We study semi-linear evolutionary problems where the linear part is the generator of a positive \(C_0\)-semigroup. The non-linear part is assumed to be quasi-increasing. Given an initial value in between a sub- and a super-solution of the stationary problem we find a solution of the semi-linear evolutionary problem. Convergence as \(t\to\infty\) is also studied for the solutions. Our results are applied to the logistic equation with diffusion, to a Lotka-Volterra competition model and the Fisher equation from population genetics.
AMS Subject Classification (2020): 34G20 (Primary) 34G20, 47N20, 47H07, 35K20 (Secondary)