Photo credit: woodleywonderworks/Creative Commons
Throughout the history of the Earth, there have been five great extinction events—periods in which there was a sharp decrease in both the diversity and abundance of life. With estimates indicating that currently one animal species is lost every 20 minutes, some have begun calling the present period the "sixth great extinction."
The loss of species alone, however, does not tell the entire story of an extinction event. According to new research, the lack of new species is also important—and the spread of invasive species may be the greatest hindrance to the process of speciation.SLIDESHOW: The World's Most Lovable Invasive Species
Alycia Stigall, a researcher at Ohio University, tracked several species through the Late Devonian period. What she found was surprising. "We refer to the Late Devonian as a mass extinction," she explains, "but it was actually a biodiversity crisis."
During the Late Devonian, a period of great vicariance—the process of isolation that allows for the adaptation of entirely new species—came to an end as sea levels rose and separate land masses became fused into one. A mixing of previously isolated species occurred, introducing new invaders to many ecosystems.
The hardiest of the invading species survived, pushing specialized locals towards extinction and preventing any new species from gaining a foothold long enough to proliferate.
The impact, especially in the oceans, was dramatic. The fossil record shows that during the period, marine ecosystems completely collapsed. Reef-forming corals were decimated—and would not return for more than 100 million years—and species of giant fishes, trilobites, sponges, and brachiopods declined dramatically.
The mechanisms that led to this collapse, Stigall's research suggests, are just as relevant today as they were in the Devonian.
Modern extinction rates, she points out, are greater than in any other period of Earth's history. Furthermore, the spread of invasive species around the globe has accelerated.
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.
To maintain Earth's ecosystems, she suggests, efforts and resources should be focused on protecting new species formation—a process that is still not completely understood.
Read more about extinction:
20% of World's Plant Species Threatened With Extinction, Human Activity is Cause
Thousands of Undiscovered Plants Face Extinction
Life on the Endangered Species Waiting List
Read more about invasive species:
Moving On Up Means More Invasive Species
The Iron Curtain Stopped Invasive Species
Epic Fail: Efforts to Fight Invasive Species Could Cause 'Ecosystem Meltdown'