A mathematical model for the plant-pollinator interaction for which the relationship is not obligate is discussed. The dynamics of the system depend on both the energetic rewards and the specificity of the pollinator to the plant. Based on this model, the interaction between herbivore, plant and pollinator is proposed and the possible effect of reducing pollinator visitation rate due to the presence of herbivore is considered. It is shown that this reduction mechanism has no effect on the qualitative behavior of the model. By using these results, the possible mechanism of enhancing pollinator visitation rate accompanied by the herbivore upon the system is also examined. It is demonstrated that such a mechanism in general can promote the persistence of this three population interaction.