Linking community, evolutionary and ecosystem ecology: another perspective on plant-herbivore interactions

Community ecology, evolutionary ecology and ecosystem ecology provide different perspectives on ecological systems, and have followed increasingly divergent pathways for decades. Integration of these perspectives is now critical to progress in our understanding of species interactions and ecological systems. A vivid example of the complexity generated by ecosystem processes on the very nature of species interactions is provided by the effect of material cycling on the ecology and evolution of plant-herbivore interactions. Even though they have a direct negative effect on plants through biomass consumption, herbivores can have a positive indirect effect on plant productivity through nutrient recycling. Theory shows that this indirect effect can be so strong as to prevail over the direct effect and exert effective selective pressures on the species involved provided that there is sufficient spatial heterogeneity in the system or trade-offs between traits associated with the direct and indirect effects. Thus, an exploitative interaction can turn into an ecological, and even an evolutionary, mutualism through ecosystem-level constraints. Species traits and evolution of species traits are ultimately constrained by ecosystem processes, just as ecosystem properties are constrained by the ecological and evolutionary history of interacting species. Therefore, merging the evolutionary and ecosystem perspectives, which have been increasingly separated in modern ecology, is fundamental to predicting the responses of ecological systems to environmental changes.