Figure 4. Saturable L-V and alternative pairwise models are not interchangeable.

Consider a commensal community with a consumable mediator C₁. (A) The mediator accumulates without reaching a steady state within each dilution cycle as the consumer S₂ gradually goes extinct (Figure 3B, Case I). After a few tens of generations, $C_1$ becomes proportional to its producer density ${\displaystyle S_1}$ (inset in left panel). In this case, a saturable L-V (dotted) but not the alternative pairwise model (dashed) is suitable. All parameters are listed in Figure 4—source data 1. (B) The consumable mediator reaches a non-zero steady state within each dilution cycle (Figure 3B, Case II). From mechanistic dynamics where initial species ratio is 1, we use two training windows to derive saturable L-V (dotted) and alternative (dashed) pairwise models. We then use these pairwise models to predict dynamics of communities starting at two different ratios. The alternative model but not the saturable L-V predicts the mechanistic model dynamics. All parameters are listed in Figure 4—source data 2. Note that in all figures, population fractions (instead of population densities) are plotted, which fluctuate less during dilutions compared to mediator concentration.

DOI: http://dx.doi.org/10.7554/eLife.25051.017