ALPINE ANIMALS 497 



lizard, the redstart, and most of the meadow mice (Microtinae) of 

 the Alps are examples. Accidental alpine animals are those which 

 temporarily or incidentally enter the alpine zone but do not develop 

 there. Migratory birds and insects carried by wind compose the ma- 

 jority of this element of the alpine zone. 



Isolation. — The wide separation of individual mountain ranges 

 may make their alpine zones insular in character— separated by low- 

 lands which are impassable to their stenozonal inhabitants. Endemic 

 forms are accordingly frequent in mountains. The high mountains of 

 Eurasia are especially discontinuous, contrasting with the Rocky 

 Mountains and Andes of the western hemisphere. The Old World 

 ibexes, for example, fall into a series of species— the common ibex 

 of the Alps, the Caucasian, Sinaitic, and Abyssinian species, and finally, 

 the widespread ibex of central Asia which is divisible into numerous 

 subspecies. The chamois and wild sheep develop distinct subspecies on 

 individual ranges. The same is true of many birds, such as the par- 

 tridges (Caccabis) of Eurasia, the hedge sparrows {Prunella), and 

 the mountain-inhabiting snow finches {Montif ring ilia). Species forma- 

 tion by isolation is notable in the hummingbirds of the Andean peaks. 

 Extremely isolated mountains, like Mount Kina Balu in Borneo, de- 

 velop a completely distinctive fauna. This subject was discussed more 

 thoroughly in Chapter VI. 



Environmental selection. — The peculiarities of the alpine environ- 

 ment all represent divergence from optimum conditions, and accord- 

 ingly operate as selective influences, excluding many animals. This 

 selection increases in intensity with approach to the snow line. Thus 

 the highest peaks exhibit great similarity of faunae. The same sys- 

 tematic groups supply the faunae of mountain peaks in Eurasia and 

 Africa. The sub-snow zone fauna of Mount Kilimanjaro of Africa 

 has almost all the beetle genera of the same zone in the Alps. 27 The 

 close relationship or even identity of the species and genera of but- 

 terflies in the alpine zone of widely separated mountain ranges is 

 astonishing. 28 The high mountains of Africa, although widely separated 

 in latitude, all have closely similar bird faunae. 29 The high mountains 

 of Java and the Philippines present striking relationships with the 

 alpine fauna of Asia. 30, 31 It is certain that ecological selection has 

 played a part in these relationships of montane faunae, though the 

 historical factor may enter also, as in the vertebrate fauna of the Alps 

 (cf. p. 102). 



Review of alpine faunae. — Insects take first place in alpine 

 faunae. Orders with a complete metamorphosis predominate, with 

 Hemiptera and Orthoptera sparsely represented, though Collembola 



