Answer
High and low levels of disruption discourage adaptive radiation, whereas intermediate levels can facilitate speciation.
Work Step by Step
Low levels of disturbance give few opportunities for new adaptations to develop or be selected due to the constant nature of the environment. High levels of disturbance have enough variability that only very well adapted and specialized species can survive, at the exclusion of others.
At intermediate levels, there is exactly enough disruption for unfilled niches to form and encourage adaptation to them.
