Research shows that pre-extinction disruption of food webs makes ecosystems more fragile, susceptible

Jonathan Mitchell, a Ph.D. student on the University of Chicago's Committee on Evolutionary Biology, Peter Roopnarine of the California Academy of Sciences, and Kenneth Angielczyk of the Field Museum have collaborated to produce a fascinating simulations-based analysis of the factors that helped dinosaurs go extinct en masse at the close of the Cretaceous era.

The authors used a food web program they wrote, which looked at dozens of species.  They looked to lay to rest debates about dinosaurs' diet (e.g. did T. rex eat Triceratops, Duck-Billed dinosaurs, or a mixture of both?) by carrying out a number of simulations with each possibility considered.  A total of 17 food webs, based on species alive at the time, were inspected

What they found was that the precise diet of dinosaurs mattered less than the relative diversity of one ecosystem versus another.  Comments Professor Angielczyk, "Using modern food webs as guides, what we have discovered is that this uncertainty is far less important to understanding ecosystem functioning than is our general knowledge of the diets and the number of different species that would have had a particular diet."

The researchers suggest that climate change in the Cretaceous led to a number of changes, including the drying of a sea in North America.  The net result was a loss of diversity.

Creataceous food web
Lower food web diversity made the dinosaurs more vulnerable to mass-extinction a new study claims. [Image Source: PNAS]

This meant that while the ecosystem was still flourishing, it was respectively more fragile than its equivalent, 13 million years before the meteorite impact at Chicxulub on the Yucatan Peninsula.  Comments Mr. Mitchell, "The ecosystems collapsed because of the asteroid impact, and nothing in our study suggests that they would not have otherwise continued on successfully.  Unusual circumstances, such as the after-effects of the asteroid impact, were needed for the vulnerability of the communities to become important."

In fact, the authors argue that the dinosaurs would likely have survived the calamity, had the meteorite hit 13 million years earlier, during the period of greater diversity.

If the meteorite hit 13 million years earlier, the dinosaurs might not have gone extinct.
[Image Source: D. Davis]

The authors say their analysis provides cautionary hints to help assess current ecosystems for vulnerability.  States Professor Rooparine, "Besides shedding light on this ancient extinction, our findings imply that seemingly innocuous changes to ecosystems caused by humans might reduce the ecosystems' abilities to withstand unexpected disturbances."

However, the authors are also careful to note that their study did not indicate more species was a significant safeguard; rather they argue it's the amount of genetic diversity across species that's important -- in other words, saving a lot of similar species may not help as much as conserving species that play unique roles in the ecosystem.

The study was published in the prestigious peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS).

Sources: Eurekalert, PNAS

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