VICTOR E. SHI I I ' iRD. 



TABLE IV. 



U.IT IKS <>v i in-: BASIS OF THE I)IMKII:I IK.N ,,i FISH BEFORI-: mi. \)H< <.IIT. 



i TABLI-: I. 



2. Floods. Abbott ('70) collected the fishes from source to 

 mouth of a small stream. After a flood he found none of the 

 ^une fish but species belonging to larger streams. Unfortunately, 

 he does not state that he again studied the stream from source 

 to mouth, and accordingly leaves the question of a general 

 upstream migration unsettled. 1 



2. Succession. 



Ecologists are frequently asked what is meant by succession 

 and what is the significance of succession. In answering the 

 first part of the question there has often been a confusion result- 

 ing from a lack of distinction bet \veen the different uses of the 

 term succession. It is used in three distinct senses. We speak of 

 (i) ecological succession, (2) seasonal succession, and (3) geological 

 .succession (Adams, '09). 



I. Geological succession is primarily succession of species 

 throughout a period or periods of geological time. It is due 



>As evidence of upstream migration of mollusca, the following seems to be 



important. Frequent examination of a section of the North Branch of the Chicago 



Rivi-r at Kdgelirook, between 1903 and 1907, shoued that l'l< /<;-... . ->-,i ,-i, -rulum and 



(.'iinif'i-luniti occur in this stream, rit-nrucrra \\-a-; not I'ound during tliis period 



MIL; .\o\ciiiln-i. 1907) above a certain point. ('inn/<t'li>nn: \\.ts found only 



-]iaiini;]>- almvi- this point. Tin- si>ring of 1908 was one of heavy rainfall and the 



in- were in tloo.l iiom April to June. On July f) the snail Pli-itnm'ni was lotind 



in nu in In i - one t"ui th .i a mile t'urtln-t up-trt-am, than formerly. < \iip,-lomu had 



Kone nearly as far. The sea-mi from November to Apiil was not dilien-nt IKUII 



LSOns anil then- i- no n-a^'Ui to a nine that the initiation ln-i;an ln-lon- the 



spring floods. Il tlii^ i- tun- tin -nails could make their way towaid the head \\atei - 



at the Kite ol at l-a-t a mile pel year, il they were intioiliiced into a lai.m- -tn-ain. 



'I hi- tnii-t lie a te-p.m-e to liotli \\.iti i pii sure and rurrent. The small \alue o! 



SUCll -ill^le oli-el \atioll- i- lero^lli/ed, 1)111 they ale ple-e|lted hi'le I.e. .lll-e the 



op|ioi tunit\- to in -111 h data i- -mall. 



