The recent advancement of agent-based modeling is characterized by higher demands on the parameterization, evaluation and documentation of these computationally expensive models. Accordingly, there is also a growing request for "easy to go" applications just mimicking the input-output behavior of such models. Metamodels are being increasingly used for these tasks. In this paper, we provide an overview of common metamodel types and the purposes of their usage in an agent-based modeling context. To guide modelers in the selection and application of metamodels for their own needs, we further assessed their implementation effort and performance. We performed a literature research in January using four di erent databases. Five di erent terms paraphrasing metamodels (approximation, emulator, meta-model, metamodel and surrogate) were used to capture the whole range of relevant literature in all disciplines. All metamodel applications found were then categorized into specific metamodel types and rated by di erent junior and senior researches from varying disciplines (including forest sciences, landscape ecology, or economics) regarding the implementation e ort and performance. Specifically, we captured the metamodel performance according to (i) the consideration of uncertainties, (ii) the suitability assessment provided by the authors for the particular purpose, and (iii) the number of valuation criteria provided for suitability assessment. We selected distinct metamodel applications from studies published in peer-reviewed journals from to . These were used for the sensitivity analysis, calibration and upscaling of agent-based models, as well to mimic their prediction for di erent scenarios. This review provides information about the most applicable metamodel types for each purpose and forms a first guidance for the implementation and validation of metamodels for agent-based models.
Sanitation felling is considered as the main measure to protect managed forests from damage due to outbreaks of the European Spruce Bark Beetle. In this study, we investigate the effectiveness of sanitation felling on stopping the spread of a bark beetle population from an un-managed to a managed forest area. For this, we advance an individual-based dispersion model of Ips typographus by adding the influence of wind on the beetle dispersion and by importing GIS data to simulate real world forests. To validate the new model version and to find reasonable parameter values, we conduct simulation experiments to reproduce infestation patterns that occurred in 2015, 2016, and 2017 within the national park Saxon Switzerland, Germany. With the then calibrated model IPS-SPREADS (Infestation Pattern Simulation Supporting PREdisposition Assessment DetailS), we investigate the impact of different factors such as the distance between beetle source trees and the forest border on the amount of damage within the managed forest stand and test the effectiveness of different levels of sanitation felling and its point of action on reducing the amount of damaged trees. As expected, the results of the model calibration show that the direction of wind plays an important role for the occurring infestation patterns and that bark beetle energy reserve is reduced during mass outbreaks. The results of the second experiment show that the main drivers for the amount of damaged trees are the primary attractiveness and the distance to beetle source trees. Sanitation felling effectiveness is highest when performed near the beetle source trees, with considerably high felling intensities and if there is at least some distance to the managed forest. IPS-SPREADS can be used in future studies as a tool for testing further management measures (e.g., pheromone traps) or to assess the risk for bark beetle infestations of forest areas near to wind-felled or already infested trees.
Background Krill and salps are key macro zooplankton grazers in the Southern Ocean ecosystem but due to differing habitat requirements, there used to be only little spatial overlap of both species. With ongoing climate change-induced seawater temperature increase and regional loss of sea ice, salps are now able to extend their spatial distribution into areas that are historically krill dominated and capable to increase rapidly due to asexual reproduction when environmental conditions are favorable. It is crucial to understand potential effects on krill since krill is a species of exceptional trophic significance of the Southern Ocean food web and negative impacts on krill could trigger cascading effects on its predators and prey. To address this question, we combined two individual-based models on salp and krill, which describe the whole life cycle of salp individuals as well as the dynamic energy budget of individual krill. The resulting new model PEKRIS (PErformance of KRIll vs. Salps) is used to simulate a krill population for 100 years under varying chlorophyll a concentration in the presence or absence of salps. Results The investigated krill population properties (dynamics of krill abundance, mean length and yearly number of released eggs) were impacted but not significant by the presence of salps. On the other hand, salp abundance was significantly reduced if krill was present. The medians of krill and salp population properties deviated when the other species was introduced by <1% (150 individuals) for krill abundance, -25% (-417,934 eggs) for krill eggs, 2% (0.49 mm) for mean length of krill and -38% (-427 individuals) for maximum seasonal salp abundance. Conclusions While no significant impact of salp presence on the krill population was detectable, a considerable reduction for eggs released by krill prevailed. In the future, the model could serve as a tool to investigate the possible effect of a climate change related increase in water temperature and the associated physiological effects on both species and, consequently, their population trends.
Linked to climate change, drivers such as increased temperatures and decreased water availability affect forest health in complex ways by simultaneously weakening tree vitality and promoting insect pest activity. One major beneficiary of climate-induced changes is the European spruce bark beetle (Ips typographus). To improve the mechanistic understanding of climate change impacts on long-term beetle infestation risks, individual-based simulation models (IBM) such as the bark beetle dispersion model IPS-SPREADS have been proven as effective tools. However, the computational costs of IBMs limit their spatial scale of application. While these tools are best suitable to simulate bark beetle dynamics on the plot level, upscaling the process to larger areas is challenging. The larger spatial scale is, nevertheless, often required to support the selection of adequate management intervention. Here, we introduce a novel two-step approach to address this challenge: (1) we use the IPS-SPREADS model to simulate the bark beetle dispersal at a local scale by dividing the research area into 250 × 250 m grid cells; and (2) we then apply a metamodel framework to upscale the results to the landscape level. The metamodel is based on Markov chains derived from the infestation probabilities of IPS-SPREADS results and extended by considering neighbor interaction and spruce dieback of each focal cell. We validated the metamodel by comparing its predictions with infestations observed in 2017 and 2018 in the Saxon Switzerland national park, Germany, and tested sanitation felling as a measure to prevent potential further outbreaks in the region. Validation showed an improvement in predictions by introducing the model extension of beetle spreading from one cell to another. The metamodel forecasts indicated an increase in the risk of infestation for adjacent forest areas. In case of a beetle mass outbreak, sanitation felling intensities of 80 percent and above seem to mitigate further outbreak progression.
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