Study finds people transformed how species associated after 300 million years

December 16, 2015 by David Tenenbaum, University of Wisconsin-Madison
Volunteer restoration efforts, focused on removing invasive trees and shrubs and introducing controlled fires, have helped return this Wisconsin oak woods closer to its conditions before human settlement. Credit: David J Tenenbaum, University of Wisconsin-Madison

A study published today finds a surprising and very recent shift away from the steady relationship among species that prevailed for more than 300 million years.

The study, published in the journal Nature, offers the first long-term view of how associated with each other for half of the existence of on Earth, says co-author Donald Waller, a professor of botany at the University of Wisconsin-Madison. "We did not expect, or predict, that we would see continuity in the fossil record for such a long time. The fraction of plant and that were positively associated with each other was mostly unchanged for 300 million years. Then that fraction sharply declined over the last 6,000 years," says Waller, a plant ecologist.

Species are 'positively associated' if they are found in the same place and time.

Starting about 6,000 years ago, negatively associated species were preponderant, meaning plants and animals are seldom found in the same place and time, a sign that longstanding relationships have been disturbed.

In assessing the cause of the dramatic change they found, the researchers first eliminated five possible sources of error. "Senior author Nicholas Gotelli, of the University of Vermont, developed careful methods to guard against false positive results," Waller says. "With a result as unexpected as this, we wanted to be very careful to make sure that the pattern was real and not an artifact of the methods we were using, or the particular datasets we looked at."

The most likely cause for the shift, the researchers state, was rapid human population growth, with ensuing effects from plant and animal agriculture. "The conclusion we reluctantly came to is that there have been systematic changes around the world in ecological conditions, prompting changes in the pattern of species coexistence," Waller says. "This is an aspect of global change that has never been noticed, or documented before."

Although the researchers do not have direct evidence for the cause of any particular species assemblage, patterns of species living together form an intricate ecological web involving predation, symbiosis, disease, nutrition, habitat and evolution, Waller points out.

The situation on continents, often recognized as having more stable species assemblages, is now starting to resemble the situation on islands, Waller says. "In general, island habitats are fragmented, and species are vulnerable and declining. Islands are models for conservation biology because they indicate what happens in the end game" as species go extinct and biodiversity declines.

Humans began altering natural world 6,000 years ago
Egyptian farmers in the Neolithic period 5,000-6,000 years ago.

The study, supported by the National Science Foundation, is more evidence that humans have substantially changed the planet, Waller adds. "The Paris accord on climate signed last week reflects a global recognition that humans have fundamentally changed our planet's climate. 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. In fact, the study even provides a way to date the start of the anthropocene."

Explore further: Deer account for almost half of long-term forest change, study finds

More information: Holocene shifts in the assembly of plant and animal communities implicate human impacts, nature.com/articles/doi:10.1038/nature16447

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3 comments

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Bongstar420
1 / 5 (5) Dec 16, 2015
Thats funny...the "past" environment cannot support modern humans

Why is it bad again? Because of some hippy morality?
Steelwolf
5 / 5 (4) Dec 17, 2015
Actually, this shows the FACT, not theory, that there has been major impact upon the ecology by human overpopulation in the past, that plants and animal species are showing this effect by their decline.

WHY this is bad, mr fake hippy bongtroll is that in changing these ecological conditions away from what was stable and working into what is now patchy, unstable and in many places, in decline. Why is this bad, well, everything from the air we breath to the food we eat and water we drink depend on a clean environment for them to be healthy. If we kill off the sea life that provide the majority of the oxygen we breath, then we are going to keel over, not in 50 years, but that year, or even within weeks of a major catastrophic environmental disaster, death of plankton in the seas, we would die very quickly. This is not theory, this is long known fact. What this study backs up is the fact that humans have been changing the ecosystem for over 6K years.

With no backups.
zambrotta_23
1 / 5 (1) Dec 18, 2015
Actually -got to love the implicit claim to insight into the actuality of reality in starting a sentence with 'actually' - there are no 'facts' just anthropocentric bedtimes stories that stress why changes in particular amounts of specific forms of life is bad - we, we, we, us, us, us, we're so goddamn important that what sustains us is thereby also goddamn important... Whatever helps you sleep at night. Just spare us the justification for you giving a shit when it is premised upon utilitarian instrumentality and 'facts'.

Otherwise, neat article! ^_^

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