648 



COLLEGE ZOOLOGY 



ZOOGEOGRAPHY The range 



Presence and absence 

 of species 



Zoogeography is that branch of zoology 

 which deals with the geographic distribution 

 of animals. The available living space on the 

 earth can be divided into 4 major habitats, 

 namely, marine, fresh-water, terrestrial, and 

 symbiotic, and these can be subdivided into 

 minor habitats. But the species of animals 

 are not exactly the same in environments of 

 the same type in different localities; many 

 bodies of fresh water capable of supporting 

 certain species are free from them; each 

 large land area usually supports a fauna that 

 is distinct from that of every other large 

 area; and certain species of parasites occur 

 in human beings in one part of the world 

 and not in others. That species are absent 

 from a locality which is well fitted for them 

 to live in is proved by the success of certain 

 introduced species in this country, such as 

 the English sparrow, starling, and gypsy 

 moth. The principal problem involved is 

 why a species does not occur wherever con- 

 ditions are suitable. 



The areas occupied by different species 

 may be small or large. Certain birds and 

 bats, because of their remarkable powers of 

 locomotion, are able to inhabit almost every 

 large land area. Other species of animals 

 may be very much restricted. Islands are 

 especially noteworthy because of the species 

 that occur there and nowhere else. Dar- 

 win's descriptions of the animals he found 

 on the Galapagos Islands read like fairy 

 tales. In many cases, the ranges of different 

 species overlap, as shown in Fig. 454, but 

 the range of each species, or genus, is 

 rather definite. The size of the range is gen- 

 erally greater for a family than for a genus, 

 and greater for a genus than for a species; 

 but great differences exist in the size of the 

 range of nearly related species. For example, 

 the genus Camponotus (the carpenter ants) 

 is found everywhere in North America (also 

 on other continents) from the tops of the 

 highest mountains to the lowest desert 

 basins, from the Atlantic to the Pacific, and 

 from the tundras of the north polar region 

 to the tropical region along the Gulf; while 

 another genus of ants, Sympheidole, has 



Figure 454. Geographic distribution of 6 different species of animals whose ranges are assumed 

 to overlap, as indicated by the different types of lines. (After Walter.) 



