Species and Species Change 



127 



o 



I f 



1933-34 



1935 



1936 



1937 



1938 



1939 



1940 



Fig. 50. Known distribution of the high plains grasshopper Dissosteira longi- 

 pennis before and after the outbreak period of 1937 to 1939. The range de- 

 creased rapidly after 1940 also. The shaded area indicates the breeding range; 

 the dotted lines indicate known areas of adult dispersal from that year's breed- 

 ing range. (Modified from Wakeland.) 



OSCILLATIONS 



Population densities of natural populations are constantly oscillat- 

 ing, as a whole, regionally, and locally. In species having a large 

 geographic range, populations in different areas of the range prob- 



