The concept of biological invasions in the Anthropocene: introductions and range expansions

In the warming world of the Anthropocene, as well as classically, biological invasions include introductions (introduced species) and range expansions, both of which describe the arrival of species into regions where they did not occur historically (but where they may have existed prehistorically). Such species may then become important actors on the ecological stage and may also impact many axes of human society, including the economy and health. Here we offer a detailed clarification on why range expansions are fully accommodated within the framework of biological invasions, based upon fundamental biogeographic and ecological-evolutionary principles. Critically, range expansions may occur owing to both dispersal by ocean currents, winds or birds, and by anthropogenic vectors transporting species into regions previously too cold for colonization. Thus, many range expansions may in fact be human-mediated introductions. We emphasize that invasion (as opposed to invasive) is a biogeographic concept and does not imply any particular type or level of impact. An invasion is an invasion, regardless of the source, vector, rates of movement, presumed evolutionary familiarity of arriving species with resident taxa in the sink region, geological history (prehistoric occurrences), genetics, ecology, biology or predicted consequences of a species' arrival, including predicted intensity of impacts. All of these attributes are fundamental aspects of understanding a species' past, present and future history, but do not remove a species from the category of being a new arrival in historical time in a community. This article is part of the theme issue 'The biosphere in the Anthropocene'.