Consequences of a biological invasion reveal the importance of mutualism for plant communities

*[I report the community-level consequences of a biological invasion that disrupts important seed-dispersal mutualisms. I show that invasion of South African shrublands by the Argentine ant, Linepithema humile, leads to a shift in composition of the plant community, owing to a disproportionate reduction in the densities of large-seeded plants. This study suggests that the preservation of mutualistic interactions may be essential for maintaining natural communities.]