We studied the evolutionary behavior of a population of mixotrophs. The mixotroph system is characterized by full material recycling, which makes it a simple but fully functioning ecosystem. The evolutionary behavior of the system depends on both intrinsic and extrinsic properties. The intrinsic properties, such as the overhead costs of assimilation, determine the shape of the trade-off curve (see figure below on the left). As such, they can induce evolutionary branching.
Because a full recycling of material is present in the system, the role of the extrinsic properties, such as the total carbon or nitrogen content, depends largely on assumptions of heterogeneity and mass conservation (see figure below). A spatial heterogeneity, for example, provides an advantage to specialized phenotypes and can thus induce evolutionary branching, as is illustrated in the figure above (on the right).