Causal Mechanisms of Food Web Structure and Function - A Tale of Three Drivers: Spatiotemporal Variation, Ecosystem Engineering, and Invasive Species

Authors

Peter J. FloodFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biology

First Advisor's Name

Peter J Flood

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Joel Trexler

Second Advisor's Committee Title

Committee member

Third Advisor's Name

William Anderson

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Evelyn Gaiser

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Alastair Harborne

Fifth Advisor's Committee Title

Committee member

Sixth Advisor's Name

Daniel Simberloff

Keywords

food webs, diet plasticity, omnivory, stable isotopes, stomach contents, environmental variation, stress gradient hypothesis, trophic disruption hypothesis, trophic niche

Date of Defense

11-10-2022

Abstract

Food webs are natural networks that provide a comprehensive framework for understanding how ecosystems function. Structure and function of food webs are predicated on resource availability, which is in turn driven by fluctuations in abiotic conditions that vary in space and time. Ecosystem engineers, such as American alligators (Alligator mississippiensis), which create and maintain novel habitats, and invasive species, such as African Jewelfish (Hemichromis letourneuxi), further influence trophic dynamics and therein ecosystem function. In my study system, Everglades National Park, African Jewelfish have recently undergone a drastic increase in density with associated declines in native fauna. In this dissertation, I quantified trophic dynamics between seasons and among habitats prior to African Jewelfish invasion. I found that consumers often underwent spatiotemporal shifts in diet and trophic niche, but that flexible omnivory facilitated relatively constant trophic positions. I used a contemporary study of alligator-engineered habitats to quantify effects of habitat modification on trophic dynamics and to test the Stress Gradient Hypothesis (SHG). I found that many consumers underwent dietary shifts in engineered habitats, that trophic niches based on stomach ix contents increased during the dry season, and that trophic niches based on stable isotopes had the opposite trend. The stomach content results suggested decreased competition in the dry season based on the Niche Variation Hypothesis and supported the SGH, while the stable isotope results suggested that other drivers such as consumption may play a more important role than competition in structuring these communities over longer time intervals. I compared shared habitats from the previous two chapters (ponds and marshes) to examine trophic effects of African Jewelfish and test the Trophic Disruption Hypothesis (TDH). Post-invasion, I found widespread trophic displacement and dispersion, increased reliance on autotrophic energy, that spatiotemporal trophic dynamics had a greater magnitude, and a fundamental shift in energy fluxes through the food web that supported the TDH. Energy fluxes that had previously traveled through small, abundant fishes were rerouted to larger fishes, including invasive Cichlids such as African Jewelfish. This dissertation emphasizes the importance of spatiotemporal variation, ecosystem engineers, and invasive species on trophic dynamics and ecosystem function.

Identifier

FIDC010949

ORCID

https://orcid.org/0000-0002-0772-4920

Recommended Citation

Flood, Peter J., "Causal Mechanisms of Food Web Structure and Function - A Tale of Three Drivers: Spatiotemporal Variation, Ecosystem Engineering, and Invasive Species" (2022). FIU Electronic Theses and Dissertations. 5167.
https://digitalcommons.fiu.edu/etd/5167