Expanding the conceptual frameworks of plant invasion ecology
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Numerous mechanisms driving alien plant invasions have been described in a rapidly growing body of literature. However these are frequently case specific, making generalizations across species and systems difficult. A number of conceptual approaches have been proposed to help synthesize the literature, stimulating healthy debate among scientists. We build on these syntheses, presenting an expanded framework that incorporates the processes contributing to invasions, and the context within which they must interact. We also provide a model template into which the framework we develop is incorporated, illustrating both with examples. Our general framework includes three contributing processes: these are (1) the characteristics of the introduced species, (2) system context, within which the invasion takes place, and (3) the features of the receiving habitat. System context refers to the influences arising outside of the receiving environment, both spatially and temporally. Each contributing process is comprised of specific mechanisms, drawn from literature on invasion ecology and other related fields. The framework invokes relevant mechanisms for a specific species or situation. Although, a number of frameworks already consider the characteristics of the invading species or those of the receiving habitat, they seldom include all possible characteristics of both. We propose that these approaches alone are inadequate to provide a comprehensive understanding of the invasion process, without explicitly examining the context within which the invasion takes place. The model template we present relates the contributing processes described for a particular invasion, to the change in habitat from one state to another. Each of the contributing processes defined in the framework modulates the degree to which the habitat is changed. We suggest that these additional tools and the explicit inclusion of all three contributing processes, provide for further synthesis and improved understanding of invasions by alien plants.