As concern arises over the problem of bioinvasion, the introduction of non-native species becomes controversial. The major issue that most people worried about is that whether non-native species threaten the natural environment. Mark Sagoff (2005) asserts that non-native species are not necessarily harmful. In response to Sagoff’s viewpoint, Simberloff comes up with opposing opinion that “major environmental impacts of non-native species…have both been demonstrated and judged by the public to be harmful” (Simberloff 2005, p595). To prove that non-native species are not always harmful, Sagoff (2005) puts forward five problems with people’s conventional understanding of non-native species. He first questions the definition of “harm
