132 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



Alpine animals whose ancestors had a much wider range in the glacial 

 times and were much larger. Their formerly continuous range has 

 been reduced and split up by the encroachment of the forest into the 

 mountains from the plains. 39 A conspicuous exception to this relation 

 appears to be the Komodo Island monitor {Varanus komodoensis) , 

 which is much larger than the Varanus salvator of the larger neighbor- 

 ing islands and the mainland. 



Small well-defined situations like islands or oases have not so many 

 species as uncircumscribed areas of similar size. The vast multiplicity 

 of animals that characterizes a continent may not be expected on an 

 island. 40 Iceland has fewer species of birds than Norway. Tasmania, 

 according to Gould's figures, has only 181 species of birds, while New 

 South Wales has 385. Sikkim, whose bird fauna is one of the richest 

 in the world, has 500 or 600 species of birds in 4015 sq. km., while 

 Celebes, almost 60 times as large, has only 393. The Azores (2388 sq. 

 km.) and the Cape Verde Islands (3851 sq. km.) each have 34 

 species of breeding birds, while a palace garden in Bonn, with only 

 8.8 hectares, has 43 species of birds nesting within its confines. This 

 difference is necessarily conditioned by the fact that the least range of 

 a species in an interbreeding community is larger than the area re- 

 quired by a single pair of the species within the range. The lessened 

 possibility of chance and increased difficulties in the way of the immi- 

 gration of new forms, on islands, are factors that do not apply to parts 

 of a mainland. 



On the other hand, broader areas, with other conditions equal, in 

 general have the richer fauna. A principal reason may be that they 

 afford a wider range of habitat conditions, and thereby increased 

 possibilities for the formation of species by adaptation. This is evi- 

 dent when the amphibian and reptile faunae of various large islands 

 with similar climatic conditions are compared: 



Island Area, sq.km. 



Borneo 715,100 



Madagascar 591,563 



Sumatra 443,234 



Celebes 200,132 



Java 131,733 



Ceylon 65,690 



New Zealand 268,461 



Cuba 118,833 



Haiti 77,253 



Jamaica 10,859 



Puerto Rico 9,314 



