They’re treated as outsiders, as opportunity-stealing intruders who ought be greeted with government crackdowns rather than open arms.

They’re immigrants — immigrant species, that is. And some ecologists say it’s time to declare amnesty, demilitarize our environmental borders and accept the inevitable reality of non-native invasion.

“People like to have an enemy, and vilifying non-native species makes the world very simple,” said ecologist Mark Davis of Macalester University. “The public got sold this nativist paradigm: Native species are the good ones, and non-native species are bad. It’s a 20t...