Investigating the causes and consequences of individual niche variation in group living badgers

Individual niche variation is increasingly being demonstrated in animal populations in a wide variety of species and taxa. Niche variation among individuals has important implications for the ecology, evolution and management of animal populations and is a subject of increasing interest. However, despite its widespread occurrence the causes and consequences of individual niche variation remain poorly understood. In this thesis I use the European badger (Meles meles), a well studied species of high ecological interest, as a model system to investigate individual niche variation. In order to achieve this I combine information on individual foraging niches derived via stable isotope analysis (SIA) of badger vibrissae with detailed life history and ecological data from a long-term study population to investigate the incidence, cause and consequence of individual niche variation within badger social groups. First I use the biomarker Rhodamine B to investigate vibrissae growth rates and patterns in badgers and demonstrate that the isotopic composition of a single vibrissa likely reflects diet over several months (Chapter 2). Next I explore the use of SIA as a tool to investigate badger diet, by comparing isotopic patterns to seasonal changes in diet measured using faecal analysis (Chapter 3). My results provide validation that SIA is powerful tool for investigating foraging variation in this species, and suggest that within badger populations substantial dietary variation may occur among individuals. Further investigation of isotopic variation Indicates that individuals within social groups differ markedly and consistently in their isotopic signature, independent of age and sex effects and that in some instances these differences are remarkably consistent across year (Chapter 4).This suggesting long term individual specialisation (Chapter 4). I find that the degree of this individual specialisation, and the relationship between specialisation and body condition is influenced by competition for resources (Chapter 5). Social groups with higher levels of competition exhibit greater specialisation and specialised individuals within these highly competitive environments are in better condition. Finally, I discuss the implications of these results for individual niche variation, for the application of SIA to study this behaviour and for badger ecology generally (Chapter 6). I also outline future directions for further research.