Date of Award
Doctor of Philosophy (PhD)
Ecology and Evolutionary Biology
Ecosystems are highly connected systems with many interacting components. Understanding the mechanisms creating ecosystem patterns requires an explicit consideration of the scales at which interactions among species and their environments occur. This dissertation focuses on the scale of temporal variability and how temporal variability is incorporated into communities’ dynamics. I first derive an abstract theory that describes the general patterns of variability propagation within communities. Next, I explore the role of species’ interaction strengths on community dynamics across time scales. Finally, I study the impact of human-induced hydrological changes of the Guadalquivir River on the European anchovy fishery in the Gulf of Cadiz.Chapter 1 uses linear response theory to extend the top down and bottom up views of ecology across time scales. Specifically, I study a tri-trophic food chain and how fluctuations in productivity filter up the food chain. I find that variability follows the pattern predicted by top-down equilibrium-based theories at slow time scales. However, at an intermediate time scale, consumers can both decrease and increase the sensitivity of lower trophic levels to variability. For example, perturbations at intermediate frequencies can excite the endogenous cycles of a community leading to resonance. Only at the fastest time scales do top down effects begin to break down as variability becomes dampened at higher trophic levels. This theory provides a robust new framework to interpret food web patterns resulting from resource pulses and other bottom up perturbations. Chapter 2 combines the metabolic theory of ecology and empirical information of consumer-resource interactions to ground the general theory developed in Chapter 1. Body size is not only a significant determinant of vital rates and but also species interaction strengths. This approach allows me to focus on biologically relevant parameter space. I predict that predators can control herbivores and producers' variability at a time scale of days to years. This theory predicts that indirect effects actively shape communities' responses across a wide range of ecologically relevant time scales. Finally, in Chapter 3, I explore the relationship between ecology and society by studying how agricultural water use is connected to the marine anchovy fishery in Spain’s Gulf of Cadiz. Using time series analysis, I explore the correlations between hydrology, the estuarine community, and anchovy recruitment to the Gulf of Cadiz. The Guadalquivir river’s mean annual discharge and seasonality have decreased over the last 90 years due to increasing river regulation and extraction. European anchovies use the river estuary as a nursery. These hydrological changes have reduced anchovy recruitment to the Gulf of Cadiz, connecting terrestrial water use with the marine fishery. I then produce a water allocation theory for terrestrial agriculture and a marine fishery. I predict that even practices that improve water efficiency will not necessarily prevent terrestrial ecosystems from total water consumption. I find that the protection of downriver ecosystem services is only protected when the benefits to marine ecosystems are considered nonsubstitutable with terrestrial ecosystems. The issue of scale – ecological and spatiotemporal – is at the heart of my thesis. My first chapter shows that the percolation of variability is not invariant across time scales. In my second chapter, I predict how body size drives differences in community responses to variability. These theories can provide new insights into how variability impacts communities. Finally, in my last chapter, I explore rivers and migration can create trade-offs between seemingly isolated ecosystems.
Simon, Franz Wesley, "Interactions among species and ecosystems determine their responses to scale-specific fluctuations" (2021). Yale Graduate School of Arts and Sciences Dissertations. 414.