66 research outputs found
Connectivity in a real fragmented landscape: distance vs movement model based approaches
No full textGraph theory derived models and measures are increasingly being used to quantify landscape connectivity in order to contribute to conservation biology and management. This is particularly relevant in the case of real landscapes in which local actions may have crucial consequences for maintaining biodiversity on large scale. A number of graphs were compared sharing an identical node weight definition and whose link weights representing functional patch-connectivity, were derived from conceptually different approaches. Habitat suitability was taken into account. Calculated patch-connectivity was compared between all the graphs and these differences, evaluated by a set of indices describing network properties at the element structure level, were investigated
Connectivity in a real fragmented landscape: distance vs movement model based approaches.
No full textGraph theory derived models and measures are increasingly being used to quantify landscape connectivity in order to contribute to conservation biology and management. This is particularly relevant in the case of real landscapes in which local actions may have crucial consequences for maintaining biodiversity on large scale. A number of graphs were compared sharing an identical node weight definition and whose link weights representing functional patch-connectivity, were derived from conceptually different approaches. Habitat suitability was taken into account. Calculated patch-connectivity was compared between all the graphs and these differences, evaluated by a set of indices describing network properties at the element structure level, were investigated
Theoretically exploring direct and indirect chemical effects across ecological and exposure scenarios using mechanistic fate and effects modelling
No full textPredicting ecosystem response to chemicals is a complex problem in ecotoxicology and a challenge for risk assessors. The variables potentially influencing chemical fate and exposure define the exposure scenario while the variables determining effects at the ecosystem level define the ecological scenario. In absence of any empirical data, the objective of this paper is to present simulations by a fugacity-based fate model and a differential equation-based ecosystem model to theoretically explore how direct and indirect effects on invertebrate shallow pond communities vary with changing ecological and exposure scenarios. These simulations suggest that direct and indirect effects are larger in mesotrophic systems than in oligotrophic systems. In both trophic states, interaction strength (quantified using grazing rates) was suggested a more important driver for the size and recovery from direct and indirect effects than immigration rate. In general, weak interactions led to smaller direct and indirect effects. For chemicals targeting mesozooplankton only, indirect effects were common in (simple) food-chains but rare in (complex) food-webs. For chemicals directly affecting microzooplankton, the dominant zooplankton group in the modelled community, indirect effects occurred both in food-chains and food-webs. We conclude that the choice of the ecological and exposure scenarios in ecotoxicological modelling efforts needs to be justified because of its influence on the prevalence and magnitude of the predicted effects. Overall, more work needs to be done to empirically test the theoretical expectations formulated here
Objects for simulation: smalltalk and ecology
No full textThe object-oriented programming environment Smalltalk is used to implement a tool for modeling and simulation of ecological systems. This PC-based tool makes it possible, and easy, to represent individuals explicitly in the simulation, and to integrate the individual-based approach with a traditional population/concentration-based approach. Object-oriented programming is used to allow for an efficient development of models. The properties of Smalltalk are exploited to make testing and investigation of the models occur interactively, supported by a user-friendly interface. In the paper, modeling and simulation concepts and elements of object-oriented programming as they relate to an individual-based approach, are introduced. The simulation extension in question (EcoTalk) is described. Two applications that make use of EcoTalk are presented, both related to population-dynamics. The discussion centers on practical implications of the approach, e.g. the system characteristics that can be expressed in EcoTalk. An indication of the performance of an application is given. It is concluded that, at present, EcoTalk can be used for medium-sized applications
Population model structure of a single bird species in a single patch.
No full text<p>A = adult numbers, J = juvenile numbers. Pre-dispersal juvenile numbers are indicated as J<sub>t-</sub> and after dispersal juvenile numbers as J<sub>t+</sub>. Competition among individuals of different species affects the recruitment. Recruitment and adult survival are affected by environmental fluctuations. A fraction of the juveniles disperses to other patches while dispersers from elsewhere are allowed to settle in the patch. Note that in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132383#pone.0132383.e001" target="_blank">Eq 1</a> the juveniles are not considered explicitly because we model pre-breeding adults: from <i>A</i>(<i>t</i>) to <i>A</i>(<i>t</i>+1).</p
An individual-based approach to model spatial population dynamics of invertebrates in aquatic ecosystems after pesticide contamination
No full textIn the present study we present a population model (Metapopulation model for Assessing Spatial and Temporal Effects of Pesticides [MASTEP]) describing the effects on and recovery of the waterlouse Asellus aquaticus after exposure to a fast-acting, nonpersistent insecticide as a result of spray drift in pond, ditch, and stream scenarios. The model used the spatial and temporal distribution of the exposure in different treatment conditions as an input parameter. A dose¿response relation derived from a hypothetical mesocosm study was used to link the exposure with the effects. The modeled landscape was represented as a lattice of 1- by 1-m cells. The model included processes of mortality of A. aquaticus, life history, random walk between cells, density dependence of population regulation, and, in the case of the stream scenario, medium-distance drift of A. aquaticus due to flow. All parameter estimates were based on expert judgment and the results of a thorough review of published information on the ecology of A. aquaticus. In the treated part of the water body, the ditch scenario proved to be the worst-case situation, due to the absence of drift of A. aquaticus. Effects in the pond scenario were smaller because the pond was exposed from one side, allowing migration from the other, less contaminated side. The results of the stream scenario showed the importance of including drift for the population recovery in the 100-m stretch of the stream that was treated. It should be noted, however, that the inclusion of drift had a negligible impact on numbers in the stream as a whole (600 m)
Data with amount of forest edge for a 10 x 10 km area in the Netherlands
No full textAmount of source of forest edge within 25x25 m grid cells, expressed as a percentage of the area of a grid cell, for a 10 x 10 km area from the Dutch national map. See Figure 1 in the publication. The data can be used to generate Figure 2 with predicted parasitism rates following the fit of a kernel logistic regression model for the empirical case study
Data from: Modelling mobile agent-based ecosystem services using kernel weighted predictors
No full text1. Agriculture benefits from ecosystem services provided by mobile agents, such as biological pest control by natural enemies and pollination by bees. However, methods that can generate spatially explicit predictions and maps of these ecosystem services based on empirical data are still scarce. 2. Here we propose a generic statistical model to derive kernel functions to characterize the spatial distribution of ecosystem services provided by mobile agents. The model is similar in spirit to a generalized linear model, and uses data of landscape composition and ecosystem services assessed at target sites to estimate parameters of the kernel. The approach is tested in a simulation study and illustrated by an empirical case study on parasitism rates of the diamondback moth Plutella xylostella. 3. The simulation study shows that the scale parameter of the exponential power kernel can be estimated with limited bias, whereas estimation of the shape parameter is difficult. For the case study the model provides biologically relevant estimates for the kernel associated with parasitism of Plutella xylostella. These estimates can be used to generate ecosystem service maps for existing or planned landscapes. The case study reveals that predictions can be sensitive to the parameter values for the width and shape of the kernel, and to the link function used in the statistical model. 4. In the last two decades numerous empirical studies assessed ecosystem services at target sites and related these to the surrounding landscape. Our method can take advantage of these data by estimating underlying kernels that can be used to map the spatial distribution of ecosystem services. However, empirical data that can discriminate between alternative kernel shapes remain critical
Usage of the Lotosphere Development Tools and ISODE for Prototyping Application Layer Protocols
No full textComparing population recovery after insecticide exposure for four aquatic invertebrate species using models of different complexity
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