An experimental test of the intermediate disturbance hypothesis using cultures of marine phytoplankton

Connell's intermediate disturbance hypothesis (IDH) predicts that species richness and diversity within a community are maximal at intermediate frequencies and intensities of disturbances. The predictions of the IDH were tested experimentally by semicontinuous multispecies cultures of marine phytoplankton. Disturbances consisted of dilutions at fixed intervals. The disturbances eliminated parts of the experimental populations but supplied fresh nutrients. Intervals between disturbances ranged from 1 to 14 d. The magnitude of dilutions ranged from 30 to 99% removal. The IDH was fully supported when the results were expressed as species numbers or as Shannon's diversity index based on biomass. On the other hand, the IDH was only partially supported when the results were expressed as Shannon's diversity index based on cell numbers.