SEAWEED CHEMICAL DEFENSES: LINKING DEMOGRAPHY TO INTRAPLANT VARIATION IN DEFENSES

Pavia, H., Toth, G. & Åberg, P. Göteborg University, Tjärnö Marine Biological Laboratory, SE‐452 96, Strömstad, Sweden Optimal defense theory (ODT) predicts that plants should allocate more resources to production of defense chemicals in parts that have the highest value in terms of fitness. In previous studies, assumptions about differences in fitness value among plant parts have been based on general reasoning, e.g. that reproductive tissue is more valuable then vegetative tissue since fitness ultimately depends on reproduction. Here we present an example of how demographic elasticity analysis can be used to generate species‐specific estimates of the fitness value among different plant parts. These estimates were used to make predictions about intraplant variation in chemical defenses of the intertidal seaweed Ascophyllum nodosum, within the framework of the ODT. We show that the pattern of variation in defence levels, as well as susceptibility to herbivory, among different tissue types of Ascophyllum is in accordance with these predictions. A stronger focus on variation in life history among species could lead to a better understanding of intraplant variation in defense levels, in seaweeds as well as vascular plants.