In the case shown, the first stage caterpillar cuts a circular trench in the leaf's mesophyll thereby reserving a small patch of edible tissue. When that is consumed the larva must move to a new leaf which has not previously been damaged. Large mature larvae can eat most of a leaf before it can mobilize increased defenses. Aside from being a drain on the plant s energy and nitrogen budget, some defenses pose danger to the plant itself. For example freezing can disrupt cells and lead to CN release in the leaves of cyanogenic glycoside-containing plants.
Thorns defend plants against large vertebrate browsers.
Optunia without spines is very edible to deer and cattle. This means that when the Acacia grows above the browse line and becomes a small tree it will no longer be wasting energy on big thorns. Mesquite does the same thing. I repeated a description of the mutualistic defense syndrome illustrated by ant acacia . The new point made had to do with this plant s lack of chemical defenses.