<P> Plant defense against herbivory or host - plant resistance ( HPR ) describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores . Plants can sense being touched , and they can use several strategies to defend against damage caused by herbivores . Many plants produce secondary metabolites , known as allelochemicals , that influence the behavior , growth , or survival of herbivores . These chemical defenses can act as repellents or toxins to herbivores , or reduce plant digestibility . </P>
how do some chemicals in plants protect them from their enemies
repellents toxins reduce plant digestibility