Dislocation from coevolved relationships: a unifying theory for plant invasion and naturalization?

Abstract

Invasions of many different plants have occurred in ecosystems around the world and theories of the mechanisms of these invasions abound. All the proposed theories have value, and many of the proposed mechanisms may at least serve as facilitating factors, but no overarching conceptual framework for the mechanisms of plant invasion has emerged. One common theme in all invasions is that the invading plant, in the process of geographic displacement, has been dislocated from its coevolved biota and relocated with a less-familiar biota. The impacts of dislocation from coevolved mutualists, parasites, and competitors are different but follow general principles. The impacts of relocation with new mutualists, parasites, and competitors are also variable and will change as the introduced plant coevolves with its new biotic environment. I propose some hypotheses to guide predictions of the outcomes of the dislocation of plants from coevolved relationships and, hence, the outcomes of plant geographic displacement. Invasiveness in plants is not determined by their life history traits or the nature of the ecosystem they are invading. Invasiveness is primarily a result of the process of invasion itself. When plants are dislocated from coevolved relationships and confronted with new relationships, they can become ecologically transformed. This transformation can affect the ability of a plant population to become established, invasive, and naturalized in a new environment.