EFFECTS of INDIVIDUAL PHENOTYPIC VARIATION on PREDATOR-PREY RELATIONSHIPS of XANTHID CRABS in NORTH INLET ESTUARY, SOUTH CAROLINA Benjamin J

University of South Carolina Scholar Commons Theses and Dissertations 8-9-2014 EFFECTS OF INDIVIDUAL PHENOTYPIC VARIATION ON PREDATOR-PREY RELATIONSHIPS OF XANTHID CRABS IN NORTH INLET ESTUARY, SOUTH CAROLINA Benjamin J. Toscano University of South Carolina - Columbia Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Biochemistry, Biophysics, and Structural Biology Commons Recommended Citation Toscano, B. J.(2014). EFFECTS OF INDIVIDUAL PHENOTYPIC VARIATION ON PREDATOR-PREY RELATIONSHIPS OF XANTHID CRABS IN NORTH INLET ESTUARY, SOUTH CAROLINA. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/2901 This Open Access Dissertation is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. EFFECTS OF INDIVIDUAL PHENOTYPIC VARIATION ON PREDATOR-PREY RELATIONSHIPS OF XANTHID CRABS IN NORTH INLET ESTUARY, SOUTH CAROLINA by Benjamin J. Toscano Bachelor of Science University of Connecticut, 2008 Submitted in Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Biological Science College of Arts and Sciences University of South Carolina 2014 Accepted by: Blaine D. Griffen, Major Professor David S. Wethey, Committee Member Jeffry L. Dudycha, Committee Member Dennis M. Allen, Committee Member David R. Chalcraft, Committee Member Lacy Ford, Vice Provost and Dean of Graduate Studies © Copyright by Benjamin J. Toscano, 2014 All Rights Reserved. ii ACKNOWLEDGEMENTS First and foremost, I wish to thank my mother, Tena, for introducing me to the natural world as a child. She passed on to me a respect for all living things and an appreciation for the infinite detail of life on Earth. I also thank my father, Nick, and my sister, Julia, for their faith in my abilities and unwavering support. I thank Kathryn Levasseur for helping me grow as a person and making my time in South Carolina unforgettable. I thank my adviser, Dr. Blaine Griffen, for his endless generosity with time and thought, and the rest of my committee for encouraging me to consider the broader significance of my work as an ecologist. I thank my collaborators, Dr. John Griffin and Cristián Monaco, for helping make research fun again. Lastly, I thank the staff of the Baruch Marine Field Laboratory and North Inlet-Winyah Bay National Estuarine Research Reserve, and in particular Dr. Dennis Allen and Paul Kenny, for allowing me to spend my summers at Hobcaw Barony; a truly special place steeped in both natural and human history. iii ABSTRACT Ecological communities and the biological interactions that regulate community structure are notoriously complex. To make these systems more tractable, ecologists traditionally measure and model communities at the population level, treating individuals as functionally equivalent. While this approach has yielded tremendous insight into the factors governing communities, it remains unclear whether accounting for individual- level variation could improve our capacity to predict the responses of communities to perturbation, a major goal in the midst of unprecedented rates of environmental change. The objective of this study was to examine the magnitude of individual-level phenotypic variation in predatory crabs (family Xanthidae), and the effects of this variation on crab trophic behavior and the strength of their interactions with bivalve prey in oyster reef communities. Specifically, I measured individual variation in crab body size, behavioral traits and parasite infection. A main aspect of this work was testing how each of these factors affected the crab functional response, i.e. the per capita rate of prey consumption depending on prey density. This response is important in scaling up prey consumption rates to the population level, and to larger spatial scales. I also explored how oyster reef habitat structure and threat from toadfish, a predator of crabs, can mediate the ecological effects of crab phenotype. The results of this work support the importance of individual-level variation for species interactions that influence the structure of reef communities. The body size iv distribution of crabs, which is in part dependent on the presence of structurally complex reef habitat, determined their top-down effects on the bivalve prey community. Furthermore, individual behavioral traits scaled with crab body size and were consistent over time in the field. Individual crab behavior also varied independently of crab body size, but could not be predicted by individual metabolic rate. Individual-level variation in crab body size, behavioral traits and parasite infection all influenced the crab functional response to bivalve prey density in different ways. This work provides a general pathway (modification of the functional response) by which the effects of individual phenotypes can scale up to influence predator-prey population dynamics. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................................ iii ABSTRACT .......................................................................................................................... iv LIST OF TABLES ................................................................................................................. vii LIST OF FIGURES ............................................................................................................... viii CHAPTER 1 INTRODUCTION ...................................................................................................1 CHAPTER 2 PREDATORY CRAB SIZE DIVERSITY AND BIVALVE CONSUMPTION IN OYSTER REEFS ...............................................................................15 CHAPTER 3 PREDATOR SIZE INTERACTS WITH HABITAT STRUCTURE TO DETERMINE THE ALLOMETRIC SCALING OF THE FUNCTIONAL RESPONSE....................46 CHAPTER 4 EFFECT OF PREDATION THREAT ON REPEATABILITY OF INDIVIDUAL CRAB BEHAVIOR REVEALED BY MARK-RECAPTURE .............................................................78 CHAPTER 5 TESTING FOR RELATIONSHIPS BETWEEN INDIVIDUAL CRAB BEHAVIOR AND METABOLIC RATE ACROSS ECOLOGICAL CONTEXTS ........................107 CHAPTER 6 TRAIT-MEDIATED FUNCTIONAL RESPONSES: PREDATOR BEHAVIORAL TYPE MEDIATES PREY CONSUMPTION .................................................136 CHAPTER 7 PARASITE MODIFICATION OF PREDATOR FUNCTIONAL RESPONSE ...................168 CHAPTER 8 CONCLUSION ..................................................................................................194 LITERATURE CITED ...........................................................................................................201 APPENDIX A COPYRIGHT PERMISSION LETTERS ................................................................236 vi LIST OF TABLES Table 2.1 Substitutive experimental design treatments .....................................................39 Table 2.2 Bivalve prey used in experiment .......................................................................40 Table 3.1 Competing models predicting mussel location ..................................................72 Table 3.2 Functional response model parameter estimates ...............................................73 Table 4.1 Factors influencing crab refuge use behavior ..................................................103 Table 4.2 Factors influencing crab behavioral change ....................................................104 Table 6.1 Influences on proportional mussel consumption .............................................164 vii LIST OF FIGURES Figure 2.1 Size frequency distributions of bivalves from North Inlet ...............................41 Figure 2.2 Total prey consumption and substitutive model predictions ............................42 Figure 2.3 Consumption of bivalve prey types ..................................................................43 Figure 2.4 Contribution of bivalve prey types to dissimilarity between treatments ..........44 Figure 2.5 Reef height and average crab body size ...........................................................45 Figure 3.1 Density-dependent mussel location ..................................................................74 Figure 3.2 Mussel consumption and functional response model fits .................................75 Figure 3.3 Size scaling of functional response parameters ................................................76 Figure 3.4 Consumption of mussels at different distances from cluster edge ...................77 Figure 4.1 Size scaling of crab refuge use behavior ........................................................105 Figure 4.2 Repeatability of crab refuge use behavior after recapture ..............................106 Figure 5.1 Repeatability of crab activity level and metabolic rate ..................................132 Figure 5.2 Effects of predation threat on individual traits of crabs .................................133 Figure 5.3 Relationships between crab movement and metabolic rate ............................134 Figure 5.4 Relationships between crab activity level and metabolic rate ........................135 Figure 6.1 Effects of crab activity level on proportional mussel consumption ...............165 Figure 6.2 Functional responses in the absence and presence of threat ...........................166 Figure 6.3 Effect of activity on small crab functional response ......................................167 Figure

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