BASES OF COACTION 107 



struction of the host. In the last case especially, it is worthy of note 

 that the effect is often exerted upon an individual by a simple com- 

 munity of countless members. 



Direct and immediate, though often partial, destruction is the gen- 

 eral basis of food coactions, best illustrated by the consumption of a 

 smaller coactee by a larger coactor. This interaction embraces such 

 widely different types as the eating of a diatom by an amoeba, the 

 engulfing of quantities of plankton by baleen whales, the capture 

 of a rabbit by a fox, or the eating of water lilies by a moose. Though 

 disparity in size is the rule for eaters, there are striking exceptions in 

 which inequality in size is compensated by number, as with a pack 

 of wolves, or by specialization, as in crotalid snakes and mustelids, 

 for example. 



Role in the Biotic Formation or Biome. The universal role of 

 coaction is to be seen in the integration of plant and animal relations 

 to constitute an organic complex, which is characterized by a certain 

 degree of dynamic balance in numbers and effects. Obviously, such a 

 balance undergoes a variety of rhythmic changes at different inter- 

 vals, and is never exactly the same after a period of stress (Chapter 5). 

 Nevertheless, it represents a general process of compensation and ad- 

 justment, in which extreme or permanent departures stand out more 

 or less vividly. Hence, it appears entirely desirable to speak of dis- 

 turbances of dynamic balance in the biome, which arise from an 

 emphasis of one or more of the normal coactions. While it is true 

 that at present little is known of the causes and detailed course of 

 such phenomena, this condition is certain to be remedied as the meth- 

 ods of quantitative ecology are focused upon them (cf. Forbes, 1880, a; 

 1883, a). 



The nature of the coactions involved in aggregation and competi- 

 tion is reserved for discussion in the next chapter, and it will suffice 

 to point out here certain examples of abnormal intensity which, 

 though not the rule, are far from infrequent. Naturally, the most 

 numerous and important of these have to do with man or his agents, 

 as a consequence of which fire, lumbering, or clearing removes the 

 climax or subclimax in whole or in part and initiates succession. As 

 an indirect human coaction, grazing is usually less thorough in its 

 effects, bringing about modification in various degrees but rarely to 

 the extent of complete destruction. Direct coactions between man and 

 animals also cause changes in abundance and composition by reason 

 of such activities as hunting, fishing, and poisoning, sometimes result- 

 ing in practical extermination over larger or smaller areas and the 

 setting up of a new sequence of effects (Fig. 20). Opposite to these 



