The mixotrophs can take up dissolved inorganic nutrients by autotrophic assimilation and detritus by heterotrophic assimilation. The trade-off between these two assimilatory pathways is derived from mechanisms underlying the costs and benefits of assimilation. For both pathways, the organisms have a certain affinity. These affinities increase their (potential) assimilation rate, but they also entail certain costs. The mutations that occur in the affinities enable the population to evolve; one of the possible evolutionary outcomes is a branching point which provides an opportunity for our mixotrophic population to split up and specialize into separate autotrophs and heterotrophs.
Branching is not a common feature of the studied system, but is found only under specific conditions. These conditions depend on the organism's metabolic mechanisms, the level of the costs and in some cases on the boundaries of trait space, but not on the environment or system properties like total nutrient content. The DEB formulation facilitates the interpretation of these criteria for specialization: it appears that in order to obtain branching there has to exist an explicit advantage to it in the underlying mechanism.