The human transport of animals across the Northern Atlantic 



per cent 

 50 T 



211 



-nnflj 



T SO 



2 3 4 



Combination of "favourable qualities" 

 Carabidae, 83 species 



DiAGR. 6. Combination of one to five "favourable qualities" (table 6, columns 1-3, 

 5-6; and p. 209), among 83 species of Carabid beetles observed on ballast places in 

 SW England. 



Black = "emigrants" (21 species). White — non-emigrants. 



From the above it can be concluded that the selection of animal species which 

 managed to cross the Atlantic by ship, first and foremost in ballast, has not been 

 a random one. Forms associated with cultivated soil, possessing low moisture 

 requirements, little specialization of food and little power of active dispersal were 

 always favoured, especially if these properties were combined with parthenogenetic 

 reproduction. 



Eastward transport 



The entire preceding part of this chapter has been devoted to the European in- 

 troductions into North America. Turning to the reverse phenomenon, the Ameri- 

 can element in the fauna of Europe, we find quite a different picture: this element 

 plays an inferior role in the European fauna. 



On page 125 a summary is given (table i) of the animal species common to 

 Europe and North America, belonging to certain selected taxonomic groups and 

 listed on page 17-124. The total number of species is 908. Of these no less than 

 309-344 species (33-38 per cent) are considered (at least in part) to be introduced 

 with man from Europe to North America. In comparison herewith, the American 

 introductions in Europe are quite unimportant, amounting to 27-34 species 

 (3-4 per cent). 



The difference is especially striking in some groups of lower terrestrial animals. 

 In the case of Carabid beetles, 37-38 species were introduced from Europe to North 

 America, none in the opposite direction; in Chilopods (Centipedes) 12-13 (o) 

 species, in Diplopods (Millipedes) 15 (o) species, in Terrestrial Isopods (Woodlice) 

 21-22 (o) species, in Lumbricids (Earthworms) 15 (2) species. Schubart (1929, 



