Modeling exposure and recovery of fish and wildlife populations after stressor mitigation serves as a basis for evaluating population status and remediation success. The Atlantic killifish (Fundulus heteroclitus) is an important and well-studied model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems. Herein, we develop a density dependent matrix population model for Atlantic killifish that analyzes both size-structure and age class-structure of the population so that we could readily incorporate output from a dynamic energy budget (DEB) model currently under development. This population modeling approach emphasizes application in conjunction with field monitoring efforts (e.g., through effects-based monitoring programs) and/or laboratory analysis to link effects due to chemical stress to adverse outcomes in whole organisms and populations. We applied the model using data for killifish exposed to dioxin-like compounds, taken from a previously published study. Specifically, the model was used to investigate population trajectories for Atlantic killifish with dietary exposures to 112, 296, and 875 pg/g of dioxin with effects on fertility and survival rates. All effects were expressed relative to control fish. Further, the population model was employed to examine age and size distributions of a population exposed to resource limitation in addition to chemical stress.
For each dietary exposure concentration of dioxin, the corresponding plots of total population size, population size structure, and age structure over time were generated. For example, exposure to 875 pg/g of dioxin resulted in a 13.1% decline in population size after 2 years, a 19.9% decline in population size after 5 years, and a 27.9% decline in population size over 10 years with plots of all size classes and age classes exhibiting declines. Further, in demonstrating the population model under both chemical stress and resource limitation (effects from dietary exposure to dioxin in combination with resource limitation scenarios), multiple scenarios were investigated and corresponding model output plots showed population level effects caused by both a further reduction to fecundity and an increase in probability that a fish is in the smaller size class within each given age class. The present study serves as an example of how matrix population models are useful tools for ecological risk assessment because they integrate effects across the life cycle, provide a linkage between endpoints observed in the individual and ecological risk to the population as a whole, and project outcomes for future generations.