The role of evolutionary time, diversification rates and dispersal in determining the global diversity of a large radiation of passerine birds

Aim: Variation in species diversity among different geographic areas may
result from differences in speciation and extinction rates, immigration
and time for diversification. An area with high species diversity may be
the result of a high net diversification rate, multiple immigration events
from adjacent regions,anda long time available for the accumulation of
species (know as the “time-for-speciation effect”). Here, we examine the
relative importance of the three aforementionedprocesses in
shaping the geographic diversity patterns of a large radiation of
passerine birds. Location: Global Time period: Early Miocene to present
Major taxa studied: Babblers (Aves: Passeriformes) Methods: Using
a comprehensive phylogeny of extant species (~90% sampled) and
distributions of the world’s babblers, we reconstructed their
biogeographic history and analysed the diversification
dynamics. We examined how species richness correlates
with the timing of regional colonization, the number of
immigration events and the rate of speciation within all 13 geographic
distribution regions. Results: We found thatbabblers likely
originated in the Sino-Himalayan Mountains (SHM) in the early Miocene,
suggesting a long time for diversification and species accumulation within
the SHM. Regression analyses showed the regional diversity of babblers can
be well explained by the timing of the first colonization within
of these areas, while differences in rates of speciation or immigration
have far weaker effects. Nonetheless, the rapid speciation
of Zosteropsduring the Pleistocene has accounted for the
increased diversification and accumulation of species in the oceanic
islands. Main conclusions: Our results suggest that the global diversity
patterns of babblers have predominantly been shaped by the
time-for-speciation effect. Our findings also support an origin centred in
tropical and subtropical parts of the SHM, with a cradle of recent
diversification in the oceanic islands of the Indo-Pacific region, which
provides new insights into the generation of global biodiversity hotspots.