Douglas Kennett Atholl Anderson and Bruce Winterhaider

Islands in Oceania were some of the last habitable land masses on earth to be colonized by humans. Current archaeological evidence suggests that these islands were colonized episodically rather than continuously, and that bursts of migration were followed by longer periods of sedentism and population growth. The decision to colonize isolated, unoccupied islands and archipelagos was complex and dependent on a variety of social, technological and environmental variables. In this chapter we develop an integrative, multivariate approach to island colonization in Oceania based on a model from behavioral ecology known as the Ideal Free Distribution. This ecological model provides a framework that considers the dynamic character of island suitability along with density-dependent and density-independent variables influencing migratory behavior. Unique among existing models, it can account for the episodic nature of certain aspects of the colonization process. Within this context we critically evaluate the role offoraging, low-level food production, and ultimately intensive food production, as important contextual variables that influenced decisions to disperse. We argue that intensive food production was one variable that contributed to decreasing suitability of island habitats, stimulating dispersal, and ultimately migrations to more distant islands in Oceania.

The processes involved in the development of food production worldwide during the last 10,000 years were complex and spatially variable. At a minimum, they involved some combination of the following set of factors: (1) the expansion of diet-breadth during the late Pleistocene and early Holocene, leading to the development of co-evolutionary relationships between humans and potential domesticates (Richards et al. 2001; Rindos 1984; Stiner et al. 1999, 2000; Winterhalder and Goland 1997); (2) intensified exploitation of wild plants and animals by some prehistoric foragers (Henry 1989); (3) translocation of wild plants and animals by foraging groups and the management or cultivation of these wild species in some instances (Piperno and Pearsall 1998); (4) the initial domestication of plants and animals in several independent centers (Cowan and Watson 1992; Price and Gebauer 1995a; Smith 1998); (5) the adoption of these plants and animals by foragers living in adjacent regions, often in different habitats; (6) subsequent experimentation

FIGURE 12.1. Map of Oceania showing the relevant islands and archipelagos.

leading to a reliance on food production or the stability of mixed subsistence strategies (low-level food production; Smith 2001a; Tucker, this volume); ( 7) continued transmission of new and improved domesticates through exchange networks (Hastorf 1999), and (8) the ultimate emergence of more intensive food production in certain locations (Smith 1998). Some of the consequences of food production included localized population growth, the spread of domesticated plants and animals along with agrarian knowledge and technology through exchange networks, the actual migration of food producers into regions occupied by foraging populations (Cavalli-Sforza 1996; Diamond and Bellwood 2003), and a general increase in human impacts on natural ecosystems (Bellwood 2001; Diamond and Bellwood 2003; Redman 1999). The demographic expansion of farming populations is linked to significant cultural, linguistic, and biological changes (Bellwood 2001). It has also been argued that the emergence of food production fostered the expan sion of anatomically modern humans into previously unoccupied territory, most notably the colonization of ever smaller and more remote islands in the Pacific, Mediterranean, and Caribbean (Diamond and Bellwood 2003; Kee-gan and Diamond 1987; Kirch 2000; Kirch and Green 2001; Patton 1996; but see Anderson 2003a).

In this chapter we explore the dispersal of people into Oceania and the role that food production may have played in this complex social and ecological process. In particular, we are interested in the migration of people onto islands in Near and Remote Oceania (Figure 12.1).1 Near Oceania consists of several large islands in the Bismarck Archipelago, positioned 100-200 km to the northwest coast of New Guinea, and the Solomon Islands, a series of smaller islands that stretch to the southeast. Prior to sea-level rise during the late Pleistocene and early Holocene, the Solomons formed a single larger island known as Greater Bougainville. Vanuatu and New Caledonia form the western boundary of Remote Oceania, which also includes 38 major archipelagos of 344 colonized islands in West and East Polynesia (Kirch 1984). West Polynesia encompasses the larger, aggregated archipelagos of Tonga and Samoa, plus some smaller archipelagos. In its early prehistory, Fiji is also regarded as West Polynesian. Except for New Zealand, islands in East Polynesia tend to be smaller and more dispersed.

All of the islands in Near Oceania lie within the tropics, but several islands in Remote Oceania are subtropical or are positioned farther to the south, and have temperate climates; for instance New Zealand lies between 35 to 45° south. Little seasonality in rainfall or temperature occurs close to the equator, but cooler temperatures and distinctive wet and dry seasons become more common to the south (Spriggs 1997; Anderson 2001a). The initial colonization of Remote Oceania involved a sixfold increase in minimum voyaging distances over those attained in Near Oceania (200 km) and distances of up to 3700 km were crossed to reach New Zealand and Hawaii.

The study of island colonization has a long history with a large body of literature developed during the last 30 years (Fitzpatrick 2004; Keegan and Diamond 1987). Much of this research was stimulated by MacArthur and Wilson's 1967 book entitled The Theory of Island Bio-geography, and by the recognition that islands provide a well-bounded context for studying cultural evolutionary processes. In the late 1980s, Keegan and Diamond (1987) synthesized the literature on island colonization in various parts of the world and concluded that biogeographi-cal principles, particularly their physical and geometrical properties, provided a useful framework for understanding the colonization process. They argued that climatic, geological, and oceanographic differences among islands shaped their terrestrial and marine productivity and influenced the ability of humans to colonize them. Superimposed on these ecological qualities are geometric properties influencing the likelihood that seafaring migrants will reach particular islands—factors like position, size, and the distance between pairs along likely routes of colonization. In this view, the likelihood that an island will be colonized decreases with distance, as does the possibility of follow-up assistance once an island is occupied. However, colonization of distant islands may be promoted by configurational effects. For instance, archipelagos consisting of larger aggregations of islands potentially provide greater resource diversity for colonists compared with individual islands. Island size also influences the probability of successful colonization because larger islands offer a greater quantity and diversity of habitats and resources.

Although physical and geometric properties are important for understanding island colonization, purely biogeographical models have shortcomings. Based on the geometry of position, distance, and size, they highlight the probabilistic elements of "blindly" reaching a particular island and surviving there. They do not help to analyze the reasons for initiating migration, nor the intentional or unintentional consequences of settlement for an island's resource potential, and thus for the long-term persistence of settlement. Although likely to be important, such factors are extraneous to biogeo-graphic models.

In Oceania, explanations for island colonization can be grouped into push or pull models. Most push models invoke demographic pressure as the primary causal force initiating dispersal (Clark and Terrell 1978; Anderson 1996). It has been argued that population levels on islands generally increase with agricultural intensification, and eventually the population exceeds carrying capacity, stimulating segments of the population to move to adjacent islands. Pull models often propose a rapid dispersal of people through Oceanic island chains, as opportunistic foragers skim off the highest-quality resources (Clark and Terrell 1978; Anderson 1996; Davidson and Leach 2001) and quickly move on to the next propitious location. Although an improvement, the combination of bio-geographic patterning and push-pull variables

Years BP

FIGURE 12.2. Colonization mobility in Oceania during the last 35,000 years (see Anderson 2001a).

Years BP

FIGURE 12.2. Colonization mobility in Oceania during the last 35,000 years (see Anderson 2001a).

does not capture the episodic nature of migratory behavior evident amongst humans and other animals (Diamond 1977), and evident in the archaeological data from Oceania (Anderson 2001b; Figure 12.2). Island colonization in Oceania also appears to be a dual phase process. Each episode seems to have a sedentary phase, perhaps representing a period of population growth, and a phase of high mobility and rapid dispersal. The speed of colonization during these unstable episodes does not suggest incremental demographic pressure, but is more reminiscent of rapid dispersal, triggered by opportunistic foraging behavior. It appears that a variety ofcontextual variables are at work; colonization of Oceania cannot be explained by invoking single variables.

In this chapter we develop an integrative, multivariate model for the colonization of Oceania within the behavioral ecology framework of the ideal free distribution (Abrahams and Healey 1990; Fretwell and Lucas 1970; Sutherland 1996). This set of ideas provides a simple framework that considers the dynamic character of habitat suitability along with density-dependent and density-independent variables that might influence dispersion and habitat selection by colonists in Oceania. In particular, we examine how food production might have influenced decisions to disperse and colonize remote islands. We argue that low-level food production (Smith 2001a), and later intensive food production, contributed to more rapid decreases in habitat suitability through degradation, but also increased the overall carrying capacity of many remote island habitats. This particular point is set within a more general argument: low level and ultimately more intensive food production was one of several variables including population growth, dynamic impacts of exploitation on fragile island environments, technological development, and the inherent ecological suitability of various island groups in Oceania. The ability of human behavioral ecology (HBE) to integrate multiple contextual variables with an emphasis on behavioral responses to changing ecological conditions make it an ideal framework to explore the causes and consequences of human dispersal onto remote islands in Oceania.

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