Fig. 1.

Compartment population exhibiting chemical and compartmental dynamics. Compartment events alter the number of compartments in the population and, in general, also their content. Chemical events act only on the compartment contents, without changing the compartment number. (A) Schematic illustration of a simple example. This system is driven by an influx of compartments containing green molecules. The compartments can then randomly undergo binary fusion events. At the same time, the content of each compartment is subject to chemical modifications of two types: a bimolecular conversion of two green molecules into a yellow one, and a constant degradation of yellow molecules. (B–D) Output of one stochastic simulation of this specific model. (B) The marginals of the joint number distribution $n\left(x_1,x_2\right)$ are shown at three time points. (C) Stochastic trajectory of the total number of compartments in the population. The positive and negative updates are caused by intake and fusion events, respectively. (D) The trajectories of the total amount of molecules in the population are affected by the chemical events and compartment influx, but not by compartment fusion.