The threat when invasives hybridize...

Rapid spread of invasive genes into a threatened native species Benjamin M. Fitzpatrick, Jarrett R. Johnson, D. Kevin Kump, Jeramiah J. Smith, S. Randal Voss and H. Bradley Shaffer PNAS Feb 2010 doi: 10.1073/pnas.0911802107 
(From the abstract): Models (in combination with field study) suggest that the rate of displacement of native by invasive alleles can be rapid and inevitable if they are favored by natural selection. The results illustrate that genetic and ecological factors need to be carefully weighed when considering different criteria for protection, because different rules could result in dramatically different geographic areas and numbers of individuals being protected.