CXXll FISHES OF ILLINOIS 



7. An analysis of our statistical data of ecological distri- 

 bution gives us many instances of a marked difference in pref- 

 erence of situation between nearly related species inhabiting 

 the same area, the effect of which is to break the force of a 

 competition between these species such as would prevail if they 

 were similarly distributed ecologically as well as geographically. 

 Closely related species are, as a consequence, often found much 

 less frequently associated in their common territory than either 

 is with widely unlike species of the same geographical range. 

 Exceptions to this rule are found where similar species occupy 

 adjacent areas of distribution which merely overlap by their 

 borders. 



8. A table of the broader ecological relations of 97 species 

 of Illinois fishes is made the basis of a few general statements, 

 but that subject as a whole is reserved for more detailed treat- 

 ment elsewhere. 



