When Professor John Birks kindly offered me the opportunity to submit an outline for a book for the Cambridge Studies in Ecology series, I decided that it would be worthwhile to analyze comprehensively ecological specialization and generalization in natural communities (commonly referred to as niche breadth, or niche width). Of course, there has been no shortage of review articles on particular groups of organisms, especially insects, looking at this question (e.g., Fox and Morrow 1981, Schemske 1983, Berenbaum 1990, Jaenike 1990, Andow 1991). Nor has there been any lack of theoretical attention (e.g., MacArthur and Levins 1967, Van Valen and Grant 1970, Roughgarden 1972, Slatkin and Lande 1976, Keast 1977, Siegismund et al. 1990). Futuyma and Moreno (1988) provided an excellent short review of this topic from an evolutionary perspective. However, it seems that a more extensive treatment of reasons for specialized or generalized resource use and its relationship to community dynamics would be an appropriate subject for a book in this series. I did not realize at the time that this seemingly well circumscribed topic would so thoroughly ramify throughout community ecology. However, a retrospective reading of Futuyma and Moreno's (1988) article had (correctly) said as much in the very first paragraph.

An important dichotomy is developed in Chapters 1 and 2 based on specialization–generalization at the local scale, and the capacity of species to occupy few or many different types of habitats.