CXV1 FISHES OF ILLINOIS 



mutually well-adjusted species, each community so adapted to its 

 environment that members of adjacent communities can not success- 

 fully intrude upon its territory. 



7 . An analysis of our statistical data of ecological distribution 

 gives us many instances of a marked difference in preference 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 distrib- 

 uted 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 treatment else- 

 where. 



