Alien plants and animals are not all bad

Introduced species have a bad rap. From American grey squirrels displacing European red ones, to Japanese knotweed displacing just about everything everywhere, their purported negative effects on nature are there for all to see. But it is only the human eye which prefers the arboreal rodents in a particular place to be red rather than grey. Ecologically, both occupy the same niche. Nor might people fret about knotweed growing at other plants’ expense if it did not also undermine human constructions such as buildings and roads.