Suchergebnisse

Population dynamics of individuals undergoing birth and death and diffusing by short or long ranged twodimensional spatial excursions (Gaussian jumps or Levy flights) is studied. Competitive interactions are considered in a global case, in which birth and death rates are influenced by all individuals in the system, and in a nonlocal but finite-range case in which interaction affects individuals in a neighborhood (we also address the noninteracting case). In the global case one single or few-cluster configurations are achieved with the spatial distribution of the bugs tied to the type of diffusion. In the Levy case long tails appear for some properties characterizing the shape and dynamics of clusters. Under non-local finite-range interactions periodic patterns appear with periodicity set by the interaction range. This length acts as a cut-off limiting the influence of the long Levy jumps, so that spatial configurations under the two types of diffusion become more similar. By dividing initially everyone into different families and following their descent it is possible to show that mixing of families and their competition is greatly influenced by the spatial dynamics. ; This work has been supported by the targeted financing project SF0690030s09, the Estonian Science Foundation through Grant No. 7466, the Balearic Government (E.H.), and Spanish MICINN and FEDER through project FISICOS (FIS2007-60327). ; Peer reviewed

PACS numbers: 02.50.Ey, 05.40.-a, 05.40.Fb. -Texto completo de ArXiv Núm: 1008.3478 ; A biological competition model where the individuals of the same species perform a two-dimensional Markovian continuous-time random walk and undergo reproduction and death is studied. The competition is introduced through the assumption that the reproduction rate depends on the crowding in the neighborhood. The spatial dynamics corresponds either to normal diffusion characterized by Gaussian jumps or to superdiffusion characterized by Lévy flights. It is observed that in both cases periodic patterns occur for appropriate parameters of the model, indicating that the general macroscopic collective behavior of the system is more strongly influenced by the competition for the resources than by the type of spatial dynamics. However, some differences arise that are discussed. ; This work has been supported by the targeted financing project SF0690030s09, Estonian Science Foundation through grant No. 7466, by the Balearic Government (EH), and by the Spanish MICINN and FEDER through project FISICOS (FIS2007-60327). ; Peer reviewed

We show that the clustering coefficient, a standard measure in network theory, when applied to flow networks, i.e., graph representations of fluid flows in which links between nodes represent fluid transport between spatial regions, identifies approximate locations of periodic trajectories in the flow system. This is true for steady flows and for periodic ones in which the time interval τ used to construct the network is the period of the flow or a multiple of it. In other situations, the clustering coefficient still identifies cyclic motion between regions of the fluid. Besides the fluid context, these ideas apply equally well to general dynamical systems. By varying the value of τ used to construct the network, a kind of spectroscopy can be performed so that the observation of high values of mean clustering at a value of τ reveals the presence of periodic orbits of period 3τ , which impact phase space significantly. These results are illustrated with examples of increasing complexity, namely, a steady and a periodically perturbed model two-dimensional fluid flow, the three-dimensional Lorenz system, and the turbulent surface flow obtained from a numerical model of circulation in the Mediterranean sea. The Lagrangian description of fluid dynamics, which focuses on the motion of the fluid particles as they are advected by the flow, provides a useful bridge between the theory of dynamical systems and the analysis of fluid transport and mixing, so that techniques and results can be transferred from one field to the other. Modern network theory has also been brought into contact with fluid dynamics and dynamical systems through the concept of flow networks, in which the motion of fluid particles between different regions is represented by links in a graph. In this paper, we use the flow network framework to show that the clustering coefficient, a standard measure in network theory, identifies periodic orbits, fundamental objects in the theory of dynamical systems, and is also of importance in the context of fluid motion. ; We acknowledge the financial support from Spanish Ministerio de Economía y Competitividad and Fondo Europeo de Desarrollo Regional under grants LAOP, CTM2015-66407-P (MINECO/FEDER) and ESOTECOS projects FIS2015-63628-C2-1-R (MINECO/FEDER), FIS2015-63628-C2-2-R (MINECO/FEDER), and from the program "Investissements d'Avenir" launched by the French Government and implemented by ANR under grants ANR-10-LABX-54 MEMOLIFE and ANR-11-IDEX-0001-02 PSL* Research University. ; No

C. R. Mirasso et al.- ArXiv Number physics/9906027 ; We report detailed measurements of the pump-current dependency of the self-pulsating frequency of semiconductor CD lasers. A distinct kink in this dependence is found and explained using rate-equation model. The kink denotes a transition between a region where the self-pulsations are weakly sustained relaxation oscillations and a region where Q-switching takes place. Simulations show that spontaneous emission noise plays a crucial role for the cross-over. ; This work was supported by the European Union through the Project HCM CHRXCT94-0594. ; Peer reviewed

In the past decades, boreal summers have been characterized by an increasing number of extreme weather events in the Northern Hemisphere extratropics, including persistent heat waves, droughts and heavy rainfall events with significant social, economic and environmental impacts. Many of these events have been associated with the presence of anomalous large-scale atmospheric circulation patterns, in particular persistent blocking situations, i.e., nearly stationary spatial patterns of air pressure. To contribute to a better understanding of the emergence and dynamical properties of such situations, we construct complex networks representing the atmospheric circulation based on Lagrangian trajectory data of passive tracers advected within the atmospheric flow. For these Lagrangian flow networks, we study the spatial patterns of selected node properties prior to, during and after different atmospheric blocking events in Northern Hemisphere summer. We highlight the specific network characteristics associated with the sequence of strong blocking episodes over Europe during summer 2010 as an illustrative example. Our results demonstrate the ability of the node degree, entropy and harmonic closeness centrality based on outgoing links to trace important spatio-temporal characteristics of atmospheric blocking events. In particular, all three measures capture the effective separation of the stationary pressure cell forming the blocking high from the normal westerly flow and the deviation of the main atmospheric currents around it. Our results suggest the utility of further exploiting the Lagrangian flow network approach to atmospheric circulation in future targeted diagnostic and prognostic studies. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No813844. RVD has been additionally supported by the Federal Ministry for Education and Research of Germany (BMBF) via the JPI Climate/JPI Oceans project ROADMAP (grant no. 01LP2002B). CL and EHG also acknowledge support from MINECO/AEI/FEDER through the María de Maeztu Program for Units of Excellence in R&D (MDM-2017-0711, Spain). ; No

Trabajo presentado en la European Geosciences Union General Assembly (EGU General Assembly 2021), celebrada online del 19 al 30 de abril de 2021. ; In the past decades, boreal summers have been characterized by a number extreme weather events such as heat waves, droughts and heavy rainfall periods with significant social, economic and environmental impacts. One of the most outstanding examples occurred in the summer of 2010 when an anomalously strong heatwave persisted over Eastern Europe for several weeks while extreme rainfalls struck Pakistan, leading to the country's worst floods in record history. Both events were related to the presence of an anomalously persistent atmospheric blocking situation - that is a large-scale, nearly stationary, atmospheric pressure pattern - over Eastern Europe. The high impact of blocking events has motivated numerous studies. However, there is not yet a comprehensive theory explaining their onset, maintenance and decay and their prediction remains a challenge. In this work, we employ a Lagrangian dynamics based, complex network description of the atmospheric transport to study the connectivity patterns associated with atmospheric blocking events. The network is constructed by associating nodes to regions of the atmosphere and establishing links based on the flux of material between these nodes during a given time interval, as described in Ser-Giacomi et al. [1]. One can then use the tools and metrics developed in the context of graph theory to explore the atmospheric flow properties. In particular, we demonstrate the ability of measures such as the network degree, entropy and harmonic closeness centrality to trace the spatio-temporal characteristics of atmospheric blocking events. ; This research was conducted as part of the CAFE Innovative Training Network (Climate Advanced Forecasting of sub-seasonal Extremes, http://www.cafes2se-itn.eu/) which has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 813844.

9 pages, 5 figures, 1 table.-- PMID: 18952317 [PubMed].-- Available online Oct 25, 2008. ; Objective detection of regime shifts remains a major challenge in ecology. There is an apparent gap between the prominence of present theoretical frameworks involving ecological thresholds and regime shifts, and the paucity of efforts to conduct simple tests and quantitative inferences on the actual occurrence of such phenomena in ecological data. There is a wide range of statistical methods and analytical techniques now available that render these questions tractable, some of them even dating half a century back. Yet, their application has been sparse and confined within a narrow subset of cases of ecological regime shifts. Raising awareness on the range of techniques available, their principles and limitations should promote a more operational approach to the analysis of ecological thresholds and regime shifts. ; This is a contribution to the THRESHOLDS integrated project funded by the 6th Framework Program of the European Union (www.thresholds-eu.org, contract # 003933-2). ; Peer reviewed

We describe the dynamical behavior found in numerical solutions of the Vector Complex Ginzburg-Landau equation in parameter values where plane waves are stable. Topological defects in the system are responsible for a rich behavior. At low coupling between the vector components, a frozen phase is found, whereas a gas-like phase appears at higher coupling. The transition is a consequence of a defect unbinding phenomena. Entropy functions display a characteristic behavior around the transition. ; Financial support from DGES (Spain) Project PB94-1167 and from the European Union TMR network QSTRUCT (Project FMRX-CT96-0077)is acknowledged. ; Peer Reviewed

Synchronization of spatiotemporally chaotic extended systems is considered in the context of coupled one-dimensional complex Ginzburg-Landau equations (CGLE). A regime of coupled spatiotemporal intermittency (STI) is identified and described in terms of the space-time synchronized chaotic motion of localized structures. A quantitative measure of synchronization as a function of coupling parameter is given through distribution functions and information measures. The coupled STI regime is shown to disappear into regular dynamics for situations of strong coupling when localized structures become unstable, hence a description in terms of a single CGLE is not appropriate. ; Financial support from DGICYT Project PB94-1167 (Spain) and European Union QSTRUCT (FMRX-CT96- 0077) are acknowledged. R.M. acknowledges support from PEDECIBA and CONICYT (Uruguay). ; Peer Reviewed

16 pages, 6 figures.-- ArXiv pre-print available at: http://arxiv.org/abs/physics/0608105 ; With the tools of lobe dynamics, the authors analyze the structures present in the velocity field obtained from a numerical simulation of the surface circulation in the northwestern Mediterranean Sea. In particular, focus is placed on the North Balearic Front, the westernmost part of the transition zone between saltier and fresher waters in the western Mediterranean, which is here interpreted in terms of the presence of a semipermanent "Lagrangian barrier," across which little transport occurs. Identified are relevant hyperbolic trajectories and their manifolds, and it is shown that the transport mechanism known as the turnstile, previously identified in abstract dynamical systems and simplified model flows, is also at work in this complex and realistic ocean flow. In addition, nonlinear dynamics techniques are shown to be powerful enough to identify the key geometric structures in this part of the Mediterranean. The construction also reveals the spatiotemporal routes along which this transport happens. Topological changes in that picture, which are associated with the crossing by eddies and may be interpreted as the breakdown of the front, are also observed during the simulation. ; A.M.M. acknowledges the MCyT (Spanish Government) for a Ramón y Cajal Research Fellowship and financial support from MEC (Spanish Government) reference MTM2004-00797 and the Royal Society-CSIC cooperation agreement reference B2003GB03. E.H.-G. acknowledges financial support from MEC and FEDER through Project CONOCE2 (FIS2004-00953). We also acknowledge M. Emelianov for communicating us results from a recent cruise before publication. D.S. and S. W. acknowledge financial support from ONR Grant No. N00014-01-1-0769. ; Peer reviewed

We study the vertical dispersion and distribution of negatively buoyant rigid microplastics within a realistic circulation model of the Mediterranean sea. We first propose an equation describing their idealized dynamics. In that framework, we evaluate the importance of some relevant physical effects: inertia, Coriolis force, small-scale turbulence and variable seawater density, and bound the relative error of simplifying the dynamics to a constant sinking velocity added to a large-scale velocity field. We then calculate the amount and vertical distribution of microplastic particles on the water column of the open ocean if their release from the sea surface is continuous at rates compatible with observations in the Mediterranean. The vertical distribution is found to be almost uniform with depth for the majority of our parameter range. Transient distributions from flash releases reveal a non-Gaussian character of the dispersion and various diffusion laws, both normal and anomalous. The origin of these behaviors is explored in terms of horizontal and vertical flow organization. ; This work is part of the "Tracking of Plastics in Our Seas" (TOPIOS) project, funded by the European Research Councilunder the European Union's Horizon 2020 research and innovation program (grant agreement no. 715386). We acknowledge publication feesupport from the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). R.F.,G.D., E.H-G and C.L acknowledge financial support from the Spanish State Research Agency through the María de Maeztu Program forUnits of Excellence in R&D (MDM-2017-0711). R.F. also acknowledges the fellowship no. BES-2016-078416 under the FPI program ofMINECO, Spain. G.D. also acknowledges financial support from the European Social Fund through the fellowship no. PD/020/2018 underthe postdoctoral program of CAIB, Spain, and from NKFIH, Hungary (grant agreement no. NKFI-124256). ; No

Short-scale interactions yield large-scale vegetation patterns that, in turn, shape ecosystem function across landscapes. Fairy circles, which are circular patches bare of vegetation within otherwise continuous landscapes, are characteristic features of semiarid grasslands. We report the occurrence of submarine fairy circle seascapes in seagrass meadows and propose a simple model that reproduces the diversity of seascapes observed in these ecosystems as emerging from plant interactions within the meadow. These seascapes include two extreme cases, a continuous meadow and a bare landscape, along with intermediate states that range from the occurrence of persistent but isolated fairy circles, or solitons, to seascapes with multiple fairy circles, banded vegetation, and "leopard skin" patterns consisting of bare seascapes dotted with plant patches. The model predicts that these intermediate seascapes extending across kilometers emerge as a consequence of local demographic imbalances along with facilitative and competitive interactions among the plants with a characteristic spatial scale of 20 to 30 m, consistent with known drivers of seagrass performance. The model, which can be extended to clonal growth plants in other landscapes showing fairy rings, reveals that the different seascapes observed hold diagnostic power as to the proximity of seagrass meadows to extinction points that can be used to identify ecosystems at risks. ; D.R.-R., D.G., T.S., E.H.-G., and N.M. acknowledge financial support from AEI/FEDER [Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, European Union (EU)] (FIS2015-63628-C2-1-R, FIS2015-63628-C2-2-R, and CGL2015-71809-P). C.M.D. was supported by King Abdullah University of Science and Technology through the baseline funding. ; We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

Self-organized spatial patterns of vegetation are frequent in water-limited regions and have been suggested as important indicators of ecosystem health. However, the mechanisms underlying their emergence remain unclear. Some theories hypothesize that patterns could result from a scale-dependent feedback (SDF), whereby interactions favoring plant growth dominate at short distances and growth-inhibitory interactions dominate in the long range. However, we know little about how net plant-to-plant interactions may change sign with inter-individual distance, and in the absence of strong empirical support, the relevance of this SDF for vegetation pattern formation remains disputed. These theories predict a sequential change in pattern shape from gapped to labyrinthine to spotted spatial patterns as precipitation declines. Nonetheless, alternative theories show that the same sequence of patterns could emerge even if net interactions between plants were always inhibitory (purely competitive feedbacks, PCF). Although these alternative hypotheses lead to visually indistinguishable patterns they predict very different desertification dynamics following the spotted pattern. Moreover, vegetation interaction with other ecosystem components can introduce additional spatio-temporal scales that reshape both the patterns and the desertification dynamics. Therefore, to make reliable ecological predictions for a focal ecosystem, it is crucial that models accurately capture the mechanisms at play in the system of interest. Here, we review existing theories for vegetation self-organization and their conflicting predictions about desertification dynamics. We further discuss possible ways for reconciling these predictions and potential empirical tests via manipulative experiments to improve our understanding of how vegetation self-organizes and better predict the fate of the ecosystems where they form. ; This work is supported by FAPESP through grants ICTP-SAIFR 2016/01343-7, and Programa Jovens Pesquisadores em Centros Emergentes 2019/24433-0 and 2019/05523-8, Instituto Serrapilheira through grant Serra-1911-31200, and the Simons Foundation (RMG); the Princeton University May Fellowship in the department of Ecology and Evolutionary Biology (CC); MINECO/AEI/FEDER through the María de Maeztu Program for Units of Excellence in R&D (MDM-2017-0711, Spain) (EHG & CL); The Gordon and Betty Moore Foundation, grant #7800 (CET & JAB); and the NSF grant DMS-2052616 (JAB). This work was partially funded by the Center of Advanced Systems Understanding (CASUS) which is financed by Germany's Federal Ministry of Education and Research (BMBF) and by the Saxon Ministry for Science, Culture and Tourism (SMWK) with tax funds on the basis of the budget approved by the Saxon State Parliament (JMC). ; No

Self-organized spatial patterns of vegetation are frequent in water-limited regions and have been suggested as important ecosystem health indicators. However, the mechanisms underlying their formation remain unclear. It has been hypothesized that patterns could emerge from a water-mediated scale-dependent feedback (SDF), whereby interactions favoring plant growth dominate at short distances while growth-inhibitory interactions dominate in the long-range. As precipitation declines, this framework predicts a sequential change from gapped to labyrinthine to spotted spatial patterns. However, we know little about how net plant-to-plant interactions may shift from positive to negative as a function of inter-individual distance, and in the absence of strong empirical support, the relevance of SDF for vegetation pattern formation remains disputed. Alternative theories show that the same sequence of patterns could emerge when interactions between plants are always inhibitory if their intensity decays sharply enough with inter-individual distance. Although these alternative hypotheses lead to visually indistinguishable spatial distributions of plants, they predict different ecosystem-level consequences for the patterns, thus limiting their potential use as ecosystem-state indicators. Therefore, to make reliable ecological predictions, models need to accurately capture the mechanisms at play in the systems of interest. Here, we review existing theories for vegetation self-organization and their conflicting ecosystem-level predictions. We discuss ways to reconcile these predictions. We focus on the mechanistic differences among models, which can provide valuable information to help researchers decide which model to use for a particular system and/or whether it requires modification. ; "RMG: FAPESP through grants ICTP-SAIFR 2016/01343-7, and Programa Jovens Pesquisadores em Centros Emergentes 2019/24433-0 and 2019/05523-8, Instituto Serrapilheira through grant Serra-1911-31200, and the Simons Foundation. CC: the Princeton University May Fellowship in the department of Ecology and Evolutionary Biology. JMC: Center of Advanced Systems Understanding (CASUS) which is financed by Germany's Federal Ministry of Education and Research (BMBF) and by the Saxon Ministry for Science, Culture and Tourism (SMWK) with tax fundson the basis of the budget approved by the Saxon State Parliament. EHG and CL: MINECO/AEI/FEDER through theMaría de Maeztu Program for Units of Excellence in R&D (MDM-2017-0711, Spain). CET & JAB acknowledge supportfrom the Gordon and Betty Moore Foundation, grant #7800. ; Peer reviewed

Marine resources stewardships are progressively becoming more receptive to an effective incorporation of both ecosystem and environmental complexities into the analytical frameworks of fisheries assessment. Understanding and predicting marine fish production for spatially and demographically complex populations in changing environmental conditions is however still a difficult task. Indeed, fisheries assessment is mostly based on deterministic models that lack realistic parameterizations of the intricate biological and physical processes shaping recruitment, a cornerstone in population dynamics. We use here a large metapopulation of a harvested fish, the European hake (Merluccius merluccius), managed across transnational boundaries in the northwestern Mediterranean, to model fish recruitment dynamics in terms of physics‐dependent drivers related to dispersal and survival. The connectivity among nearby subpopulations is evaluated by simulating multi‐annual Lagrangian indices of larval retention, imports, and self‐recruitment. Along with a proxy of the regional hydroclimate influencing early life stages survival, we then statistically determine the relative contribution of dispersal and hydroclimate for recruitment across contiguous management units. We show that inter‐annual variability of recruitment is well reproduced by hydroclimatic influences and synthetic connectivity estimates. Self‐recruitment (i.e., the ratio of retained locally produced larvae to the total number of incoming larvae) is the most powerful metric as it integrates the roles of retained local recruits and immigrants from surrounding subpopulations and is able to capture circulation patterns affecting recruitment at the scale of management units. We also reveal that the climatic impact on recruitment is spatially structured at regional scale due to contrasting biophysical processes not related to dispersal. Self‐recruitment calculated for each management unit explains between 19% and 32.9% of the variance of recruitment variability, that is much larger than the one explained by spawning stock biomass alone, supporting an increase of consideration of connectivity processes into stocks assessment. By acknowledging the structural and ecological complexity of marine populations, this study provides the scientific basis to link spatial management and temporal assessment within large marine metapopulations. Our results suggest that fisheries management could be improved by combining information of physical oceanography (from observing systems and operational models), opening new opportunities such as the development of short‐term projections and dynamic spatial management. ; M. Hidalgo acknowledges support of two contracts funded by the Spanish national program "Ramon y Cajal" (RYC‐2015‐18646) and by the regional government of the Balearic Islands, the later co‐funded by the European Social Fund 2014‐2020. V. Rossi acknowledges support of a post‐doctoral 'Juan de la Cierva Incorporacion' fellowship (IJCI‐2014‐22343) provided by the Spanish MICINN and a networking grant through the HYDROGENCONNECT project funded by the French program MISTRALS ENVI‐Med. E. Ser‐Giacomi thanks French program "Investissements d'Avenir" (ANR‐10‐LABX‐54 MEMOLIFE and ANR‐11‐IDEX‐0001‐02 PSL Research University). This work was also supported by the Spanish National projects LAOP (CTM2015‐66407‐P) P. Monroy and E. Hernandez‐Garcia and CLIFISH (CTM2015‐66400‐C3‐1‐R) and to M. Hidalgo, B. Guijarro, and E. Massuti (AEI/FEDER, EU). P. Reglero and M. Hidalgo acknowledge funding of the H2020 PANDORA project (Nr. 773713). ; Peer reviewed