More ancient influence of the Nanling Range on bird occurrence
Despite the mountains’ current, limited effect on gene flow in some
passerine species, our examination of the occurrence of all species of
birds in the Nanling region indicates substantial differences between
areas north, south, and in the range itself. These differences suggest
the mountains have had a strong historical effect. The chi-square tests
of family variation indicated the significant differences between South
Nanling and North Nanling, which support Cheng and Chang’s (1956)
division of Chinese zoogeographic regions that used the Nanling
Mountains as the boundary between the Central China and South China.
Statistical tests of family divergence based on occurrence records
across the mountains indicate that pronounced taxonomic divergence
exists among the three areas compared (Supporting information). For
example, both South Nanling and the Nanling mountains themselves hold
more members of the Leiothrichidae
when compared to North Naling, and the Nanling Mountains showed
exceeding abundance in species in Phasianidae,
Phylloscopidae and Leiothrichidae
compared to south and north of the mountain range. Phasianids are mainly
terrestrial forest species (Tobias et al. 2020). Members of
Phylloscopidae are small leaf warblers known to have experienced recent
evolutional radiation since c. 11.7MYA (Alström et al. 2018).
Leiothrichidae is also a recent group, originating c. 14.73 MYA in the
mid-Miocene (Cai et al. 2020). In the mid-Miocene, climatic conditions
became humid and more tropical (Guo et al. 2008), giving rise to more
broad-leafed vegetation worldwide and general diversification of
tropical and subtropical bird groups (Jacques et al. 2011). In addition
to the Leiothrichidae, multiple other babbler families originated in the
mid-Miocene (Cai et al. 2020). Muscipcapidae species are also more
numerous in South Nanling compared to North Nanling. All The muscicapids
are a diverse group of old-world flycatchers, assumed to originate c. 34
MYA, (Sangster et al. 2010, Kumar et al. 2017), at the end of Eocene.
The end of the Eocene and beginning of the Oligocene was a major
transition time for birds, as the extensive tropics in northern
latitudes shifted southward and many older tropical lineages suffered
extinction and were eventually replaced by more modern groups (Mayr
2013, Oliveros et al. 2019, Sheldon et al. 2015). Except for the the
phasianids, all taxa are recently formed, indicating the current bird
community has been shaped after this period. Habitat differences in
north and south of the mountains clearly help maintain or accentuate
those differences. South of the Nanling Range, there is more subtropical
forest, where an enhancement of forest inhabitants would be expected.
The Nanling Range was formed in the Cretaceous and remained stable
thereafter. Its long existence likely allowed ancestral montane lineages
of birds to be conserved during the Oligocene extinction by virtue of
the mountain’s landscape heterogeneity in the face of changing climate.
The uplift of mountains would also have led to differentiated climatic
conditions between the coast and southcentral China, and stimulating
adaptive and allopatric diversification (Hoorn et al. 2018). Being in
the subtropical monsoon climate, Nanling could also drive climatic
divergence by slowing down or block seasonal winds, forming
differentiate climatic environment in southern China. The results of
this study indicate that that the development of bird diversity in
southern China had been directly or indirectly shaped by the existence
of the Nanling Mountains.s