D3274: Modeling the influence of seasonal pattern and herbivore specialization on plant allocation towards growth and defense

Most current plant defense theory models predict a dilemma exists between a plant’s need to compete and its need to survive (i.e., to grow or defend, respectively). Predictions of such models are largely based on resource availability. However, seasonal variation and herbivore specialization may have effects as well. Using continuously growing insect populations (e.g., aphids and scales) and plants with inducible chemical defenses as a model system, we created a dynamic optimization model with forward simulations to determine how plants allocate resources towards growth and defense to maximize fitness over a predictable set of seasonal patterns and how those effects change when faced with herbivory from a generalist vs. a specialist population. Assuming fitness increases with plant size and decreases with insect herbivore density, we found younger plants are likely to invest heavily in defense, irrespective of herbivore density, which is consistent with empirical studies. Likewise, we found allocation towards growth, whether partial or complete, confined to optimal seasonal conditions. These effects increased with herbivore specialization.