Relationships between species that persisted for more than 300 million years suddenly started being disturbed approximately 6,000 years ago, researchers from the University of Wisconsin-Madison have revealed in a new study—and it may be all humanity’s fault.
Writing in the latest edition of the journal Nature, UW botany professor Donald Waller and his colleagues explained that they had conducted the first long-term analysis of how different types of living organisms interacted with one another throughout the history of life on Earth.
“We did not expect, or predict, that we would see continuity in the fossil record for such a long time,” Waller said in a statement. “The fraction of plant and animal species that were positively associated with each other was mostly unchanged for 300 million years.”
Afterwards, however, there was a sharp decline in those positive associations (species that are found in the same place at the same time) over the past 6,000 years. At that point, an abundance of negatively associated plant and animal species started to arise, which means that longstanding relationships were starting to become disturbed for some reason.
So what caused this sudden shift? Humans, of course!
After eliminating possible causes for erroneous results, the researchers found that the patterns were real and were most likely the result of rapid human population growth. The spread of men and women caused “systematic changes around the world in ecological conditions,” explained Waller, “prompting changes in the pattern of species coexistence.”
This is a part of global change that had previously been unnoticed and undocumented, he noted, and while the UW researchers do not have direct evidence for the cause of any specific species assemblage, they did find that species living together tended to form an intricate ecological web that included predatory behavior, symbiosis, disease, and evolution, among other things.
Typically, island habitats tend to be more fragmented and have more vulnerable species, while continents tended to be safer and more stable. Recently, however, continents are starting to look increasingly like islands, which Waller said are good examples of what can happen once species begin to die off and the biodiversity becomes compromised.
“The Paris accord on climate signed last week reflects a global recognition that humans have fundamentally changed our planet’s climate,” he added. “Now we present evidence that humans are changing the Earth in another fundamental way: how species are associated with one another. It’s fossil evidence that we have entered the ‘anthropocene,’ a geologic era marked by human dominance of the planet.”
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Feature Image: David J. Tenenbaum, University of Wisconsin-Madison
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