1 ANIMALS 



in other large carnivores, wolf num- 

 bers are self-limited largely through 

 behavioral intolerances. Ordinarily 

 there is one pack, most commonly 

 around 15 animals, in which breeding 

 takes place, and only one female will 

 bear young. There has obviously 

 been a high mortality among young 

 wolves. 



The remains of more than 400 dead 

 moose — nearly all wolf kills — have 

 been examined on Isle Royale and 

 their ages determined by tooth char- 

 acteristics. On this basis, a composite 

 life table and survivorship curve for 

 the moose herd has been constructed. 



(See Figure IX-12) This illustrates 

 a relatively high mortality of calves 

 in the first year of life. In the next 

 five years of its life, a moose evi- 

 dently is at the peak of health and 

 vigor, for it is seldom taken by 

 wolves. From age 6 to the maximum 

 age of 17 + , the moose is increasingly 

 liable to be killed; the average adult 

 taken is 9 to 10 years old. Correlated 

 with advancing age and a higher 

 mortality rate is an increasing in- 

 cidence of physical disorders. 



The high selectivity for old and 

 debilitated moose has been evident in 

 the hunting habits of wolves. An 



Figure IX-12 — LIFE EXPECTANCY AND SURVIVORSHIP 

 OF ISLE ROYALE MOOSE 



EXPECTATION OF LIFE IN YEARS 

 10 



PERCENT MORTALITY 

 100 



12 3 4 5 6 7 



B 9 10 11 12 



AGE IN YEARS 



13 14 15 16 



average of 12 moose have been ap- 

 proached and brought to bay for 

 every one killed. Vulnerable moose 

 appear to be detected readily, while 

 animals capable of strong defense 

 are quickly passed by. In effect, the 

 wolf culls the moose population and 

 preserves a stock that can utilize the 

 plant food supply most efficiently in 

 producing new generations to sup- 

 port wolves. 



Implications of the Isle Royale 

 Findings 



This information reveals working 

 mechanisms that confer durability on 

 the ecosystem. It may be pointed out 

 that population stabilization and turn- 

 over rate in the wolf could only be 

 studied where this species is protected 

 from unnatural mortality. The natu- 

 ral age structure of the moose herd 

 and the selection effect of the preda- 

 tor could be ascertained only where 

 moose are protected from hunting 

 and exposed to natural predation. 

 Isle Royale National Park is perhaps 

 the only area in the world where these 

 conditions are met at present. 



The relationship of predator to 

 prey has other, more direct, implica- 

 tions, since big game herds are most 

 commonly managed in the absence 

 of effective natural enemies. The 

 chief dependence in population limi- 

 tation is on the gun and such factors 

 as highway kill. Such artificial selec- 

 tion will in time alter the direction 

 of speciation and change the nature 

 of such wild species as the deer. In 

 the preservation of wild fauna and 

 flora, for whatever benefits are to be 

 realized, there are evident advantages 

 in understanding the character and 

 dynamics of the original associations 

 in which living things developed. 



305 



