Concerning invasive species: a reply to Brown and Sax

Biological invasions have commonly occurred, and to a lesser degree continue to do so, without human assistance. It is, however, a combination of the rate and magnitude, as well as the distances and agency involved, that separates human-driven invasion processes from self-perpetuated colonization events. Exotic species are a pervasive and major component of human-induced global change. Decisions to manage invasive species will require judgements to be communicated from scientists to policy makers, because scientists may often be the only ones in the position to make them.