Functional trait is a trait that strongly influences organisms’ performances (e.g., adult body mass, eye size, leg length). The relationship between community assemblage and environment (e.g., environmental filtering) is associated with functional traits, and by taking functional traits into account, we can understand the comprehensive mechanisms of community assemblage. Forest has a complex three-dimensional structure and provides distinct sets of abiotic and biotic factors among vertical strata, which contributes to the determination of community assemblage along vertical strata. Thus, we can understand how vertical structure drives community assembly in forests by comparing functional traits between vertical strata. In this study, we compared the functional traits of trunk- and ground-dwelling ant assemblages to evaluate how their functional traits were associated with the differences in community compositions between tree trunks and forest floors. We tested the following hypotheses: (i) as each vertical stratum provides distinct abiotic factors, the community structures of ants differ between them; (ii) as functional traits contribute to adaptation to specific abiotic factors, the average functional trait of the ant assemblages will differ between vertical strata. We collected ants with pitfall traps and compared their community structures and community-weighted mean (CWM) of ant functional traits between vertical strata.
  All but one of the ant species collected in the traps were ground-nesting ants. Differences in ant community structure were associated with canopy openness and vertical strata (trunk, forest floor). Some CWMs of ant functional traits were different between vertical strata. These results indicate that the differences in community structure could be determined by the frequency of tree trunk use of each ant species. In addition, this frequency may be related to some functional traits. Therefore, our results suggest an environmental filter between the trunk and the forest floor against ants. This filter selected species that are adapted to the trunk use, and the functional traits are related to this process.