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Abstract: Agricultural land management has important impacts on land use and vegetation that can rapidly induce ecosystem change. Birds are often used as indicators of such impacts of landscape change on ecosystems. However, predicting the response of birds to changes in their environment is an ongoing challenge. Agent-based models (ABMs) have the potential to provide useful insights but have not been widely used in such studies to date. This paper illustrates the use of agent-based modelling for policy decision-making, using the case study of the impacts of the removal of set-aside land on Skylark populations in Denmark. In order to address the importance of critical interpretation of ABMs, we introduce a novel methodology with which to analyze the sensitivity of an ABM, Bayesian Analysis of Computer Code Outputs (BACCO). BACCO constructs an emulator of the model in order to provide a rapid and thorough sensitivity analysis. This allows us to identify input parameters in the model that require more rigorous parameterization, as some parameters are highly sensitive and are found to produce spurious results when varied even a small amount. [Copyright &y& Elsevier]

Abstract: Individual-based modelling approaches are being used to simulate larger complex spatial systems in ecology and in other fields of research. Several novel model development issues now face researchers: in particular how to simulate large numbers of individuals with high levels of complexity, given finite computing resources. A case study of a spatially-explicit simulation of aphid population dynamics was used to assess two strategies for coping with a large number of individuals: the use of ‘super-individuals’ and parallel computing. Parallelisation of the model maintained the model structure and thus the simulation results were comparable to the original model. However, the super-individual implementation of the model caused significant changes to the model dynamics, both spatially and temporally. When super-individuals represented more than around 10 individuals it became evident that aggregate statistics generated from a super-individual model can hide more detailed deviations from an individual-level model. Improvements in memory use and model speed were perceived with both approaches. For the parallel approach, significant speed-up was only achieved when more than five processors were used and memory availability was only increased once five or more processors were used. The super-individual approach has potential to improve model speed and memory use dramatically, however this paper cautions the use of this approach for a density-dependent spatially-explicit model, unless individual variability is better taken into account. [Copyright &y& Elsevier]

Abstract: A spatially explicit individual-based simulation model has been developed to represent aphid population dynamics in agricultural landscapes. The application of the model to Rhopalosiphum padi (L.) population dynamics is detailed, including an outline of the construction of the model, its parameterisation and validation. Over time, the aphids interact with the landscape and with one another. The landscape is modified by varying a simple pesticide regime, and the multi-scale spatial and temporal implications for a population of aphids is analysed. The results show that a spatial modelling approach that considers the effects on the individual of landscape properties and factors such as wind speed and wind direction provides novel insight into aphid population dynamics both spatially and temporally. This forms the basis for the development of further simulation models that can be used to analyse how changes in landscape structure impact upon important species distributions and population dynamics. [Copyright &y& Elsevier]