346 



Illinois Natural History Survey Bulletin 



Vol. 28, Art. 2 



Other hypotheses by Thompson & Hunt 

 sutiijest that in certain species the entire 

 population is confined to a certain stream 

 size of very narrow limits. In the 1959 

 collections, none of the species (among 

 those taken in sufficient numbers to sup- 

 port such a conclusion) was confined to 

 a certain stream size in more than two or 

 three of the five county drainages con- 

 sidered here. This lack of restricted dis- 

 tribution was due probably to the lack of 

 restricted habitats ; in streams of the sizes 

 found in Champaign County, some habi- 

 tats that are characteristic of large streams 

 were found upstream and many habitats 

 that are characteristic of small streams 

 were found downstream. Even ecological 

 factors most closely related to stream size, 

 such as bottom materials and vegetation, 

 were not restricted to a degree that was 

 known to limit the distribution of any 

 species. 



In both 1928 and 1959, young and 

 adults of most species occurred abundantly 

 in the same areas. However, the young of 

 some of the suckers had their greatest fre- 

 quency of occurrence upstream. The fol- 

 lowing species (in addition to most of the 

 suckers, with their well-known upstream 

 movements to spawn in spring) showed 

 proportionately greater numbers of small 

 fish than large in the upstream areas: 



Canipostonut (inor/iali/rn 



Cy prill us carpio 



Hybognathus nitchalis 



Ictahtrits tuitfdis 



A nihlopliti's rupestris 



Le porn is macrochirus 



Micropterus dolomieui 



Microptents puncttdatus 



Conclusions on Relationships 



Information from the 1959 collections 

 reinforced the hypotheses of Thompson i5: 

 Hunt regarding the distribution of num- 

 ber of species and number of individuals 

 per unit area in relation to stream size, 

 and it agreed moderately well with their 

 theories regarding average size of fish and 

 distribution of weight per unit area. 

 Some of the other suggested relationships 

 between the fishes and stream size appear 

 less tenable, probably because of the 

 great variation in habitat currently found 

 in Champaign County streams. These re- 

 lationships generally follow the ecological 



succession of streams as illustrated by 

 Shelford ( 191 1 ) in his collections of fishes 

 from creeks in the Chicago region. Shel- 

 ford's work and the studies of Champaign 

 County fishes are based on the assumption 

 that similar fish communities occupy sim- 

 ilar ph\siographic stages in aging (base 

 leveling) of a stream. Thompson & Hunt 

 contributed several clear, practical expres- 

 sions and interpretations of stream suc- 

 cession, and their use of drainage area as 

 an expression of stream size can be con- 

 sidered a substantial contribution. The 

 1959 survey adds further to the knowledge 

 of succession in warm-water streams. It 

 provides data to substantiate many parts 

 of the concept of succession, but at the 

 same time offers an explanation for the 

 many examples of failure of fish distribu- 

 tion to fit the theoretical sequence of 

 stream succession. The major reason for 

 this failure is that base leveling does not 

 often produce a perfect geologic succes- 

 sion and a uniform progression of eco- 

 logical factors. 



DISTRIBUTION AND 

 POLLUTION 



Types of pollution have changed con- 

 siderably during the years spanned by the 

 three surveys of Champaign County fishes. 

 Organic pollution, which began even be- 

 fore the period of the backyard privy, has 

 existed to the present time with its mod- 

 ern scientific treatment of domestic 

 wastes. Sources of chemical pollution have 

 appeared ; some of these have disappeared 

 while others continue to threaten aquatic 

 life. Pollution becomes most severe in 

 areas of dense population and industrial 

 development ; thus, in Champaign Coun- 

 ty, it is most severe in the region of 

 Champaign-Urbana, which serves as the 

 focus of the present study. (The State of 

 Illinois Sanitary Water Board in 1951 

 defined pollution to include alteration of 

 the physical, chemical, and biological 

 properties of any waters to render them 

 harmful to fish or other aquatic organisms. 

 This definition, which would include the 

 effects of temperature change, sediments, 

 and abnormal chemical levels in effluents, 

 will be followed here.) 



At the time Forbes & Richardson made 

 their collections in the West Branch, 

 around 1899, untreated organic wastes 



