Ecologists, Environmentalists, Experts, and the Invasion of the ‘Second Greatest Threat’

Abstract

The commonplace, quantitative assertion that 'invasions' of exotic (introduced) organisms constitute the 'second greatest threat' of species extinction debuted in Edward O. Wilson's 1992 book, The Diversity of Life. Based only on three interrelated publications summarising concerns about the conservation status of North American freshwater fishes, Wilson laconically extended the claim to planetary significance. This inspired the most-cited article ever published in the American journal BioScience, subsequently underpinning thousands of peer-reviewed publications, government reports, academic and popular books, commentaries, and news stories. While carefully recounting the origin, promotion, and deployment of the 'second greatest threat', I argue that its uncritical acceptance exemplifies confirmation bias in scientific advocacy: an overextended claim reflexively embraced by conservation practitioners and lay environmentalists because it apparently corroborated one particular, widely shared dismay about modern society's regrettable effects on nature.