XVI International Botanical Congess

The production of secondary metabolites by individual plants is commonly influenced by physical factors, including irradiance, nutrients, and CO2, even though their functions may be related to biotic actors. The responses include both qualitative and quantitative modifications, occur in diverse metabolic pathways, and contribute to the variation confronted by herbivores and other plant predators and parasites. Such phenotypic responses (or norms of reaction) have been used to test theories of how secondary metabolites evolve,particularly models that consider costs and constraints. However, the direction of evolutionary change need not follow the manner or direction of phenotypic response to physical conditions. Depending on how herbivore distribution is related to plasticity, the plastic variation itself may be adaptive by contributing to resistance.