ONTOGENIC DEVELOPMENT OF CHEMICAL DEFENSE BY SEEDLING RESIN BIRCH - ENERGY-COST OF DEFENSE PRODUCTION

Whether production of chemical defenses by plants is or is not an ener getically costly process is an important, but unresolved, question in chemical ecology. We suggest studies of the ontogenetic development of plant defense systems can help resolve the question. As an example of this approach to the cost question, we explore the problems associate d with production of immobile chemical defenses that defend juvenile r esin birches against browsing by mammals. From this exploration we dra w two conclusions: (1) Shortly after germination, production of chemic al defenses by small-seeded species, such as birch, is energetically c ostly. (2) Opposing selection for defense versus competitive ability i n the seedling stage of birch has resulted in a trade-off in allocatio n of carbon to production of immobile chemical defense versus allocati on of carbon to production of storage reserves. We suggest this trade- off results in a large indirect cost of defense because carbon used fo r production of immobile chemical defenses is unavailable for support of growth in the future, but stored carbon can be used to support futu re growth.