Effects of Compensatory Mortality upon Population Abundance

Abstract

A graph of the relation between maturing progeny produced, and the size of the adult stock which produced them is called a "reproduction curve". When the two axes are in comparable units, maximum reproduction is often produced by a stock density less than maximum, and less even than the replacement level. In the latter event, the stage is set for periodic changes in abundance. These are damped and tend to disappear if the descending limb of the reproduction curve has a slope between 0 and -1, but are self-perpetuating when the slope is steeper. For populations which have more than one age in the spawning stock, this leads to cycles whose period is twice the mean time from parental to filial egg production, provided there is at least one generation lag in achieving maturity. When there are moderate to large environmental influences upon reproduction, they interact with the reproduction curve to produce an irregular series of changes that differ in several respects from what either would produce by itself.