Alien plants and animals are not all bad

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.Until the middle of the 20th century, moving around the world was reckoned a normal, often valuable, thing to do, while the consequences of their accidental movement were rarely considered. It was not until the publication in 1958 of “The Ecology of Invasions by Animals and Plants”, by Charles Elton, one of the founders of scientific ecology, that values began to change. is, as the name implies, a conservative business. Those involved often value “nativism”—the idea that the species mix in a particular place should remain as unchanged as possible. But this is just an opinion. Other opinions are possible.