The response was immediate — and signed by 141 scientists, many of them specialists in the field known as invasion biology. Their approach, they said, was already sufficiently “nuanced,” thank you very much.

“Most conservation biologists and ecologists do not oppose nonnative species per se,” wrote Daniel Simberloff, a professor of environmental science at the University of Tennessee, who led the group that wrote the rebuttal. He added that Dr. Davis and his colleagues had vastly played down the severe harm that alien species caused.

But in the five years since that contentious exchange, the idea that invasive species should be assumed guilty until proven innocent has begun to wane, the shift prompted in part, Dr. Davis speculated, by concerns over the use of chemical pesticides and the disruption of landscapes caused by many eradication efforts.

Some alien species are undeniably harmful, a fact that neither Dr. Davis nor others who share his view dispute. The fungus that causes chestnut blight, for example, decimated thousands of trees and changed the American landscape in the early 1900s. The Zika virus is invading new regions, carried by infected mosquitoes that some say are being driven northward by warmer temperatures. The vampirelike lamprey, sneaking into the Great Lakes in the 19th century, gradually champed its way through the fish population.

Islands and mountaintops are especially vulnerable to damage from invaders because their native species often evolved in isolation and lack natural defenses against predators or immunity to exotic diseases. The brown tree snake, accidentally transported to Guam, has virtually eliminated the bird population there.