SUMMARY 309 



by civilization the multiplicity of interrelationships in any habitat still exists. Thus anv less- 

 ening of direct decimation of a game species through a reduction of predators would be only 

 one phase of the result. In the long run, the indirect effects might often be of much greater 

 importance. For example, it is possible that, before being checked by some other limiting 

 factor, rodents might increase until they had seriously damaged the suitability of the cover for 

 the game population. Illustrative of the possible ramifications is the situation attributed to a 

 certain part of England where it is said red clover would not grow because the absence of 

 hawks, owls and similar predators permitted field mice to increase to the point where they 

 exterminated the bumble bees, through destroying their combs and nests, thus removing the 

 pollanizing agent of the clover. More pertinent perhaps is the observation of Farrow"'^ that 

 on some English heaths too many rabbits cause the heather to be replaced by grass or 

 bracken, both of which are relatively worthless for Scotch grouse food and cover. There is 

 much more to the problem than meets the eye. 



Although the nature of its operation among wild life populations is not vet fully under- 

 stood, predation seems, as Errington*^ has jiointed out. "to be essentially a by-product of 

 population [surpluses]". It may be a new concept to some readers, but it is nevertheless 

 necessary to all species that they be prevented from realizing their reproductive potential*. 

 Otherwise their abundance would exceed that c<)m|)atible with their environment. 



To one who in an all day tramp has started but one or two grouse or a half dozen raiiliits it 

 may be difticult to envision the possil)ilit\ of o\cr-abundancc. Yet simple arithmetic will show 

 ihat. without some check on their increase, one |)air of grouse would produce a population 

 of over 33,000 individuals in only six years. 



Losses from predation are largely concerned with such surpluses. But. more important 

 still. Nature's system of checks is quite flexible. If one is removed, others "take over" so that 

 the ultimate result is essentially the same. The effect of the shift, however, may not be 

 immediately apparent. A striking example is the history of the mule deer population in 

 the Kaibab National Forest in Arizona. Following elimination of their principal pre- 

 dator, the mountain lion, the deer increased until they exhausted their food supply and starva- 

 tion became the limiting factor. Furthermore progressive depletion of the forage ultimately 

 resulted in a lower population than had been maintained before the lions were removed. Simi- 

 larly, following the virtual elimination of its natural enemies, the white-tailed deer is at 

 present overtaxing its winter food supply over large sections of its eastern range. 



It is extremely unlikely that grouse would ever have a comparable effect on their environ- 

 ment. The species seems to have an aversion to densities above a bird to about four acres of 

 cover and tends under such circumstances to disperse to less occupied territory. Although 

 not proven there are indications that on occasion disease may also become a controlling 

 influence among excessive populations. Thus a reduction in predators cannot be expected to 

 bring about anv lasting increase in a grouse population, for instance, except possibly in 

 individual coverts where for some reason predation is holding the species below carrying 

 capacity. 



On the other hand, if through predator control an increased fall surplus could be pro- 

 duced, and the hunter be enabled to harvest it. the sport of grouse hunting would be greatly 

 benefited, even though the breeding population remained relatively stable from year to year. 

 Nevertheless, it must constantly be borne in mind that an apparently simple and innocuous 

 action may have startling and unpredictable consequences. 



* Sec Chapter VIII, p. 351. 



