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| Many insular taxa possess extraordinary abilities to disperse but may differ
in their abilities to diversify and compete. While some taxa are widespread
across archipelagos, others have disjunct (relictual) populations. These types
of taxa, exemplified in the literature by selections of unrelated taxa, have
been interpreted as representing a continuum of expansions and contractions
(i.e. taxon cycles). Here, we use molecular data of 35 out of 40 species of the
avian genus Pachycephala (including 54 out of 66 taxa in Pachycephala pectoralis
(sensu lato), to assess the spatio-temporal evolution of the group. We also
include data on species distributions, morphology, habitat and elevational
ranges to test a number of predictions associated with the taxon-cycle hypothesis.
We demonstrate that relictual species persist on the largest and highest
islands across the Indo-Pacific, whereas recent archipelago expansions resulted
in colonization of all islands in a region. For co-occurring island taxa, the earliest
colonists generally inhabit the interior and highest parts of an island, with
little spatial overlap with later colonists. Collectively, our data support the idea
that taxa continuously pass through phases of expansions and contractions (i.e.
taxon cycles). | |
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