126 



Species and Species Change 



Fig. 49. Known range of the high plains grasshopper Dissosteira longipennis. 

 The dark central area indicates the greatest extent of breeding; the broken 

 line indicates the extent of adult dispersal beyond the breeding area. ( Modified 

 from Wakeland.) 



hopper Dissosteira longipennis increased and decreased greatly 

 during the period from 1937 to 1940 (Fig. 50) (Wakeland, 1958). 

 Both the spread and contraction of the range were somewhat con- 

 centric around the earlier small range. 



Population 



The average population of most species runs into astronomical 

 numbers, but for a few species it is small. Among those species 

 whose range may have been little affected by man, the population 

 of Ross' goose Anser rossii was found to be 1,951 in 1949 (Hanson, 

 Queneau, and Scott, 1956), and the total breeding population of 

 the gannet Sula hassana was found to be approximately 78,000 

 pairs in 1935 (Edwards, Lockley, and Salmon, 1936). The lowest 

 possible population before the species is in danger of becoming 

 extinct is not known. Interesting in this connection is the North 

 American whooping crane Griis amcricana, whose total population 

 has oscillated between about 15 and 30 individuals since the 1940's. 



