Temperature and historical land connectivity jointly shape the floristic relationship between Hainan Island and the neighbouring landmasses

Abstract

Present-day biodiversity in insular biota results from the interplay among geographical barriers, environmental filtering, and historical biogeography, but how these factors interact on insular biodiversity patterns is poorly understood. Here, we analysed the geographical patterns of beta diversity of seed plants between Hainan Island and the neighbouring landmasses in relation to space and the environmental factors to assess the relative effects of historical processes and ecological gradients on community assembly. We assessed beta diversity patterns by quantifying the turnover and nestedness components and used clustering and ordination to investigate the relationships between local floras from Hainan and the neighbouring landmasses. Utilising simple linear regression and linear mixed effect models, we evaluated the importance of historical processes and environmental gradients in shaping these beta diversity patterns. Our results show that the contributions of nestedness and turnover components to the total beta diversity vary across space. The flora of Hainan predominantly nests with the flora of Vietnam but shows larger species turnover with Guangdong, Guangxi, and Taiwan. Clustering and ordination analyses indicate that Hainan is first merged with Vietnam, after which it is grouped with mainland China and finally with Taiwan and the Philippines. The results of the linear mixed effect models consistently reveal that temperature, followed by the historical land connectivity, has the most important role in shaping the floristic dissimilarity. We conclude that the flora of Hainan is of continental origin and has the highest floristic affinity with Vietnam. The periodic emergence of a land bridge during Quaternary glacial cycles determines the origin of Hainan's flora, and temperature shapes the floristic dissimilarities via environmental filtering. Our study highlights the critical roles of historical sea level change and current environmental limitation in structuring the plant communities on Southeast Asian islands.