Date of Award

8-2020

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Environmental Biology

First Advisor

Jarrett E. K. Byrnes

Second Advisor

Jennifer L. Bowen

Third Advisor

Ron J. Etter

Abstract

Coastal ecosystems are some of the most valuable habitats on Earth but are under constant threat from human activities such as habitat destruction, pollution, or the spread of invasive species. Human effects in particular are known to disproportionally impact species at the tops of marine food webs (i.e. predators). Predators affect their prey through consumptive and non-consumptive effects, but also have a difficult to determine role on overall ecosystem functioning through control of overall community dynamics or species interactions. In this dissertation I examine the role of predators in structuring coastal ecosystem food webs, changing species interactions, and regulating ecosystem functioning. Using both surveys and long term field experiments I (1) examine how an invasive, cross-ecosystem predator, the feral hog Sus scrofa, affects the recovery and resilience of coastal Georgia salt marshes, (2) investigate the role of this invasive predator on plant community dynamics in a Georgia brackish marsh ecosystem, and (3) test how variation in predator identity and abundance throughout New England marshes affects community dynamics and ecosystem multifunctionality. In salt marshes along the southeastern US, the feral hog tramples vegetation and consumes ribbed mussels, Geukensia demissa, reversing the outcome of a resilience enhancing Spartina¬ – mussel mutualism. While hog destructive activity decreases recovery from disturbance on multiple spatial scales in salt marshes, hog trampling and foraging also changes competitive hierarchies in brackish marsh sedges. Hogs destroy less nutritious but dominant space-holding grasses, making room for a more nutritious competitive inferior by moving borders between these plant species up to 1m/year and suggesting they have strong controls on the persistence and coexistence of brackish marsh plant communities. In New England marshes, I found strong positive relationships between predator diversity and abundance on marsh-scale multifunctionality The positive additive effect of both bird and marine predator guilds on ecosystem functions like decomposition and sedimentation rate was consistent in our experiment as plots where both predator guilds had access performed more functions at higher rates than others. My results indicate that predators control the structure and function of salt marshes up and down the coast by affecting species interactions, controlling response to disturbances and driving multifunctionality. Predators that control food web structure have the ability to affect wide reaching processes and understanding how these roles may change in the future is crucial to successful coastal management and conservation.

Comments

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Available for download on Saturday, December 18, 2021

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