AND INTRODUCED FAUNAS 509 



Immense reduction has also taken place among aquatic species of 

 Diptera, Neuroptera, etc.^ 



Among naturalists of the last half century there has been a strong 

 belief that the introduced fauna and flora have been directly responsible 

 for the diminution of many, and the disappearance of some indigenous 

 animals and plants^. 



Thus Darwin in the Origin of Species says : 



From the extraordinary manner in which European productions have 

 recently spread over New Zealand, and have seized on places which must 

 have been previously occupied, we may believe, if all the animals and plants 

 of Great Britain were set free in New Zealand, that in the course of time 

 a multitude of British forms would become thoroughly naturalised there, 

 and would exterminate many of the natives. On the other hand, from what 

 we see now occurring in New Zealand, and from hardly a single inhabitant 

 of the southern hemisphere having become wild in any part of Europe, 

 we may doubt, if all the productions of New Zealand were set free in 

 Great Britain, whether any considerable number would be enabled to 

 seize on places now occupied by our native plants and animals. (The 

 italics are mine.) 



In examining this subject in connection with the introduced plant 

 life I think it will be shown that where man does not interfere with 

 the vegetation, the indigenous species can hold their own against the 

 imported forms. It is human intervention — either direct or indirect — 

 which completely alters the conditions. The same probably holds 

 good to some extent of the animal life, only the problem is more 

 difficult to follow out. 



Against the wholesale destruction of native animals wjhich has 

 taken place within the last half century, there have to be recorded 

 some cases of increase in the native fauna, apparently due to some 

 adaptation to the altered conditions. 



One of the most interesting cases is that of the bell-bird or mako- 

 mako (Anthornis melanura). This species has very largely disappeared 

 from the North Island, though I cannot learn from any one why it 



1 Mr Elsdon Best reports the disappearance of the grayling from the rivers on 

 the east coast of the North Island. Mr O'Regan also records the same for the rivers 

 on the west coast of the South Island. The latter says the popular belief is that the 

 trout have exterminated them, but he says these fish disappeared from the Inangahua 

 before trout were introduced, and he never heard of trout eating graylings. Though 

 formerly they were very common on the west coast, he does not now know of any 

 river where they may be found. 



Mr Miirray Campbell says the graylings come up the Cascade River in South 

 Westland in great shoals for the greater part of the year. (April, 1910.) 



* A. R. Wallace (in Darmnism, 3rd edition, p. 34) says: "A native fly is being 

 supplanted by the European house-fly." This kind of statement is the sort of terse 

 sentence which is apt to be quoted by writers, but it is both utterly indefinite 

 and quite misleading. No one can say what native fly is meant, nor is it certain 

 what European house-fly is referred. It may however be stated definitely that no 

 species of European fly has supplanted a native fly. 



