Dynamic Critical approach to Self-Organized Criticality

A dynamic scaling Ansatz for the approach to the Self-Organized Critical (SOC) regime is proposed and tested by means of extensive simulations applied to the Bak-Sneppen model (BS), which exhibits robust SOC behavior. Considering the short-time scaling behavior of the density of sites ($\rho(t)$) below the critical value, it is shown that i) starting the dynamics with configurations such that $\rho(t=0) \to 0$ one observes an {\it initial increase} of the density with exponent $\theta = 0.12(2)$; ii) using initial configurations with $\rho(t=0) \to 1$, the density decays with exponent $\delta = 0.47(2)$. It is also shown that he temporal autocorrelation decays with exponent $C_a = 0.35(2)$. Using these, dynamically determined, critical exponents and suitable scaling relationships, all known exponents of the BS model can be obtained, e.g. the dynamical exponent $z = 2.10(5)$, the mass dimension exponent $D = 2.42(5)$, and the exponent of all returns of the activity $\tau_{ALL} = 0.39(2)$, in excellent agreement with values already accepted and obtained within the SOC regime.Comment: Rapid Communication Physical Review E in press (4 pages, 5 figures

Geographical Embedding of Scale-Free Networks

A method for embedding graphs in Euclidean space is suggested. The method connects nodes to their geographically closest neighbors and economizes on the total physical length of links. The topological and geometrical properties of scale-free networks embedded by the suggested algorithm are studied both analytically and through simulations. Our findings indicate dramatic changes in the embedded networks, in comparison to their off-lattice counterparts, and call into question the applicability of off-lattice scale-free models to realistic, everyday-life networks

ECOPAMPA: A new tool for automatic fish schools detection and assessment from echo data

Accurate identification of aquatic organisms and their numerical abundance calculation using echo detection techniques remains a great challenge for marine researchers. A software architecture for echo data processing is presented in this article. Within it, it is discussed how to obtain energetic, morphometric and bathymetric fish school descriptors to accurately identify different fish-species. To accomplish this task it was necessary to have a development platform that allowed reading echo data from a particular echosounder, to detect fish aggregations and then to calculate fish school descriptors that would be used for fish-species identification, in an automatic way. This article also describes thoroughly the digital processing algorithms for this automatic detection and classification, as well as the automatic process required for surface and bottom line detection, which is necessary to determine the exploration range. These algorithms are implemented within the ECOPAMPA software, which is the first Argentinean system for marine species identification. Finally, a comparative result over experimental data of ECOPAMPA against EchoviewTM Software Pty Ltd (formerly Myriax Software Pty Ltd), is carefully examined

Spectrum of genetic diversity and networks of clonal organisms

Clonal organisms present a particular challenge in population genetics because, in addition to the possible existence of replicates of the same genotype in a given sample, some of the hypotheses and concepts underlying classical population genetics models are irreconcilable with clonality. The genetic structure and diversity of clonal populations was examined using a combination of new tools to analyze microsatellite data in the marine angiosperm Posidonia oceanica. These tools were based on examination of the frequency distribution of the genetic distance among ramets, termed the spectrum of genetic diversity (GDS), and of networks built on the basis of pairwise genetic distances among genets. The properties and topology of networks based on genetic distances showed a "small-world" topology, characterized by a high degree of connectivity among nodes, and a substantial amount of substructure, revealing organization in sub-families of closely related individuals. Keywords: genetic networks; small-world networks; genetic diversity; clonal organismsComment: Replaced with revised versio

Ictiobot-40 a low cost AUV platform for acoustic imaging surveying

Autonomous Underwater Vehicles (AUVs) are suitable platforms for a wide type of applications in the oceanic environment. These applications are developed in various fields such as scientific surveying, off-shore industry and defense. The employment of AUVs requires less human support and reduces operation costs. Due to the changing marine environment these vehicles must deal with uncertain and hostile conditions to perform its tasks. In the marine robotics matter, the INTELYMEC group has developed in 2012 an AUV prototype called Ictiobot, a low cost experimental platform for multipurpose missions. In this paper an upgrade of the original prototype is presented, the Ictiobot-40, conceived to perform acoustic imaging surveying missions of up to two hours and maximum depths of 40 meters. The new software and hardware architectures and mechanical structure improvements, are detailed. In addition to these technical details, initial experimental results of the AUV performance in quiet waters will be discussed. Also, the new approaches for systems under development are presented.Trabajo presentado en OCEANS 2019 (Marsella, 17 al 20 de junio de 2019

The geographic scaling of biotic interactions

A central tenet of ecology and biogeography is that the broad outlines of species ranges are determined by climate, whereas the effects of biotic interactions are manifested at local scales. While the first proposition is supported by ample evidence, the second is still a matter of controversy. To address this question, we develop a mathematical model that predicts the spatial overlap, i.e. co-occurrence, between pairs of species subject to all possible types of interactions. We then identify the scale of resolution in which predicted range overlaps are lost. We found that co-occurrence arising from positive interactions, such as mutualism (+/+) and commensalism (+/0), are manifested across scales. Negative interactions, such as competition (-/-) and amensalism (-/0), generate checkerboard patterns of co-occurrence that are discernible at finer resolutions but that are lost and increasing scales of resolution. Scale dependence in consumer-resource interactions (+/-) depends on the strength of positive dependencies between species. If the net positive effect is greater than the net negative effect, then interactions scale up similarly to positive interactions. Our results challenge the widely held view that climate alone is sufficient to characterize species distributions at broad scales, but also demonstrate that the spatial signature of competition is unlikely to be discernible beyond local and regional scales. © 2013 The Authors.Peer Reviewe

Estudio del comportamiento crítico y de la evolución espacio-temporal en sistemas de partículas interactuantes

Facultad de Ciencias Exacta

Biogeography revisited with network theory: retracing the history of hydrothermal vent communities

"This is an electronic version of an article published in Systematic Biology. Systematic Biology is available online at informaworld: http://sysbio.oxfordjournals.org/content/61/1/127" -- 11 páginas, 4 figuras, 1 tabla.Defining biogeographic provinces to understand the history and evolution of communities associated with a given kind of ecosystem is challenging and usually requires a priori assumptions to be made. We applied network theory, a holistic and exploratory method, to the most complete database of faunal distribution available on oceanic hydrothermal vents, environments which support fragmented and unstable ecosystems, to infer the processes driving their worldwide biogeography. Besides the identification of robust provinces, the network topology allowed us to identify preferential pathways that had hitherto been overlooked. These pathways are consistent with the previously proposed hypothesis of a role of plate tectonics in the biogeographical history of hydrothermal vent communities. A possible ancestral position of the Western Pacific is also suggested for the first time. Finally, this work provides an innovative example of the potential of network tools to unravel the biogeographic history of faunal assemblages and to supply comprehensive information for the conservation and management of biodiversity.Peer reviewe

Using species co-occurrence networks to assess the impacts of climate change

Viable populations of species occur in a given place if three conditions are met: the environment at the place is suitable; the species is able to colonize it; co-occurrence is possible despite or because of interactions with other species. Studies investigating the effects of climate change on species have mainly focused on measuring changes in climate suitability. Complex interactions among species have rarely been explored in such studies. We extend network theory to the analysis of complex patterns of co-occurrence among species. The framework is used to explore the robustness of networks under climate change. With our data, we show that networks describing the geographic pattern of co-occurrence among species display properties shared by other complex networks, namely that most species are poorly connected to other species in the network and only a few are highly connected. In our example, species more exposed to climate change tended to be poorly connected to other species within the network, while species more connected tended to be less exposed. Such high connectance would make the co-occurrence networks more robust to climate change. The proposed framework illustrates how network analysis could be used, together with co-occurrence data, to help addressing the potential consequences of species interactions in studies of climate change and biodiversity. However, more research is needed to test for links between co-occurrence and network interactions. © 2011 The Authors.This study is part of a broader research program sponsored by the CSIC-PUC International Laboratory for Global Change (LINC-Global); MBA is also funded by EC FP6 ECOCHANGE project (036866-GOCE) and by the Spanish Ministry of Science and Innovation (CGL2008-01198-E/BOS); CR thanks the Danish National Research Foundation for its support of the Center for Macroecology, Evolution and Climate. PAM acknowledges support from FONDECYT-FONDAP 1501-0001, ICM P05-002 and CONICYT PFB-23.Peer Reviewe