Low Nutritive Quality as a Defense Against Optimally Foraging Herbivores

Using a simple optimization model, we analyze whether low nutritive quality in terms of low nutrient concentration can be a profitable anti-herbivore strategy for individual plants. Contrary to most previous studies, ours has considered vertebrate herbivores feeding on discrete food items such as trees. The food items are regarded as patches and exploited according to the marginal-value theorem. Low-nutrient strategies (possibly associated with correspondingly high levels of defense compounds) are expected if the browsing pressure is high (i.e., high encounter rate with individual plants and/or long handling time set by large interplant distances) in inherently fast-growing plants and in plants with long exposure time to potentially deleterious herbivory. Moreover, the critical size for escape from deleterious herbivory influences the optimal solution. We predict that plants in resource-poor habitats should tend to maximize their nutritive quality and therefore rely on carbon-based defenses, further incre...