EVOLUTIONARILY STABLE GROWTH-RATES IN SIZE-STRUCTURED POPULATIONS UNDER SIZE-RELATED COMPETITION

The competitive interactions between individuals in size-structured po pulations usually change as a function of the individuals' sizes. A ge neral model of a density-dependent size-structured population is used to investigate the size-specific birth and death rates that result whe n growth rates can be adjusted adaptively. If there is no cost associa ted with faster growth, the evolutionarily stable growth rates result in an ideal free distribution of individuals among size classes, provi ded that competition within size classes is stronger than competition between size classes. When the population is stationary, this ideal fr ee distribution is characterized by identical ratios of expected numbe r of offspring per unit time to probability of death per unit time for all size classes with growth rates less than the physiologically maxi mum level. If more rapid growth reduces birth rate or increases death rate, the size-specific ratios of births to mortality increase with th e organism's size. If the population is growing in a density independe nt manner, but there is a cost to growth, there should be an increase with size in the ratio of reproductive output to the quantity (populat ion growth rate minus survival probability). Available evidence about size-specific birth and death rates in some size-structured population s is discussed. (C) 1994 Academic Press, Inc.