scholarly journals Interaction modifications lead to greater robustness than pairwise non-trophic effects in food webs

2018 ◽  
Author(s):  
J. Christopher D. Terry ◽  
Rebecca J. Morris ◽  
Michael B. Bonsall
Keyword(s):  
Theoretical Research ◽  
Order Effects ◽  
List Type ◽  
Dynamic Simulations ◽  
Dynamic Complexity ◽  
Trophic Effects ◽  
Trophic Networks ◽  
Pairwise Interactions ◽  
Species Vulnerability ◽  
Interaction Modifications

AbstractConsiderable emphasis has been placed recently on the importance of incorporating non-trophic effects in to our understanding of ecological networks. Interaction modifications are well established as generating strong non-trophic impacts by modulating the strength of inter-specific interactions.For simplicity and comparison with direct interactions within a network context, the consequences of interaction modifications have often been described as direct pairwise interactions. The consequences of this assumption have not been examined in non-equilibrium settings where unexpected consequences of interaction modifications are most likely.To test the distinct dynamic nature of these ‘higher-order’ effects we directly compare, using dynamic simulations, the robustness to extinctions under perturbation of systems where interaction modifications are either explicitly modelled or represented by corresponding equivalent pairwise non-trophic interactions.Full, multi-species representations of interaction modifications resulted in a greater robustness to extinctions compared to equivalent pairwise effects. Explanations for this increased stability despite apparent greater dynamic complexity can be found in additional routes for dynamic feedbacks. Furthermore, interaction modifications changed the relative vulnerability of species to extinction from those trophically connected close to the perturbed species towards those receiving a large number of modifications.Future empirical and theoretical research into non-trophic effects should distinguish interaction modifications from direct pairwise effects in order to maximise information about the system dynamics. Interaction modifications have the potential to shift expectations of species vulnerability based exclusively on trophic networks.

scholarly journals Trophic interaction modifications disrupt the structure and stability of food webs

2018 ◽  
Author(s):  
J. Christopher D. Terry ◽  
Rebecca J. Morris ◽  
Michael B. Bonsall
Keyword(s):  
Trophic Interaction ◽  
Community Interactions ◽  
Additional Species ◽  
Trophic Effects ◽  
Trophic Networks ◽  
Empirical Information ◽  
Interaction Modifications ◽  
Underlying Network ◽  
The Stability ◽  
The Impact

AbstractTrophic interaction modifications, where a consumer-resource interaction is influenced by an additional species, are established as being prevalent throughout ecological networks. Despite this, their influence on the structure of interaction distributions within communities has not yet been examined. Although empirical information about the distribution of interaction modifications is currently sparse, the non-trophic effects they induce will be structured by the underlying network of trophic interactions. Here we test the impact of interaction modifications, introduced under a range of distributional assumptions to artificial and empirical trophic networks, on the overall structure of interactions within communities. We show that local stability and reactivity is critically dependent on the inter-relationship between the trophic and non-trophic effects. Depending on their distribution, interaction modifications can generate significant additional structure to community interactions making analyses of the stability of ecological systems based solely on trophic networks unreliable. Empirical information on the topological and strength distributions of interaction modifications will be a key part of understanding the dynamics of communities.

scholarly journals Deconstructing higher-order interactions in the microbiota: A theoretical examination

2019 ◽  
Author(s):  
Yitbarek Senay ◽  
Guittar John ◽  
Sarah A. Knutie ◽  
C. Brandon Ogbunugafor
Keyword(s):  
Gut Microbiota ◽  
Evolutionary Genetics ◽  
Infection Risk ◽  
Higher Order ◽  
Microbial Interactions ◽  
Order Effects ◽  
List Type ◽  
Linear Effect ◽  
Pairwise Interactions ◽  
Host Infection

AbstractThe animal gut is a complex ecosystem containing many interacting species. A major objective of microbiota research is to identity the scale at which gut taxa shape hosts. However, most studies focus solely on pairwise interactions and ignore higher-order interactions involving three or more component taxa. Higher-order interactions represent non-additive effects that cannot be predicted from first-order or pairwise interactions.Possible reasons as to why studies of higher higher-order interactions have been scarce is that many host-associated systems are experimentally intractable, gut microbiota are prohibitively species rich, and the influence of any given taxon on hosts is often context-dependent. Furthermore, quantifying emergent effects that represent higher-order interactions that are not simply the result of lower-order interactions, present a combinatorial challenge for which there are few well-developed statistical approaches in host-microbiota studies.In this perspective, our goal is to quantify the existence of emerging higher-order effects and characterize their prevalence in the microbiota. To do so, we adapt a method from evolutionary genetics used to quantify epistatic effects between mutations and use it to quantify the effects of higher-order microbial interactions on host infection risk.We illustrate this approach by applying it to an in silico dataset generated to resemble a population of hosts with gut-associated microbial communities. We assign each host a pathogen load, and then determine how emergent interactions between gut taxa influence this host trait.We find that the effect of higher-order interactions generally increases in magnitude with the number of species in the gut community. Based on the average magnitude of interaction for each order, we find that 9th order interactions have the largest non-linear effect on determining host infection risk.Our approach illustrates how incorporating the effects of higher-order interactions among gut microbiota can be essential for understanding their effects on host infection risk. We conclude that insofar as higher-order interactions between taxa may profoundly shape important organismal phenotypes (such as susceptibility to infection), that they deserve greater attention in microbiome studies.

scholarly journals Growth tradeoffs produce complex microbial communities on a single limiting resource

2018 ◽  
Author(s):  
Michael Manhart ◽  
Eugene I. Shakhnovich
Keyword(s):  
Microbial Growth ◽  
Growth Traits ◽  
Fundamental Problem ◽  
Higher Order ◽  
Microbial Populations ◽  
Order Effects ◽  
Pairwise Interactions ◽  
Lag Times ◽  
The Relationship ◽  
Higher Order Effects

The relationship between the dynamics of a community and its constituent pairwise interactions is a fundamental problem in ecology. Higher-order ecological effects beyond pairwise interactions may be key to complex ecosystems, but mechanisms to produce these effects remain poorly understood. Here we show that higher-order effects can arise from variation in multiple microbial growth traits, such as lag times and growth rates, on a single limiting resource with no other interactions. These effects produce a range of ecological phenomena: an unlimited number of strains can exhibit multi stability and neutral coexistence, potentially with a single keystone strain; strains that coexist in pairs do not coexist all together; and the champion of all pairwise competitions may not dominate in a mixed community. Since variation in multiple growth traits is ubiquitous in microbial populations due to pleiotropy and non-genetic variation, our results indicate these higher-order effects may also be widespread, especially in laboratory ecology and evolution experiments.

Mixing and the Jet Flap

1956 ◽  
Vol 7 (2) ◽  
pp. 85-105 ◽  
Author(s):  
B. S. Stratford
Keyword(s):  
First Principles ◽  
Second Order ◽  
Experimental Results ◽  
Order Effects ◽  
List Type ◽  
Two Dimensional ◽  
Form Drag ◽  
First Approximation ◽  
Close Proximity ◽  
Thrust Characteristics

SummaryOne of the main problems associated with the “ Jet Flap ” concerns the discrepancy in thrust between idealised theory and the experimental results. This discrepancy is attributable to the mixing with the surrounding flow of the thin two-dimensional jet while still in close proximity to the aerofoil. The effect of the mixing may be calculated to a first approximation from a formula derivable from first principles, while certain second order effects, which can be significant, may be considered qualitatively.It is concluded that.(i) the full thrust should be experienced by a jet flapped aircraft at cruise,(ii) it should be possible to attain a low form drag at cruise in comparison with a conventional aircraft,(iii) at take-off, an aircraft using a shrouded jet flap would have better thrust recovery than one using a pure jet flap (which shows appreciable losses),(iv) the use of by-pass engines would further improve the thrust characteristics,(v) the practical gains from thrust augmentation, as obtained by controlling the mixing, seem likely to be small.

scholarly journals Collapse and rescue of evolutionary food webs under global warming

2019 ◽  
Author(s):  
Youssef Yacine ◽  
Korinna T. Allhoff ◽  
Avril Weinbach ◽  
Nicolas Loeuille
Keyword(s):  
Global Warming ◽  
Food Webs ◽  
Environmental Changes ◽  
Extinction Risk ◽  
Well Being ◽  
Feeding Preference ◽  
List Type ◽  
Trophic Networks ◽  
Evolutionary Rescue ◽  
Fast Evolution

AbstractGlobal warming is severely impacting ecosystems and threatening ecosystem services as well as human well-being. While some species face extinction risk, several studies suggest the possibility that fast evolution may allow species to adapt and survive in spite of environmental changes.We assess how such evolutionary rescue extends to multitrophic communities and whether evolution systematically preserves biodiversity under global warming.More precisely, we expose simulated trophic networks of co-evolving consumers to warming under different evolutionary scenarios, which allows us to assess the effect of evolution on diversity maintenance. We also investigate how the evolution of body mass and feeding preference affects coexistence within a simplified consumer-resource module.Our simulations predict that the long-term diversity loss triggered by warming is considerably higher in scenarios where evolution is slowed down or switched off completely, indicating that eco-evolutionary feedback indeed helps to preserve biodiversity. However, even with fast evolution, food webs still experience vast disruptions in their structure and functioning. Reversing warming may thus not be sufficient to restore previous structures.Our findings highlight how the interaction between evolutionary rescue and changes in trophic structures constrains ecosystem responses to warming with important implications for conservation and management policies.

The Part Played by Wind Tunnels in Modern Aeronautics

1963 ◽  
Vol 67 (632) ◽  
pp. 463-475 ◽  
Author(s):  
G. M. Lilley
Keyword(s):  
Wind Tunnel ◽  
Research And Development ◽  
Experimental Research ◽  
Measurement Techniques ◽  
Current Trend ◽  
Theoretical Research ◽  
Wind Tunnels ◽  
List Type ◽  
Early Form ◽  
Basic Fluid

Summary:The wind tunnel has been the main instrument for experimental research in aeronautics since the turn of the century and its history is as brief as powered flight itself. It has always played a leading rdle in aeronautics right from the time of the Wright Brothers to the present day.The early form of wind tunnels as developed at the National Physical Laboratory and other research establishments have been replaced over the years by larger and more elaborate facilities, each having a particular speed range and specific role in aeronautical research and development. Modern wind tunnels having continuous operation of the type installed at the Royal Aircraft Establishment involve powers of up to 100 000 h.p. and cost in the neighbourhood of £10 000 000. In spite of this cost it is a sobering thought that, if anything, the overall cost of each data point is less today than it was in the early days of aeronautics. Such tunnels are highly complex instruments for research and development and although they play a rôle similar in many respects to that of a computer, they have the advantage of always dealing with a real fluid. Indeed no known computer could cope with the range of problems that can be solved in a wind tunnel, ranging from such complex problems as the structure of turbulent flow to the pressures in separated flow regimes, to quote just two examples. This fact must always be kept in perspective when arguments are presented for more and more work on digital computers to solve basic fluid motion problems. Of course we cannot overlook the problems of interpretation of wind tunnel data and the difficulties encountered in extrapolating these data to flight conditions.The development of theories for such problems together with answers is of ever increasing importance, especially as the problems in aeronautics are becoming more and more complex. These solutions have the important function not only of high-lighting certain aspects of the flow, but of pin-pointing the important parameters in a problem together with providing better than order of magnitude results. However, theories must be based on physical facts and these can only be determined in the final analysis from experiments.The wind tunnel has three highly significant roles in modern aeronautics:(i) Experimental research as a forerunner to future theoretical research.(ii) Experimental research as a confirmation and extension of theory.(iii) Current research and development work on a given aircraft.The current trend in bringing strong theoretical and experimental groups together, plus the employment of rapid measurement techniques in wind tunnels, promises the greatest possible productive utilisation of these highly important and expensive facilities. In most cases today they are playing a strong, if not the leading, role in aeronautical development.

scholarly journals Enabling Systems Innovation in Climate Change Adaptation: Exploring the Role for MEL

2022 ◽  
pp. 159-172
Author(s):  
Robbie Gregorowski ◽  
Dennis Bours
Keyword(s):  
Climate Change ◽  
Climate Change Adaptation ◽  
Reference Group ◽  
Field Testing ◽  
Wicked Problems ◽  
List Type ◽  
Dynamic Complexity ◽  
Socioecological Systems ◽  
Technical Evaluation ◽  
Innovation Approach

AbstractTraditional monitoring, evaluation, and learning (MEL) approaches, methods, and tools no longer reflect the dynamic complexity of the severe (or “super-wicked”) problems that define the Anthropocene: climate change, environmental degradation, and global pandemics. In late 2019, the Adaptation Fund’s Technical Evaluation Reference Group (AF-TERG) commissioned a study to identify and assess innovative MEL approaches, methods, and technologies to better support and enable climate change adaptation (CCA) and to inform the Fund’s own approach to MEL. This chapter presents key findings from the study, with seven recommendations to support a systems innovation approach to CCA: Promote and lead with a CCA systems innovation approach, engaging with key concepts of complex systems, super-wicked problems, the Anthropocene, and socioecological systems. Engage better with participation, inclusivity, and voice in MEL. Overcome risk aversion in CCA and CCA MEL through field testing new, innovative, and often more risky MEL approaches. Demonstrate and promote using MEL to support and integrate adaptive management. Work across socioecological systems and scales. Advance MEL approaches to better support systematic evidence and learning for scaling and replicability. Adapt or develop MEL approaches, methods, and tools tailored to CCA systems innovation.

scholarly journals Interaction modifications lead to greater robustness than pairwise non‐trophic effects in food webs

2019 ◽  
Vol 88 (11) ◽  
pp. 1732-1742 ◽  
Author(s):  
J. Christopher D. Terry ◽  
Rebecca J. Morris ◽  
Michael B. Bonsall
Keyword(s):  
Food Webs ◽  
Trophic Effects ◽  
Interaction Modifications

Optimization of hydrodynamic parameters for underwater glider based on the electromagnetic velocity sensor

2019 ◽  
Vol 233 (14) ◽  
pp. 5019-5032
Author(s):  
Wei Ma ◽  
Yanhui Wang ◽  
Shuxin Wang ◽  
Gege Li ◽  
Shaoqiong Yang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Sensor Data ◽  
Theoretical Research ◽  
Underwater Glider ◽  
Unknown Parameters ◽  
Dynamic Simulations ◽  
Velocity Sensor ◽  
Sea Trial ◽  
Hydrodynamic Parameters

With the development of autonomous underwater glider technology, the gliders integrated with multitype sensors have been widely applied in the ocean scientific research. Among those sensors, electromagnetic velocity sensor provides a new way to acquire the unknown parameters of Petrel‐II glider. Based on the analysis of computational fluid dynamics, the optimized layout position and distance of electromagnetic velocity sensor is determined. Petrel‐II integrated with electromagnetic velocity sensor conducted a series of sea‐trials to obtain sailing data under different attitudes. By combining sea‐trial data with dynamic model of deepsea glider, the relationships between pitch, hydrodynamic forces/moment, and angle of attack are yielded. The buoyance model in the dynamics is validated by suspension experiment of glider. The dynamic simulations in the longitudinal plane with different hydrodynamic parameters obtained by, that is, optimization with electromagnetic velocity sensor, data statistical analysis combining computational fluid dynamics and parameter identification, and calculation by computational fluid dymanics, are conducted and compared with experimental results to verify validity and accuracy of those parameters. Results show that hydrodynamic parameters optimized by integrating electromagnetic velocity sensor on the glider can exhibit dynamic behavior more accurately. This work contributes to the calculation of vertical water velocities from glider and theoretical research of glider.

scholarly journals Microscopy & Microanalytical Support for NASA's Microgravity Materials Science Programs

2004 ◽  
Vol 12 (5) ◽  
pp. 8-11
Author(s):  
Donald C. Gillies
Keyword(s):  
Phase Separation ◽  
Crystal Growth ◽  
Process Modeling ◽  
Materials Science ◽  
Interfacial Phenomena ◽  
Theoretical Research ◽  
Advisory Group ◽  
List Type ◽  
Science Program ◽  
Type Number

The Materials Science Program of NASA's Office of Biological and Physical Research (OB PR) has attacked futidamental problems of materials science as defined by an external advisory group, known as the Discipline Working Group (DWG). These have been:•Nucleation and Metastable States•Prediction and Gontrol of Micrestructures•Crystal Growth and Detect Generation•Phase Separation and Interfacial Phenomena•Thermophysical Properties and Process Modeling.While the program's primary objectives are science-based and despite the fact that 90% of these programs concentrate on pre-cursor and theoretical research on the ground, NASA demands that there be a microgravity rationale driving the research.

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