A large fraction of community ecology has focused on processes that operate within communities to control species richness; however, most natural localities are open to dispersal. Dispersal can mediate community structure and functioning by introducing novel species and promoting coexistence at multiple spatial scales. Using experiments, I tested the effects of dispersal in complex, multi-trophic communities. Results suggest that dispersal of novel species is an important determinant of species richness, community composition and ecosystem properties across a range of environmental conditions. Dispersal also promoted coexistence in a network of communities with different environmental conditions, possibly by subsidizing failing populations with individuals of successful populations. Together, these results broaden our understanding of community and ecosystem-level effects of dispersal beyond terrestrial plant communities and highlight mechanisms of coexistence that may be unique to mobile animals.