3.3.1.1.2: Herbivory

When an animal feed on parts of another organism (usually a plant), herbivory occurs. For example, the koala eats the eucalyptus leaves (figure \(\PageIndex{a}\)) or a cicada feeds a plant's sap (figure \(\PageIndex{b}\)). Like predators, herbivores may feed on multiple individuals over their lives; however, herbivores do not necessarily kill the plants that they eat.

Figure \(\PageIndex{a}\): Koalas are herbivores that feed exclusively on eucalyptus leaves. They are thus considered specialists because the specialize on just one type of food. Image by Dr. Umesh Behari Mathur (CC-BY).

Figure \(\PageIndex{b}\): This floury baker cicada feeds on plant sap by piercing the tree with needle-like mouth parts. Image by Toby Hudson (CC-BY-SA).

Plant species have evolved numerous defenses that reduce herbivory. Thorns are an example of a mechanical defense that discourages large herbivores from feeding on a plant (Figure \(\PageIndex{c}\)-a). Many plant species produce secondary plant compounds that serve no function for the plant except that they are toxic to animals and discourage consumption, acting as a chemical defense. For example, the foxglove produces several compounds, including digitalis, that are extremely toxic when eaten (Figure \(\PageIndex{c}\)-b). (Biomedical scientists have repurposed the chemical produced by foxglove as a heart medication, which has saved lives for many decades.)

Figure \(\PageIndex{c}\): The (a) honey locust tree uses thorns, a mechanical defense, against herbivores, while the (b) foxglove uses a chemical defense: toxins produces by the plant can cause nausea, vomiting, hallucinations, convulsions, or death when consumed. (credit a: modification of work by Huw Williams; credit b: modification of work by Philip Jägenstedt)

Attribution

Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)