The Fur Animals of Louisiana 69 



In this California region one of nature's checks on an 

 abundance of earth-bound animals had been wiped out by 

 man when these tiny mammals began to roll up in num- 

 bers. And the mice played havoc with agriculture. Indeed, 

 ic was estimated that the losses that coyotes, bobcats, 

 skunks and other mammals might have caused the sheep- 

 growers of that region, and for which they were poisoned, 

 trapped and shot out, were less in value than the damage 

 the plague of mice did to the agricultural interests. 



According to Mr. Hall, it should be pointed out "that in 

 the normal, or usual, state of population of animals, one 

 given carnivore feeds on several species of prey, but when 

 for any reason one species of prey becomes more numer- 

 ous than the others, the carnivore naturally, because of the 

 ease and readiness with which the prey can be secured, con- 

 centrates upon that one. There is, then, a certain optimum 

 point of population-size for a species that calls forth the 

 maximum effectiveness of the other animals that prey on it. 



"When the usual relative numbers of all the different 

 species, both carnivores and herbivores, are present, this 

 optimum point seldom is passed or even reached, and the 

 condition of an over-population is thus prevented by the 

 animals that play the carnivorous role. 



"It is known that house mice attain sexual maturity by 

 the time they are three months old at most and that, on the 

 average, under favorable circumstances they produce a lit- 

 ter at least each month. The litters average from five to 

 six. In two years' time, then, breeding at this rate and as- 

 suming that all the mice lived to reproduce their kind, two 

 adult mice producing a litter at the end of the first month, 

 have a potentiality of 3,701,257. 



"Let us suppose, for the sake of illustration, and not for 

 the sake of assuming that the number selected is correct as 

 to the actual number produced by one pair here, that at 

 Buena Vista Lake one pair of house mice was responsible 

 for one one-thousandth of this number — that is, 3,701. Four 

 pairs of mice then would, at the end of two years, be re- 



