# Given a linear growth trajectory, increasing survival increases optimal maturation age and size.

As annual survival *s* increases, the growth curve is unchanged, but the iso-fitness curves become less steep and the age-0 intercepts increase (see Fig 8), so optimal age and length increase along the growth curve. From this point of view the reaction norm curve is the same as the growth curve. Colored lines show level sets of fitness function *R*_{0} in (A, B) and level sets of *r* in (C, D); corresponding colored points show optimal age and length to maximize the fitness function for each level of annual survival rate *s* (red: 0.25, orange: 0.50, green: 0.70, blue: 0.80). This linear growth trajectory has *k* = 266.2 mm/yr, *c* = 0. (A, C) With log-length on the vertical axis, iso-fitness lines are straight. (B, D) With linear length on the vertical axis, the linear growth curve is a straight line, but iso-fitness lines are curved.