TERRITORY 167 



on the mechanism of competition and biotic control, as they have not 

 yet been worked out. He called attention to the work of Pemberton 

 and Willard (1918, a and 1918, b), relative to a number of insect 

 parasites of the fruitfly introduced into the Hawaiian Islands. A 

 species of Opius was most effective, as it parasitized a large percentage 

 of the host; a species of Dichasraa was less so, but when both placed 

 eggs in a host larva the less effective Dichasma overcame the Opius 

 and survived. The conclusion was reached that the end result of the 

 operation of both parasites cannot exceed that of the more successful 

 one in any event. 



The equipment of competitors and the course of the process is 

 generally more evident in animals than in plants, but even in the 

 simpler examples too little is known about these as yet. However, 

 the effect or the outcome is frequently visible in subordination, sup- 

 pression, changes in habit, numbers, and so forth, and hence is felt in 

 varying degree in the composition of the community concerned. Fin- 

 ally, competition, like coaction in general, is sometimes important in 

 connection with food, at other times in connection with shelter, space, 

 or territory. Birds and mammals regularly exhibit a more or less 

 definite competition for mates, and in some form this occurs in the 

 large majority of animals; different herds or flocks in gregarious 

 species not infrequently compete for what may well be termed eco- 

 nomic position. 



Because of the difficulties attendant upon them, experimental stud- 

 ies of competition among larger land animals are practically unknown, 

 and until extensive exclusion and inclusion areas are available such 

 study will be difficult. Except for the recent inquiries into competi- 

 tion among insects and minute or microscopic aquatic invertebrates 

 (Allee, 1931, a), little experimental work has been done. 



TERRITORY 



Territory among Birds. Although but recently reinvestigated, the 

 concept of territory may be traced back for more than a century, but 

 with only occasional mention or consideration until the work of 

 Howard in England (1907, 1914, 1920; cf. Miller, 1931; Nice, 1933; 

 ]\Iichencr and JMichener, 1935). It has now become the favorite 

 theme of many ornithologists and has been taken up in other fields, 

 such as those of mammals and insects. In the most typical instances 

 among birds, it involves both direct and indirect coaction — combat, 

 song, and the choice of a mate all exemplifying the former. 



In spite of the late emergence of the idea, territory has been much 

 defined and redefined, and will doubtless experience much more re- 



