From individuals to ecosystem services: Using individual based models to predict population level ecological functions in response to chemical induced changes in invertebrate feeding activity

The aim of this thesis was to explore how information on chemical impacts on the feeding activity of freshwater invertebrates can be used to predict population level effects on ecosystem functions and considering the implications for associated ecosystem services. The research focuses on the effects of feeding inhibition on ecological functions, examining both individual-level impacts and differences in sensitivity among functional feeding groups (FFGs). Using Dynamic Energy Budget Individual-Based Models, the study examines population-level responses of freshwater shredders Gammarus pulex and Asellus aquaticus, revealing how chemical stress affects the performance of ecological functions within a recreational fishery.
Of the 1500+ chemicals for which toxicity data were available, differences in sensitivity between FFGs could not be evaluated for lack of data across multiple species. Of the 48 chemicals with sufficient data, differences in sensitivity between FFGs were not detected for 70% of chemicals, likely due to species biases in the data. When modelling single-species population responses to individual effects, populations exhibited resistance to feeding inhibition, but were most affected by reductions in assimilation efficiency (reflecting both resource quality and consumer digestion) and food availability—factors that are often overlooked in traditional risk assessments. When interspecific competition was considered, impact thresholds were significantly lower than those for single-species populations, with the initial ratio and density of competing species influencing population resistance to feeding inhibition. Regarding the performance of ecological functions, leaf processing was most responsive and most greatly impacted compared to impacts on prey provision.
The study emphasises the importance of considering both ecological and environmental contexts in risk assessments. Species diversity and varying sensitivity within the same FFG can alter the effects of chemical stress of service providing units. The thesis emphasises the need to consider interspecific competition in predicting chemical stress impacts, advocating for broader risk assessments that include species interactions.