Introduction: The outstanding diversity of Amazonian forests is predicted to be the result of several processes. We argue that at a regional level, lineages have dispersed across the Amazon repeatedly. Whereas, interactions between plant and insects could be a principal mechanism structuring community assembly at a local scale.

Methods: Using metabolomic and phylogenetic approaches, we are investigating the patterns of historical assembly of plant communities across South America using the Neotropical genus of trees Inga (Leguminosae) at four, widely separated sites.

Results: Our results show a lack of phylogenetic and chemical structure at a regional scale suggesting that the metacommunity for any regional community in the Amazon is the entire Amazon basin. Local communities are assembled by ecological processes, with the suite of Inga at a given site more divergent in chemical defenses than expected by chance

Implications/Conclusions: Our results suggest that Inga species have dispersed freely across the Amazon. Nevertheless, what seems to determine which species are allowed to coexist within a single community are natural enemies. Thus, interactions between plants and herbivores are a major factor shaping community composition at local scale in tropical rain forests.