TUE STAGE SETTING 



1«» 



\y ritjlil /'it re, 



The ell'ect of differences in environiiient upon the same s[)e(ies of tree (Piiins 

 ponderosa). Here molar agencies are largely responsible for Ihi; changed ai)pear- 

 ance of the tree. 



areas, but it also fells much timber, breaks off branches, and destroys 

 crops. Winds may either help or hinder in the migration of insects. 

 The cotton boll weevil travels north more rapidly in the years when 

 more wind is recorded. Winds blow birds and insects out to sea, 

 thus destroying them, or they may land them in a new location where 

 they may multiply rapidly. Currents of air as well as water currents 

 distribute plants and animals. Many animal forms react to wind 

 and water currents. Fish head upstream, an adaptation favorable to 

 food-getting. The swiftness of the current not only determines tiic 

 distribution of fishes, but also of other forms, such as caddis fly 

 larvae and "water pennies." 



Biotic Factors 



These are factors arising from the presence of other li^•ing organ- 

 isms. One is concerned when studying ecology not only with the 

 environment of living things but also with how li\ing things react 

 on others in their immediate environment. There is competition 

 not only between plants and animals, but al.so between plants of the 



