Competition for One Resource

Three simple mechanistic models of scramble competition for a single limiting resource are considered: 1) competition during starvation growth in a chemostat, 2) a serial transfer regime in which a fixed fraction of the fully grown population is transferred to fresh medium at each step, and 3) a serial transfer regime in which a fixed number of individuals is transferred at each step. In contrast to standard theories in population genetics and ecology, which specify no mechanism of competition, the outcome of scramble competition for a limiting resource can be predicted before any competition experiment is initiated. In all three models, selection is shown to be frequency dependent. Coexistence is not possible during chemostat competition. Coexistence is possible in serial transfer, but only within a very narrow zone where selection favors one competitor at high resource levels and then, as consumption proceeds, the other competitor at low resource levels. Serial transfer with a fixed number of individuals transferred allows for both coexistence and priority effects. The impacts of lag and death phases are described.