Numbers

Introduced species often comprise a substantial fraction of a regional entomofauna. For example, in Great Britain there are about 21,000 native insects and about 200 established, introduced ones (comprising ~1% of the total). For the contiguous United States, approximately 84,000 native species have been identified, as have 1862 established, introduced species (~2% of the total). Florida has relatively more introduced species: 11,509 native and 993 introduced (8%). For oceanic islands, the introduced proportion can be much greater. Thus, for the Hawaiian Islands, there are about 5400 native insects and 2600 introduced ones (32% introduced), whereas the mid-Atlantic island Tristan da Cunha has 84 native insects and 32 introduced ones (28% introduced). The greater proportions of introduced species on islands probably result more from the mathematics of smaller numbers of native species and relatively larger numbers of attempted introductions than from some inherent invasibility of island communities or stronger "biotic resistance" of continental ones.

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