What Causes Mass Extinctions

Humanity has moved about in such a way, disrupting many fragile ecosystems the world over, and introduced new and often harmful species into these environments, to a point that mass extinction could be on its way, according to a new study that looked at the effect invasive species have and had on biodiversity.

“We refer to the Late Devonian as a mass extinction, but it was actually a biodiversity crisis,” said Alycia Stigall, a scientist at Ohio University and author of the PLoS ONE paper.

The Late Devonian period saw Earth’s marine life collapse between 378 to 375 million years ago. Though the actual rate of species loss was not higher than the natural rate, the “biodiversity crisis” arose in the lack of new species that arose to fill the vacant spots left by the dying species.

“This research significantly contributes to our understanding of species invasions from a deep-time perspective,” said Lisa Boush, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research.

“The knowledge is critical to determining the cause and extent of mass extinctions through time, especially the five biggest biodiversity crises in the history of life on Earth. It provides an important perspective on our current biodiversity crises.”

Vicariance is the division of a species by long-term natural events, such as the formation of a mountain range of a river channel that splits a species in two and forces it to adapt to new surroundings, thus creating a new species. The research suggests that during the Late Devonian period, there was almost no vicariance taking place, as a result of the introduction of invasive non-local species that adapted to the region and inhibited the other species from evolving and adapting.

Sea levels rose, continents closed in and new land masses arose, creating access to locations species had not had access to beforehand. As a result, the invasive species spread, and the hardiest of them thrived in new environments, basically prohibiting any other species from making a go of it.

“The main mode of speciation that occurs in the geological record is shut down during the Devonian,” said Stigall. “It just stops in its tracks.”

As with many studies, this new research is relevant in a day and age where the current biodiversity crisis has introduced a large number of invasive species into new ecosystems, and where the modern extinction rate is actually higher than the event that wiped out the dinosaurs some 65 million years ago.

“Even if you can stop habitat loss, the fact that we’ve moved all these invasive species around the planet will take a long time to recover from because the high level of invasions has suppressed the speciation rate substantially,” Stigall said.
“The more we know about this process, the more we will understand how to best preserve biodiversity.”

Source: National Science Foundation
Image Source: Ohio University

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