I40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



enemies " in other parts of the world, nevertheless in America for 

 instance, a large number of predators, including hawks, owls, crows, 

 jays, skunks, weasels, and foxes eagerly welcomed the new food. 



More Theoretical Aspects of Indiscriminancy by Predators 



The experience we have when we place inviting food supplies in 

 abundance before the birds indicates what must happen in nature 

 under similar circumstances. If we imagine a world of food available 

 to predators we must realize that the elements composing it will be 

 utilized very much in proportion to their abundance. This is only 

 what would be expected if there is or ever was such a thing as the 

 oft-mentioned " balance of nature." To preserve a balance, natural 

 checks must be in proportion to population. If they were not appar- 

 ently so, no balance would have been observed and the term balance 

 of nature would never have been invented. 



Distribution of predation in proportion to population also is what 

 we should expect if the theory of adaptive radiation, or the occupation 

 of every possible ecologic niche is correct. Given the world of prey 

 to exploit it is inevitable that predation will extend in all possible 

 directions. No source of food will be left untouched if by any possi- 

 bility it can be drawn upon. Under so searching a campaign for food 

 each inevitably will be utilized in proportion to its abundance. 



That this principle actually is at work is well shown by a series ^ of 

 studies by Harry B. Weiss which indicate that regardless of locality 

 there is a more or less fixed set of ratios between types of food habits 

 of insects. Thus from several widely separated areas the insect popu- 

 lation groups into from 45 to 55 per cent of phytophagous species, 

 from 15 to 27 per cent of saprophagous, from 14 to 19 per cent 

 harpactophagous, from 10 to 12 per cent parasitic, and from i to 

 4 per cent of species of miscellaneous feeding habits. 



^ Insect food habits and vegetation. Ohio Juurn. Sci., vol. _'4, no. 2, pp. 100- 

 106, Mar., 1924. 



Ratios between the food liabits of insects. Ent. News., vol. 35, no. 10, pp. 

 362-364, Dec, 1924. 



Notes on the ratios of insect food Iiabits. Proc. Biol. Soc. Wasli., vol. 38. 

 pp. 1-4, Jan., 1925. 



Insect food habit ratios on Qnelpart Island. Psyclie, vol. 3-', no. 2, pp. 92-94, 

 Apr., 1925. 



The similarity of insect food habit types on the Atlantic and Western Arctic 

 Coasts of America. Amer. Nat., vol. 60, no. i, pp. 102-104, Jan.-Feb., 1926. 



