The human transport of animals across the Northern Atlantic 



139 



(From EssiG, 1931.) 



FIG. 6. Spread of the Alfalfa Weevil, Phytonomiis posticus Gyll. (variabilis Hbst.) 



in Central and Western U.S.A. since its introduction in Utah about 1902. 



Black area = before and incl. of 1910 



Densely hatched area = before and incl. of 1919 



Thinly hatched area = ,, ,, ,, ,, 1952. 



Since 1952 the beetle has appeared also in the eastern states. 



(According to TiTUS, 191 1, Reeves, 1927, and information from Bureau of Agriculture, 

 Washington, D.C.) 



foundland. Other Carabid beetles showing almost as wide a gap in their North 

 American distribution are Carabus granulatus L. (fig. 8), C. nemoralis Miill. (fig. 7), 

 Agonum miilleri Hbst., Clivina fossor L., and Pterostichus melanarius 111. (for further 

 examples, vide p. 144). This pattern of distribution in introduced species holds also 

 true for terrestrial Molluscs (Pilsbry, 1948, p. 522). An "immature" distribution 

 as a sign of introduction in Newfoundland is shown by Bembidion tetracolum Say 

 (ustulatum auctt.), Clivina fossor L. (maps, figs. 12-13), and many others. 



3. THE ECOLOGICAL CRITERION. The ecology of a species may indicate its 

 character of a foreigner. It is most striking to a European biologist that in North 

 America the "culture steppe", the open, dry (artificially drained) land in and 

 around ports and other settlements, especially along the Atlantic coast, is inhabited 

 by a flora and fauna of pronounced European character. Certain indigenous North 

 American species may invade such spots too, but a plant or an animal restricted to 

 this habitat is very likely to be a recent introduction. 



An instance is given by the ground-beetle genus Amara. With very few excep- 

 tions, its members are confined to dry, open ground, some of them inhabiting 



