Synergy among hypotheses in the invasion process of alien plants: A road map within a timeline

Abstract Plant invasion is among the most serious of global challenges, affecting ecological processes and threatening biodiversity. With alien plant species (APS) continuously invading new environments, understanding the mechanisms involved in the invasion process will provide important insights for the prediction and control of APS. After over 60 years of invasion biology research, numerous hypotheses to explain successful invasions were proposed. However, due to the dynamic nature of invasions, a great deal of overlap exists among hypotheses and no single hypothesis can account for all invasions. Most hypotheses only focus on a single factor (e.g. biotic or abiotic) contributing to invasion at a given single invasion phase. Synthesizing the suite of hypotheses by considering all of them in tandem across the invasion timeline will allow an integrative understanding of plant invasions. In this current review, we integrate the major hypotheses into an idealized invasion process by their importance towards invasion. In this framework, we grouped hypotheses into intrinsic habitat invasibility and invasiveness of the invasive plant, and describe the relationships among hypotheses where enhanced mutualistic interactions with local biota, elevated competitive ability, and new adaptations drive invasion at the establishment phase. Alternate ways to invasive spread are also discussed. The hypotheses were fitted onto the invasion timeline according to their importance during each invasion phase. Our framework presents how the mechanisms suggested by the hypotheses jointly contribute to invasiveness over time. This invasion road map unifies the many disparate but related hypotheses on APS invasions, and highlights the potential targets for future management and research.