Temporal variability within disturbance events regulates their effects on natural communities.

Disturbances are processes inherently variable in time and space. This variability comprises a key determinant of ecosystem responses to disturbance. Temporal patterns can, however, vary significantly both among and within individual disturbance events. While recent research has demonstrated an importance of the former, studies on the effects of variability within perturbations have consistently confounded temporal variability with other disturbance attributes (e.g. overall intensity or duration). We established a field experiment to test explicitly the hypothesis that the temporal pattern within perturbations can drive ecosystem responses independently of other disturbance traits. We examined the effects of two disturbance regimes comprising sediment pulses of contrasting temporal pattern (constant and temporally variable intensities) on the benthic invertebrate assemblage of a headwater stream. The overall intensity, duration, timing and frequency of the perturbations were, however, identical. Invertebrates drifting during the temporally variable pulses were more abundant and differed in taxonomic and trophic structure than those exposed to constant perturbations. Moreover, whereas temporal patterns of disturbance events had no immediate effect on benthic invertebrate assemblages in situ, assemblages exposed to the constant perturbations took longer to recover from sediment disturbances than those exposed to temporally variable perturbations. Our results demonstrate that variability in the temporal pattern of intensity within individual perturbations can regulate, independently of other disturbance attributes, the extent and type of ecosystem responses to, and recovery from, disturbances. Effective environmental management and policy therefore necessitate the explicit quantification of temporal patterns of intensity both within and among perturbations.