136 VICTOR E. SHELFORD. 



general ph\ -iographic relations during .1 o m-idcr.il >le period of 

 time, there i- .1 succession of conditions due to the accumulation 

 of detritus just as there is a succession <it conditions in a si ; earn 

 due to phx sjographic changes. 



Since the channel^ of c< >mmtmicali< m between the different 

 ponds have been open until recently, the present arrangement 

 of the species of tish is \ ery probably a helnreior adjustment to the 

 changed and changing conditions just so far as barriers have 

 permitted. 



\\ see from the arrangement and mode of origin of the ponds 

 that our oldest pond number 14. Map I., and Fig. I, was once 

 in tin- -a me relation to the lake as Pond I is now. At such a time 

 it was in a condition similar to that of the present Pond I. 

 Ponds 5 and 7 are intermediate in conditions between Ponds i 

 and 14. We ha\e the same general basis for the discussion of 

 ecological succession as in the streams. The changes in these 

 ponds have depended mainly upon physiographic stability within 

 each pond, rather than upon physiographic changes, and have 

 been due to tin- action of the nryuiisnis present on their o\cn cm-iron- 

 vnent. 1 This is true because after a given pond is once separated 

 from the lake (Fig. i) the changes due to the organisms go on 

 \\ithotit regard to further separation and the lowering of the 

 lake lexvl. Fvidently the level of the water has remained much 

 the same in the ponds after their separation from the lake proper 

 regardless ( ,| the lowering of the lake level (Fig. l). 



The method of deducing succession herein employed is similar 

 to that used in the case of the streams. The easily obsen. able 

 Facl thai animals occupying similar conditions are ecologicallv 

 similar (i. e., similar in habits and some main features of their 

 phx sjologv of external relations) is used as a starting point, and 

 the conclusions drawn are to ihe effecl th.it \\hen the older 

 habit a i \\.i-in the stage of a younger habitat, it \\.is occupied by 

 fishes i-inli>"t/iil/y similar to those now in the younger halntat. 

 Whether lhe\ \\ere the same or different species is often of little 

 import. nice lo ecological succession. With this simple explana- 

 tion as a background, and \\ith the use ot Figure i, xve will 



1 The- change--; \vlii. 1 1 are caused \<\ I li>- tilling it i hr | >n>l \\ it li plant iii.i 1 1 -i i;i I 

 are pli\ -iMjuplii. , hut tin' hint . ecl is the more im|m[ t.mt . and \M- m. iv 



i-;s the < 1 I hy hiuldvi, al I. .1 



