Invasion Slows Evolution
Few artists create masterpieces when invading armies are sweeping through their homelands. The creative process of nature is slowed by invasion as well.
When species arrive in a new environment where no natural predators can limit their population size, they disrupt the native ecosystem. While problems affiliated with invasive species are common today as a result of modern transportation making it easy for organisms to hitchhike around the globe, invasive species have also wreaked havoc on the planet in the past. During one of Earth's major extinction events in the late Devonian period, invasive species played a major role according to research by Alycia Stigall at Ohio University.
Invasive species slow the divergence of new species from larger populations. Species spreading and out-competing native species reduced the rate of new species appearance in the fossil record of the Devonian period, according to the research, which was published in the journal PloS ONE.
"We refer to the late Devonian as a mass extinction, but it was actually a biodiversity crisis," said Stigall in a National Science Foundation press release.
The number of species lost during the late Devonian, starting around 364 million years ago, wasn't actually higher than the average background rate of extinction. But, there were few species developing.
On a long time scale, this meant that new species did not emerge to replace those that went extinct. Instead the Earth's oceans were dominated by a only a few species with large ranges.
What this means for the modern world is that the spread of invasive species, like zebra mussels, cane toads and kudzu, could slow the development of biodiversity. Coupled with a rapid extinction rate, habitat loss, and numerous other factors, invasive species could have a serious impact on the resiliency of Earth's ecosystem.
The rich diversity of life our ancestors knew is no more, and it may take a very long time for the Earth to recover from the current crises.
"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.
To conduct her research, Stigall looked at the mussel-like bivalve Leiopteria; two brachiopods, Floweria and Schizophoria; and the predatory crustacean Archaeostraca.
Stigall compared the rate of evolution of new species before the event known as the Devonian extinction, with rates during and after the event.
Most of the species Stigall studied lost biodiversity. Floweria even went extinct.
Geological events in the late Devonian had allowed species access to new regions. The hardiest of these species out competed locally adapted animals and squeezed them out.
The invadors were so prolific and successful that new species did not get a chance to develop.
The lessons of this research should hit home with modern nations dealing with invasive species, which cause billions of dollars of damage to infrastructure, agriculture and other industries around the world.
What's more, invasive species can reduce once vibrant ecosystems to nothing but kudzu and feral hogs.
IMAGE: (top) Artistic interpretation of a Devonian forest, by Eduard Riou, 1872: Wikimedia commons