Introduced species threaten native biodiversity, but whether exotic species can competitively displace native species remains contested. Building on theory that predicts multi-species coexistence based on a competition-colonisation tradeoff, we derive a mechanistic basis by which human-mediated species invasions could cause extinctions through competitive displacement. In contrast to past invasions, humans principally introduce modern invaders, repeatedly and in large quantities, and in ways that can facilitate release from enemies and competitors. Associated increases in exotic species' propagule rain, survival and competitive ability could enable some introduced species to overcome the tradeoffs that constrain all other species. Using evidence from metacommunity models, we show how species introductions could disrupt species coexistence, generating extinction debts, especially when combined with other forms of anthropogenic environmental change. Even though competing species have typically coexisted following past biogeographic migrations, the multiplicity and interactive impacts of today's threats could change some exotic species into agents of extinction.
Bibliographical noteFunding Information:
We thank Richard Duncan, Adam Clark and Kyle Naish for comments that helped us improve the paper. We acknowledge funding from the Australian Research Council (DE120102221 to J.A.C.; DE130100572 to M.B.), the ARC Centre of Excellence for Environmental Decisions (to J.A.C. and M.B.), and the US National Science Foundation Long-Term Ecological Research Program, including DEB-0620652 and DEB-1234162. Cedar Creek Ecosystem Science Reserve and the University of Minnesota provided further support.
© 2018 The Author(s).