Classic ecological theory suggests that species must differ in their resource use patterns in order to co-exist. Although much recent empirical work has shown that resource use generally increases with greater species diversity, it has nonetheless proven difficult to demonstrate that resource partitioning truly underlies this pattern. Progress has been limited by the fact that differences among species in resource use typically are confounded with other species-specific attributes (size, metabolic rate, fecundity, etc.). 

Results/ConclusionsWe overcame this obstacle by co-opting plasticity in host choice among a community of aphid parasitoids, in order to manipulate the breadth of resource use independent of parasitoid species identity and diversity. We found that aphid suppression improved with greater specialist, but not generalist, parasitoid diversity. Thus, it was resource partitioning among species that fostered greater resource consumption in multi-species communities, rather than greater biodiversity per se. Our study demonstrates that flexible foraging behavior among animal consumers can be exploited to learn more about the specific mechanisms underlying biodiversity-ecosystem function relationships.