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| 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. | |
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