BIOGEOGRAPHY 



smaller proportion of endemics is not surprising. Lest thirty-seven species 

 of birds for a small group of islands sound like a large number, the num- 

 ber of species on a restricted continental area may be given for compari- 

 son. The 1944 checklist of birds on the campus of the University of 

 California at Berkeley lists 105 regular residents or seasonal migrants and 

 forty species which have been recorded as occasional visitors. 



The Amphibia and terrestrial mammals, though not the bats, are usually 

 entirely absent from oceanic islands. When they have been introduced by 

 man, they frequently have multiplied so greatly as to become a nuisance. 

 The west coast toad, Biifo mariniis, for example, was introduced into 

 Hawaii in the hope that it would aid in the control of insects; but the 

 toads themselves have now become a nuisance in the islands. Yet these 

 groups are unable to cross large water barriers (or salt water barriers in 

 the case of the Amphibia, which are quickly killed by salt water). But 

 a barrier across which a mouse, for example, could not swim, might be 

 easily flown by a bat. Had all species been created in the places where 

 they now exist, then Amphibia and terrestrial mammals should be as 

 frequent on oceanic islands as on comparable continental areas. Certainly 

 terrestrial mammals should have been created on these islands as fre- 

 quently as were bats. But bats are the very mammals which should reach 

 the islands most readily if all mammals arose first on the continental land 

 masses and then subsequently invaded such territories as they could. 



Finally, the inhabitants of the several islands of an archipelago are 

 commonly specifically distinct, yet plainly closely related; all of them, 

 however, show a less close relationship to the inhabitants of the nearest 

 mainland. Thus, when the Beagle visited the Galapagos Archipelago, lo- 

 cated between 500 and 600 miles west of South America, Darwin felt that 

 he was stepping upon American soil because of the obvious similarity of 

 the plants and animals of these islands to those of the South American 

 continent. The Galapagos Islands include 332 species of flowering plants. 

 Of these, 172 species, more than half of the total, are endemic, and many 

 species are restricted to one or a few islands in the archipelago. Yet all 

 of these plants show close relationship to South American plants. But the 

 climate and the geological character of the islands are utterly different 

 from those of South America, hence the relationship of their plants cannot 

 be understood on the basis of creation of similar plants for similar lands, 

 but only on the basis of migration of plants from the continent to the 

 outlying islands, with subsequent differentiation. The Bermuda Islands 

 are located about 700 miles off of the coast of North Carolina, and their in- 

 habitants are all North American in character. Many terrestrial vertebrates 

 have been successfully introduced into the islands, but only one, a lizard, 

 is native there. It belongs to a North American genus, but the species is 

 endemic. Land birds are represented by many species, but none are en- 

 demic, for Bermuda is on one of the major migration routes for North 

 American birds; hence it is not at all isolated from the viewpoint of the 

 birds. Bats are also common to the mainland and the islands because these 

 flying mammals can readily cross the water barrier. But the land molluscs 



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