Mortality Required to Prevent Population Increase

BIOLOGISTS have often calculated the vast numbers which would be reached in a relatively short period by the descendants of a single pair of insects or other fecund animals if all of them reproduced at the normal rate before dying. Such calculations are used to illustrate the high potential rates of population increase, or the severity of the natural checks to increase, or to show the very high mortality required to keep a fecund population within normal limits. It should, of course, be recognized that, in many cases, reductions in the rates of reproduction and development also play an important part in limiting increase. However, the purpose of this note is to direct attention to the fact that, in certain calculations of the 'necessary mortality' , there is a striking fallacy.