ABSTRACT
In his seminal work on the impact of European flora and fauna intentionally and inadvertently brought to the Americas, Alfred Crosby emphasized the asymmetry of biotic exchange between the old and new worlds (Crosby, 1972, 1986). Europe had received few problem species in return for the plethora of notorious invasive non-natives inflicted on North America, not least the ‘English’ sparrow and the starling, which had ‘dispossessed millions of American birds’. However, as John MacKenzie has pointed out, the flow of troublesome transatlantic traffic was not quite so one-directional. For MacKenzie, Crosby’s perspective was a ‘strikingly American one, for anyone who lives in the British Isles is almost daily brought face to face with the fact that ecological colonialism has been a two-way process’. Plenty of extra-European species caused headaches for wildlife and habitat conservationists (MacKenzie, 2001a, 2001b). Crosby remained unmoved. ‘How often’, he rejoined, ‘have American species swamped and driven to the verge of extinction native species in Great Britain? Do you have over there, for instance, millions of American rats as we do millions of Old World brown and black rats? If there are equivalently successful aliens in the UK, I would like to know about them’ (MacKenzie, 2001b).
