In a 2017 review for Science, University of Tasmania marine ecology professor Gretta Pecl and colleagues wrote, “[C]limate change is impelling a universal redistribution of life on Earth. For marine, freshwater, and terrestrial species alike, the first response to changing climate is often a shift in location.” In fact, Pecl says, data suggest that at least 25% and perhaps as much as 85% of Earth’s estimated 8.7 million species are already shifting ranges in response to climate change.

But when they arrive, will they be welcome? Traditional definitions classify species according to place. “Native” species arrived without human help and usually before widespread human colonization, so are likely to have natural predators and are unlikely to go rogue. Non-natives are newcomers and suspect. Though 90% cause no lasting damage, 10% become invasive — meaning that they harm the environment, the economy or human health. Last year a multinational report flagged invasive species as a key driver of Earth’s biodiversity crisis.

How we define species is critical, because these definitions influence perceptions, policy and management. The U.S. National Invasive Species Council (NISC) defines a biological invasion as “the process by which non-native species breach biogeographical barriers and extend their range” and states that “preventing the introduction of potentially harmful organisms is … the first line of defense.” But some say excluding newcomers is myopic.

“If you were trying to maintain the status quo, so every time a new species comes in, you chuck it out,” says Camille Parmesan, director of the French National Centre for Scientific Research, you could gradually “lose so many that that ecosystem will lose its coherence.” If climate change is driving native species extinct, she says, “you need to allow new ones coming in to take over those same functions.”

As University of Florida conservation ecologist Brett Scheffers and Pecl warned in a 2019 paper in Nature Climate Change, “past management of redistributed species … has yielded mixed actions and results.” They concluded that “we cannot leave the fate of biodiversity critical to human survival to be randomly persecuted, protected or ignored.”

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