Exotic Species, Naturalisation, and Biological Nativism

Contrary to frequent characterisations, exotic species should not be identified as damaging species, species introduced by humans, or species originating from some other geographical location. Exotics are best characterised ecologically as species that are foreign to an ecological assemblage in the sense that they have not significantly adapted with the biota constituting that assemblage or to the local abiotic conditions. Exotic species become natives when they have ecologically naturalised and when human influence over their presence in an assemblage (if any) has washed away. Although the damaging nature and anthropogenic origin of many exotic species provide good reasons for a negative evaluation of such exotics, even naturally-dispersing, nondamaging exotics warrant opposition. Biological nativists’ antagonism toward exotics need not be xenophobic and can be justified as a way of preserving the diversity of ecological assemblages from the homogenising forces of globalisation. Implications for Yellowstone National Park policy are explored.