366 POLAR PROBLEMS 



MAMMALS INTRODUCED BY MAN 



No fresh-water fishes are found on any island south of 55° S., 

 and neither the Antarctic Continent nor any of the sub-Antarctic 

 islands have native land mammals. The nearest approach to a sub- 

 Antarctic insular mammal was the now extinct Falkland Island fox. 

 That the absence of mammals is due to isolation, rather than to 

 rigorous climate or scanty food supply, is shown by the fact that 

 rats, reindeer, and horses, introduced by man, thrive in a feral state 

 at South Georgia. The rats have existed at this island for well over 

 a century, feeding both upon vegetation, such as the tussock grass, 

 and upon burrowing petrels and their eggs. To some of the native 

 birds they have apparently become a serious menace. During their 

 three hundred or more generations of residence at the island, the rats, 

 according to Lonnberg,'^ have evolved a longer and denser coat of fur 

 than that characteristic of their northern progenitors. This, together 

 with certain other peculiarities, justifies, he believes, the description 

 of the South Georgia rat as a new subspecies,-^ although, with the 

 persistent yet groundless legend of Darwin's Porto Santo rabbit as 

 a warning, the matter needs further inquiry.^" In contrast with the 

 ability of the adaptable rat and the naturally acclimated reindeer to 

 survive, it has been found that neither rabbits nor sheep can endure 

 the heavy snowfall and the unvarying even though seldom extreme 

 cold of South Georgia. At Macquarie Island, on the contrary, both 

 rabbits and sheep can flourish. 



Richness of the Marine Life, and Its Basis 



Whatever wealth of land life is wanting in the region under dis- 

 cussion is amply compensated for by the profusion of life in the sea. 

 These austral waters make up the coldest marine area on the globe 

 according to Andersson,^^ with depth temperatures a degree or more 

 below the centigrade zero, and yet they are so teeming with life 

 that no expedition has failed to obtain many new species at all depths 

 in which collecting has been undertaken. 



The food substances of all forms of life in the ocean comprise car- 

 bonic acid, nitrites and nitrates of calcium and magnesium, etc., 

 phosphates, silica, and salts containing a few other elements. These 

 all exist in very small quantities, at most in the proportion of a few 



28Einar Lonnberg: Contributions to the Fauna of South Georgia, I: Taxonomic and Biological 

 Notes on Vertebrates, K. Svenksa Vetenskaps-Akad. Handl., Vol. 40, 1906, No. 5; reference on pp. 

 21-23. 



" R. C. Murphy: Faunal Conditions in South Georgia, Science, Vol. 46, 1917, pp. 112-113. 



^° G. S. Miller: Catalogue of the Mammals of Western Europe (Europe exclusive of Russia), 

 in the Collection of the British Museum, London, 1912, p. 494. 



'^ K. A. Andersson: Das hohere Tierleben im antarktischen Gebiete (Wissenschaftliche Ergeb- 

 nisse der Schwedischen Siidpolar-Expedition 1901-1903, herausg. von Otto Nordenskjold, Vol. S (Zo- 

 ologj% I), No. 2, pp. 1-58), Stockholm, 1905. 



