

64 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



the difference between its northeast slope and the Malay Peninsula. 31 

 The fauna of Victoria south of the Great Dividing Range is much 

 closer to that of Tasmania than to the fauna north of the range, which 

 agrees with that of New South Wales. 32 Mountains, if sufficiently 

 high, font more effective barriers to the distribution of snails than 

 does the sea. 



The direction of mountain ranges has an important influence on 

 their attendant climatic effects. When they parallel the lines of lati- 

 tude, they coincide in general with climatic limits, and intensify them. 

 In some, such as the Himalayas, the cold North is directly juxtaposed 

 to the tropical South, and faunae of diverse composition may then be 

 brought into immediate contact. If, on the contrary, they extend from 

 north to south, they form veritable highways upon which polar or 

 temperate forms may extend far to the south. In Eurasia the principal 

 mountains, the Pyrenees, Alps, Carpathians, Caucasus, Hindu Kush, 

 Himalaya, Tien Shan, and Altai, extend from east to west. They 

 thereby prescribe definite east-west or west-east lines of dispersal for 

 many animals, and prevent dispersal from north to south. In America, 

 with its Cordillera extending from Canada to Chile, the puma has been 

 able to spread from Alaska to Patagonia. 33 



Deserts make a sharply defined boundary for all terrestrial animals, 

 as distinguished from flying animals, especially when they are a nearly 

 continuous series, as from Senegal to Mongolia. The Sahara forms 

 the faunal division between north Africa and central and south 

 Africa, and the only interchange occurs in the Nile Valley. This inter- 

 change is limited by the narrowness of the valley, and does not affect 

 the essential distinctiveness of the two faunae. The fauna of the Cape 

 is also separated from that of central Africa by the Kalahari Desert, 

 and contains a number of endemic genera, such as, among the tiger 

 beetles, Manticora, Dromica, and Myrmecoptera. 3 * 



The means of dispersal for terrestrial animals are very varied and 

 of unequal effectiveness. Active motion appears in the most complete 

 gradation. Leaving out of consideration the sea birds, for which the 

 power of flight is of greater importance than swimming as a means of 

 distribution, relatively few terrestrial animals can swim any consider- 

 able distance. The crocodiles are among the best swimmers, ranging 

 to the Solomon and Fiji Islands; two individuals of Crocodylus porosus 

 are known to have withstood the 900-km. sea journey to the Keeling 

 Islands. 35 Many snakes also swim well. Snakes have repeatedly been 

 washed up on the Keelings, usually arriving dead or dying, but some 

 survive the journey. The European grass snake (Natrix natrix) is a 

 good swimmer. It has been found in the sea off the Finisterre Coast, 



