Ecosystem Shift 6,000 Years Ago Is Blamed on Darned Humans

Human hunting and farming has been linked to an ecosystem shift on Earth about 6,000 years ago that affected how terrestrial plants and animal species coexisted, according to a study in the science journal Nature.

"Life has an amazing capacity to respond to change and adapt, but it appears that in just a short amount of time, we've disrupted that," said one of the scientists involved in the study, without explaining what the alternative was for humans at the time.

The study found those two human activities reached a tipping that appeared to change the natural world, said Smithsonian magazine. The study published on Thursday was led by S. Kathleen Lyons of the Evolution of Terrestrial Ecosystems program at the Smithsonian Institution's National Museum of Natural History,

Researchers examined 359,896 pairs of plants and animals at 80 sites as they sought to find out if the pairs were living together or segregated in some way, said a news release from the University of California, Merced.

"The surprise discovery was that for 300 million years, it was more common for species pairs to occur together – to aggregate on a landscape – than it was for them to segregate. Then the pattern flipped around 6,000 years ago in North America," said Kim Cutlip of Smithsonian.com.

"Around the same time the human population was expanding and becoming dependent on agriculture, plant and animal communities shifted to a pattern dominated by segregation," she said.

The co-occurring species pairs remained stable from the late Paleozoic period until the increase in human activity, even overcoming major climate changes, mass extinction along with new plants and mammals emerging, said Cindy Looy in a University of California, Berkeley news release.

"The decline of coupled species pairs in the Holocene also cannot be explained by the transition from the last glacial to the current interglacial at the end of the Pleistocene, as this happened too early," said Looy, who participated in the study. "Instead, it is more likely caused by an increase in human population size and the resulting land use and agriculture."

Another co-author, Jessica Blois, a professor at the University of California, Merced, said the results of the study concerned her, but she has not put a value judgement on the change's impact.

"Life has an amazing capacity to respond to change and adapt, but it appears that in just a short amount of time, we've disrupted that," said Blois. "If species were aggregated because of some significant interactions and we’ve changed that, it could be harder to recover from."


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