Matrix population models are useful tools for ecological risk assessment because they integrate effects across the life cycle, link endpoints observed in the individual and ecological risk to the population, and project outcomes for many generations in the future. The Atlantic killifish (Fundulus heteroclitus) has a range including the Atlantic coast from Florida to the Maritime Provinces of Canada, and is an important model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems. We developed a density dependent logistic matrix population model for Atlantic killifish by modifying a model developed for fathead minnow (Pimephales promelas) that has proved to be extremely useful, e.g. to incorporate data from laboratory studies and project effects of endocrine disrupting chemicals. This model accounts for both size structure and age class structure of the fish population over time and can readily incorporate output from a dynamic energy budget (DEB) model. To demonstrate this model, we investigated population response of a killifish population exposed to varying levels of dioxin with effects on both fertility and survival rates. Furthermore, this population model was employed to examine dynamics of the population exposed to resource limitation in addition to chemical stress.
Results/Conclusions
Population trajectories were demonstrated for Atlantic killifish with exposures to 112, 296, and 875 pg/g of dioxin. Each exposure concentration of dioxin resulted in impacts on total population size, population size structure, and population age structure over time. For example, exposure to 875 pg/g of dioxin resulted in an approximate 17% decline in population size after 3 years, a 23% decline in population size after 6 years, and a decline that exceeded 28% after 10 years. In addition, plots for all size classes and age classes exhibited declining trends. 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. This modeling approach could be implemented in additional studies across multiple species and sites in conjunction with field monitoring efforts (e.g., through effects-based monitoring programs) and/or laboratory analysis to link effects due to chemical stress and resource limitation to adverse outcomes in whole organisms and populations.