Contrasts in the Ecology of Plant Chemical Defenses Against Herbivores

move about 66% of above-ground production2. Given the large allocation to below-ground structures, this may be no more than about 33% of total production, about r/3 to ‘12 of the rates in marine communities. In both marine and terrestrial systems, herbivory is generally greater in tropical than in temperate areas, but the highest rates of herbivory on tropical coral reefs can be ten to IO0 times greater than the highest rates in tropical forestst,s. Most herbivory in terrestrial systems is due to insects and vertebrate homeotherms4,5. Insects are largely absent from marine systems, and most herbivory is due to vertebrate ectotherms (fishes1 and a diverse array of invertebrates that are present all year and rarely undergo diapause (sea urchins, gastropods, polychaetes and a variety of marine crustaceansP. Because virtually all marine herbivores are ectotherms, changes in temperature may affect herbivory rates more in marine than in terrestrial systems’. With decreasing temperature, herbivory decreases in marine systems, but may increase in terrestrial communities because of the increased energy demands that low temperatures place on vertebrate homeothemrs. Terrestrial herbivores cope with the large amounts of relatively indigestible cellulose, hemicellulose and lignin that occur in terrestrial plants by f I ) timing their life cycles such that the feeding stages cooccur with the seasonal flush of new, high-quality leaves; (2) sucking