Microbial community assembly in a multi-layer dendritic metacommunity

ABSTRACT A major goal of metacommunity ecology is to infer the local- and regional-scale processes that underlie community assembly. In dendritic ecological networks (e.g., stream metacommunities), branching and directional dispersal connectivity can alter the balance between local and regional factors during assembly. However, the implications of vertical habitat structure (e.g., planktonic versus benthic sediments) in dendritic metacommunities remain unclear. In this study, we analyzed the bacterial metacommunity of a fifth-order mountain stream network to assess habitat differences in the (1) dominant community assembly processes, (2) spatial scaling of community assembly processes, and (3) longitudinal variation in community assembly. Using taxonomic and phylogenetic null modeling approaches, we found habitat-specific spatial patterns of community assembly across the dendritic network. Compositional differences between planktonic and benthic communities were maintained by divergent species sorting, but stochasticity influenced assembly at local scales. Planktonic communities showed scale-dependent assembly, transitioning from convergent sorting at local scales to divergent sorting at regional scales, while sediment community assembly was less scale dependent (convergent sorting remained important across all scales). While divergent sorting structured headwaters in both habitat types, sediment communities converged in structure downstream. Taken together, our results show that vertical habitat structure regulates the scale-dependent processes of community assembly across the dendritic metacommunity.