284 



POPULATIONS 



servations of the California quail {Lop- 

 hortijx calif ornica) . This study was con- 

 ducted over three complete years at the 

 University of California Farm. The findings 

 are well illustrated in Figure 83 and by the 

 author's comment: 



"The age ratio [of immature to adult birds] 

 in November 1936 was 150:100, indicating a 



contrasted with the estimated normal 33%. The 

 population by November, 1937 had dropped to 

 87, 70% of the 1936 level, and at the same 

 time showed a strong preponderance of im- 

 mature birds, 235:100. It is evident here that 

 the better than average replacement indicated 

 by the high age ratio was insuflBcient to make 

 up for the severe loss of adults during the 

 year. Reduced to a numerical basis the summer 



NDJFMAMJJASONDJFMAMJJASONDJFMAMJJASOND 



1935 1936 1937 1938 



Fig. 83. Changes in quail population at the University of California farm at Davis, 1935 

 to 1938. Columns show population size and age distribution for four successive Novembers. 

 (From Emlen.) 



YEARS 

 Fig. 84. Schematic illustration of changes in year-class composition of a hypothetical popula- 

 tion of marine fishes. All the bars are identifiable in the 1934 group. These are, from right 

 to left, year-classes older than 1930; 1930 classes; 1931, 1932, and 1933 year-classes. (From 

 Sverdrup, Johnson, and Fleming.) 



net summer replacement of 60% for 1936; 

 somewhat less than the yearly replacement of 

 67% estimated to be normal for the area. De- 

 spite this subnormal increment of young birds, 

 the population had increased during 1936, and 

 by November was 116% of that of November 

 1935. A high annual survival was obviously 

 involved. Solving for the equation S = P(100 

 — R)**, the survival is found to be 46% as 

 ** Where S = the survival, R = the replace- 

 ment, and P given by the ratio: 



(Current population level) 

 (Previous population level) 



replacement was 70% (118% of normal), the 

 total annual survival only 21% (63% of nor- 

 mal). In 1938 the population decreased to 52. 

 The low replacement, indicated by the sub- 

 normal age ratio of 138:100 can account for 

 part of this reduction, the rest is a consequence 

 of high adult mortality. The summer replace- 

 ment was 58% (69% of normal), the annual 

 survival, 25% (75% of normal)" (p. 96). 



This discussion is well ended by quoting 

 a passage from Tlie Oceans (Sverdrup. 

 Johnson, and Fleming) that illustrates 



