Invasive Species Plagued Earth 450 Million Years Ago in North America

Invasive species aren't a new phenomenon. It turns out that they also plagued the Earth about 450 million years ago. Scientists have discovered that the rise of an early phase of the Appalachian Mountains and cooling oceans allowed invasive species to upset the North American ecosystem, revealing how a changing climate can upset natural balances in our world.

During the Ordovician period, a dramatic ecological shift took place. At the time, North America was part of an ancient continent called Laurentia that sat near the equator and had a tropical climate. Yet Earth's shifting tectonic plates gave rise to the Taconic Mountains, which were forerunners of the Appalachian Mountains. This geological shift left a depression behind the mountain range, flooding the area with cool water from the surrounding deep ocean.

This ecological shift can be found recorded in the fossil record of the time period. It also shows that during that time, there was a massive influx of invasive species into the newly created ocean basin. Yet actually how these invaders got there has remained a mystery until now.

The invasive species that entered the ecosystem during this time were species within the groups of animals that inhabited Laurentia. Within the brachiopods, corals and cephalopods, for example, there were some species that were invasive and some that were not.

In order to better understand exactly how these species managed to gain a foothold in the area, the researchers examined the fossils of 53 species of brachiopods that dominated the Laurentian ecosystem. They then created several phylogenies of reconstructed evolutionary relationships in order to examine how individual speciation events occurred.

So what did they find? As the geological changes slowly occurred over a million years, two patterns of survival emerged. During the early stage of mountain building and ocean cooling, native species became geographically divided and evolved into different species. Then, species from other regions of the continent began to directly invade habitats. Aggressive, invasive species were able to quickly overwhelm native ones--a phenomenon that we see occur to this day.

The findings reveal the pattern of speciation during this time period. This, in turn, allows scientists to better understand how species react to changing conditions. It also may show a little bit more about our modern biodiversity crisis, as well.

"Only one out of 10 invaders truly become invasive species," said Alycia Stigall, one of the researchers, in a news release. "Understanding the process can help determine where to put conservation resources."

The findings are published in the journal PLOS One.