Transience and constancy of interactions in a plant-frugivore network

Plant-animal mutualistic interactions such as frugivory and seed dispersal display great variation in time due to fluctuations in fruit abundance, animal abundance, and behavior. In particular, some species participate in interactions with other species only transiently, while other species are active for longer periods of time. Species with a longer period of activity are able to interact with more species, and thus engage in constant participation in an interaction network. Species with high constancy would thus be expected to help maintain the biodiversity of a community; however, the manner in which constant species link to their partners may be critical to species coexistence. Because species that interact with many partners concurrently could create more competition compared to those species that interact sequentially with many partners, evaluating the concurrence in an interaction network sheds light on how the network can maintain biodiversity. In this study, we investigate how phenological patterns of fruit production and frugivore presence affect the temporal variation of a plant-frugivore network, and focus on the manner in which high degree species collect their interactions over time. We found a clear separation of activity periods: most species appeared only briefly and participated in relatively few interactions, or showed activity for longer time periods and participated in more interactions. Species that were active for longer time periods often shifted interactions, resulting in a sequential collection of their partners in time, rather than concurrence. For the seed dispersal mutualism in particular, sequential accumulation of partners may allow plant species more opportunities to disperse their seeds compared to concurrence. We suggest that for temporally and spatially heterogeneous landscapes, sequential accumulation of partners would serve to reduce competition and facilitate coexistence of species. Copyright © 2013 Yang et al

Common-offset CRS for advanced imaging in complex geological settings

Increasingly challenging exploration targets with respect to the geological complexity and data quality require more accurate seismic imaging. The common-offset CRS method provides an extension of the CRS technology to such targets as we demonstrate in this case study for complex 2D over thrust data. While both zero- and common-offset CRS stack provide similar noise reduction compared to the conventional PreSTM in areas with relatively simple structure and good coupling, the common-offset results are far superior on very poor data. Moreover, using the CO CRS stack in depth velocity model building can help in event picking and provides a better defined semblance.3744-374

What determines the temporal changes of species degree and strength in an oceanic island plant-disperser network?

Network models of frugivory and seed dispersal are usually static. To date, most studies on mutualistic networks assert that interaction properties such as species\u27 degree (k) and strength (s) are strongly influenced by species abundances. We evaluated how species\u27 degree and strength change as a function of temporal variation not only in species abundance, but also in species persistence (i.e., phenology length). In a two-year study, we collected community-wide data on seed dispersal by birds and examined the seasonal dynamics of the above-mentioned interaction properties. Our analyses revealed that species abundance is an important predictor for plant strength within a given sub-network. However, our analyses also reveal that species\u27 degree can often be best explained by the length of fruiting phenology (for plants degree) or by the number of fruiting species (for dispersers degree), which are factors that can be decoupled from the relative abundance of the species participating in the network. Moreover, our results suggest that generalist dispersers (when total study period is considered) act as temporal generalists, with degree constrained by the number of plant species displaying fruits in each span. Along with species identity, our findings underscore the need for a temporal perspective, given that seasonality is an inherent property of many mutualistic networks. © 2012 González-Castro et al

Relative importance of phenotypic trait matching and species\u27 abundances in determining plant - Avian seed dispersal interactions in a small insular community

Network theory has provided a general way to understand mutualistic plant-animal interactions at the community level. However, the mechanisms responsible for interaction patterns remain controversial. In this study we use a combination of statistical models and probability matrices to evaluate the relative importance of species morphological and nutritional (phenotypic) traits and species abundance in determining interactions between fleshyfruited plants and birds that disperse their seeds. The models included variables associated with species abundance, a suite of variables associated with phenotypic traits (fruit diameter, bird bill width, fruit nutrient compounds), and the species identity of the avian disperser. Results show that both phenotypic traits and species abundance are important determinants of pairwise interactions. However, when considered separately, fruit diameter and bill width were more important in determining seed dispersal interactions. The effect of fruit compounds was less substantial and only important when considered together with abundance-related variables and/or the factor \u27animal species\u27. © The Authors 2014

Re-designing the substrate binding pocket of laccase for enhanced oxidation of sinapic acid

Iterative saturation mutagenesis was performed over six residues delimiting the substrate binding pocket of a high-redox potential chimeric laccase with the aim of enhancing its activity over sinapic acid, a lignin-related phenol of industrial interest. In total, more than 15000 clones were screened and two selected variants, together with the parent-type laccase, were purified and characterized. The new variants presented shifted pH activity profiles and enhanced turnover rates on sinapic acid and its methyl ester, whereas the oxidation of related phenols was not significantly enhanced. Neither the enzyme's redox potential nor the mechanism of the reaction were affected. Thus, quantum mechanics and molecular dynamics calculations were done to rationalize the effect of the selected mutations, revealing the critical role of the residues of the enzyme pocket to provide the precise binding of the substrate that enables an efficient electron transfer to the T1 copper. The results presented highlight the power of combining directed evolution and computational approaches to give novel solutions in enzyme engineering and to understand the mechanistic reasons behind them, offering new insights for further rational design towards specific targets

An NLO+PS generator for t¯t and Wt production and decay including non-resonant and interference effects

We present a Monte Carlo generator that implements significant theoretical improvements in the simulation of top-quark pair production and decay at the LHC. Spin correlations and off-shell effects in top-decay chains are described in terms of exact matrix elements for $p p \to \ell^+\nu_{\scriptscriptstyle\ell}\, l^-\bar{\nu}_{\scriptscriptstyle l} b \bar{b}$ at NLO QCD, where the leptons $\ell$ and $l$ belong to different families, and $b$ quarks are massive. Thus, the contributions from $t\bar{t}$ and $Wt$ single-top production as well as their quantum interference are fully included. Matrix elements are matched to the Pythia8 parton shower using a recently proposed method that allows for a consistent treatment of resonances in the POWHEG framework. These theoretical improvements are especially important for the interpretation of precision measurements of the top-quark mass, for single-top analyses in the $Wt$ channel, and for $t\bar{t}$ and $Wt$ backgrounds in the presence of jet vetoes or cuts that enhance off-shell effects. The new generator is based on a process-independent interface of the OpenLoops amplitude generator with the POWHEGBOX framework.Comment: 49 pages, 22 figure

Equilibrium to off-equilibrium crossover in homogeneous active matter

We study the crossover between equilibrium and off-equilibrium dynamical universality classes in the Vicsek model near its ordering transition. Starting from the incompressible hydrodynamic theory of Chen et al. [Critical phenomenon of the order-disorder transition in incompressible active fluids, New J. Phys. 17, 042002 (2015)NJOPFM1367-263010.1088/1367-2630/17/4/042002], we show that increasing the activity leads to a renormalization group (RG) crossover between the equilibrium ferromagnetic fixed point, with dynamical critical exponent z=2, and the off-equilibrium active fixed point, with z=1.7 (in d=3). We run simulations of the classic Vicsek model in the near-ordering regime and find that critical slowing down indeed changes with activity, displaying two exponents that are in remarkable agreement with the RG prediction. The equilibrium to off-equilibrium crossover is ruled by a characteristic length scale, beyond which active dynamics takes over. The larger the activity is, the smaller is such a length scale, suggesting the existence of a general trade-off between activity and the system's size in determining the dynamical universality class of active matter.Fil: Cavagna, Andrea. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; ItaliaFil: Di Carlo, Luca. Università degli studi di Roma "La Sapienza"; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Giardina, Irene. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; Italia. Istituto Nazionale di Fisica Nucleare; ItaliaFil: Grigera, Tomas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; Argentina. Consiglio Nazionale delle Ricerche; ItaliaFil: Pisegna, Giulia. Università degli studi di Roma "La Sapienza"; Italia. Consiglio Nazionale delle Ricerche; Itali

Le ferromagnétisme marginal à basse température explique les corrélations à longue portée dans les essaims d'oiseaux

We introduce a new ferromagnetic model capable of reproducing one of the most intriguing properties of collective behaviour in starling flocks, namely the fact that strong collective order coexists with scale-free correlations of the modulus of the microscopic degrees of freedom, that is, the birds´ speeds. The key idea of the new theory is that the single-particle potential needed to bound the modulus of the microscopic degrees of freedom around a finite value is marginal, that is, it has zero curvature. We study the model by using mean-field approximation and Monte Carlo simulations in three dimensions, complemented by finite-size scaling analysis. While at the standard critical temperature, Tc, the properties of the marginal model are exactly the same as a normal ferromagnet with continuous symmetry breaking, our results show that a novel zero-temperature critical point emerges, so that in its deeply ordered phase the marginal model develops divergent susceptibility and correlation length of the modulus of the microscopic degrees of freedom, in complete analogy with experimental data on natural flocks of starlings.Nous introduisons un nouveau modèle ferromagnétique capable de reproduire l'une des propriétés les plus intrigantes du comportement collectif des essaims d'oiseaux, à savoir le fait qu'un ordre collectif fort coexiste avec des corrélations sans échelle du module des degrés de liberté microscopiques, à savoir les vitesses des oiseaux. L'idée-clé de la nouvelle théorie est que le potentiel à un corps nécessaire pour lier le module des degrés de liberté microscopiques autour d'une valeur finie est marginal, c'est-à-dire qu'il a une courbure nulle. Nous étudions le modèle en utilisant l'approximation du champ moyen et les simulations de Monte-Carlo en trois dimensions, complétées par l'analyse à l'échelle finie. Alors qu'à la température critique standard, Tc , les propriétés du modèle marginal sont exactement les mêmes que celles d'un ferromagnétique normal avec rupture de symétrie continue, nos résultats montrent qu'un nouveau point critique à température nulle émerge, de sorte que, dans sa phase profondément ordonnée, le modèle marginal développe une susceptibilité divergente et une longueur de corrélation du module des degrés de liberté microscopiques, en analogie complète avec les données expérimentales sur des essaims naturels d'oiseaux.Fil: Cavagna, Andrea. Consiglio Nazionale delle Ricerche; ItaliaFil: Culla, Antonio. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; ItaliaFil: Di Carlo, Luca. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; ItaliaFil: Giardina, Irene. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; Italia. Istituto Nazionale Di Fisica Nucleare.; ItaliaFil: Grigera, Tomas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; Argentin