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

      DiNapoli, R.J.; Crema, E.R.; Lipo, C.P.; Rieth, T.M.; Hunt, T.L.; The Honors College and School of Anthropology, University of Arizona, Tucson, AZ, United States (Nature Research, 2021)
      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. © 2021, The Author(s).
    • Population structure drives cultural diversity in finite populations: A hypothesis for localized community patterns on Rapa Nui (Easter Island, Chile)

      Lipo, C.P.; DiNapoli, R.J.; Madsen, M.E.; Hunt, T.L.; Honors College and School of Anthropology, University of Arizona (Public Library of Science, 2021)
      Understanding how and why cultural diversity changes in human populations remains a central topic of debate in cultural evolutionary studies. Due to the effects of drift, small and isolated populations face evolutionary challenges in the retention of richness and diversity of cultural information. Such variation, however, can have significant fitness consequences, particularly when environmental conditions change unpredictably, such that knowledge about past environments may be key to long-Term persistence. Factors that can shape the outcomes of drift within a population include the semantics of the traits as well as spatially structured social networks. Here, we use cultural transmission simulations to explore how social network structure and interaction affect the rate of trait retention and extinction. Using Rapa Nui (Easter Island, Chile) as an example, we develop a model-based hypothesis for how the structural constraints of communities living in small, isolated populations had dramatic effects and likely led to preventing the loss of cultural information in both community patterning and technology. © 2021 Public Library of Science. All rights reserved.
    • Thermal imaging shows submarine groundwater discharge plumes associated with ancient settlements on rapa nui (Easter Island, Chile)

      DiNapoli, R.J.; Lipo, C.P.; de Smet, T.S.; Hunt, T.L.; Honors College, University of Arizona; School of Anthropology, University of Arizona (MDPI AG, 2021)
      Submarine groundwater discharge (SGD) is an important component of many coastal environments and hydrologic processes, providing sources of nutrients to marine ecosystems, and potentially, an important source of fresh water for human populations. Here, we use a combination of unpiloted aerial systems (UAS) thermal infrared (TIR) imaging and salinity measurements to characterize SGD on the remote East Polynesian island of Rapa Nui (Easter Island, Chile). Previous research has shown that coastal freshwater seeps are abundant on Rapa Nui and strongly associated with the locations of ancient settlement sites. We currently lack, however, information on the differential magnitude or quality of these sources of fresh water. Our UAS‐based TIR results from four locations on Rapa Nui suggest that locations of variably‐sized SGD plumes are associated with many ancient settlement sites on the island and that these water sources are resilient to drought events. These findings support previous work indicating that ancient Rapa Nui communities responded to the inherent and climate‐induced hydrological challenges of the island by focusing on these abundant and resilient freshwater sources. Our results highlight the efficacy of using UASbased TIR for detecting relatively small SGD locations and provide key insights on the potential uses of these water sources for past and current Rapa Nui communities. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    • Triumph of the commons: Sustainable community practices on rapa nui (easter island)

      Dinapoli, R.J.; Lipo, C.P.; Hunt, T.L.; Franke Honors College and School of Anthropology, University of Arizona (MDPI, 2021)
      The history of Rapa Nui (Easter Island) has long been framed as a parable for how societies can fail catastrophically due to the selfish actions of individuals and a failure to wisely manage common‐pool resources. While originating in the interpretations made by 18th‐century visitors to the island, 20th‐century scholars recast this narrative as a “tragedy of the commons,” assuming that past populations were unsustainable and selfishly overexploited the limited resources on the island. This narrative, however, is now at odds with a range of archaeological, ethnohistoric, and environmental evidence. Here, we argue that while Rapa Nui did experience large‐scale deforestation and ecological changes, these must be contextualized given past land‐use practices on the island. We provide a synthesis of this evidence, showing that Rapa Nui populations were sustainable and avoided a tragedy of the commons through a variety of community practices. We discuss this evidence in the context of Elinor Ostrom’s “core design principles” for sustainable communities and argue that Rapa Nui provides a model for long‐term sustainability. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.