EVOLUTION OF INTERSPECIES INTEGRATION AND ECOSYSTEM 



725 



dant. The inability of introduced termites 

 to invade native habitats, particularly on 

 continents, is illustrated by other species 

 numerous enough to indicate a general rule 

 (Emerson, 1936). 



Secondly, let us consider a number of 

 examples of successful introduction or inva- 

 sion of ecologically simple habitats in 

 which man has not necessarily played a 

 modifying role. In these cases the intro- 

 duced form may become established in the 

 simple natural community, but be unable 

 to invade a more complex community. 

 Islands and island-like habitats do not have 

 such strong biotic barriers as may be pres- 

 ent on the edges of continental communi- 

 ties (see p. 661). 



the endemic land birds in the south Atlan- 

 tic island of Tristan da Cunha (Murphy, 

 1938). The introduced ant, Pheidole mega- 

 cephala, probably originally from central 

 Africa (Weber, 1943), has destroyed many 

 endemic species of ants in the Hawaiian 

 Islands, West Indies, and Madeira. 

 Wheeler, (1928b, p. 320) says that P. 

 megacephala does not invade virgin forest 

 in Austraha, but is successful in neighbor- 

 ing habitats modified by man. On Madeira, 

 P. megacephala was in turn replaced by 

 another introduced ant, Iridomyrmex hu- 

 milis. Still another ant, Plagiolepis longipes, 

 introduced into Reunion from Cochin 

 China, replaced endemic species of ants 

 (Wheeler, 1926). 



Fig. 262. Distribution of various species of Prorhinotermes, a genus of termites confined 

 to islands or shores of mainlands that may recently have been islands. The species are prob- 

 ably dispersed in floating logs. They survive in areas of low competition in the tropics, but 

 have been unable to survive in continental areas of high competition. 



For example, the mongoose was intro- 

 duced on Caribbean islands and South 

 American shores where it has reached pest 

 proportions, but it has been unable to in- 

 vade the continental rain forest a few miles 

 inland from the region of its marked suc- 

 cess along the shore. Likewise, the house 

 mouse may enter and survive natural con- 

 ditions if introduced on islands or into re- 

 gions of low competition such as occur in 

 coastal Chile." 



Endemic species on islands have often 

 succumbed to introduced forms. House rats 

 on Lord Howe Island off the coast of 

 Australia caused the extinction of endemic 

 birds (Hesse, Alice, and Schmidt, 1937). 

 Introduced hogs and rats eliminated all 



* Personal communication from W. H. Os- 

 good. 



The same species introduced on an is- 

 land may be successful, but fail to become 

 established on a continent. The biotic bar- 

 riers of continental communities may be 

 eflFective for millions of years. For example, 

 the termite genus Prorhinotermes (Fig. 

 262) is found on Ceylon, but is absent 

 from India; it is found on Madagascar, 

 Mauritius, and the Seychelles, but not in 

 Africa; in the Netherlands East Indies, but 

 not on the Malay peninsula; on Formosa, 

 but not on the China coast; on various 

 oceanic islands of the Pacific, but not in 

 Austraha; and in the West Indies and the 

 coastal mangrove swamps of Florida and 

 Central America (which may have been is- 

 lands in recent geological times), but is rare 

 or absent in the interior. Speciation in this 

 genus has occurred in the various isolated 



