Fruit secondary metabolites shape seed dispersal effectiveness

Plant secondary metabolites (PSMs) play a central role in seed dispersal and fruit defense, with potential for large impacts on plant fitness and demography. Yet because PSMs can have multiple interactive functions across seed dispersal stages, we must systematically study their effects to determine the net consequences for plant fitness. To tackle this issue, we integrate the role of fruit PSMs into the seed dispersal effectiveness (SDE) framework. We describe PSM effects on the quantity and quality of animal-mediated seed dispersal, both in pairwise interactions and diverse disperser communities, as well as trade-offs that occur across dispersal stages. By doing so, this review provides structure to a rapidly growing field and yields insights into a critical process shaping plant populations. Secondary metabolites in fruits can shape plant fitness and demography by mediating interactions with both antagonists (seed predators and pathogens) and mutualists (seed dispersers).The effects of fruit secondary metabolites on the outcome of seed dispersal can be described using the seed dispersal effectiveness framework, which quantifies the number of new adult plants produced through the activities of a disperser.By examining how fruit secondary metabolites not only mediate pairwise interactions, but also shape interactions with broad communities of seed dispersers, we describe a wide range of potential effects on plant fitness.Because the same metabolites can serve multiple functions across different seed dispersal stages, with the potential for complex trade-offs, examining their effects under multiple contexts is necessary to understand their adaptive significance.