Figure 18.17 The intermediate disturbance hypothesis. (a) When disturbances are frequent or of high intensity, only those species that are adapted to these conditions can persist. When disturbances are rare or of low intensity, competition becomes more intense and only those species that are well adapted to compete can persist. At intermediate levels of disturbance, species from both extremes can persist, which results in a higher species richness. (b) In a study that manipulated snail density to create different intensities of disturbance from herbivory, there was strong support for the intermediate disturbance hypothesis.

Data from J. Lubchenco. Plant species diversity in a marine intertidal community: Importance of herbivore food preference and algal competitive abilities, American Naturalist 112 (1978): 23–39.