Influences on Lactation Length and the Timing of Weaning Events in Colobus Vellerosus
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University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2016-01-29 Influences on Lactation Length and the Timing of Weaning Events in Colobus vellerosus Crotty, Angela Crotty, A. (2016). Influences on Lactation Length and the Timing of Weaning Events in Colobus vellerosus (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/26523 http://hdl.handle.net/11023/2800 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Influences on Lactation Length and the Timing of Weaning Events in Colobus vellerosus by Angela M. M. Crotty A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS GRADUATE PROGRAM IN ANTHROPOLOGY CALGARY, ALBERTA JANUARY, 2016 © Angela M. M. Crotty 2016 Abstract I explored variation in maternal investment strategies. I investigated whether infant sex, food availability, female feeding competition or infanticide risk influenced lactation length, the context of nursing cessation and the extent to which mothers can simultaneously gestate and lactate in a wild colobine. I combined long-term records and new observations of Colobus vellerosus. I extracted 40 nursing cessations, 13 exact lactation lengths, and 26 durations between nursing cessation and subsequent births. The independent variables did not influence lactation length, and nursing cessation did not differ by infant sex or cluster with food availability. Lactation length, maternal age, infant sex, infanticide risk, feeding competition, and potential infant handlers available did not influence the duration length to the next birth. This study eliminated some potential variables that may have explained nursing cessation and lactation length variation in our species, although it is evident that other underlying factor(s) are causing the variation. ii Acknowledgements I am forever fortunate and grateful for my supervisor Dr. Pascale Sicotte, for taking a shot on a rough-around-the-edges Maritimer like myself. From your trust and often tedious investment, I have gained invaluable work ethic, courage and the confidence to achieve anything. I am also thankful to Drs. Linda Fedigan, Warren Wilson, Peter Dawson and Steig Johnson for taking the time and consideration to serve as my proposal and/or defense committee members. Thank you to the Ghanaian Wildlife Division and the people of Boabeng and Fiema for allowing me to live and conduct research in their beautiful forest. I am incredibly fortunate for the funding provided by the Graduate Research Scholarship, University of Calgary Research Committee scholarship and the Department of Anthropology and Archaeology. An enormous thank you to the Department of Anthropology and Archaeology, specifically the wonderful staff (Monika Davison, Julie Boyd and Courtney Wright) running the administration for solving any unforeseeable problems I had without a hitch. Thank you to Dr. Fernando Campos for sharing your R genius, Dr. Tak Fung for solving my mixed model confusion and Dr. Urs Kalbitzer for advice. This project would not have been possible without the generous access to the long-term BFMS records collected by Dr. Eva Wikberg, Lisa MacDonald, Josie Vayro and Stephanie Fox. I vividly remember how difficult it is to collect every piece of data, and I appreciate you sharing your hard work with me. To my Canadian field assistants Bethany Hansen and Rebecca Ollenberger – you two are an inspiration in work ethic, determination, and positive attitude. I am forever grateful to you two for keeping me from becoming malnourished, picking off ants and saving me from falling over. If given the chance, I would choose you again. To my two iii Ghanaian assistants, Robert Korangteng and Charles Kodom, I appreciate your endless work ethic, jokes, Twi lessons and friendship. I am forever indebted to Josie Vayro for her patience, tips and life-long friendship. I am eternally grateful that we sat beside one another in the van so many years ago – it has ‘mostly’ been a pleasure. Thank you to my University of Calgary network, especially Monica Myers, Stephanie Fox and Mackenzie Bergstrom for your friendship, wine/beer and assistance whenever asked. Ultimately, none of this would have been imaginable or achievable without the help of my loving “loan shark” parents, brothers and life-long friends that have all stuck it out with me. Thank you for the never failing encouragement, love and the perspective you gave when things seemed tough. iv Dedication To the wonderful people of Boabeng and Fiema: thank you for teaching me the true meaning of hard work, happiness and life in general. If the world were as generous, welcoming and appreciative as you are, it would be a beautiful place. ! v Table of Contents Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iii Dedication ........................................................................................................................................v Table of Contents ......................................................................................................................... viii Table of Figures ............................................................................................................................ ix CHAPTER ONE: OVERVIEW ...................................................................................................... 1 1.1 Introduction ......................................................................................................................... 1 1.2 Literature review ................................................................................................................ 2 1.2.1 Constraints on Lactation length ..................................................................................... 2 1.2.2 Primate lactation ............................................................................................................ 3 1.2.3 Weaning age as a life history variable ........................................................................... 5 1.2.4 Colobine life history characteristics ............................................................................... 7 1.2.5 Factors influencing intra-specific variation in lactation length ................................... 10 1.2.5.1 Food availability and group size as influential factors ......................................... 10 1.2.5.2 Infanticide as an influential factor ........................................................................ 13 1.2.5.3 Simultaneous gestation and lactation .................................................................... 16 1.3 Thesis aims ......................................................................................................................... 18 1.3.1 Hypotheses and predictions ......................................................................................... 18 CHAPTER TWO: METHODS ..................................................................................................... 22 2.1 Study Site ........................................................................................................................... 22 2.2 Study Species ..................................................................................................................... 22 2.3 Data Collection .................................................................................................................. 24 2.3.1 Demographic data table and study subjects ................................................................. 24 2.3.2 Phenological Data ........................................................................................................ 25 2.4 Data Analysis ..................................................................................................................... 26 2.4.1 Analysis Part One: Factors influencing lactation length .............................................. 26 2.4.1.1 The effect of sex .................................................................................................... 27 2.4.1.2 The effect of male group composition .................................................................. 27 2.4.1.3 The effect of adult female group size ................................................................... 27 2.4.2 Analysis Part Two: Analyzing the Context of Nursing Cessation ............................... 28 2.4.3 Analysis Part Three: Duration between nursing cessation and subsequent birth ........ 31 2.4.3.1 The correlation between lactation length and duration to the next birth .............. 32 2.4.3.2 The effect of sex on duration to the next birth ...................................................... 32 2.4.3.3 The effect of maternal age on duration to the next birth ....................................... 32 2.4.3.4 The effect of male group composition on duration to the next birth