Random Search by Herbivorous Insects: A Simulation Model

A stochastic simulation model that relates the success of various herbivore searching behaviors to the density and arrangement of food plants was developed. It was designed to be field—testable with all model parameters directly measurable in field experiments. The model uses probability distributions and parameter ranges that are in accordance with published herbivore movement data. In the model, herbivore insect searching success depends in a complex manner upon parameters such as insect move lengths, turning angle concentration, reactive distance, risk of mortality while searching, plant density, plant dispersion, and plant stand size. Simulation results preclude simple generalizations and indicate that the outcome of interactions between plant density, plant dispersion, and herbivore searching behavior depends heavily upon parameter values. I argue that species—to—species shifts in the details of the simple searching process that I simulate could explain the (experimentally observed) high variation in herbivore response to vegetation texture. I discuss plant and insect strategies that are o ptimal" within biological constraints. For example, results from the model suggest that under many conditions clumping by plants can be an effective escape strategy from searching herbivores. This contradicts the claim that plant spatial distribution does not affect insect searching success, a claim that is justified only if it is assumed that organisms search (infinitely long) without biological cost. The importance of considering the cost of ineffective search is emphasized.