Eastern Illinois University The Keep Masters Theses Student Theses & Publications 2015 Trophic Interactions in a Semiaquatic Snake Community: Insights into the Structure of a Floodplain Food Web Cynthia M. Carter Eastern Illinois University This research is a product of the graduate program in Biological Sciences at Eastern Illinois University. Find out more about the program. Recommended Citation Carter, Cynthia M., "Trophic Interactions in a Semiaquatic Snake Community: Insights into the Structure of a Floodplain Food Web" (2015). Masters Theses. 2392. https://thekeep.eiu.edu/theses/2392 This is brought to you for free and open access by the Student Theses & Publications at The Keep. It has been accepted for inclusion in Masters Theses by an authorized administrator of The Keep. 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I have conferred with my graduate faculty advisor. My signature below indicates that I have read and agree with the abt>ve statements,Jild herebyfgive my permission to allow Booth Library to reproduce and distr\bute my th¢sis. My a9viso/s sign�tµfeindicates concurrence to reproduce and distribute the thesis. Gfa¢ate tanlfidate Signtlttre "': Aft. lAR.TFR PrintedCvrJr111A Name Graduate Degree Program Date Please submit in duplicate. TROPHIC INTERACTIONS IN A SEMIAQUATIC SNAKE COMMUNITY: INSIGHTS INTO THE STRUCTURE OF A FLOODPLAIN FOOD WEB. BY CYNTHIAM. CARTER THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN THE GRADUATE SCHOOL, EASTERN ILLINOIS UNIVERSITY CHARLESTON, ILLINOIS 2015 I HEREBY RECOMMEND THAT THIS THESIS BE ACCEPTED AS FULFILLING THIS PART OF THE GRADUATE DEGREE CITED ABOVE THESIS COMMITTEE CHAIR DATE / DEPARTMENT�OOL CHAIR �·DATE slr:s-- O�AIR'S DESIGNEE • 1HESIS COMMITTEE MEMBER DATE THESIS COMMITTEE MEMBER DATE THESIS COMMITTEE MEMBER DATE THESIS COMMITTEE MEMBER DATE Copyright© Cynthia M. Carter 2015 All rights reserved ABSTRACT Food webs provide a useful conceptual framework for evaluating the relationships that exist within ecological systems. Characterizing the interactions within these webs can improve our understanding of how communities are structured and what mechanisms stabilize them. Untangling these interactions can be an intractable problem in complex systems and insights gained from conventional methods are often accompanied by inherent sources of bias. This study used stable isotope analysis, an alternative to traditional methods, to investigate the roles and relative contributions of consumers at the top of a food web to community structure and stability. I compared the niche parameters of five syntopic semi-aquatic snake species using the ratios of naturally occurring carbon and nitrogen isotopes to determine their relative trophic positions and estimate the contributions of potential prey sources to their diets. Analyses using Bayesian mixing models revealed evidence of niche partitioning among consumer groups and indicated that competitive dynamics have helped to shape the structure of this community. I identified ontogenetic differences in the trophic niches occupied by distinct age classes from three consumer species. I also detected temporal shiftsin trophic structure that might be the result of intra-annual variation in resource availability. While competition appears to play a role in structuring this community, the trophic niches occupied by consumer groups seem to be somewhat plastic. Temporal shifts in resource availability have the potential to influence not only the relationships among competing consumers, but also their interactions with prey groups. Future research should examine how periodic fluctuations in prey abundance influences the connectivity, and by extension the stability, of this community. DEDICATION For MEBC, SLC, and KRLN ii ACKNOWLEDGMENTS "Working hard is notjust effort- it'slearning. It's tryingnew things, things that interest you that you might be scared to do or think you won't be able to do. Learningmore is all about taking chances." - Dolly Parton Dr. Stephen Mullin and I took a chance when we developed this project. At the time, there were plenty of reasons why it might have been smarter to take things in a different direction. Our ideas were logistically challenging and the risk that we might not succeed was very real. But my fear of falling flat on my face, and Steve's practical nature were superseded by our fascination with the critters and questions at the heart of this research. I am incredibly grateful for his unwavering encouragement of my enthusiasm. I am also thankful for the support and guidance of my committee members, Dr. Zhiwei Liu and Dr. Robert Colombo. Collectively, they have taught over half of the courses I have taken as a graduate student and have both added new dimensions to my research interests. Their counsel has been priceless. There is not doubt that this research could not have happened without my collaborators at Mingo National Wildlife Refuge. The entire staff provided me with invaluable assistance throughout my project. I am particularly grateful for the support of Ben Mense, Brad Pendly, and Lindsey Landowski. I felt more at home while at Mingo than I ever did in Charleston, and the idea of concluding my work there is truly heartbreaking. This research also would not have been possible without permission from the U.S. Fish and Wildlife Service and the Missouri Department of Conservation and, perhaps more importantly, funding from Eastern Illinois University in the form of a graduate assistantship, a Graduate iii School Research and Creative Activity Award, and a grant from the President's Fund for Research and Creative Activity. The advice and assistance I received from Thomas Maddox of the University of Georgia Analytical Chemistry Laboratory was instrumental in the success of this project. The faculty and staff of the Department of Biological Sciences have also supported me in innumerable ways. I am particularly grateful for the help of Drs. Scott Meiners, Karen Gaines, Gary Bulla, Eden Effert, Britto Nathan, Ruth Chesnut, and Paul Switzer. I am also thankful for the dependable assistance provided by Marschelle McCoy, Sandra Baumgartner, Derrick Douros, and Megan Przygoda. I am grateful to members of the Mullin lab; especially those who helped me sample preparation, particularly Adriana Reppell, Glenn Curry, Jacqueline Herman, Margaret Thomas, Lindsey Johnson, Sarah Manka, and Joseph Zigler. This project would not be what it is without the input I received from Andrew Durso, Meagan Thomas, and Dr. Eden Effert, who introduced me to the world of stable isotopes and helped me to navigate its murky waters. My final thanks go to the group of people who have helped in ways that are difficult to define, but whose contributions have been invaluable - Tara Hohoff, David Petry, Clint Morgeson, Todd Pierson, Anna Weyers, Meagan Thomas, Marci Gallagher, Abbie Stone, Ansley Dickinson, Kyle Nelson, Dr. Eloise Carter, Stefanie Carter, Cleave Pierce, Dr. John Maerz, and Dr. Joseph Mendelson. iv TABLE OF CONTENTS LIST OF TABLES ............................................................................................... vi LIST OF FIGURES ...............................................