*2.3. Determining Community Structure and Species Interactions*

2.3.1. Community Evolution and Assembly

DNA barcoding has played a significant role in expanding collaboration between systematists, who focus on species identification and evolutionary relationships, and ecologists, who investigate species interactions and patterns of associations [109]. As noted above for work conducted on Barro Colorado Island in Panama, plant DNA barcoding has been a boon to community ecologists seeking to understand the factors, such as species diversity pools and functional traits, that control the assembly of species into ecological communities [100,106]. Estimating a third component that may determine species assembly, namely evolutionary history, has always been hampered by the lack of well-resolved phylogenetic hypotheses on species relationships in communities. Determining if species in a community are more closely related than by chance (phylogenetic clustering), more distantly related than by chance (phylogenetic overdispersion), or randomly distributed across the plant tree of life is now readily ascertained by building a DNA barcode-based phylogenetic tree. The assumption follows that species in a community that are phylogenetically clustered are more likely to have similar ecological niches (i.e., phylogenetic niche conservation) and have been assembled via abiotic filtering. The contrasting assumption is that phylogenetic overdispersion in a community is the result of biotic interactions among sympatric species. Based on these assumptions the impact of evolutionary history on community structure has been investigated using DNA barcodes across stages of forest succession [99], among habitats within a forest type [62,110,111], among forests across habitat gradients [112], and among communities across an entire country [113,114] and across the globe [45,115]. The generation of such community phylogenies has grea<sup>t</sup> promise for further testing the basic assumptions and rules governing species assemblies in plant communities (see [45]).
