In the study of population dynamics not only the abundance of a population is important but
also its composition in terms of the relative frequency of individuals with different stages of
development or body size. Size determines the nature of many ecological interactions, e.g.
food choice, foraging capacity, growth, reproduction and mortality (Peters, 1983; Ebenman and
Persson, 1988b,a), hence size also influences population dynamics. By describing the physiological
processes at the individual level and simulating their life history events (reproduction,
mortality), the population dynamics is the result of tracing all individuals over time.