March, 1963 



Larimore & Smith: Fishes of Champaign County 



337 



Example : 



10 collections of chubs _ 



20 collections over 30% sand 



50 per cent of collections over this 

 bottom contained chubs 



Thus, in the examples above, five creek 

 chubs vv^ere taken per collection over 30 

 per cent sand bottom material, and creek 

 chubs were present in 50 per cent of such 

 collections. 



Ecological associations were determined 

 for collections from each drainage system 

 and then for the entire county. 



The association figures revealed ( 1 ) 

 ecological factors that comprised the gen- 

 eral habitat of each species (used in assign- 

 ing species to stream habitats in the pre- 

 ceding section) ; (2) inconsistencies that 

 appeared when a species was related to a 

 specific ecological factor in one stream 

 system and not in another; and (3) the 

 absence of any single factor that deter- 

 mined the distribution or abundance of 

 most species. 



Such ecological associations may be of 

 definite value in defining the general habi- 

 tat of a species but are quite misleading 

 in determining its environmental require- 

 ments, for the influences of each environ- 

 mental factor in a natural habitat cannot 

 be separately evaluated. We cannot be 

 sure just which factor or factors in a 

 habitat have a controlling influence on 

 a species. For example, gizzard shad 

 showed a high degree of association with 

 deep, quiet pools. However, they may 

 have been responding not to depth or to 

 low water velocity but to the soft sands 

 and silts usually found in such pools. 

 Too, a species might have been closely 

 associated with a specific factor that did 

 not comprise a noticeable part of the habi- 

 tat. 



A few species were closely restricted to 

 rather specialized habitats. The restric- 

 tions, while quite obvious during field 

 collecting, were not always shown by our 

 calculations. Some of the most notable 

 examples were Amrnocrypta pellucida, 

 which occurred only in clear water flow- 

 ing over clean sand ; Esox americanus, 

 which reached its greatest abundance in 

 quiet, silt-bottomed pools choked with 

 vegetation; Noturus flavus, which seemed 



to prefer deep riffles or shallow pools 

 with moderate current and scattered rub- 

 ble and flat rocks; and Aphredoderus say- 

 anus, which was invariably in mud-bot- 

 tomed pools of streams with little current. 

 However, in general, most fishes showed 

 a remarkable plasticity in their environ- 

 mental tolerance. 



Species Associated With 

 Other Species 



Associations between species can be 

 determined ( 1 ) through examining which 

 species are mutually associated with a set 

 of ecological factors and (2) through ex- 

 amining the mutual occurrence and abun- 

 dance of two or more species. The degree 

 of association between pairs of several 

 kinds of common Champaign County fishes 

 was determined by calculating the coef- 

 ficient of correlation (r) between their 

 numbers in 100 square yards of stream. 

 Coefficients were determined for the col- 

 lections from each drainage system, as 

 well as for the entire county. Several 

 definite and sometimes surprising associa- 

 tions were evident. 



Notropis dorsalis — Ericymba buc- 

 cota. — Champaign County is on the edge 

 of the range of each of these species, No- 

 tropis dorsalis becoming more abundant 

 westward and Ericymba buccata becoming 

 more abundant eastward. Because of the 

 east-west separation in distribution, these 

 tw^o species usually do not occur abun- 

 dantly in the same drainage system. They 

 have been considered ecological equiva- 

 lents, and competition between the two 

 has been implied. Trautman (1957:376) 

 noted the shrinking in size of the Ohio 

 range of A^ dorsalis and the invasion and 

 great increase in numbers of E. buccata in 

 a territory formerly occupied by dorsalis. 

 However, in our Sangamon River collec- 

 tions, where both species were abundant, 

 they occurred together in a highly signifi- 

 cant degree (P less than 0.01) of associ- 

 ation, table 11. This situation indicates 

 their preference for similar habitats and 

 disputes the idea that there is strong 

 competition between the two. A^. dorsalis, 

 although occurring in two other Cham- 

 paign County drainages (Kaskaskia and 

 Middle Fork), was abundant only in the 

 Sangamon, so that further comparisons 

 could not be made. 



