166 AGGREGATION, COMPETITION AND CYCLES 



ANIMAL COMPETITION 



Nature and Kinds. It is desirable to stress again the fact that 

 competition comprises a relatively small number of the countless coac- 

 tions among animals, and involves only those in which two or more 

 individuals seek to secure the same object, class of objects, or space. 

 Such competition is an evident coaction when it is direct, but it leads 

 to a wholly different type of interaction in the destruction of one of 

 the competitors. Competition between carnivores may often result 

 in a third coaction, namely, that of combat, also not infrequent 

 among herbivores when competing for mates. 



It is a well-known principle, emphasized by Darwin, that the 

 struggle for existence is keener the more nearly identical the de- 

 mands, and hence that competition is usually greatest between individ- 

 uals of the same species. However, the investigation of competition by 

 definite methods will doubtless reveal many exceptions. From its 

 nature, competition is determined in the main by life form and in 

 detail by behavior or life habit, though size or peculiarities of activity 

 may also play a large part. All the animals of a particular district 

 are in potential and often direct competition, though the smaller 

 carnivores may take what is left of the kill of the larger ones. In 

 nearly all cases the food preferences are overlapping near their mar- 

 gins, rather than identical at the center or first choice. 



All examples of supposed competition outside of controlled con- 

 ditions are open to some question. The black rat reached North 

 America about 1775 and became well established before the brown 

 or Norway rat arrived nearly a century later. Upon the arrival of 

 the Norway rat, the black rat began to decrease in numbers and 

 gradually disappeared until it has become rare. In the United States 

 and Canada it appears to have survived in some large buildings in 

 large cities because of its smaller size and has also survived in some 

 one or two remote sections of the country districts. Whether the 

 brown rat attacked and destroyed the black rat, or merely appropri- 

 ated all the nesting places and food, there is no doubt that competi- 

 tion was a factor. The large wolf was early reduced in numbers and 

 extirpated from many areas, and this was followed by a great in- 

 crease in coyotes. Apparently the wolf does not prey upon the coyote, 

 but competition probably involved suitable home sites and hunting 

 territory. 



Chapman (1931) is probably correct in referring to the limits of 

 population imposed in cultures of Drosophila and of Tribolium in 

 small spaces as due to competition, but has not presented the data 



