Simulation Models

Abstract

Simulations models have the advantage of providing estimates for processes or conditions that are difficult to observe. However, they typically must be calibrated or refined before being applied for a particular investigation. The results of fate and transport models are used to generate causal evidence by combining them with measures of the biological response. The evidence can be used to judge whether candidate causes occur at sufficient levels at the same time and place as effects. Like empirical stressor-response models, simulation models can be used to determine whether the exposure was sufficient to cause the observed effects. The simplest mechanistic ecotoxicological models are the exposure additivity and the effect additivity models for chemical mixtures. Ecological models of populations, communities, and ecosystems can be used to estimate the combined effects of multiple causes. Organism, population, and ecosystem models are worth the effort they require if they deliver realism and relevance.