CHAPTER XIV 



PRAIRIE ANIMAL COMMUNITIES 



I. Introduction 



We have noted that a part of the region about Chicago is to be 

 classed as savanna and that the savanna is made up of trees in groves 

 and along the streams, and of forest margin and prairie. Prairie may 

 roughly be separated into high and low. The low prairie commonly 

 exists in depressions in the moraine, lower places in the plain of old 

 Lake Chicago. They are usually covered with water in the spring. 

 The high prairie is above water and is dominated by different plants. 

 As the depressions are filled or become better drained, high prairie 

 plants capture the habitat. 



II. Prairie Formations 



We have noted that the low prairie is covered by water in spring 

 (Figs. 280, 281). As the water dries up, which usually occurs by the 

 middle of May, the prairie plants begin to grow and the prairie animals 

 make their appearance. This change does not take place abruptly, 

 but gradually. There is a succession of adult-stage animals through 

 the summer. This is what is known as seasonal succession. 



I. SEASONAL SUCCESSION 



When the snow melts in March and the frost goes out of the ground, 

 the salamander {Ambly stoma tigrinum) comes out of the ground and 

 soon deposits masses of eggs in the water. The young of Eubranchipus, 

 Cyclops, and rotifers appear after a few days and often reach adult size 

 by April 1. On April 6, 1908, Mr. Dimmit found adult Eubranchipus, 

 Cyclops, and rotifers in the pond south of Jackson Park. The sala- 

 manders had disappeared. On April 12 three species of flatworms 

 {Vortex viridis, Planaria velata Stringer, and Dendrocoelum) had appeared, 

 and the first frogs were noted. On April 14 he found frogs' eggs and 

 the red crustacean (Diaptomus). Eubranchipus was at its maximum 

 abundance. On April 19 he found Daphnidae, rhabdocoel worms, and 

 tadpoles. On May 3 but few Eubranchipus were found. Diaptomus was 

 plentiful, perhaps at its maximum abundance. Daphnidae was more 

 abundant than before. Planaria were near their maximum. On May 10 



278 



