Functional trait and phylogenetic tests of community assembly across spatial scales in an Amazonian forest

Despite a long history of the study of tropical forests, uncertainty about the importance of different ecological processes in shaping tropical tree species distributions persists. Trait- and phylogenetic-based tests of community assembly provide a powerful way to detect community assembly processes but have seldom been applied to the same community. Both methods are well suited to testing how the relative importance of different ecological processes changes with spatial scale. Here we apply both methods to the Yasuni Forest Dynamics Plot, a 25-ha Amazonian forest with >1100 tree species. We found evidence for habitat filtering from both trait and phylogenetic methods from small (25 m(2)) to intermediate (10 000 m(2)) spatial scales. Trait- based methods detected even spacing of strategies, a pattern consistent with niche partitioning or enemy-mediated density dependence, at smaller spatial scales (25-400 m(2)). Simulation modeling of community assembly processes suggests that low statistical power to detect even spacing of traits at larger spatial scales may contribute to the observed patterns. Trait and phylogenetic methods tended to identify the same areas of the forest as being subject to habitat filtering. Phylogenetic community tests, which are far less data-intensive than trait-based methods, captured much of the same. ltering patterns detected by trait-based methods but often failed to detect even-spacing patterns apparent in trait data. Taken together, it appears that both habitat associations and niche differentiation shape species co-occurrence patterns in one of the most diverse forests in the world at a range of small and intermediate spatial scales.