Theory shows that dispersal among environmentally forced communities can have strong effects on population and community-level stability. Dispersal can allow species to persist at the landscape-scale by both mediating competitive coexistence and allowing species to escape the negative effects of environmental forcing by utilizing spatially and temporally varying environmental refuges. Such landscape-scale persistence combined with dispersal can further facilitate compensatory responses of species to environmental forcing, enhancing community-level stability (a spatial insurance effect). Such stabilizing effects are predicted to be particularly strong at low to intermediate rates of dispersal and when environmental forcing is asynchronous among local communities (i.e., when exhibiting negative covariation). Here we present an experimental test of spatial insurance effects on population/community stability using a lab-based planktonic system composed of three competing species of zooplankton feeding on a diverse algal assemblage. Two-patch metacommunities were exposed to two crossed treatments: an environmental forcing treatment in the form of pH oscillations (unforced, synchronous pH variation and asynchronous pH variation between patches) and three dispersal treatments (none, low or high dispersal among patches). Plankton dynamics were followed over 108 days.

Results/Conclusions

Dispersal and environmental forcing had interactive effects on zooplankton stability. In the absence of environmental perturbations, dispersal destabilized population and community-level abundance (increasing temporal CV’s). In synchronously varying metacommunities, dispersal had weak effects on stability. In contrast, in asynchronously varying metacommunities, dispersal had stabilizing effects on both population- and community-level stability (reducing temporal CV’s).  Stabilizing effects of dispersal in asynchronously varying systems were associated with the increasing strength of compensatory dynamics among zooplankton and weak spatial synchrony among species populations. These results highlight the importance of spatial dynamics in the persistence and stability of competitive communities and show that both dispersal rates and the structure of spatiotemporal environmental variation must be considered to understand the community-level impacts of species dispersal.