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Multiple Scales (multiple + scale)
Selected AbstractsAn Introduction to Simulation and Visualization of Biological Systems at Multiple Scales: A Summer Training Program for Interdisciplinary ResearchBIOTECHNOLOGY PROGRESS, Issue 1 2006Rajan Munshi Advances in biomedical research require a new generation of researchers having a strong background in both the life and physical sciences and a knowledge of computational, mathematical, and engineering tools for tackling biological problems. The NIH-NSF Bioengineering and Bioinformatics Summer Institute at the University of Pittsburgh (BBSI @ Pitt;www.ccbb.pitt.edu/bbsi) is a multi-institutional 10-week summer program hosted by the University of Pittsburgh, Duquesne University, the Pittsburgh Supercomputing Center, and Carnegie Mellon University, and is one of nine Institutes throughout the nation currently participating in the NIH-NSF program. Each BBSI focuses on a different area; the BBSI @ Pitt, entitled "Simulation and Computer Visualization of Biological Systems at Multiple Scales", focuses on computational and mathematical approaches to understanding the complex machinery of molecular-to-cellular systems at three levels, namely, molecular, subcellular (microphysiological), and cellular. We present here an overview of the BBSI@Pitt, the objectives and focus of the program, and a description of the didactic training activities that distinguish it from other traditional summer research programs. Furthermore, we also report several challenges that have been identified in implementing such an interdisciplinary program that brings together students from diverse academic programs for a limited period of time. These challenges notwithstanding, presenting an integrative view of molecular-to-system analytical models has introduced these students to the field of computational biology and has allowed them to make an informed decision regarding their future career prospects. [source] Grid services for earthquake scienceCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6-7 2002Geoffrey Fox Abstract We describe an information system architecture for the ACES (Asia,Pacific Cooperation for Earthquake Simulation) community. It addresses several key features of the field,simulations at multiple scales that need to be coupled together; real-time and archival observational data, which needs to be analyzed for patterns and linked to the simulations; a variety of important algorithms including partial differential equation solvers, particle dynamics, signal processing and data analysis; a natural three-dimensional space (plus time) setting for both visualization and observations; the linkage of field to real-time events both as an aid to crisis management and to scientific discovery. We also address the need to support education and research for a field whose computational sophistication is rapidly increasing and spans a broad range. The information system assumes that all significant data is defined by an XML layer which could be virtual, but whose existence ensures that all data is object-based and can be accessed and searched in this form. The various capabilities needed by ACES are defined as grid services, which are conformant with emerging standards and implemented with different levels of fidelity and performance appropriate to the application. Grid Services can be composed in a hierarchical fashion to address complex problems. The real-time needs of the field are addressed by high-performance implementation of data transfer and simulation services. Further, the environment is linked to real-time collaboration to support interactions between scientists in geographically distant locations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multi-scale system reliability analysis of lifeline networks under earthquake hazardsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2010Junho Song Abstract Recent earthquake events evidenced that damage of structural components in a lifeline network may cause prolonged disruption of lifeline services, which eventually results in significant socio-economic losses in the affected area. Despite recent advances in network reliability analysis, the complexity of the problem and various uncertainties still make it a challenging task to evaluate the post-hazard performance and connectivity of lifeline networks efficiently and accurately. In order to overcome such challenges and take advantage of merits of multi-scale analysis, this paper develops a multi-scale system reliability analysis method by integrating a network decomposition approach with the matrix-based system reliability (MSR) method. In addition to facilitating system reliability analysis of large-size networks, the multi-scale approach enables optimizing the level of computational effort on subsystems; identifying the relative importance of components and subsystems at multiple scales; and providing a collaborative risk management framework. The MSR method is uniformly applied for system reliability analyses at both the lower-scale (for link failure) and the higher-scale (for system connectivity) to obtain the probability of general system events, various conditional probabilities, component importance measures, statistical correlation between subsystem failures and parameter sensitivities. The proposed multi-scale analysis method is demonstrated by its application to a gas distribution network in Shelby County of Tennessee. A parametric study is performed to determine the number of segments during the lower-scale MSR analysis of each pipeline based on the strength of the spatial correlation of seismic intensity. It is shown that the spatial correlation should be considered at both scales for accurate reliability evaluation. The proposed multi-scale analysis approach provides an effective framework of risk assessment and decision support for lifeline networks under earthquake hazards. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of landscape composition and substrate availability on saproxylic beetles in boreal forests: a study using experimental logs for monitoring assemblagesECOGRAPHY, Issue 2 2006Heloise Gibb Intensive forestry practises in the Swedish landscape have led to the loss and fragmentation of stable old-growth habitats. We investigated relationships between landscape composition at multiple scales and the composition of saproxylic beetle assemblages in nine clear-cut, mature managed and old-growth spruce-dominated forest stands in the central boreal zone of Sweden. We set out fresh spruce and birch logs and created spruce snags in 2001,2002 to experimentally test the effects of coarse woody debris (CWD) type and forest management on the composition of early and late successional, and red-listed saproxylic beetle assemblages. We examined effects of CWD availability at 100 m, and landscape composition at 1 and 10 km on saproxylic beetle abundances. Additionally, we tested whether assemblage similarity decreased with increasing distance between sites. We collected beetles from the experimental logs using eclector and window traps in four periods during 2003. CWD was measured and landscape composition data was obtained from maps of remotely sensed data. The composition of saproxylic beetles differed among different CWD substrates and between clear-cuts and the older stand types, however differences between mature managed and old-growth forests were significant only for red-listed species. Assemblage similarities for red-listed species on clear-cuts were more different at greater distances apart, indicating that they have more localised distributions. CWD availability within 100 m of the study sites was rarely important in determining the abundance of species, suggesting that early successional saproxylic beetles can disperse further than this distance. At a larger scale, a large area of suitable stand types within both 1 and 10 km resulted in greater abundances in the study sites for several common and habitat-specific species. The availability of suitable habitat at scales of 1,10 km is thus likely to be important in the survival of many saproxylic species in forestry-fragmented areas. [source] An integrative approach to understanding microbial diversity: from intracellular mechanisms to community structureECOLOGY LETTERS, Issue 9 2010Ivana Gudelj Ecology Letters (2010) 13: 1073,1084 Abstract Trade-offs have been put forward as essential to the generation and maintenance of diversity. However, variation in trade-offs is often determined at the molecular level, outside the scope of conventional ecological inquiry. In this study, we propose that understanding the intracellular basis for trade-offs in microbial systems can aid in predicting and interpreting patterns of diversity. First, we show how laboratory experiments and mathematical models have unveiled the hidden intracellular mechanisms underlying trade-offs key to microbial diversity: (i) metabolic and regulatory trade-offs in bacteria and yeast; (ii) life-history trade-offs in bacterial viruses. Next, we examine recent studies of marine microbes that have taken steps toward reconciling the molecular and the ecological views of trade-offs, despite the challenges in doing so in natural settings. Finally, we suggest avenues for research where mathematical modelling, experiments and studies of natural microbial communities provide a unique opportunity to integrate studies of diversity across multiple scales. [source] Scales of association: hierarchical linear models and the measurement of ecological systemsECOLOGY LETTERS, Issue 6 2007Sean M. McMahon Abstract A fundamental challenge to understanding patterns in ecological systems lies in employing methods that can analyse, test and draw inference from measured associations between variables across scales. Hierarchical linear models (HLM) use advanced estimation algorithms to measure regression relationships and variance,covariance parameters in hierarchically structured data. Although hierarchical models have occasionally been used in the analysis of ecological data, their full potential to describe scales of association, diagnose variance explained, and to partition uncertainty has not been employed. In this paper we argue that the use of the HLM framework can enable significantly improved inference about ecological processes across levels of organization. After briefly describing the principals behind HLM, we give two examples that demonstrate a protocol for building hierarchical models and answering questions about the relationships between variables at multiple scales. The first example employs maximum likelihood methods to construct a two-level linear model predicting herbivore damage to a perennial plant at the individual- and patch-scale; the second example uses Bayesian estimation techniques to develop a three-level logistic model of plant flowering probability across individual plants, microsites and populations. HLM model development and diagnostics illustrate the importance of incorporating scale when modelling associations in ecological systems and offer a sophisticated yet accessible method for studies of populations, communities and ecosystems. We suggest that a greater coupling of hierarchical study designs and hierarchical analysis will yield significant insights on how ecological processes operate across scales. [source] Dispersal, spatial scale, and species diversity in a hierarchically structured experimental landscapeECOLOGY LETTERS, Issue 5 2005Marc W. Cadotte Abstract Although there has been growing interest in the effect of dispersal on species diversity, much remains unknown about how dispersal occurring at multiple scales influences diversity. We used an experimental microbial landscape to determine whether dispersal occurring at two different scales , among local communities and among metacommunities , affects diversity differently. At the local scale, dispersal initially had a positive effect and subsequently a neutral effect on diversity, whereas at the metacommunity and landscape scales, dispersal showed a consistently negative effect. The timing in which dispersal affected beta diversity also differed sharply between local communities and metacommunities. These patterns were explained by scale- and time-dependent effects of dispersal in allowing spread of species and in removing spatial refuges from predators. Our results suggest that the relative contribution of opposing mechanisms by which dispersal affects diversity changes considerably over time and space in hierarchical landscapes in which dispersal occurs at multiple scales. [source] The metacommunity concept: a framework for multi-scale community ecologyECOLOGY LETTERS, Issue 7 2004M. A. Leibold Abstract The metacommunity concept is an important way to think about linkages between different spatial scales in ecology. Here we review current understanding about this concept. We first investigate issues related to its definition as a set of local communities that are linked by dispersal of multiple potentially interacting species. We then identify four paradigms for metacommunities: the patch-dynamic view, the species-sorting view, the mass effects view and the neutral view, that each emphasizes different processes of potential importance in metacommunities. These have somewhat distinct intellectual histories and we discuss elements related to their potential future synthesis. We then use this framework to discuss why the concept is useful in modifying existing ecological thinking and illustrate this with a number of both theoretical and empirical examples. As ecologists strive to understand increasingly complex mechanisms and strive to work across multiple scales of spatio-temporal organization, concepts like the metacommunity can provide important insights that frequently contrast with those that would be obtained with more conventional approaches based on local communities alone. [source] Uses and abuses of fractal methodology in ecologyECOLOGY LETTERS, Issue 3 2004J. M. Halley Abstract Fractals have found widespread application in a range of scientific fields, including ecology. This rapid growth has produced substantial new insights, but has also spawned confusion and a host of methodological problems. In this paper, we review the value of fractal methods, in particular for applications to spatial ecology, and outline potential pitfalls. Methods for measuring fractals in nature and generating fractal patterns for use in modelling are surveyed. We stress the limitations and the strengths of fractal models. Strictly speaking, no ecological pattern can be truly fractal, but fractal methods may nonetheless provide the most efficient tool available for describing and predicting ecological patterns at multiple scales. [source] Interplay of actors, scales, frameworks and regimes in the governance of biodiversityENVIRONMENTAL POLICY AND GOVERNANCE, Issue 3 2009Jouni Paavola Abstract This article examines the key contributions of the political science and systems theory based literatures on environmental governance, and uses them to analyse the governance of biodiversity in Europe. The article suggests that the key insights of the two bodies of literature are a distinction between governance frameworks and regimes on one hand, and the importance of multifaceted and multiple scales on the other. These key insights draw attention to horizontal and vertical forms of interplay. The article suggests that interplay, both between actors and levels and between frameworks and regimes, is ubiquitous and ambivalent: it can either foster or hinder environmental governance. The article illustrates this discussion in the context of governance of biodiversity in Europe, highlighting how vertical and horizontal interplay between the governance framework for biodiversity and the broader institutional setting or regime have characterized the implementation of the Habitats Directive, both complicating and fostering the governance of biodiversity in Europe. Copyright © 2009 John Wiley & Sons, Ltd and ERP Environment. [source] Ecological research in the office of research and development at the U.S. Environmental Protection Agency: An overview of new directions,,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000Rick A. Linthurst Abstract In virtually every major environmental act, Congress has required that the U.S. Environmental Protection Agency (U.S. EPA) ensure not only that the air be safe to breathe, the water safe to drink, and the food supply free of contamination, but also that the environment be protected. In response, the U.S. EPA's Office of Research and Development (ORD) has established research to improve ecosystem risk assessment and management, identifying it as one of the highest priority research areas for investment over the next 10 years. The research is intended to provide environmental managers with new tools and flexible guidance that reflect a holistic environmental management perspective of science and that can be applied both to common and unique problems. In keeping with its responsibility to provide the U.S. EPA with science that supports a dynamic changing regulatory agenda, the ORD has set the goal of its Ecological Research Program to "provide the scientific understanding required to measure, model, maintain and/or restore, at multiple scales, the integrity and sustainability of ecosystems now, and in the future." In the context of this program, ecological integrity is defined in relative terms as the maintenance of ecosystem structure and function characteristic of a reference condition deemed appropriate for its use by society, and sustainability is defined as the ability of an ecosystem to maintain relative ecological integrity into the future. Therefore, the research program will emphasize relative risk and consider the impact of multiple stressors, at multiple scales and at multiple levels of biological organization. The program will also shift from chemical to biological and physical stressors to a far greater extent than in the past. The purpose of this paper is to provide an introduction to the U.S. EPA's changing ecological research program. [source] Computational physiology and the physiome projectEXPERIMENTAL PHYSIOLOGY, Issue 1 2004Edmund J. Crampin Bioengineering analyses of physiological systems use the computational solution of physical conservation laws on anatomically detailed geometric models to understand the physiological function of intact organs in terms of the properties and behaviour of the cells and tissues within the organ. By linking behaviour in a quantitative, mathematically defined sense across multiple scales of biological organization , from proteins to cells, tissues, organs and organ systems , these methods have the potential to link patient-specific knowledge at the two ends of these spatial scales. A genetic profile linked to cardiac ion channel mutations, for example, can be interpreted in relation to body surface ECG measurements via a mathematical model of the heart and torso, which includes the spatial distribution of cardiac ion channels throughout the myocardium and the individual kinetics for each of the approximately 50 types of ion channel, exchanger or pump known to be present in the heart. Similarly, linking molecular defects such as mutations of chloride ion channels in lung epithelial cells to the integrated function of the intact lung requires models that include the detailed anatomy of the lungs, the physics of air flow, blood flow and gas exchange, together with the large deformation mechanics of breathing. Organizing this large body of knowledge into a coherent framework for modelling requires the development of ontologies, markup languages for encoding models, and web-accessible distributed databases. In this article we review the state of the field at all the relevant levels, and the tools that are being developed to tackle such complexity. Integrative physiology is central to the interpretation of genomic and proteomic data, and is becoming a highly quantitative, computer-intensive discipline. [source] Riverine landscapes: taking landscape ecology into the waterFRESHWATER BIOLOGY, Issue 4 2002JOHN A. WIENS 1.,Landscape ecology deals with the influence of spatial pattern on ecological processes. It considers the ecological consequences of where things are located in space, where they are relative to other things, and how these relationships and their consequences are contingent on the characteristics of the surrounding landscape mosaic at multiple scales in time and space. Traditionally, landscape ecologists have focused their attention on terrestrial ecosystems, and rivers and streams have been considered either as elements of landscape mosaics or as units that are linked to the terrestrial landscape by flows across boundaries or ecotones. Less often, the heterogeneity that exists within a river or stream has been viewed as a `riverscape' in its own right. 2.,Landscape ecology can be unified about six central themes: (1) patches differ in quality (2) patch boundaries affect flows, (3) patch context matters, (4) connectivity is critical, (5) organisms are important, and (6) the importance of scale. Although riverine systems differ from terrestrial systems by virtue of the strong physical force of hydrology and the inherent connectivity provided by water flow, all of these themes apply equally to aquatic and terrestrial ecosystems, and to the linkages between the two. 3.,Landscape ecology therefore has important insights to offer to the study of riverine ecosystems, but these systems may also provide excellent opportunities for developing and testing landscape ecological theory. The principles and approaches of landscape ecology should be extended to include freshwater systems; it is time to take the `land' out of landscape ecology. [source] ,GLOCAL' MOVEMENTS: PLACE STRUGGLES AND TRANSNATIONAL ORGANIZING BY INFORMAL WORKERSGEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 2 2009Ilda Lindell ABSTRACT. This paper investigates the scalar practices of collectively organized informal workers and the political implications of such practices. It illustrates how the studied group organizes across scales , hence, a ,glocal movement', and stresses the importance of an analysis that integrates these multiple scales of collective organizing, as they may have a bearing on each other. In so doing, it contests a common tendency to analytically privilege one or other scale of resistance and agency. In particular, I argue that networking across scales may be of significance for local struggles and thus play a role in local politics. The transnational activities of the studied group assist it in challenging local power relations and dominant place projects that repress informal livelihood activities. This paper comprises a conceptual discussion of notions of scale, of conceptions of the spatialities and scales of resistance as well as of place, followed by an empirical illustration that refers to an association of informal vendors in Maputo, Mozambique, and its international connections. The analysis is based on interviews with vendors, leaders of the association and with the international partners of the association. [source] Broad-scale environmental response and niche conservatism in lacustrine diatom communitiesGLOBAL ECOLOGY, Issue 5 2010Joseph R. Bennett ABSTRACT Aim, (1) To resolve theoretical debates regarding the role of environment versus dispersal limitation, the conservatism of niches across distances and the prevalence of environmental specialists in diatom communities. (2) To provide guidance on the use of diatom communities and other microbial analogues to analyse ecological response to environmental change. Location, Eight hundred and ninety-one lakes in five regional datasets from north-western Europe and four regional datasets from north-eastern North America. Methods, Lacustrine diatom communities were analysed at three scales: inter-continental, intra-continental and regional. Nested partial redundancy analyses (RDAs) were used to determine spatial versus environmental components of community variation. Weighted-averaging (WA) regression and calibration, as well as logistic and quadratic regressions, were used to detect niche conservatism and the prevalence of environmental specialists. Results, Community patterns indicate that dispersal limitation acts predominantly at the inter-continental scale, while at the regional (less than c. 1,000,000 km2) scale, a single environmental variable (pH) explains more than five times the community variation as spatial (dispersal-related) variables. In addition, pH niche components appear to be conserved at the inter-continental scale, and environmental specialization does not impose relative rarity, as specialists apparently readily disperse to suitable environments. Main conclusions, Analysis at multiple scales is clearly important in determining the influences of community variation. For diatom communities, dispersal limitation acts most strongly at the broadest scales, giving way to environment at the scales considered by most analyses. The availability of a wide variety of propagules with consistent niches across regions indicates that diatom communities reflect the succession of taxa according to local environmental conditions, rather than disequilibrium with the environment or adaptation of local populations. While multi-scale analyses must be undertaken for other groups to resolve debates over community drivers and determine appropriate scales for prediction, for diatoms (and probably other microbial communities), responses to environmental change can be inferred using analogue datasets from large geographic areas. [source] Enabling regional management in a changing climate through Bayesian meta-analysis of a large-scale disturbanceGLOBAL ECOLOGY, Issue 3 2010M Aaron MacNeil ABSTRACT Aim, Quantifying and predicting change in large ecosystems is an important research objective for applied ecologists as human disturbance effects become increasingly evident at regional and global scales. However, studies used to make inferences about large-scale change are frequently of uneven quality and few in number, having been undertaken to study local, rather than global, change. Our aim is to improve the quality of inferences that can be made in meta-analyses of large-scale disturbance by integrating studies of varying quality in a unified modelling framework that is informative for both local and regional management. Innovation, Here we improve conventionally structured meta-analysis methods by including imputation of unknown study variances and the use of Bayesian factor potentials. The approach is a coherent framework for integrating data of varying quality across multiple studies while facilitating belief statements about the uncertainty in parameter estimates and the probable outcome of future events. The approach is applied to a regional meta-analysis of the effects of loss of coral cover on species richness and the abundance of coral-dependent fishes in the western Indian Ocean (WIO) before and after a mass bleaching event in 1998. Main conclusions, Our Bayesian approach to meta-analysis provided greater precision of parameter estimates than conventional weighted linear regression meta-analytical techniques, allowing us to integrate all available data from 66 available study locations in the WIO across multiple scales. The approach thereby: (1) estimated uncertainty in site-level estimates of change, (2) provided a regional estimate for future change at any given site in the WIO, and (3) provided a probabilistic belief framework for future management of reef resources at both local and regional scales. [source] Upgrading, uneven development, and jobs in the North American apparel industryGLOBAL NETWORKS, Issue 2 2003Jennifer Bair In this article we examine the developmental consequences of globalization at multiple scales, using a commodity chains framework to investigate the case of the North American apparel industry. In the first section we outline the apparel commodity chain and offer a brief typology of its lead firms. In the second section we discuss the concept of industrial upgrading and describe several main export roles in the global apparel industry. In the third section we focus on the regional dynamics resulting from the North American Free Trade Agreement (NAFTA). We contrast the Mexican experience with that of countries in the Caribbean Basin to show the impact of distinct trade policies on export-oriented development. We argue that NAFTA is creating upgrading opportunities for some Mexican firms to move from the low value-added export-oriented assembly (or maquila) model to full-package production. In the fourth section we explore the unevenness of upgrading dynamics through a comparison of two blue jeans manufacturing clusters in the United States and Mexico: El Paso and Torreon. Our conclusions about upgrading and uneven development in the North American apparel industry emphasize the importance of local, national and regional institutional contexts in shaping inter-firm networks and their development impact. [source] Catchment processes and heterogeneity at multiple scales,benchmarking observations, conceptualization and predictionHYDROLOGICAL PROCESSES, Issue 16 2010D. Tetzlaff First page of article [source] Analysis of microstructure development in shearbands by energy relaxation of incremental stress potentials: Large-strain theory for standard dissipative solidsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2003Christian Miehe Abstract We propose a fundamentally new approach to the treatment of shearband localizations in strain softening elastic,plastic solids at finite strains based on energy minimization principles associated with microstructure developments. The point of departure is a general internal variable formulation that determines the finite inelastic response as a standard dissipative medium. Consistent with this type of inelasticity we consider an incremental variational formulation of the local constitutive response where a quasi-hyperelastic stress potential is obtained from a local constitutive minimization problem with respect to the internal variables. The existence of this variational formulation allows the definition of the material stability of an inelastic solid based on weak convexity conditions of the incremental stress potential in analogy to treatments of finite elasticity. Furthermore, localization phenomena are interpreted as microstructure developments on multiple scales associated with non-convex incremental stress potentials in analogy to elastic phase decomposition problems. These microstructures can be resolved by the relaxation of non-convex energy functionals based on a convexification of the stress potential. The relaxed problem provides a well-posed formulation for a mesh-objective analysis of localizations as close as possible to the non-convex original problem. Based on an approximated rank-one convexification of the incremental stress potential we develop a computational two-scale procedure for a mesh-objective treatment of localization problems at finite strains. It constitutes a local minimization problem for a relaxed incremental stress potential with just one scalar variable representing the intensity of the microshearing of a rank-one laminate aligned to the shear band. This problem is sufficiently robust with regard to applications to large-scale inhomogeneous deformation processes of elastic,plastic solids. The performance of the proposed energy relaxation method is demonstrated for a representative set of numerical simulations of straight and curved shear bands which report on the mesh independence of the results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Surmounting City Silences: Knowledge Creation and the Design of Urban Democracy in the Everyday EconomyINTERNATIONAL JOURNAL OF URBAN AND REGIONAL RESEARCH, Issue 1 2009NANCY ETTLINGER This essay presents segregation as a fundamental, longstanding and widespread problem that impedes democratic urban life and is intelligible from a critical geographic perspective. Ignorance is spatially produced by segregation at multiple scales so as to legitimize and perpetuate silence about problems among marginalized groups. This spatialized understanding explains inequality, problematizes and difference prompts an agenda that forefronts the creation of new social knowledges. The focus here is on the everyday economy as a crucial but commonly overlooked context for developing such knowledges. I re-present a theory of knowledge creation developed for the pursuit of commercial competitiveness and reconfigure it to mesh socio-political and economic goals. A central challenge is to change prevailing discourses by cultivating new practices that entail meaningful interaction among people otherwise segregated. Efficiency becomes a means to social as well as economic ends, as respect and trust grow from collaborative experience among people who might otherwise not interact. Résumé Ce travail présente la ségrégation comme un problème fondamental, persistant et généralisé qui handicape la vie urbaine démocratique et qui peut être appréhendé d'un point de vue critique géographique. L'ignorance est le résultat, sur le plan spatial, d'une ségrégation à plusieurs échelons aux fins de justifier et de perpétuer le silence sur les problèmes qui existent dans les groupes marginalisés. Cette appréhension spatiale explique l'inégalité, tandis que la problématisation de la différence conduit à mettre en évidence la création de nouveaux savoirs sociaux. L'intérêt porte ici sur l'économie du quotidien, considérée comme un contexte essentiel, quoique très souvent négligé, pour le développement de ces savoirs. L'auteur revisite une théorie de la création du savoir élaborée dans le but d'accroître la compétitivité commerciale, et la reconfigure pour qu'elle concorde avec des objectifs sociopolitiques et économiques. L'un des principaux défis consiste à changer la rhétorique dominante en cultivant de nouvelles pratiques qui supposent une interaction porteuse de sens entre des gens par ailleurs ségrégués. L'efficience devient un moyen à des fins sociales et économiques, le respect et la confiance se nourrissant de la collaboration vécue entre des personnes qui, autrement, n'auraient peut-être pas été en relation. [source] Prey dispersal rate affects prey species composition and trait diversity in response to multiple predators in metacommunitiesJOURNAL OF ANIMAL ECOLOGY, Issue 5 2010Jennifer G. Howeth Summary 1.,Recent studies indicate that large-scale spatial processes can alter local community structuring mechanisms to determine local and regional assemblages of predators and their prey. In metacommunities, this may occur when the functional diversity represented in the regional predator species pool interacts with the rate of prey dispersal among local communities to affect prey species diversity and trait composition at multiple scales. 2.,Here, we test for effects of prey dispersal rate and spatially and temporally heterogeneous predation from functionally dissimilar predators on prey structure in pond mesocosm metacommunities. An experimental metacommunity consisted of three pond mesocosm communities supporting two differentially size-selective invertebrate predators and their zooplankton prey. In each metacommunity, two communities maintained constant predation and supported either Gyrinus sp. (Coleoptera) or Notonecta ungulata (Hemiptera) predators generating a spatial prey refuge while the third community supported alternating predation from Gyrinus sp. and N. ungulata generating a temporal prey refuge. Mesocosm metacommunities were connected at either low (0·7% day,1) or high (10% day,1) planktonic prey dispersal. The diversity, composition and body size of zooplankton prey were measured at local and regional (metacommunity) scales. 3.,Metacommunities experiencing the low prey dispersal rate supported the greatest regional prey species diversity (H') and evenness (J'). Neither dispersal rate nor predation regime affected local prey diversity or evenness. The spatial prey refuge at low dispersal maintained the largest difference in species composition and body size diversity between communities under Gyrinus and Notonecta predation, suggesting that species sorting was operating at the low dispersal rate. There was no effect of dispersal rate on species diversity or body size distribution in the temporal prey refuge. 4.,The frequency distribution, but not the range, of prey body sizes within communities depended upon prey dispersal rate and predator identity. Taken together, these results demonstrate that prey dispersal rate can moderate the strength of predation to influence prey species diversity and the local frequency distribution of prey traits in metacommunities supporting ecologically different predators. [source] Interacting effects of management and environmental variability at multiple scales on invasive species distributionsJOURNAL OF APPLIED ECOLOGY, Issue 6 2009Jeffrey M. Diez Summary 1. The distribution and abundance of invasive species can be driven by both environmental variables and land management decisions. However, understanding these relationships can be complicated by interactions between management actions and environmental variability, and differences in scale among these variables. The resulting ,context-dependence' of management actions may be well-appreciated by ecologists and land managers, but can frustrate attempts to apply general management principles. 2. In this study, we quantify the effects of land management and environmental variability at different scales on the occurrence and abundance of Hieracium pilosella, a major agricultural weed in New Zealand. We used a hierarchical study design and analysis to capture relevant scales of variation in management actions and environmental heterogeneity, and test hypotheses about how these factors interact. 3. We show that fertilizing and grazing interact with environmental gradients at the scale of management application (farm paddocks) to influence the establishment and local abundance of H. pilosella. 4. We further show that H. pilosella's relationships with fine-scale abiotic and biotic factors are consistent with expected mechanisms driven by larger-scale management actions. Using data on occurrence and local abundance, we tease apart which factors are important to establishment and subsequent local spread. 5.Synthesis and applications. A major challenge for environmental scientists is to predict how invasive species may respond to ongoing landscape modifications and environmental change. This effort will require approaches to study design and analysis that can accommodate complexities such as interacting management and environmental variables at different scales. Management actions will be more likely to succeed when they explicitly account for variation in environmental context. [source] Effects of bird predation on arthropod abundance and tree growth across an elevational gradientJOURNAL OF AVIAN BIOLOGY, Issue 4 2010W. Scott Schwenk Considerable uncertainty surrounds the conditions under which birds can cause trophic cascades. In a three-year experiment, we studied the direct and indirect effects of insectivorous birds on arthropod abundance, herbivory, and growth of striped maple Acer pensylvanicum saplings in a northern hardwood forest of central New Hampshire, USA. We manipulated bird predation by erecting exclosures around saplings and directly manipulated herbivory by removing herbivores. We also examined how climate modifies these interactions by replicating the experiment at three locations along an elevational gradient. Effects of bird predation were variable. Overall, mean arthropod biomass was 20% greater on saplings within bird exclosures than on controls (p<0.05). The mean biomass of leaf-chewing herbivores, primarily Lepidoptera larvae, was 25% greater within exclosures but not statistically different from controls. To a lesser degree, mean herbivore damage to foliage within exclosures exceeded that of controls but differences were not significant. We also did not detect significant treatment effects on sapling shoot growth. The high understory vegetation density relative to bird abundance, and low rate of herbivory during the study (mean 5% leaf area removed, controls), may have limited the ability of birds to affect sapling growth. Climate effects operated at multiple scales, resulting in a complex interplay of interactions within the food web. Regional synchrony of climatic conditions resulted in annual fluctuations in herbivore abundance and tree growth that were shared across elevations. At the same time, local environmental variation resulted in site differences in the plant, herbivore, and bird communities. These patterns resulted in a mosaic of top,down strengths across time and space, suggesting an overall pattern of limited effects of birds on plant growth, possibly interspersed with hotspots of trophic cascades. [source] Plant dispersal across multiple scales: linking models and realityJOURNAL OF ECOLOGY, Issue 4 2008James M. Bullock No abstract is available for this article. [source] Species richness,standing crop relationship in stream bryophyte communities: patterns across multiple scalesJOURNAL OF ECOLOGY, Issue 1 2001Risto Virtanen Summary 1,We tested for a unimodal (,hump-backed') relationship between species richness and standing crop at various spatial scales in stream bryophyte communities. Bryophyte species and their biomasses were determined from 20 to 25 quadrats in eight river and six stream sites in northern Finland. 2,Regression analyses revealed a quadratic relationship between richness and biomass in only two of the river sites and a positive correlation in one other. A quadratic relationship was detected in three stream sites and richness increased linearly with biomass in another. 3,We also tested for the hump-shaped pattern across individual stream boulders, representing an elevational gradient from continuously submerged to permanently dry conditions, with an intermediate zone with fluctuating water level. 4,Species richness-standing crop relationship conformed to the hump-backed model only when samples from all three microhabitats were included in the analysis. A significant positive correlation occurred in the exposed low biomass end of the gradient which is characterized by semi-aquatic species, whereas the relationship tended to be negative in permanently submerged areas with high biomass of large canopy-forming species. Quadrats close to the water level had intermediate standing crop and highest species richness. 5,Species dominant at either end of the gradient appeared unable to monopolize space in the intermediate zone where disturbances (e.g. scouring by ice) detach mosses from the substratum, creating vacant gaps for colonization. The unimodal relationship between richness and biomass is likely to occur only in streams that contain large boulders protruding above the water line, thus providing scope for community diversification along very short vertical distances. [source] Generation and visualization of large-scale three-dimensional reconstructions from underwater robotic surveysJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2010Matthew Johnson-Roberson Robust, scalable simultaneous localization and mapping (SLAM) algorithms support the successful deployment of robots in real-world applications. In many cases these platforms deliver vast amounts of sensor data from large-scale, unstructured environments. These data may be difficult to interpret by end users without further processing and suitable visualization tools. We present a robust, automated system for large-scale three-dimensional (3D) reconstruction and visualization that takes stereo imagery from an autonomous underwater vehicle (AUV) and SLAM-based vehicle poses to deliver detailed 3D models of the seafloor in the form of textured polygonal meshes. Our system must cope with thousands of images, lighting conditions that create visual seams when texturing, and possible inconsistencies between stereo meshes arising from errors in calibration, triangulation, and navigation. Our approach breaks down the problem into manageable stages by first estimating local structure and then combining these estimates to recover a composite georeferenced structure using SLAM-based vehicle pose estimates. A texture-mapped surface at multiple scales is then generated that is interactively presented to the user through a visualization engine. We adapt established solutions when possible, with an emphasis on quickly delivering approximate yet visually consistent reconstructions on standard computing hardware. This allows scientists on a research cruise to use our system to design follow-up deployments of the AUV and complementary instruments. To date, this system has been tested on several research cruises in Australian waters and has been used to reliably generate and visualize reconstructions for more than 60 dives covering diverse habitats and representing hundreds of linear kilometers of survey. © 2009 Wiley Periodicals, Inc. [source] Spatial integration at multiple scales: rice markets in MadagascarAGRICULTURAL ECONOMICS, Issue 3 2009Christine Moser Market integration; Prices; Rice Abstract The dramatic increase in the price of rice and other commodities over the past year has generated new interest in how these markets work and how they can be improved. This article uses an exceptionally rich data set to test the extent to which markets in Madagascar are integrated across space at different scales of analysis and to explain some of the factors that limit spatial arbitrage and price equalization within a single country. We use rice price data across four quarters of 2000,2001 along with data on transportation costs and infrastructure availability for nearly 1,400 communes in Madagascar to examine the extent of market integration at three different spatial scales,subregional, regional, and national,and to determine whether non-integration is due to high transfer costs or lack of competition. The results indicate that markets are fairly well integrated at the subregional level and that factors such as high crime rates, remoteness, and lack of information are among the factors limiting competition. [source] A new perturbation solution for systems with strong quadratic and cubic nonlinearitiesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 6 2010Mehmet Pakdemirli Abstract The new perturbation algorithm combining the method of multiple scales (MS) and Lindstedt,Poincare techniques is applied to an equation with quadratic and cubic nonlinearities. Approximate analytical solutions are found using the classical MS method and the new method. Both solutions are contrasted with the direct numerical solutions of the original equation. For the case of strong nonlinearities, solutions of the new method are in good agreement with the numerical results, whereas the amplitude and frequency estimations of classical MS yield high errors. For strongly nonlinear systems, exact periods match well with the new technique while there are large discrepancies between the exact and classical MS periods. Copyright © 2009 John Wiley & Sons, Ltd. [source] Bodyscapes, Biology, and HeteronormativityAMERICAN ANTHROPOLOGIST, Issue 4 2009Pamela L. Geller ABSTRACT The term bodyscape encourages thinking about representation of bodies at multiple scales,from different bodies as they move through space to the microlandscape of individual bodily differences. A hegemonic bodyscape's representations tend to idealize and essentialize bodies' differences to reinforce normative ideas about a society's socioeconomic organization. But, a dominant bodyscape is never absolute. Bodyscapes that depart from or subvert hegemonic representations may simultaneously exist. In Western society, the biomedical bodyscape predominates in scientific understandings of bodily difference. Its representation of sex differences conveys heteronormative notions about gender and sexuality. Because the biomedical bodyscape frames studies of ancient bodies, investigators need recognize how their considerations of labor divisions, familial organization, and reproduction may situate modern (hetero)sexist representations deep within antiquity. To innovate analyses of socioeconomic relations, queer theory allows scholars to interrogate human nature. Doing so produces alternative bodyscapes that represent the diversity of past peoples' social and sexual lives. [Keywords: bodyscape, heteronormativity, queer theory, bioarchaeology, paleoanthropology] [source] Issues of scale and monitoring status and trends in biodiversityNEW DIRECTIONS FOR EVALUATION, Issue 122 2009Elizabeth T. Kennedy Designing a framework that can generate data to meet multiple audience objectives must consider interactions across levels and multiple scales of interest. One solution is to define targets using global criteria such that units are discrete. This aids identification of the types of data to collect in order to enable aggregation and reporting across relevant scales. By striving to standardize measurable targets and data requirements, we improve our ability to format monitoring information and tailor indicators for different reporting and decision-making purposes. We outline the application of a nested approach presently used by Conservation International and describe some of its advantages and limitations. © Wiley Periodicals, Inc. [source] | |||||||||||||||||||