The relationship between the palaearctic and nearctic faunas 



277 



FIG. 46. Distribution of long- 

 winged (white) and short- 

 winged (black) Bembidion 

 grapei Gyll. (fig. 44) in Ice- 

 land. The two main refuge 

 areas during the last glaciation 

 are indicated. Cf. fig. 45. 



during last glaciation (Wiirm), whereas a purely macropterous population inhabits 

 the eastern parts of Sweden and almost all of Finland (fig. 45). 



Iceland is too small an area to have retained, in any part of the island, a purely 

 macropterous population. The postglacial period has been sufficiently long to 

 allow a universal colonization of the brachypterous form as well, and no obstacle 

 comparable to the mountain range of Scandinavia has prevented its dispersal. 

 The geographical distribution of the two forms (fig. 46) therefore, at first glance, 

 seems rather confused and due to chance. That is not the case, however. The 

 brachypterous form is most marked within two areas, around the EyjafjallajokuU 

 in the extreme South and along the coastal margin of the Vatnajokull in the 

 Southeast, which for other reasons are regarded as the main refuges during the 

 Wiirm-glaciation (Lindroth, 193 1, p. 489 a. f.). The index macropterous: brachyp- 

 terous is here 0.2 and o.i, respectively. For the rest of the island this figure is 

 0.7, slightly less in the Southwest, 0.6; in the North 0.9, in the isolated north- 

 western peninsula 1.5. 



The interesting contribution to our present discussion is that in Iceland, outside 

 the two main refuge areas, there is a marked contrast in the occurrence of the 

 brachypterous form of Bembidion grapei in the immediate vicinity of hot springs, 

 as compared with other localities. Apparently the species is favoured by the warm 

 conditions. One would expect, then, that the hot springs would absorb in the 

 first place the most easily dispersed individuals from the mixed populations of 

 the surroundings and that consequently the macropterous form would be in the 

 majority around them. 



The exact opposite is the case. The index macropt.: brachypt. for individuals 

 from the vicinity of hot springs is 0.3, for all others (outside the two refuge areas 

 of the South), 1.3 (diagr. 8). 



