Rapid Trait Changes and Eco-Evolutionary Feedbacks Mediate Microbial Food Web Thermal Responses

Abstract

Predicting food web dynamics under global climate change is a pressing goal in ecology. Rapid trait changes, whether through rapid evolution or phenotypic plasticity, significantly influence contemporary food web dynamics through altering species interactions and subsequent trophic cascades. Therefore, understanding how rapid trait changes in interacting species affect population dynamics and food web structure is crucial for predicting how food webs and ecosystems will respond to future climates. My dissertation addresses the overarching question of how species traits rapidly respond to biotic and abiotic changes and how these trait responses feed back through eco-phenotypic and eco-evolutionary processes across trophic levels, ultimately shaping microbial food webs.In Chapter 2, I experimentally manipulated temperature and nutrient levels in microbial food webs to investigate how warming and eutrophication jointly influence ecological and phenotypic dynamics. Using time-series analysis, I found that the joint—and often interactive—effects of temperature and nutrients were strongest at higher trophic levels. Our results uncover how feedbacks between ecological and phenotypic dynamics mediate food web responses to environmental change. These results suggest important but previously unknown ways that temperature and nutrients might jointly control the rapid eco-phenotypic feedbacks that determine food web dynamics in a changing world. In Chapter 3, using experimental evolution and mathematical modeling in microbial food webs of prey algae and ciliate predators, I tested 1) how temperature affects prey evolution; and 2) how the context of the food web—i.e., predator identity, abundance, and competition between predators—mediates prey evolutionary dynamics. Our findings reveal that evolutionary outcomes under warming are shaped by the broader food web context of species, suggesting that the same species may exhibit different eco-evolutionary responses in different food webs under novel climates.In Chapter 4, I used experimental microcosms and mathematical modeling to ask 1) how prey rapid defensive responses affect predator-prey dynamics when predators also undergo trait shifts, and 2) how prey rapid defenses affect predator biomass. The observed trait-mediated trophic transfer efficiency and reversal of predator-prey cycles highlighted the key role of rapid trait changes in predicting food web and ecosystem functions.Together, my dissertation shows that climate change-driven environmental stressors change species population dynamics and species interactions. Moreover, species traits respond rapidly to changes in environmental conditions and species interactions, and in turn mediate those interactions. These rapid trait responses can fundamentally change population dynamics, predator-prey cycles, and trophic transfer efficiency, ultimately shaping food web responses in a warming world.