Assembly of microbial communities across miniature landscapes

Abstract

Bacteria are the cornerstones of all ecosystems, but our understanding of the factors that govern the temporal and spatial distribution of bacteria remains limited. Bacterial communities are often treated as well-mixed, but it is clear that, in most environments, they occupy discrete habitat patches that contain different abiotic conditions and different sets of interacting species. While there have been many studies that have investigated spatial structure at micrometer scales (e.g. biofilms) and at kilometre scales (e.g. biogeographic distributions), there are few studies that have investigated the role of spatial heterogeneity at the meso-scale (mm to cm). The meso-scale may be particularly important for understanding the assembly and dynamics of bacterial communities because it is the scale at which most bacterial dispersal occurs. This thesis assesses how environmental heterogeneity impacts the assembly of bacterial communities occupying discrete habitat patches which are connected by dispersal within miniature landscapes. The results from these experiments using bacterial ‘metacommunities’ indicate that factors associated with dispersal (e.g. species arrival timing and geographic distance) produce local variation in population sizes despite landscape-level conservation of community structure. Furthermore, the impact of environmental heterogeneity on the evolution and distribution of bacteria depended on their capacity to disperse around the landscape. We therefore propose that understanding the details of bacterial community assembly requires further understanding of the interaction between dispersalbased processes and environmental heterogeneity.