In this paper, we are concerned with the role of the age structure
of a prey in the dynamic of a predator prey model. Specifically, we
study the  effect of predation on a non-reproductive class of the
prey, when the reproductive class of the prey presents a group
defense mechanism. Three different scenarios are analyzed: (1)
Constant predation rate on the nonreproductive class, no defense
mechanism; (2) Predation of Type II of Holling on the
non-reproductive class, no defense mechanism; and (3) Predation of
Type II of Holling on the non-reproductive class, defense
mechanism.