Key points A mechanistic effect models (MEM) is a logical and consistent representation of some aspect of eco(toxico)logical reality, based on an explicit simplification of the underlying processes.MEMs allow extrapolations beyond the range of empirical data, and the goodness-of-fit provides information on the underlying processes.The most important step in the development of a MEM is the specification of the simplifying assumptions, and providing support for them.If the assumptions are not provided, or not well supported, users should not trust the extrapolations from such a model, no matter how good the correspondence to data.
