Co-occurrence pattern of congeneric tree species provides conflicting evidence for competition relatedness hypothesis.

In plants, negative reproductive interaction among closely related species (i.e., reproductive interference) is known to hamper the coexistence of congeneric species while facilitation can increase species persistence. Since reproductive interference in plants may occur through interspecific pollination, the effective range of reproductive interference may reflects the spatial range of interspecific pollination. Therefore, we hypothesized that the coexistence of congeners on a small spatial scale would be less likely to occur by chance but that such coexistence would be likely to occur on a scale larger than interspecific pollination frequently occur. In the present study, we tested this hypothesis using spatially explicit woody plant survey data. Contrary to our prediction, congeneric tree species often coexisted at the finest spatial scale and significant exclusive distribution was not detected. Our results suggest that cooccurrence of congeneric tree species is not structured by reproductive interference, and they indicate the need for further research to explore the factors that mitigate the effects of reproductive interference.

Range expansion and lineage admixture of the Japanese evergreen tree Machilus thunbergii in central Japan.

We investigated the range expansion histories of Machilus thunbergii populations in the Kinki region of central Japan on the basis of nuclear microsatellite data. In the Kinki region, M. thunbergii is typically found in the coastal area, with some fragmented populations inland, around Lake Biwa. Phylogenetic and Bayesian clustering analysis (STRUCTURE analysis) revealed that the inland populations have different genetic components between the west and east sides of Lake Biwa. The population located on the north side of the lake has an admixture of the two genetically differentiated lineages, contributing to an increase in the genetic diversity of the population. Populations around Lake Biwa had lost rare alleles and the F value obtained from STRUCTURE analysis was lower in the coastal populations than in the lake populations. These results suggest that populations around Lake Biwa experienced a bottleneck due to a founder effect during the initial migration to the lake and that glacial refugia of M. thunbergii in the Kinki region existed along the coast.