Variability and predictability in a zooplankton community: The roles of disturbance and dispersal1

Disturbances are expected to increase variability and/or decrease predictability in ecosystems, while dispersal (or immigration) may have positive or negative effects on ecosystem stability. We conducted a mesocosm experiment with pelagic zooplankton to examine the independent and interactive effects of a nutrient pulse and immigration from neighbouring lakes on (a) temporal variation in the mesocosm communities and (b) variation among spatial replicates. Surprisingly, nutrient enrichment had no significant effect on among-replicate variability in algal or zooplankton biomass, and it decreased both among-replicate variability in zooplankton community composition and temporal variability of algal biomass (measured as the coefficient of variation). The nutrient pulse increased temporal variation in zooplankton biomass but decreased temporal change in relative species abundances. However, both these effects depended on dispersal, suggesting a contextdependent role of dispersal in community stability. We discuss the importance of considering multiple measures and aspects of community variability.