Ylt I"R E. SHELFORD. 



Up to such a stage, Pond 14 must have become from the fir-t 

 more and more favorable to di\cr-itv of ecological types, and 

 accordingly possessed .it Midi .1 time its greatest number of species 

 of fish. When Pond 14 was at a stage comparable to the present 

 Pond i, tlif li-li community present and all the other organisms 

 "ciatcd \\ith it, so acied on their environment (just as they 

 are acting on their environment in Pond I at present) as to 

 make the habitat less favorable to the fish of the earlier pond 

 M.I-CS, and more and more favorable for those dependent upon 

 and tolerating deii^- vegetation, absence of bare bottom, and 

 lower oxygen content. As a result of this action of the biota on 

 its eii\ ironmeiit, tlu- fishes of ecological constitution similar to 

 that of the sunfishes and basses now present in Pond I, disap- 

 peared either by emigration or death. In the absence of these, 

 and in the more favorable conditions of competition and denser 

 vegetation, fish, such as the golden shiner, were able to find a 

 suitable habitat. At such a stage Pond 14 possessed a fish 

 community of the ecological character of that now found in 

 1 '< >nd $c. Here the i >ioneer element is reduced to a single species, 

 tin perch, which is very hardy i llankinson, '07). 



The same process continued and caused the disappearance of 

 the perch and like ecological types. A fish community ecologically 

 like that now in Pond 56 (Table I., column 3) then existed. The 

 absenceof the perch in 5/>and its presence in 5c may be explained, 

 judging from the general habits of the perch (Forbes and Rich- 

 ardson, '08), by the fact that neither pond appears to be favor- 

 able for perch and they have been able to move out of Pond 56, 

 but not out of Pond 5*;. An experimental comparison of tin- 

 behavior of perch from I'ond 5c and other perch habit. its would 

 have an important bearing on our problem. 



The fish community of Pond 56 is made up of the chub sucker 

 and the golden shiner, which are abundant, the spot ted bullhead. 

 the tadpole cat and the mud minnow. The spotted bullhe.nl 

 is the only one known to use bare bottom for nesting. There i- 

 only a little bare bottom in Pond 56. Tin- spotted bullhead 

 usually builds its nest under :o\er ( Kycleslivmer, '<>! ). 



When such a fish community occupied Pond 14, the biota 

 present gradually changed its <.\\n environmental conditions as 



