From Equilibrium to Non-equilibrium Dynamics: Ecological Theory for a Changing World

Abstract

While ecological theory has made significant strides towards understanding the stability behind nature’s complex networks of interactions, food webs have historically been modeled under greatly simplified temporal and spatial assumptions, leaving us with an ecosystem theory that is ill-prepared to interpret the impacts of global change. In this thesis, I take a modular approach to food web theory as a step towards mechanistically understanding how various axes of global change regulate ecosystem functioning and resilience. Across four chapters I demonstrate how general theoretical concepts can be unified and applied across multiple systems and highlight the importance of non-local dynamics (e.g., transients) in a changing world. In each study, I show that global change can generate complex and unexpected outcomes, however the geometric characteristics of the modules (i.e., deterministic skeletons) allow us to unpack interactions between local and non-local dynamics driving these results. First, I find that periodic environments can drive both complex coupled oscillators and fluctuation-driven stabilization in consumer-resource interactions, depending on the speed of environmental periodicities. I find a highly general set of dynamical outcomes that depend on asymmetries in local stability properties and between environmental and underlying system periodicities. Second, I show that periodic environments can also mediate competitive interactions, including environmentally-mediated competitive exclusion that would not be expected based on underlying deterministic characteristics. Here, I show how temporal asymmetries in competing species’ growth and competition can exacerbate unexpected outcomes of global change. Third, in a more applied module for coral reefs, I show that multi-stressors and environmental disturbances can cause unexpected state shifts, long transients and noise-driven alternate states. The geometric characteristics of this model allow us to unpack when and why we might see these unexpected outcomes and highlight context-dependent effects of multi-stressors. Finally, I show how modular theory can be applied to heavily-impacted socio-ecological systems. I show that under multi-species harvesting, reduced effort may benefit both biodiversity and livelihood security and that certain ecological and economic characteristics can amplify this result. The chapters presented here each contribute novel theory to the systems they are inspired by, and together contribute to a growing body of theoretical ecology for a changing world.