Development of a Toxin-Mediated Predator-Prey Model Applicable to Aquatic Environments in the Athabasca Oil Sands Region

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  • Industrial contaminants are one of the leading causes of pollution worldwide. It has been shown that 13 elements considered priority water pollutants by the US Environmental Protection Agency are present in the Athabasca River and are found in oil sands process-affected water. There are likely natural and anthropogenic sources of these toxins in the receiving environment. To protect ecological environments and aquatic species in Alberta, it is necessary to assess the risk of toxins to aquatic organisms, and find important factors that determine the persistence and extirpation of populations or species. While previous work has considered the effect of a toxin on the population dynamics of a single trophic level, such as fish, we focus on the impacts of toxins on the population dynamics of aquatic food webs to understand possible outcomes. Mathematical models have been widely applied to perform chemical risk assessments on all levels of the biological hierarchy, from cells to organs to organisms to populations to entire ecosystems. Here we develop a toxin-mediated predator-prey model that includes population dynamics. We use the model to evaluate the flow of toxins through the aquatic food web into the aquatic ecosystem and study how the transfer of toxins between trophic levels changes the food web dynamics. We analyze the model by studying the existence and stability of steady states and the effect of toxin level in the environment on steady states. The model is then connected to experimental data via model parameterization. In particular, we consider the toxic effects of methylmercury on rainbow trout (Oncorhynchus mykiss) and its prey (small fish or aquatic insects) and obtain an appropriate estimate for each model parameter. The results of model parameterization and model analysis are used to numerically solve the model, and the results of the effect of the methylmercury on the end behavior of rainbow trout and its prey (small fish or aquatic insects) are provided. From our analysis and numerical exploration of the food web toxin model we found that different toxin concentrations affect organisms at different trophic levels in many different ways. For example, high toxin concentrations in the environment are harmful to both species, and may lead to extirpation of both species. However, low toxin concentrations produce counterintuitive results. That is, contaminant effects on predators can actually lead to increased abundance of the prey. The existence of limit cycles, where both population levels fluctuate around coexistence equilibrium, is found in most classical predator-prey models. Our findings show that increasing toxin level may reduce and prevent populations from fluctuating when the predator and the prey are exposed simultaneously to a toxin. Unlike most standard predator-prey systems, where populations will eventually tend toward only one stable state, our findings indicate that with a toxic effect, predator-prey systems may lead to multiple possible long-term outcomes. In this scenario, the initial population level will determine the final fate.

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    Attribution 3.0 International