Resource competition shapes biological rhythms and promotes temporal niche differentiation in a community simulation

Competition for resources often contributes strongly to defining an organism9s ecological niche. Biological rhythms are important adaptations to the temporal dimension of niches, but the role of other organisms in determining such temporal niches have not been much studied, and the role specifically of competition even less so. We investigate how interspecific and intraspecific competition for resources shapes an organism9s activity rhythms. For this, communities of one or two species in an environment with limited resource input were simulated. We demonstrate that when organisms are arrhythmic, one species will always be competitively excluded from the environment, but the existence of activity rhythms allows niche differentiation and indefinite coexistence of the two species. Two species which are initially active at the same phase will differentiate their phase angle of entrainment over time to avoid each other. When only one species is present in an environment, competition within individuals of the species strongly selects for niche expansion through arrhythmicity, but the addition of an interspecific competitor facilitates evolution of increased rhythmic amplitude when combined with additional adaptations for temporal specialization. Finally, if individuals preferentially mate with others who are active at similar times of day, then disruptive selection by intraspecific competition can split one population into two reproductively isolated groups. In summary, these simulations suggest that biological rhythms are an effective method to temporally differentiate ecological niches, and that competition is an important ecological pressure promoting the evolution of rhythms and sleep.