ANIMAL AND ITS ENVIRONMENT 471 



others spend a part of the year in an inactive stage, such as the egg, 

 or the pupa. The life cycle of an organism must be adjusted to the 

 annual climatic cycle of the climate in which it lives. Some idea 

 of the variations in the number of insects during the year may be 

 gained from a study of the accompanying charts (Figs. 201 and 202) 

 giving the average catch with one hundred sweeps of an insect net 

 at different seasons. 



A study of the abundance of Protozoa in an artificial lake (Fig. 

 203) shows a similar difference in the time of abundance of the 

 various species. 



Summary 



This chapter has considered very briefly the distribution of the 

 biotic communities of North America in relation to climate. The 

 phenomena of succession and seasonal fluctuation of populations 

 have been discussed, with examples. Attention has been directed 

 toward the community rather than toward the individual organism 

 or the species. Similarly the sum total of physical environment as 

 expressed in climate has been stressed rather than single factors, 

 such as moisture, temperature, light, etc. The animal in nature is 

 subject always to the action of a complex environment and its dis- 

 tribution and reactions are the result of its response to the whole. 



References 







Chapman, R. N. : Animal Ecology, New York, 1931, McGraw-Hill Book Company. 

 Elton, Charles S. : Animal Ecology, London, 1927, Sedgwick and Jackson. 

 Hesse, Richard, et al.: Ecological Animal Geography, New York, 1937, John 



Wiley & Sons, Inc. 

 Pearse, A. S.: Animal Ecology, New York, 1926, McGraw-Hill Book Company. 

 Shelf ord, V. E. : Animal Communities in Temperate America, Chicago, 1927, 



University of Chicago Press. 

 Welch, P. S.: Limnology, New York, 1935, McGraw-Hill Book Company. 



