Bias against non-native species is not xenophobic (Nature 474, 153–154; 2011) — it has a sound scientific foundation.

The non-native status of a species is highly relevant to assessing its potential environmental and economic impact. Unrestrained growth and environmental damage follow when there are no natural enemies in newly colonized areas. This is not necessarily a sign of an invader's superior evolutionary fitness: it may lead to a population collapse due to overexploitation of resources.

Non-native species can increase the variety of species in a community, but it is an oversimplification to equate this with increased biodiversity, of which species richness is only one component. Surviving populations of native species may shrink or become restricted to poor-quality marginal habitats. Such unevenness hardly contributes to a more diverse community.

The genetic diversity of invaded communities may decrease because of bottlenecks: native genotypes disappear as populations fall, whereas the invaders originate from very few initial colonizers.

Establishment of non-native species inevitably decreases global diversity. Australia, for example, was unique in having no placental mammals; their introduction by humans made the continent ecologically more similar to the rest of the world.