8^4 >-,BW 



FIG. 12-4 Peck-dominance between the lowest four birds in a 

 flock of seven common pigeons. All four birds were dominated 

 by the three other birds of the flock. The ratios show the 

 proportion of times each bird was successful in its encounters 

 with other individuals (Masure and Allee 1934). 



golden-crowned sparrow (Tompkins 1933) and may 

 likely be found in many other species. 



There have been few studies of social despotism 

 as an interspecific phenomenon (Neuman 1956). 

 The range of aggressiveness between individuals 

 within any species is so wide that strong individ- 

 uals of one species may be despotic over weak indi- 

 viduals of another even though the majority of 

 individuals in the first species are submissive. How- 

 ever, the sharp-tailed grouse is usually dominant 

 over the ring-necked pheasant, and the latter is usu- 

 ally dominant over the prairie chicken (Sharp 1957). 

 The manner in which different species fit into a social 

 hierarchy may be the key to structure and organiza- 

 tion of communities. 



tact an individual has with each member of the group, 

 Figure 12-4 shows bird BR successfully subdued GW 

 in 21 encounters but was subdued by GW in 4 en- 

 counters. Thus, an individual can occupy any position 

 in the hierarchy as long as he is able to maintain that 

 position against all challengers. The individual who 

 loses a challenge from below is without position, and 

 can gain a position only by successful challenge. The 

 individual who has successfully challenged a higher 

 position from a lower moves up to the higher, leav- 

 ing the lower position open — who shall fill the va- 

 cated position is determined by combat among those 

 eligible to try for it, among whom is the former 

 holder of the higher position. Plainly the positions in 

 the hierarchy are fixed in order, but occupancy of 

 those positions is fluid. A more fluid form of social 

 aggressiveness is supersedence, in which a success- 

 fully challenging individual usurps the position of an- 

 other individual momentarily possessing special ad- 

 vantages in the presence of food or some other thing. 

 This type of relation has been described for the 



Territory and home range 



The establishment of territories, especially dur- 

 ing the breeding season, is another expression of 

 despotism, but a special one. A territory is any area 

 defended against intruders. It may be the entire 

 home range over which the animal is active, or only 

 a small portion around the nest. Although many ani- 

 mals tend to be gregarious during the non-breeding 

 seasons, they frequently take up isolated positions 

 and become intolerant of the close presence of others 

 when undertaking reproduction. A home range is 

 that area regularly traversed by an individual in 

 search of food and mates, and caring for young. 



The establishment of territories is best developed 

 in birds (Hinde 1956), but also occurs in some other 

 vertebrates (Carpenter 1958), possibly including 

 some amphibians (Sexton 1960), and certain inver- 

 tebrates (wood ant, Elton 1932; dragonflies, Jacobs 

 1955). There is increasing evidence that most adult 

 animals, except for small aquatic species, establish 



Mockingbird 



Robin 9 



Ground >- Chipping 



dove sparrow 



Towhee — >White-1hroa1ed-« — Blue jay- 

 sparrow 



Myrtle- 

 warbler 



•Tufted 

 titnnouse 



FIG, 12-5 A social hierarchy between species of birds visiting 

 feeding station during the winter (Dennis 1950). 



1 84 Ecological processes and dynamics 



