No evidence for trade-offs in plant responses to consumer food web manipulations

Plants face a range of trade-offs as they attempt to maximize their fitness within a complex web composed of competitors, mutualists, and herbivores. In addition to growth–defense and competition–defense trade-offs, plants must balance their response to a wide range of potential enemies including pathogens and vertebrate and invertebrate herbivores. We tested for trade-offs in plant species’ responses to different types of consumers using a foodweb manipulation experiment in which we selectively excluded large vertebrate herbivores and removed foliar fungi, soil fungi, and insects from natural and experimentally planted grassland communities. We found no evidence for trade-offs in the ability of plants to defend themselves against different sets of consumers, although plants varied widely in their responses to removal of different consumer groups. In addition, the species-level responses to consumer removal in monoculture were uncorrelated with each species’ response in more diverse communities, highlighting the important role of local context (e.g., competition and apparent competition) in determining the effects of consumers. Plants must balance their allocation of energy among a wide variety of tasks including growing, competing for limited resources, and defending themselves against an array of potential enemies. We found that while plant species differed greatly in their response to the removal of consumers, species that were susceptible to the effects of one consumer group (e.g., insect herbivores) also were susceptible to other consumer groups (e.g., fungal pathogens). This suggests that plants differ in their overall allocation to defense, but defense investment can proffer protection against a wide array of natural enemies. We also found that plant responses to consumers depended on the diversity of the surrounding plant community, suggesting that among-plant interactions can alter their susceptibility to the impacts of consumers.