ANIMAL AGGREGATIONS 



413 



ment and to general prowess. Although 

 there is much active fighting, the combats 

 may be formalized, and in many species, 

 singing and other kinds of more passive 

 defense are common. As an example among 

 mammals, hordes of howling monkeys 

 maintain territories tliat they defend from 

 invasion by neighboring hordes by howUng 

 encounters, not by active fighting (Carpen- 

 ter, 1934). Development of substitutes for 

 actual combats conserves much energy and 

 prevents fatigue and inattention to the ap- 

 proach of predators. 



The territorial habit has a number of 

 hypothetical and, to a certain extent, even 

 probable values, among which may be 

 listed: (1) the more or less automatic or- 

 ganization of a local population into a sort 

 of well-spaced aggregation; (2) the pro- 

 motion of monogamy, which is often im- 

 portant in rearing helpless young; (3) 

 Limitation of the breeding population and 

 hence partial control of an increase in num- 

 bers beyond the carrying capacity of the 

 habitat; (4) the provision of a reserve of 

 unmated males and females, making pos- 

 sible the prompt replacement of a lost 

 mate in a breeding territory; (5) with 

 larger territories, the insurance of an ade- 

 quate supply of easily accessible food; (6) 

 a reduction in the rate of spread of para- 

 sites or disease; (7) close acquaintance 

 with the locahty, giving an advantage to the 

 territory holder in hiding from predators; 

 and finally, (8) for psychological reasons 

 that are not wholly known, there is an in- 

 creased vigor of defense by the occupant 

 and decreased aggressiveness by the in- 

 vader that make for social stabiUty. Some- 

 times, at least, these psychological factors 

 may be effective outside a delimited terri- 

 tory, but bear a recognizable relation to the 

 relative distance of the birds from their 

 territorial centers (Odum, 1941, 1942). 



TerritoriaUty also has evolutionary con- 

 notations (pp. 376 and 691). 



SOCIAL HIERARCHIES 



Territorial organization has close inter- 

 relations with the dominance-subordinance 

 hierarchies that develop in many small 

 groups of fishes, lizards, birds, and mam- 

 mals. A few green sunfish {Lepomis cyan- 

 ellus), for example, housed in a small 

 aquarium, soon organize themselves into a 

 dominance hierarchy as a result of a series 



of pair contacts. With larger space avail- 

 able, the males often take up territories, 

 especially as the breeding season ap- 

 proaches, and territorial establishment is 

 the easier if the habitat is already partially 

 subdivided into niches. When a liierarchy 

 passes over into a territorial organization, 

 the most subordinate fish is the last to ob- 

 tain a territory that it is able to defend and, 

 under many conditions, may not be able 

 to gain a place it can defend against all 

 comers (Greenberg, 1947). 



Development of knowledge of social 

 hierarchies illustrates some of the possibili- 

 ties of the intei'play between laboratory and 

 field studies in ecology. The modern devel- 

 opment of this subject is based on the 

 work of Schjelderup-Ebbe (1922), using 

 the common domestic fowl, and has been 

 much elaborated by, among others, Alice 

 and Iris associates with various laboratory 

 animals (Allee, 1938, 1945; Collias, 1944). 

 Eventually the laboratory findings were 

 tested in the field with frequent substan- 

 tiation and extension (e.g., Odum, 1941, 

 1942; Emlen and Lorenz, 1942; Carpenter, 

 1940, 1942; Jenkins, 1944). 



Many workers have summarized the 

 quahties that make for high social status 

 in groups of vertebrates. There is fairly 

 general agreement on the following fist: 



1. The stronger individual usually wins 

 its pair contracts, but there are frequent 

 exceptions because experience may be more 

 important than strength. On first meeting, 

 robust animals usually defeat those that are 

 ill. 



2. Mature animals usually dominate 

 those less mature; thus hens dominate 

 younger chickens, and dominance based on 

 age may continue long after the younger 

 animals are physically superior to their 

 elders. This rule has many exceptions, such 

 as are furnished by the fact that newly 

 matured canaries may dominate their fully 

 mature associates, and half-grown kittens 

 can keep old cats away from food. 



3. In many animal groups, such as fishes, 

 turtles, Uzards, and chimpanzees, the larger 

 animals usually have higher social rank 

 than their smaller associates. When the dif- 

 ference in size is not great (and sometimes 

 when it is), larger size does not insure 

 dominance. In White Leghorn hens the 

 "degree of determination of success" by 

 weight in a series of staged pair contacts 



