Mechanisms of Associational Effects of Sika Deer Browsing: Relationships Between Plant Nutrients and Foraging Behavior

ABSTRACT The susceptibility of plants to ungulate herbivory is affected by herbivore foraging selection, which is influenced by neighboring plants within a patch (associational effect). However, the role of plant nutritional characteristics in herbivore foraging behavior, which generates associational effects, remains poorly understood. In this study, we examined the relationships among plant nutritional characteristics, sika deer (deer) foraging behavior, and deer browsing patterns at the patch scale. We conducted a cafeteria experiment to determine the palatability of each plant species. We then conducted a polyculture cafeteria experiment to evaluate browsing patterns and foraging behavior among plant patches, with Boehmeria silvestrii as the focal plant and nine neighboring plants. We analyzed plant nutrients, including crude protein, minerals, and crude fiber. The time spent in the patch and avoidance behavior after contact with the plant were important foraging behaviors for predicting the direction and strength of the associational effects, and these behaviors determined the browsing patterns in the plant patches. Plant nutrients, such as the crude protein and macromineral contents of neighboring plants, partly explained the foraging behavior and browsing patterns of deer in plant patches. Determining the relative importance of other factors, such as plant defense traits and deer browsing pressure, that may influence deer foraging behavior is a future challenge for understanding the mechanisms of deer browsing patterns at the patch scale.