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241.
M. Scheffer J. M. Baveco D. L. DeAngelis K. A. Rose E. H. van Nes 《Ecological modelling》1995,80(2-3)
Modelling populations on an individual-by-individual basis has proven to be a fruitful approach. Many complex patterns that are observed on the population level have been shown to arise from simple interactions between individuals. However, a major problem with these models is that the typically large number of individuals needed requires impractically large computation times. The common solution, reduction of the number of individuals in the model, can lead to loss of variation, irregular dynamics, and large sensitivity to the value of random generator seeds. As a solution to these problems, we propose to add an extra variable feature to each model individual, namely the number of real individuals it actually represents. This approach allows zooming from a real individual-by-individual model to a cohort representation or ultimately an all-animals-are-equal view without changing the model formulation. Therefore, the super-individual concept offers easy possibilities to check whether the observed behaviour is an artifact of following a limited number of individuals or of lumping individuals, and also to verify whether individual variability is indeed an essential ingredient for the observed behaviour. In addition the approach offers arbitrarily large computational advantages. As an example the super-individual approach is applied to a generic model of the dynamics of a size-distributed consumer cohort as well as to an elaborate applied simulation model of the recruitment of striped bass. 相似文献
242.
A variety of animals use olfactory appendages bearing arrays of chemosensory neurons to detect chemical signatures in the water or air around them. This study investigates how particular aspects of the design and behavior of such olfactory appendages on benthic aquatic animals affect the patterns of intercepted chemical signals in a turbulent odor plume. We use virtual olfactory `sensors' and `antennules' (arrays of sensors on olfactory appendages) to interrogate the concentration field from an experimental dataset of a scalar plume developing in a turbulent boundary layer. The aspects of the sensors that we vary are: (1) The spatial and temporal scales over which chemical signals arriving at the receptors of a sensor are averaged (e.g., by subsequent neural processing), and (2) the shape and orientation of a sensor with respect to ambient water flow. Our results indicate that changes in the spatial and temporal resolution of a sensor can dramatically alter its interception of the intermittency and variability of the scalar field in a plume. By comparing stationary antennules with those sweeping through the flow (as during antennule flicking by the spiny lobster, Panulirus argus), we show that flicking alters the frequency content of the scalar signal, and increases the likelihood that the antennule encounters peak events. Flicking also enables a long, slender (i.e., one-dimensional) antennule to intercept two-dimensional scalar patterns. 相似文献
243.
Overflows and leakage from aboveground storage tanks and pipelines carrying crude oil and petroleum products occur frequently. The spilled hydrocarbons pose environmental threats by contaminating the surrounding soil and the underlying ground water. Predicting the fate and transport of these chemicals is required for environmental risk assessment and for remedial measure design. The present paper discusses the formulation and application of the Oil Surface Flow Screening Model (OILSFSM) for predicting the surface flow of oil by taking into account infiltration and evaporation. Surface flow is simulated using a semi-analytical model based on the lubrication theory approximation of viscous flow. Infiltration is simulated using a version of the Green and Ampt infiltration model, which is modified to account for oil properties. Evaporation of volatile compounds is simulated using a compositional model that accounts for the changes in the fraction of each compound in the spilled oil. The coupling between surface flow, infiltration and evaporation is achieved by incorporating the infiltration and evaporation fluxes into the global continuity equation of the spilled oil. The model was verified against numerical models for infiltration and analytical models for surface flow. The verification study demonstrates the applicability of the model. 相似文献
244.
Cormenzana JL García-Gutiérrez M Missana T Junghanns A 《Journal of contaminant hydrology》2003,61(1-4):63-72
Effective diffusion coefficients (D(e)) are usually measured by means of "through-diffusion" experiments in which steady state is reached, and the "time-lag" methods are used to estimate the apparent diffusion coefficient (D(a)). For sorbing radionuclides (as caesium), the time needed to reach steady-state conditions is very large, and the precision in D(a) determinations is not satisfactory. In this paper, a method that allows determining simultaneously effective and apparent diffusion coefficients in compacted bentonite without reaching steady-state conditions is described. Basically, this method consists of an "in-diffusion" experiment in which the concentration profile in the bentonite sample is used to estimate D(a), and the temporal evolution of the solute concentration in the reservoir is used to estimate D(e). This method has several advantages over the typical "through-diffusion" experiments, in particular: (a) experiment duration is significantly shorter, (b) D(a) values are measured with greater precision and (c) it is not necessary to maintain a constant solute concentration in the reservoir. This new method has been used to estimate the effective and apparent diffusion coefficients for caesium in FEBEX bentonite and in order to validate it, the results have been compared with results previously obtained with standard methods. Experimental results have been satisfactorily modelled using a simple model of diffusion in porewater and the measured value of D(e)(Cs) is very similar to D(e)(HTO) in the same bentonite. There is no evidence of "surface diffusion" in FEBEX bentonite for caesium. 相似文献
245.
Visibility impairment from regional haze is a significant problem throughout the continental United States. A substantial portion of regional haze is produced by smoke from prescribed and wildland fires. Here we describe the integration of four simulation models, an array of GIS raster layers, and a set of algorithms for fire-danger calculations into a modeling framework for simulating regional-scale smoke dispersion. We focus on a representative fire season (2003) in the northwestern USA, on a 12 km domain, and track the simulated dispersion and concentration of PM2.5 over the course of the season. Simulated visibility reductions over national parks and wilderness areas are within the ranges of measured values at selected monitoring sites, although the magnitudes of peak events are underestimated because these include inputs other than fire. By linking the spatial and temporal patterns of haze-producing emissions to climatic variability, particularly synoptic weather patterns, and the stochastic nature of fire occurrence across the region, we can provide a robust method for estimating the quantity and distribution of fire-caused regional haze under climate-warming scenarios. 相似文献
246.
Walter W. Piegorsch 《Environmental and Ecological Statistics》1994,1(2):153-162
Hierarchical models are considered for estimating the probability of agreement between two outcomes or endpoints from an environmental
toxicity experiment. Emphasis is placed on generalized regression models, under which the prior mean is related to a linear
combination of explanatory variables via a monotone function. This function defines the scale over which the systematic effects
are modelled as additive. Specific illustration is provided for the logistic link function. The hierarchical model employs
a conjugate beta prior that leads to parametric empirical Bayes estimators of the individual agreement parameters. An example
from environmental carcinogenesis illustrates the methods, with motivation derived from estimation of the concordance between
two species carcinogenicity outcomes. Based on a large database of carcinogenicity studies, the inter-species concordance
is seen to be reasonably informative, i.e. in the range 67–84%. Stratification into pertinent potency-related sub-groups via
the logistic model is seen to improve concordance estimation: for environmental stimuli at the extremes of the potency spectrum,
concordance can reach well above 90%. 相似文献
247.
Hubert?ChansonEmail author Richard?Brown John?Ferris Ian?Ramsay Kevin?Warburton 《Environmental Fluid Mechanics》2005,5(6):553-575
In natural systems, mixing is driven by turbulence, but current knowledge is limited in estuarine zones where predictions
of contaminant dispersion are often inaccurate. A series of detailed field studies was conducted in a small sub-tropical creek
in eastern Australia. Hydrodynamic, physio-chemical and ecological measurements were conducted simultaneously to assess the
complexity of the estuarine zone, notably the interactions between turbulence and environment. The measurements were typically
performed at high frequency over a tidal cycle. The results provide an original data set to complement long-term monitoring
and a basis for a more detailed study of mixing in sub-tropical systems. Unlike many long-term observations, velocity and
water quality scalars were measured herein with sufficient spatial and temporal resolutions to determine quantities of interest
in the study of turbulence, while ecological indicators were sampled systematically and simultaneously. In particular the
results yielded contrasted outcomes, and the finding impacts on the selection process for key water quality indicators. 相似文献
248.
The Hamilton–Zuk hypothesis proposes that females prefer male secondary sexual traits because they are honest indicators of
parasite resistance. Despite the attention that this hypothesis has received, its role in sexual selection remains equivocal.
This study presents the first field test in guppies of two key predictions of the Hamilton–Zuk hypothesis: (1) that within
populations, the most highly ornamented males have the fewest parasites and (2) that among populations, males in high parasite
populations have the most conspicuous ornaments. Five hundred male guppies from 19 distinct populations in the Northern Range
of Trinidad were inspected for Gyrodactylus parasites and photographed. Eight measures of orange spot ornamentation were used to test the predictions: hue, saturation,
lightness, relative area, number, and area-weighted hue, saturation, and lightness. Parasite load had no significant effect
on any of these measures. There was also no relationship between orange spot ornamentation and parasite abundance among populations.
Guppies from high-predation environments had significantly more parasites, and their orange coloration was lighter and less
saturated than that in guppies from low-predation environments. Despite previous lab results, this study found no relationship
between parasite load and male orange spot ornamentation. 相似文献
249.
火炬松浆材建筑材林经营模型系统的研究 总被引:1,自引:0,他引:1
根据火炬松样地资料,建立火炬松林分生长模型、结构模型、商品材产量预估模型、营林措施(含间伐、施肥、整地、抚育等)效应模型及营林效益评估模型,构成火炬松纸浆材与建筑材林经营的模型系统,为火炬松纸浆材与建筑材林定向培育和优化决策提供了系列模型. 相似文献
250.