scholarly journals Coupled local facilitation and global hydrologic inhibition drive landscape geometry in a patterned peatland

2015 ◽  
Vol 12 (1) ◽  
pp. 1247-1277 ◽  
Author(s):  
S. Acharya ◽  
D. A. Kaplan ◽  
S. Casey ◽  
M. J. Cohen ◽  
J. W. Jawitz
Keyword(s):  
Model Performance ◽  
Characteristic Pattern ◽  
Positive Feedbacks ◽  
Self Organized ◽  
Lower Elevation ◽  
Sediment Redistribution ◽  
Anisotropic Soil ◽  
Patch Density ◽  
Density Patch ◽  
Fractal Landscapes

Abstract. Self-organized landscape patterning can arise in response to multiple processes. Discriminating among alternative patterning mechanisms, particularly where experimental manipulations are untenable, requires process-based models. Previous modeling studies have attributed patterning in the Everglades (Florida, USA) to sediment redistribution and anisotropic soil hydraulic properties. In this work, we tested an alternate theory, the self-organizing canal (SOC) hypothesis, by developing a cellular automata model that simulates pattern evolution via local positive feedbacks (i.e., facilitation) coupled with a global negative feedback based on hydrology. The model is forced by global hydroperiod that drives stochastic transitions between two patch types: ridge (higher elevation) and slough (lower elevation). We evaluated model performance using multiple criteria based on six statistical and geostatistical properties observed in reference portions of the Everglades landscape: patch density, patch anisotropy, semivariogram ranges, power-law scaling of ridge areas, perimeter area fractal dimension, and characteristic pattern wavelength. Model results showed strong statistical agreement with reference landscapes, but only when anisotropically acting local facilitation was coupled with hydrologic global feedback, for which several plausible mechanisms exist. Critically, the model correctly generated fractal landscapes that had no characteristic pattern wavelength, supporting the invocation of global rather than scale-specific negative feedbacks.

scholarly journals Coupled local facilitation and global hydrologic inhibition drive landscape geometry in a patterned peatland

2015 ◽  
Vol 19 (5) ◽  
pp. 2133-2144 ◽  
Author(s):  
S. Acharya ◽  
D. A. Kaplan ◽  
S. Casey ◽  
M. J. Cohen ◽  
J. W. Jawitz
Keyword(s):  
Model Performance ◽  
Characteristic Pattern ◽  
Positive Feedbacks ◽  
Self Organized ◽  
Lower Elevation ◽  
Sediment Redistribution ◽  
Anisotropic Soil ◽  
Patch Density ◽  
Density Patch ◽  
Fractal Landscapes

Abstract. Self-organized landscape patterning can arise in response to multiple processes. Discriminating among alternative patterning mechanisms, particularly where experimental manipulations are untenable, requires process-based models. Previous modeling studies have attributed patterning in the Everglades (Florida, USA) to sediment redistribution and anisotropic soil hydraulic properties. In this work, we tested an alternate theory, the self-organizing-canal (SOC) hypothesis, by developing a cellular automata model that simulates pattern evolution via local positive feedbacks (i.e., facilitation) coupled with a global negative feedback based on hydrology. The model is forced by global hydroperiod that drives stochastic transitions between two patch types: ridge (higher elevation) and slough (lower elevation). We evaluated model performance using multiple criteria based on six statistical and geostatistical properties observed in reference portions of the Everglades landscape: patch density, patch anisotropy, semivariogram ranges, power-law scaling of ridge areas, perimeter area fractal dimension, and characteristic pattern wavelength. Model results showed strong statistical agreement with reference landscapes, but only when anisotropically acting local facilitation was coupled with hydrologic global feedback, for which several plausible mechanisms exist. Critically, the model correctly generated fractal landscapes that had no characteristic pattern wavelength, supporting the invocation of global rather than scale-specific negative feedbacks.

scholarly journals On the spatial organization of the ridge slough patterned landscape

2015 ◽  
Vol 12 (3) ◽  
pp. 2975-3010 ◽  
Author(s):  
S. T. Casey ◽  
M. J. Cohen ◽  
S. Acharya ◽  
D. A. Kaplan ◽  
J. W. Jawitz
Keyword(s):  
Spatial Organization ◽  
Patch Size ◽  
Model Performance ◽  
Formation Mechanisms ◽  
Central Feature ◽  
Scale Free ◽  
Characteristic Wavelength ◽  
Dominant Feature ◽  
Using Data ◽  
Density Patch

Abstract. A century of hydrologic modification has altered the physical and biological drivers of landscape processes in the Everglades (southern Florida, USA). Restoring the ridge-slough patterned landscape, a dominant feature of the historical system, is a priority, but requires an understanding of pattern genesis mechanisms. Physical experiments to evaluate alternative pattern formation mechanisms are limited by the time scales of peat accumulation and loss, necessitating model-based comparisons, where support for a particular mechanism is based on model replication of extant patterning and trajectories of degradation. However, multiple mechanisms yield a central feature of ridge-slough patterning (patch elongation in the direction of historical flow), limiting the utility of that characteristic for discriminating among alternatives. Using data from vegetation maps we investigated the statistical features of ridge-slough spatial patterning (ridge density, patch perimeter, elongation, patch-area scaling, and spatial periodicity) to establish rigorous criteria for evaluating model performance, and to inform controls on pattern variation across the contemporary system. Mean water depth explained significant variation in ridge density, total perimeter, and length : width ratios, illustrating significant pattern response to existing hydrologic gradients. Two independent analyses (2-D periodograms and patch size distributions) provide strong evidence against regular patterning, with the landscape exhibiting neither a characteristic wavelength nor a characteristic patch size, both of which are expected under conditions that produce regular patterns. Rather, landscape properties suggest robust scale-free patterning, indicating genesis from the coupled effects of local facilitation and a global negative feedback operating uniformly at the landscape-scale. Critically, this challenges widespread invocation of meso-scale negative feedbacks for explaining ridge-slough pattern origins. These results help discern among genesis mechanisms and provide an improved statistical template against which to compare model outputs, as well as landscape trajectories with future restoration.

scholarly journals Landscape-Scale Relationships Between Abundance of Marbled Murrelets and Distribution of Nesting Habitat

The Condor ◽  
2002 ◽  
Vol 104 (2) ◽  
pp. 331-342 ◽  
Author(s):  
Martin G. Raphael ◽  
Diane Evans Mack ◽  
Brian A. Cooper
Keyword(s):  
Spatial Configuration ◽  
Nesting Habitat ◽  
Road Density ◽  
Forest Patch ◽  
Brachyramphus Marmoratus ◽  
Marbled Murrelet ◽  
Restoration Technique ◽  
Patch Density ◽  
Density Patch ◽  
Marbled Murrelets

AbstractWe used radar to count numbers of Marbled Murrelets (Brachyramphus marmoratus) flying inland within 10 river drainages on the Olympic Peninsula, Washington, during 1998–2000. We tested whether the numbers of murrelets entering drainages could be predicted from the amount and spatial configuration of low-elevation, late-seral forest (potential murrelet nesting habitat) within drainages. The maximal number of murrelet radar targets was positively correlated with the amount of late-seral forest in each of the three years sampled; this relationship persisted in 1999 and 2000 when controlling for drainage size. Murrelet radar counts were not correlated with the combined amounts of harvested, developed, and agricultural lands in any year. Numbers of murrelets increased as the amount of core area of late-seral forest and proximity of patches increased, and decreased with increasing amounts of edge of late-seral patches. Numbers were not correlated with the percent of late-seral forest, patch density, patch size, road density, or the overall diversity of all habitat types within landscapes. Neither the maximal nor the mean number of inbound Marbled Murrelets differed among years; the effect of year was small relative to the effect of habitat on murrelet numbers. Our results suggest that changes in the amount or distribution of nesting habitat should result in detectable changes in murrelet numbers at the scale of individual drainages. Thus, the amount and distribution of nesting habitat may play a role in the regulation of Marbled Murrelet populations, supporting the contention that providing nesting habitat is an effective conservation and restoration technique for this species.Relaciones a Escala del Paisaje entre la Abundancia de Brachyramphus marmoratus y la Distribución de Hábitat de NidificaciónResumen. Durante 1998–2000 utilizamos radares para contar el número de individuos de Brachyramphus marmoratus que volaron tierra adentro a lo largo de 10 cuencas de ríos que desaguan en la Península Olímpica, Washington, USA. Evaluamos si el número de individuos de B. marmoratus que entran por las cuencas puede ser predicho por la cantidad y configuración espacial de bosques de baja elevación que se encuentran en estadíos sucesionales tardíos (potencial hábitat de nidificación para estas aves) en cada cuenca. En cada uno de los tres años, el máximo número de individuos de B. marmoratus detectados estuvo positivamente correlacionado con la cantidad de bosque sucesional tardío; luego de controlar por el área de las cuencas esta relación persistió en 1999 y 2000. Durante todos los años, los conteos de B. marmoratus mediante radares no se correlacionaron con la cantidad combinada de tierras cosechadas, desarrolladas y agrícolas. El número de individuos de B. marmoratus aumentó con el área núcleo de bosque sucesional tardío y con el aumento de la proximidad entre parches, y decreció con el aumento de la cantidad de borde en los parches sucesionales tardíos. El número de aves no se correlacionó con el porcentaje de bosque sucesional tardío, densidad y área de parches, densidad de calles, ni diversidad total de todos los tipos de hábitats en el paisaje. Ni el número máximo ni el promedio de individuos de B. marmoratus que volaron en dirección tierra adentro diferió entre años; el efecto del año fue pequeño en comparación con el efecto del hábitat o del número de aves. Nuestros resultados sugieren que los cambios en la cantidad o distribución de hábitat para la nidificación deberían resultar en cambios detectables en el número de individuos de B. marmoratus a la escala individual de cada cuenca. Por lo tanto, la cantidad y distribución de hábitat para nidificación puede jugar un papel importante en la regulación de poblaciones de B. marmoratus, lo cual apoya la idea que proveer de hábitat para nidificación es una técnica efectiva para la conservación y restauración de esta especie.

scholarly journals Interdecadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures

2016 ◽  
Vol 62 (232) ◽  
pp. 310-322 ◽  
Author(s):  
TOM MATTHEWS ◽  
RICHARD HODGKINS
Keyword(s):  
Energy Balance ◽  
Surface Energy Balance ◽  
Model Performance ◽  
Changing Climate ◽  
Degree Day ◽  
Glacier Melt ◽  
Air Temperatures ◽  
Lower Elevation ◽  
Significant Downward Trend ◽  
Study Sites

ABSTRACTThe skill of degree-day glacier melt models is highly dependent on the choice of degree-day factor (DDF), which is often assumed to remain constant in time. Here we explore the validity of this assumption in a changing climate for two locations on Vestari Hagafellsjökull (1979–2012) using a surface energy-balance (SEB) approach that isolates the effect of changes in the prevailing weather on the DDF. At lower elevation, we observe stable DDF during the period of study; however, at higher elevation, DDF is noted to be more variable and a statistically-significant downward trend is observed. This is found to result from an inappropriate threshold air temperature (Tcrit) from which to initiate the positive-degree-day sum, and is removed by setting Tcrit to −1.83°C, rather than the usual value of 0°C used in degree-day melt models. The stationarity of DDF once Tcrit is adjusted contradicts previous research and lends support to the use of constant DDF for projecting future glacier melt. Optimizing Tcrit also improves the skill of melt simulations at our study sites. This research thus highlights the importance of Tcrit for both melt model performance and the evaluation of DDF stationarity in a changing climate.

scholarly journals Hydrologic controls on aperiodic spatial organization of the ridge–slough patterned landscape

2016 ◽  
Vol 20 (11) ◽  
pp. 4457-4467 ◽  
Author(s):  
Stephen T. Casey ◽  
Matthew J. Cohen ◽  
Subodh Acharya ◽  
David A. Kaplan ◽  
James W. Jawitz
Keyword(s):  
Spatial Organization ◽  
Patch Size ◽  
Model Performance ◽  
Formation Mechanisms ◽  
Central Feature ◽  
Size Distributions ◽  
Scale Free ◽  
Characteristic Wavelength ◽  
Dominant Feature ◽  
Density Patch

Abstract. A century of hydrologic modification has altered the physical and biological drivers of landscape processes in the Everglades (Florida, USA). Restoring the ridge–slough patterned landscape, a dominant feature of the historical system, is a priority but requires an understanding of pattern genesis and degradation mechanisms. Physical experiments to evaluate alternative pattern formation mechanisms are limited by the long timescales of peat accumulation and loss, necessitating model-based comparisons, where support for a particular mechanism is based on model replication of extant patterning and trajectories of degradation. However, multiple mechanisms yield a central feature of ridge–slough patterning (patch elongation in the direction of historical flow), limiting the utility of that characteristic for discriminating among alternatives. Using data from vegetation maps, we investigated the statistical features of ridge–slough spatial patterning (ridge density, patch perimeter, elongation, patch size distributions, and spatial periodicity) to establish more rigorous criteria for evaluating model performance and to inform controls on pattern variation across the contemporary system. Mean water depth explained significant variation in ridge density, total perimeter, and length : width ratios, illustrating an important pattern response to existing hydrologic gradients. Two independent analyses (2-D periodograms and patch size distributions) provide strong evidence against regular patterning, with the landscape exhibiting neither a characteristic wavelength nor a characteristic patch size, both of which are expected under conditions that produce regular patterns. Rather, landscape properties suggest robust scale-free patterning, indicating genesis from the coupled effects of local facilitation and a global negative feedback operating uniformly at the landscape scale. Critically, this challenges widespread invocation of scale-dependent negative feedbacks for explaining ridge–slough pattern origins. These results help discern among genesis mechanisms and provide an improved statistical description of the landscape that can be used to compare among model outputs, as well as to assess the success of future restoration projects.

THE PHYSICS OF BURNING PLASMAS IN TOROIDAL MAGNETIC FIELD DEVICES

2008 ◽  
Vol 23 (08) ◽  
pp. 1165-1172 ◽  
Author(s):  
FULVIO ZONCA
Keyword(s):  
Transport Processes ◽  
Collective Effects ◽  
Energetic Ions ◽  
Positive Feedbacks ◽  
Self Organized ◽  
Magnetically Confined ◽  
Long Time ◽  
Simulation And Experiment ◽  
Burning Plasmas ◽  
Fast Ion

Some of the crucial physics aspects of burning plasmas magnetically confined in toroidal systems are presented from the viewpoint of nonlinear dynamics. Most of the discussions specifically refer to tokamaks, but they can be readily extended to other toroidal confinement devices. Particular emphasis is devoted to fluctuation induced transport processes of mega electron volts energetic ions and charged fusion products as well as to energy and particle transports of the thermal plasma. Long time scale behaviors due to the interplay of fast ion induced collective effects and plasma turbulence are addressed in the framework of burning plasmas as complex self-organized systems. The crucial roles of mutual positive feedbacks between theory, numerical simulation and experiment are shown to be the necessary premise for reliable extrapolations from present day laboratory to burning plasmas. Examples of the broader applications of fundamental problems to other fields of plasma physics and beyond are also given.

Problem behavior in autism spectrum disorders: A paradigmatic self-organized perspective of network structures

2019 ◽  
Vol 42 ◽  
Author(s):  
Lucio Tonello ◽  
Luca Giacobbi ◽  
Alberto Pettenon ◽  
Alessandro Scuotto ◽  
Massimo Cocchi ◽  
...  
Keyword(s):  
Autism Spectrum Disorder ◽  
Problem Behaviors ◽  
Autism Spectrum ◽  
The Self ◽  
Network Structures ◽  
Self Organized ◽  
Critical Equilibrium ◽  
Self Organized Criticality ◽  
Acute Agitation ◽  
Spectrum Disorders

AbstractAutism spectrum disorder (ASD) subjects can present temporary behaviors of acute agitation and aggressiveness, named problem behaviors. They have been shown to be consistent with the self-organized criticality (SOC), a model wherein occasionally occurring “catastrophic events” are necessary in order to maintain a self-organized “critical equilibrium.” The SOC can represent the psychopathology network structures and additionally suggests that they can be considered as self-organized systems.

Predictors of Purchasing a Hearing Aid After an Evaluation Period: A Prospective Study in Dutch Older Hearing Aid Candidates

2019 ◽  
Vol 28 (3S) ◽  
pp. 802-805 ◽  
Author(s):  
Marieke Pronk ◽  
Janine F. J. Meijerink ◽  
Sophia E. Kramer ◽  
Martijn W. Heymans ◽  
Jana Besser
Keyword(s):  
Help Seeking ◽  
Hearing Aid ◽  
Model Performance ◽  
Area Under The Curve ◽  
Secondary Data ◽  
Support Program ◽  
Evaluation Period ◽  
A Prospective Study ◽  
Study Participants ◽  
Baseline Covariates

Purpose The current study aimed to identify factors that distinguish between older (50+ years) hearing aid (HA) candidates who do and do not purchase HAs after having gone through an HA evaluation period (HAEP). Method Secondary data analysis of the SUpport PRogram trial was performed ( n = 267 older, 1st-time HA candidates). All SUpport PRogram participants started an HAEP shortly after study enrollment. Decision to purchase an HA by the end of the HAEP was the outcome of interest of the current study. Participants' baseline covariates (22 in total) were included as candidate predictors. Multivariable logistic regression modeling (backward selection and reclassification tables) was used. Results Of all candidate predictors, only pure-tone average (average of 1, 2, and 4 kHz) hearing loss emerged as a significant predictor (odds ratio = 1.03, 95% confidence interval [1.03, 1.17]). Model performance was weak (Nagelkerke R 2 = .04, area under the curve = 0.61). Conclusions These data suggest that, once HA candidates have decided to enter an HAEP, factors measured early in the help-seeking journey do not predict well who will and will not purchase an HA. Instead, factors that act during the HAEP may hold this predictive value. This should be examined.

Constructing and Deconstructing Concepts

2016 ◽  
Vol 63 (5) ◽  
pp. 249-262 ◽  
Author(s):  
Charles A. Doan ◽  
Ronaldo Vigo
Keyword(s):  
Information Theory ◽  
Model Performance ◽  
Unsupervised Classification ◽  
Family Resemblance ◽  
Category Membership ◽  
Formal Models ◽  
Human Beings ◽  
One Dimensional ◽  
Relational Patterns ◽  
Optimal Classification

Abstract. Several empirical investigations have explored whether observers prefer to sort sets of multidimensional stimuli into groups by employing one-dimensional or family-resemblance strategies. Although one-dimensional sorting strategies have been the prevalent finding for these unsupervised classification paradigms, several researchers have provided evidence that the choice of strategy may depend on the particular demands of the task. To account for this disparity, we propose that observers extract relational patterns from stimulus sets that facilitate the development of optimal classification strategies for relegating category membership. We conducted a novel constrained categorization experiment to empirically test this hypothesis by instructing participants to either add or remove objects from presented categorical stimuli. We employed generalized representational information theory (GRIT; Vigo, 2011b , 2013a , 2014 ) and its associated formal models to predict and explain how human beings chose to modify these categorical stimuli. Additionally, we compared model performance to predictions made by a leading prototypicality measure in the literature.

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