According to recent competition theory, the population dynamics of phytoplankton species in monoculture can be used to make a priori predictions of the dynamics and outcome of competition for light. The species with lowest “critical light intensity” should be the superior light competitor. To test this theory, we ran monoculture experiments and competition experiments with two green algae (Chlorella vulgaris and Scenedesmus protuberans) and two cyanobacteria (Aphanizomenon flos‐aquae and a Microcystis strain) in light‐limited continuous cultures. We used the monoculture experiments to estimate the critical light intensities of the species. Scenedesmus had by far the highest critical light intensity. The critical light intensities of Chlorella, Aphanizomenon, and Microcystis were rather similar. According to observation, Aphanizomenon had a slightly lower critical light intensity than Chlorella and Microcystis. However, according to a model fit to the monoculture experiments, Chlorella had a slightly lower critical light intensity than Microcystis, which in turn had a slightly lower critical light intensity than Aphanizomenon. These subtle differences between observed and fitted critical light intensities could be attributed to differences in the light absorption spectra of the species. The competition experiments were all consistent with the competitive ordering of the species according to the fitted critical light intensities: Chlorella displaced all three other species, Microcystis displaced both Aphanizomenon and Scenedesmus, and Aphanizomenon only displaced Scenedesmus. Not only the final outcomes, but also the time courses of competition predicted by the theory, were in excellent agreement with the experimental results for nearly all species combinations.

We investigate biological mechanisms that generate oscillations and chaos in multispecies competition models. For this purpose, we use a competition model concerned with competition for abiotic essential resources. Because phytoplankton and plants consume quite a number of abiotic essential resources, the model is particularly relevant for phytoplankton communities and terrestrial vegetation. We show that the predicted dynamics depend crucially on the relationship between the resource requirements and the resource consumption characteristics of the species. More specifically, the model predicts that competition generates (1) stable coexistence if species consume most of the resources for which they have high requirements, (2) oscillations and chaos if species consume most of the resources for which they have intermediate requirements, and (3) competitive exclusion with a winner that depends on the initial conditions if species consume most of the resources for which they have low requirements. The theoretical predictions are compared with available data on resource utilization patterns of phytoplankton species.

This paper investigates the extent to which the predictions of an elementary model for light‐limited growth are matched by laboratory experiments with light‐limited phytoplankton. The model and experiments link the population dynamics of phytoplankton species with changes in the light gradient caused by phytoplankton shading. The model predicts that a phytoplankton population should continue to grow until, at steady state, the light intensity at the bottom of the water column equals its critical light intensity. The experimental results were in good agreement with the theoretical predictions: (1) the steady‐state population density increased with an increase of the incident light intensity, (2) the steady‐state population density (per unit volume) was inversely proportional to mixing depth, (3) the steady‐state population size (per unit area) decreased linearly with mixing depth, (4) the critical light intensity decreased with an increase of the incident light intensity, (5) the critical light intensity was approximately the same at each mixing depth, and (6) the time courses predicted by the model were in line with the observed time courses of population density and light penetration. Implications for phytoplankton ecology and aquatic production biology are discussed.