Reconciling supertramps, great speciators and relict species with the taxon cycle stages of a large island radiation (Aves: Campephagidae)

Aim: The taxon cycle concept provides a geographically explicit and testable set of hypotheses for exploring the evolutionary processes underlying the distribution of species in space and time. Here, we test taxon cycle predictions within a large avian island radiation, the core Campephagidae and explicitly integrate the concepts of ‘supertramps’, ‘great speciators’ and relictualization. Location: The Indo-Pacific, Australia, Asia and Africa. Taxon: Corvoid passerine birds. Methods: We constructed a new time-calibrated molecular phylogeny of the core Campephagidae (cuckooshrikes, cicadabirds and trillers) using Bayesian phylogenetic methods. Ancestral range estimation methods and diversification rate analyses were used to explore the dispersal and diversification history of the group. We used an extensive dataset on wing morphology and range distributions to test for correla- tions between evolutionary age of species and dispersal capacity, diversification and distribution, while accounting for phylogenetic non-independence. Results: The core Campephagidae represents an ecologically homogeneous radiation distributed across the Indo-Pacific, Australia, Southeast Asia and Africa. Its members represent a continuum of dispersal abilities; some species are widespread and undif- ferentiated (‘supertramps’) or show strong differentiation of local populations (‘great speciators’), and a few are endemic to single islands (relicts). We show that older spe- cies relative to younger species inhabit fewer and larger islands at higher elevations. The level of intraspecific variation measured as the number of subspecies also de- creases with species age, and is highest in ‘great speciators’ with intermediate levels of dispersal abilities (as per hand-wing index). Main conclusions: Based on trait correlations with species age, we infer phases of range expansion and contraction over millions of years (taxon cycles), within a single monophyletic group of birds. These observations demonstrate reconciliation of the concepts of ‘supertramps’, ‘great speciators’ and relictual palaeoendemics within the temporal stages of the taxon cycle.