A stable isotope (δ¹³C and δ¹⁵N) perspective on human diet on rapa nui (Easter Island) ca. AD 1400–1900

Abstract

Ecological and environmental evidence suggests that Rapa Nui was among the most marginally habitable islands in Eastern Polynesia, with only a fraction of the biotic diversity found on archipelagos to the west, and capable of sustaining many fewer cultigens traditionally transported by Polynesian colonizers. However, archaeological evidence for human dietary adaptations under such restrictions is limited. Little is known about the particulars of the subsistence base and dietary changes on Rapa Nui that may be associated with a hypothesized late prehistoric decline in the quality and diversity of food sources. To better understand prehistoric Rapa Nui diet we examined stable carbon and nitrogen isotope compositions of human teeth along with archaeological faunal material thought to comprise the Rapa Nui food web. Our results indicate that contrary to previous zooarchaeological studies diet was predominantly terrestrial throughout the entire sequence of occupation, with reliance on rats, chickens and C3 plants. While a few individuals may have had access to higher trophic level marine resources, this is evident only later in time (generally post-AD 1600). A decline in (15)N through time was observed, and may be attributed to declines in available terrestrial proteins; however, presently we cannot rule out the effect of changing soil and plant baseline δ(15)N. Our results also suggest differential access to higher trophic level marine resources among contemporaneous populations, but more research is required to clarify this observation.

Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience

“…These values, along with similar faunal data, are comparable with bulk collagen results from other Rapa Nui studies (Commendador et al, 2013; Fogel et al, 1997; Polet & Bocherens, 2015). The δ 13 C and δ 15 N values of a prehistoric totora reed sample were −26.6‰ and 22.6‰, respectively, whereas the carbon and nitrogen isotopic values of a modern totora reed sample were −26.1‰ and 2.3‰, respectively.…”

“…This is of particular relevance in isotopic studies as most invasive grasses on Rapa Nui are C 4 plants in the subfamilies Chloridoideae and Panicoidae, which make up ∼60% of the grass species, whereas indigenous grasses were dominantly C 3 plants (Finot et al, 2015). Secondly, Commendador et al (2013) showed that the Rapa Nui humans exhibited particularly high δ 15 N values, an observation also noted by Fogel et al (1997). Both studies suggested environmental factors, including the effect of seabird guano, as possible influences on this raised baseline.…”

“…Apparent variation in the archaeozoological record has been thought to relate to temporal differences and/or social stratification (e.g., Martinsson‐Wallin & Wallin, 1999). Existing studies of carbon and nitrogen stable isotope ratios in Rapa Nui prehistoric human collagen (Commendador, Dudgeon, Finney, Fuller, & Esh, 2013; Polet & Bocherens, 2015) suggest that seafood only contributed a minor part of dietary protein, and that the focus of subsistence was on consumption of chickens and rats. Similar patterns have been suggested elsewhere in prehistoric Pacific contexts (Richards, West, Rolett, & Dobney, 2009).…”

“…Up to now, all stable isotope studies from Rapa Nui have used bulk collagen δ 13 C and δ 15 N values related to a reconstructed food web based on measured or hypothesized plant and faunal isotopic end members (Commendador et al, 2013; Fogel, Tuross, Johnson, & Miller, 1997; Polet & Bocherens, 2015). A disadvantage with this method is that it relies heavily on the appropriateness of selected reference values for the local environment.…”

“…A disadvantage with this method is that it relies heavily on the appropriateness of selected reference values for the local environment. In their study of Rapa Nui bulk collagen isotopic composition, Commendador et al (2013) used terrestrial end member δ 13 C (–20.5‰) and δ 15 N (6.5‰) values derived from published modern data for C 3 plants from Pacific islands other than Rapa Nui, concluding that only a minor proportion of prehistoric diets came from marine resources. Although using modern bulk data is common practice in archaeology, the approach is problematic for Rapa Nui for several reasons.…”