Phylogenetic structure of a palm community in the central Amazon: changes along a hydro-edaphic gradient

Abstract

The concepts of phylogenetic community structure (PCS) and phylogenetic niche conservatism (PNC) allow ecologists to address the role of species’ evolutionary history in community assembly. It is important to test the role of historical legacies relative to environmental constraints at local scales, where communities are assembled. We studied phylogenetic structure and niche conservatism for palms (Arecaceae) in the 64-km2 Ducke Reserve in the central Amazon, near Manaus. The 72 study plots, each covering 0.1 ha, were distributed regularly in a terra firme forest along a hydro-edaphic gradient. We compared the observed palm PCS with assemblages generated by null models. We also analyzed whether morphological and ecological traits are labile or conserved along the phylogeny and quantified the spatial structure of morphological traits in each plot. We found an overall neutral PCS in combination with low PNC (labile traits), suggesting that evolutionary history poses little constraint on palm community assembly in this Amazonian landscape. Still, there was a tendency towards phylogenetic overdispersion in bottomlands, suggesting competitive exclusion among close relatives or, more likely, environmental filtering acting on convergent traits that affect co-occurrence in flood-prone areas. We conclude that (1) PCS of local communities is random as a whole and morphological traits are overall labile, but that (2) the hydro-edaphic gradient within terra firme forests leads to differences in species co-occurrence so that closely related species occur less often than expected in bottomlands due to diffuse competition among close relatives or environmental filtering on convergent traits.