Multiple predator species alter prey behavior, population growth, and a trophic cascade in a model estuarine food web

Predators can influence prey population dynamics by affecting prey behaviors with strong fitness consequences, with cascading effects on lower trophic levels. Here, we demonstrate that multiple predator species can nonconsumptively influence prey population growth and the strength of a trophic cascade in a model marine community. We exposed the herbivorous amphipod Ampithoe longimana to olfactory and visual cues from three common predators (pinfish, mud crabs, brown shrimp) singly and together in a multiple-predator assemblage to quantify the nonconsumptive effects (NCEs) of predator identity and the presence of multiple predators on prey population and community-level metrics. The presence of predator cues, particularly those of the pinfish and the multiple-predator treatments, decreased prey population growth and influenced primary and secondary production. To explore mechanisms underlying the observed NCEs in the experimental communities and their potential influence in the field, we quantified individual prey behavioral responses (changes in grazing rate, diet preference, dispersal, colonization) in the presence of predator cues. Predator cues decreased prey grazing, dispersal, and colonization but did not affect prey diet preference. Given the persistence of NCEs over time and the fact that trophic cascades are common features of marine systems, changes in marine predator communities may have widespread effects on predator-prey behavioral interactions with consequences for ecosystem function even in areas of weak predation pressure

SUPPRESSION of ELECTRON THERMAL CONDUCTION in the HIGH β INTRACLUSTER MEDIUM of GALAXY CLUSTERS

Understanding the thermodynamic state of the hot intracluster medium (ICM) in a galaxy cluster requires knowledge of the plasma transport processes, especially thermal conduction. The basic physics of thermal conduction in plasmas with ICM-like conditions has yet to be elucidated, however. We use particle-in-cell simulations and analytic models to explore the dynamics of an ICM-like plasma (with small gyroradius, large mean free path, and strongly sub-dominant magnetic pressure) driven by the diffusive heat flux associated with thermal conduction. Linear theory reveals that whistler waves are driven unstable by electron heat flux, even when the heat flux is weak. The resonant interaction of electrons with these waves then plays a critical role in scattering electrons and suppressing the heat flux. In a 1D model where only whistler modes that are parallel to the magnetic field are captured, the only resonant electrons are moving in the opposite direction to the heat flux, and the electron heat flux suppression is small. In 2D or more, oblique whistler modes also resonate with electrons moving in the direction of the heat flux. The overlap of resonances leads to effective symmetrization of the electron distribution function and a strong suppression of heat flux. The results suggest that thermal conduction in the ICM might be strongly suppressed, possibly to negligible levels

Non-steroidal antiinflammatory drugs fail to enhance healing of acute hamstring injuries treated with physiotherapy

The effects of two non-steroidal anti-inflammatory drugs (NSAIDs), meclofenamate and diclofenac, in combination with physiotherapy modalities on the rate of healing of acute hamstring muscle tears were studied in a doubleblind, placebo-controlled trial. Forty-four of the 75 patients with this injury recruited were assessed and randomly allocated to one of three treatment groups: meclofenamate (100 mg 3 times a day), diclofenac (50 mg 3 times a day) and placebo. All patients received the same intensive physiotherapy treatment over the 7-day treatment period. Patient assessments were performed on days 1, 3 and 7 of the 7-day study period and included pain assessment (visual analogue scale), swelling measurement (thigh circumference measurement at the site of the muscle tear) and isokinetic muscle performance testing. Treatment produced a significant improvement in all measurements in all groups, but there was no difference in any measurement between groups. However, when only the more severe injuries were analysed, the reported pain score at day 7 was significantly lower in the placebo group than in either the  eclofenamate group or the diclofenac group (P < 0,05). Hence this study did not find any additive effect on the healing of acute muscle injuries when meclofenamate or diclofenac was added to standard physiotherapeutic modalities. The study therefore does not support the use of NSAIDs in the treatment of acute hamstring muscle injuries.S Afr Med J 1995; 85: 517-52

A direct image of the obscuring disk surrounding an active galactic nucleus

Active galactic nuclei (AGN) are generally accepted to be powered by the release of gravitational energy in a compact accretion disk surrounding a massive black hole. Such disks are also necessary to collimate powerful radio jets seen in some AGN. The unifying classification schemes for AGN further propose that differences in their appearance can be attributed to the opacity of the accreting material, which may obstruct our view of the central region of some systems. The popular model for the obscuring medium is a parsec-scale disk of dense molecular gas, although evidence for such disks has been mostly indirect, as their angular size is much smaller than the resolution of conventional telescopes. Here we report the first direct images of a pc-scale disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured AGN. The disk is viewed nearly edge-on, and individual clouds within the ionised disk are opaque to high-energy radiation, consistent with the unifying classification scheme. In projection, the disk and AGN axes align, from which we infer that the ionised gas disk traces the outer regions of the long-sought inner accretion disk.Comment: 14 pages, LaTeX, PSfig, to appear in Nature. also available at http://hethp.mpe-garching.mpg.de/Preprint

Suppression of Electron Thermal Conduction by Whistler Turbulence in a Sustained Thermal Gradient.

The dynamics of weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field is explored with particle-in-cell simulations and modeling. Two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude, δB/B_{0}≃1, and resonantly scatter the electrons, significantly reducing the heat flux. Surprisingly, the resulting steady-state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high-β astrophysical plasmas such as hot accretion flows and the intracluster medium of galaxy clusters

Likelihood inference for exponential-trawl processes

Integer-valued trawl processes are a class of serially correlated, stationary and infinitely divisible processes that Ole E. Barndorff-Nielsen has been working on in recent years. In this Chapter, we provide the first analysis of likelihood inference for trawl processes by focusing on the so-called exponential-trawl process, which is also a continuous time hidden Markov process with countable state space. The core ideas include prediction decomposition, filtering and smoothing, complete-data analysis and EM algorithm. These can be easily scaled up to adapt to more general trawl processes but with increasing computation efforts.Comment: 29 pages, 6 figures, forthcoming in: "A Fascinating Journey through Probability, Statistics and Applications: In Honour of Ole E. Barndorff-Nielsen's 80th Birthday", Springer, New Yor

Decreased mass specific respiration under experimental warming is robust to the microbial biomass method employed

Hartley et al. question whether reduction in Rmass, under experimental warming, arises because of the biomass method. We show the method they treat as independent yields the same result. We describe why the substrate-depletion hypothesis may not solely explain observed responses, and urge caution in interpretation of the seasonal data. © 2009 Blackwell Publishing Ltd/CNRS

Creativity and Autonomy in Swarm Intelligence Systems

This work introduces two swarm intelligence algorithms -- one mimicking the behaviour of one species of ants (\emph{Leptothorax acervorum}) foraging (a `Stochastic Diffusion Search', SDS) and the other algorithm mimicking the behaviour of birds flocking (a `Particle Swarm Optimiser', PSO) -- and outlines a novel integration strategy exploiting the local search properties of the PSO with global SDS behaviour. The resulting hybrid algorithm is used to sketch novel drawings of an input image, exploliting an artistic tension between the local behaviour of the `birds flocking' - as they seek to follow the input sketch - and the global behaviour of the `ants foraging' - as they seek to encourage the flock to explore novel regions of the canvas. The paper concludes by exploring the putative `creativity' of this hybrid swarm system in the philosophical light of the `rhizome' and Deleuze's well known `Orchid and Wasp' metaphor

High Energy Cosmic Rays From Supernovae

Cosmic rays are charged relativistic particles that reach the Earth with extremely high energies, providing striking evidence of the existence of effective accelerators in the Universe. Below an energy around $\sim 10^{17}$ eV cosmic rays are believed to be produced in the Milky Way while above that energy their origin is probably extragalactic. In the early '30s supernovae were already identified as possible sources for the Galactic component of cosmic rays. After the '70s this idea has gained more and more credibility thanks to the the development of the diffusive shock acceleration theory, which provides a robust theoretical framework for particle energization in astrophysical environments. Afterwards, mostly in recent years, much observational evidence has been gathered in support of this framework, converting a speculative idea in a real paradigm. In this Chapter the basic pillars of this paradigm will be illustrated. This includes the acceleration mechanism, the non linear effects produced by accelerated particles onto the shock dynamics needed to reach the highest energies, the escape process from the sources and the transportation of cosmic rays through the Galaxy. The theoretical picture will be corroborated by discussing several observations which support the idea that supernova remnants are effective cosmic ray factories.Comment: Final draft of a chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and Paul Murdi

The inevitable youthfulness of known high-redshift radio galaxies

Radio galaxies can be seen out to very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that for any model of radio-galaxy evolution in which the luminosity decreases with time after an initial rapid increase (that is, essentially all reasonable models), all observable high-redshift radio-galaxies must be seen when the lobes are less than 10^7 years old. This means that high-redshift radio galaxies can be used as a high-time-resolution probe of evolution in the early Universe. Moreover, this result helps to explain many observed trends of radio-galaxy properties with redshift [(i) the `alignment effect' of optical emission along radio-jet axes, (ii) the increased distortion in radio structure, (iii) the decrease in physical sizes, (iv) the increase in radio depolarisation, and (v) the increase in dust emission] without needing to invoke explanations based on cosmology or strong evolution of the surrounding intergalactic medium with cosmic time, thereby avoiding conflict with current theories of structure formation.Comment: To appear in Nature. 4 pages, 2 colour figures available on request. Also available at http://www-astro.physics.ox.ac.uk/~km