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Researchers Explain Story Of Ancient Invasive Species In North America

August 22, 2013
Image Caption: Glyptorthis, one of the species of brachiopods studied. Credit: David Wright

Brett Smith for redOrbit.com – Your Universe Online

A new study from researchers at Ohio State University tells the story of an invasion and domination that took place around 450 million years ago in North America.

During the Ordovician period, a dramatic ecological shift occurred near what are now the Appalachian Mountains, as represented in the fossil record. In the study, which was published recently in the journal PLOS ONE, Ohio State paleontologists provide evidence of significant geological events altering the ecosystems of the ancient seas, which were dominated by brachiopods, corals, trilobites and crinoids at the time.

At this time, a large swath of North America was part of an ancient tropical continent called Laurentia, which was positioned near the equator. As the Earth’s tectonic plates began to shift, they gave rise to the Taconic Mountains, which would eventually become the Appalachian Mountains. The shift in plates also created a depression behind the mountain range that was flooded with cool water from the nearby ocean. These changes resulted in a considerable influx of invasive species to the newly created ocean basin that scientists had previously been unable to explain.

“The rocks of this time record a major oceanographic shift, pulse of mountain building and a change in evolutionary dynamics coincident with each other,” said co-author Alycia Stigall, an Ohio University associate professor of geological sciences. “We are interested in examining the interactions between these factors.”

By analyzing 53 species of Laurentian brachiopods that dominated the ecosystem, Stigall and her co-author David Wright constructed several phylogenies, or evolutionary relationships, to help them understand how individual speciation events may have occurred.

The Ohio researchers found that the invasive species that proliferated during this time period were native to Laurentia. For example, within the various species of brachiopods, corals and cephalopods, some species are invasive and some are not.

They also saw two patterns of survival emerge as the geological changes slowly played out over approximately one million years. At first, the native organisms that became geographically divided separated and began to evolve according to their niche habitats. This chain of events is known as vicariance, and it is the primary mechanism by which new species originate.

Eventually, species from other regions of the continent began invading habitats, a process known as dispersal. While this process boosts biodiversity at first, it also allows a few aggressive species to take over many sites quickly, dominating those ecosystems and reducing biodiversity in the long run.

The same Ohio State researchers found a similar pattern of speciation in a 2010 study on invasive species that brought about mass extinction during the Devonian period about 375 million years ago. That study also found a shift from vicariance to dispersal that contributed to a long-term decline in biodiversity.

Stigall noted that evidence of the pattern can be seen during modern times as well.

“Only one out of 10 invaders truly become invasive species. Understanding the process can help determine where to put conservation resources,” she said.

From plants to animals, invasive species can be found taking over ecosystems, from Asian carp in the Mississippi River to Japanese hops in Wisconsin forests.


Source: Brett Smith for redOrbit.com - Your Universe Online



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