Distribution and extirpation of pigs in Pacific Islands: a case study from Palau

Archaeology in Oceania
by Geoffrey Clark, Fiona Petchey, Stuart Hawkins, Christian Reepmeyer,Ian Smith and W. Bruce Masse

ABSTRACT
Neolithic arrival in the Pacific involved, as in other parts of the world, the translocation of domesticated plants and animals by pottery-making cultures in prehistory. Globally uncommon, though, was the abandonment of pottery on some islands and the extirpation of the pig (Sus scrofa/verrucosus) and dog (Canis familiaris) – the two largest mammalian quadrupeds introduced to Oceania – from the subsistence and cultural systems. This paper examines the extirpation of pigs from the Palau Islands as a case study to understand why an important domesticate has such an uneven prehistoric distribution. When suids are fed agricultural produce required to sustain the human population, it has been proposed that competition and extirpation will result, especially on small islands with limited arable land. However, pigs are considered problem animals in many environments because of the damage they cause to horticultural production, particularly the effects of free-range pigs on gardens and plantations. It is suggested that extirpation and low-level animalkeeping are a response to the threat that pigs pose to plant food yields and social relations.

The loss of domesticated animals in Pacific prehistory is a perplexing phenomenon, because pigs and other commensals were significantly involved in the ethnographically observed economic, social and ritual systems of many oceanic societies (Ellis 1833; Harrisson1937; Rappaport 1967). Island size has been related to extinction/extirpation of pigs when the size of the human population reaches a level at which there is competition between pigs and people for staple foods (Bay-Petersen1983). Kirch et al. (2000) noted that trophic competition –the loss of calorific energy to large herds of pigs fed on agricultural crops – increased the likelihood of pigelimination on small relatively isolated islands (overnight sailing or greater to nearest island) with a high human population density (>200 persons per km of arable land),intensive forms of agriculture and endemic warfare.Statistical testing of geographical variables by Giovas(2006) supported the view that island/archipelago size is critical to pig survival using the species–area relationship in biogeography, in which the smaller the landmass, the more vulnerable are its biota to extinction.

The central tenet of the trophic competition hypothesis is that as pig herds grow larger, they are fed increasing amounts of garden products required to sustain the human population. Under conditions of high resource stress and competition, the subsistence return from pigs on small islands is economically unsustainable, leading to the attrition and extirpation of pigs despite the high cultural value of suids. However, in many islands and environments pigs are reckoned to be problematic animals because of the damage they cause to gardens and social relations, rather than for the amount of produce they require to be fed (Heise-Pavlov & Heise-Pavlov 2003;Hide 2003: 160-161; Hughes 1970: 276; Sillitoe 1981).Rappaport’s (1967) seminal study of pig keeping by the Tsembaga people of New Guinea suggested that withou tperiodic slaughtering the pig population would grow quickly and cause serious damage to food crops. Historical and traditional records of pig–human interaction in Oceania similarly highlight the threat that pigs constitute to garden productivity (Dumont d’Urville 1987: 199; Ellis1833: 67; Robertson 1973: 72). It follows that variability in the prehistoric record of pigs in the Pacific, particularly the absence/extirpation of suids on islands, is the result of strategies aimed, at least in part, at controlling the negative impact of pigs on horticultural yields and social relations.

In this paper, we examine the absence/extirpation of pigs on Pacific Islands by establishing, first, the prehistoric loss of pigs in the Palau Islands (Western Micronesia)in the second millennium AD by AMS dating of archaeological pig bone. Palau is an important case, asRieth (2011) has suggested that trophic competition and archipelago size do not fully explain the extirpation of pigs, due to its size (415 km), low population density (75 people per km) and abundant marine resources. Second, we consider the chronological record of pig keeping onPacific Islands. For example, were pigs absent during the colonisation phase, did they become extinct later in prehistory or were they extirpated in the late prehistoric/ early historical era after centuries of domestication? The aim is to propose a broader range of explanations for the patchy geographical and temporal distribution of the pig in the Pacific.

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