90 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



the fauna of Celebes. Of the species of birds 28% are endemic, of 

 reptiles 36%, of amphibians 40%, of mammals 40%, of land snails 

 79%, and of land planarians 91%. 



Islands close to the mainland are often little differentiated in their 

 fauna; the genera and often the species are identical with those of the 

 mainland. Trinidad is zoogeographically indistinguishable from adja- 

 cent South America; of 65 mammals and 64 reptiles very few are 

 confined to it, and only 13 out of 63 land snails are endemic. 64 It is 

 true that about one-third of the 41 fresh-water fishes are endemic, 

 even so, they are mostly local races of widespread forms, but with 2 

 endemic genera. 65 



The fauna of Tasmania is closely similar to that of Victoria south 

 of the Dividing Range; the species are identical or in vicarious pairs; 

 there are no endemic genera of vertebrates, disregarding the Tasmanian 

 wolf, Thylacinus, and the Tasmanian devil, Sarcophilus, which are 

 recently extinct in Australia, or of fresh-water fishes or land and fresh- 

 water snails. The vagility of the respective groups governs the amount 

 of endemism in species ; only 10% of the species of birds are endemic, 

 as compared with 81% of the land snails. 66 



Environmental difference in the isolated area is also an important 

 factor for the transformation of isolated species, but isolation operates 

 to produce new forms without differences in habitat. Thus the genus of 

 birds Certhiola of the family Coerebidae occurs in Central and South 

 America and in the West Indies; with only 4 species on the mainland, 

 there are 16 species in the Antilles, often with an endemic species on 

 each island. 67 In the Rhio-Linga Archipelago, a series of small islands 

 off the east coast of Sumatra, with an area of about 1/90 that of 

 Sumatra, there are no less than 8 well-distinguished subspecies of 

 dwarf deer, Tragulidae, while all the similar deer on Sumatra and on 

 the Malay Peninsula north to Tenasserim belong to a single species, 

 Tragulus napu. G8 There can be no question that the habitat conditions 

 on these small islands are less varied than in Sumatra and the main- 

 land area. The islands of the Aegean Sea each have special varieties 

 of the clausilid snail Albinaria coerulea, in spite of the great uni- 

 formity of the insular conditions, especially for snails. 



The mainland does not afford the possibility of such complete iso- 

 lation as do islands. A few areas exist which are surrounded by mighty 

 barriers, such as the 3600-m. high plateau of Tibet, bounded on the 

 north by the Kwen-lun, Altyn-dag, and Nan-shan, and on the south 

 by the Himalayas. The Tibetan mammal fauna is perhaps the most 

 peculiar of any on a continental area; 5 of the 28 genera and 30 of the 

 46 species are endemic. 69 



