‘native’ and ‘alien’ - a biogeographical perspective

The concepts of native and alien species are essential to biogeography. They are fundamental to our understanding of why organisms grow where they do. Many species are easy to allocate to one or other category (eg, New World species in the Old World), although there are also of course doubtful cases. The biogeographical use of the terms as factual descriptions of modes of origin should be distinguished from their use in evaluating species for conservation purposes.