Florida International University FIU Digital Commons FIU Electronic Theses and Dissertations University Graduate School 6-15-2020 Beyond Predation: How Do Consumers Mediate Bottom-up Processes in Ecosystems? Bradley Austin Strickland [email protected] Follow this and additional works at: https://digitalcommons.fiu.edu/etd Part of the Behavior and Ethology Commons, Biodiversity Commons, Marine Biology Commons, Population Biology Commons, Terrestrial and Aquatic Ecology Commons, and the Zoology Commons Recommended Citation Strickland, Bradley Austin, "Beyond Predation: How Do Consumers Mediate Bottom-up Processes in Ecosystems?" (2020). FIU Electronic Theses and Dissertations. 4520. https://digitalcommons.fiu.edu/etd/4520 This work is brought to you for free and open access by the University Graduate School at FIU Digital Commons. It has been accepted for inclusion in FIU Electronic Theses and Dissertations by an authorized administrator of FIU Digital Commons. For more information, please contact [email protected]. FLORIDA INTERNATIONAL UNIVERSITY Miami, Florida BEYOND PREDATION: HOW DO CONSUMERS MEDIATE BOTTOM-UP PROCESSES IN ECOSYSTEMS? A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in BIOLOGY by Bradley Austin Strickland 2020 To: Dean Michael R. Heithaus College of Arts, Sciences and Education This dissertation, written by Bradley Austin Strickland, and entitled Beyond Predation: How Do Consumers Mediate Bottom-up Processes in Ecosystems?, having been approved in respect to style and intellectual content, is referred to you for judgment. We have read this dissertation and recommend that it be approved. _______________________________________ Frank J. Mazzotti _______________________________________ Yannis P. Papastamatiou _______________________________________ Jennifer S. Rehage _______________________________________ Joel C. Trexler _______________________________________ Michael R. Heithaus, Major Professor Date of Defense: June 15, 2020 The dissertation of Bradley Austin Strickland is approved. _______________________________________ Dean Michael R. Heithaus College of Arts, Sciences and Education _______________________________________ Andrés G. Gil Vice President for Research and Economic Development and Dean of the University Graduate School Florida International University, 2020 ii © Copyright 2020 by Bradley Austin Strickland All rights reserved. iii DEDICATION To Katherine, my lovely wife, whose beauty and love inspires me every day. And to my parents, Delmer and Suanna, who always give me encouragement. iv ACKNOWLEDGMENTS I appreciate the work of my advisor, Mike Heithaus, who has taught me so much about how to communicate science. He has been an inspiring role model and an encouraging and energetic teacher every step of the way. I could not have done this work without the support of my committee. Joel Trexler is one of the most significant mentors I have had in my career. I really appreciate his patience and the many hours spent molding me into a better scientist. Jennifer Rehage has always been supportive and has taught me so much about the Everglades. Frank Mazzotti is likely the most influential crocodilian researcher alive; I have greatly benefited from his expertise and incredible understanding of alligators. Yannis Papastamatiou and his incredible knowledge of movement ecology and physiology has been a valuable contribution to my work. I would like to acknowledge the University Graduate School at FIU for providing both the Doctoral Evidence Acquisition Fellowship and the Dissertation Year Fellowship. These two awards were instrumental in helping me collect data and write my dissertation. I also appreciate the Everglades Foundation and FIU who provided a research fellowship that allowed me to develop and fund part of my dissertation. Much of the research within this dissertation was graciously funded by the National Science Foundation’s Long-Term Ecological Research grant to the Florida Coastal Everglades site. It is a pleasure to be a part of such an awesome team of FCE scientists working hard to understand the Everglades. John Kominoski and Evelyn Gaiser have been wonderful mentors and champions for graduate student development. I also want to thank a huge number of people who have given their time and energy to help in both the field and lab. Kirk Gastrich, Phil Matich, Rob Nowicki, and v Adam Rosenblatt have set fantastic examples as scientists and have been so generous with their time and help. Bill Chamberlain, Valerie Hall, Rafael Gonzalez, SERC, Institute of Water, FIU, and Everglades National Park staff have been incredible in their logistical support. Sarah Sisco, Yamilla Samara, and Laura Garcia Barcia dedicated hundreds of hours to make this work possible. Jordan Massie, Ross Boucek, and Natasha Viadero are awesome field biologists and I have been happy to learn from them. There is no way this work could have been done without the muscle and brains of Peter Flood; he is both a great friend and collaborator. I also want to thank Maurits van Zinnicq Bergmann and Zoran Bursac for help with statistical modeling and Megan Kelley with her expertise in nutrient transportation. Venus Garcia, Maria Sabando, and countless other technicians and volunteers across multiple labs have helped in both the field and lab. I also appreciate all of the Croc Docs team (especially Jeff Beauchamp, Michiko Squires, Seth Farris, Mike Cherkiss, and others) that helped deploy tags. I have a large group of friends at FIU who have made this journey a pleasure and I could not imagine a better group of people. I have benefited greatly from my friendship with Alex Ontkos and his understanding of the Everglades. I appreciate all of my lab mates, in particular the incredible support of Camila Cáceres, Frances Farabaugh, and Valeria Paz. I want to thank both Richard Brinn and Lorilee Valientes for making me a better instructor, and I appreciate all the professors who have made me a better scientist. I am so grateful to have a supportive and loving family. My parents, Delmer and Suanna, have always worked hard in life to provide for me, and have encouraged me to focus on making myself a better person. Their sacrifices made me who I am today. I am blessed with the close friendship of both of my siblings, Carrie and Alex. I am also vi grateful to have married into a kind and generous family. Lastly, I want to thank my wife, Katherine. She has been instrumental in my ability to do this work. This dissertation is as much hers as it is mine. Her love and encouragement is the reason words ever made it to paper. vii ABSTRACT OF THE DISSERTATION BEYOND PREDATION: HOW DO CONSUMERS MEDIATE BOTTOM-UP PROCESSES IN ECOSYSTEMS? by Bradley Austin Strickland Florida International University, 2020 Miami, Florida Professor Michael R. Heithaus, Major Professor By eating and scaring prey, predators can exert strong effects on communities and ecosystems. In addition, some animals may physically alter habitats and may recycle nutrients through digestion, both of which affect resources available to producers. Bottom-up effects initiated by large predators have not been well-studied and could prove to be important for understanding food webs and how ecosystems function. American alligators (Alligator mississippiensis) are abundant mobile predators that are capable of engineering aquatic habitats by moving organic material across ecosystem boundaries and creating and maintaining alligator ponds. In this dissertation, I documented the scale of ecological impacts of alligators by studying movement and habitat use across a range of environmental conditions. I observed cross-ecosystem movements against a productivity gradient from nutrient-rich marine habitats, intermediately productive mid- estuary zones, and oligotrophic upstream freshwater marshes. Individual variation in movement behavior may manifest into different ecological roles of individuals within the population. I also found that alligator movement and habitat use is strongly tied to hydrology and thus alligators are sensitive to the effects of restoration of freshwater viii inflow into wetlands. A field study of alligator ponds in the oligotrophic Everglades freshwater marsh revealed the engineering effects of alligators on both community structure and ecosystem function. Alligator-engineered habitats were phosphorus- enriched and had dissimilar trophic structure including differences in algal, plant, and consumer communities compared to the surrounding marsh. Alligator ponds also showed shifted energy flow towards algal production compared to more detrital pathways in the marsh. Overall, I found that consumer-mediated bottom-up effects through nutrient transport and engineering are ecologically important especially in areas where increased habitat heterogeneity and nutrient enrichment may yield positive effects on primary producers and lower trophic levels. This dissertation emphasizes the importance of considering multiple pathways of trophic effects in food web models. Future work may allow us to partition the effects of the diversity of a predator and engineer’s role on trophic structure and accurately predict the effects of loss of function in one or more of these roles. Such a model will greatly enhance our understanding of community and ecosystem dynamics. ix TABLE OF CONTENTS CHAPTER PAGE I. GENERAL INTRODUCTION ....................................................................................... 1 Literature Cited ......................................................................................................