CONSEQUENCES AND COSTS OF CHEMICAL COMPLEXITY: THE EVOLUTIONARY ECOLOGY OF DIRECT PHYTOCHEMICAL DEFENSE AGAINST HERBIVORES

Phytochemical defenses, plant-produced compounds that can deter or slow herbivores, are critical in influenc-ing the interactions between herbivores and their host plants—some of the most diverse and abundant organisms on earth. We discuss the foundational findings and theories related to the direct defense of plants against herbivores by these compounds, as well as continuing research questions in this field. We highlight the costs associated with phytochemical defense production and variation within individual plants in the distribution of phytochemicals, both spatially and temporally. We then discuss coevolutionary theory and the adaptations of herbivores to cope with phytochemical defense compounds. Last, we delve into the incredible diversity of phytochemical compounds, the role of diversity in herbivory, and new ways of measuring and understanding phytochemical diversity.