126 ILLINOIS ACADEMY OF SCIENCE. 
SEASONAL SUCCESSION IN OLD FOREST PONDS. 
BY W. C. ALLEE, 
University of Chicago. 
The phenomenon of seasonal variation in animal habitats has 
long been recognized, yet I have been unable to find any exact 
data on the subject in ecological literature. The investigations of 
which this is a preliminary report are being carried on with a 
view to help fill this deficiency. The results given are based on 
collections which have been made regularly since the summer of 
1909. 
DEFINITION. 
Seasonal succession may be defined as the gradual replacing of 
one complex of animal life by another. These different complexes 
may be designated in terms of the species or taxonomic group of 
animals that are dominant at any given time. This dominance is 
composed of two factors : (1) pure numerical dominance, and (2) 
distribution in the pond. Either of these may vary without notice- 
ably affecting the other. But since many of the forms never rise 
to a dominant position, seasonal succession requires a study of the 
seasonal development of each member of the complex. 
This work on seasonal succession is important because of its 
bearing on ecological succession. The animal associations in one- 
pond vary more at different times of the year than the associations 
of many ecologically related habitats studied at the same season. 
The seasonal changes have brought the same errors into the study 
of ecological succession that a disregard of daily migration would 
bring into work on seasonal succession. 
AREA. ' 
The ponds under consideration are in the oldest part of the 
slough system at the south end of Lake Michigan, where the 
subsidence of the lake has exposed a series of long sloughs and 
ridges. There are about one hundred of these between the lake 
and the last of the old Lake Chicago beaches. The ponds most 
carefully studied are in the ninety-third depression back from the 
lake. A part of this depression which has been isolated from the 
rest of the slough by artificial grades, has been the basis of most 
of the collections. In this pond the marginal areas are being 
invaded by bushes; the shallower part of the open water is over- 
grown by equisetum in the summer, and a smaller zone of lilypads 
occupies the deeper water. 
