The Experts below are selected from a list of 193035 Experts worldwide ranked by ideXlab platform
Mark Emmerson - One of the best experts on this subject based on the ideXlab platform.
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Interaction Strength food web topology and the relative importance of species in food webs
Journal of Animal Ecology, 2010Co-Authors: Eoin J Ogorman, Ute Jacob, Tomas Jonsson, Mark EmmersonAbstract:1. We established complex marine communities, consisting of over 100 species, in large subtidal experimental mesocosms. We measured the Strength of direct Interactions and the net Strength of direct and indirect Interactions between the species in those communities, using a combination of theoretical and empirical approaches. 2. Theoretical predictions of Interaction Strength were derived from the Interaction coefficient matrix, which was parameterised using allometric predator-prey relationships. Empirical estimates of Interaction Strength were quantified using the ln-ratio, which measures the change in biomass density of species A in the presence and absence of species B. 3. We observed that highly connected species tend to have weak direct effects and net effects in our experimental food webs, whether we calculate Interaction Strength theoretically or empirically. 4. We found a significant correlation between our theoretical predictions and empirical estimates of direct effects and net effects. The net effects correlation was much stronger, indicating that our experimental communities were dominated by a mixture of direct and indirect effects. 5. Re-calculation of the theoretical predictions of net effects after randomising predator and prey body masses did not affect the negative relationship with connectance. 6. These results suggest that food web topology, which in this system is constrained by body mass, is overwhelmingly important for the magnitude of direct and indirect Interactions and hence species importance in the face of biodiversity declines.
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temperature predator prey Interaction Strength and population stability
Global Change Biology, 2009Co-Authors: Bjorn C Rall, Olivera Vucicpestic, Roswitha B Ehnes, Mark Emmerson, Ulrich BroseAbstract:Warming could strongly stabilize or destabilize populations and food webs by changing the Interaction Strengths between predators and their prey. Predicting the consequences of warming requires understanding how temperature affects ingestion (energy gain) and metabolism (energy loss). Here, we studied the temperature dependence of metabolism and ingestion in laboratory experiments with terrestrial arthropods (beetles and spiders). From this data, we calculated ingestion efficiencies (ingestion/metabolism) and per capita Interaction Strengths in the short and long term. Additionally, we investigated if and how body mass changes these temperature dependencies. For both predator groups, warming increased metabolic rates substantially, whereas temperature effects on ingestion rates were weak. Accordingly, the ingestion efficiency (the ratio of ingestion to metabolism) decreased in all treatments. This result has two possible consequences: on the one hand, it suggests that warming of natural ecosystems could increase intrinsic population stability, meaning less fluctuations in population density; on the other hand, decreasing ingestion efficiencies may also lead to higher extinction risks because of starvation. Additionally, predicted long-term per capita Interaction Strengths decreased with warming, which suggests an increase in perturbation stability of populations, i.e., a higher probability of returning to the same equilibrium density after a small perturbation. Together, these results suggest that warming has complex and potentially profound effects on predator–prey Interactions and food-web stability.
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measurement of Interaction Strength in nature
Annual Review of Ecology Evolution and Systematics, 2005Co-Authors: Timothy J Wootton, Mark EmmersonAbstract:▪ Abstract Understanding and predicting the dynamics of multispecies systems generally require estimates of Interaction Strength among species. Measuring Interaction Strength is difficult because of the large number of Interactions in any natural system, long-term feedback, multiple pathways of effects between species pairs, and possible nonlinearities in Interaction-Strength functions. Presently, the few studies that extensively estimate Interaction Strength suggest that distributions of Interaction Strength tend to be skewed toward few strong and many weak Interactions. Modeling studies indicate that such skewed patterns tend to promote system stability and arise during assembly of persistent communities. Methods for estimating Interaction Strength efficiently from traits of organisms, such as allometric relationships, show some promise. Methods for estimating community response to environmental perturbations without an estimate of Interaction Strength may also be of use. Spatial and temporal scale may ...
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predator prey body size Interaction Strength and the stability of a real food web
Journal of Animal Ecology, 2004Co-Authors: Mark Emmerson, Dave RaffaelliAbstract:Summary 1We examined the empirical relationship between predator–prey body size ratio and Interaction Strength in the Ythan Estuary food web. 2We have refined a previously published version of the food web and explored how size-based predatory effects might affect food web dynamics. To do so, we used four predatory species Crangon crangon (Linnaeus), Carcinus maenas (Linnaeus), Pomatoschistus microps (Kroyer) and Platichthys flesus (Linnaeus) and one common prey species Corophium volutator (Pallas) from the food web. 3All predators and prey were sorted into small, medium and large size classes and placed into mesocosms in all possible pairwise combinations of size and species identity to determine per capita effects of predators on prey (aij). 4Using Lotka–Volterra dynamics the empirical body size relationships obtained from these experiments and other relationships already available for the Ythan Estuary, we parameterized a food web model for this system. The local stability properties of the resulting food web models were then determined. 5We found that by choosing Interaction Strengths using an empirically defined scaling law, the resulting food web models are always dynamically stable, despite the residual uncertainties in the modelling approach. This contrasts with the statistical expectation that random webs with random parameters have a vanishingly improbable chance of stability. 6The patterning of predator and prey body sizes in real ecosystems affects the arrangement of Interaction Strengths, which in turn determines food web stability.
Xia-ji Liu - One of the best experts on this subject based on the ideXlab platform.
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Polariton-polariton Interaction beyond the Born approximation: A toy model study
Physical Review A, 2020Co-Authors: Hui Deng, Xia-ji LiuAbstract:We theoretically investigate the polariton-polariton Interaction in microcavities beyond the commonly used Born approximation (i.e., mean field), by adopting a toy model with a contact Interaction to approximately describe the attraction between electrons and holes in quantum well and by using a Gaussian pair fluctuation theory beyond mean field. We obtain a density or chemical potential independent polariton-polariton Interaction Strength even in two dimensions, which result from coupling to the photon field. We show that quantum fluctuations lead to about a factor of 2 reduction in the polariton-polariton Interaction Strength within our toy model. Together with corrections to the $1s$ exciton approximation at very strong light-matter coupling, we find the polariton-polariton Interaction Strength under typical experimental conditions is overestimated by a factor of 3 in the widely used theories, if our toy model can qualitatively simulate the polariton Interaction in GaAs quantum wells. We compare our prediction with the most recent measurement and argue that the beyond-Born-approximation effect to the polariton-polariton Interaction Strength is crucial for a quantitative understanding of the experimental data by Estrecho et al. [Phys. Rev. B 100, 035306 (2019)].
J J Johnson - One of the best experts on this subject based on the ideXlab platform.
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sidelobe suppression in an acousto optic filter with a raised cosine Interaction Strength
Applied Physics Letters, 1992Co-Authors: D A Smith, J J JohnsonAbstract:We have demonstrated a 10‐dB reduction in the intensity sidelobes of an apodized‐Interaction‐Strength guided‐wave acousto‐optic filter with a center passband of 1530 nm. Acoustic‐intensity weighting was achieved by launching a surface acoustic wave (SAW) beam in a straight acoustic waveguide, and gradually transferring this SAW intensity to the active device, and back out, by evanescent‐wave coupling across a 20 μm barrier over a 19‐mm Interaction length. The intensity sidelobe was −5 dB for an unapodized filter with abrupt onset and cutoff of the Interaction, but sidelobes were reduced to at most −15 dB for a SAW intensity with raised‐cosine weighting. A conversion efficiency of 97% was achieved with 80 mW input power for the 2.0‐nm‐wide apodized filter.
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sidelobe suppression in an acousto optic filter with a raised cosine Interaction Strength
Integrated Photonics Research (1992) paper ME1, 1992Co-Authors: D A Smith, J J JohnsonAbstract:The acousto-optic filter (AOF) is becoming increasingly important in optical communication research because of its unmatched potential in densely-packed WDM systems. In comparison to the Fabry-Perot, their main competitor, AOFs have a larger tuning range-to-bandpass /ratio, are more than a thousand times faster, are free of hysteresis (a problem with all-fiber Fabry-Perots), are able to parallel process many wavelength channels at a time (the Fabry-Perot is a single-state device, unless ganged in a complicated and inherently lossy way) and are able to be configured as a 4-port switch
Keith A Nelson - One of the best experts on this subject based on the ideXlab platform.
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direct measurement of polariton polariton Interaction Strength
Nature Physics, 2017Co-Authors: Yongbao Sun, Mark Steger, Ken W. West, Loren Pfeiffer, Yoseob Yoon, Gangqiang Liu, D W Snoke, Keith A NelsonAbstract:Exciton–polariton condensates have garnered interest as a means to access macroscopic displays of quantum phenomena such as Bose–Einstein condensation and superfluidity. In this work, a direct measure of the polariton–polariton Interaction is obtained.
Ken W. West - One of the best experts on this subject based on the ideXlab platform.
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Direct measurement of polariton-polariton Interaction Strength in the Thomas-Fermi regime of exciton-polariton condensation
Physical Review B, 2019Co-Authors: Eliezer Estrecho, Mark Steger, Ken W. West, Loren Pfeiffer, Tingge Gao, Nataliya Bobrovska, D. Comber-todd, M. D. Fraser, Jesper Levinsen, Meera M. ParishAbstract:Bosonic condensates of exciton polaritons typically coexist and interact with an incoherent reservoir, which undermines measurements of key parameters of the condensate. Here, the authors overcome this limitation by creating a high-density polariton condensate in an optically induced box trap. In this Interaction-dominated Thomas-Fermi regime, the condensate is fully separated from the reservoir, which enables a direct measurement of the polariton-polariton Interaction Strength. The results of the measurement are in agreement with theoretical predictions.
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direct measurement of polariton polariton Interaction Strength
Nature Physics, 2017Co-Authors: Yongbao Sun, Mark Steger, Ken W. West, Loren Pfeiffer, Yoseob Yoon, Gangqiang Liu, D W Snoke, Keith A NelsonAbstract:Exciton–polariton condensates have garnered interest as a means to access macroscopic displays of quantum phenomena such as Bose–Einstein condensation and superfluidity. In this work, a direct measure of the polariton–polariton Interaction is obtained.
