Plant Compensatory Responses: Bud Dormancy as an Adaptation to Herbivory

Some plants can compensate, and even overcompensate, for the loss of productivity caused by herbivory. The presence of latent meristems, or dormant buds, is one of the basic prerequisites of such compensation mechanisms. We present a mathematical model in order to analyze compensation responses in relation to the intensity of herbivory. The model generates a number of qualitatively different kinds of compensation curves when seed production is plotted against the proportion of active meristems lost per grazed plant. The shape of the curves depends on the proportion of dormant buds and their activation sensitivity in relation to meristem loss. Overcompensation is most probable when dormant buds are easily activated. When plants are grazed only once, as assumed in our model, selection favors high bud sensitivity. However, we expect that repeated damage may select for a more restrained pattern of bud activation. When relatively few buds remain dormant, plants can overcompensate for low levels of damage only. On the other hand, when most buds remain dormant, they can overcompensate even for high levels of damage. We consider compensation capacity a potential benefit of bud dormancy when plants are subject to damage. However, bud dormancy may also imply costs on plant productivity and fecundity in the absence of herbivory. Still, intense herbivory may favor bud dormancy in spite of the potential costs. Selection for bud dormancy requires both that the risk of herbivory is high and that herbivores remove a large fraction of active meristems per plant. Consequently, overcompensation is a theoretically plausible possibility, and intense herbivory is a potential selective force that favors bud dormancy. None of these results, however, imply that herbivory is beneficial to plants. In our case, plants with bud dormancy never have higher seed production than plants that have no dormant buds and that are not grazed.