PS 7-93 - Plastic and evolutionary responses of plants to sea level rise impacts predictions of marsh ecosystem processes: Lessons from a joint eco-evolutionary model

Abstract: Organismal responses to rapid environmental change can strongly impact ecosystem dynamics. While plastic (or induced) responses to environmental change are increasingly being integrated into predictive ecosystem models, evolution by natural selection remains largely absent, despite evidence that the rapid evolution of organismal traits can influence ecosystems at magnitudes large enough to modify selection pressures (i.e., an “eco-evolutionary feedback”). Here, we constructed an eco-evolutionary model of coastal marsh accretion by joining together an applied ecosystem model of marsh accretion and a theoretical model of trait evolution in response to environmental change. We focused on how one plant trait (root-to-shoot ratio) responded to one environmental pressure (sea level rise) and how changes in this trait then influenced ecosystem dynamics, while accounting for eco-evolutionary feedbacks. We used simulations of the model to examine three scenarios, wherein: (1) root-to-shoot ratio remained constant across the simulation, (2) root-to-shoot ratio responded plastically to changes in flooding (“plastic-only”), and (3) root-to-shoot ratio responded both plastically and via evolution by natural selection in response to flooding (“evolutionary + plastic”). When comparing across these scenarios, we found that failing to account for plasticity and evolution of marsh plant root-to-shoot ratios resulted in overpredictions of marsh resiliency to sea level rise. Specifically, the average vertical accretion rates for the “plastic-only” and for the “evolutionary + plastic” scenarios were 7% and 5% lower than the scenario wherein root-to-shoot ratio was kept constant; and carbon accumulation rates were 16% and 12% lower, respectively. Notably, evolution mitigated the negative impact of plasticity on root-to-shoot ratio, which then had downstream consequences on ecosystem dynamics. Sensitivity analyses highlighted parameters, such as the environmental sensitivity of selection, that need to be well-constrained to clearly understand the relative roles of plasticity and evolution in mediating ecosystem dynamics. Overall, our findings illustrate that coupled eco-evolutionary modeling frameworks are useful scaffolds for investigating the role of evolution in regulating the dynamics of at-risk ecosystems, like coastal marshes, that are subject to rapid environmental change.