부산대학교 도서관

Competition is one of the key mechanisms determining species range limits, community structures, and ecological speciation. At geographic scale, competitive exclusion is often proposed to be a cause of parapatric distribution between species that have similar niche requirements. However, it is exceedingly difficult to demonstrate competitive exclusion in natural settings. In this study, I used ecological niche modeling to predict potential distributions of two closely-related avian species in Asia, Paradoxornis webbianus, and P. alphonsianus. The current-day distributions of the two species indicate that they share an area of potential sympatric zone in Southwestern China, within which both species exhibit non-random spatial distributions (P. webbianus in the northeastern region, and P. alphonsianus in the southwestern region). The niche identity test shows that the two species occupy different niches within the sympatric zone. Furthermore, the discriminant analysis points to temperature variability as the most likely niche dimensions along which P. webbianus and P. alphonsianus differentiate. Paradoxornis webbianus appears to be more tolerant of temperature fluctuations than P. alphonsianus. The potential distributions of the two species during the last glacial maximum (21,000 years ago) suggest that they have maintained a similar area of potential sympatry since their divergence approximately 30,000 to 25,000 years ago. Therefore, their spatial segregation within the current-day sympatric zone is more likely a result of competition than secondary contact. In conclusion, this study provided strong support for the role of competition in maintaining parapatric distribution between two recently-diverged species. Ecological speciation through competition and niche partitioning, therefore, might play a key role in the rapid divergence among closely-related species such as P. webbianus and P. alphonsianus.