Alongside species richness, the complementarity in resource use among species in a community (i.e., partitioning of resources) can play an influential role in driving ecosystem productivity and function. This resource-use complementarity is implied in the architecture of interactions among species, as species partition their use of both mutualist and resource ‘niches’. However, experimental studies linking interaction structure to functioning are rare, and it remains unclear how this relationship may change with phylogenetic diversity of resources and consumers, or increasing dominance of exotic plant species. To address these knowledge gaps, we used empirical plant-herbivore interaction networks from 180 experimental above- and belowground mesocosm communities that varied in plant phylogenetic diversity and exotic plant dominance. We tested the predictions that 1) high plant-resource-use complementarity will increase herbivore community productivity; 2) resource-use complementarity of herbivores will be positively related to the phylogenetic diversity of plants and herbivores; and 3) exotic plant dominance will alter the strength of these relationships.
Results/Conclusions
Consistent with our first prediction, herbivore biomass increased in communities that exhibited higher resource-use complementarity, indicating that community productivity can be predicted based on how organisms partition their resources. Contrary to our second prediction, resource-use complementarity of herbivores was unrelated to the phylogenetic diversity of both the plant and herbivore community, suggesting that greater diversity of resources and consumers alone does not result in higher community productivity. Resource-use complementarity also did not change with increasing dominance of the community by exotic plants. However, the positive complementarity-productivity relationship for herbivores was stronger in plant communities dominated by exotic compared to native plant species, supporting our third prediction. This effect was driven by higher herbivore diversity, via increased establishment success of experimentally introduced herbivores in exotic-dominated communities. We also explore these hypotheses for plant-pathogen and plant-mycorrhizal interactions. Our findings have important implications for understanding the mechanisms underlying biodiversity-ecosystem function relationships, the consequences of global change, and predicting outcomes of ecosystem management practices for ecosystem productivity and function.