Number of ecotypes as a function of resource influx for different levels of trade-off. A low influx creates a pressure for the population to split into different ecotypes because it this enables selection to differentiate between phenotypes that use different resources at different abundances. The degree of specialization does not diminish when the influx decreases (see Discussion). More specialists evolve when trade-offs are more severe, essentially creating one niche per resource for the highest cost. Even when having a high resource affinity is not penalized, the population still fragments into on average two stable lineages. Blue markers: (σ1,σ2) = (10,1), green: (σ1,σ2) = (1,0.1), red: (σ1,σ2) = (0.1,0.01), black: (σ1,σ2) = (0,0). N=1000, μ=0.05. Each datum is the average of 20 simulations and error bars are s.e.m.