Influence of priority effects and environmental filters on the assembly of microbial communities in aquatic environments

Environmental filters and priority effects are two integral concepts thought to drive dynamics in community assembly. Priority effects can shape community assemblage in both positive and negative ways. A host that facilitates subsequent colonisation can be positive but a host that inhibits the abundance of co-existing species can be negative.

Environmental filters are abiotic limiting factors that prevent the establishment or persistence of species. This study aims to simulate environmental filters with applied salinity gradients and priority effects with the staged addition of differing water types to identify the influence this has on the assembly of aquatic microbial communities.

Twenty-four tubes infused with hay substrate were filled to half their capacity with either pond or rainwater. Each water type contained six varying salt dilutions from “A: Fresh Water” (No salt) to “F: Seawater” (35 g L-1). Samples were allowed a week to establish then community richness and composition was assessed.

After the first assessment, pond and rainwater were topped up in 12 tubes and the remaining 12 tubes had the alternate water type added. At the end of the next two weeks, they were re-assessed for richness and composition.

Results indicate priority effects were not a factor as richness varied significantly between treatments over time. An increase in richness over time was observed at high salinity levels while at low levels it appeared to decline.

This suggests salinity is a limiting factor that allows for the co-existence of salt tolerant species by limiting exclusion by dominant species which demonstrates that environmental filtering narrows species niche dimensions which greatly influences the assemblage of these communities.

Keywords: Environmental filtering, priority effect, aquatic microbes, community assembly, limiting factors, niche differences