There are mounting concerns that the management of our natural global heritage is failing to arrest the rapid loss of biodiversity. The problem may be traced to the extinction of enormous numbers of ‘specialised’ species, especially in the tropics. These species either have highly particular resource requirements, such as food or nesting hollows, or specific needs for certain types of habitat, such as wetlands. This book is about specialisation and generalisation in the use of resources and habitats. The author uses a broad ecological perspective to address three main questions. How do ecologists study variation in resource and habitat use, and what do we know from these studies? How well does existing theory account for observations, and what are the common threads between disciplines? Finally, what is the relationship between resource and habitat use? This is the first book to provide a comprehensive analysis of ecological versatility.