot be linked directly to community functions or processes, and this problem prevents clear estimation of functional consequences of environmental changes. In this article, we highlight the need to focus research efforts on the trophic ecology of alpine streams for several reasons. 1) The trophic ecology of invertebrates is remarkably understudied in the field of alpine stream ecology (only 7% of published studies), but the trophic ecology of invertebrates underlies crucial functions in these ecosystems. 2) Classifications of species into functional feeding groups, traits often used to express the functionality of invertebrate communities, are missing for several alpine species or have been deduced from classifications based on higher taxonomic levels. 3) Most investigators focused on a few trophic levels, ...

Quantification of the physical and biological environmental factors that influence the spatial distribution of higher trophic species is central to inform management and develop ecosystem models, particularly in light of ocean changes. We used tracking data from 184 female Antarctic fur seals (Arctocephalus gazella) to develop habitat models for three breeding colonies for the poorly studied Southern Ocean winter period. Models were used to identify and predict the broadly important winter foraging habitat and to elucidate the environmental factors influencing these areas. Model predictions closely matched observations and several core areas of foraging habitat were identified for each colony, with notable areas of inter-colony overlap suggesting shared productive foraging grounds. Seals displayed clear choice of foraging habitat, travelling through areas of presumably poorer quality to access habitats that likely offer an energetic advantage in terms of prey intake. The relationships between environmental predictors and foraging habitat varied between colonies, with the principal predictors being wind speed, sea surface temperature, chlorophyll a concentration, bathymetry and distance to the colony. The availability of core foraging areas was not consistent throughout the winter period. The habitat models developed in this study not only reveal the core foraging habitats of Antarctic fur seals from multiple colonies, but can facilitate the hindcasting of historical foraging habitats as well as novel predictions of important habitat for other major colonies currently lacking information of the at-sea distribution of this major Southern Ocean consumer.

Differences among species and their ecological requirements are considered fundamental in determining the outcome of species interactions as well as in coexistence. Thus, species that co-occurs tends to differ in the use of resources as a way to mitigate the effects of interspecific competition, facilitating interactions between pairs of species. So, this study used a set of seven small-sized characid species with similar morphology and feeding strategies, in order to investigate the hypothesis that the coexistence these species is facilitated by the differential use of food resources. Samplings were conducted in the rivers Verde and Sao Domingos, Upper Parana River basin, Brazil, in hydrological periods rainy and dry. The analysis of 1055 stomach contents, by the volumetric method, indicated that the species consumed mainly allochthonous items, such as seeds, terrestrial plants and insects. In addition, they showed inter- and intraspecific differences in the diet composition between hydrological periods, which allowed the identification of items that particularise each species and contribute to the trophic segregation between them. Despite the wide variety of food items used, it was not possible to observe a consistent pattern of widening or narrowing of the food spectrum between hydrological periods, as expected. The trophic niche overlap showed intermediate and low values in both periods. In this sense, resource partitioning among species of small characids, facilitated by exploitation of different preferential resources as well as the intraspecific variation in response to seasonal availability of resources, became evident. The alternation of items and proportions of items in the diet as well as changes in feeding behaviour in opportune moments was probably the key for the coexistence of these species.

In this work the effects of kleptoparitism in a multi-trophic food-web, in which an omnivorous species scavenges the kills of a top predator, are investigated. Scavengers are assumed to be able to steal predators’ kills by direct interference and aggression. The amount of prey shared depends on the relative competitive abilities of omnivores and predators and on their abundances. To make the proposed model consistent, scavenging is accompanied by other features. First, the predator can prey only on the juvenile life stage of scavengers (i.e. not on adult individuals) as well as on a different species of herbivores. Hence, an age structure is enforced within scavengers, so that they belong to the guild of preys when they are young and vulnerable. Second, predators can switch between prey species selecting the most abundant one. This condition grants the competitive exclusion of the two vegetation eaters, allowing them to co-exist: the omnivore and the herbivore compete for the same vegetation pool but pure herbivores are indeed assumed to be more efficient in its exploitation. The omnivorous species is not able to kill the herbivores, but nonetheless it may exploit their carcasses after they have been killed by predators. Finally, the juvenile/adult ratio of omnivores varies depending on the available resources and predators’ amount. In such a scenario it is shown that kleptoparasitism can modify to a large extent the stability of the system, leading either to a regularization or to chaos, depending both on the scavenger's and the predator's functional response. Moreover, an excess of kleptoparasitism is shown to compromise the whole trophic web, making extinct both predators and scavengers. As far as the authors are aware of, this paper is the first one to explicitly introduce kleptoparasitism in trophic web models.

The trophic guild concept has proved useful in distilling the diverse feeding inter-actions displayed by fish in temperate estuaries into a standardised subset that simplifies the application of trophic information to management. However, the high species richness displayed by tropical flora and fauna introduces the potential for feeding diversity within presumed guilds, potentially reducing the value of the standard guild concept. We evaluated within-guild consistency for a group of tropical estuarine fish species comprising a presumably coherent trophic zoobenthivore feeding guild (i.e. fish that feed primarily on zoobenthic prey) within 10 estuarine systems in tropical northeastern Australia. The zoobenthivore assemblage did not form a single coherent trophic group, rather the different components of the zoobenthivore guild responded to the broad spectrum of available prey in distinctly different ways. Some species displayed quite general diets while others fed principally on particular types of zoobenthic prey. The distinct prey specialisations often lead to different members of the presumed guild participating in different food chain pathways within the estuarine food web. As a result, substantial and important trophic differences would be masked if these disparate components were aggregated into a single trophic guild. While simplifications can be valuable, and often necessary, in data-poor situations, the complexity uncovered in this study emphasises that caution is required in applying a broad simplified scheme such as the guild concept to specific situations. Caution must be used when applying a guild approach that imports interpretation from other species and/or locations and should be explicitly recognised as an interim position until more specific data can be acquired.

Summary The cascading effect of predators on the functioning of adjacent ecosystems can occur when the life cycles of their prey include two ecosystems. However, there has been little consideration of which habitat attributes can modify the strength of these cross-ecosystem trophic cascades. Habitat size can mediate the strength of predator–prey interactions, and thus affect within-ecosystem trophic cascades. We hypothesise that similar effects of habitat size might affect cross-ecosystem trophic cascades. It has been shown that terrestrial predators (e.g. spiders) can capture terrestrial adult insects as they attempt to oviposit in the waters of bromeliads. Such terrestrial predators could therefore alter the trophic structure and functioning of the aquatic food web. If spiders affect an aquatic trophic level that is influenced by bromeliad size, then the strength of the cross-ecosystem trophic cascade will also depend on bromeliad size. To test this general hypothesis, we manipulated the presence of a funnel-web spider (Aglaoctenus castaneus, Lycosidae), which builds a single web over water-filled bromeliads, in bromeliads differing in size and examined effects on the aquatic invertebrate community and on ecosystem functions (decomposition, detrital nitrogen flux). The effects of spiders were largely independent of bromeliad size. Spiders did initiate changes in the trophic structure of aquatic food webs, reducing the biomass of predators, especially damselflies and dytiscid beetles. Spiders also increased decomposition despite having no effect on detritivore biomass or composition. These results are most parsimoniously explained by (i) a behaviourally mediated trophic cascade, whereby damselfly adults avoid bromeliads with spiders, and aquatic detritivores increase rates of detrital processing in the absence of damselfly larvae, and (ii) stimulation of decomposition through nutrients added from spider faeces and prey carcasses. We believe that this is the first study to show that terrestrial predators can affect decomposition by reducing the flux of keystone aquatic predators with complex life cycles.

The classification of species in trophic guilds facilitates studies on the ecology interactions. However, the large number of definitions of terms used and the overlap has hampered the standardization of trophic guilds, especially bottom-feeder fishes. In this context, this study aimed to quantify, by a scientometrics analysis, the research involving species of bottom-feeder fishes and trophic guilds in which they are classified, and discuss the definitions used for each trophic guild. A survey in the Scopus and Web of Knowledge was performed and the publications were analyzed according to the type of trophic guild, publication year, the first author ´s country, the journal of publication, approach used, climate, the type of environment, subject and trophic guilds definitions. The trophic guild of the bottom-feeder fishes's fall among the least studied, however, we observed an increased number of publications since 1990. The climatic regions with the highest number of publications were the Tropical and Temperate hot climate, especially the United States, Brazil and Holland in the number of published papers. The publications, mainly observational, were developed mainly in freshwater environments, with emphasis on dietary studies. We found the occurrence of different definitions to bottom-feeder fishes, and the classification criteria were based mainly on food resource and feeding site. Considering the great diversity of food resource present in the sediment of aquatic environments, the classification of the bottom-feeder fishes in various trophic guilds is justified. However, there needs to be a standardization of the criteria for classification, thus it will generate fewer conflicts regarding the nomenclature used to determine the trophic guilds of fish.

How species interactions shape habitat structure is a longstanding question in ecology. A curious phenomenon reflecting ecological self-organization around reef habitat structures exists on coral reefs: large-scale (hundreds to hundreds of thousands of m2) halo-like patterns surrounding patch reefs, i.e., individual coral reefs that are often separated by seagrass or macroalgal meadows. These “halos,” long known to occur in various locations worldwide, reflect a distinct band of unvegetated sediments surrounding coral patch reefs. However, the full suite of mechanisms controlling them have never been rigorously explored, perhaps due to the common assumption dating back nearly 50 years that they arise solely from reef-based herbivory patterns shaped by anti-predator behavior. Here we provide empirical evidence from a set of halos within Australia's Great Barrier Reef that risk-averse foraging and a previously unrecognized functional group contribute to halo formation, demonstrating that these halos cannot be explained by any one mechanism in isolation. Our results show that halos are a more complex ecological phenomenon than previously assumed by the majority of studies of halos. Specifically, risk-averse grazing by herbivores is likely a key mechanism behind the formation of halos, as generally assumed, but bioturbators also play a central role. This knowledge furthers our understanding of how small-scale species interactions can structure habitat at landscape scales. These large-scale habitat features are important because they affect at least one important ecosystem function, carbon storage, and potentially others (e.g., biological nutrient transfer). These results also raise the question of whether other self-organized ecological patterns may be more nuanced than is currently assumed. This study capitalizes on recent advances in high resolution satellite imagery accessibility that allow ecologists to measure landscape-scale habitat features nearly everywhere on land and in shallow seas. Our results suggest that halos may hold potential as the basis for a tool for remotely observing ecological interactions and measuring large-scale ecosystem change on coral reefs.

The growing demand for aquaculture products can only be maintained by increasing the production of lower trophic species such as bivalves and tunicates. Low trophic species avoid the energy losses during trophic transfers to build animal protein, making them ideal candidates to exploit available resources in coastal waters. In the particular case of fjords, forced upwelling of deep nutrient-rich waters can promote phytoplankton growth, or in other words, the growth of bivalve and tunicate food. However, the density at which bivalves and tunicates are cultured can compromise phytoplankton populations and consequently, marine food chains. A highly configurable environmental model was constructed to study the ecosystem effects and potential biomass production of hypothetical bivalve and tunicate aquaculture scenarios in a Norwegian fjord under forced upwelling conditions. The simulations objectively determined the level of aquaculture development that maximizes the sustainable utilization of resources towards bivalves and tunicates biomass production. The model also highlighted the positive effect of the forced upwelling on both cultured production and phytoplankton abundance under aquaculture scenarios. Finally, the model predicted that tunicates would be more efficient than mussels at extracting resources due to their lower metabolic cost and higher filtration capacity. Although a full economic analysis would be required to decide on the preferred species to be cultured, these results encourage current pilot studies in which tunicates are explored as a sustainable way to efficiently exploit marine resources for aquafeed production.

The southeastern Gulf of California is located where two major ocean systems meet: the California Current at the north and the North Equatorial current at the south, however the ecosystem-level effects that have such confluence remain unknown. In this study, we compared the structure and function of this ecosystem between two periods 1994–1997 and 2006–2007. We based the comparison on food web models built with Ecopath with Ecosim (EwE) modeling software and assumed local sea surface temperature anomalies (1993–2009) as an environmental indicator. We analyzed the ecosystem function using indicators estimated by EwE. We performed structural analysis using topological centrality indices to analyze the role of trophic species in the food web. We found that the structure and function of the ecosystem differed among the two periods, which were characterized by two clearly different levels of variation (low variability in 1994–1997 and high variability in 2006–2007). The total biomass, total system throughput, net production of the system, connectance and Finn’s cycling index decreased from 1994–1997 to 2006–2007. The mean transfer efficiency (MTE) revealed that in the period, the energy flow among trophic levels was more efficient. During 2006/07, there was an increase in the ecosystem’s organization, but at the same time, the ecosystem may have been more vulnerable to external perturbations because its resilience decreased. In relation to the structural role of trophic compartments, there were differences in both periods. We found that most groups change their trophic role under different oceanographic conditions. We discuss that the changes in the ecosystem are related to local variability in sea surface temperature.

Paleontology Modern carnivore communities include species that span a range of body sizes. For example, on the African savannah, there are small species (mongooses), medium species (wild dogs), and large species (lions). This variation reflects available prey sources that best suit each group. Carnivorous dinosaur communities, however, were missing species that fall into the middle, or mesocarnivore, group as adults. Schroeder et al. looked across communities, space, and time and found that this absence appears to have been driven by the distinctive biology of dinosaurs, in which giant adults start out as tiny hatchlings. Growing juvenile dinosaurs thus filled the other niches and limited trophic species diversity. Science , this issue p. [941][1] [1]: /lookup/doi/10.1126/science.abd9220

We studied the effects of land use change from grassland to Eucalyptus spp. plantation on macro and mesofauna soil food webs in two sites in the Rolling Pampas. We expected to find differences in the parameters that characterize the structure of soil food webs, as the implantation of Eucalyptus implies changes in the characteristics of the resources and the microhabitat conditions. We also expected to find differences in the communities in terms of diversity, abundance, and species present. The treatments were: grasslands; 10-year-old Eucalyptus plantations and 20-year-old Eucalyptus plantations. Seasonal samplings were performed for the extraction of soil fauna in winter, spring, summer and autumn. For the analysis of food webs, we worked with “trophic species'': groups of organisms that have the same prey and the same predators. A total of 25 food webs were laid out using bibliographical information of feeding habits from the identified taxa. From each food web, we obtained a predator overlap graph, in which the consumers that share the same source or prey are linked by an arrow. In addition, the Shannon-Wiener index was calculated. We found that trophic species densities were different among the treatments: communities from grassland and the younger plantations were dominated by earthworms and other secondary decomposers, while the community in the older plantation showed a greater contribution of primary decomposers (Shymphyla, Isopoda and Diplopoda). No significant differences between treatments were found in the parameters that characterize the structure of soil food webs, i.e. connections number, number of trophic species nor connectivity. However, the diversity of the community was lower in the youngest plantations than in the other treatments, and it shows evidence of compartmentalization in the predator overlap graphs. Our findings suggest that the meso and macrofauna communities in the 10-years-old plantations represent a transition between the communities from grasslands and the oldest plantations. We conclude that the effects of forestation with Eucalyptus on soil fauna communities are evident through changes in functional groups rather than changes in the parameters that characterize the structure of soil food webs., Trophic species, Disturbance, Soil fauna, Land use, Biodiversity, Detrital food webs.

Collembola are among the most abundant, diverse and functionally important groups of soil animals. Collembolans inhabit different litter and soil layers and their food objects are intimately related to their habitat. Morphological differences that separate high rank taxa of collembolans have clear functional meaning in relation to life style and habitat requirements (including position in the soil profile). However, no study has tested the hypothesis that the species within the major functional groups also differ in terms of trophic positions. This hypothesis was tested for the first time using stable isotope analysis. We compiled original and published data on the stable isotope composition of 82 collembolan species in temperate forest ecosystems. The δ 13 C and δ 15 N values of collembolans were found related to their life forms, reflecting a shift in available food objects across different habitat layers and matching the vertical isotopic gradient of soil organic matter. The trophic niche of species varied among different collembolan orders and families, indicating a pronounced phylogenetic signal and supporting the trophic niche conservatism hypothesis. Considering stable isotope compositions, as well as the taxonomic identity and life form of species, we outlined four collembolan functional guilds that use different types of food and perform different ecosystem functions.

Understanding how omnivorous consumers are affected by their resources and how this is expressed through the food chain is a fundamental issue in ecology. We used stable isotope analysis of archived scales of two pelagic single-chain omnivorous fish species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix), to reconstruct historical trophic interactions patterns along a gradient of resources. We found that, although bighead carp and silver carp utilize the similar resources from the pelagic food chain, they can coexist and persist not only by regulating their trophic position and trophic dissimilarity, but also by regulating trophic niche width. Omnivorous fish often exhibit flexible foraging strategies, which is closely related to the availability of ecologic context. We found a positive relationship between trophic dissimilarity and zooplankton density, which may indicate that the competitive interactions induce strong top-down effects on zooplankton, and/or that high zooplankton availability release the between-population trophic interaction through bottom-up effect. The trophic niche width of bighead carp was positively related with zooplankton availability, probably reflecting that the niche of an omnivore at a higher trophic position is more sensitive to high quality resources. Our results indicate how different aspects of the trophic partitioning of coexisting omnivores may be regulated by different ecological contexts. These alternatives are not mutually exclusive and further theoretical work should include both these mechanisms to re-evaluate the effects of omnivory on food web properties.

http://dx.doi.org/10.5007/2175-7925.2016v29n3p29Este trabalho teve como objetivo conhecer os invertebrados bentônicos, bem como caracterizar os grupos funcionais tróficos (coletores, coletores-catadores, coletores-filtradores, fragmentadores, predadores e raspadores) encontrados em substrato rochoso em períodos sazonais no Rio Palmital, município de União da Vitória, Paraná, Brasil. As amostragens foram realizadas no período seco (junho/julho-2011) e chuvoso (novembro/dezembro-2011). Os dados obtidos indicam que o grupo funcional dos coletores foi o mais frequente. Os resultados sugerem que há influências dos distúrbios provocados pela precipitação na fauna de invertebrados, durante o período de chuvas, sendo que determinadas espécies tróficas encontradas podem estar relacionadas com a presença de matéria orgânica como um recurso alimentar na dieta dos invertebrados aí presentes.

Eutrophication in aquatic ecosystem is known to cause an intensification of primary production, with consequences for the ecosystem degradation. Various researches provided evidences about food web structure variations during eutrophication process, but there were few attempts to empirically investigate the relationship between energy availability and trophic relationships, which is an important goal with relevance for management of eutrophic lakes. As a large shallow lake, Lake Taihu has suffered long-term eutrophication. Here, the species compositions of Lake Taihu food web in three different trophic periods (oligotrophic stage, beginning of eutrophication, and developed stage of eutrophication) were conducted. Food web matrixes and Ecopath model were used to estimate the dynamic of food web structure and energy availability. The results showed that the number of trophic species, trophic links, and the length of food chain declined during the eutrophication process from 1960s to 2000s, which means food web structure of Lake Taihu was simplified even though entrophication brought sufficient nutrient into ecosystem. Meanwhile, the total transfer efficiency of food web declined from 24.1% in 1960s to 23.3% in 1990s and 21.9% in 2000s. These results suggest that long-term eutrophication altered the energy availability of food web, and then influenced the food web structure gradually.

Community level ecological traits are thought to affect invasibility as more diverse communities with complex trophic interactions may be associated with greater biotic resistance. Elucidation of the nature of this relationship is often hampered by difficulties in characterising food webs, particularly where field data are lacking. We attempted to overcome this by coupling food web modelling with information-theoretic analysis of the modelled webs. In addition, we also investigated the possibility that species level trends in trophic traits of established aliens might reflect exploitation of empty niches. We constructed hypothetical food webs of 26 natural and artificial lentic habitats from a data set consisting of 370 fish species representing 71 families. Using these food webs, we investigated associations at the community level between food web traits and network topology and number of alien fish species using an information-theoretic approach based on a set of competing a priori hypotheses. At the species level, we similarly tested for trends in trophic traits of established alien fishes using the information-theoretic approach in addition to nMDS of diet data. We found that native species richness in a community was the most important determinant of the number of alien fish taxa, displaying an inverse relationship. Our data also show that alien fish generally feed lower down the food web. Our findings suggest that the biotic resistance hypothesis, though scale dependent, can result in observable effects in animal communities. Moreover, we also found that the ability to exploit low energy yield food sources could favour the establishment of alien species via avoidance of resistive forces from native taxa.

Food uptake ability of higher trophic level species are more complicated and interesting due to their choice and availability of food and consequently their growth. In the present study, the effect of top predator interference on the dynamics of a tritrophic food chain model involving an intermediate and a generalist type top predator are considered. It is assumed that the interaction between the logistically growing prey and intermediate predator follows the Volterra scheme, while that between the top predator and its favorite food i.e. the intermediate predator follows Crowley–Martin type functional response. Also, it is considered that the growth of top predator is by sexual reproduction. The boundedness of the system, existence of an attracting set, local and global stability of non-negative equilibrium points and uniform persistence are established by very complicated and highly nonlinear biological considerations. With the help of empirical results from different field and laboratory experiment, it is clarified that Crowley–Martin type functional response gives better result than other predator dependent functional responses for the issue of interference among own population. Also it is clarified from literature survey that high trophic species are mostly generalist type i.e. they can survive rather than their favorite food depending upon the present environmental situation and their growth rate depends upon the mating success. Moreover, increasing the top predator interference stabilizes the system, while increasing the normalization of the residual reduction in the top predator population destabilizes the system. Different numerical examples support these ecological phenomenon.

The aim of this study was to quantify changes in food webs based on ontogenetic dietary shifts of a top fish predator (here brown trout Salmo trutta L.). Here, the food web of a river in Central Spain (River Tormes) was studied to test the hypothesis that food web structural properties may change according to age-related changes in feeding habits of brown trout. Thus, the food web was established separately for age-0, age-1 and age-2 brown trout using a forward procedure (individual, modular and river networks); next the complete trophic networks were established. Overall, the networks were characterized by generalist predators with numerous prey types; specialized feeding was limited to a low number of taxa. Food web structural properties (number of links, connectance and linkage density) had the highest values in the age-1 scenario. The highest trophic level (i.e. the highest number of energy steps) was also found in the age-1 scenario, but the lowest in the age-0 scenario. Vulnerability and generalization tend to be higher in age-1 and age-0 scenarios, respectively. The present study exemplifies that age-specific brown trout predation on invertebrate predators emerged as the key factor to understand the changes in food web structural properties among age scenarios. I conclude that ontogenetic dietary shifts of brown trout promote changes in food web structural properties. This conclusion underscores the importance of considering different life history stages of species (i.e. to cover their ontogenetic dietary shifts) in food web construction.

We reconstructed the structure of a tropical marine food web and then analyzed it to evaluate how the trophic network could respond to anthropogenic pressures such as the removal of species by fisheries. To reconstruct the presence/absence of predator-prey interactions, we assembled detailed quantitative information from the scientific literature on the stomach contents of 80 predator species (elasmobranchs, teleosts and invertebrates) collected in the Golfo de Tortugas (Colombia) between 1990 and 2009. We tested three conceptual models of network structure (random, small-world, and scale-free), characterized by different system properties and tolerance to perturbations, to evaluate which one better fitted the reconstructed food web. Our results suggest that this network has small-world structure and scale-free properties. An impact on one species may therefore spread to many species through short interaction chains; only a few nodes with high centrality values would support the network structure. However, contrary to current theory, our analysis revealed no clear relationships between species with high centrality and the large-scale structural patterns observed in the network (small-world and scale-free properties). This observation indicates that ecosystem-based fisheries management should prioritize not only high-centrality species (e.g., shrimps, which furthermore are species of high commercial value in the area), but should also consider species with unique structural properties such as those with little or no topological redundancy such as large sharks. For this reason, top predator conservation needs more attention than currently received in fisheries management.

Life history strategies affect population dynamics; however, their effects on community dynamics remain poorly understood. A food web model with stage-structured populations (structured food web) and an equivalent model with unstructured populations (unstructured food web) were developed, and their structures and dynamics were compared. Both models incorporated energetic processes and allowed populations to go extinct and invade over time. The results from the two models shared some similarities. For example, all of the initial randomly formed food webs were unstable, but the extinction and invasion rates of populations declined over time. However, there were also clear differences between them. For example, preventing trophic interactions among similar-sized organisms led to a large increase in the number of persisting consumer populations under the unstructured food web, but the number was almost unchanged under the structured food web. Furthermore, an increase in the carrying capacity of primary producers caused an increase in the population extinction rate of consumers under the structured food web, but the extinction rate declined under the unstructured food web. Finally, the average trophic level of consumers in the unstructured food web was often at 2, indicating the food web primarily consisted of herbivores. On the other hand, the average trophic level in the structured food web was significantly higher, indicating the existence of trophic interactions among consumers. These results suggest the importance of incorporating stage structures into food web models to bridge the current theories of food web dynamics and empirical observations because nature consists of structured populations. In particular, I conclude that if one wants to study trophic interactions beyond herbivory, it is crucial to incorporate structured populations into food web models.

Global change continues to push individual species towards extinction and in many cases these species cannot be expected to disappear silently, without a trace, from the communities in which they reside. Importantly, the loss of certain species can trigger a cascade of secondary extinctions, resulting in further degradation of a system with potential effects on ecosystem functioning. It is thus crucial to better our understanding of the types of species which, if lost, will affect community structure the most, because in this context they are analogous to keystone species. Here, using a dynamical approach and simulating species loss in model communities, we study whether the importance of species changes as the structure of the food web changes by analyzing the potential importance of 11 species traits during food web collapse following simulated extinctions. We find that the keystone status of species traits is context dependent, with the identity of the most important trait changing during food web collapse. The relative importance of two trait categories tend to be inversely related, with body size based traits being important in intact to moderately degraded webs and interaction strength based species traits being important in highly collapsed food webs. The results of our study furthermore suggest that the response of communities to small and large perturbations may be related in the sense that the same kinds of species are important in both situations.

Invasive species can cause substantial ecological impacts on native biodiversity. While ecological theory attempts to explain the processes involved in the trophic integration of invaders into native food webs and their competitive impacts on resident species, results are equivocal. In addition, quantifying the relative strength of impacts from non‐native species (interspecific competition) versus the release of native conspecifics (intraspecific competition) is important but rarely completed.Two model non‐native fishes, the globally invasive Cyprinus carpio and Carassius auratus, and the model native fish Tinca tinca, were used in a pond experiment to test how increased intra‐ and interspecific competition influenced trophic niches and somatic growth rates. This was complemented by samples collected from three natural fish communities where the model fishes were present. The isotopic niche, calculated using stable isotope data, represented the trophic niche.The pond experiment used additive and substitutive treatments to quantify the trophic niche variation that resulted from intra‐ and interspecific competitive interactions. Although the trophic niche sizes of the model species were not significantly altered by any competitive treatment, they all resulted in patterns of interspecific niche divergence. Increased interspecific competition caused the trophic niche of T. tinca to shift to a significantly higher trophic position, whereas intraspecific competition caused its position to shift towards elevated δ13C. These patterns were independent of impacts on fish growth rates, which were only significantly altered when interspecific competition was elevated.In the natural fish communities, patterns of trophic niche partitioning between the model fishes was evident, with no niche sharing. Comparison of these results with those of the experiment revealed the most similar results between the two approaches were for the niche partitioning between sympatric T. tinca and C. carpio.These results indicate that trophic niche divergence facilitates the integration of introduced species into food webs, but there are differences in how this manifests between introductions that increase inter‐ and intraspecific competition. In entirety, these results suggest that the initial ecological response to an introduction appears to be a trophic re‐organisation of the food web that minimises the trophic interactions between competing species. A plain language summary is available for this article.

Understanding patterns in predator:prey systems and the mechanisms that underlie trophic interactions provides a basis for predicting community structure and the delivery of natural pest control services. The functional response of predators to prey density is a fundamental measure of interaction strength and its characterisation is essential to understanding these processes. We used mesocosm experiments to quantify the functional responses of five ground beetle species that represent common generalist predators of north-west European arable agriculture. We investigated two mechanisms predicted to be key drivers of trophic interactions in natural communities: predator:prey body size ratio and multiple predator effects. Our results show regularities in foraging patterns characteristic of similarly sized predators. Ground beetle attack rates increased and handling times decreased as the predator:prey body-mass ratio rose. Multiple predator effects on total prey consumption rates were sensitive to the identity of the interacting species but not prey density. The extent of interspecific interactions may be a result of differences in body mass between competing beetle species. Overall these results add to the growing evidence for the importance of size in determining trophic interactions and suggest that body mass could offer a focus on which to base the management of natural enemy assemblages.

Aggregation of species on the basis of their trophic relationships is a fundamental step for quantifying, visualizing and thereby uncovering the structure of food webs. Although the Additive Jaccard Similarity (AJS) has been widely used to measure trophic similarity between species, it has also been criticized for its limited ability to find species with equivalent trophic roles, especially when they do not share the same predators and prey. In this study, we proposed a new trophic similarity measure, the Extended Additive Jaccard Similarity (EAJS), which quantifies trophic similarity between species based not only on the similarity of their shared predators and prey at adjacent trophic levels but at all trophic levels throughout a food web. Average linkage clustering was then used to aggregate species in the mammalian food web for the Serengeti ecosystem in northern Tanzania and southern Kenya on the basis of both trophic similarity measures. Compared to groups identified on the basis of AJS values, groups derived using EAJS had greater within-group similarity in terms of species' trophic relationships and greater discrimination vs. those in other groups. Groups based on EAJS values also better reflected ecological factors known to structure food webs, including producer-level habitat segregation and mammalian body mass. The advantage of EAJS lies in the fact that it is designed to consider species feeding relations in food webs that is not limited to adjacent trophic levels. Our approach provides a means for revealing the patterns of trophic relations among species in food webs and exploring known and unknown factors shaping food web structure.

To understand the effects of predator removal in marine ecosystems requires accurate estimates of trophic position and trophic structure that have been difficult to obtain to date. For example, most sharks are classified as diet generalists that feed around trophic position 4, but this classification contradicts observations of diverse feeding behaviour among large species, suggesting that trophic structure has been oversimplified among upper trophic level species. To test this assumption, bulk δ 15 N and δ 13 C values of 13 shark species constituting the large shark assemblage off southern Africa were integrated into (i) a hierarchical Bayesian model, accounting for body size and variable sample sizes among species, and (ii) a dietary δ 15 N-dependent enrichment model to quantify individual and assemblage-wide trophic position and structure. Compound specific isotopic analysis of amino acids (CSIA-AAs) for a subset of species was used to verify results. Although discrepancies occurred between methods, overall these data confirm that large sharks, including several globally threatened species, feed at markedly higher trophic positions and across a broader trophic range than is currently assumed. This identifies a lower degree of functional equivalence among the assemblage. Such complex trophic structure among large sharks suggests that cascading effects from species-specific removals in food webs may be weaker but more pervasive than currently assumed. Reassignment of the trophic structure of large marine predators has important consequences for any potential regulatory and stabilizing roles in marine food webs.

15 pages; International audience; How food webs are structured has major implications for their stability and dynamics. While poorly studied to date, arctic food webs are commonly assumed to be simple in structure, with few links per species. If this is the case, then different parts of the web may be weakly connected to each other, with populations and species united by only a low number of links. We provide the first highly resolved description of trophic link structure for a large part of a high-arctic food web. For this purpose, we apply a combination of recent techniques to describing the links between three predator guilds (insectivorous birds, spiders, and lepidopteran parasitoids) and their two dominant prey orders (Diptera and Lepidoptera). The resultant web shows a dense link structure and no compartmentalization or modularity across the three predator guilds. Thus, both individual predators and predator guilds tap heavily into the prey community of each other, offering versatile scope for indirect interactions across different parts of the web. The current description of a first but single arctic web may serve as a benchmark toward which to gauge future webs resolved by similar techniques. Targeting an unusual breadth of predator guilds, and relying on techniques with a high resolution, it suggests that species in this web are closely connected. Thus, our findings call for similar explorations of link structure across multiple guilds in both arctic and other webs. From an applied perspective, our description of an arctic web suggests new avenues for understanding how arctic food webs are built and function and of how they respond to current climate change. It suggests that to comprehend the community-level consequences of rapid arctic warming, we should turn from analyses of populations, population pairs, and isolated predator-prey interactions to considering the full set of interacting species.

Some mammalian predators acquire both food and shelter from their prey, by eating them and using the refugia the prey construct. I searched the literature for examples of predators that exhibit this behavior and summarize their taxonomic affiliations, relative sizes, and distributions. I hypothesized that size ratios of species involved in this dynamic would be near 1.0, and that most of these interactions would occur at intermediate and high latitudes. Seventeen species of Carnivorans exploited at least 23 species of herbivores as food and for their refugia. Most of them (76.4 %) were in the Mustelidae; several small species of canids and a few herpestids were exceptions. Surprisingly, the average predator/prey weight ratio was 10.51, but few species of predators were more than ten times the weight of the prey whose refugia they exploit. This may be why the long and thin Mustelines commonly exploit this habit. A number of predators appropriate the refugia of their key prey during winter when their prey occupies thermally secure nests. Indeed, most of the predator–prey pairs that engage in this relationship occur in intermediate and high latitudes, though there may be a reporting bias. Predators that depend on prey as food and for shelter, and whose fates are linked strongly to a few key prey species, may be particularly vulnerable to changes in climate that affect the subnivean habitats of their prey. Mammals that create refugia that can be used by other species (among them predators) may play disproportionately important roles in their communities.

Acute toxicity data of six heavy metals [Cu, Hg, Cd, Cr(VI), Pb, Zn] to aquatic organisms were collected and screened. Species sensitivity distributions (SSD) curves of vertebrate and invertebrate were constructed by log-logistic model separately. The comprehensive comparisons of the sensitivities of different trophic species to six typical heavy metals were performed. The results indicated invertebrate taxa to each heavy metal exhibited higher sensitivity than vertebrates. However, with respect to the same taxa species, Cu had the most adverse effect on vertebrate, followed by Hg, Cd, Zn and Cr. When datasets from all species were included, Cu and Hg were still more toxic than the others. In particular, the toxicities of Pb to vertebrate and fish were complicated as the SSD curves of Pb intersected with those of other heavy metals, while the SSD curves of Pb constructed by total species no longer crossed with others. The hazardous concentrations for 5 % of the species (HC5) affected were derived to determine the concentration protecting 95 % of species. The HC5 values of the six heavy metals were in the descending order: Zn > Pb > Cr > Cd > Hg > Cu, indicating toxicities in opposite order. Moreover, potential affected fractions were calculated to assess the ecological risks of different heavy metals at certain concentrations of the selected heavy metals. Evaluations of sensitivities of the species at various trophic levels and toxicity analysis of heavy metals are necessary prior to derivation of water quality criteria and the further environmental protection.

Unique morphologies along with associated differences in habitat use and feeding behavior can result in fish at the top of piscine food chains differing in trophic level. Broad size ranges inherent within large species provide opportunity for size-related trophic shifts. Such relationships between size and trophic level can be species specific. Furthermore, individual-based diet variation can bring about differences among similar-sized organisms. A challenge to aquatic ecologists is deciphering these patterns of trophic change both between and within species. Stable isotope analysis has emerged as a powerful tool for evaluating such patterns. Employing stable isotope analyses, we assessed trophic differentiation in 4 large predatory fish species from a coastal-plain stream. We established the trophic base by including 2 herbivorous invertebrates in the analysis and identified a trophic hierarchy among species, with 2 specialized, generally open-water piscivores, Lepisosteus osseus (Longnose Gar) ...

Rarity of species is often considered to set priorities for biodiversity conservation. Less abundant species are expected to be at higher risk of extinction and make significant contribution to food web functioning. However, the relationship between species abundance and position in food webs is still unclear. Here we tested possible correlations between species abundance and structural position in Prince William Sound food web. Species abundance was inferred from biomass data and structural position was characterized by 13 centrality indices.We found that less abundant species have higher trophic positions and display more generalist feeding strategies. However, positive correlations link most of the centrality indices to population size. Thus, being locally rare translates into more peripheral food web positions and implies marginal roles in the spread of indirect effects. Species characterized by largest population size are responsible for the transfer of largest amounts of biomass and regulate the transmission of indirect effects. Less abundant species are of marginal structural importance and are exposed to impacts mediated by larger populations. In Prince William Sound ecosystem, rarity is associated with critical food web positions and does not simply reflect a marginal contribution to biodiversity.We suggest that knowing the food web position of rare species might help to formulate more effective, system-level solutions for their conservation, rather than simply focusing on the direct treatment of symptoms.

The positive effects of biodiversity on the functioning of ecosystems are well demonstrated in laboratory microcosms but the precise mechanisms underlying higher ecosystem process rates in natural assemblages are less well understood. We investigated, under semi-natural conditions (field enclosures), the potentially interactive effects of species identity and trophic function (i.e., feeding guild) on consumer growth, using a fish assemblage in a tropical stream. We tested the relative importance of species identity and trophic function on consumer growth by placing 2 fish of either (i) the same species, (ii) different species but of similar trophic function, or (iii) different species of different trophic functions in each of 72 stream enclosures for 48 days and measuring biomass change, individual diet composition and behavior. We predicted that if functional diversity had a larger impact than species diversity, then fish growth would be highest for pairs of species from different functional groups (i.e., those with the highest diet complementarity), intermediate for different species within a guild, and lowest for the same species (those with the lowest complementarity and highest niche overlap), such that functional variation between species in different guilds would exceed functional differences within guilds. Our results show that functional heterogeneity rather than species diversity per se had the greatest impact on food resources used complementarily, leading to higher biomass accrual. Mechanistically, higher growth rates were driven by concomitant increases in resource intake and reductions in antagonistic interactions. Together, these results underscore the importance of functional diversity on macroconsumer production in natural assemblages.

There is an increasing focus on the recovery of proteinaceous components from marine biomass. In the future it is expected that more food and feed will come globally from the oceans. A lot of marine biomass is today under-utilized or used for low value products. In other cases, the biomass is from under-utilized marine resources such as seaweed, low trophic species or mesopelagic species. The reason why they are not being used can be due to difficult catching or harvesting methods or due to insufficient availability of processes and infrastructure. Much of this biomass is suitable for human consumption; however, the right processing technologies are not put into place in order to make these products available. In this chapter, the focus will be on marine biomass that is currently of low value or currently wasted, and possible solutions for use of these will be evaluated. An overview of possible products from a variety of marine biomasses is presented, the desired properties of the different products towards specific markets are described and the possibilities of these products becoming a commodity that can be produced in large volumes is evaluated based on technological and market possibilities.

Food webs (i.e., networks of species and their feeding interactions) share multiple structural features across ecosystems. The factors explaining such similarities are still debated, and the role played by most organismal traits and their intraspecific variation is unknown. Here, we assess how variation in traits controlling predator-prey interactions (e.g., body size) affects food web structure. We show that larger phenotypic variation increases connectivity among predators and their prey as well as total food intake rate. For predators able to eat only a few species (i.e., specialists), low phenotypic variation maximizes intake rates, while the opposite is true for consumers with broader diets (i.e., generalists). We also show that variation sets predator trophic level by determining interaction strengths with prey at different trophic levels. Merging these results, we make two general predictions about the structure of food webs: (i) trophic level should increase with predator connectivity, and (ii) interaction strengths should decrease with prey trophic level. We confirm these predictions empirically using a global dataset of well-resolved food webs. Our results provide understanding of the processes structuring food webs that include functional traits and their naturally occurring variation.

The difficulty of experimentally quantifying non-trophic species interactions has long troubled ecologists. Increasingly, a new application of the classic "checkerboard distribution" approach is used to infer interactions by examining the pairwise frequency at which species are found to spatially co-occur. However, the link between spatial associations, as estimated from observational co-occurrence, and species interactions has not been tested. Here we used nine common statistical methods to estimate associations from surveys of rocky intertidal communities in the Northeast Pacific Ocean. We compared those inferred associations with a new data set of experimentally determined net and direct species interactions. Although association methods generated networks with aggregate structure similar to previously published interaction networks, each method detected a different set of species associations from the same data set. Moreover, although association methods generally performed better than a random model, associations rarely matched empirical net or direct species interactions, with high rates of false positives and true positives, and many false negatives. Our findings cast doubt on studies that equate species co-occurrences to species interactions and highlight a persistent, unanswered question: how do we interpret spatial patterns in communities? We suggest future research directions to unify the observational and experimental study of species interactions, and discuss the need for community standards and best practices in association analysis.

The complexity of food webs can be reduced to fundamental modules of trophic interactions that repeat to form reticulate webs. Omnivory, defined as feeding on more than one trophic level, is a module that is found in food webs more often than predicted by chance, likely because it confers stability. Yet, little is known about how omnivore and other food web modules affect individuals in the food web. Here, we constructed four different experimental food web modules using a blue mussel predator, zooplankton consumer, and phytoplankton resource. By manipulating the predator's access to the consumer and providing resource subsidies, we produced exploitative competition, food chain and omnivory food web modules, and a consumer-resource interaction. We used RNA:DNA ratios to measure the growth rate of the consumer in each food web. In 24-h experiments, growth rates of the consumer in the omnivory food web were significantly higher and more variable than in the other modules. Our results suggest that higher growth rates and variation at the individual scale may weaken the strength of predator–consumer interactions and help explain the ubiquity of omnivory in real food webs.

1.Habitat destruction, characterized by habitat loss and fragmentation, is a key driver of species extinction in spatial extended communities. Recently, there has been some progress in the theory of spatial food webs, however to date practically little is known about how habitat configurational fragmentation influences multi-trophic food web dynamics. \ud \ud 2.To explore how habitat fragmentation affects species persistence in food webs, we introduce a modelling framework that describes the site occupancy of species in a tri-trophic system. We assume that species dispersal range increases with trophic level, exploiting pair-approximation techniques to describe the effect of habitat clustering. \ud \ud 3.In accordance with the trophic rank hypothesis, both habitat loss and fragmentation generally cause species extinction, with stronger effects occurring at higher trophic levels. However, species display diverse responses (negative, neutral or positive) to habitat loss and fragmentation separately, depending on their dispersal range and trophic position. \ud \ud 4.Counter-intuitively, prey species may benefit from habitat loss due to a release in top-down control. Similarly, habitat fragmentation has almost no influence on the site occupancy of the intermediate consumer in the tri-trophic system, though it decreases those of both basal species and top predator. Consequently, species' responses to habitat destruction vary as other species become extinct. \ud \ud 5.Our results reiterate the importance of the interplay between bottom-up and top-down control in trophically linked communities, and highlight the complex responses occurring in even a simple food chain.