Life history traits, social organisation and the drivers of sociality in an invasive ground squirrel by Anne Marie van der Marel A thesis submitted to the Faculty of Graduate Studies of The University of Manitoba in partial fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY Department of Biological Sciences University of Manitoba Winnipeg, MB, Canada Copyright © 2019 by Anne Marie van der Marel Thesis abstract Sociality evolves when the benefits outweigh the costs of interacting with conspecifics and can be influenced by genetic, phylogenetic, life history, or ecological constraints. Many groups are formed by natal philopatry with the environment constraining levels of sociality. For example, diurnal rodents living in harsh environments can be social to avoid the costs of predation. I used the invasive population of the Barbary ground squirrel (Atlantoxerus getulus) on the arid island of Fuerteventura, Spain, as my study system to explore this idea. Two Barbary ground squirrels were introduced to Fuerteventura in 1965. As they are invasive, I first questioned whether life history traits influenced their invasion success. Then, I used observational, experimental and genetic data to investigate whether they are social and whether predator avoidance is a selective pressure influencing their social patterns by studying their vigilance and alarm vocalisations. Barbary ground squirrels have large and frequent litters, and thus show potential for rapid population growth with a generation time of approximately one year, which may have contributed to their invasion success. They are social, as both males and females interact throughout the day, but they show sexual segregation of sleeping burrows. As group size increased, individual vigilance did not decrease, but collective vigilance did increase and they use alarm calls to warn group members of danger. Hence, they show partial collective detection of predators. The absence of a group-size effect can be explained since the squirrels synchronise their vigilance bouts. Thus, the constraints of living as a diurnal species in an arid environment and predation pressure are possible selective pressures explaining sociality in the invasive Barbary ground squirrel. This thesis advances our understanding of sociality in African ground squirrels, but also provides valuable insight into population growth and corresponding invasion success of an introduced species, as invasive ii species provide a unique framework to study evolution of sociality and population biology over a relatively short timeframe. iii Acknowledgements First and foremost, I thank my supervisor Jane Waterman and my collaborator Marta López-Darias for giving me the opportunity to take on this PhD project, for your patience and motivation, and for teaching me how to tell a clear story. Together with my committee members James Hare and Nicola Koper, you provided me with invaluable assistance and guidance along this journey making me a better researcher. I also thank my fellow graduate students, the past and present Roth and Waterman lab members, particularly my lab and office mates Elaine Anjos, Rebecca Lem, and Philip Shimel, for their friendship and all the support these last years. Since I spent 19 months on Fuerteventura to perform my field work, I cannot forget to thank all the people on the island that made my field work an amazing experience. Thank you to the landowners of my study sites because without the consent of the landowners this thesis would not have been possible. To the students Megan Miraglia, Elise Koole, Julien Piquet and Kat Kratzer for their help in the field. To the CSIC for helping me with the logistics, the Cabildo of Fuerteventura for allowing me to stay at the Estación Biológica de La Oliva, and the staff at the station for their hospitality. To Alejandro for being my translator, for teaching me the Majorero culture, and together with the people from Joyas surf school for not allowing me to become the crazy chica de las ardillas (‘crazy squirrel lady’). Especially, I thank my family back in The Netherlands, who supported me throughout this journey and motivated me to pursue my childhood dream of becoming an animal researcher. Most of all, I thank my boyfriend and best friend Chris for always being there for me, for believing in me, for supporting me through both the lows and highs of writing this thesis, and for the countless times he picked me up from university, so I did not have to take the bus in -30˚ C. iv Dedication To my grandmother, Anneke Homan-van der Weel v Table of contents Thesis abstract ............................................................................................................................. ii Acknowledgements .................................................................................................................... iv Dedication ................................................................................................................................... v Table of contents ........................................................................................................................ vi List of Tables ............................................................................................................................ viii List of Figures ............................................................................................................................ xi List of Appendices .................................................................................................................... xiii Chapter 1 General introduction ................................................................................................. 1 Sociality ................................................................................................................................... 1 Constraints on sociality ........................................................................................................... 1 Rodents as a study system ....................................................................................................... 4 Objectives and thesis organisation........................................................................................... 5 Literature cited ......................................................................................................................... 7 Chapter 2 Exploring the role of life history traits and introduction effort in understanding invasion success in mammals ....................................................................................................... 17 Abstract .................................................................................................................................. 18 Introduction ........................................................................................................................... 19 Methods ................................................................................................................................. 23 Results ................................................................................................................................... 29 Discussion .............................................................................................................................. 31 Acknowledgements ............................................................................................................... 38 Literature cited ....................................................................................................................... 38 Chapter 3 Unique social organisation in a North African ground squirrel .............................. 55 Abstract .................................................................................................................................. 56 Introduction ........................................................................................................................... 57 Methods ................................................................................................................................. 62 Results ................................................................................................................................... 70 Discussion .............................................................................................................................. 74 Acknowledgements ............................................................................................................... 81 Literature cited ....................................................................................................................... 81 vi Chapter 4 Group-enhanced predator detection and quality of vigilance in a social ground squirrel ........................................................................................................................... 103 Abstract ................................................................................................................................ 104 Introduction ......................................................................................................................... 105 Methods ............................................................................................................................... 108 Results ..................................................................................................................................114 Discussion .............................................................................................................................118