Indiana University Bloomington Bloomington, Indiana, United States
Abstract: Background/Question/Methods
Organisms and resources are at the mercy of the flow of currents. These currents determine the length of time the organisms and resources spend in a system, or their residence time. Residence time can be estimated as a ratio of the volume of a system (V) to the flow rate of the system (Q; τ = V/Q). Short residence times allows for large amounts of immigration but fast turnover prevents establishment of species unable to quickly replicate or adhere to surfaces to prevent washout. Long residence times decrease resource input requiring species that persist to be adapted to low resource environments. Residence time has effects on lakes, wastewater treatment plants, and the gastrointestinal tract, but only recently has a theoretical framework been developed to help understand the evolutionary ecology of these flowing systems. To test model predictions, we inoculated a series of chemostats with lake microbial communities and subjected them to 20 days of altered flow rates to achieve a gradient of residence time and then sampled post-treatment to measure microbial community structure and function.
Results/Conclusions
Residence time shaped microbial community structure and function in our experimental chemostats. Microbial abundance, species richness, and species evenness all increased with residence time, while species turnover decreased non-linearly with increasing residence time. Whole community microbial productivity decreased non-linearly with increasing residence time and whole community resource use decreased linearly with increasing residence time. This study aimed to isolate the effect of residence time and these results show that residence time controls community structure and function with the patterns observed generally matching model predictions. Differences between observations and model predictions may be the result of differences in particle movement in the 3D system compared to the 2D model, testing a single volume of system over a range of flow rates, or due to biological processes not captured by the simulated organisms such as biofilm formation. Overall, this study highlights the importance of further study and consideration of residence time in flowing systems as a driver of community structure and function.
