Approximate Bayesian Computation of radiocarbon and paleoenvironmental record shows population resilience on Rapa Nui (Easter Island)

Abstract

Examining how past human populations responded to environmental and climatic changes is a central focus of the historical sciences. The use of summed probability distributions (SPD) of radiocarbon dates as a proxy for estimating relative population sizes provides a widely applicable method in this research area. Paleodemographic reconstructions and modeling with SPDs, however, are stymied by a lack of accepted methods for model fitting, tools for assessing the demographic impact of environmental or climatic variables, and a means for formal multi-model comparison. These deficiencies severely limit our ability to reliably resolve crucial questions of past human-environment interactions. We propose a solution using Approximate Bayesian Computation (ABC) to fit complex demographic models to observed SPDs. Using a case study from Rapa Nui (Easter Island), a location that has long been the focus of debate regarding the impact of environmental and climatic changes on its human population, we find that past populations were resilient to environmental and climatic challenges. Our findings support a growing body of evidence showing stable and sustainable communities on the island. The ABC framework offers a novel approach for exploring regions and time periods where questions of climate-induced demographic and cultural change remain unresolved.

Bayesian analyses question the role of climate in Chulmun demography

“…Their findings indicate that the variations in population levels are largely not associated with climatic changes. In a similar vein, DiNapoli et al 55 observe the population trend of Rapa Nui between the time of initial human settlement (ca. 800 cal.…”

Triumph of the Commons: Sustainable Community Practices on Rapa Nui (Easter Island)

“…Similar analyses of obsidian hydration dates from several sites also support these results [143][144][145][146]. While Lima et al [30] have argued that SPD analyses of radiocarbon dates show population declines associated with palm forest reduction and climate change, these claims are not robust to the effects of the calibration curve or sampling error, confounding issues that Lima et al largely ignored [39]. Robust modeling of the radiocarbon and paleoenvironmental records using an Approximate Bayesian Computation approach instead demonstrates patterns consistent with logistic population dynamics on Rapa Nui-i.e., relatively rapid population growth followed by a plateau that lasted until the timing of European arrival in 1722 AD (Figure 8).…”

“…and animals (rats, chickens), along with a variety of knowledge about subsistence strategies (e.g., fishing, cultivation), economic practices (e.g., lithic tool quarrying and manufacture), and cultural traditions (e.g., monument construction). Starting with these components, Rapa Nui communities quickly grew in size and transformed the island from a palm forest to an anthropogenic landscape [26,39,149]. From the available archaeological evidence, populations resided in multiple, functionally redundant dispersed communities (e.g., [150][151][152]), which appear to have cooperatively managed common-pool resources at both local (e.g., agricultural land, fishing locations, water sources) and island-wide scales (e.g., lithic quarries) in a resilient and sustainable way for multiple centuries (Figure 9).…”

“…While in recent years, most aspects of this "extreme" collapse narrative have been debunked, many continue to argue for some form of environmentally-induced largescale crisis in demography, land use, and/or cultural practices in pre-contact Rapa Nui (e.g., [30][31][32][33]). Emerging evidence, however, demonstrates that Rapa Nui communities were sustainable in several respects and continued their lifeways and traditions despite the changing ecological conditions and inherent environmental constraints imposed by their marginal island (e.g., [18,19,26,[34][35][36][37][38][39][40][41]). Here, we review current evidence for Rapa Nui community practices within the context of ecological economics research on sustainable management of common-pool resources.…”

The spread of agriculture in Iberia through Approximate Bayesian Computation and Neolithic projectile tools

“…The Approximate Bayesian Computation approach [ 96 ] has become popular in the last years to deal with Bayesian inference where the likelihood function is impossible or expensive to achieve (see [ 71 , 87 , 97 – 103 ] for applications of the method in archaeology and culture evolution). It relies on simulation in order to create posterior distributions from the data.…”