A modelling framework to explore bioenergetic effects of environmental stress and interspecific interactions

Abstract

The overarching theme of this thesis research was to further develop methods to improve ecological risk assessment of anthropogenic stressors. The main objective was to develop a bioenergetic, individual-based multi-species model that could be used to predict population-level dynamics arising from indirect energetic interactions between species. Ultimately, the goal would be to apply such a model to predict effects of chemical stressors on ecological receptors. To facilitate model development and evaluation, several experiments were performed—one to calibrate single species sub-models, and another to demonstrate the effectiveness of the model in predicting population dynamics in single and multi-species scenarios. The two focal organisms were Daphnia magna and Lymnaea stagnalis for their environmental and regulatory relevance. Individual bioenergetic models for each species were developed from Dynamic Energy Budget models. These bioenergetic models were then inserted into individual based models specific to each organisms’ behavioral characteristics. D. magna models were greatly influenced by localized density dependent effects termed ‘Neighborhood Effect’ and L. stagnalis models were greatly influenced by their movement pattern and ‘S’-shaped growth patterns. Connecting the individual models in a single, multi species model required modelling indirect energetic facilitation from L. stagnalis to D. magna by using a model simplification whereby snail waste was functionally converted to daphnia resources as algae. Experimental results from D. magna populations supported the individual daphnid model and the importance of the ‘Neighborhood Effect.’ Multi species experimental observations confirmed the existence of indirect energetic facilitation between snails and daphnid populations and provided valuable insight into graded levels of facilitation. In summary, the results of this thesis demonstrate that a combination of model and experimental methods exist that can provide useful linkages between single species energetic data and higher levels of biological organization. More importantly, the success of the multi-species model emerged from rather simple connections between individual species models. This provides a very useful framework for linking models for single species responses to chemical stressors that may prove valuable to ecotoxicological research and ecological risk assessment.The over