Conservation by simulation: an individual-based spatially explicit model to simulate population dynamics in fragmented habitat
This thesis describes PatchMapper, a model combining a population simulator based on individual behaviour, with a spatially explicit representation of a landscape. To investigate the robustness of the technique, representatives of three major taxa were modelled: the nuthatch (Sitta europaea L.), the white-footed mouse (Peromyscus leucopus Rafinesque) and the black hairstreak (Satyrium pruni L.). For the nuthatch and white-footed mouse, the performance of PatchMapper was compared with published models of the same species, but using different approaches, including, for the nuthatch, a comparison against observed numbers in a real landscape. To investigate the behaviour of the model, a sensitivity analysis was also undertaken. Written in Java, for portability, the model enables the user to select demographic and behavioural parameters via an interactive interface and includes a real-time (computer) display of the position of individuals during the simulation. Novel aspects of the model include perceptual range and field-of-view. Internally generated neutral landscapes can be used for modelling general cases, with imported digitised landscapes enabling specific study areas to be modelled. Habitat area and habitat quality dynamics can also be modelled. Dispersal flow diagrams can be generated, providing a visual explanation of the effects of landscape changes on inter-patch dispersal paths and populations in target patches. Performance compared well with published models, predicting a feasible match with observed numbers of nuthatches in the real landscape. Revealing predictable and realistic responses, the sensitivity analysis revealed that the model coding was valid. The value of specific case studies was illustrated, along with the dangers of relying on intuition when evaluating the response of species to habitat fragmentation. The individual-based SEPM approach was found to be best suited to the modelling of univoltine territorial species (such as nuthatch), with a single dispersal phase between fledging and territorial establishment. When demonstrating the model, the visual outputs proved particularly effective. Providing a set of features not seen in published models and enabling modelling at both local and landscape scales, PatchMapper is offered as a prediction tool for those engaged in activities such as biodiversity conservation and habitat management
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