ii BARRIERS TO DISTRIBUTION 79 



Jaguar to America, and so forth. The entire expanse of country 

 which is inhabited by an animal is called its area of distribution. 

 Such areas are larger or smaller. The Lion ranges over the whole 

 of Africa, a small part of India, and some neighbouring countries ; 

 on the other hand, the Insectivore Solenodon is limited to Cuba 

 and Hayti, a separate species to each. Among other groups of 

 animals are instances of an even more restricted range. There 



O 



are humming-birds confined to the slopes of a single mountain, 

 and fishes limited in their range to a single small lake. 



A species may be found everywhere within the area of its 

 distribution, or it may be confined to a number of limited tracts 

 within that area. In this case it is usual to speak of " stations." 

 In such cases the species in question is generally suited to some 

 particular kind of environment. Thus the Otter and other 

 aquatic mammals will only be found where there is water; and 

 intervening tracts of waterless country will contain no Otters. 

 Goats and Chamois live only upon mountains ; the intervening 

 plains are destitute of them. This discontinuity of distribution 

 within the area is very general. But a discontinuity of area is 

 also seen not so commonly however ; and, indeed, when it does 

 occur, it is a matter of a genus and not of a species. Thus the 

 Tapir is found in the East Indies on the one hand and in South 

 and Central America on the other, being absent in the inter- 

 mediate tracts. 



It is clear that tracts of country eminently suitable for the 

 housing of a particular mammal do not always possess that kind, 

 or even an allied form. Africa, for example, possesses no arboreal 

 Anteaters ; there are no Anteaters at all (of the order Edentata) 

 in Australia, though there are plenty of ants for them to feed upon, 

 and tropical conditions of climate prevail. But as in these cases 

 the inference may be denied on the grounds that no experiments 

 exist to prove or to disprove the assertion, the matter may be 

 better emphasised by such cases as the introduction of the Eabbit 

 into Australia, and various mammals, such as Goats, into oceanic 

 islands. The plague caused by the former is a matter of notoriety. 

 But although climate and conditions and animal inhabitants do 

 not march accurately together, there is certainly some connexion 

 between temperature and the range of animals. Mr. Lydekker 

 writes on this point as follows : " The llama -like animals, re- 

 spectively known as vicunas and guanacos, are met with in 



