Web Topology Research Articles

Can planktonic food web topology be retraced by biomass measurements without internal and input flows (production and grazing rate) in freshwater marshes?

An accurate way to estimate the planktonic food web topology is to consider biomass and flows. However, measurements of flows, as production and grazing rate, are time-consuming. In this paper, we retrace food web topology based on three different degrees of information: input flows (production), internal flows (grazing rate) and plankton biomass in freshwater marshes. For that, a meta-analysis of datasets from 4 freshwater marshes of the Charente-Maritime (French Atlantic coast) were used, corresponding to 47 stations/dates and thus to different geographical and temporal situations. The main results were that, globally, the biomass can yield good results in terms of characterization of the contrasted topology of food web, as the herbivorous food web, the microbial food web and the multivorous food web. However, in order to properly distinguish weak, ‘normal‘ multivorous and strong multivorous food web, the only measure of biomass did not appear to be sufficient. To better separate these different types of multivorous food webs, measurements of primary productions or heterotrophic prokaryote biomass, which correlated well with primary productions, appear interesting. This approach can be applied in all aquatic ecosystems.

Food web attributes to assess spatial–temporal dynamics in estuarine benthic ecosystem

Threatened benthic ecosystems need urgent tools for effective bioassessment and relevant management. EU Marine Strategy Framework Directive (MSFD) obligates member states to achieve GES (Good Environmental Status) for 11 descriptors of environmental state (MSFD; 2008/56/EC). From all of the descriptors, D4 that focuses on Food Webs is the most functional-oriented indicator, but also the most challenging to implement due to our limited knowledge on benthic interactions. Particularly, it is still unclear how spatially and temporally regulated abiotic variables determine the entire benthic food webs, and which benthic food web attributes best respond to these spatially and temporally derived environmental variations. To fill this gap, we measured the natural isotopic ratios (δ13C and δ15N) of macrobenthic organisms and their food sources and build twelve food web topologies across three distinct sites (Navigator, Gambia, Tróia) in summer and winter during two consecutive years. To assess these food web topologies, we applied isotopic metrics, further integrated with univariate and multivariate analysis to find food web-based indicators that best respond to these spatial and temporal variability.We found clear spatial patterns associated to an increase in primary production and quantity and quality of organic matter (OM). Sites with higher organic load and less quality OM (Navigator and Gambia) had simpler food webs, likely associated to high abundance of opportunistic meiobenthic species. Site located inside protected area (Tróia) with high quality OM had the most complex food web characterized by high diversity of specialist consumers that used more efficiently available resources. Similarity metrics were valuable complementary tool that helped to further disentangle the causes of spatial variability, in this case distinguishing between two food webs (Navigator and Gambia) that had similar structures but different resource utilization.The temporal patterns were not so evident than the spatial patterns, although significant differences were reported between sampling occasions for the same metrics (maximum trophic position and the percentage of carnivores and omnivores, p < 0.05). The most complex Tróiás food web demonstrated greater responsiveness in capturing temporal differences in resource use, suggesting that more complex food webs are better equipped to reflect temporal variability. The integration of isotopic metrics complemented with multivariate and univariate analyses proved to be an important tool for the analysis of different aspects of the benthic food web complexity in a spatial–temporal context providing a promising approach to assess the functional integrity of the estuarine ecosystems, especially in the context of the descriptor 4 within MSFD.

Amino acid-specific isotopes reveal changing five-dimensional niche segregation in Pacific seabirds over 50 years

Hutchison’s niche theory suggests that coexisting competing species occupy non-overlapping hypervolumes, which are theoretical spaces encompassing more than three dimensions, within an n-dimensional space. The analysis of multiple stable isotopes can be used to test these ideas where each isotope can be considered a dimension of niche space. These hypervolumes may change over time in response to variation in behaviour or habitat, within or among species, consequently changing the niche space itself. Here, we use isotopic values of carbon and nitrogen of ten amino acids, as well as sulphur isotopic values, to produce multi-isotope models to examine niche segregation among an assemblage of five coexisting seabird species (ancient murrelet Synthliboramphus antiquus, double-crested cormorant Phalacrocorax auritus, Leach’s storm-petrel Oceanodrama leucorhoa, rhinoceros auklet Cerorhinca monocerata, pelagic cormorant Phalacrocorax pelagicus) that inhabit coastal British Columbia. When only one or two isotope dimensions were considered, the five species overlapped considerably, but segregation increased in more dimensions, but often in complex ways. Thus, each of the five species occupied their own isotopic hypervolume (niche), but that became apparent only when factoring the increased information from sulphur and amino acid specific isotope values, rather than just relying on proxies of δ15N and δ13C alone. For cormorants, there was reduction of niche size for both species consistent with a decline in their dominant prey, Pacific herring Clupea pallasii, from 1970 to 2006. Consistent with niche theory, cormorant species showed segregation across time, with the double-crested demonstrating a marked change in diet in response to prey shifts in a higher dimensional space. In brief, incorporating multiple isotopes (sulfur, PC1 of δ15N [baselines], PC2 of δ15N [trophic position], PC1 and PC2 of δ13C) metrics allowed us to infer changes and differences in food web topology that were not apparent from classic carbon–nitrogen biplots.

Stable diverse food webs become more common when interactions are more biologically constrained

Ecologists have long sought to understand how diversity and structure mediate the stability of whole ecosystems. For high-diversity food webs, the interactions between species are typically represented using matrices with randomly chosen interaction strengths. Unfortunately, this procedure tends to produce ecological systems with no underlying equilibrium solution, and so ecological inferences from this approach may be biased by nonbiological outcomes. Using recent computationally efficient methodological advances from metabolic networks, we employ for the first time an inverse approach to diversity-stability research. We compare classical random interaction matrices of realistic food web topology (hereafter the classical model) to feasible, biologically constrained, webs produced using the inverse approach. We show that an energetically constrained feasible model yields a far higher proportion of stable high-diversity webs than the classical random matrix approach. When we examine the energetically constrained interaction strength distributions of these matrix models, we find that although these diverse webs have consistent negative self-regulation, they do not require strong self-regulation to persist. These energetically constrained diverse webs instead show an increasing preponderance of weak interactions that are known to increase local stability. Further examination shows that some of these weak interactions naturally appear to arise in the model food webs from a constraint-generated realistic generalist-specialist trade-off, whereby generalist predators have weaker interactions than more specialized species. Additionally, the inverse technique we present here has enormous promise for understanding the role of the biological structure behind stable high-diversity webs and for linking empirical data to the theory.

Temperature, productivity, and habitat characteristics collectively drive lake food web structure.

While many efforts have been devoted to understand variations in food web structure among terrestrial and aquatic ecosystems, the environmental factors influencing food web structure at large spatial scales remain hardly explored. Here, we compiled biodiversity inventories to infer food web structure of 67 French lakes using an allometric niche-based model and tested how environmental variables (temperature, productivity, and habitat) influence them. By applying a multivariate analysis on 20 metrics of food web topology, we found that food web structural variations are represented by two distinct complementary and independent structural descriptors. The first is related to the overall trophic diversity, whereas the second is related to the vertical structure. Interestingly, the trophic diversity descriptor was mostly explained by habitat size (26.7% of total deviance explained) and habitat complexity (20.1%) followed by productivity (dissolved organic carbon: 16.4%; nitrate: 9.1%) and thermal variations (10.7%). Regarding the vertical structure descriptor, it was mostly explained by water thermal seasonality (39.0% of total deviance explained) and habitat depth (31.9%) followed by habitat complexity (8.5%) and size (5.5%) as well as annual mean temperature (5.6%). Overall, we found that temperature, productivity, and habitat characteristics collectively shape lake food web structure. We also found that intermediate levels of productivity, high levels of temperature (mean and seasonality), as well as large habitats are associated with the largest and most complex food webs. Our findings, therefore, highlight the importance of focusing on these three components especially in the context of global change, as significant structural changes in aquatic food webs could be expected under increased temperature, pollution, and habitat alterations.

Ecological Constraints on the Evolution of Consumer Functional Responses

Intrinsically generated oscillations are a defining feature of consumer-resource interactions. They can have important consequences for the evolution of consumer functional responses. Functional response traits that maximize resource fitness (low attack rate and long handling time) and consumer fitness (high attack rate and short handling time) generate high-amplitude oscillations that can predispose species to extinction during periods of low abundances. This suggests that the ecological consequences of consumer-resource oscillations may impede evolutionary outcomes that maximize fitness. Data suggest this to be a strong possibility. Time series analyses reveal consumer-resource cycles to be infrequent in real communities, and functional response studies show a preponderance of low attack rates and/or short handling times that preclude oscillations but maximize neither species' fitness. Here I present a mathematical model to address this tension between ecological dynamics and the evolution of functional response traits. I show that the empirically observed attack rate-handling time distributions emerge naturally from the interplay between individual-level selection and the population-level constraint of oscillation-induced extinction. Extinction at low abundances curtails stabilizing selection toward trait values that maximize fitness but induce large-amplitude oscillations. As a result, persistent interactions are those in which the mean attack rate is low and/or the mean handling time is short. These findings emphasize the importance of incorporating oscillation-induced extinction into models that link food web topology to community persistence.

The effect of fish life-history structures on the topologies of aquatic food webs

Biological organisms can vastly change their ecological functionality due to changes in body size and diet across their life. Consequently, it has been increasingly recognized that to attain sufficient biological realism, food webs may need to include life-history structures. The objective of the work is to study theoretically whether and how the inclusion of life-history structures affects the food web topology. Topological research was done by applying network theory metrics for three different food web types with two different sizes that were generated by using the niche-model. The dynamical modeling was performed by using an allometric trophic network modeling approach. The different types included food webs with and without the life-history structure for top predators (three fish species). Each of the generated random food webs analyzed reached dynamical equilibrium conditions with respect to the biomass densities of the species prior to the network analysis. Our results suggest that food web topologies are not largely affected by the inclusion of age- or stage-structure. In addition to the topological study, the relationship between the metrics used in this work was investigated by using Pearson correlation. Results suggested that only a few pairs of metrics had a strong positive correlation and most of the correlations did not change with food web size or type.

Persistent homology of the cosmic web – I. Hierarchical topology in ΛCDM cosmologies

ABSTRACT Using a set of Lambda cold dark matter simulations of cosmic structure formation, we study the evolving connectivity and changing topological structure of the cosmic web using state-of-the-art tools of multiscale topological data analysis (TDA). We follow the development of the cosmic web topology in terms of the evolution of Betti number curves and feature persistence diagrams of the three (topological) classes of structural features: matter concentrations, filaments and tunnels, and voids. The Betti curves specify the prominence of features as a function of density level, and their evolution with cosmic epoch reflects the changing network connections between these structural features. The persistence diagrams quantify the longevity and stability of topological features. In this study, we establish, for the first time, the link between persistence diagrams, the features they show, and the gravitationally driven cosmic structure formation process. By following the diagrams’ development over cosmic time, the link between the multiscale topology of the cosmic web and the hierarchical buildup of cosmic structure is established. The sharp apexes in the diagrams are intimately related to key transitions in the structure formation process. The apex in the matter concentration diagrams coincides with the density level at which, typically, they detach from the Hubble expansion and begin to collapse. At that level many individual islands merge to form the network of the cosmic web and a large number of filaments and tunnels emerge to establish its connecting bridges. The location trends of the apex possess a self-similar character that can be related to the cosmic web’s hierarchical buildup. We find that persistence diagrams provide a significantly higher and more profound level of information on the structure formation process than more global summary statistics like Euler characteristic or Betti numbers.

Out-of-plane compression of a novel hybrid corrugated core sandwich panel

Lightweight sandwich panels with fluid-through cellular cores are promising for applications requiring simultaneous load-bearing and heat dissipation such as the combustion chamber of scramjet. While existing core topologies have exhibited good designability for specific thermal or mechanical requirements, the increasing demand for multifunctional attributes usually points to different core topology designs. Finding a single core topology that possesses excellent mechanical and thermal properties simultaneously remains challenging. To address the issue, the concept of a hybrid core (termed herein as the N core) that combines the conventional corrugated core with the web core was proposed to mitigate confliction between thermal and mechanical designs. Out-of-plane compressive characteristics of the hybrid cored sandwich panel was investigated theoretically, numerically and experimentally. An elastic–plastic analytical model was developed to predict the out-of-plane compressive behavior, with connection strength between facesheets and core as well as non-uniform strut thickness accounted for. For validation, test sample was fabricated using 3D-printing technology and tested under quasi-static out-of-plane compression. The validated model was then employed to exploit optimal configuration of the N core and maximum load capacity of the panel at minimal weight. It was demonstrated that, due to non-uniform strut thickness, the hybrid structure exhibited stepwise deformation, i.e., initial, subsequent and ultimate failures. Under the constraint of equal mass, the load capacity of either the hybrid or corrugated core is superior to the web core, while both the hybrid and web cores outperform the corrugated core in terms of active cooling capacity. For multifunctional applications, the proposed hybrid corrugated core possesses comprehensive thermal and mechanical advantages over conventional corrugated and web topologies.

Spider Web-Inspired Lightweight Membrane-Type Acoustic Metamaterials for Broadband Low-Frequency Sound Isolation.

Membrane-type acoustic metamaterial (MAM) has exhibited superior sound isolation properties, as well as thin and light characteristics. However, the anti-resonance modes of traditional MAMs are generated intermittently in a wide frequency range causing discontinuities in the anti-resonance modes. Achieving broadband low-frequency sound attenuation with lightweight MAM design is still a pivotal research aspect. Here, we present a strategy to realize wide sound-attenuation bands in low frequency range by introducing the design concept of bionic configuration philosophy into the MAM structures. Built by a polymeric membrane and a set of resonators, two kinds of MAM models are proposed based on the insight of a spider web topology. The sound attenuation performance and physical mechanisms are numerically and experimentally investigated. Multi-state anti-resonance modes, induced by the coupling of the bio-inspired arrangement and the host polymer film, are systematically explored. Significant sound attenuation is numerically and experimentally observed in both the lightweight bio-inspired designs. Remarkably, compared with a traditional MAM configuration, a prominent enhancement in both attenuation bandwidth and weight-reduction performance is verified. In particular, the bio-inspired MAM Model I exhibits a similar isolation performance as the reference model, but the weight is reduced by nearly half. The bio-inspired Model II broadens the sound attenuation bandwidth greatly; meanwhile, it retains a lighter weight design. The proposed bio-inspired strategies provide potential ways for designing sound isolation devices with both high functional and lightweight performance.

Construction strategy and performance simulation of quantum satellite wide area network based on cobweb structure

Quantum satellite communication is a research hotspot and frontier in the field of communication. It has the advantages of ideal information security and wide coverage, which is of great significance in constructing a global quantum satellite wide area network. However, problems such as network reliability, security and routing relay still need to be improved when transmitting information over long distances. In this paper, the spider web is used as a unique natural communication topology to transform the natural spider web into an artificial spider web topology. The quantum information transmission adopts N-order quantum teleportation routing scheme, and the transmission delay is basically unchanged. On this basis, the spider web topology quantum wide area network transmission model is constructed. The bit error rate, throughput rate and security key generation rate of the network model are simulated and analyzed. Taking 9-node ring network and 9-node cobweb for example, the quantitative analysis and qualitative analysis are both conducted in this paper. The results show that the cobweb topology has higher reliability. When the average power spectral density of the noise is given and there is no relay, the bit error rate increases with the transmission distance increasing, so the introduction of relay should be considered. When the transmission distance and noise power spectral density are constant, the bit error rate decreases with the number of relay nodes increasing, so the appropriate routing process should be selected in the spider web topology. With the increase of the probability of transmitting entangled photon pairs, the throughput rate gradually increases. With the increase of transmission delay in the network, the throughput rate Q gradually decreases. However, the transmission delay is basically unchanged in this routing scheme, and the transmission delay of cobweb structure is very small. Therefore, the throughput rate of the topology quantum WAN of cobweb network based on N-order quantum teleportation proposed in this paper will not significantly decrease. When the transmission distance of quantum information increases, the network key generation rate decreases gradually. With the increase of the number of network relay nodes, the key generation rate increases gradually. Thus, it can be seen that using cobweb topology and N-order quantum teleportation routing scheme to construct a quantum satellite WAN has good advantages.

Seasonal Food Web Dynamics in the Antarctic Benthos of Tethys Bay (Ross Sea): Implications for Biodiversity Persistence Under Different Seasonal Sea-Ice Coverage

Determining food web architecture and its seasonal cycles is a precondition for making predictions about Antarctic marine biodiversity under varying climate change scenarios. However, few scientific data concerning Antarctic food web structure, the species playing key roles in web stability and the community responses to changes in sea-ice dynamics are available. Based on C and N stable isotope analysis, we describe Antarctic benthic food webs and the diet of species occurring in shallow waters (Tethys Bay, Ross Sea) before and after seasonal sea-ice break-up. We hypothesized that the increased availability of primary producers (sympagic algae) following sea-ice break-up affects the diet of species and thus food web architecture. Basal resources had distinct isotopic signatures that did not change after sea-ice break-up, enabling a robust description of consumer diets based on Bayesian mixing models. Sympagic algae had the highest δ13C (∼−14‰) and red macroalgae the lowest (∼−37‰). Consumer isotopic niches and signatures changed after sea-ice break-up, reflecting the values of sympagic algae. Differences in food web topology were also observed. The number of taxa and the number of links per taxon were higher before the thaw than after it. After sea-ice break-up, sympagic inputs allowed consumers to specialize on abundant resources at lower trophic levels. Foraging optimization by consumers led to a simpler food web, with lower potential competition and shorter food chains. However, basal resources and Antarctic species such as the bivalve Adamussium colbecki and the sea-urchin Sterechinus neumayeri were central and highly connected both before and after the sea-ice break-up, thus playing key roles in interconnecting species and compartments in the web. Any disturbance affecting these species is expected to have cascading effects on the entire food web. The seasonal break-up of sea ice in Antarctica ensures the availability of resources that are limiting for coastal communities for the rest of the year. Identification of species playing a key role in regulating food web structure in relation to seasonal sea-ice dynamics, which are expected to change with global warming, is central to understanding how these communities will respond to climate change.

Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay

Food web dynamics outline the ecosystem processes that regulate community structure. Challenges in the approaches used to capture topological descriptions of food webs arise due to the difficulties in collecting extensive empirical data with temporal and spatial variations in community structure and predator–prey interactions. Here, we use a Kohonen self-organizing map algorithm (as a measure of community pattern) and stable isotope-mixing models (as a measure of trophic interaction) to identify food web patterns across a low-turbidity water channel of a temperate estuarine-coastal continuum. We find a spatial difference in the patterns of community compositions between the estuarine and deep-bay channels and a seasonal difference in the plankton pattern but less in the macrobenthos and nekton communities. Dietary mixing models of co-occurring dominant taxa reveal site-specific but unchanging food web topologies and the prominent role of phytoplankton in the trophic base of pelagic and prevalent-detrital benthic pathways. Our approach provides realistic frameworks for linking key nodes from producers to predators in trophic networks.

Foundation Species Abundance Influences Food Web Topology on Glass Sponge Reefs

Foundation species support communities across a wide range of ecosystems. Non-trophic interactions are considered the primary way foundation species influence communities, with their trophic interactions having little impact on community structure. Here we assess the relative trophic importance of a foundation species and assess how its abundance can influence food web topology. Using empirical data and published trophic interactions we built food web models for 20 glass sponge reefs to examine how average live reef-building sponge abundance (proxied by percent cover) at the reef level is correlated with community structure and food web network topology. Then, using a generalized food web model and stable isotope data we examined the relative importance of sponges. Sponges were consumed by all species examined and contributed significantly to their diets. Additionally, sponges were the second most important node in our generalized reef food web. Several metrics of food web topology (connectance, clustering, and median degree) and community structure exhibited a threshold response to reef-building sponge cover, with the change point occurring between 8 and 13% live sponge cover. Below this threshold, as average sponge cover increases, the consumers observed on a reef rely on fewer sources and are consumed by fewer predators, resulting in food webs that are more clustered and less connected. Above the threshold, as average sponge cover increases, the reefs’ food webs are less clustered and more connected, with consumers utilizing more sources and having more predators. This corresponds with the finding that several generalist predators (e.g., rockfishes) are associated with high sponge cover reefs. Our results are not consistent with previous reports that increasing foundation species abundance decreases connectance in food webs. We propose that the influence of foundation species on food web topology may be dependent on palatability, and therefore relative trophic importance, of the foundation species. Finally, our findings have important implications for sponge reef conservation and management, as they suggest that reefs below the 10% sponge cover threshold support different communities than high live sponge cover reefs.

The effects of intraspecific and interspecific diversity on food web stability

Although the effects of species diversity on food web stability have long been recognized, relatively little is known about the influence of intraspecific diversity. Empirical work has found that intraspecific diversity can increase community resilience and resistance, but few theoretical studies have attempted to use modeling approaches to determine how intraspecific diversity will affect food web stability. To begin to address this knowledge gap, we added intraspecific diversity to May’s classic random food web model. We found that, like species diversity, intraspecific diversity decreased stability. These effects on stability were not simply attributable to changes in interaction strengths, suggesting that intraspecific diversity can have its own independent effects on stability. Its effect depends on the relationship between inter- and intra-genotype interactions; when competition within genotypes was stronger than among them, food webs were generally more stable than when the converse was true. Overall, our model suggests that determining the direction and the magnitude of intraspecific diversity’s effects on stability in natural systems will require more empirical information about how its inclusion alters patterns of interaction strength and food web topology.

Benthic trophic networks of the southern North Sea: contrasting soft-sediment communities share high food web similarity

We examined whether taxonomically distinct benthic communities from contrasting sediments in the German Bight (southern North Sea) also differ in their trophic structure. As a case study, we compared the Amphiura filiformis community (AFC) of silty sands and the Bathyporeia− Tellina community (BTC) of fine sands using a combination of stable isotope analysis and data on trophic interactions. Differences between the food webs were evident in the feeding guild compo� sition of important primary consumers: deposit and interface feeders are the most diverse primary consumer guilds in the AFC, whereas suspension and interface feeders play a major role in the BTC, reflecting differences in physical properties and food availability at the sediment−water interface. While all primary consumer guilds had the same trophic level (TL) in the AFC, deposit feeders of the BTC occupied a trophic position intermediate between other primary and higher� order consumer guilds, likely explained by partially incomplete knowledge of their trophic eco - logy and selective feeding, including the ingestion of meiofauna. Most food web properties, how�ever, were similar between the AFC and BTC: they mainly depend on pelagic primary production, reach TL 4 and are characterized by a prevalence of generalist higher-order consumers. Further� more, both trophic networks had similar linkage densities and high directed connectance, the lat�ter feature suggesting considerable food web robustness. Our findings suggest that although com�munities in the German Bight differ in some aspects of their trophic structure, they share a similar food web topology, indicating a comparable degree of resilience towards natural and anthro�pogenic disturbances.

Climate effects on fish body size–trophic position relationship depend on ecosystem type

The energetic demand of consumers increases with body size and temperature. This implies that energetic constraints may limit the trophic position of larger consumers, which is expected to be lower in tropical than in temperate regions to compensate for energy limitation. Using a global dataset of 3635 marine and freshwater ray‐finned fish species, we addressed if and how climate affects the fish body size–trophic position relationship in both freshwater and marine ecosystems, while controlling for the effects of taxonomic affiliation. We observed significant fish body size–trophic position relationships for different ecosystems. However, only in freshwater systems larger tropical fish presented a significantly lower trophic position than their temperate counterparts. Climate did not affect the fish body size–trophic position relationship in marine systems. Our results suggest that larger tropical freshwater fish may compensate for higher energetic constraints feeding at lower trophic positions, compared to their temperate counterparts of similar body size. The lower latitudinal temperature range in marine ecosystems and/or their larger ecosystem size may attenuate and/or compensate for the energy limitation of larger marine fish. Based on our results, temperature may determine macroecological patterns of aquatic food webs, but its effect is contingent on ecosystem type. We suggest that freshwater ecosystems may be more sensitive to warming‐induced alterations in food web topology and food chain length than marine ecosystems.

Food Web Topology and Nested Keystone Species Complexes

Important species may be in critically central network positions in ecological interaction networks. Beyond quantifying which one is the most central species in a food web, a multinode approach can identify the key sets of the most central n species as well. However, for sets of different size n, these structural keystone species complexes may differ in their composition. If larger sets contain smaller sets, higher nestedness may be a proxy for predictive ecology and efficient management of ecosystems. On the contrary, lower nestedness makes the identification of keystones more complicated. Our question here is how the topology of a network can influence nestedness as an architectural constraint. Here, we study the role of keystone species complexes in 27 real food webs and quantify their nestedness. After quantifying their topology properties, we determine their keystone species complexes, calculate their nestedness, and statistically analyze the relationship between topological indices and nestedness. A better understanding of the cores of ecosystems is crucial for efficient conservation efforts, and to know which networks will have more nested keystone species complexes would be a great help for prioritizing species that could preserve the ecosystem’s structural integrity.

Médialab stories: How to align actor network theory and digital methods

The history of laboratories may become controversial in social sciences. In this paper, the story of Sciences Po Médialab told by Venturini et al. is discussed and completed by demonstrating the incoherence in the choice of digital methods at the Médialab from the actor network theory perspective. As the Médialab mostly used web topologies as structural analysis of social positions, they were not able to account for the propagation of ideas, considered in actor network theory as non-humans that have their own agency. The main arguments in favour of the ‘more continuous social’ developed at the Médialab (quali-quanti, following the actors, zooming) proved to be as misleading as the network metaphor. The distribution of agency that actor network theory so successfully expands was paradoxicallty reduced to structures and individual preferences, to the detriment of the agency of replications that circulate entities in the form of messages, content or memes, and that should now become the next step for actor network theory-style digital methods.

Hunting high or low: body size drives trophic position among and within marine predators

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 597:39-46 (2018) - DOI: https://doi.org/10.3354/meps12584 Hunting high or low: body size drives trophic position among and within marine predators Guilherme Dalponti1,*, Rafael D. Guariento1, Adriano Caliman2 1Universidade Federal do Mato Grosso do Sul, Inbio, Caixa Postal 549, Avenida Costa e Silva, Pioneiros, Campo Grande (MS), 79070-900, Brazil 2Universidade Federal do Rio Grande do Norte, Departamento de Ecologia, Caixa Postal 1524, Natal (RN), 59078-900, Brazil *Corresponding author:guilhermedalponti@gmail.com ABSTRACT: A positive relationship between body size and trophic position amplitude is expected based on mobility and gape size. Using a dataset of marine consumers’ diet, we illuminated mechanisms driving the relationship between consumers’ body mass (a proxy for body size) and trophic position parameters within and among populations. We found that across a body size gradient, maximum trophic position increased, while minimum trophic position did not vary, resulting in a positive relationship between species body size and trophic position amplitude. However, using single individuals as data points, we found a positive correlation between trophic position and body mass. The correlation was stronger for larger species, indicating that as mean species body size increased, there was an increasing tendency for smaller individuals to forage on lower levels and larger individuals to forage mainly on higher levels. Therefore, the wider variation in trophic positions we observed for larger species is possibly related to an ontogenetic diet shift in size-structured populations. Our results corroborate the idea that on an individual level larger consumers do not show a positive relationship between body size and diet niche breadth, and support the notion that ontogenetic niche differences can drive the amplitude of trophic position among marine predator species. KEY WORDS: Trophic chain · Ontogenetic diet shifts · Niche breadth · Consumer-resource interactions · Food web topology Full text in pdf format Supplementary material PreviousNextCite this article as: Dalponti G, Guariento RD, Caliman A (2018) Hunting high or low: body size drives trophic position among and within marine predators. Mar Ecol Prog Ser 597:39-46. https://doi.org/10.3354/meps12584 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 597. Online publication date: June 11, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.