Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry and Environmental Studies

First Advisor

Schmitz, Oswald

Abstract

Understanding how organisms shape ecosystems is a central goal of ecology, particularly in an era of rapid environmental change. While ecosystem models have traditionally emphasized species-level diversity and abiotic controls, this dissertation provides evidence that trait variation within species—driven by phenotypic plasticity and transgenerational effects—can have consequences for ecosystem structure and function. Intraspecific variation is increasingly recognized as a key component of biodiversity-ecosystem function relationships, yet its effects remain underrepresented in empirical studies and predictive frameworks. By integrating multigenerational field experiments, multi-trait assessments, and detailed ecosystem measurements in a long-term, well-characterized study system, this dissertation bridges evolutionary ecology and ecosystem science to explore how population-level trait differences and plastic responses drive patterns of nutrient cycling, plant community composition, and ecological resilience. In Chapter 1, I use a common gardening experiment to demonstrate that grasshopper populations with distinct climatic histories differ in their ecosystem effects. Populations from warm versus cool regions had divergent impacts on soil carbon, nitrogen mineralization rates, and plant diversity. The variation in ecosystem outcomes due to population differences was greater than the variation attributed to geographic location, suggesting that population-level variation in consumer traits can rival abiotic gradients in shaping ecosystem function. Chapter 2 examines transgenerational plasticity in behavioral and physiological traits across multiple grasshopper populations. I find that historical climate and predator exposure, not environmental predictability, best explain patterns of transgenerational plasticity. Individuals from cooler regions consistently reduced canopy height across generations, while those from warmer regions do so only in response to predator exposure. No transgenerational shifts are observed in respiration rates, suggesting that behavioral plasticity plays a more prominent role in inherited responses to environmental stress. Chapter 3 shows that predator-induced transgenerational plasticity can amplify ecosystem effects across generations. Second-generation grasshoppers from predator-exposed lineages drive greater suppression of goldenrod, changes in plant community structure, and enhanced soil carbon retention compared to non-exposed lineages. These effects are mediated by persistent changes in habitat use, demonstrating that the legacy of predation can cascade through ecosystems. Finally, Chapter 4 presents a conceptual framework and toy model to explore how different types of trait plasticity may be deployed in response to varying dimensions of global change. The model highlights that the ecological and evolutionary consequences of plasticity depend on the scale, predictability, and structure of environmental variation. The conceptual framework then leads to practical, specific recommendations for future research on phenotypic plasticity under global change. Together, these chapters show that intraspecific variation is not merely a modifier of ecological outcomes—it is a core driver of ecosystem function. By highlighting the ecological importance of population-level trait differences, inherited behavioral responses, and the context-dependence of plasticity, this work bridges the fields of evolutionary ecology and ecosystem science. It also makes a broader case for place-based, applied ecology—one that recognizes variation within species as critical to understanding, managing, and sustaining ecosystems under environmental change.

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