Phylogenetic evidence for the Taxon Cycle: contemporary tests across island and continental systems

Abstract Modern phylogenetic evidence offers novel opportunities to test classic models in island biogeography. One of the earliest, E. O. Wilson’s Taxon Cycle, proposed that insular lineages progress through sequential and predictable phases, beginning with geographic expansion, followed by ecological specialization, and ultimately range contraction (and even extinction), shaped by dispersal and interspecific competition. However, despite renewed interest in the Taxon Cycle, the extent of empirical support for its predictions and its broader significance within contemporary evolutionary biogeography remain unclear. Here, we evaluated the strength of support across 50 studies of diverse archipelagos and taxonomic groups using an evidence-graded classification scheme based on data type and inferential strength. We found evidence for taxon cycles in 82% of these studies, with 54% supported by time-calibrated phylogenies and 32% also providing explicit tests of ecological and evolutionary mechanisms. Notably, one-third of studies supporting taxon-cycle dynamics were not designed as explicit tests of the Taxon Cycle yet recovered patterns consistent with its predictions. Support based on temporal or mechanistic evidence was concentrated in Oceanian, Australasian, and Neotropical systems, with lineage origins most frequently estimated at approximately 5–20 Ma. Trait-mediated dispersal and ecological interactions were identified as key mechanisms associated with stage transitions. However, we did not find strong support for continental examples (based on habitat mosaics). Together, these results show that the Taxon Cycle has evolved into an increasingly generalized predictive framework for understanding island diversification, with potential applications to biodiversity conservation, especially concerning invasive species.