2000-Year-Old Rat Remains Reveal Human Impact on Island Ecosystem

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2000-Year-Old Rat Remains Reveal Human Impact on Island Ecosystem

                                                                                                 French Polynesian Island / Photo by Pixabay


Scientists recently discovered the impact of human activity on three Polynesian island systems through a chemical analysis of rat remains. The researchers reconstructed the rats’ diet which enabled them to determine local environmental changes caused by humans as well as identify native species and changes to soil nutrients and food chains.

The research establishes that the earth is currently in a new era called Anthropocene where human beings cause a significant and lasting impact on the planet. Although most ecologists and geologists believe that that this era began about 50 to 300 years ago, a large number of archeologists argue that the impact of human action on biodiversity, climate, and geology dates back to one millennium. Scientists also note that recent human impact on the environment is easier to identify today as opposed to ancient human impact on the environment.

In a recent study published in the journal Proceedings of the National Academy of Sciences, researchers from the Max Plank Institute of the Science of Human History, in collaboration with the University of California, developed a new mechanism used to detect and quantify changes made by humans on local ecosystems in the past. Using the new model, researchers were able to determine clues that show ancient human modifications on island ecosystems from the remains of rats that were discovered in archeological sites.

The study shows that the most widespread human migration recorded in history started 300 years ago when people began voyaging through the Pacific Ocean. About a millennia ago, humans had explored the Polynesia region which comprises the Hawaiian Islands, the Easter Island, and Aotearoa. Unaware of what they would encounter in the new lands, ancient voyagers carried with them familiar plants and animals. Rats were also transported aboard canoes during the voyages.



The researchers note that the arrival of these rats into the Pacific islands had an immense impact on the ecosystem because they hunted local birds and also consumed seeds from various tree species. In addition, these rats lived near human settlements and therefore survived on similar foods consumed by humans. Unlike domestic animals whose food consumption was dependent on humans, the rats’ diets were not managed by human settlers and therefore provide more insight on the types of foods available at the human settlements as well as possible changes to the ecosystem in the Pacific islands.

To reconstruct the diet from rat remains, the researchers observed the biochemical composition of the rats’ bones that they recovered from archeological sites in the Polynesian region. They also conducted a carbon and nitrogen isotope analysis of preserved proteins in the bones. The researchers discovered the types of plants consumed by these rats from the carbon isotope analysis and the position of the rats in the food web from the nitrogen isotope analysis.

The isotope analyses were conducted on rat remains from seven different islands in the Pacific. Results from the study demonstrate the effects of human activity like hunting, forest clearance and developing agricultural landscapes on resources available and food webs. The scientists further discovered changing patterns on nitrogen isotopes in the bones of the archeological rat remains. They linked these changes to the extinction of native species and changes in the nutrient cycles of soils that occurred after the voyagers inhabited these islands. They also discovered significant changes in the carbon and nitrogen isotopes which correspond to subsistence choices, agricultural expansion, and human site activity.

Author of the study and correspondent at the Max Planck Institute for Science and Human History Jillian Swift said that they have strong lines of evidence showing that humans made modifications to past ecosystems.  "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," she added.

The researchers noted that the isotopic methods enabled them to quantify how human activity led to significant changes to the island ecosystems. The development and application of the new isotope analysis method increase the possibility of tracking modifications made by humans to the environment in other parts of the world.

"Commensal species, such as the Pacific rat, are often forgotten about in archaeological assemblages. Although they are seen as less glamorous 'stowaways' when compared to domesticated animals, they 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," said co-author of the study Patrick Roberts.

The researchers note that the study reveals how human activity can highly impact and modify the ecosystem. They also establish that humans have an extraordinary capacity to re-engineer the ecosystem and transform the world especially since the present human population has abilities that enable a better understanding and measure of these environmental impacts.


                                                                                                 Pacific rat / Photo by Flickr.com