We develop a perturbation theory for strongly continuous backward evolutionary systems and their adjoint systems. The theory is not based on generating families but on certain operator families called step responses and cumulative outputs. The perturbation problem is reduced to solving an abstract Stieltjes integral equation of nonconvolution type. The theory is well suited for treating structured population models.
"Perturbing evolutionary systems by step responses and cumulative outputs." Differential Integral Equations 8 (5) 1205 - 1244, 1995.