Conclusion
Combing distinct genetic clades from different geographic areas with
correlative niche models and morphological evolution models, we have
shown considerable variations in the degree of realized niche expansion
and unfilling across the clades within S. boulengeri toads in the
Qinghai-Tibet Plateau region. In the case of S. boulengeri toads,
niche divergence occurs accompanied by niche expansion rather than
unfilling, niche expansion are more prevalent than niche unfilling in E.
A, E. B and E. C clades, while niche unfilling presents just in W. b
clade.
Meanwhile, niche divergence caused by niche expansion indeed accompanies
key morphological innovations of preadaption in novel climates than
niche unfilling and stability. Factors such as enlarged body size and
enhanced locomotor performance have been shown to increase expansion
success by helping toads to cope with novel conditions.
Recognizing true niche shifts accompanied by key morphological
innovations do exist, further assessments should seek to understand
molecular mechanisms of key morphological innovations or related life
strategies combined that have allowed these particular clades to expand
their niches dramatically. It would be particularly interesting to use
the same framework to test whether the same pattern is found in other
organisms, especially in such widespread species or clades in future.