Tannins and other phenolic compounds represent a different mode of chemical defense. These are large molecules based on carbon, and lacking nitrogen, they are less costly in terms of limited nutrients. This is caused by the tannins leaching out of the decaying leaves which compose the litter of these forests. One appealing theory of plant chemical defense predicts such ecosystem-level phenomena. Some kinds of herbivores 1.
Most vertebrate herbivores are relatively general in diet.
Even Bison , which subsist largely on grasses, not only use a wide variety of those but also feed on herbaceous dicots. These animals rely on gut microbes for detoxification and digestion of the plants they eat. They tend to switch between plant species during feeding, a behavior that reduces the chances of eating too much of any one plant's defensive compounds. Their fungus gardens inside the nest contain fungi which convert leaves to fungal products which the ants eat. Cows feed grass to their gut bacteria and digest the bacteria and their products.