This paper is devoted to how heterogeneous environmental effects can greatly change the dynamical behaviour of a population model. The author considers the competition model given by
where and , denotes a smooth bounded domain in , are nonnegative functions over , and are positive constants. Throughout this paper the author supposes that and satisfy homogeneous Dirichlet boundary conditions. The author shows that there exists a critical number such that (1) behaves as if is a positive constant if , but if , then interesting new phenomena occur. This shows that heterogeneous environmental effects on population models are not only quantitative, but can be qualitative as well.