Data from: Demographic stochasticity alters expected outcomes in experimental and simulated non-neutral communities

Theory has shown that the effects of demographic stochasticity on
communities may depend on the magnitude of fitness differences between
species. In particular, it has been suggested that demographic
stochasticity has the potential to significantly alter competitive
outcomes when fitness differences are small (nearly neutral), but that it
has minimal effects when fitness differences are large (highly
non-neutral). Here we test such theory experimentally and extend it to
examine how demographic stochasticity affects exclusion frequency and mean
densities of consumers in simple, but non-neutral, consumer-resource
communities. We used experimental microcosms of protists and rotifers
feeding on a bacterial resource to test how varying absolute population
sizes (a driver of demographic stochasticity) affected the probability of
competitive exclusion of the weakest competitor. To explore whether
demographic stochasticity could explain our experimental results, and to
generalize beyond our experiment, we paired the experiment with a
continuous-time stochastic model of resource competition, which we
simulated for 11 different fitness inequalities between competiting
consumers. Consistent with theory, in both our experiments and our
simulations we found that demographic stochasticity altered competitive
outcomes in communities where fitness differences were small. However, we
also found that demographic stochasticity alone could affect communities
in other ways, even when fitness differences between competitors were
large. Specifically, demographic stochasticity altered mean densities of
both weak and strong competitors in experimental and simulated
communities. These findings highlight how demographic stochasticity can
change both competitive outcomes in non-neutral communities and the
processes underlying overall community dynamics.