Dynamic anti-herbivore defense in ant-plants: the role of induced responses

We compare the dynamic nature of anti-herbivore defense in ant-plants to other plant-herbivore systems. Previous studies have neglected the dynamic nature of defense in ant-plants. Changes in environmental cues can trigger modifications in a plant's defensive strategy (induced responses). In ant-plants, many cues and signals controlled by the plant and the environment can enhance defense by influencing recruitment, patrolling, and persistence of ants. Leaf damage may trigger plant signals such as the release of plant sap or green leaf volatiles that attract ant defenders. Similarly, disturbance and mammalian breath may themselves induce ants to recruit. We also review studies that have looked for changes in extrafloral nectar production induced by herbivory. Induced responses to herbivory that stimulate changes in nectar volume, sugar concentration, and amino acid concentration of extrafloral nectar have been reported. This should increase patrolling by defending ants. We propose that non-nectary mediated ant recruitment should also occur, but may be restricted to tightly linked ant-plant systems. We suggest that induced responses to herbivory are common in ant-plants.