BIOME AND BIOME-TYPE IN WORLD DISTRIBUTION 



597 



with endemic faunas, some of which are so 

 sharply defined as to cut across almost all 

 taxonomic groups, is a phenomenon re- 

 quiring isolation through great periods of 

 geological time. The same principle apphes 

 to the development of floral regions, but 

 with some radical differences primarily 

 traceable to different geological ages of 

 origin, and to quite radically different 

 modes of dispersal. The emigrations of 

 biotic elements and the shifts of whole bio- 

 tas are known primarily from paleontologi- 

 cal evidence. Theoretically and quite ob- 

 viously, these movements imply a basis of 

 paleoecology. Paleoecology, however, like 

 paleogeography, is of necessity based on 

 fragmentary evidence, sometimes even more 

 fragmentary than are the animal and plant 

 remains on which paleontology is based. 



A large hterature, unequal in merit, of 

 animal and plant geography, differing 

 sometimes in point of view, and with the 

 historical and the ecological factors often 

 not distinguished, affords direct evidence 

 as to the outUnes of the geological history 

 of land life. An introduction to this history, 

 and to the paleogeographic controversy as 

 to the history of connections between the 

 continents envisaged by many as essential 

 to explain the patterns of the present dis- 

 tribution of land animals, may be obtained 

 from "Climate and Evolution" by W. D. 

 Matthew (1915). For the more general 

 aspects of animal geography it is still 

 necessary to refer to the introduction to 

 Wallace's The Geographical Distribution of 

 Animals (1876) and to his more popularly 

 written Island Life (1880). Plant geog- 



raphy is provided with a recent summary 

 by Cain (1944). 



The historical animal geography of the 

 sea, because of the essential continuity of 

 its waters, is even more inextricably inter- 

 woven with ecological factors than is that 

 of the land fauna. Nevertheless, major iso- 

 lation effects have left discernible marks 

 on the distribution of marine life. Ekman's 

 excellent summary (1935), for example, 

 gives an easily accessible account of the 

 results of the marine connection of the 

 Pacific and Atlantic across Central America. 

 This lasted through much of Tertiary time, 

 and has produced a remarkable pairing 

 of species within genera ("geminate spe- 

 cies"), many Caribbean species having a 

 Pacific coast counterpart. The major geo- 

 graphic barrier to the benthos has been the 

 open Pacific between the South Sea Is- 

 lands and the American coast, and the in- 

 fluence of the East Indian centers of distri- 

 bution extends eastward through the Pa- 

 cific Islands to this barrier, and westward 

 via the ancient sea beaches of Tethys 

 through the Mediterranean to the West 

 Indies. Excellent documentation of this 

 history is supplied by the marine fossils of 

 the Mediterranean region. 



Other major biotic provinces of the 

 ocean appear to be quite sharply defined by 

 temperature zones, to which whole faunas 

 have become adjusted in geological time, 

 and by the effect on fertility of upwelling 

 waters on the western coasts of the conti- 

 nents. Minor provinces as well as major 

 ones tend to be tied together by wide-rang- 

 ing pelagic forms (Ekman, 1935). 



