614 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1964 



theoretical and "common sense" calculations as to how things work 

 out in natural equations. 



Intercompensatory trends in rates of population gains and losses 

 go a long way toward conferring a singular degree of biological safety 

 upon species that are subject to vicissitudes. In a resilient population, 

 severe loss rates may in effect substitute for each other without mount- 

 ing up excessively high in their totality. Extraordinary losses 

 through one agency may automatically protect from losses through 

 many other agencies. The death of one individual may mean little 

 more than improving the chances for living of another one. Fur- 

 thermore, in some species, extraordinary losses may be compensated 

 by accelerated reproduction, more young being produced in conse- 

 quence of more being destroyed. 



From these considerations, it can be perceived why I am not inclined 

 to accept mere conventional vital statistics as a suitable base for ap- 

 praising the population effects of predation. More may be needed 

 than figures as to how many individuals are brought into the world 

 and how many or what proportions die through predaceous agencies. 



Whether the population resiliences permitted by the compensatory 

 trends enable a species to escape being dangerously reduced by great 

 trials, or to resist changes in status quo, or to fill up biological frontiers 

 with explosive rapidity, they obviously can be an important part of 

 Life. Whether the purposes of human manipulations of animal popu- 

 lations are to encourage or discourage a particular species, in con- 

 nection with nature protection, fish and game management, or pest 

 control, we cannot afford to forget the fact that natural compensations 

 can nullify much of the thinking that fails to take them into proper 

 account. 



The renesting prowess of some popular game birds is sufficient to 

 confound many of the pencil-and-paper figurings of laymen, who 

 easily become emotional at the thought of a crow or a skmik destroy- 

 ing a clutch of eggs. To the bobwhite quail and the ring-necked 

 pheasant, the loss of a clutch or two early in the nesting season does 

 not necessarily signify a corresponding net decrease in productivity 

 of young. For species that are constituted to hatch only one clutch of 

 eggs per year and that have a long breeding season and several possible 

 nesting trials with which to do it, half to three-quarters of their nests 

 may fail and still allow the breeding females to fill their one-brood 

 "quota" for the breeding season. The more resilient nesters among 

 waterfowl seem to be almost as persistent and as ultimately successful 

 in their renesting efforts. Within broad limits set by physiology and 

 climate, it may not really matter whether the crows, skunks, raccoons, 

 or other wild egg eaters plunder a large proportion of the nests or 

 whether they do not. It may all come out much the same in the end. 



