The relationship between niche breadth and range size of beech (Fagus) species worldwide

Aim: This work explores whether the commonly observed positive range size-niche breadth relationship exists for Fagus, one of the most dominant and widespread broad-leaved deciduous tree genera in temperate forests of the Northern Hemisphere. Additionally, we ask whether the 10 extant Fagus species' niche breadths and climatic tolerances are under phylogenetic control. Location: Northern Hemisphere temperate forests. Taxon: Fagus L. Methods: Combining the global vegetation database sPlot with Chinese vegetation data, we extracted 107,758 releves containing Fagus species. We estimated biotic and climatic niche breadths per species using plot-based co-occurrence data and a resource-based approach, respectively. We examined the relationships of these estimates with range size and tested for their phylogenetic signal, prior to which a Random Forest (RF) analysis was applied to test which climatic properties are most conserved across the Fagus species. Results: Neither biotic niche breadth nor climatic niche breadth was correlated with range size, and the two niche breadths were incongruent as well. Notably, the widespread North American F. grandifolia had a distinctly smaller biotic niche breadth than the Chinese Fagus species (F. engleriana, F. hayatae, F. longipetiolata and F. lucida) with restricted distributions in isolated mountains. The RF analysis revealed that cold tolerance did not differ among the 10 species, and thus may represent an ancestral, fixed trait. In addition, neither biotic nor climatic niche breadths are under phylogenetic control. Main Conclusions: We interpret the lack of a general positive range size-niche breadth relationship within the genus Fagus as a result of the widespread distribution, high among-region variation in available niche space, landscape heterogeneity and Quaternary history. The results hold when estimating niche sizes either by fine-scale co-occurrence data or coarse-scale climate data, suggesting a mechanistic link between factors operating across spatial scales. Besides, there was no evidence for diverging ecological specialization within the genus Fagus. National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC); Ministry of Science and Technology of ChinaMinistry of Science and Technology, China; National Key Research and Development Program of China; Grantova Agentura Ceske RepublikyGrant Agency of the Czech Republic; Chinese Scholarship CouncilChina Scholarship Council; Independent Research Fund Denmark; Villum Fonden; German Research FoundationGerman Research Foundation (DFG); Ministry of Education, Youth and Sport of the Czech Republic, program Inter-Excellence; Natural Sciences project TREECHANGE National Natural Science Foundation of China; Ministry of Science and Technology of China; National Key Research and Development Program of China; Grantova Agentura Ceske Republiky; Chinese Scholarship Council; Independent Research Fund Denmark; Natural Sciences project TREECHANGE; Villum Fonden; German Research Foundation; Ministry of Education, Youth and Sport of the Czech Republic, program Inter-Excellence