The Organisation of Polydomous Nesting in Wood Ant Colonies: Behaviour, Networks, Foraging and Resource Redistribution
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The organisation of polydomous nesting in wood ant colonies: behaviour, networks, foraging and resource redistribution. Samuel Ellis PhD University of York Biology April 2015 Abstract Social behaviours are an important component of evolutionary success. This is perhaps most evident in the societies of social insects: the interactions between individuals underlie the organisation of their highly complex, and highly successful, societies. An important socially organised determinant of ecological success for social insects is nesting strategy. Many ant species can have a polydomous nesting strategy: a polydomous colony inhabits several spatially separated, but socially connected, nests. How this complex nesting strategy is organised is largely unknown. I undertook a series of studies to investigate how polydomous colonies of the ecologically important red wood ant Formica lugubris are organised at the individual, nest and colony levels. I found that resources are redistributed locally, between nests, within polydomous wood ant colonies. Further investigation showed that this local resource redistribution is mediated by individual workers treating other nests of the colony as food sources. I also investigated the role that nests which do not appear to be foraging are playing in polydomous wood ant colonies. I found that these non-foraging nests, rather than having a specialised role, are part of the colony expansion process. I explored the importance of resource acquisition to individual nests by investigating the effect that position in the colony nest-network has on the survival, reproduction and growth of nests within a polydomous colony. I found that position within a dynamic nest-network was an important determinant of life-history success for individual nests in wood ant colonies. My results suggest that little behavioural innovation is needed for a colony to become polydomous, and indicate benefits a polydomous nesting strategy may provide a colony. These results highlight how understanding the proximate mechanism and development of a social behaviour, can give important insights into the ultimate function and evolution of a life-history strategy. ii Contents Abstract .................................................................................................................................................. ii Contents ................................................................................................................................................ iii List of Figures ........................................................................................................................................ v List of Tables ........................................................................................................................................ vi Acknowledgements ............................................................................................................................. vii Author Declaration ............................................................................................................................ viii Chapter 1: Introduction ....................................................................................................................... 1 1.1 General Introduction ................................................................................................ 1 1.2 Polydomy ................................................................................................................. 1 1.3 The Formica rufa group ........................................................................................... 5 1.4 The Longshaw Estate ............................................................................................... 7 1.5 Thesis outline ........................................................................................................... 9 Chapter 2: Polydomy in Red Wood Ants .......................................................................................... 11 2.1 Introduction ............................................................................................................ 12 2.2 The relationship between polydomy and polygyny ............................................... 15 2.3 Ecological advantages of polydomy ...................................................................... 18 2.4 Consequences of polydomy for red wood ant colonies ......................................... 24 2.5 Future Directions ................................................................................................... 26 2.6 Conclusions ............................................................................................................ 27 Chapter 3: Resource redistribution in polydomous ant nest-networks: local or global? ............. 29 3.1 Introduction ............................................................................................................ 30 3.2 Methods.................................................................................................................. 31 3.3 Results .................................................................................................................... 37 3.4 Discussion .............................................................................................................. 40 Chapter 4: Inter-nest food sharing within wood ant colonies: a simple behavioural mechanism promotes nesting strategy plasticity .............................................................................. 45 4.1 Introduction ............................................................................................................ 46 4.2 Methods.................................................................................................................. 46 4.3 Results .................................................................................................................... 51 4.4 Discussion .............................................................................................................. 56 Chapter 5: The role of non-foraging nests in polydomous wood ant colonies ............................... 62 5.1 Introduction ............................................................................................................ 63 5.2 Methods.................................................................................................................. 66 5.3 Results and Discussion .......................................................................................... 71 5.4 General Discussion ................................................................................................ 82 iii Chapter 6: Survival, reproduction and growth: how position in a dynamic network impacts life-history .............................................................................................................................. 84 6.1 Introduction ............................................................................................................ 85 6.2 Methods.................................................................................................................. 85 6.3 Results .................................................................................................................... 94 6.4 Discussion .............................................................................................................. 98 Chapter 7: Discussion ....................................................................................................................... 101 7.1 Thesis Overview .................................................................................................. 101 7.2 Polydomy in red wood ants .................................................................................. 101 7.3 Limitations and future work ................................................................................. 104 7.4 General Discussion .............................................................................................. 108 Appendices ......................................................................................................................................... 111 Notes on the Appendices ................................................................................................. 111 Appendix A: Colony Maps .............................................................................................. 112 Appendix B: Nest properties vs. Network Properties ...................................................... 125 Appendix C: Assortativity by colony............................................................................... 126 Appendix D: Trail Strength vs. Trail Betweenness ......................................................... 127 Appendix E: Trail Type vs. Trail Betweenness ............................................................... 128 Appendix F: Chapter 4 GLMM details ............................................................................ 129 Appendix G: Chapter 5 GLMM details ........................................................................... 130 Appendix H: Chapter 6 GLMM details ........................................................................... 131 References .......................................................................................................................................... 132 iv List of Figures Figure 1.1 Traits associated with polydomous nesting in ants. ............................................... 3 Figure 1.2 The distribution of the F. rufa group in