Frontiers of Biogeography

The acquisition of evidence pertaining to island syndrome often relies on opportunistic observations, yet prior researchers have gradually compiled a body of examples that collectively shed light on its occurrence patterns and dynamics. Our comprehensive literature review revealed that island syndrome dominantly occurs in angiosperms on oceanic islands, with a notable abundance of taxa exhibiting high endemism and possessing functional traits associated with facultative and generalized biotic interactions. While acknowledging the influence of unequal research interest and sampling efforts on the observed patterns, deviations from prevailing sampling biases evident in global plant databases and herbarium collections lend credence to genuine differences in the occurrence of island syndrome. The disproportionate incidence of island syndrome, delineated by taxonomic groups, traits, and specific islands, can be ascribed to the distinct biogeography of oceanic islands and the presence of idiosyncratic ecological and evolutionary processes that contribute to its development. Within an evolutionary framework, our overarching hypothesis posits island syndrome as a transformative trajectory away from the diverse strategies adopted by mainland plants to the alternative strategies exhibited on islands due to their isolation and ecological simplicity. This perspective fosters a more holistic perspective, encompassing the myriad and graded responses of plants to evolutionary pressures encountered on islands. Rather than dismissing the biased occurrence patterns in the examples of island syndrome, we contend that their underlying insights hold substantial value in formulating a general, mechanistic model that enhances our understanding of the development of island syndrome and its evolutionary implications.