Rat remains reveal 2,000 years of human impact on Pacific island ecosystems

"We clearly have long had the capability as a species of massively transforming the world around us," said archaeologist Nicole Boivin.
By Brooks Hays  |  June 5, 2018 at 5:28 PM
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June 5 (UPI) -- New analysis of ancient rat remains have helped scientists trace the impacts of humans on Pacific island ecosystems as far back as 2,000 years ago.

Many scientists argue the Earth has entered a new geological epoch called the Anthropocene, an era defined by humans' growing impact on the planet's ecosystems. While some believe the era began between 50 and 300 years ago, a growing body of research suggests humans began altering the planet's geology, biodiversity and climate several thousands of years ago.

Several studies, for example, have shown early human populations in South America left a definite ecological signature on the parts of the Amazon.

But measuring the ecological impacts of early humans isn't easy.

As part of the latest study, scientists looked to rat remains on a variety of Pacific Islands for clues to how human altered the environment.

The rats themselves are evidence of the impact of the humans. The nonnative rodent arrived on Pacific Islands by hitching a ride on the boats of settlers as early as 2,000 years ago. The newcomers ate the seeds of native trees and hunted native seabirds, altering local island ecosystems.

But in addition to ecological disruptors, the rats also served as a time capsule. Their evolving diets mirrored the ecological changes triggered by the arrival of humans on the islands.

By measuring the shifting ratios of nitrogen and carbon isotopes in rat bones collected across three Polynesian island systems, researchers from the Max Planck Institute for the Science of Human History were able to glean details about changes in vegetation, soil quality, land use, humidity and other ecological and climatic factors.

"Commensal species, such as the Pacific rat ... offer an unparalleled opportunity to look at the new ecologies and landscapes created by our species as it expanded across the face of the planet," scientist Patrick Roberts said in a news release. "The development and use of stable isotope analysis of commensal species raises the possibility of tracking the process of human environment modification, not just in the Pacific, but around the world where they are found in association with human land use."

When scientists compared the changes in rat diets with timelines of human activities compiled using broader surveys of archeological evidence on the islands, they were able to link the ecological changes with agricultural expansion, technological innovation and other shifts in human behavior.

"We have many strong lines of archaeological evidence for humans modifying past ecosystems as far back as the Late Pleistocene," said lead researcher Jillian Swift. "The challenge is in finding datasets that can quantify these changes in ways that allow us to compare archaeological and modern datasets to help predict what impacts human modifications will have on ecosystems in the future."

Swift and her colleagues published their work this week in the journal PNAS.

"We clearly have long had the capability as a species of massively transforming the world around us," said archaeologist Nicole Boivin. "What's new today is our ability to understand, measure, and alleviate these impacts."

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