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

This is the code and dataset for the article entitled "Resource
competition shapes biological rhythms and promotes temporal niche
differentiation in a community simulation," in the journal Ecology
and Evolution. Competition for resources often contributes strongly to
defining an organism’s ecological niche. Endogenous biological rhythms are
important adaptations to the temporal dimension of niches, but how other
organisms influence such temporal niches have not been much studied, and
the role of competition in particular has been even less examined. We
investigated how interspecific and intraspecific competition for resources
shape an organism’s activity rhythms. To do this, we simulated communities
of one or two species in an agent-based model. Individuals in the
simulation move according to a circadian activity rhythm and compete for
limited resources. Probability of reproduction is proportional to an
individual’s success in obtaining resources. Offspring may have variance
in rhythm parameters, which allow for the population to evolve over time.
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 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 separated in
activity time. 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. This is the first study to use ecological modeling to
examine biological rhythms.