104 ANIMAL ECOLOGY 



processes and genetic phases or sequences throughout 

 this book. As Holmes (1905, p. 108) has well pointed 

 out, behavior consists of relatively fixed and relatively 

 changeable responses, with intergradations. There are 

 thus two avenues of approach which he sums up as 

 follows (p. 112) : "In the trial and error method the 

 random character of the movement impresses us 

 most; in the tropisms, the element of direct deter- 

 mination by the environment. Both of these factors 

 run through the behavior of all animals, but they are 

 mingled in various proportions in different forms. 

 In the lives of most, if not all animals both are essen- 

 tial elements in the adjustment of the organism to 

 its conditions of existence." And in regard to those 

 responses which do not change in form with experience, 

 he says (p. 106) : "The element of spontaneous 

 undirected activity is one of vast if not essential 

 importance in the life of nearly all animals. The 

 simpler animals profit by their varied experience, 

 although they may not learn, and thus secure some 

 of the advantages which it is generally considered 

 the special function of intelligence to confer." Thus 

 to the ecologist studying the sequences of changes 

 in the environment, and changes in the organism, it is 

 but natural and consistent for him to apply the same 

 methods to behavior, in order to facilitate their 

 mutual relations and aid in their interpretation. In 

 a study of the environment we also have the relatively 

 stable elements and the relatively rapidly changing 

 ones, and any adequate understanding of animals 

 must correlate these four variables : two relatively 



