512 I'liODUCriVITY Of GROUSE I'OI'VLATIONS 



The sex ratio lias aMnagcd nearly even dining liie Jnvesligatiuii luil a Iciulcncy has been 



noted for a regular seasonal variation to lake place, (p. 51 1). 

 Average survival rates observed have been approximately 01 per cent for nests, 40 per cent 



for chicks and 46 per cent among adults on areas where no hunting occurred. (,p. 525, 



527, 531). 

 A considerable proportion of the hunting losses usually experienced appear to be deductible 



from the overwinter mortality which would otherwise take place. (,p. 58!vt. 

 Individual coverts vary in their ability to support grouse populations over winter, depending 



basically on the quality of the cover. This concept has been termed carrying capacity. 



(p. 522). 



Densities of population tend to he higher in disconnected "woodlot" coverts than on wilder- 

 ness range, (p. 520). 



Adults tend to avoid crowding above an average of one bird to four acres of grouse cover 

 even in the best habitats, (p. 521). 



Grouse tend quite rapidly to move into a covert whose population has been depleted out of 

 proportion to those surrounding it. (p. 522). 



Over a period of years productivity oscillates first to one side and then to the other of "dead 

 center", (p. 546). 



Management may bring about a rise in the average population level but, once it has reached 

 the improved plane, the tendency toward equilibrium will again assert itself, ip. 546). 



Real abundance, like real scarcity, is an abnormal situation, to correct which Nature is con- 

 stantly striving for a balance, (p. 553 j. 



The potential productivity of most organisms is very high. As an entomologist has 

 pointed out, a single pair of plant lice and its offspring could produce enough progeny in 12 

 years to cover completely the surface of the earth if all the various causes of mortality were 

 removed. Grouse differ only in degree*. 



But in actuality unimpeded increase is seldom, if ever, approached. From its first appear- 

 ance each species has faced constant conllict witli a more or less adverse environment. As a 

 result it has become adapted to a distinct biological niche, entailing innumerable interrela- 

 tionships with other species and influences. In this way its productivity has been controlled. 

 As stated by Yapp'°°: 



"We may perhaps regard the organisms, both plants and animals, occupying any given 

 habitat as woven into a complex but unstable web of life. The charaitcr of the web may 

 change as new organisms a|)pear on the scene and old ones disajjpear duriii^i the ])hases 

 of succession, but the web itself remains." 



The mechanism of regulation, however, is liigliiy complex iind is only bcfrinning to be 



understood. 



One of the early attempts to explain it was that of Malthus'" who came to the conclusion that 



populations are directly controlled by competition for food and that they always increase to the 



* Sec Chaplri Vni, p. 351. 



