HABITAT PREFERENCE 31 



b) Seasonal changes. — These involve great changes in the physio- 

 logical states. Inactivity is the rule in winter; growth and activity in 

 the other seasons. The plants and animals of a locality do not all reach 

 sexual maturity or the greatest growth activity at the same time during 

 the growing season, but different species succeed each other as the season 

 advances (47). The food and enemies of a given species, which is present 

 in an animal community for a large part of the growing season, differ 

 from time to time. 



c) Weather changes. — These constitute fluctuations of conditions 

 calling forth special types of behavior. Some animals hide when the 

 wind begins to blow; some burrow into the ground on cool and cloudy 

 days. 



4. HABITAT PREFERENCES 



By virtue of being unlike or possessing different properties, the various 

 animal species require different conditions for the best adjustment 

 of their internal processes. For example, the carp lives in shallow and 

 muddy ponds and rivers, while the brook trout lives only in clear swift 

 streams. These two organisms are able to move about and find places 

 to which they are suited. The differences between them are clearly 

 indicated by the differences in the habitats which they prefer. 



By observation and by experimentation it has been shown that 

 animals select their habitats. By this we do not mean that the animal 

 reasons, but that selection results from regulatory behavior (p. 29). 

 The animal usually tries a number of situations as a result of random 

 movements, and stays in the set of conditions in which its physiological 

 processes are least interfered with. This process is called selection by 

 trial and error. If animals are placed in situations where a number of 

 conditions are equally available, they will almost always be found living 

 in or staying most of the time in one of the places. The only reason to 

 be assigned for this unequal or local distribution of the animals is that 

 they are not in physiological equilibrium in all the places. However, 

 some animals move about so much that it is with some difficulty that we 

 determine what their true habitats are. 



5. THE MOST IMPORTANT ACTIVITIES OF ANIMALS 



Animal activities are classified as feeding, breeding, hiding, sleeping, 

 etc. The strength of a chain is the strength of its weakest link; the 

 activity which determines the range of conditions under which a species 

 will be successful is the activity which takes place within the narrowest 

 limits. This is usually the breeding activity. The breeding instincts 



