The extension of the taxon cycle model to island plants: insights from the Canarian vascular flora.

Taxon cycle models describe eco-evolutionary patterns of lineage colonization, diversification, and decline across archipelagos, inferring an important role for competition amongst ecologically similar taxa in driving concurrent niche changes. Hitherto described in detail only for animal taxa (notably ants and land birds), we extend the application of taxon cycle analysis to the flora of the Canary Islands, in the process describing several variants on the classic model. Our analysis is based on the premise that taxon cycle dynamics are driven by interactions within closely related species, represented here by congenerics. We compiled distributional and phylogenetic data for 556 species (59% of the native vascular flora), enabling us to allocate the members of each colonist lineage to one of five taxon cycle distributional stages (colonization and range expansion, diversification, range contraction and further diversification, becoming threatened, and extinction). We then grouped the genera into six models: classic taxon cycle (23% of flora), intra-lineage taxon cycle (39%), spontaneous taxon cycle (22%), incomplete taxon cycle (4%), evolutionary stasis (5%), and no taxon cycle (6%). We discuss the drivers that may be shaping these distributions and evaluate how well they conform to the taxon cycle paradigm. We also highlight the use and limitations of stem and crown ages as a tool to test or refine taxon cycle attributions. Our analyses demonstrate that the taxon cycle provides a plausible framework for the analysis of the flora of an oceanic archipelago, while highlighting that both its general applicability and the mechanisms responsible for it will require further independent verification.