The effect of periodic disturbances and carrying capacity on the significance of selection and drift in complex bacterial communities

Abstract

Understanding how periodical disturbances affect the community assembly processes is vital for predicting temporal dynamics in microbial communities. However, the effect of dilutions as disturbances are poorly understood. We used a marine bacterial community to investigate the effect of disturbance (+/−) and carrying capacity (high/low) over 50 days in a dispersal-limited 2 × 2 factorial study in triplicates, with a crossover in the disturbance regime between microcosms halfway in the experiment. We modelled the rate of change in community composition between replicates and used this rate to quantify selection and ecological drift. The disturbed communities increased in Bray-Curtis similarity with 0.011 ± 0.0045 (Period 1) and 0.0092 ± 0.0080 day −1 (Period 2), indicating that selection dominated community assembly. The undisturbed communities decreased in similarity at a rate of −0.015 ± 0.0038 day −1 in Period 1 and were stable in Period 2 at 0.00050 ± 0.0040 day −1 , suggesting drift structured community assembly. Interestingly, carrying capacity had minor effects on community dynamics. This study is the first to show that stochastic effects are suppressed by periodical disturbances resulting in exponential growth periods due to density-independent biomass loss and resource input. The increased contribution of selection as a response to disturbances implies that ecosystem prediction is achievable.

Robust bacterial co-occurence community structures are independent of r- and K-selection history

“…The dataset used for this article is previously published 14 , but we include a brief summary for completeness: Natural seawater was collected and used to inoculate microcosms in a 2 × 2 factorial crossover design with 3 replicates conducted for 50 days, which were sampled 18 times during the experiment. Half of the microcosms were given high (H) resource supply, whereas the other half were given low (L) resource supply.…”

“…For each sample, the bacterial density was quantified using flow cytometry (BC Accuri C6) 14 . In brief, the bacterial communities were diluted in 0.1x TE buffer, mixed with 2x SYBR Green II RNA gel stain (ThermoFisher Scientific) and incubated in the dark at room temperature for 15 minutes.…”

“…The selection-switch dataset was acquired directly from the authors 14 . This dataset consists of a total of 206 samples.…”

“…Given our research questions, we found the dataset from Gundersen et al 14 to be particularly useful. This is a 2 × 2 factorial crossover microcosm experiment that tested varying feeding regime and resource availability (high/low).…”

“…What made the Gundersen dataset 14 particularly suited for our analysis, was that approximately halfway into the experiment (i.e. between day 28 and 29), the r - and K -selection regimes were switched such that each microcosm was subjected to both selection regimes.…”