Commensal rats record Polynesian resource shifts

A study of ancient rat remains from Polynesia finds that isotopic trends reflect resource depression and reshaping of nutrient flows by early human settlers. Although little direct archaeological evidence exists to quantify the impacts of human colonization on local ecosystems, commensal animals, which accompany human habitation but are not domesticated, can preserve a record of ecosystem change in the isotopic composition of their remains. Jillian A. Swift and colleagues analyzed isotope trends in Pacific rats dating between 800 BC and 1800 AD from three Polynesian island systems, covering the period of colonization. The authors report that nitrogen-15 isotope values declined over time in all three systems. The declines may reflect shifts in food sources for both humans and rats that are supported by other evidence, as humans transitioned from slash-and-burn agriculture to agroforestry, and from offshore fishing to nearshore and terrestrial food sources. Other shifts include the loss of seabirds from rat diet and loss of seabird guano inputs to terrestrial systems, which may be due to extirpation or extinction. One island did not show a similar decline in nitrogen-15, and evidence suggests that constant human occupation at this site provided rats high-quality diets through continued access to marine foods rich in nitrogen-15. According to the authors, the results suggest that human colonization reshaped nutrient flows and that commensal animal isotopes can document human impacts on natural ecosystems.

Article #18-05787: "Restructuring of nutrient flows in island ecosystems following human colonization evidenced by isotopic analysis of commensal rats," by Jillian A. Swift, Patrick Roberts, Nicole Boivin, and Patrick V. Kirch.

MEDIA CONTACT: Jillian A. Swift, Max Planck Institute for the Science of Human History, Jena, GERMANY; tel: +49 03641 686 734, +49 176 24265934; e-mail: <swift@shh.mpg.de>

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