EXAMINING NICHE PARTITIONING AND DIETARY CHANGE IN PYGOSCELIS PENGUINS USING STABLE ISOTOPES Michael J. Polito A Dissertation Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Department of Biology and Marine Biology University of North Carolina Wilmington 2012 Approved by Advisory Committee Stuart R. Borrett Heather N. Koopman Bongkeun Song William P. Patterson Steven D. Emslie Chair Accepted by Robert D. Roer Dean, Graduate School TABLE OF CONTENTS ABSTRACT……………………………………………………………………………………………….v ACKNOWLEDGMENTS………………………………………………………………………………..vii DEDICATION…………………………………………………………………………………………...viii LIST OF TABLES……………………………………………………………………………………..….ix LIST OF FIGURES………………………………………………………………………………………..x CHAPTER ONE: Tissue-Specific Isotopic Discrimination Factors In Gentoo Penguin ( Pygoscelis Papua ) Egg Components: Implications For Dietary Reconstruction Using Stable Isotopes……………………... 11 Introduction............................................................................................................................... 11 Materials and Methods.............................................................................................................. 13 Captive Penguin Diet and Tissue Collection ........................................................................ 13 Wild Penguin Diet and Tissue Collection............................................................................. 13 Sample Preparation and Isotopic Analysis ........................................................................... 14 Model and Statistical Analysis.............................................................................................. 19 Results....................................................................................................................................... 21 Captive Penguin Diet ............................................................................................................ 21 Isotopic Values of Captive Penguin Tissues......................................................................... 21 Diet-Tissue Discrimination Factors ...................................................................................... 22 Stable Isotope Values and Diet Composition of Wild Penguins .......................................... 22 Discussion................................................................................................................................. 23 Discrimination Factors in Avian Egg Components .............................................................. 25 Mixing Models, Discrimination Factors, and Dietary Reconstruction................................. 27 References................................................................................................................................. 30 CHAPTER TWO: Dietary Isotopic Discrimination In Gentoo Penguin ( Pygoscelis Papua ) Feathers…..35 Introduction............................................................................................................................... 35 Materials and Methods.............................................................................................................. 37 Results....................................................................................................................................... 39 Discussion................................................................................................................................. 41 References................................................................................................................................. 47 CHAPTER THREE: Ontogenetic And Oceanographic Factors Influence The Stable Isotope Values Of A Keystone Species, The Antarctic Krill ( Euphausia Superba ): Implications For Dietary Studies Of Krill Predators…………………………………………………………………………………………………..51 Introduction............................................................................................................................... 51 Materials and Methods.............................................................................................................. 54 Krill and oceanographic data collection. .............................................................................. 54 Sample preparation and isotopic analyses. ........................................................................... 56 Statistical analysis of krill samples....................................................................................... 57 ii Krill predator stable isotope values and dietary models. ...................................................... 58 Results....................................................................................................................................... 61 Variation in Antarctic krill and oceanographic factors......................................................... 61 Factors affecting the stable isotope values of Antarctic krill................................................ 63 Krill predator stable isotope values and dietary modeling.................................................... 63 Discussion................................................................................................................................. 67 Ontogenetic variation in the stable isotope values of krill.................................................... 69 Oceanographic factors and krill stable isotope values.......................................................... 70 Krill predator stable isotope values and dietary mixing models........................................... 71 Conclusion ................................................................................................................................ 74 References................................................................................................................................. 74 CHAPTER FOUR: Integrating Stomach Content and Stable Isotope Analyses to Quantify the Diets of Pygoscelid Penguins ……………………………………………………………………………………... 81 Introduction............................................................................................................................... 81 Materials and Methods.............................................................................................................. 83 Ethics statement .................................................................................................................... 83 Stomach contents, feather and prey samples ........................................................................ 84 Stable isotope analysis .......................................................................................................... 85 Isotopic mixing models......................................................................................................... 86 Statistical analysis................................................................................................................. 87 Results....................................................................................................................................... 89 Stomach content analysis...................................................................................................... 89 Isotopic signatures of chick feathers and prey...................................................................... 91 Two-source SIAR models..................................................................................................... 94 Multi-source SIAR models ................................................................................................... 94 Discussion................................................................................................................................. 98 Stomach content analysis...................................................................................................... 98 Two-source, SIAR models.................................................................................................. 100 Multiple-source, SIAR models ........................................................................................... 102 Integrating SCA and SIA when estimating seabird diets.................................................... 103 References............................................................................................................................... 104 CHAPTER FIVE: Stable Isotopes Reveal Regional Heterogeneity In The Pre-Breeding Distribution And Diets Of Sympatrically Breeding Pygoscelis Penguins ……………………………………………... …108 Introduction............................................................................................................................. 108 Materials and Methods............................................................................................................ 112 Study area and sample collection........................................................................................ 112 Sample preparation and isotopic analysis........................................................................... 113 Statistical and dietary analysis............................................................................................ 114 Results..................................................................................................................................... 116 Inter-specific and spatial variation in eggshell isotopic values .......................................... 116 Prey items and pre-breeding diet composition...................................................................