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Simulation Modelling (simulation + modelling)
Selected AbstractsAnalysis of the trophy sport fishery for the speckled peacock bass in the Rio Negro River, BrazilFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2008M. H. HOLLEY Abstract, The middle portion of the Rio Negro River in Brazil near the equator supports a popular recreational sport fishery for speckled peacock bass, Cichla temensis (Humboldt). The objective of this study was to determine the effect of fishing mortality on this population. Fish were collected from sport-fishing (n = 72) and commercial (n = 103) catches and otoliths were aged to estimate longevity, growth and natural mortality. Recreational anglers in this region seek to catch, then release, larger speckled peacock bass; and fish larger than 62 cm standard length (SL) (about 4.5 kg) served as a bench mark to assess the potential impact of subsistence and commercial harvest on the abundance of larger fish in the sport fishery. Time of opaque band formation on otoliths generally coincided with the dry season (November to April); these bands appeared to form once per year, but formation was highly variable. Speckled peacock bass grew to 62 cm SL on average in 6.4 years, but some fish obtained this size in 4,5 years. Maximum age was 9 years, but most fish were less than 7 years. Instantaneous annual natural mortality (M) estimated from maximum size, longevity and growth ranged from 0.19 to 0.44. Simulation modelling predicted that exploitation rates of fish >25 cm SL similar to the estimated natural mortality rates would reduce the abundance of fish >62 cm by 67,89% compared with no harvest. Even modest exploitation rates of 5% and 10% would result in approximately 30,50% reduction, respectively, of these larger fish. Abundance of large speckled peacock bass that sustains the sport fishery is susceptible to low rates of exploitation in this remote region of Brazil. [source] Simulation modelling of human intestinal absorption using Caco-2 permeability and kinetic solubility data for early drug discoveryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2008Simon Thomas Abstract Measurement of permeation across a monolayer of the human adenocarcinoma cell line, Caco-2, is a popular surrogate for a compound's permeation across the human intestinal epithelium. Taken alone, however, Caco-2 permeability has certain limitations in the prediction of the extent of absorption of an orally-administered compound, because it does not take into account confounding factors such as solubility and dissolution in the gastrointestinal (GI) tract fluids. A simulation model is described that uses Caco-2 permeability measured in the apical to basolateral direction plus kinetic solubility in buffered solution (both measured at pH 7.4) to predict human intestinal absorption. The model features novel treatment of time-varying fluid volume in the GI tract, as a consequence of secretions into, and absorption of fluid from, the upper part of the GI tract. The model has been trained and cross-validated with data for 120 combinations of compound and dose. It has superior predictive power to recently published simulation and quantitative structure property relationship models, and is suitable for high-throughput screening during lead identification and lead optimisation in drug discovery. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4557,4574, 2008 [source] Patterns and causes of species richness: a general simulation model for macroecologyECOLOGY LETTERS, Issue 9 2009Nicholas J. Gotelli Abstract Understanding the causes of spatial variation in species richness is a major research focus of biogeography and macroecology. Gridded environmental data and species richness maps have been used in increasingly sophisticated curve-fitting analyses, but these methods have not brought us much closer to a mechanistic understanding of the patterns. During the past two decades, macroecologists have successfully addressed technical problems posed by spatial autocorrelation, intercorrelation of predictor variables and non-linearity. However, curve-fitting approaches are problematic because most theoretical models in macroecology do not make quantitative predictions, and they do not incorporate interactions among multiple forces. As an alternative, we propose a mechanistic modelling approach. We describe computer simulation models of the stochastic origin, spread, and extinction of species' geographical ranges in an environmentally heterogeneous, gridded domain and describe progress to date regarding their implementation. The output from such a general simulation model (GSM) would, at a minimum, consist of the simulated distribution of species ranges on a map, yielding the predicted number of species in each grid cell of the domain. In contrast to curve-fitting analysis, simulation modelling explicitly incorporates the processes believed to be affecting the geographical ranges of species and generates a number of quantitative predictions that can be compared to empirical patterns. We describe three of the ,control knobs' for a GSM that specify simple rules for dispersal, evolutionary origins and environmental gradients. Binary combinations of different knob settings correspond to eight distinct simulation models, five of which are already represented in the literature of macroecology. The output from such a GSM will include the predicted species richness per grid cell, the range size frequency distribution, the simulated phylogeny and simulated geographical ranges of the component species, all of which can be compared to empirical patterns. Challenges to the development of the GSM include the measurement of goodness of fit (GOF) between observed data and model predictions, as well as the estimation, optimization and interpretation of the model parameters. The simulation approach offers new insights into the origin and maintenance of species richness patterns, and may provide a common framework for investigating the effects of contemporary climate, evolutionary history and geometric constraints on global biodiversity gradients. With further development, the GSM has the potential to provide a conceptual bridge between macroecology and historical biogeography. [source] Modelling radiation and moisture content in fire spreadINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2007L. Ferragut Abstract A numerical method is developed for fire spread simulation modelling. The model is a two-dimensional one which takes into account moisture content and radiation. We consider the combustion of a porous solid, where a simplified energy conservation equation is applied. The effect of the vegetation moisture and endothermic pyrolysis is incorporated in the model by means of a multivalued function representing the enthalpy. Some of the three-dimensional effects are incorporated in the model, i.e. heat losses in the vertical direction and non-local radiation from the flame above the vegetal layer. Also the radiation model allows to cope with wind and slope effects. The approximate solution is obtained using a finite element method. A semi-implicit Euler algorithm in time is applied. The resolution of the multivalued operator is done using the Yosida approximation of a perturbed multivalued operator. The characteristic method combined with a discrete ordinate method is used to solve the radiation equation. Finally, several representative examples are solved and compared with experimental data. Copyright © 2006 John Wiley & Sons, Ltd. [source] A comparison of management options for leatherjacket populations in organic crop rotations using mathematical modelsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2009Rod P. Blackshaw Abstract 1,Pest management in organic systems is challenged by the paucity of options for direct interventions to control damaging populations compared with conventional agriculture. Consequently, a greater emphasis has to be placed on managing pest numbers through a rotation. In the present study, simulation modelling is used to evaluate the effects of different management options on populations of Tipula paludosa (leatherjackets) in organic rotations. 2,The growth of leatherjacket populations in grass was simulated over 5 years for different starting numbers. A significant risk of leatherjacket attack to subsequent crops can be avoided by limiting the fertility building phase of a rotation to a maximum of 2 years. 3,The effect of cultural control through additional cultivation interventions was compared in rotations comprising a grass/clover fertility building phase with host and/or nonhost crops. It is concluded that the effects are marginal and that prophylactic use cannot be recommended. 4,The prophylactic use of biological control agents in permanent grass and grass/arable rotations was investigated. Maximum population reductions in grass were achieved through annual autumn applications but the optimal economic strategy was less frequent than this. Application in the autumn preceding a spring-sown arable crop provided the best risk reduction. 5,A model decision support system for the control of pests in organic systems using data for leatherjacket damage to spring barley is presented. Economic threshold concepts are used to define when cultural control (as additional cultivation) and biocontrol applications should be used. 6,The present study shows the potential benefits of simulation modelling for the rapid evaluation of a wide range of pest management options. Any conclusions drawn from such simulations, however, are provisional until they can be tested experimentally. [source] The importance of biological inertia in plant community resistance to invasionJOURNAL OF VEGETATION SCIENCE, Issue 3 2003Betsy Von Holle Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long-term patterns of invasions by native species. In this paper, we review literature in palaeo-ecology, forest-stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre-existing community (and/or its legacy) in addition to the other biotic and abiotic factors. [source] Timothy growth in Scandinavia: combining quantitative information and simulation modellingNEW PHYTOLOGIST, Issue 2 2001M. Höglind Summary Timothy (Phleum pratense) is the most widely grown sown grass species for silage and hay production in the Nordic countries; it is also common in many other areas with a cold maritime climate. Research on timothy has identified many environmental factors and plant characteristics that determine timothy growth. However, much of the literature that analyses timothy growth presents only qualitative estimates of the importance of the different growth-determining factors. Here we present a review of quantitative information on timothy. Moreover, we analyse to what extent this quantitative information is sufficient to permit the construction of a simple process-based model of timothy growth. We then use such a model to identify the major growth-determining factors. Simulations with the model showed that the major processes to be elucidated in future research on timothy are tillering dynamics and the formation and loss of leaves from tillers. We conclude that a combination of literature review and analysis by means of simulation modelling, such as we attempted here, is an effective approach to identify and prioritize research goals. [source] SIMULATING THE WESTERN SEAWAYSOXFORD JOURNAL OF ARCHAEOLOGY, Issue 4 2009RICHARD CALLAGHAN Summary Recent debates on the introduction of Neolithic features to Britain have emphasized the role of the western maritime routes and the possibility of direct or indirect connections from Brittany to Ireland and Argyll. Here we present the results of simulation modelling of maritime voyaging by paddled or sail-powered boat, indicating the likely lengths of the journeys that would have been required. The issue of direct travel vs. short crossings and coasting is explored, and the implications for specific connections, such as those posited to account for cattle remains in a pre-Neolithic context in Ireland, are considered. [source] Testing options for the commercialization of abalone selective breeding using bioeconomic simulation modellingAQUACULTURE RESEARCH, Issue 9 2010Nick Robinson Abstract The genetic response and economic benefit from alternative breeding programme designs for blacklip and greenlip abalone (Haliotis rubra and Haliotis laevigata, respectively) were evaluated using a computer simulation model. Two selection criteria were investigated, one used family breeding values for liability to disease challenge test infection and the other used a direct selection of the best performing individuals across families for growth rate. Five scales of breeding programme were tested and the model predicted that if growth rate is the only selection criterion, breeding programmes of a scale using 150 families of each species each generation would result in 12,13% genetic improvement in initial generations and have the greatest beneficial economic impact on the Australian abalone industry of the options tested. The model predicts an average discounted benefit,cost ratio of 48:1, total added discounted benefit of AU$4.90 for each kilogram of abalone produced and nominal economic effect on operating income of over AU$16 million per year after 10 years. If disease resistance is the only selective breeding criterion, 100 families of each species would result in the highest benefit,cost ratio of the options tested, although some genetic gain would need to be sacrificed to reduce inbreeding to acceptable levels in this scenario. A strategy for a stand-alone abalone selective breeding cooperative was also modelled. For a farm of current tank area yielding 100 t year,1, participation is expected to yield over AU$0.7 million in discounted total added production value and annual discounted returns of over AU$0.4 million per annum by year 10. [source] Climate change impacts on investment in crop sowing machinery,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 2 2009Ross Kingwell A model of investment in crop sowing machinery is applied to wheat production under current and projected climatic conditions at several locations in south-western Australia. The model includes yield responses to time of sowing at each location given current and projected climatic conditions. These yield relationships are based on wheat growth simulation modelling that in turn draws on data from a down-scaled global circulation model. Wheat price distributions and cost of production data at each location, in combination with the time of sowing yield relationships are used to determine a farmer's optimal investment in crop sowing work rate under each climate regime. The key finding is that the impacts of climate change on profit distributions are often marked, yet mostly modest changes in investment in work rate form part of the profit-maximising response to climate change. The investment response at high versus low rainfall locations mostly involves increases and decreases in work rates, respectively. However, changes to investment in work rate within a broadly similar rainfall region are not always uniform. The impacts of climate change on investments in work rate at a particular location are shown to require knowledge of several factors, especially how climate change alters the pattern of yield response to the time of sowing at that location. [source] | |||||||||||||