102 ECOLOGY Part II 



reaches its highest development in the insects — termites, wasps, bees, and ants. 

 Their organization has a complexity comparable to that attained by vertebrates 

 but of an entirely dift'erent character. It is a strictly defined and inflexible 

 division of labor in which the various needs of the community are attended to 

 by individuals whose structures and functions mark them, with rare exceptions, 

 inescapably as members of particular castes with special work to do. Among 

 bees such specialists are the queen, the workers always females, and the male 

 drones (Chap. 30). 



Organization of Vertebrate Groups. This is based upon three general prin- 

 ciples: the holding of territory, social hierarchies in which dominance and 

 power exist in a graded order from highest to lowest, and leadership-follower- 

 ship. 



Territorial Rights. Birds take possession of a parcel of good habitat, 

 sing loudly from a prominent perch and defend it against trespass, driving off 

 members of their own or other species. American song sparrows sing special 

 proclamations of their ownership of territory and defend the mating and nest- 

 ing grounds by fighting. The willow wrens that migrate into England every 

 spring have a regular system of dividing up their usual territory into roughly 

 equal parts, and the males fight among themselves for their respective rights. 



Social Hierarchies. Groups in which one individual dominates all the 

 others have been observed in birds, rats, cats, dogs, apes, and human groups. 

 A dominance known as peck right, observed in small flocks of domestic hens, 

 has been investigated mainly by Alice and his co-workers. In these flocks one 

 particular hen pecks any other hen without being pecked in return, that is, she 

 is dominant with peck right over the whole flock. Below her a small group of 

 hens peck those of lower social levels than themselves without receiving return 

 pecks. Below them again, similar levels occur down to the lowest level, the 

 hen which is pecked by all others yet does not peck back. During observations 

 each hen was tagged for identification by colored leg bands and other mark- 

 ings. Observations were taken with great care and repeated many times. The 

 dominance of a hen was generally first established by fights. Ailing hens and 

 those newly installed were in the low levels, and regular members which were 

 taken from the flock lost their positions by being absent. Similar social hier- 

 archies or grades of power exist among flocks of male fowls. Flocks of white- 

 throat sparrows represent social hierarchies similar to those of domestic fowls 

 but are less fixed. 



Leadership and Followership. The leader of a group may or may not be 

 its dominant member. The leader is the individual that wiU not desert the 

 group in any emergency and that its members will follow. It is the experienced 

 "knowing" animal, not necessarily the largest or fastest. In herds of Scottish 

 red deer a stag is ordinarily the dominant member, but in crises the males 

 leave the group and a female assumes leadership. With real leadership the 



