217,585 research outputs found
Spatially explicit non-Mendelian diploid model
We introduce a spatially explicit model for the competition between type
and type alleles. Each vertex of the -dimensional integer lattice is
occupied by a diploid individual, which is in one of three possible states or
genotypes: , or . We are interested in the long-term behavior of
the gene frequencies when Mendel's law of segregation does not hold. This
results in a voter type model depending on four parameters; each of these
parameters measures the strength of competition between genes during meiosis.
We prove that with or without a spatial structure, type and type
alleles coexist at equilibrium when homozygotes are poor competitors. The
inclusion of a spatial structure, however, reduces the parameter region where
coexistence occurs.Comment: Published in at http://dx.doi.org/10.1214/09-AAP598 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Tracking uncertainty in a spatially explicit susceptible-infected epidemic model
In this paper we conceive an interval-valued continuous cellular automaton for describing the spatio-temporal dynamics of an epidemic, in which the magnitude of the initial outbreak and/or the epidemic properties are only imprecisely known. In contrast to well-established approaches that rely on probability distributions for keeping track of the uncertainty in spatio-temporal models, we resort to an interval representation of uncertainty. Such an approach lowers the amount of computing power that is needed to run model simulations, and reduces the need for data that are indispensable for constructing the probability distributions upon which other paradigms are based
An Agent-Based Spatially Explicit Epidemiological Model in MASON
This paper outlines the design and implementation of an agent-based epidemiological simulation system. The system was implemented in the MASON toolkit, a set of Java-based agent-simulation libraries. This epidemiological simulation system is robust and extensible for multiple applications, including classroom demonstrations of many types of epidemics and detailed numerical experimentation on a particular disease. The application has been made available as an applet on the MASON web site, and as source code on the author\'s web site.Epidemiology, Social Networks, Agent-Based Simulation, MASON Toolkit
A spatially explicit Markovian individual-based model for terrestrial plant dynamics
An individual-based model (IBM) of a spatiotemporal terrestrial ecological
population is proposed. This model is spatially explicit and features the
position of each individual together with another characteristic, such as the
size of the individual, which evolves according to a given stochastic model.
The population is locally regulated through an explicit competition kernel. The
IBM is represented as a measure-valued branching/diffusing stochastic process.
The approach allows (i) to describe the associated Monte Carlo simulation and
(ii) to analyze the limit process under large initial population size
asymptotic. The limit macroscopic model is a deterministic integro-differential
equation.Comment: 31 pages, 1 figur
Stochastic spatial models of host-pathogen and host-mutualist interactions I
Mutualists and pathogens, collectively called symbionts, are ubiquitous in
plant communities. While some symbionts are highly host-specific, others
associate with multiple hosts. The outcomes of multispecies host-symbiont
interactions with different degrees of specificity are difficult to predict at
this point due to a lack of a general conceptual framework. Complicating our
predictive power is the fact that plant populations are spatially explicit, and
we know from past research that explicit space can profoundly alter plant-plant
interactions. We introduce a spatially explicit, stochastic model to
investigate the role of explicit space and host-specificity in multispecies
host-symbiont interactions. We find that in our model, pathogens can
significantly alter the spatial structure of plant communities, promoting
coexistence, whereas mutualists appear to have only a limited effect. Effects
are more pronounced the more host-specific symbionts are.Comment: Published at http://dx.doi.org/10.1214/105051605000000782 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
The Spatial Limitations of Current Neutral Models of Biodiversity
The unified neutral theory of biodiversity and biogeography is increasingly accepted as an informative null model of community composition and dynamics. It has successfully produced macro-ecological patterns such as species-area relationships and species abundance distributions. However, the models employed make many unrealistic auxiliary assumptions. For example, the popular spatially implicit version assumes a local plot exchanging migrants with a large panmictic regional source pool. This simple structure allows rigorous testing of its fit to data. In contrast, spatially explicit models assume that offspring disperse only limited distances from their parents, but one cannot as yet test the significance of their fit to data. Here we compare the spatially explicit and the spatially implicit model, fitting the most-used implicit model (with two levels, local and regional) to data simulated by the most-used spatially explicit model (where offspring are distributed about their parent on a grid according to either a radially symmetric Gaussian or a ‘fat-tailed’ distribution). Based on these fits, we express spatially implicit parameters in terms of spatially explicit parameters. This suggests how we may obtain estimates of spatially explicit parameters from spatially implicit ones. The relationship between these parameters, however, makes no intuitive sense. Furthermore, the spatially implicit model usually fits observed species-abundance distributions better than those calculated from the spatially explicit model's simulated data. Current spatially explicit neutral models therefore have limited descriptive power. However, our results suggest that a fatter tail of the dispersal kernel seems to improve the fit, suggesting that dispersal kernels with even fatter tails should be studied in future. We conclude that more advanced spatially explicit models and tools to analyze them need to be developed
Spatially Explicit Model of Deforestation in Bolivia
A GIS compiled by the Departmental Government of Santa Cruz, Bolivia offers data that may help to resolve some competing theories of tropical deforestation. The GIS contains many attributes relating to land use at two points in time, 1989 and 1994, and allow us to address questions like: 1. What has been the impact of past road construction on deforestation and land use? 2. What impacts might be expected from future road construction? 3. What impact do zoning policies such as forest concessions and protected areas have? 4. What influence do cultural factors have on forest clearing and fragmentation? We discuss our methodology and report interim results. We seek to provoke discussion on appropriate statistical procedures for such analyses
Applying Geographically Weighted Regression to Conjoint Analysis: Empirical Findings from Urban Park Amenities
The objective of this study is to develop spatially-explicit choice model and investigate its validity and applicability in CA studies. This objective is achieved by applying locally-regressed geographically weighted regression (GWR) and GIS to survey data on hypothetical dogrun facilities (off-leash dog area) in urban recreational parks in Tokyo, Japan. Our results show that spatially-explicit conditional logit model developed in this study outperforms traditional model in terms of data fit and prediction accuracy. Our results also show that marginal willingness-to-pay for various attributes of dogrun facilities has significant spatial variation. Analytical procedure developed in this study can reveal spatially-varying individual preferences on attributes of urban park amenities, and facilitates area-specific decision makings in urban park planning.Choice experiments, conjoint analysis, dogrun, geographically weighted regression, spatial econometrics, Research Methods/ Statistical Methods, Resource /Energy Economics and Policy,
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