Nature Doesn’t Care Where a Species Is From

A new study finds that large herbivores have the same impact on plant diversity whether they’re native or introduced.

Originally published by The Atlantic

February 2, 2024

by Emma Marris

“Conservationists can be quite conservative. It is right there in the name, after all. They like things the way they used to be, in a better past, real or imagined. Their thinking can be slow to change. One idea that has been very slowly changing in conservation science is the popular notion that “invasive species” are very bad for ecosystems—that they are apt to take over or eat native species into oblivion.

For more than 20 years, conservation scientists have been debating whether this is a useful framework. Researchers in invasion biology—the subfield of conservation biology that studies the effects of non-native species—have long allowed that most introduced species are not problematic, and that some are actually beneficial. More recently, some conservationists have argued that the origin of a species does not reliably predict whether it will cause a problem in a particular ecosystem. After all, plenty of native species cause problems too. (White-tailed deer spring to mind.) I’ve been following this debate since 2005, and I’ve seen how acrimonious it can get. My reporting has led me to conclude that the “invasive species” framework is simply unhelpful. My opinion has been noted by the field. I once showed up alongside the late philosopher Mark Sagoff, Science Friday’s Ira Flatow, the author Michael Pollan, and many other writers and scientists on a list of “invasive-species denialists” published in a scientific journal.

This week, a study published in the prestigious journal Science strengthened the case for the “denialist” position. The study looked at a subset of introduced species, herbivores weighing more than 99 pounds. Many such animals are considered invasive: pigs in Hawaii and the American South; horses and burros in the American Southwest; goats on the Galápagos Islands; horses, donkeys, and camels in the Australian outback. Because these animals eat, uproot, and trample native plants, they have been considered walking environmental disasters, and many have been poisoned, trapped, shot from helicopters, or otherwise killed by conservationists. The question the study’s authors asked was pretty simple: Does whether an animal is native or not predict how much its presence decreases plant abundance or diversity?”