ANIMAL AGGREGATIONS 



395 



GROUP SURVIVAL VALUES 



GENERAL CONCEPTS 



We can now introduce an important set 

 of ideas. Helpful interactions between or- 

 ganisms are evidence of the existence of 

 cooperation" (Allee, 1931), or at least of 

 proto-cooperation, even in the simplest 

 ecosystems; cooperation is accepted in this 

 sense by Clements and Shelf ord (1939). 

 Opposing, harmful tendencies may be 

 termed disoperation. The two sets of proc- 

 esses are in fundamental opposition. With 

 all lower forms of animal life, and often 

 with liigher ones, including man, such co- 

 operation or disoperation is wholly non- 

 conscious. The nonconscious character of 

 the efiFects and of their underlying causa- 

 tion is especially evident in poorly inte- 

 grated assemblages in which man is not 

 represented. This consideration does not 

 affect the fundamental nature of the re- 

 sulting disoperation or cooperation. It is 

 essential to remember that, possible neu- 

 tral efiFects aside, the survival values in 

 biotic ecosystems illustrate in simplest 

 terms the basic social antithesis between 

 beneficial (cooperative) and harmful (dis- 

 operative) relationships. 



Competition furnishes a special phase 

 both of cooperation and of disoperation. In 

 general, competition occurs when there is 

 a common demand on a limited supply. 

 Among other situations, this criterion ap- 

 plies to the competition of two males for 

 the same mate, of animals with similar food 

 habits for a limited food supply, of organ- 

 isms in general for limited ecological 

 niches. 



Competition frequently results in dis- 

 operation, although the two are not synony- 

 mous. Two protozoans in a drop culture 

 are often in competition for a hmited 

 amount of food. The competition may re- 

 sult in the stunting or death of both, or in 

 one surviving at the expense of the other. 



Cooperative competition also is known. 

 An example is furnished by the mass phys- 

 iology of the spermatozoa of sea urchins. 

 In nature, these spermatozoa, hke those of 



** Many aspects of proto-cooperation may be 

 called physiological facilitation, and the entire 

 spread between proto-cooperation and conscious 

 cooperative social life at the human level is 

 bridged by the addition of the concepts of bio- 

 social and psycho-social facilitation (p. 410; 

 Schneirla, 1946; Allee, 1949). 



many other marine organisms, are shed 

 into sea water where they may fertiUze the 

 eggs that have been similarly shed. In 

 making sperm suspensions for experimental 

 use, the male sea urchin is placed upside 

 down in a clean, dry watch glass. If 

 sexually "ripe," the spermatozoa How out 

 through the aboral genital pores in a vis- 

 cous mass. Sperm so collected is called 

 "dry" sperm, since it is undiluted with sea 

 water. The massed spermatozoa of many 

 animals, sea urchins among them, Hve 

 longer and retain their fertihzing power 

 longer than do those in diluted sperm 

 suspensions. When the spermatozoa are 

 shed in a mass into sea water, those near 

 the center are activated last, and such 

 sperm retain fertilizing power longer than 

 if all were activated at once on escaping 

 from the body. 



The physiological processes involved are 

 complex, but at least a part of the greater 

 longevity of the crowded sperm mass 

 comes from the fact that the individual 

 spermatozoa do not move when closely 

 packed together, as in "dry" sea urchin 

 sperm. Also, they are relaxed under these 

 crowded conditions, in contrast with being 

 highly active when diluted with sea water. 

 The relaxation is indicated by the fact that 

 the rate of respiration of the same number 

 of spermatozoa is much greater when the 

 sperm are less crowded. 



It seems reasonable to assume that in- 

 activity of densely packed spermatozoa re- 

 sults from the lack of free space. Over a 

 considerable range of dilution the specific 

 activity of a spermatozoon is directly re- 

 lated to the cube root of the volume of sea 

 water in which a given number of sperma- 

 tozoa are suspended. Under such condi- 

 tions the total initial activity is propor- 

 tional to the number of sperms present and 

 to the average amount of free space for 

 each. If the available space is much re- 

 stricted, the competition for it results in an 

 inhibition of movement, a lowering of the 

 rate of oxygen consumption, and a conser- 

 vation of essential diflFusible materials; and 

 all this is accompanied by a decided in- 

 crease in longevity. Competition here has 

 distinctly beneficial results for all the com- 

 petitors; it is cooperative, as contrasted 

 with being disoperative. This is an impor- 

 tant consideration for general ecology, the 

 more so since all the individuals in the 

 sperm mass benefit from the competition. 



