Almost two decades ago, Karl Butzer outlined his "contextual approach" in the seminal volume, Archaeology as Human Ecology (Butzer, 1982). In many ways, his notion that the archaeological record is best studied as a reflection of the human ecosystem has come to be epitomized in most contemporary research efforts that contain a geoarchaeological component or focus. And at a more specific level, viewing a human ecosystem as an adaptive network within which communities interacted spatially, economically, and socially with the environment is now implicit to most research designs. An understanding of the "distribution" of human groups across the ancient landscape is an essential component in reconstructing past human ecosystems. Capturing such distributions, however, does not define a "settlement system," as this entails much more than merely plotting the locations of prehistoric communities. Beyond identifying the locations of sites across a landscape and describing their static relationships, an understanding of the dynamic aspects of occupations is crucial to defining settlement strategies and reconstructing past human ecology. Perhaps the two most important clues to understanding the dynamic relationships of occupations across a landscape concern the seasonality and residential mobility of human groups-the focal topic of this volume.
In their introduction (Chapter 1), Bar-Yosef and Rocek point to three areas of research common to studies of settlement systems: (1) the recognition of those factors that induce settlement variability (e.g., economic and social needs and their demographic consequences); (2) the gathering of information needed to identify season, duration, and extent of occupations; and (3) the examination of the economic, social, and ideological factors that go into shaping systems. Methodological issues form the dominant theme of the volume, but to some extent each of these areas of study of settlement systems is touched upon in many of the papers. Kelly's paper stands apart from the others in focusing on the theoretical relationships of economic and demographic factors that condition settlement mobility. Robert Kelly's paper (Chapter 2), largely drawn from his impressive book (Kelly, 1995), focuses on relationships between individual foraging and group (family) movement especially as they relate to a shift to sedentism. He employs "optimal foraging" theory to examine net return rates of food (measured in caloric yields) against other variables (e.g., distance to foraging area, next camp distance, camp breakdown times, etc.) that influence residential mobility. While one might question if his models overemphasize food resources, perhaps neglecting to explore the importance of water, fuel, storage, shelter, and so forth (he touches upon some of these), like all models, Kelly's simply are intended to provide general insights into the relationships of some of the complex variables affecting the mobility of foragers. The significance of some of these insights is underscored in Kelly's closing comments in which he describes alternative settings that may have given rise to sedentism. He suggests that ultimately "sedentism is a product of local abundance in the context of effective regional scarcity."
Arturo Mun Λiz (Chapter 3) presents a cautionary paper that stresses the importance of fully understanding the phenology (annual recurrence of biotic phenomena as effected by seasonal and climatic changes) of organisms in the context of the climatic-environmental conditions at the time of their deposition. Seasonality studies often rely upon our understanding of the contemporary phenologies of organisms, even though these may have been quite different in the past, especially during the Pleistocene. Mun Λiz shows the phenological lability of Iberian avifauna and describes how higher latitude nesting areas would have been impacted by Pleistocene glaciation. This, of course, would have induced seasonal