COMMUNITY ORGANIZATION: METABOLISM 



517 



and have renamed it "food niche" to diflFer- 

 entiate it from the "niche" of other authors 

 where the term was used as the home or a 

 part of the physical environment. In this 

 latter sense, the term "habitat niche" has 

 been defined previously (Chap. 26). 



A puzzling problem in the study of food 

 webs is the qualitative relationship of sev- 

 eral adjacent meshes. One can observe an 

 animal feeding, or examine its stomach con- 

 tents, or its feces, and may be able to state 

 that this animal was eating, or had eaten, 

 certain foods. The question arises as to the 

 ecologic interpretation of these data, in 

 terms of the food web. This basic question 

 has fathered a long controversy, which is 

 still with us, as to the relative importance, 

 frequency, or significance of general and 

 specific food habits. 



A clearly drawn diflFerence of opinion on 

 this question developed in the late 1920's. 

 Elton (1927, p. 47) stated that "it is one 

 of the commonest things in nature to find 

 a herbivorous animal which is attached 

 solely to one plant for food, or for breeding 

 purposes, or for both." Shelford (1929, p. 

 131) stated that few phytophagous animals 

 "are restricted to one food plant." 



Earlier, many students had reported by 

 observation, stomach examination, and feces 

 analvsis, on the food of animals (Forbes, 

 1880, 1882). An analysis of the stomach 

 contents of some 80,000 birds led McAtee 

 (1932) to stress the availability factor as 

 determining the general food habits of ani- 

 mals, especially of birds. McAtee found that 

 his data showed birds to have indiscrimi- 

 nate feeding habits, eating plants and ani- 

 mals in proportion to their relative frequen- 

 cv. Dunn (1935) felt that McAtee's data 

 could be interpreted diflFerently, that birds 

 were not so indiscriminate in their choice 

 of foods as McAtee believed. Hamilton 

 (1940a, 1940b) joined the discussion by 

 finding that McAtee's general view on in- 

 discriminate feeding could be applied to 

 the summer food of the robin and to the 

 food of larval newts (Triturus viridescens) . 

 In other instances both sides of the 

 argument could be strengthened by material 

 presented in the same investi station. Wol- 

 cott (1937), in a thorough study of 

 meadow and pasture in northern New York, 

 found that the robin, twice as abundant as 

 all other birds in the grasslands studied, ate 

 every insect of reasonable size that was 



available in its habitat. In the same study, 

 Wolcott found that cows did not eat such 

 pasture plants as moss, sorrell, buttercup, 

 Canada thistle, everlasting, lichens, iron- 

 weed, bluets, yarrow, St. Johnswort, and 

 moth mullein. 



No categorical solution of this problem 

 may be given, since we know only a few 

 feeding habits with reference to the total 

 number of described species. We are cer- 

 tainly a long way from this knowledge. 

 What an animal eats in its food web is not 

 necessarily the same food that it will accept 

 in an unnatural situation. Any unbalance of 

 the web may impose hunger on the 

 occupants of a mesh, and the satisfaction 

 of growing physiological demands will be 

 met often by eating distasteful, even harm- 

 ful, substances. For example, no one would 

 assume that leather was the diet of man- 

 kind, but an uncritical observer might be- 

 lieve this were so were he to see starving 

 snowbound men boiling their belts and 

 moccasins in a last attempt to survive. To a 

 less absurd extent, what animals eat, when 

 confined in a laboratory cage, must be con- 

 sidered with great care before the informa- 

 tion can be utilized intelligently. Domesti- 

 cated animals eat what they are allowed to 

 have. Another striking illustration is found 

 in caterpillars of the corn earworm (Heli- 

 othis armi^era) . These normally phyto- 

 phagous larvae turn cannibalistic when 

 they are confined together without food 

 (Essig. 1942, p. 427). The Question, in so 

 far as the community is concerned, is not 

 what an animal will eat, but what does it 

 normally eat as a mesh of the food web. 



In the second place, what an individual 

 eats under natural circumstances may or 

 may not be its chief, or only, source of food. 

 Observation or experimentation upon an in- 

 dividual or a group can seldom settle the 

 question rapidly, since the organism or 

 group of organisms forms only a part of a 

 species population (p. 374). Animals of 

 the same species may feed on different 

 meshes at different parts of their life cycle 

 (vide stipra). They may feed upon different 

 meshes in the same community as a regular 

 feature of their daily life (many animals 

 feed normally upon more than one species 

 of food), upon different meshes of the same 

 community at different seasons of the year, 

 or upon different meshes in different com- 

 munities within their geographic range 



