Prehistoric invasive species effects provide clues to tackle modern intruders and aid wildlife conservation

New research on a species invasion that took place nearly 450 million years ago could inform how we preserve biodiversity today.

When we think of invasive species, we usually (rightly) think of the impact of human activity on ecosystems. But our ecosystems have undergone intrusions by new organisms for millions of years.

Ian Forsythe, a geology graduate student at the University of Cincinnati, has performed an analysis of a well-known invasion of animals that impacted on an ecosystem in the late Ordovician period. The Ordovician took place around 488-444 million years ago. Forsythe presented his findings to the annual conference of the Geological Society of America (GSA) on October 11.

Forsythe studied a phenomenon called the ‘Richmondian Invasion’ which occurred about 446 million years ago. Species encountered each other for the first time in the late Ordovician, causing a disruption of the shallow sea ecosystems of the time.

“We are a catalyst for these things today. But these biotic invasions happened in the past, too,” says Forsythe.

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He was able to build a very detailed picture of how the late Ordovician seas in the US Midwest changed over geologically minute timescales of thousands of years. Such analysis is testament to the rich fossil record from the time left behind in Ohio, Indiana and Kentucky, which were submerged in salty sea filled with starfish, crinoids, brachiopods and other molluscs 450 million years ago.

“We have really incredible fossil deposits here. They’re globally exceptional,” Forsythe says. “The quantity of fossils gives us an awesome window to the past. It’s an amazing natural laboratory.”

Australia has a pretty harrowing recent history with invasive species brought by humans. Animals like cane toads,  cats, foxes, sheepo, goats and cattle, and many birds have massively disrupted the island continent’s natural ecosystems and driven many species to extinction.

Unlike this unfortunate result of human-catalysed species invasion, the native species of the late Ordovician thrived even after their ecosystems were overrun with new animals. Forsythe concluded that this is because the original organisms were generalists that didn’t need specialised habitats or food requirements. They instead adapted and made room for the newcomers.

“Generalists are more successful during invasions because they can contract their niche to accommodate novel competitors,” Forsythe explains. The invaders were lower on the food chain, causing little disruption.

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Forsythe’s project began at Ohio University in Alycia Stigall’s lab.

Stigall, now a professor at the University of Tennessee, told the GSA: “The Richmondian invasion is one of the most intensively studied fossil invasion events in terms of ecosystem and species impacts. But Ian’s work is truly groundbreaking; he was able to examine changes at the community level at a very fine temporal level of a few thousand years and relate this directly to changes in sea level and the timing of the invaders’ arrival.”

Forsythe stressed that we can learn about the resilience of today’s ecosystems by studying changes in ecological networks millions of years in the past.

“That’s what drew me to invasion science. It’s a big issue today with so many outstanding questions,” Forsythe says. “We can’t answer how these things play out in longer timescales without a long data set.”

Invaders which sit higher on the food chain present a greater existential threat to native species, especially specialists (as opposed to generalist species). “It’s a guiding principle for what imperilled species might require attention first,” Forsythe adds.