Comparison of Shifts of Potential Distributions in Gleditsia (Fabaceae) Between Eastern Asia and Eastern North America.

The mechanism underlying the uneven distribution of biodiversity has attracted considerable interest. In Eastern Asia (EAS) and Eastern North America (ENA), a more heterogeneous environment in the EAS is a key factor explaining the uneven distributed biodiversity. To test the hypothesis, shifts of potential distributions of Gleditsia (Fabaceae) from past to future were compared through ecological niche modeling (ENM). In the 58 environmental variables used for modeling, ENM, multivariate environmental similarity surfaces and most dissimilar variable analyses showed soil and temperature were the primary factors affecting the distributions. In the past, most species experienced contractions in the last glacial maximum (LGM) while expansions during the Middle Holecene. Distribution range sizes during the LGM in the EAS were much larger. In the future (2050 and 2070), northward movements and range expansions were shared between the EAS and ENA species. Projections of niche of the EAS species to the ENA region resulted in significantly smaller areas in the ENA, while similar areas were found for the vice versa projections. Principal component analysis indicated that ecological niches of the ENA species differed from those of EAS species. Niche identity and background tests showed that most species pairs (10/11) rejected (fully or partially) the null hypothesis of ecological niche equivalence. In conclusion, differences in environmental heterogeneity, historical environmental changes, and niches of Gleditsia species between the EAS and ENA contribute to different distribution shift patterns. This study provide additional insights into the biodiversity distribution bias observed in the Northern Hemisphere.