The effects of nutrient enrichment on an aquatic host-parasite system: Connecting individual consumer physiology to community-level infection risk Restricted; Files Only
Bradley, LM (Summer 2025)
Abstract
Nutrient enrichment and limitation profoundly shape the structure and function of ecosystems. For example, transient resource pulses leave long-lasting impacts on the systems they perturb. Beyond pulses, resource quantity and quality are highly dynamic, but previous conventions assume static resource quality in consumer-resource studies. Host-parasite dynamics present unique opportunities for studying consumer-resource interactions in nutritionally dynamic environments because, fundamentally, parasites must sustain themselves entirely by stealing energy and nutrients from their hosts. Thus, feedback between resources, consumer hosts’ performance, and parasite abundance can elucidate mechanisms important for building ecological theory and addressing applied challenges in human health, agriculture, and biogeochemistry. In this dissertation, I primarily use a snail-schistosome system to study such feedbacks. Schistosomes are freshwater trematode parasites that cyclically infect humans and snails, causing schistosomiasis, a Neglected Tropical Disease with dire impacts on the health and economies of people worldwide. In this host-parasite system, increased resource consumption by snails directly boosts per-snail parasite production, translating to increased human infection risk. However, it is not well understood how changes in resource quantity or quality impact host-parasite dynamics.
This dissertation studies the impact of resource quality and competition on the snail-schistosome system at different levels of ecological organization (i.e., individual-, population, and community-levels). Additionally, this dissertation presents a general bioenergetic model framework for connecting elemental nutrient content in resources to consumer metabolism, even under fluctuating conditions of resource quantity and quality. Through studying resource pulses in an artificial pond experiment (i.e., mesocosm), I confirm that snails rapidly respond to sudden release from resource competition and significantly increase release of schistosome parasites. However, this response depends on population size structure and feeding history, which has implications for translating these results to human schistosomiasis infection risk. Additionally, through an individual-level experiment manipulating snail diets, I show that snail host life history traits (i.e., growth, reproduction) are differentially sensitive to the type and degree of elemental nutrient limitation. Finally, I present a theoretical framework for consumer-resource dynamics, incorporating empirical findings from the first two chapters by incorporating diet hysteresis and allowing for different nutrient requirements between somatic and reproductive processes.
Table of Contents
Chapter I—Introduction: 1
Background: 1
Summary of Dissertation Chapters: 5
Figures: 8
References: 9
Chapter II—Eat fast and die big: Competitor biomass and individual body size mediate the intensity of resource pulse impacts on a host-parasite system: 15
Abstract: 16
Introduction: 18
Methods: 20
Results: 28
Discussion: 30
Figures: 35
Supplementary Information: 38
References: 44
Chapter III—Nutrients for thee, not for me: How schistosome infection and nutrient supplementation interact in an intermediate freshwater snail host, Biomphlaria glabrata: 49
Abstract: 50
Introduction: 51
Methods: 54
Results: 62
Discussion: 62
Acknowledgements: 72
Figures: 73
Tables: 80
Supplementary Information: 82
References: 90
Chapter IV—DEBstoich: Merging Dynamic Energy Budget and Ecological Stoichiometry theories to model life in our nutritionally dynamic world: 96
Abstract: 97
Introduction: 98
Model Formulation: 103
System Dynamics: 103
Ingestion flux: 106
Assimilation and Egestion Fluxes: 106
Somatic Maintenance Fluxes: 108
Developmental Maintenance Fluxes: 111
Growth Fluxes: 112
Maturity and Reproduction Buffer Fluxes: 114
Reserve Mobilization Fluxes: 115
Simulation Study Methods: 116
Simulation Study Results: 118
Discussion: 119
Tables: 122
Figures: 130
References: 138
Chapter V—Conclusions: 143
Summary and Discussion of Previous Chapters: 143
Future Directions: 146
About this Dissertation
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File download under embargo until 21 August 2026 | 2025-07-22 13:33:00 -0400 | File download under embargo until 21 August 2026 |
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