Although Ayala's results do not invalidate the previous results, they suggest that simple logistic models cannot describe all situations of competition between organisms. Tilman examined these conditions experimentally with the diatoms Asterionella formosa and Cyclotella meneghiniana . He found that predictions he made held up well experimentally as seen in Figure 21-13 . Disturbance Essentially, when populations are segregated, coexistence is possible. Unfortunately, many species seem to coexist without any noticeable differences in resource utilization.
Plankton are good examples.
Natural disturbance can influence the outcome of competition. Competitive exclusion may not come into play because disturbance may keep all populations well below carrying capacity, so that competitive effects are not seen and segregation is not necessary. These systems would be nonequilibrium systems because stable equilibria predicted by the logistic model would never be reached. Consumers can influence the outcome of competition between species. Herbivores can keep dominant species of plants in check so that other species can grow.