Rapid displacement of native species by invasive species: effects of hybridization

The introduction of non-native populations can lead to the competitive exclusion (displacement) of native populations. This has been hypothesized to be further exacerbated by the potential of hybridization, which can dilute or genetically assimilate the native genotype leaving no "pure" natives. With relatively moderate to high rates of immigration, the loss of the native species can be rapid with or without hybridization. Using single-locus, two-allele models, I find that species replacement can occur very rapidly and the time to displacement decreases rapidly with increasing immigration and selection differential. Immigration and selection act in two different ways: increasing immigration results in displacement by overwhelming the native; whereas increasing the selection differential in favor of the invader leads to displacement via genetic assimilation. The implications of these results are the need for more empirical studies on the immigration patterns of invasive species and their potential for interbreeding with natives. (C) 1999 Elsevier Science Ltd. All rights reserved.