Inferring Lévy walks from curved trajectories: A rescaling method

Tromer R.M., Barbosa M.B., Bartumeus F., Catalan J., Da Luz M.G.E., Raposo E.P., Viswanathan G.M. (2015) Inferring Lévy walks from curved trajectories: A rescaling method. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. 92: 0-0.
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Doi: 10.1103/PhysRevE.92.022147

Resum:

An important problem in the study of anomalous diffusion and transport concerns the proper analysis of trajectory data. The analysis and inference of Lévy walk patterns from empirical or simulated trajectories of particles in two and three-dimensional spaces (2D and 3D) is much more difficult than in 1D because path curvature is nonexistent in 1D but quite common in higher dimensions. Recently, a new method for detecting Lévy walks, which considers 1D projections of 2D or 3D trajectory data, has been proposed by Humphries et al. The key new idea is to exploit the fact that the 1D projection of a high-dimensional Lévy walk is itself a Lévy walk. Here, we ask whether or not this projection method is powerful enough to cleanly distinguish 2D Lévy walk with added curvature from a simple Markovian correlated random walk. We study the especially challenging case in which both 2D walks have exactly identical probability density functions (pdf) of step sizes as well as of turning angles between successive steps. Our approach extends the original projection method by introducing a rescaling of the projected data. Upon projection and coarse-graining, the renormalized pdf for the travel distances between successive turnings is seen to possess a fat tail when there is an underlying Lévy process. We exploit this effect to infer a Lévy walk process in the original high-dimensional curved trajectory. In contrast, no fat tail appears when a (Markovian) correlated random walk is analyzed in this way. We show that this procedure works extremely well in clearly identifying a Lévy walk even when there is noise from curvature. The present protocol may be useful in realistic contexts involving ongoing debates on the presence (or not) of Lévy walks related to animal movement on land (2D) and in air and oceans (3D). © 2015 American Physical Society.

Llegeix més

Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes

de Mendoza G., Ventura M., Catalan J. (2015) Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes. Ecology and Evolution. 5: 2518-2532.
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Doi: 10.1002/ece3.1522

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Aiming to elucidate whether large-scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in-lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in-lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances. © 2015 The Authors.

Llegeix més

Atmospheric deposition of polybromodiphenyl ethers in remote mountain regions of Europe

Arellano L., Fernández P., López J.F., Rose N.L., Nickus U., Thies H., Stuchlik E., Camarero L., Catalan J., Grimalt J.O. (2014) Atmospheric deposition of polybromodiphenyl ethers in remote mountain regions of Europe. Atmospheric Chemistry and Physics. 14: 4441-4457.
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Doi: 10.5194/acp-14-4441-2014

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Polybromodiphenyl ethers (PBDEs) were analyzed in bulk atmospheric deposition collected in four European remote mountain areas over a period of two years (2004-2006): Lake Redon (Pyrenees, Catalonia, Spain), Gossenköllesee (Alps, Austria), Lochnagar (Grampian Mountains, Scotland) and Skalnate (Tatras, Slovakia). In all sites, the PBDE distributions were dominated by BDE209. BDE47 and BDE99 were the major low-brominated congeners, followed by BDE100 and BDE183. This composition is consistent with predominant inputs from the commercial mixtures decaBDE and pentaBDE. The total congener site-averaged fluxes ranged between 100 ng m-2 mo-1 (Alps) and 190 ng m-2 mo-1 (Tatras). Significant correlations between PBDE deposition and percent of North Atlantic backwards air mass trajectories in the collected samples of the westernmost sites, Lochnagar and Redon, suggested an impact of transcontinental transfer of these pollutants from North American sources into Europe. Skalnate, and to a lower extent Redon, recorded another main PBDE source from central Europe corresponding to secondary emissions of the pentaBDE commercial mixture. The fluxes of these secondary emissions were temperature dependent and correlated to total particle deposition and rainfall. Higher PBDE fluxes were observed at increasing temperature, particle deposition and precipitation. Another specific PBDE source was observed in United Kingdom and recorded in Lochnagar. Photolytic degradation during transport decreased the relative abundance of BDE209 and modified the emitted pentaBDE technical mixtures by depletion of the relative composition of BDE99 and, to a lower extent, BDE47. The transformations were more intense in the sites located above 2000 m (Redon and Gossenköllesee) and, particularly, during the warm periods. © Author(s) 2014.

Llegeix més

Air temperature-driven CO2 consumption by rock weathering at short timescales: Evidence from a Holocene lake sediment record

Catalan J., Pla-Rabes S., Garcia J., Camarero L. (2014) Air temperature-driven CO2 consumption by rock weathering at short timescales: Evidence from a Holocene lake sediment record. Geochimica et Cosmochimica Acta. 136: 67-79.
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Doi: 10.1016/j.gca.2014.04.005

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The role that air temperature plays in the interaction between atmospheric CO2 levels and continental rock weathering at relatively short time scales is still a matter of debate. Laboratory studies reveal a strong dependence of mineral dissolution on temperature, but field comparisons among watersheds under different climate conditions often indicate correlations with other environmental factors. Using a paleolimnological approach, here we show that there has been an extremely good coupling between rock weathering, water alkalinity (CO2 consumption), and air temperature during the last 10,000years at sub-millennial time scales in a small watershed of silicate bedrock and scarce vegetation. The calculation of apparent activation energy for the weathering reaction (as a means to describe the temperature dependence of the process) provides a value (Ea=67±7kJmol-1) that is comparable to those found for silicate rocks similar to those in the watershed in laboratory experiments and some field studies. Our results provide evidence that regulatory constraints between air temperature, atmospheric CO2 and silicate rock weathering can be fine-tuned at geological timescales and may not be negligible in the current context of global change. © 2014 Elsevier Ltd.

Llegeix més

Nitrogen-Cycling Genes in Epilithic Biofilms of Oligotrophic High-Altitude Lakes (Central Pyrenees, Spain)

Vila-Costa M., Bartrons M., Catalan J., Casamayor E.O. (2014) Nitrogen-Cycling Genes in Epilithic Biofilms of Oligotrophic High-Altitude Lakes (Central Pyrenees, Spain). Microbial Ecology. 68: 60-69.
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Doi: 10.1007/s00248-014-0417-2

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Microbial biofilms in oligotrophic environments are the most reactive component of the ecosystem. In high-altitude lakes, exposed bedrock, boulders, gravel, and sand in contact with highly oxygenated water and where a very thin epilithic biofilm develops usually dominate the littoral zone. Traditionally, these surfaces have been considered unsuitable for denitrification, but recent investigations have shown higher biological diversity than expected, including diverse anaerobic microorganisms. In this study, we explored the presence of microbial N-cycling nirS and nirK (denitrification through the conversion of NO2 - to NO), nifH (N2 fixation), anammox (anaerobic ammonium oxidation), and amoA (aerobic ammonia oxidation, both bacterial and archaeal) genes in epilithic biofilms of a set of high-altitude oligotrophic lakes in the Pyrenees. The concentrations of denitrifying genes determined by quantitative PCR were two orders of magnitude higher than those of ammonia-oxidizing genes. Both types of genes were significantly correlated, suggesting a potential tight coupling nitrification-denitrification in these biofilms that deserves further confirmation. The nifH gene was detected after nested PCR, and no signal was detected for the anammox-specific genes used. The taxonomic composition of denitrifying and nitrogen-fixing genes was further explored by cloning and sequencing. Interestingly, both microbial functional groups were richer and more genetically diverse than expected. The nirK gene, mostly related to Alphaproteobacteria (Bradyrhizobiaceae), dominated the denitrifying gene pool as expected for oxygen-exposed habitats, whereas Deltaproteobacteria (Geobacter like) and Cyanobacteria were the most abundant among nitrogen fixers. Overall, these results suggest an epilithic community more metabolically diverse than previously thought and with the potential to carry out an active role in the biogeochemical nitrogen cycling of high-altitude ecosystems. Measurements of activity rates should be however carried out to substantiate and further explore these findings. © 2014 Springer Science+Business Media New York.

Llegeix més

Mountain waters as witnesses of global pollution

Catalan J., Bartrons M., Camarero L., Grimalt J.O. (2013) Mountain waters as witnesses of global pollution. Living with Water: Targeting Quality in a Dynamic World. : 31-67.
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Doi: 10.1007/978-1-4614-3752-9_2

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Mountains lakes, streams, and rivers, collectively known as headwaters, are popularly seen as waters of the highest quality. However, human-related pollution has reached remote areas of the planet everywhere through atmospheric transportation. Mountain freshwater ecosystems are extreme environments for life and thus are particularly sensitive to some new stressors. This chapter begins by summarizing the main features of mountain freshwater ecosystems and then comments on the effects they have historically suffered. It focuses particularly on two environmental problems: (1) acidification and (2) contamination with persistent organic pollutants. These problems are at different stages of development and knowledge. Acidification mechanisms are well understood, and mitigation actions have been applied successfully. The pace of recovery and interaction with climate change are now focusing research interests. In contrast, the environmental problem of persistent organic pollutants in mountain waters has been unveiled only recently. Some initially unexpected findings, such as the increasing concentration of some pollutants with altitude, have stirred further investigations on bioaccumulation processes, which are summarized here. Actions against contamination of sites far from the pollution sources, such as mountains, require the development of international protocols. The fight against acidification constitutes a successful example of such actions, and efforts against other atmospheric pollutants are following suit. These large-scale actions require adequate long-term monitoring networks, models for interpretating the results, and sound understanding of the mechanisms that underlie the observed patterns. Research may focus on: (1) increasing understanding of biotransformation of organic pollutants in natural conditions; (2) better evaluation of toxicological effects on both organisms and ecosystems as a whole; and (3) the ways that climate change influences the transport, accumulation, and toxicity of pollutants, a subject that cuts across all freshwater quality issues. © 2013 Springer Science+Business Media New York. All rights are reserved.

Llegeix més

Global change revealed by palaeolimnological records from remote lakes: A review

Catalan J., Pla-Rabes S., Wolfe A.P., Smol J.P., Ruhland K.M., Anderson N.J., Kopacek J., Stuchlik E., Schmidt R., Koinig K.A., Camarero L., Flower R.J., Heiri O., Kamenik C., Korhola A., Leavitt P.R., Psenner R., Renberg I. (2013) Global change revealed by palaeolimnological records from remote lakes: A review. Journal of Paleolimnology. 49: 513-535.
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Doi: 10.1007/s10933-013-9681-2

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Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship. © 2013 Springer Science+Business Media Dordrecht.

Llegeix més

Atmospheric phosphorus deposition may cause lakes to revert from phosphorus limitation back to nitrogen limitation

Camarero L., Catalan J. (2012) Atmospheric phosphorus deposition may cause lakes to revert from phosphorus limitation back to nitrogen limitation. Nature Communications. 3: 0-0.
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Doi: 10.1038/ncomms2125

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Recent findings indicate that increased atmospheric deposition of nitrogen of human origin has caused changes in the pattern of ecological nutrient limitation in lakes in the northern hemisphere. An increase in the nitrogen to phosphorus ratio, and hence a shift from pristine nitrogen limitation to human-induced phosphorus limitation of phytoplankton growth, seems to have been driven by deposition of atmospheric nitrogen. These findings challenge the classical paradigm of lake phytoplankton productivity being naturally limited by phosphorus availability. However, atmospheric phosphorus deposition may also be highly relevant. Here we show how dissolved inorganic nitrogen concentration has decreased in the Pyrenean lake district over recent decades, despite there being an increase in deposition of atmospheric nitrogen. This is related to an increased atmospheric phosphorus load in the lake water, as a result of higher atmospheric inputs. These changes are causing phytoplankton to revert from being phosphorus-limited to being nitrogen-limited. © 2012 Macmillan Publishers Limited. All rights reserved.

Llegeix més

Diatom-based reconstruction of the pelagic environment of Burg Lake (Pyrenees) during Late Glacial and Early Holocene: does it make sense to use a single proxy for reconstructing several environmental variables?.

  1. Rivera-Rondón CA, Catalan J (2012) Diatom-based reconstruction of the pelagic environment of Burg Lake (Pyrenees) during Late Glacial and Early Holocene: does it make sense to use a single proxy for reconstructing several environmental variables?  12th International Paleolimnology Symposium. Glasgow, Scotland, August 21st – 24th. Poster.

The algal group indexes (IGA, IGA2) for assessing ecological status of lakes and reservoirs within the Water Framework Directive.

  1. Caraballo T, Pahissa J, de Hoyos C, Catalan J (2012) The algal group indexes (IGA, IGA2) for assessing ecological status of lakes and reservoirs within the Water Framework Directive. XIV Congreso de la Asociación  Ibérica de Limnología. Guimaraes (Portugal) , 2 a 6 de julio.

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