Exotics are species that are foreign to an ecological assemblage in the sense that they have not significantly adapted to resident biota or to local abiotic conditions, and resident species have not significantly adapted to them. Although they need not be human introduced nor damaging, when they are, a negative appraisal of such exotic species can be justified. Human introduction of exotics into natural systems typically increases human influence over those systems, thus diminishing their wildness. Valuing nature for its wildness is a rationale for the national parks policy of letting nature take its course. Thus, Yellowstone Park has a strong reason for removing human-introduced exotics and for welcoming naturally migrating exotics. Disvaluing exotics that are neither human introduced nor damaging simply because they are foreign smacks of xenophobia. But given that wanton human mixing of species threatens to homogenize the earths biological communities, biological nativism is justified as a way to preserve the diversity between such communities.
"Defining and evaluating exotic species: issues for Yellowstone park policy,"
Western North American Naturalist: Vol. 61
, Article 2.
Available at: http://scholarsarchive.byu.edu/wnan/vol61/iss3/2