Individual-based models of wood mice in ecotoxicology

• Main Author: Liu, Chun
• Published: University of Reading 2013
• Subjects: 577.279
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590671

The wood mouse (Apodemus sylvaticus) is a common and widespread species in Europe and therefore often used as a focal species in the risk assessments of pesticides. Recent years have seen a growing interest in the use of ecological models in ecological risk assessments. The purpose of this PhD project was to construct and apply population models of the wood mouse to support risk assessment of pesticides. In the thesis I first reviewed the current practice of risk assessment and the weaknesses and the advantages of ecological models, in particular individual-based models. Following a modelling cycle, the PhD project started with a literature review of the basic ecology of the wood mouse and relevant information for modelling purposes. A conceptual model was then constructed, based on which an individual-based model was developed. The model was fully described and its ecological credibility was evaluated by the "pattern-oriented" validation method. The model was then used to link the spatial choice of wood mice and their potential exposure to pesticide application in the field. Analyses of the model showed that when the population density reached a high level in the off-crop hedgerows, which act as the source habitat for wood mice, the surplus were driven to the crop fields and thus have a high risk of exposure if pesticides are applied. The model was further developed by incorporating a sub module of toxicokinetic processes which represented exposure as internal concentration instead of ingested dose. The interactions between the spatial patterns of foraging provided by the individual-based model and the temporal patterns of absorption and elimination provided by the toxicokinetic model were explored. The combined model showed little further reduction of risk than either of the two models respectively alone. It suggested that such a combined approach is most likely to bring added value when the spatio-temporal patterns of feeding are at the intermediate level, i.e. when mice divide their foraging between exposed crop and unexposed areas. I then used the model to explore the population-level sensitivity in terms of both population size and population growth rate, to detrimental effects on individual-level life-history traits. The results showed the two indices had different sensitivities to changes in life-history traits. Thus, endpoint from the models used in risk assessments should take into account whether the protection goal is to ensure that the population remains stable or that it grows. The overall high level of sensitivity to survival also indicated that protection should be more focused on acute effects than chronic effects. Finally I summarised the major findings in the thesis and discussed the need for future research, as well as the lessons learnt about conventional risk assessment approach and the opportunities ecological modelling brings for a more realistic and ecologically relevant risk assessment for pesticides.