key concept 38.2 Plants Have Mechanical and Chemical Defenses against Herbivores

Herbivores—animals that eat plants—depend on plants for energy and nutrients. Their foraging activities cause physical damage to plants, and they often spread disease among plants as well. While the majority of herbivores are insects (Figure 38.4), every major class of vertebrates includes at least a few herbivores. Plants cannot evade their consumers by running away, but they have many other ways of protecting themselves against herbivory.

image
Figure 38.4 Insect Herbivores The great majority of herbivores are insects. (A) Some herbivores, such as this locust, are generalists that will attack nearly any plant. (B) Others are specialists, like this tobacco hornworm, which feeds only on tobacco and related plants.

focus your learning

  • Plants can defend themselves against herbivores by mechanical methods.

  • Secondary metabolites are plants’ constitutive chemical defenses against herbivory.

  • Herbivory induces plants to activate elicitors, which in turn activate signal transduction pathways.

  • Signal transduction pathways involve membrane signaling, reactive oxygen species, and hormone signaling.

  • The hormone jasmonic acid and its derivatives are key to the expression of many defenses against herbivory.