Another reason is that the harm done by an invasive species isn't always immediate. Sometimes a non-native species can arrive and live quietly for years before erupting into a full-fledged invasive species. The Brazilian pepper shrub was imported to Florida from South America in the mid-19th century as an ornamental plant, and posed no problems for nearly a century. But in the 1930s it began to spread unchecked, and now infests over 700,000 acres across Florida, the plant's dense canopy inhibiting the growth of native species.
"We're not good at figuring out which species might be damaging," Simberloff said.
But the management of invasive species usually happens on a very tight budget, said Peter Kareiva, chief scientist at The Nature Conservancy. Every day, according to Kareiva, policymakers and ecologists try to figure out which species might be harmful, which invasive species are doing the most damage, and which of these might respond best to eradication efforts.
"Most ecologists think in terms of invasive or not invasive," Kareiva said. "If a species is non-native and not invasive, then we wouldn't pay much attention to it."
Researchers have spent years trying to answer the question of what makes a non-native species become invasive, but Kareiva would like to see them answer another question.
"When invasive species first show up, can we predict which ones are going to become major modifiers of ecosystems or harm other species?" asked Kareiva.
The answer to this question may help ecologists and conservation managers take more steps to maintain native biodiversity and ecosystem functioning—the ultimate goal of all sides in this debate.