109 



cal succession or the succession of species, in that species may 

 be ignored, except as names are necessary, and only the habits 

 of the forms taken into consideration. 



II. Area studied. The area studied is at the head of Lake 

 Michigan w'here deposition of sand and the recession of the 

 lake have caused the formation of a series of long sloughs 

 parallel with the shore. Attention has been concentrated on 

 the first, fifth, seventh, and fourteenth of these, as counted 

 from the lake. The first is youngest. The fifth may be con- 

 sidered as at least five times as old as the first ; the seventh, 

 seven times as old; and the fourteenth, fourteen times as old. 



III. Succession. Slough XIV was once in the same stage 

 as slough I, and was then occupied by fish ecologically similar 

 to those in slough I at present. The vegetation grew and humus 

 accumulated, making it impossible for the ecological types of 

 slough I to continue, and these were succeeded by the ecologi- 

 cal types such as we now find in slough V; in due time these 

 gave way to the ecological types in slough VII, and these like- 

 wise to those of slough XIV. 



IV. Causes. This includes causes of succession of fish, and 

 the factors governing the distribution of fish with reference to 

 the disappearance of the food fishes (large mouthed black bass, 

 the green sunfish, and bluegill) from the sloughs as they grow 

 older or in other words their absence from all but slough I 

 when they colud have gotten into the other until recently, when 

 certain railroad culverts were discontinued and filled. 



1. Sise and depth. It is not due to their selecting the largest 

 and deepest bodies of water. These fishes are found in the 

 shallowest and smallest of the ponds (slough I). 



2. Chemistry of zmtcr. An analysis has shown difference 

 too slight to be recognized by fish. 



3. Food. The fish are not where the food supply is greatest. 



a. Food has been shown to be greatest in the sloughs which 

 do not contain these fish. 



b. The fish food consumed in each slough is about the 

 same, but the consumers in the older sloughs are different and 

 undesirable fishes. 



