Macroalgal Models in Testing and Extending Defense Theories

The ecological roles of secondary metabolites have become one of the most expansive areas of research within plant ecology during the last two to three decades. They have also become one of the most theory-laden fields of plant ecology, if not ecology in general, with a number of general models (theories) seeking to explain and predict patterns of chemical defenses in plants. (We use the terms model or theory rather than hypothesis because we define the latter term in a more restricted way: a testable prediction that is logically derived from an explanatory model/ theory.) The discovery and characterization of tens of thousands of natural products in terrestrial plants and marine organisms during the last century called for models that could provide explanations and categorizations to this ample form of biodiversity. Suggestions that the primary function of these so-called secondary metabolites was as a defense against consumers (Dethier 1954; Fraenkel 1959) led ecologists to formulate a series of general defense models, especially during the 1970s and 1980s, to explain the distribution and variation of secondary metabolites. These defense models have allowed natural product chemists and chemical ecologists to put their specific work into a broader context and they have become a significant driving force for further studies of secondary metabolites and their ecological roles.