134 



I. THE INFLUENCE OF SIZE AND DEPTH 



Size and depth have a marked influence on the rate of succession. 

 If the lake is large, like Lake Michigan, its waves beat upon the shores 

 with such force as to prevent the development of vegetation or the 

 establishment of any of the formations just discussed. Smaller lakes 

 have proportionally less efficient wave-action, and situations which would 

 not be protected to any marked degree in a lake like Lake Michigan are 

 relatively free from effective wave-action. The formations succeed one 

 another rapidly where wave-action is slight. The various parts of the 

 shore of a small kettle-hole with a regular shore-line would pass through all 

 these stages at nearly the same rate. Depth is an important factor also 

 because the various formations cannot succeed over the deep water until 

 the deeper parts are filled (or drained), which often requires long periods. 

 The rate of succession in lakes is then directly proportional to their size 

 and depth. The small lakes pass through all the stages more quickly 

 than the larger lakes. Those considered here have for the most part, at 

 present, become dominated by the late stages. The lakes of the inland 

 type which are large enough to maintain all the formations discussed are 

 among the most complex of all our habitats. 



2. INFLUENCE OF MATERIAL AND MODE OF ORIGIN 



At the very beginning the kind of material in which a lake is situated 

 is important but as time goes on it becomes less and less important. If 

 the lake is in clay, at the outset there are no sandy areas, but the action 

 of the waves soon removes the finer material and leaves sand (the finer 

 materials being deposited on the bottom of the lake). Young lakes in 

 rock are probably very different from those in clay, but even here sandy 

 shores are soon formed and occupied by the same animals as sandy 

 shores of different origin. 



The distinction between lakes and ponds is a purely artificial one. 

 The ponds have the same communities at the outset as the lakes, but 

 the changes proceed so rapidly that very young ponds are rare. All 

 lakes and ponds tend to become ecologically similar, regardless of mode 

 of origin and kind of material. 



LIST II 



The following Entomostraca have been taken from Wolf Lake: * indicates the 

 species is found in Fox Lake; f in Butler's Lake; % in the series of ponds at the 

 head of Lake Michigan: Copepods: J*f Cyclops serrulatus Fischer; *ft C. albidus 

 Jurine; \C. viridis brevispinosus Herrick. Cladocerans: Acroperus harpae Baird; 

 t Scapholeberis mucronata Muel.; % Pleuroxus denticidatus Birge; Diaphanosoma 

 brachyurum Liev.; J Chydorus sphaericus Muel. ; Polyphemus pediculus Linn; Macrothrix 

 rosea Jurine; \Ceriodaphniareticulata Jurine; \Simocephalusserrulatus Koch; Bosmina 

 obtusirostris Sars. Ostracods : Potamocypris smaragdina Vav. 



