The cumulative consequences of multispecies invasions and the great shuffle of biodiversity

A global shuffling of biodiversity is underway, propelled by human transport across natural dispersal barriers. We review the dissolution of biogeographic isolation, showing that modern biotic mixing is global, accelerating, and characterized by a diversity of nonnative species. Strategies to curb introductions now exist, but understanding how impacts accumulate with additional invasions remains critical. To characterize the consequences of this Great Shuffle, we first synthesize evidence that multiple invaders, including those with modest effects, can collectively inflict substantial ecological harm. Second, we review paleontological studies of prehistoric biotic exchanges showing how the number of species exchanged and the spatial extent of mixing correlate with long-term consequences. Because modern invasions are occurring more frequently and over broader scales than ancient events, their consequences may be more severe. By integrating contemporary and prehistoric insights, we highlight research needs and offer a framework for understanding the cumulative and long-term impacts of multispecies invasions.