AbstractCompetition for resources often contributes strongly to defining an organism’s 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 organism’s 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.Author summaryWhy do we sleep? We are interested in the ecological factors which promote the evolution of biological rhythms like the sleep-wake cycle, focusing especially on competition. When animals compete with each other for resources, they often evolve to avoid each other by specializing to use different resources or separating their activity in other ways. To test hypotheses about how competition shapes rest-activity rhythms, we performed computer simulations of a community of animals who move, reproduce, and compete for resources. We show that biological rhythms let two species divide time so that one species is active while its competitor is resting, thus avoiding depleting shared resources. When a species has no competitors in the simulation, competition between members of the same species cause population and individual rhythms to decrease, since resource availability is low when everybody is active at the same time. However, having competitors allows strong rhythms to evolve from originally arrhythmic organisms. Competition can even cause a single population to split into two species which are separated in time. In summary, these results suggest that competition is a strong factor promoting rest-activity rhythms.
Competition and the origins of novelty: experimental evolution of niche-width expansion in a virus
