I02 ANIMAL AGGREGATIONS 



the multiplicity of eyes in the group, or can attack or defend them- 

 selves more effectively by the multiphcity of claws or of teeth. Most 

 of the experimental approaches to this subject have been similarly 

 limited. 



The impressive array of facts, accumulated by observation and 

 experiment, which indicates that loosely integrated aggregations 

 have harmful effects will be summarized in the present chapter so far 

 as the rate of growth is concerned. The next following chapters will 

 give other facts concerning harmful effects upon the rate of reproduc- 

 tion and upon longevity. 



Dermestes beetles feeding on a limited amount of carrion exhaust 

 their food sooner when more than one is present. This is also true of 

 leaf-eating caterpillars, sap-sucking aphids, or tissue-filling parasites. 

 It is only with well integrated groups of predators catching lively 

 creatures as food that the feeding aggregation becomes of value. A 

 school of young minnows is much more likely to catch a given Daph- 

 nia than is a single individual, and each member of the group is more 

 likely to feed upon the Daphnia stirred up than if he swam alone. 

 This type of group advantage increases with group organization, as 

 shown by the grasshopper drives of African storks. 



The same number of relatively defenseless individuals are more 

 easily gobbled down by an enemy when aggregated than when 

 scattered. One of the insect sleeping-clubs described by the Raus 

 would provide a substantial breakfast for the proverbial early bird, 

 and a hungry centipede would have easy picking in a group of aesti- 

 vating land isopods. In locust control measures, men take advantage 

 of the tendency of locusts to collect in dense overnight aggregations. 



There is a general ecological assumption that the accumulation of 

 the waste products of a given species in their habitat tends, with 

 most animals, to limit the time of their occupancy, at the same time 

 preparing the way for another species to come in. This is sometimes 

 considered one of the major biological factors causing ecological suc- 

 cession, a process well illustrated by the sequence of fauna in a pro- 

 tozoan infusion. 



PLANT TOXINS 



It has long been thought that one of the major causes of such suc- 

 cession among plants is the accumulation of more or less specifically 



