Plant growth–defense trade-offs are general across interactions with fungal, insect, and mammalian consumers

Abstract

Plants face trade-offs between allocating resources to growth, while also defending against herbivores or pathogens. Species differences along defense trade-off axes may promote coexistence and maintain diversity. However, few studies of plant communities have simultaneously compared defense trade-offs against an array of herbivores and pathogens for which defense investment may differ, and even fewer have been conducted in the complex natural communities in which these interactions unfold. We tested predictions about the role of defense trade-offs with competition and growth in diversity maintenance by tracking plant species abundance in a field experiment that removed individual consumer groups (mammals, arthropods, fungi) and added nutrients. Consistent with a growth–defense trade-off, plant species that increased in mass in response to nutrient addition also increased when consumers were removed. This growth–defense trade-off occurred for all consumer groups studied. Nutrient addition reduced plant species richness, which is consistent with trade-off theory. Removing foliar fungi increased plant diversity via increased species evenness, whereas removal of other consumer groups had little effect on diversity, counter to expectations. Thus, while growth–defense trade-offs are general across consumer groups, this trade-off observed in wild plant communities does not necessarily support plant diversity maintenance.